Designing with engineering Plastics - Tecno Plastic … · Engineering plastics are becoming increasingly popular in machine and plant construction as design engineers recognise their

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Designing with engineering Plastics

Titel Konstruieren 27.10.2004 10:19 Uhr Seite 1

Licharz on the web

Certified quality management according to DIN EN ISO 9001 : 2000 DIN EN ISO 9001:2000

Certificate No 01 100 040034

Konstr. Kunststoffe engl.7/04 27.10.2004 7:32 Uhr Seite 2

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Contents

Polyamides (PA) 6-10

Oilamid® 11-13

Calaumid® 612 / Calaumid® 1200 14-15

Calaumid® 612-Fe / Calaumid® 1200-Fe 16

Polyacetal (POM) 17-19

Polyethylene terephthalate (PET) 20-21

Polyethylene (PE) 22-24

Polypropylene (PP) 25-26

Polyvinyl chloride (PVC) 27-28

Polyvinylidene fluoride (PVDF) 29

Polytetrafluoroethylene (PTFE) 30-31

Polyetheretherketone (PEEK) 33

Polysulphone (PSU) 34

Polyether imide (PEI) 35

Tolerances 105-113

Machining guidelines 114-118

Physical material standard values and chemical resistances 119-133

Information on how to use this documentation / Bibliography 134

Foreword – Engineering plastics as design materials 4

Material overview 5

Structure and properties of plastic 36-43

Behaviour in fire 44-45

Resistance to radiation and weathering 46-47

Storage information 48

Plastic friction bearings 49-60

Plastic sliding panels 61-64

Plastic castors 65-75

Plastic rope pulleys 76-85

Plastic gear wheels 86-100

Plastic spindle nuts 101-104


Engineering plastics are becoming increasingly popular in machine and plant construction as designengineers recognise their advantages and economic significance.

The use and development of materials is subject to continuous change. This also applies to plastics.Many machined parts that were manufactured exclusively from conventional metals just ten yearsago are now being made from modern engineered plastics.

We can expect this change to continue in the future – perhaps at an even faster pace than we haveexperienced to date. This change can be attributed to the enormous rise in the number of en-gineering plastics available along with their many different modifications, characteristics andpossible applications. Due to their specific properties, many plastics are equal or superior inmany ways to conventional design materials. In many cases, engineering plastics have alreadyreplaced conventional materials due to their superior performance properties.

The main advantages of engineering plastics in comparison to conventional metals are: weight reduc-tion, resistance to wear, good vibration absorption and the fact that plastics are easier to machine.Additionally, their high level of chemical resistance, the increasing thermal stability of several types ofplastic and improved recycling possibilities are further positive arguments for choosing engineeringplastics.

The task of design engineers will increasingly be to find an optimal material for a specific applica-tion while keeping production costs down. Often there is a lack of awareness regarding the actualvolume prices of plastics compared to conventional metal materials. Even high quality modifiedpolyamides can be less expensive than many types of metals. In addition, the much lower quantityof chips when plastics are machined is another factor that influences the price / performance ratioin comparison to metals.

The experience that LICHARZ has gained during the last 40 years in manufacturing, processingand utilizing engineering plastics for machine and equipment design, automotive industry appli-cations and other areas has made LICHARZ one of the leading companies in this industry in Euro-pe (world wide???). Over the years, we have come to focus on applications that are subject to slipand wear stresses and have achieved extensive success.

The majority of semi-finished products as describes in this document, especially all variants of castpolyamides, and finished parts, are produced in our plant or manufactured by us on cutting edgeCNC controlled machines.

In order to make it easier for design engineers and users to determine which plastic is best fortheir specific applications, we have summarised our experience in the form of material descriptionsand design and machining information in this brochure.

Please do not hesitate to contact us with any questions you may have.

3rd edition, July 2004

Foreword

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Material overview

The most important engineering plastics are

Polyamide (PA)Polyacetal (POM) Polyethyleneterephthalate (PET)

Many different material modifications of these engineering plastics are used in components that are subject to sliding and wear loads.

Other materials are only used occasionally for sliding applications and mainly for applications where there is chemical demand. These include

Polyethylene (PE)Polypropylene (PP)Polyvinylchloride (PVC) Polyvinylidenefluoride (PVDF) Polytetrafluoroethylene (PTFE)

High-performance plastics are another group of modern materials that are characterised by their high level of rigidity and stability at high temperatures. The disadvantage is the high price, which in some cases can be as much as 30 times the cost of engineering plastics. High-performance plastics include

Polyetheretherketone (PEEK)Polysulphone (PSU) Polyether imide (PEI)


Polyamides (PA)


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PA

Polyamides are subdivided into various basic types. The most important are PA 6, PA 66 and PA 12.The differences in physical properties are in the composition and structure of the molecule chains.

In the manufacture of semi-finished products, a distinction is made between moulded and extruded materials.

The key properties of polyamide are:• High mechanical stability, hardness, rigidity and toughness• High mechanical damping properties• Good fatigue resistance• Very high wear resistance• Good sliding and emergency running properties• Good machining properties

Because of the higher crystallinity, semi-finished products manufactured by casting have muchbetter physical properties than extruded polyamides.

Extruded Polyamides

Polyamide 6is the best known extruded polyamide. PA 6 offers a good combination of mechanical stability,impact resistance and damping, but compared to PA 6 G it has much lower wear resistance, absorbs more moisture and has less dimensional stability. Applications: parts that are subject toshock and impact, gear wheels, hammer heads.Colour: natural, black

Polyamide 66is used in smaller applications. Compared to PA 6 it is harder and is more resistant to wear, howe-ver, it does have less impact resistance. Applications: friction bearings, sliding panels. It has similarmechanical properties to PA 6 G, which is much less expensive and is generally used instead of PA66.Colour: natural

Polyamide 12has very good impact behaviour, it is tough and, because of its very low water absorption, it is dimensionally stable. It is available in small quantities as semi-finished products, but is not generally considered for construction applications due to its high price (3-4 times more expensivethan PA 6).

Polyamides (PA)


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PA

The so-called monomer moulding process, in which semi-finished products are created by meansof a controlled chemical reaction, is a significant improvement compared to conventional extrusion or injection moulding processes and is especially important for the performance of thismaterial. Typical physical properties are improved in a targeted manner.

Range of cast polyamide materials

PA 6 GCast polyamide for components in machine and equipment designs that are subject to wear (standard quality).Colours: natural, black, blue

Oilamid®

PA 6 G with integrated lubrication, self-lubricating effect, improved wear resistance. Colours: black, yellow, natural

PA 6 G/WSEssentially similar to the standard quality but better protected with a thermal stabiliser againstthermal-oxidative degradation.Colour: natural

PA 6 G/MoSEssentially similar to the standard quality, but this type has a higher degree of crystallinity due tomolybdenum sulphide constituents.Colour: black

Calaumid®612Co-polyamide based on PA 6/12-G with higher impact and shock resistance, less water absorptionand improved creep resistance compared to pure PA 6 G.Also available as Calaumid®612-Fe with a steel core (see separate material description).Colour: natural

Calaumid®1200Cast polyamide based on laurin lactam. Very good impact behaviour, toughness, excellent dimen-sional stability, lowest water absorption, very good creep resistance, hydrolysis resistance, goodchemical resistance. PA 12 G is far superior to extruded PA 12 in every respect. Also available as Calaumid®1200-Fe with a steel core (see separate material description).Colour: natural

Cast polyamides


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PA

PA 6 G is a beige coloured, firm, homogeneous, stress-relieved material with a high degree ofcrystallinity. Specific properties are also developed through modification, special settings and additives.

Material properties

PA 6 G offers tried and tested characteristic material properties:High abrasion and wear resistance at low to medium speeds compared to cast iron, steel or bronze – especially under rough conditions (sand, dust).

Vibration and noise absorptionProlongs the life of machine parts through the visco-elasticity of the plastic and complies with environmental requirements, e.g. noise absorption via PA 6 G rollers, gear wheels, etc.

Low weightWith a specific weight of 1.15 g/cm3, PA 6 G only weighs approx. 13% of the same volume of bronze, 15% of steel and 43% of aluminium, which means less centrifugal force and imbalance inrotating parts.

Chemical resistanceAgainst weak acids and alkalis as well as all conventional organic solvents.

Very good sliding propertiescharacterise PA 6 G as a traditional friction bearing material for machine parts that are subject toa lot of wear, such as bearing bushes, sliding panels, guide panels, gear wheels and sprocketwheels and rollers. Because of the low coefficient of friction, lubrication is often unnecessary oronly an initial lubrication is required when the parts are being installed.

Stability of physical propertiesThe property values of PA 6 G are influenced by temperature and moisture. When temperaturesincrease or water is absorbed, tensile and compressive strength are reduced, modulus of elasticityand hardness are reduced, while impact resistance and expansion increase.

PA 6 G


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PA

Dimensional stabilityThis is also dependent on temperature and moisture. However, the high crystallinity of PA 6 G reduces moisture absorption considerably. Water is only absorbed very slowly. The rate of absorp-tion reduces progressively with the depth of penetration.

Guiding values for moistureSaturation level in a standard climate (23°C/50% RH) depending on type: 1.5 – 2%.Linear deformation due to moisture absorption: approx. 0.15 – 0.20% per 1% water absorbed. Linear deformation due to temperature changes: approx. 0.1% per 10°C temperature difference.

MachiningPA 6 G can easily be machined on equipment that is normally used for metal and wood pro-cessing. To prevent deformation, material should be removed equally from all sides. If material isto be removed unevenly it is recommended that the workpiece be pre-worked, annealed and stored for 24 hours before the final processing work is carried out. Because of the notch sensitivityof plastics in general, sharp-edged transitions should be avoided.

PA 6 G

Notch impact resistance

of polyamide 6 G at low temperatures

Notch impact resistance

of polyamide 6 G with different watercontents

Water absorption

of polyamide 6 G in water at roomtemperature and standard climate(Test piece: standard small rod)

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Oilamid®


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Oila

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Oilamid is a high-molecular thermoplastic based on PA 6 G. Oilamid has a fine crystalline structurewith high wear-resistant and self-lubricating properties. The high level of wear resistance and theextraordinary sliding properties are specifically developed by adding oil, solid lubricants and stabilisers.

Increased abrasion and wear resistanceThe oil is added before the polymerisation process and gives the material a self-lubricating effect.The coefficient of friction is reduced by 50%, which makes Oilamid an ideal design material forhighly loaded, slow moving, dry-running sliding elements with up to 10 times more wear resistance than unfilled polyamide. At slow to medium speeds, and especially in rough conditions(sand, dust), Oilamid has considerably more abrasion and wear resistance than cast iron, steel orbronze. Generally a pv factor is given as a load limit for sliding elements. Oilamid can work underhigher loads and speeds than PA 6 G. The influence on the level of sliding abrasion is subject tothe parameters of the surface roughness of the metallic mating component, surface pressure, sliding speed, sliding surface temperature and lubrication. Because of its low coefficient of friction, Oilamid has a low rate of abrasion and is suitable for dry-running in special applications.

Vibration and noise absorptionOilamid’s vibration and noise absorption prolongs the life of machine parts through the visco-elasticity of the plastic and complies with environmental requirements, e.g. noise absorption viaOilamid gear wheels and rollers.

Excellent sliding propertiesDue to its lubrication supporting effect, Oilamid is becoming an important friction bearing material for machine and equipment parts such as bearing bushes, sliding panels, guide panels,guide curves, gear wheels and sprocket wheels.

Oilamid®

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Sliding abrasion as a function of the bearing load

Load within the permissible pv range; lubrication: dry-running; sliding surface temperature: 80 ºC; surface roughness of the steel counterpart Rz = 2µm

For sliding elements that are intended to be used in dry-running applications, it is recommendedthat they are given an initial lubrication to alleviate break-in loading. The coefficient of slidingfriction of Oilamid remains stable as the pressure increases. The stick-slip behaviour is better thanother thermoplastics.

Because of the low coefficients of sliding friction, the friction heat of Oilamid sliding elements islower than other polyamide grades, which means that they can operate at higher loads andspeeds.

Polyamide 6 G

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Friction ring ST 50 K (v = 1m/s)

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Sliding friction of polyamide 6 G and Oilamid friction ring ST 50 K (v=1m/s)

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Calaumid®/Calaumid®-Fe


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Calaumid®

Calaumid 612 is a co-polyamide based on PA 6/12 G. Compared to pure PA 6 G, shock and impactresistance are higher in Calaumid 612, moisture absorption is lower and creep resistance is improved. Because of these material properties Calaumid 612 is especially suitable for use in areaswhere increased shock loads are expected or where higher fatigue resistance and flexibility are re-quired.

Typical applications are:• Gear wheels• Toothed racks• Pinions• Outrigger float pads

Calaumid 1200 is the trade name for PA 12 G, which is also manufactured from the raw materiallaurin lactam in a pressureless monomer moulding process. The seamless transition from polyme-risation to crystallisation creates a high-crystalline structure. This produces material propertiesthat are far superior to extruded PA 12.

Advantages of Calaumid 1200 compared to other polyamides:• Low water absorption compared to other polyamides• This makes it dimensionally stable and reduces the effects of water content on mechanical

properties to an absolute minimum• Good creep resistance, even at high temperatures• Good shock and notch impact resistance, also at temperatures as low as –50°C• Good resistance to hydrolysis and chemicals in the pH 2-14 range• Temperature stability from –60 to +110°C• Good slip and abrasion resistance• Resistant to stress cracking• Low specific weight

The combination of these properties makes Calaumid 1200 an ideal material for gear components, especially if steel hubs are being moulded in during manufacture. These properties are not completelyachieved by other thermoplastics or bronze.

Dependence of the mechanical properties on the water content for Calaumid 1200

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Cal

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eCalaumid-Fe

Calaumid-Fe is moulded in a pressureless process in a form-fit and non-positive manner around a 2to 2.5mm deep knurled steel core. Combinations with aluminium, stainless steel and brass are alsopossible. The plastic can be either Calaumid 612 or Calaumid 1200.

The combination of the plastic outside and the metal core is especially suitable for optimised torque transmission for component parts such as

• Spur wheels• Worm wheels• Bevel wheels• Sprocket wheels• Castors, guide rollers and rope pulleys• Cam disks

The combination of a steel core and a plastic casing unites the unique properties of steel and plastic that are so highly valued in design. The shaft-hub connection is calculated in the same wayas steel, thus offering the possibility of a high degree of power transmission. The advantages ofCalaumid-Fe:

• Maintains the time-tested metallic shaft-hub connection• Runs quietly• Weight advantage compared to pure steel designs• Good noise absorption and vibration behaviour• Good dry and emergency running properties• Optimum power transmission (calculated like steel)• Precise bearing seat, high degree of fitting accuracy• High degree of true running

Calaumid

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Fe-Kern

Material: Calaumid®-FeVSteel core: Ø 60mm x 38mmCalaumid disk: Ø 140mm x 38mmKnurl: Axial and circumferential

knurl, DIN 82-RKE 2.0Material steel: Machining steel 9 SMn 28K

Max. axial load: 100 kN

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Material: Calaumid®-FeVSteel core: Ø 80mm x 20mmCalaumid disk: Ø 200mm x 33mmKnurl: Axial and circumferential

knurl, DIN 82-RKE 2.0Material steel: Machining steel 9 SMn 28K

Max. torque: 4,45 kNm

Axial load experiment Torque transmission test

Result of axial load: Result of torque transmission:


POM/PET


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POMPolyacetal (POM)

Polyacetal is a high crystalline thermoplastic with a high level of stability and rigidity as well asgood sliding properties and wear resistance with a low level of moisture absorption. Its good dimensional stability, exceptional fatigue resistance and excellent machining properties make polyacetal a versatile design material also for complex components. POM satisfies high surface finish requirements.

Stability, rigidity and dimensional stability can be further improved by adding glass fibres as a filler, although this decreases sliding properties.

A distinction is made between homopolymers (POM-H) and copolymers (POM-C); homopolymershave a higher density, hardness and stability due to their higher degree of crystallinity. However,copolymers have a higher impact resistance, greater abrasion resistance and better thermal/chemical stability.

The polyacetal semi-finished products that we offer – from which we also manufacture finishedproducts– are produced from copolymers in an extrusion process.

Main properties• High stability• High rigidity• High hardness• Good impact resistance, also at low temperatures• Low level of moisture absorption (at saturation 0.8%)• Good creep resistance• High dimensional stability• Resistant to hydrolysis (up to +60°C)• Physiologically safe

Colours:POM – C : natural/blackPOM – C + GF: black

Slip Sliding propertiesPOM-C has excellent sliding properties and good wear resistance. Together with its other out-standing properties, POM-C is well suited for sliding applications with medium to high loads. Thisalso applies to applications where high levels of humidity or wetness are to be expected.

Because of the close static and dynamic coefficients of friction, low start-up moments can be implemented.

This does not apply to the types filled with glass as their sliding properties are much less than theunfilled types.

Weathering effectsPOM-C is not resistant to UV rays. UV rays, in combination with atmospheric oxygen, oxidise the surface, and discolouration occurs or the surface becomes matt. If the material is subject to the effects of UV rays for a long time, it tends to become brittle.

Chemical resistancePOM is resistant to weak acids, weak and strong alkaline solutions, organic solvents and petrol,benzole, oils and alcohols.

POM-C is not resistant to strong acids (pH < 4) or oxidising materials.


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POM

Behaviour in firePOM-C is rated as normal flammable. When the source of ignition is removed, POM-C continues toburn, forming droplets. During thermal decomposition, formaldehyde can form. The oxygen index (= the oxygen concentration required for combustion) at 15% is very low compared to otherplastics.

Areas of use• General machine engineering• Vehicle construction• Precision mechanics• Electrical industry• Information technology

Applications• Spring elements• Bushes• Gear wheels• Sliding elements• Insulators• Pump components• Casing parts• Valves and valve bodies• Counter parts• Precision parts

MachiningPOM-C develops a fragmented chip and is thus ideally suited for machining on automatic lathes,but it is also possible to machine it on cutting machine tools. The semi-finished products can bedrilled, milled, sawed, planed and turned on a lathe. It is also possible to cut threads or insertthreaded parts in the material. Generally no cooling or lubricating emulsion is necessary.

To limit material deformation due to internal residual stress in semi-finished products, the partsshould always be machined from the geometrical centre of the semi-finished product, removingan even quantity of material from all sides.

If maximum dimensional stability is demanded from the finished components, the parts to be manufactured should be rough pre-machined and stored for an interim period or heat treated.The parts can then be completed. More detailed information on interim storage and heat treat-ment, as well as other information about machining, is provided in the chapter on “Machiningguidelines”.


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PETPolyethyleneterephthalate (PET)

The molecule structure of polyethyleneterephthalate can be produced either as an amorphous orsemi-crystalline thermoplastic. The amorphous type is crystal clear with lower mechanical stabilityand inferior sliding properties.

The semi-crystalline types, on the other hand, have a high level of hardness, rigidity and stabilitywith excellent sliding properties and low sliding abrasion. Because of its good creep resistance,low level of moisture absorption and excellent dimensional stability, the material is ideally suitedfor complex parts with the highest demands on dimensional stability and surface finish. For thereasons mentioned above, only the semi-crystalline type is suitable for sliding applications.

The wear resistance and sliding properties of PET-GL have been improved compared to pure PETby adding a special, homogeneously distributed solid lubricating agent.

The polyethylene terephthalate semi-finished products that we offer – and from which we alsomanufacture all finished products – are manufactured from semi-crystalline types in an extrusionprocess.

Main properties• High stability• High rigidity• High hardness• Low moisture absorption (at saturation 0.5%)• Very good creep resistance• Very high dimensional stability• Constantly low sliding friction• Very little sliding abrasion• Resistant to hydrolysis (up to +70°C)• Physiologically safe

ColoursPET: natural, blackPET-GL: light grey

Sliding propertiesPET has excellent sliding properties, very good wear resistance and, in combination with its otherproperties, is an excellent material for highly loaded sliding applications. This also applies to applications where high levels of humidity or wetness are expected.

The modified type PET-GL is especially suitable for highly loaded sliding applications in dry running operations due to its integrated solid lubricating agent. The solid lubricating agent “selflubricates” the PET-GL, which gives it excellent sliding properties and highest wear resistance witha much higher load-bearing strength (pv limiting value) compared to pure PET. It also preventsthe stick-slip effect. The other properties are equal to those of pure PET.

Weathering effectsPET is not resistant to UV rays. The material surface changes when subjected to UV rays in com-bination with atmospheric oxygen. If the material is to be subjected to UV rays for longer periods,a black coloured type is recommended.


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PET

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Chemical resistancePET is resistant to weak acids and alkaline solutions, salt solutions, perchlorinated and fluorinatedhydrocarbons, oils, fuels, solvents and surface-active substances. Strong polar solvents have an irreversible swelling effect. PET is not resistant to strong acids or alkaline solutions, esters, ketonesor chlorinated hydrocarbons.

Behaviour in firePET is rated as normal flammable. When the source of ignition is removed, PET continues to burn,forming droplets. The oxygen index (the oxygen concentration required for combustion) at 23%is average compared to other plastics.

Areas of use Applications• General machine engineering • Ratchet wheels• Vehicle construction • Bushes• Precision mechanics • Gear wheels• Electrical industry • Sliding elements• Information technology • Insulators

• Casing parts• Counter components• Precision bearings• Cam disks

MachiningPET develops a brittle, flowing chip and is suitable for machining on automatic lathes, but it canalso be machined on cutting machine tools. The semi-finished products can be drilled, milled, sawed, planed and turned on a lathe. It is also possible to cut a thread into the material or insert athreaded element. Generally no cooling or lubricating emulsion is necessary.


Plastics that are highly resistant to chemicals


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Polyethylene is a semi-crystalline thermoplastic with high toughness and chemical resistance, ratherlow mechanical strength in comparison to other plastics and cannot be used at high temperatures.The individual polyethylenes differ in regard to their molar mass (molecular weight), which isimportant for the respective physical properties. This means that in addition to the commonproperties that all types have, certain ones have type-specific properties.

The polyethylene semi-finished products that we offer – from which we also manufacture finishedproducts – consist of high density polyethylene types produced by extrusion or moulding proces-ses.

Main properties• Low density compared to other materials (0.94 g/cm3)• High impact resistance, also at low temperatures• Minimum water absorption (< 0.01%)• Excellent chemical resistance• High corrosion resistance• Anti-adhesive• Very good electrical insulator• High vibration absorption• Physiologically safe (does not apply to regenerate semi-finished products)

ColoursPE – HD: natural, blackPE – HMW: natural, greenPE – UHMW: natural, green, black

Other colours on request.

Sliding propertiesPE-HD (PE 300; molar mass approx. 200,000 g/mol) is very suitable for welding due to its relativelylow molar mass; however, it is not abrasion resistant and has low stability values. This leads to ahigh level of sliding abrasion, which excludes its use in sliding applications.

PE-HMW (PE 500; molar mass approx. 500,000 g/mol) has better sliding properties because of itshigher molar mass and is also more abrasion resistant than PE-HD. In combination with its goodtoughness, it is suitable for use in low stress components that are not subject to any high degreeof sliding abrasion.

PE-UHMW (PE 1000; molar mass approx. 4,500,000 g/mol). Because of its high molar mass it hasvery good wear resistance, bending strength and impact resistance and good noise absorbtion.Due to its excellent sliding properties and low sliding abrasion, it is the ideal material for lightlyloaded components.

Both PE-HMW und PE-UHMW are also available as regenerated material, although it must be noted that the respective physical properties are slightly reduced.

Chemical resistanceAll PE types are resistant to acids, alkaline solutions, salts and salt solutions, alcohols, oils, fats, waxes and many solvents. Aromatics and halogenated hydrocarbons cause swelling. All PE typesare not resistant to strong oxidising materials (e.g. nitric acid, chromic acid or halogens), and there is a danger of stress corrosion cracking.

Polyethylene (PE)

PE


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PE

Weathering effectsAs a general rule, no PE types are resistant to UV rays. This does not apply to the black coloured types, which are resistant to UV rays (also in combination with atmospheric oxygen).

Behaviour in fireAll PE types are rated as normal flammable. When the source of ignition is removed they continueto burn and form drops. However, apart from carbon dioxide, carbon monoxide and water, onlysmall quantities of carbon black and molecular constituents of the plastic develop as conflag-ration gases. The oxygen index (the oxygen concentration required for combustion) at 18% is lowcompared to other plastics.

Areas of use ApplicationsPE-HD PE-HD• Electroplating industry • Component parts in chemical plant construction• Chemical industry • Fittings• Chemical apparatus construction • Inserts

• Stacking boxes

PE-HMW PE-HMW• Food industry • Cutting table surfaces• Meat processing industry • Agitator blades• Sporting venue construction • Wall linings in refrigeration rooms

• Impact bands• Knife blocks

PE-UHMW PE-UHMW• Electroplating industry • Rope pulleys, guide rollers• General machine engineering • Sprocket wheels and pinions• Coal processing • Gear wheels• Packaging industry • Chain guides• Conveying technology • Slides• Paper industry • Suction plates• Electrical industry • Knife-over roll coaters

• Chute linings for silos• Conveyor trough linings• Abrasion protection strips

MachiningIn addition to the good welding properties ofPE-HD and PE-HMW, all PE types can also bemachined on machine tools. The semi-finishedproducts can be drilled, milled, sawed, planedand turned on a lathe. It is also possible to cut athread into the material or insert a threadedelement. As a rule, no cooling or lubricatingemulsion is necessary.


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PP

Polypropylene is a semi-crystalline thermoplastic with high rigidity and very good chemical resi-stance. Characteristic for polypropylene is a CH3 side-group in the monomer structural unit, whichcan be aligned in various spatial positions during polymerisation. The various spatial alignmentsare significant for the physical properties and differ according to the following:

• Isotactic (regular, one-sided alignment in the macromolecule)• Syndiotactic (regular, double-sided alignment in the macromolecule)• Atactic (irregular, random alignment in the macromolecule)

AlignmentA distinction is also made between homopolymers and copolymers; copolymers are tougher buthave less mechanical and chemical stability.

As the physical properties improve considerably with the increase in the isotactic concentration inthe polymer, isotactic polypropylene homopolymers should be the first choice for use in the technical area. The polypropylene semi-finished products that we offer – from which we also manufacture finished products – are produced by extrusion or moulding processes.

Main properties• Low density compared to other materials (0,91 g/cm3)• Minimum water absorption (< 0.01%)• Excellent chemical resistance, also to solvents• High corrosion resistance• Relatively high surface hardness• Very good electrical insulator• Physiologically safe

ColoursNatural (white), grey (≈ RAL 7032)Other colours available on request.

Slip propertiesPP-H is subject to strong sliding abrasion and is thus not suitable for use in sliding applications.

Chemical resistancePP-H is resistant to acids, alkaline solutions, salts and salt solutions, alcohols, oils, fats, waxes andmany solvents. Aromatics and halogenated hydrocarbons cause swelling. PP-H is not resistant tostrong oxidising materials (e.g. nitric acid, chromic acid or halogens) and there is a danger of stresscorrosion cracking.

Behaviour in firePP-H is rated as normal flammable. When the source of ignition is removed PP-H continues toburn, forming droplets. However, apart from carbon dioxide, carbon monoxide and water, onlysmall quantities of carbon black and molecular constituents of the plastic develop as conflag-ration gases.

The oxygen index (the oxygen concentration required for combustion) at 18% is low compared toother plastics.

Polypropylene (PP)


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PP

Weathering effectsPP-H is not resistant to UV rays. UV rays, in combination with atmospheric oxygen, oxidise the surface and discolouration occurs. If the material is exposed to the effects of UV rays for a longerperiod, this will cause irreparable damage and decomposition of the surface.

Areas of use Applications• Electroplating industry • Pump parts• Chemical industry • Component parts in chemical apparatus construction• Machine engineering • Fittings• Stamping/punching plants • Valve bodies

• Product holders for electroplating processes• Punching pads

MachiningIn addition to its good welding properties, PP-H can also be machined on machine tools. The semi-finished products can be drilled, milled, sawed, planed and turned on a lathe. It is also possible tocut a thread into the material or insert a threaded element. Generally no cooling or lubricatingemulsion is necessary.

During cutting, it is very important to ensure that the tools that are used are always adequatelysharp. Blunt tools cause the surface to heat, which can cause “smearing” and consequently unacceptable surface finishes.


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PVC

Polyvinylchloride (PVC)

Polyvinylchloride – hard (PVC-U) is an amorphous thermoplastic with no added plasticiser. It has ahigh hardness and rigidity. According to DIN 16 927 the material is classified as normal shock resistant, however its toughness values border on being rated as highly shock resistant, whichgives it a high degree of safety in regard to the design of components. The polyvinylchloridesemi-finished products that we offer – from which we also manufacture finished products – areproduced in extrusion or moulding processes.

Main properties• Hard surface• High rigidity• Low water absorption• Excellent chemical resistance• Fire resistant (UL 94 V 0)• Easily thermoformed • Can be bonded• Good cutting properties

Coloursgrey (≈ RAL 7011), black, red, transparent

Other colours available on request.

Sliding propertiesPVC-U is not subject to any major sliding abrasion and is thus suitable for use in sliding appli-cations.

Weathering effectsPVC-U is not resistant to the effects of UV rays. In combination with atmospheric oxygen, the surface oxidises and discolouration occurs. If the material is exposed to UV rays and atmosphericoxygen for longer periods, irreparable damage and decomposition of the surface will occur.

Food law suitabilityPVC-U does not comply with the requirements of the German Federal Institute for Risk Assess-ment (BgVV) or the FDA and may not be used for manufacturing consumer goods that come intodirect contact with food.

Chemical resistancePVC-U is resistant to acids, alkaline solutions, alcohols, oils, fats, aliphatic hydrocarbons and petrol.PVC-U is not resistant to benzole, chlorinated hydrocarbons, ketones or esters.In combination with strong oxidising materials (e.g. nitric acid or chromic acid), there is a dangerof stress corrosion cracking.

Behaviour in firePVC is rated as fire resistant in the highest category, even without additives. When the source ofignition is removed, PVC is self-extinguishing.The oxygen index (the oxygen concentration required for combustion) at 40% is very high com-pared with other plastics.


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PVC

Areas of use Applications• Electroplating industry • Pump parts• Machine engineering • Fittings• Filling plants • Valve bodies• Photo industry • Component parts in chemical plant construction

• Feed tables• Machine and equipment covering

MachiningIn addition to its good welding properties and the possibility of bonded connections, PVC-U canalso be machined on machine tools. The semi-finished products can be drilled, milled, sawed, planed and turned on a lathe. It is also possible to cut a thread into the material or insert a threaded element. Generally no cooling or lubricating emulsion is necessary.

During processing it is very important to ensure that the tools that are used are always adequatelysharp. If this is not the case, the high temperatures caused by the blunt cutting edge can cause thematerial to decompose and, in combination with atmospheric moisture, can cause small quanti-ties of hydrochloric acid to form as aerosols.

In addition, because of its hard-brittle properties, we recommend that elastomer or thermoplasticwashers are used for PVC-U component parts that are to be fastened by screwing. The use of washers such as this reduces the danger of transmitting high stresses by tightening the screws andthe stress cracking around the edge of the drilled hole that this causes.


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PVD

F

Polyvinylidenefluoride (PVDF)

Polyvinylidenefluoride is a high crystalline thermoplastic with good mechanical, thermal and electrical properties. As a fluoroplastic, polyvinylidene fluoride has excellent chemical resistancewithout the disadvantages of low mechanical values and difficult workability of other fluoro-plastics. Our polyvinylidene semi-finished products – from which we also manufacture all finishedproducts – are manufactured in extrusion or moulding processes.

Main properties • Low density in comparison to other • High chemical resistance

fluoroplastics • Good hydrolytic stability• Good mechanical stability compared to • Weather resistant

other fluoroplastics • Radiation resistant• Can be used continuously at high temperatures • Good electric insulator

(+140°C in air) • Fire resistant (UL 94 V 0)• Absorbs practically no water • Physiologically safe• Good dimensional stability • High abrasion resistance

Coloursnatural (white to ivory)

Sliding propertiesPVDF has good sliding properties, is resistant to wear and is very suitable for chemically stressedsliding applications that are also subjected to thermal influences. However, in constructive design,the relatively high coefficient of thermal expansion should be considered.

Resistance to radiation / Weathering effectsPVDF is resistant to both b-rays and g-rays as well as UV rays in connection with atmospheric oxygen. Hence PVDF is ideal for use in the pharmaceutical and nuclear industries and under weathering effects.

Chemical resistancePVDF is resistant to acids and alkaline solutions, salts and salt solutions, aliphatic and aromatichydrocarbons, alcohols and aromatics. PVDF is not resistant to ketones, amines, fuming sulphuricacid, nitric acid or to several hot alkalis (concentration related). Dimethyl formamide and dimethyl acetamide dissolve PVDF..

Behaviour in fireEven without additives, PVDF is rated in the highest category as fire resistant. When the source of ignition is removed, PVDF extinguishes itself. At 78%, the oxygen index (= the concentration of oxygen required for combustion) is very high compared to other plastics.

Areas of use Applications• Chemical and petrochemical industries • Pump parts• Pharmaceutical industry • Fittings and fitting components• Textile industry • Valves and valve components• Paper industry • Seals• Food industry • Friction bearings

• Component parts in plant/apparatus engineering

MachiningIn addition to its good welding suitability, PVDF can also be machined on machine tools. With therespective surface treatment, PVDF can be bonded with a special solvent adhesive. Fluoropolymers decompose at temperatures above approx. 360°C and form highly aggressive and toxichydrofluoric acid. As polymer dust can form when the material is being machined, smokingshould not be permitted at the workplace.


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PTFE

Polytetrafluoroethylene is a high crystalline thermoplastic with excellent sliding properties, anti-adhesive surfaces, excellent insulation properties, an almost universal chemical resistance and anexceptionally broad temperature deployment spectrum. However, this is offset by low mechanicalstrength and a high specific weight compared to other plastics. To improve the mechanical properties, polytetrafluoroethylene is compounded with fillers such as glass fibre, coal or bronze.The polytetrafluoroethylene semi-finished products that we offer – from which we also manufac-ture all finished parts – are produced in pressure sintering and ram extrusion processes, films areproduced in a peel process.

Main properties• Excellent sliding properties• Highest chemical resistance, also to solvents (limited with PTFE + bronze)• Resistant to hydrolysis (limited with PTFE + bronze)• High corrosion resistance (limited with PTFE + bronze)• Broad temperature deployment spectrum (-200°C to +260°C)• Resistant to weathering• Does not absorb moisture• Physiologically safe (not PTFE + coal / + bronze)• Good electrical insulator (not PTFE + coal / + bronze)• Good thermal insulator (not PTFE + coal / + bronze)• Anti-adhesive• Virtually unwettable with liquids• Fire resistant

ColoursPTFE pure: weißPTFE + glass: light greyPTFE + coal: blackPTFE + bronze: brown

Sliding propertiesPTFE has excellent sliding properties and because of its very close static and dynamic abrasion values, it prevents the “stick-slip effect”. However, due to its low mechanical strength, PTFE hashigh sliding abrasion and a tendency to creep (cold flow). Hence, unfilled PTFE is only suitable forsliding applications with low mechanical load. Its load bearing capacity can be constructively improved by equipping the sliding element with several chambers. It must be ensured that thechamber is fully enclosed so that the slip lining cannot escape (“flow out”).

PTFE + glass has worse slip properties than pure PTFE due to the filler, but it can bear much higherloads. Sliding abrasion and the coefficient of elongation are reduced, while creep resistance anddimensional stability increase. The glass particles embedded in the material cause higher wear onthe mating part than pure PTFE.

PTFE + coal has similarly good slip properties as pure PTFE, but because of the addition of a filler, ithas much better mechanical stability. As with glass as a filler, sliding abrasion and the coefficientof elongation are reduced while creep resistance and dimensional stability increase. Sliding ele-ments filled with coal can be used for applications that are occasionally or constantly surroundedby water.

PTFE + bronze has the best mechanical values of all filled PTFE types and is very suitable for slidingapplications. The filler causes the lowest sliding abrasion of all PTFE types. In addition to this, ther-mal conductivity, and consequently the dissipation of friction heat from the friction bearing, isconsiderably improved compared to other sliding materials, which leads to a longer life.

Polytetrafluoroethylene (PTFE)


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PTFE

Weathering effectsAll PTFE types are very resistant to UV rays, even in combination with atmospheric oxygen. No oxidation or discolouration has been observed.

Chemical resistanceUnfilled PTFE is resistant to almost all media apart from elemental fluorine, chlorotrifluoride andmolten or dissolved alkali metals. Halogenated hydrocarbons cause minor, reversible swelling. Inthe case of filled PTFE, due to the filler one can reckon with a lower chemical resistance, althoughit is the filler that forms the reaction partner to the medium, not the PTFE.

As a rule, it can be said that the types filled with coal are not much less resistant than pure PTFE.The types filled with glass are resistant to acids and oxidising agents but less resistant to alkalis.The types filled with bronze have a much lower chemical resistance than pure PTFE.

Before using filled PTFE types in chemically burdened environments, their resistance to the respec-tive medium should always be tested.

Behaviour in firePTFE is rated as fire resistant in the highest category. It does not burn when an ignition source isadded. The oxygen index (the oxygen concentration required for combustion), at 95% is one ofthe highest compared to other plastics.

Areas of use Applications• Chemical industry • Friction bearings• Machine engineering • Bearing bushes• Precision mechanics • Shaft seals• Electrical industry • Piston rings• Textile industry • Valve seats/seat rings• Paper industry • Insulators• Food industry • Flat seals• Aerospace industry • O rings• Building and bridge construction • Test jacks

• Thread guides• Anti-adhesive liners

MachiningPTFE is difficult to weld and that only by using a special process. It can be machined on machinetools. The semi-finished products can be drilled, milled, sawed, planed and turned on a lathe. It isalso possible to cut a thread into the material or insert a threaded element. PTFE can also be bonded when the surface has been suitably treated by etching with special etching fluid.

Up to approx. 19°C, PTFE is subject to a phase transition which is normally accompanied by an increase in volume of up to 1.2%. This means that finished parts that are dimensionally stable at23°C can have considerable dimensional deviations at temperatures below 19°C. This must be considered in the design and dimensioning of PTFE components. When the material is being machined, attention must be paid that good heat dissipation is guaranteed for parts with mini-mum tolerances, otherwise the good insulation properties can lead to dimensional deviations infinished parts after cooling because of the heat build-up and thermal expansion.

Fluoropolymers decompose above approx. 360°C forming highly aggressive and toxic hydrofluoricacid. As polymer dust can form when the material is being machined, smoking should not be permitted at the workplace.


High performance plastics


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Polyetheretherketone is a semi-crystalline thermoplastic with excellent sliding properties, verygood mechanical properties, even under thermal load and an excellent resistance to chemicals.The high continuous working temperature rounds out the profile of this high-performance plasticand makes it a virtually universally useable design material for highly stressed parts. Thepolyetheretherketone semi-finished products that we offer – from which we also manufacturefinished parts – are produced in extrusion or moulding processes.

Main properties• High continuous working temperature • High dimensional stability

(+250°C in air) • Excellent chemical resistance• High mechanical strength • Resistant to hydrolysis• High rigidity • Good electrical insulator• High creep resistance, also at high temperatures • Radiation resistant• Good sliding properties • Physiologically safe• High wear resistance • Fire resistant (UL 94 V 0)

Colournatural (≈ RAL 7032), black

Sliding propertiesPEEK ideally combines good sliding properties with high mechanical strength and thermal stabi-lity as well as excellent chemical resistance. Because of this, it is suitable for sliding applications.Modified types containing carbon fibre, PTFE and graphite – with highest wear resistance, a lowcoefficient of friction and a high pv limiting value – are available for component parts that aresubject to especially high abrasion and wear.

Resistance to weatheringPEEK is resistant to X rays, b-rays and g-rays. Hence PEEK is ideal for use in the pharmaceutical andnuclear industries. PEEK is not resistant to UV rays in combination with atmospheric oxygen.

Chemical resistancePEEK is resistant to non-oxidising acids, concentrated alkaline solutions, salt solutions, cleaningagents or paraffin oils. It is not resistant to oxidising agents such as concentrated sulphuric acid,nitric acid or hydrogen fluoride.

Behaviour in firePEEK is rated fire resistant in the highest category. When the source of ignition is removed PEEK isself-extinguishing. The oxygen index (the oxygen concentration required for combustion) is 35%.

Areas of use Applications• Chemical and petrochemical industries • Gear wheels• Pharmaceutical industry • Friction bearings• Food industry • Bobbins• Nuclear industry • Fittings (e.g. casing for hot water meters)• Aerospace industry • Valves• Defence technology • Piston ring

• Parts for car engines (e.g. bearing cages)MachiningIn addition to its good welding and bonding properties PEEK can be easily machined. The semi-finished products can be drilled, milled, sawed, planed and turned on a lathe. It is also possibleto cut a thread into the material or insert a threaded element. Generally no cooling or lubricatingemulsion is necessary.

Polyetheretherketone (PEEK)

PEEK


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PSU

Polysulphone is an amorphous thermoplastic with high mechanical stability and rigidity and remarkably high creep resistance across a wide temperature range and high continuous workingtemperature for an amorphous plastic. In addition, polysulphone is transparent because of itsamorphous molecule structure. Its very good resistance to hydrolysis and very good dimensionalstability round out the profile. The polysulphone semi-finished products that we offer – fromwhich we also manufacture finished parts – are produced by extrusion.

Main properties• High continuous working temperature (+160°C in air)• Very good resistance to hydrolysis (suitable for repeated steam sterilisation)• High toughness, also at low temperatures• High dimensional stability• Good electrical insulator• High mechanical stability• High rigidity• High creep resistance across a wide temperature range• Good resistance to radiation• Physiologically safe• Fire resistant (UL 94 V 0)

ColourNatural (honey yellow, translucent)

Sliding propertiesPSU is subject to strong sliding abrasion and is thus unsuitable for sliding applications.

Resistance to radiation/weathering effectsPSU is resistant to X rays, b-rays, g-rays and microwaves. Hence PSU is ideally suited for use in thepharmaceutical, food and nuclear industries.

Chemical resistancePSU is resistant to inorganic acids, alkaline solutions and salt solutions, as well as cleaning agentsand paraffin oils. It is not resistant to ketones, esters, chlorinated hydrocarbons or aromatic hy-drocarbons.

Behaviour in firePSU is rated as fire resistant in the highest category. When the source of ignition is removed, PSUis self-extinguishing. The oxygen index (the oxygen concentration required for combustion) is30%.

Areas of use Applications• Electro-technology • Bobbins• Electronics • Inspection glasses• Vehicle construction • Sealing rings• Equipment engineering • Equipment casing• Aerospace industry • Insulating sleeves

MachiningIn addition to its good welding and bonding properties PSU can be easily machined. The semi-finished products can be drilled, milled, sawed, planed and turned on a lathe. It is also possibleto cut a thread into the material or insert a threaded element. Generally no cooling or lubricatingemulsion is necessary.

Polysulphone (PSU)


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PEI

Polyetherimide is an amorphous thermoplastic with high mechanical stability and rigidity as wellas remarkably high creep resistance across a wide temperature range and high continuous working temperature for an amorphous plastic. In addition, polyether imide is transparent because of its amorphous molecule structure. Its very good resistance to hydrolysis and very gooddimensional stability round out the profile.

The polyetherimide semi-finished products that we offer – from which we also manufacture finishedparts – are produced by extrusion.

Main properties• High continuous working temperature (+170°C in air)• High mechanical stability• High rigidity• High creep resistance across a broad temperature range• High dimensional stability• Very good resistance to hydrolysis (suitable for repeated steam sterilisation)• Good electrical insulator• Good resistance to radiation• Physiologically safe• Fire resistant (UL 94 V 0)

ColourNatural (amber, translucent)

Sliding propertiesPEI is subject to strong sliding abrasion and is thus unsuitable for sliding applications.

Resistance to radiation/weathering effectsPEI is resistant to x-rays, b-rays and g-rays as well as UV-rays in combination with atmospheric oxygen. Hence PEI is ideally suited for use in the pharmaceutical and nuclear industries and underweathering effects.

Chemical resistancePEI‘s resistance should be tested before it is used with ketones, aromatic hydrocarbons or halo-genated hydrocarbons. Alkaline reagents with pH values > 9 should be completely avoided.

Behaviour in firePEI is rated as fire resistant in the highest category, also without additives. When the source of ig-nition is removed, PEI is self-extinguishing. The oxygen index (the oxygen concentration requiredfor combustion), at 47% is very high compared to other plastics.

Areas of use Applications• Electro-technology • Bobbins• Electronics • Inspection glasses• Vehicle construction • Equipment casing• Equipment engineering • Insulating sleeves

Polyetherimide (PEI)


Structure and properties of plastics

(CH2)5

HN – CO

–– ––

–– [NH – (CH2)6 – NH – (CO – CH2)4 – CO ]n ––2

–– [NH – (CH2)11 – CO]n ––


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1. Fundamentals

In general terms, plastics are macromolecular compounds manufactured from existing naturalsubstances by chemical conversion or by synthesising products from the chemical decompositionof coal, petroleum or natural gas. The raw material plastic fusions produced by conversion or synthesis are usually formed into semi-finished products or finished products by applying tempe-rature and pressure. These processes include, among others, injection moulding and extrusion. Exceptions to this are the polyamide semi-finished products manufactured by Licharz in static andcentrifugal moulding processes, as these methods work without pressure.

2. Structure

2.1 ClassificationUsually plastics are classified in two main groups – thermoplastics and duroplastics.

• When they are heated to an adequate degree, thermoplastics soften until they are melted andthen harden again on cooling. Forming and reforming thermoplastics is based on this repeata-ble process. Provided the heating does not cause excess thermal stress leading to chemical decomposition, there is no change to the macromolecules.

• Because of their molecular structure, duroplastics cannot be reformed after they have been originally formed, not even at high temperatures. The original formation is based on a chemicalreaction of intermediates – most of which are not macromolecular – to closely cross-linkedmacromolecules.

In DIN 7724, plastics are classified according to their behaviour when subjected to different temperatures. This leads to the following classification:

• Plastomers (= thermoplastics) are non-cross-linked plastics that react energy-elastically (metal-elastically) within their service temperature range, and which soften and melt from a material-specific temperature onwards.

• Thermoplastic elastomers are physically or chemically coarse-meshed, cross-linked plastics or plastic mixtures. In their normal service temperature range they behave entropy-elastically (rubber-elastically) but at high temperatures they soften to the point of melting.

• Elastomers are coarse-grained, temperature-stable, cross-linked plastics which are entropy-elastic (rubber-elastic) in their service temperature range. They can be formed reversibly and donot flow until they reach their decomposition temperature range.

• Duromers (= duroplastics) are close-meshed, cross-linked plastics, which react energy-elastically(metal-elastically) in their service temperature range and which do not flow until they reachtheir decomposition temperature range.

2.2 Structure and form of the macromoleculesApart from a few exceptions, the plastics that are produced today are generally based on the ability of carbon to form long chains through atomic bonds. As opposed to ion bonds, the outershell of the carbon atom fills to the noble-gas configuration with eight electrons. Bond partnerscan be complete atom groups or single atoms such as hydrogen, oxygen, nitrogen, sulphur or carbon.

Structure and properties of plastics


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Through synthesis many individual small molecules (= monomers) of one or more starting pro-ducts are bonded together chemically into macromolecules (= polymers). As a rule, the resultingchains are between 10-6 and 10-3 mm long. The size of the macromolecules is expressed by the degree of polymerisation n or by the molecular weight. As it is not possible to achieve a homo-geneous distribution of the chain length in polymerisation, the values are given as averages. Intechnology, it is usual to state a measure for the viscosity (e.g. melt index, M.F.I.) instead of the de-gree of polymerisation or the molecular weight. The higher n is, the higher the viscosity.

In the formation of macromolecules a distinction is made between linear, branched and cross-linked molecule structures.

Linear or branched macromolecules produce thermoplastics, weak cross-linked ones produce elastomers and strongly cross-linked macromolecules produce duromers.

As Licharz has specialised in the manufacture and marketing of semi-finished products and finished parts from thermoplastics (plastomers), we will only consider the thermoplastic groupand its various sub-groups in the following. There is adequate literature available that deals withthe other groups of plastics.

2.3 Molecular bonding forceThe coherence of macromolecules is based on chemical and physical bonding forces.

For polymer materials these are:

• the primary valency forces as a chemical bonding force• the secondary valency force (van der Waals forces) as a physical bonding force

The primary valency forces are essentially responsible for the chemical properties of the plastic,while the secondary valency forces are responsible for the physical properties and the alignmentof the macromolecules.

2.3.1 Primary valency forcesThe primary valency forces that are generated by the bond distance and the bonding energy come from the atomic bond of the polymers. The smaller the bond distance between the indivi-dual atoms in the polymer chain, the higher the bonding energy. The bonding energy is also increased with the number of bonds of the individual atoms.

• If the monomers are bonded with one another at twopoints (bifunctional) this forms a threadlike, linearmacromolecule.

• If the individual monomers are bonded at more thantwo points this produces molecule branches.

• If monomers are mainly bonded with one another atthree points (trifunctional) this forms a spatial, weaklyor strongly cross-linked macromolecule.


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2.3.2 Secondary valency forces (Secondary bonding forces)The secondary valency forces come from the intermolecular bonds. They consist of three forces:

1. Dispersion forces

are the forces of attraction between the individual molecules in the substance. These are greaterthe closer the molecules are to one another. In the crystalline ranges of the semi-crystalline plastics, these forces are especially high because of this. This explains their mechanical superioritycompared to amorphous plastics.

Increasing the distances between the molecules drastically reduces the forces. One reason for increasing distances could be vibration caused by heating the polymer material. But intercalatingforeign atoms between the molecules (e.g. solvent or water) can also increase the distance.

By intercalating plasticisers in the molecule chain, this effect can be used to produce plastics thatare rubber-elastic at room temperature.

2. Dipole forces

are not found in all plastics. They only occur if the ato-mic bond has a strong overweighting to one side dueto the alignment of the atoms in the galvanic series.This can only happen if dissimilar partners form abond. The more electronegative atom of a bond drawsthe electron pair towards itself ( polarisation) and adipole is formed. The neighbouring polarised groups attract one another because of the unequalelectrical charges.

Polymer materials with a dipole character are generally less soluble (with the exception of strongpolar solvents) and soften at higher temperatures than polymer materials without a dipole character. PVC is the most significant polymer material with a dipole character.

3. Hydrogen bridges

These are bonds of opposite oxygen and hydrogen molecules of different molecule chains due totheir high affinity to one another. This type of bond is the most stable of all secondary valencybonds. The hydrogen bridges are only dissolved with very strong forces and immediately reformthemselves as soon as the displacement forces cease, rather like Velcro. The excellent properties,like a high melting point or extraordinary toughness, of various polymer materials such as polyamides are due to hydrogen bridges.

Other purely physical intermolecular bonds are entanglement, looping of chains or bonding inthe semi-crystalline ranges. These are described as network points that allow molecule-interlocking power transmission.

In very thin and symmetrical molecule chains, the secondary valency powers are generally not sopronounced, apart from molecule parts in the semi-crystalline ranges. The molecule chains of polymer materials such as this can easily slide past one another if they are subject to mechanicalstress. These materials have very good sliding properties, but at the same time they are subject tohigh wear due to abrasion, and they have a high tendency to creep. Examples of this are PE-UHMW and PTFE.

- + - + - + - +

+ - + - + - + -


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2.4 Order of the macromoleculesThermoplastics are classified in two groups according to the order of their macromolecules. A distinction is made between

• amorphous thermoplastics with completely disordered macromolecules(wadding-like structure) due to the form of the basic units and /or the alignment of any side groups that exist. Amorphous thermoplastics arehard, brittle and transparent.

• semi-crystalline thermoplastics with some highly ordered, parallel posi-tioned macromolecule chains that form crystallites. A large number ofcrystallites form so-called spherulites. Complete crystallisation ( semi-crystalline plastic) is not possible because of chain looping during poly-merisation. Semi-crystalline plastics are tough and opaque to white.

Semi-crystalline plastics have different properties than amorphous plastics due to the higher se-condary valency forces. They soften later, can be subjected to more mechanical stress, are more resis-tant to abrasion, are tough-elastic rather than brittle and are generally more resistant to chemicals.Because of this, the semi-crystalline thermoplastics are more significant for engineering plastics.

2.5 Alignment of the molecules in the macromoleculeBasically there are three different alignment possibilities of the substitute “R” in the molecule chain.

1. AtacticRandom alignment in the chain

2. IsotacticRegular, one-sided alignment in the chain

3. SyndiotacticRegularly changing alignment in the chain

The polymer material can only have a crystalline structure if a regular chain alignment exists for aspecific length of the complete sequence. As a result of this, the molecule alignment has a directinfluence on the mechanical properties.

2.6 Homopolymers / copolymersPlastics that are polymerised from the same monomer structural elements are called homopoly-mers. Plastics that consist of two or more monomer units are described as copolymers. When copolymers are being produced, the monomer units are not just mixed, but chemically integratedinto the molecule chain. With copolymerisation it is possible to improve specific material properties in a targeted manner.

Essentially, a distinction is made between four different types of copolymers:

1. Statistic chain structure (random distribution of the different monomer units)2. Alternating chain structure (regular change of the different individual monomer units)3. Block-like chain structure (regularly changing blocks of the different monomer units)4. Graft polymers (homogeneous chain of one unit with grafted side chains of

a different unit)

C

R

C


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Another alternative to change the properties is to (physically) mix two polymers. The materialsproduced from this are known as polyblends.

3. Properties

The above-described molecular structure of the plastics produces a range of special properties andunique characteristics. In the following, several of these will be introduced and described in moredetail.

3.1 Mechanical propertiesThe mechanical properties of plastics are primarily determined by the secondary bonding forces.The more pronounced these are, the better the mechanical properties.

Because of the morphological structure of plastics, the properties are dependent on factors suchas

• time• temperature• moisture• chemical influences

and fluctuate strongly depending on the influence of one of more factors.

3.1.1 Visco-elastic behaviourAll plastics have a more or less pronounced visco-elasticity. Mechanical stress dissolves the secondary bonds in the molecule structure, and the molecule chains slide past one another. Thelonger the stress is applied, the further the chains moveaway from each other.

This means that compared to metallic materials, plastics deform when subjected to high stress over a long period (r cold flow). When maximum expansion has been reached,the plastic solidifies again and expansion is reduced. Theweaker the secondary bonds in the macromolecule are, themore pronounced these properties are.

A simple molecule structure with no entangled side-groups,or a low degree of crystallinity in the plastic, encourages thechains to glide past one another.

This deformation is further promoted by thermal influences. The molecules are stimulated to vibrate which leads to greater distances between the chains and consequently to weaker secondary bonds. Hence, stability values for dimensioning component parts cannot be used as asingle point value, but rather they must be included in the static calculation in relation to stress time and thermal effects.

3.1.2 Moisture absorptionIn particular plastics produced by polycondensation (r polymerisation with the cleavage of e.g.water) have a tendency to absorb water from the surroundings via inward diffusion. This processis a reversible balanced reaction in which the more water which is available, the more the plasticsabsorb. The intercalated water molecules increase the distance between the molecule chains and

seconds

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r

r


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weaken the secondary bonds. The chains become more mobile, which results in a reduction in mechanical values andan increase in elasticity as well as swelling.

In the case of polyamides the hydrogen bridges do not justensure excellent mechanical properties such as good abrasionresistance, mechanical stability and toughness, they also leadto intercalation of water in the molecule chains.

As both water and the polyamide molecules are capable offorming hydrogen bridges when the water has diffused intothe molecule chain, it separates the existing hydrogen bridgeand occupies the free valences. The water molecules make thepolymer chain slightly more mobile which gives room for more water molecules. This process continues until the saturation point has been reached. When the water concen-tration in the surroundings falls again, the process is reversed.Water absorption is favoured by increasing temperatures andhigh ambient moisture. By absorbing water, the polyamidesbecome more tough-elastic and less solid and rigid.

For applications in which these properties are required, it ispossible to increase the water concentration by storing thematerials in hot water (r conditioning).

For water absorption through atmospheric moisture, it should be noted that the process in thick-walled component parts only takes place close to the surface and that generally no waterabsorption – with the described results – should be expected in the inner area of the component part.

3.1.3 Chemical influencesChemicals can attack and separate the primary and secondary bonds of the molecule chains,which can be seen by swelling or decomposition of the plastic. Swelling of the plastic is caused bythe chemical diffusing into the molecule structure, leading to a loss of stability. In a purely chemical attack, the loss of stability can occur with no noticeable increase in volume or weight.

The inward diffusion of the foreign molecules reduces the secondary valency powers to such anextent that the internal stresses in the material or external forces can cause (stress) cracking (rstress corrosion cracking).

3.2 Chemical resistanceCompared to metallic materials, plastics have a high resistance to chemicals. This can be attributedto the fact that the molecules are linked through atomic bonding. Because of their physical nature, the secondary valency powers only play a subordinate role. Most plastics are resistant tomany acids and alkaline solutions as well as aqueous salt solutions and solvents.

However, oxidising acids and organic solvents can be a problem in many cases, but this problemcan be resolved by using special plastics.

Resistance to chemicals decreases as the temperature and exposure time increase. This can be seenby an increase in weight and volume as well as a decline in mechanical values. A lack of resistanceto a specific medium can generally be seen by a swelling of the plastic with no appreciable chemical attack, or in a chemical attack with medium to severe swelling.

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3.3 Electrical propertiesBecause of the atomic bonding of their molecules, plastics, unlike metallic materials with ionbonds, do not have free electrons and are thus classified as non-conductors. However, the insulati-on properties can be greatly reduced or even completely negated through water absorption and /or the addition of metallic fillers, graphite or carbon black.

Many plastics are suitable for use in high-frequency areas as their dielectric losses are very low andthey only heat up a little.

Losses in the area of application should be

• for high frequency insulators er. tan d < 10-3

• for high frequency heating er. tan d > 10-2

Plastics generally have a surface resistance of >108 Ω . In the event of friction with a second non-conductor, this leads to electrostatic charging due to electron transfer at the boundary surface. Plastics are not suitable for use in explosion protected areas without any conductance additives, as sparks can be caused when they touch earthed objects.

3.4 Dimensional stabilityIncreasing heat or intercalation of foreign molecules (e.g. water or solvent) in the chain com-pound of the molecule chains increases the distance between the chains. This causes the volumeof the plastic components to change, resulting in a change in its dimensions. Vice versa, as the surroundings become colder, or when the water concentration decreases, the volume is reducedwhich is accompanied by the corresponding shrinking and size reduction.

Plastics are generally formed or reformed to semi-finishedproducts from the melt. As a rule, the semi-finished productswe manufacture are thick-walled products with high volu-mes, such as solid rods, slabs and blocks. As plastics are badheat conductors, the edges of the products cool muchquicker than the core. However, because of heat expansion,this has a greater volume than the edges. The outer area hasalready solidified with a loss of volume and the associatedshrinking. The shrinking of the core causes inner stresses that“freeze” as the product cools. These stresses can be mini-mised by heat treatment (r annealing, similar to stress-freeannealing of steel). However, some residual stress can remain. These decrease over a period of time due to the visco-elastic behaviour of the plastics (r relaxation).

These residual stresses can be released by one-sided machining or heating and can become obvious through dimensional changes or distortion.

The above-described properties of the plastics are more or less pronounced and can be compen-sated and kept under control relatively easily with constructive measures. But they must be ade-quately considered in the design of components. The following chapters deal with special issuessuch as behaviour in fire, storage, material-compliant tolerances in components and many otherfactors.

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1. Behaviour of plastics in fire and fire ratings

Generally, plastics are organic substances or modifications of organic substances, which, like otherorganic substances are threatened by chain breakage, cleavage of substitutes and oxidation athigh temperatures. Therefore, apart from a few exceptions, plastics are more or less combustiblewhich is something that can be a serious technical problem in the specific use of plastics.

1.1 CombustibilityIf plastics are heated locally or over large surfaces to above their specific decomposition tempe-rature, they release volatile, low molecular constituents. In many cases together with the ambientoxygen, these form a flammable gas mixture which can ignite if an ignition source is added andan adequate supply of oxygen is available.

The amount of heat that is fed in and the volume of the combustible surface that this can affectare both very significant for the evolution of a fire and the course of the fire. Another decisive factor is the atmospheric oxygen concentration.

For instance, it is possible that a large quantity of heat which affects a large volume with a largesurface area but a lack of oxygen only leads to pyrolytic cleavage in the beginning (r release ofhighly flammable, volatile and low molecular constituents). If one adds oxygen in the right concentration, under unfavourable conditions this can result in a deflagration or an explosion.

However, with the same volumes and a lower heat input, as well as an adequately high oxygenconcentration, the same substance only burns slowly.

Because of this behaviour, it is very difficult, if not impossible, to make any fire-technical forecasts.

1.2 Conflagration gasesAs with the combustion of other substances, when plastics burn they produce various conflagra-tion gases. As a rule, these are said to be highly toxic. This is not absolutely correct as, on the onehand, the toxicity depends on the type and quantity of the plastic involved in the fire and, on theother, all conflagration gases resulting from a (substance-independent) fire should be regarded astoxic.

One example is the conflagration gases resulting from the incineration of polyethylene, which, inaddition to small quantities of soot and low molecular plastic constituents, almost exclusively contain carbon monoxide, carbon dioxide and water. This is comparable with the conflagrationgases that occur when wood or stearine are burned.

On the other hand, when polyvinyl chloride is burned, there is a danger of chlorine being released, which in combination with atmospheric moisture or extinguishing water forms to hydrochloric acid.

Many plastics produce a lot of soot when they burn, which makes it difficult for the fire brigadesto reach the source of the fire. These plastics include the polyolefins PE and PP as well as styreneplastics such as PS and ABS.

This must be considered for designs in fire-critical areas.

Behaviour in fire


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1.3 Behaviour in fireAlmost all plastics are combustible. Exceptions to this are PTFE and silicones, which are virtuallynon-combustible. Most plastics continue to burn after they have been ignited and the source ofignition has been removed. Several extinguish when the ignition source is removed, while otherscannot be ignited. In many cases, the plastic melts due to the heat of combustion and forms burning droplets which can promote the spread of the fire. The degree of combustibility can bereduced by adding the corresponding additives.Additives based on the following mechanisms are used:

• EndothermyThe temperature of the plastic is reduced by the decomposition or vaporisation of the additive.This is possible for example with water stores (aluminium hydroxide) or phosphorous com-pounds being added to the plastic.

• Radical bondingThe radicals that form during the fire are bonded by the additive, which slows down the thermaldecomposition and consequently the release of flammable, volatile constituents.

• Formation of heavy gasesHeavy gases are formed through the thermal effects on the additive, preferably halogens, whichshield the plastic from atmospheric oxygen and thus prevent oxidation.

But the use of fire retarding additives does not make plastics non-combustible. Only plastics thatare regarded as being non-flammable are suitable for applications that demand non-combustibi-lity of the plastic.

1.4 Fire ratingsOften, to assess how plastics behave in fire, imprecise terms such as “highly flammable” or “fire resistant” or “non combustible” are used. These terms inadequately reflect the actual behaviour of the plastics and only provide a limited inference for the usability of a plastic for aspecific application. To assess how plastics behave in fire in the areas of electro-technology, traffic,building, etc. there are currently approx. 700 national and international test methods. In the electrical sector the method UL 94 HB or UL 94 V from Underwriters Laboratories (USA) has become the most widely accepted. These tests refer to the burning time and the burning behaviour of plastics. In test UL 94V a distinction is made betweenclassifications V0 to V2, V0 beingthe most favourable rating.

Another possibility of comparingthe flammability of plastics is theoxygen index. In a controllableO2/N2 mixture a vertical plasticsample is ignited and the mini-mum volume of O2 required toburn the plastic is measured. Thistest also allows the effects of flame retardants to be observed.The diagram opposite contains several oxygen indices for com-parison. Index values ≤ 21% can lead tocontinued burning after the sour-ce of ignition has been removed.

PA 6

PA 66

POM

PET

PC

PE

PP

PVC

PVDF

PTFE

PSU

PEI

PEEK

Oak (as a comparison)

0 10 20 30 40 50 60 70 80 90 100Oxygen index (%)


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1. Plastics’ resistance to radiation and weathering

Changes in plastics due to weathering effects and high-energy rays are often described as»aging«, with reference to the process of biological degradation. This is quite an accurate descrip-tion since plastics, as organic materials, do not just have an analogy to natural substances in theirconstituents but also in their macromolecular structure.

The parallels are also obvious by the fact that we often speak of the “life” of a plastic product.The duration is determined by the decomposition of the plastic. It may be relatively long com-pared to other natural substances, but it is still limited.

1.1 RadiationThe majority of plastics are subject to decomposition or a cross-linking of the macromolecularstructure when affected by high-energy radiation. The changes in the molecular structure that actually occur depend on the atmospheric oxygen.

When oxygen is present, generally oxidative decomposition of the plastic occurs. This is especiallythe case when the dose of radiation is small, the surface area of the product is large and the wallsare thin. Under these prerequisites, the atmospheric oxygen has sufficient time to diffuse into theplastic and to occupy the valences that are made free by the radiation.

In the absence of oxygen, the plastic is partially decomposed by the main chains breaking up andpartially cross-linked. Generally decomposition and cross-linking reactions happen at the same time, although one of the reactions is stronger.

In any case, the changes in the plastics caused by radiation are accompanied by a loss of mechani-cal properties such as mechanical stability, rigidity and hardness or brittleness. Plastics that aresubject to cross-linking can experience a change in properties even leading to a rubber-elasticcondition. Besides this, during both the cross-linking and decomposition of the plastics, smallamounts of gaseous substances such as carbon monoxide or carbon dioxide are released.

Attention should be paid to the fact that the described changes are very gradual and that there isno sudden, unannounced change in properties. The effects of radiation on plastics depend on thegeometry of the component, dosage, mechanical stress, temperature and the surrounding medium. Therefore, it is not possible to make a generalised statement about the damaging dosesfor individual plastics.

1.2 Weathering effectsWeathering resistance is mainly evaluated by the visual change of the surface. However, this leaves the question unanswered as to how the mechanical values change. On the one hand, it can-not be ruled out that plastics which are not subject to any great visual changes have a serious lossof mechanical properties and, on the other hand, plastics with considerable visual changes sufferno great loss of mechanical properties. But to evaluate weathering resistance correctly, themechanical properties must be a measured. Some results of weathering are a decline in stabilityand hardness as well as an increase in elasticity or brittleness. The surface of the plastic can appearbleached or oxidatively decomposed or stress cracks can form.

The changes in plastics as a result of weathering are mainly caused by thermal and photo-oxi-dative reactions as well as by the intercalation of water molecules in the plastic’s chain structure.

UV rays and warming by direct sunlight lead to chain decomposition and free valences that are saturated by oxygen diffusing inwards. The surface becomes yellow or bleached.

In the case of semi-crystalline plastics there could be secondary crystallisation resulting in increased hardness and rigidity. Consequently these plastics are also more brittle and lose a largepart of their elasticity. Frozen residual stresses from the manufacturing process can relax and


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cause deformation through the effects of warming – similar to an annealing process. This is especially serious for thin-walled finished parts.

By absorbing water, the plastics become tough-elastic and stability and rigidity decline, which canalso be a problem with thin-walled finished parts.

Weathering resistance can be improved with additives – in a similar way that fire retardant additives are used. However, it is not possible to provide a complete protection against decompo-sition caused by the effects of weathering.

Unfortunately no valid testing standard or standard parameters are defined regarding artificialweathering and its variables that could be used to compare resistances. However it can be saidthat plastics that have been coloured with carbon black or stabilised against UV rays with additives are more stable against light and weathering effects than light coloured or naturalcoloured grades. Exceptions to this are PVDF and PTFE, which have outstanding resistance to lightand weathering effects even without colouring or additives.

When evaluating weathering resistance, it should also be remembered that changes caused byweathering effects are generally in the surface areas of the product. Deeper layers are usually notattacked, so that thick-walled parts are less affected by change than thin-walled parts.


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Information for material-related handling of plastics at receipt and in storage

The material properties and special features of plastics described in the previous sections clearly illustrate that plastic products can suffer unwanted quality losses due to environmental effects.

Therefore to maintain the high quality and functionality of our products – also over longer periods – several factors should be considered when handling and storing them.

1. Plastics become brittle at low temperatures and become hard, less elastic and sensitive to impact. In this condition the danger of breaking or splitting through external forces is very high– especially for finished products. Cold plastic products should never be thrown, shaken ordropped.

2. The properties of plastics can change due to weathering effects. The material properties cansuffer irreversible negative effects through sunlight, atmospheric oxygen and moisture (e.g.bleaching and/or oxidation of the surface, water absorption, etc.). If the products are subject todirect sunlight or one-sided heat, there is a danger of permanent deformation through heat expansion and released internal residual stresses. Therefore finished products should not bestored outdoors and semi-finished products should be stored outdoors for as short a period aspossible.

3. Plastics have scratch sensitive surfaces. Sharp edges on shelves, nails in pallets, large dirt particles between the products and other sharp objects can cause scratches and/or grooves,which in turn can cause breakage and notching. When transporting and storing plastic productsit should be ensured that the surface remains scratch and groove free and that no rough particles are allowed to adhere to the surface.

4. Not all plastics are equally resistant to chemicals, solvents, oils or fats. Several are attacked bythese substances, which can lead to surface opacity, swelling, decomposition and permanentchanges in the mechanical properties. Therefore, substances that can attack and damage plastics must be kept away from the products during storage.

5. Plastics are subject to reversible dimensional changes when affected by extreme temperaturefluctuations due to shrinking or expansion. Dimension checks can only be carried out imme-diately on receipt of the goods if the products are at room temperature (≈ +23°C). Products witha higher or lower temperature could produce incorrect measured values due to shrinkage or expansion of the plastic. Too warm/cold products must be stored temporarily in a dry place andbe brought up/down to room temperature before dimensions are checked.

6. Because of the production process, plastics, and finished products manufactured from them,can have residual stresses, in spite of annealing. These have a tendency to relax when the products are stored for long periods and subjected to temperature effects (e.g. direct sunlight).Polyamides also tend to absorb water when the humidity is high, which in turn causes the volume to increase. These processes are generally accompanied by dimensional and shape changes due to deformation.

Therefore for long-term storage we recommend closed boxes and constant conditions (≈ standardclimate +23°C/50% RH). The expected dimensional and shape changes are thus kept to a minimumand generally have no effect on the function of the product.


Plastic friction bearings


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1. Use of thermoplastics for friction bearings

Requirements for a friction bearing material such as

• Good sliding and emergency running properties• Wear resistance• Pressure resistance• Long life• Heat deflection temperature

are easily fulfilled by today’s modern thermoplastics.

Plastics are especially used where

• Dry running or mixed friction occurs• Special plastic-specific properties are required• Low manufacturing costs are advantageous even with low quantities

The following plastic-specific properties are especially valued:

• Good sliding properties• Low coefficients of friction• High wear resistance• Good damping properties• Low weight• Good dry and emergency running properties• Corrosion resistance• Chemical resistance• Low maintenance after initial one time lubrication• Physiologically safe in some cases

Disadvantages such as low heat conductivity, temperature-dependent stability values, relativelyhigh heat expansion, creeping when subject to long-term stress and in some cases the tendency toabsorb moisture can be kept under control to a great extent by material-related design measures.

1.1 MaterialsOf the large number of plastics that are available, those with semi-crystalline or high crystallinemolecular structures are most suitable for use as sliding elements. Several materials belonging tothis group, and how they have been modified for slide applications, are listed in Table 1.

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Material Short description Property

Polyamide 6 cast PA 6 G High abrasion resistance

Polyamide 6 cast PA 6 G + MoS2 Higher crystallinity than PA 6 G + Molybdenum disulphide

Oilamid® PA 6 G + OIL Highest abrasion resistance, low coefficient of friction

Calaumid® 1200 PA 12 G High abrasion resistance, high load bearing strength

Polyamide 6 PA 6 Medium abrasion resistan

Polyamide 66 PA 66 High abrasion resistance

Polyacetal (Copolymer POM Medium abrasion resistance, compression resistant

Polyethylene terephthalate PET High abrasion resistance, low coefficient of friction

Polyethylene terephthalate PET-GL High abrasion resistance, very low coefficient and lubricant of friction

Polyethylene UHMW PE - UHMW Low coefficient of friction, low rigidity, acid-resistant

Polytetrafluoroethylene PTFE Very good sliding properties, low rigidity

Polytetrafluoroethylene Partially good sliding properties and glass fibre PTFE + Glass good rigidity

Polytetrafluoroethylene PTFE + Coal Very good sliding properties, good rigidity and coal

Polyetheretherketone PEEK High pv, high loadability, high price

Polyetheretherketone PEEK - GL Best sliding propertiesmodified highest pv value and highest price

Table1: Friction bearing materials and properties

1.2 ManufactureFriction bearings can be manufactured by machining or injection moulding. Polyamide bearingsmanufactured by injection moulding are much less wear resistant than those produced by machining due to their amorphous proportions in the molecular structure. The fine crystallinestructure of the low stress polyamide semi-finished products manufactured by casting guarantees optimum wear resistance.

Compared to injection moulded friction bearings, machined bearings allow high dimensional precision. The high machining performance of conventional machine tools, lathes and CNC processing centres allow the cost-effective manufacturing of individual parts as well as small tomedium sized batches. Flexible, almost limitless design possibilities, especially for thick walledparts are another advantage of machined friction bearings.

1.3 Sliding abrasion/matingSliding abrasion is primarily dependent on the materialand surface properties of the mating component. Themost favourable mating component for plastic has pro-ven to be hardened steel with a minimum hardness of50 HRc. If surfaces with a lower hardness are used thereis a danger of rough tips breaking off and causing in-creased plastic/metal abrasion in friction bearings.

The influence of surface roughness on sliding abrasionand the sliding friction coefficient can be evaluated indifferent ways. For the more abrasion resistant, lessroughness sensitive plastics (e.g. PA and POM) it can

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be observed that the sliding friction coefficientis relatively high, especially for particularlysmooth surfaces (Figure 1).

As the roughness increases, it is reduced to a minimum and then increases again in the further course. The sliding abrasion becomeshigher with increasing roughness.

On the other hand, the more abrasion sus-ceptible plastics (e.g. PE-UHMW, PTFE) show asteadily increasing sliding friction coefficientwith increasing roughness. The range in whichthe sliding friction coefficient improves with increasing roughness is minimal. The sliding abrasionincreases with increasing roughness.

The model idea to explain this behaviour assumes that abrasion in friction bearings takes over alubricating function. It can be observed that a favourable sliding condition exists when the quantity and form of abrasion are optimum.

With the plastics that are less sensitive to roughness, adhesion forces and adhesive bridges havean effect in the low roughness range of the mating component. Due to the smooth surface, thereis no great abrasion that can take over the lubricating function. As roughness increases, the movement-hindering forces decrease so that the sliding friction coefficient improves with in-creasing abrasion. From a specific degree of roughness, the plastic begins to abrade, which re-quires higher movement forces. The amount of abrasion exceeds the optimum. Because of thesemechanisms, the sliding friction coefficient deteriorates.

As the optimum abrasion volume is very small with the plastics that are sensitive to roughness,these plastics only have a very narrow range in which the sliding behaviour can be improved byabrasion. With increasing roughness, the effects of the abrasion become predominant. It is nolonger possible to improve the sliding behaviour. On the other hand, by this token the sliding behaviour only worsens due to a lack of abrasion on materials that have mating components withan extremely smooth surface.

The surface roughness of the plastics plays no role in this observation, as they are soft comparedto the metallic mating component and quickly adapt to its contact pattern. Hence, important forchoosing the surface quality of the steel sliding surface is the question whether the functionalityof the sliding element is affected by either the amount of sliding abrasion or the sliding frictioncoefficient. For combination with plastic friction bearings, the mating components in Table 2 withthe associated surface grades can be recommended:

Table 2: Recommended surface qualities for mating components

Low surface hardness and smaller/greater surface roughnesses than those specified promote sliding abrasion in the bearing and thus shorten its useful life.

PA 6 G PA 12 G PA 6 PA 66 PA 12 POM PET PE- PTFEUHMW

Mating Hardnesscomponent HRc min. 50 50 50 50 50 50 50 50 50hardenedsteel Rz [µm] 2 – 4 2 – 4 2 – 4 2 – 4 2 – 4 1 – 3 0,5 – 2 0,5 – 2 0,2 – 1

Mating Material POM POM POM POM POM PA PA/POM PA/POM PA/POM/PETcomponentthermo- Rz [µm] 10 10 10 10 10 10 10 10 5plastic

Average depth of roughness µm

PET

PE-UHMW

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Figure 2

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In addition to the above-mentioned factors, running speed, surface pressure and temperature also have an effect on sliding abrasion. High running speeds, surface pressure and temperaturesalso increase sliding abrasion.The following table contains guiding values for the sliding abrasion of plastics.

Table 3: Sliding abrasion of plastics

Material Sliding abrasion Material Sliding abrasionin µm/km in µm/km

Oilamid® 0,05 POM-C 8,9

PA 6 G 0,1 PET 0,35

PA 6 0,23 PET-GL 0,1

PA 66 0,1 PE-UHMW 0,45

PA 12 0,8 PTFE 21,0

The stated values depend on the sliding system and can also change due to changes in the slidingsystem parameters.

1.4 Lubrication/dry runningAt present there are no general valid lubrication rules for plastic friction bearings. The same lubricants that are used for metallic friction bearings can also be used for plastic bearings. It is advisable to use a lubricant despite the good dry running properties of plastics, as the lubricantreduces the coefficient of friction and thus the frictional heat. In addition, continuous lubricationalso helps dissipate heat from the bearing. Lubricating the friction bearings gives them a higherload bearing capacity and reduces wear, which in turn gives them longer life. However, if the bearings are to be used in a very dusty application it is advisable not to use any lubrication, as thedust particles become bonded in the lubricant and can form an abrasive paste which causes considerable wear. The plastic bearing materials recommended in the table on page 53 are resistant to most commonly used lubricants.

An alternative to external lubrication are plastics with self-lubricating properties such as OILAMIDand PET-GL. Due to the lubricants that are integrated into the plastic, these materials have the lowest wear rates as well as excellent dry and emergency running properties. When design reasons require to do so, it is also possible to operate plastic friction bearings without lubrication.

However, attention must be paid that the load values are within the pv values stated in Table 4. Inany case, a one time lubrication should be carried out during installation if possible, even if thebearings will run dry. This considerably improves the start-up behaviour and can prolong the life of the product. It is also possible to lubricate the bearings subsequently at intervals to be determined empirically.

1.5 Contamination/corrosionThe steel shaft of friction bearings that are operated in dry running conditions is in danger of corroding due to migrating moisture. When the surface of the mating component is damaged bycorrosion, this increases sliding abrasion and can cause the bearing to malfunction prematurely.This can be prevented by sealing the bearing against moisture. Other effective measures are toplate the mating component with chromium or to manufacture the mating component fromstainless steel.

Because of their low coefficients of sliding friction, plastic friction bearings tend to suffer muchless from frictional corrosion than metallic bearing materials. Wear caused by frictional corrosioncan be reduced even further by lubrication. Compared to metallic bearing materials, wear in plastic friction bearings caused by contamination such as dust or abrasion is much lower, as plastics, and especially polyamides, have the ability to embed dust particles and thus prevent the


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abrading effects. When operating in environments with high dust levels, it is recommended thatthe bearing is fitted with lubrication grooves. The lubricant contained there binds the dust particles and keeps them away from the slide zone.

1.6 Load limitsLoad limits for thermoplastic friction bearings are defined by the compressive strength and bearing temperature. The bearing temperature is directly related to the running speed and theambient temperature, and, with dynamically stressed friction bearings, also to the duration of operation. The mating components, their surface quality and the chosen type of operation (lubricated or unlubricated) also have an effect on the bearing temperature of a thermoplasticfriction bearing.

Table 4 contains guiding values for individual plastics. For statically loaded bearings or frictionbearings with very low running speeds, the figures for sustained pressure loading can be applied.For dynamically loaded bearings, usually the pv value (product of surface pressure and averagerunning speed) is used as a characteristic variable. It must be noted that this value is not a materialcharacteristic value, as the load limit of the plastics depends on the above-mentioned variables.

Table 4: Material guiding values

Sustained pressure load static MPaNot equipped with cham-bers, Deformation < 2% 23 20 24 15 18 10 22 35 33 5 5 12 57 68

Equipped with cham-bers; Deformation < 2% 70 60 - 50 60 43 74 80 75 20 20 - 105 120

Coefficient of friction µ 0,36 0,18 0,40 0,38 0,35 0,32 0,30(average value) - - - - - - 0,30 0,25 0,2 0,29 0,08 0,1 - 0,11Dry running on steel 0,42 0,23 0,60 0,42 0,42 0,38 0,38

pv-guiding valueMPa . m/sDry running/Installation lubricationV = 0,1 m/s 0,13 0,23 0,12 0,11 0,13 0,08 0,15 0,15 0,25 0,08 0,05 0,40 0,34 0,66V = 1,0 m/s 0,08 0,15 0,10 0,07 0,08 0,10 0,10 0,15 0,05 0,22 0,42Continuously lubricated 0,50 0,50 0,35 0,40 0,50 0,50 0,50 0,50 0,50 0,40 0,40 0,50 1,0 1,0

Coefficient of thermal expansion+20°C bis +60°C in 10-5 . K-1 8 8 10 9 8 10 10 8 8 18 20 11 5 4,5

Maximum permissiblebearing temperature incontinuous operation (RF< 80%) +90 +90 +90 +80 +90 +80 +90 +80 +90 +50 +160 +200 +250 +250

Moisture absorptionin % at 23°C/50% RF 2,2 1,8 0,9 2,1 3,1 0,8 0,2 0,2 0,2 0 0 0 0,2 0,14when saturated in water 7,0 7,0 1,4 10 9 1,5 0,8 0,5 0,4 < 0,01 < 0,01 < 0,01 0,45 0,3

PA 6

G

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2. Constructional design

2.1 Bearing playWhen designing friction bearings, a distinction is made between operating play h0, installationplay he and manufacturing play hf (see Figure 3).

• The operating play (basic play or minimum play)h0 is the minimum clearance that must exist underthe most unfavourable conditions to prevent thebearing from sticking.

• The installation play he is the clearance in an installed but not yet warm operating state.

• The manufacturing play hf is the measure des-cribing the excess size that the internal diameterof the bearing must have compared to the shaftdiameter to ensure operating play under ope-rating conditions.

The required operating bearing play h0 can be seen in Diagram 1. If guiding requirements are higher, the bearing play can be less. Literature recommends the following as a calculation basis

h0 = 0,015Mdw whereh0 = operating bearing play in mmdw = spindle diameter in mm

However, for arithmetical determination, the precise operating conditions must be known, asotherwise the temperature and moisture effectscannot be taken fully into account.

2.2 Wall thickness/bearing widthThe wall thickness of thermoplastic friction bearings is very important in regard to the good insulati-on properties of the plastics. To ensure adequate heat dissipation and good dimensional stability,the friction bearing wall must be thin. However, the bearing wall thickness also depends on theamount and type of load. Bearings with high circumferential speeds and/or high surface pressuresshould have thin walls, while those with high impact loads should be thicker. Diagram 2 shows thebearing wall thicknesses that we recommend in relation to the shaft diameter and the type of load.

Where thermoplastic friction bearings are to be used as a replacement for bearings made fromother materials, the wall thicknesses are generally defined by the existing shafts and bearing

housings. In cases such as this, attentionshould be paid that the minimum wallthicknesses in Diagram 2 are maintained. Toprevent a build-up of heat in the centre ofthe friction bearing it should be ensuredthat it is in the range of 1 – 1.5 dw when thebearing width is being determined. Expe-rience has shown that a bearing width of approx. 1.2 dw is ideal to prevent an accumu-lation of heat in the middle of the bearing.

D

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Figure 3: Diagram of different bearing play

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05

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Diagram 1: Required operating bearing play

Diagram 2: Recommended bearing wall thickness

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2.3 AllowancesFor friction bearings that are to be used in environments with high temperatures, a certain dimensional change due to thermal expansion should be allowed for when the bearing is being dimensioned.

The expected dimensional change is calculated from

∆ l = sL. kw [mm]

where∆ l = dimensional changesL = bearing wall thicknesskW = correction factor for heat expansion

The correction factor kW for the respective max. ambient temperatures is shown in Diagram 3.

The calculated dimensional change must be added to the operating bearing play.

If it is foreseeable that polyamide friction bearings are to be used permanently under conditionswith increased humidity or water splashing, an additional dimensional change due to moistureabsorption must be taken into account.

The expected dimensional change is calculated from

∆ l = sL . kF [mm]

where∆l = dimensional changesL = bearing wall thicknesskF = correction factor for moisture absorption

Diagram 4 shows the correction factor kF forthe respective max. humidity

The calculated dimensional change must beadded to the operating bearing play.

The two values are determined and added for operating conditions that require a correction dueto temperature and moisture. The total is the required allowance.

2.4 Design as slit bearing bushFor use in extreme moisture and temperatu-re conditions, a bearing bush with an axialslit running at an angle of 15° -30° to theshaft axis has proven to be the best soluti-on.

The slit absorbs the circumferential expansionof the bearing bush so that a diameter chan-ge caused by the effects of temperature ormoisture does not have to be consideredwhen calculating bearing play. Only the wallthickness change has to be included, although

20 40 60 80 100

0,04

0,03

0,02

0,01

0

Bearing temperature in °C

Co

rrec

tio

n f

acto

r k

w

50 60 70 80 90 100

Relative humidity in %

0,06

0,05

0,04

0,03

0,02

0,01

0

Co

rrec

tio

n f

acto

r k F

0 50 100 150 200 250 300 350

Bearing diameter in mm

16

14

12

10

8

6

4

2

0

Wid

th o

f sl

it in

mm

Diagram 3: Correction factor kw

Diagram 5: Width of slit

Diagram 4: Correction factor kF

1,5% of UL

1% of UL


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this is minor compared to the change in diametercaused by circumferential expansion.

In lubricated bearings, the slit can also fulfil therole of a lubricant depot and collect abrasion particles.

The width of the slit depends on the diameter of thebearing and the requirements of the operating conditions. We recommend a slit approx. 1 – 1.5% ofthe circumference of the friction bearing.

2.5 Fixing

In practice it has proved expedient to press over-dimensional friction bearings into a bearing bore. When it is being set in, the bearing bush iscompressed by the amount of the oversize.Therefore this oversize must be considered as anallowance to the operating bearing play on theinternal diameter of the bush. Diagram 6 showsthe required oversize.

As a result of temperature increases, the stressesin the bearing become greater and there is adanger of relaxation when it cools. This can lead to a situation where the force of pressure is nolonger adequate to keep the friction bearing in the bearing seat under pressure. Because of thiswe recommend an additional safeguard for temperatures above 50°C with a securing form-fit element commonly used in machine engineering.

3. Calculating dynamically loaded friction bearings

As opposed to friction bearings that are only burdened by a static normal force, statically loadedfriction bearings are also subjected to a tangential force. This leads to an increase in transversestress in the plastic and consequently to higher material stress.

3.1 Continuous operationGenerally the pv value (the product of the average surface pressure and the average runningspeed) is used as a characteristic value for the dynamic load bearing capacity of friction bearings.To calculate the dynamic load bearing capacity of radial bearings, it is necessary to determine thepvduration value.

The average surface pressure for radial bearings is

whereF = bearing load in NdW = shaft diameter in mmL = bearing width in mm

0,007

0,006

0,005

0,004

0,003

0,002

0,001

20 40 60 80 100 120 140 160 1800

Outer diameter of the friction bearing

Pres

s-fi

t o

vers

ize

per

mm

Da

dw

SL

LD

Radial bearing

[MPa]F

p =dw

.L

Diagram 6: Required press-fit oversize

Figure 5: Radial bearing

15°- 30°

[mm]

[mm]


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The average running speed for radial bearings is

dw.π.n

v = –––––––– [m/s]60000

wheredW = shaft diameter in mmn = speed in min-1

Hence pvduration for dynamic loading for radial bearings without lubrication is

r F i r dw . p . n i

pvduration=e––––––e. e–––––––––– e [MPa . m/s]qdw

. L t q 60000 t

The calculated pvduration value should be less or equal to the material-specific pv value shown in Table 4.

3.2 Intermittent operationThe dynamic load bearing capacity of thermoplastic friction bearings is very much dependent onthe heat that builds up during operation. Accordingly, friction bearings in intermittent operationwith a decreasing duty cycle become increasingly loadable. This is accounted for by using a correction factor for the relative duty cycle (= ED).

Under these conditions, the following applies to radial bearings in intermittent operation

pvdurationpv

int = ––––––––-

fwheref = correction factor for ED

The relative duty cycle ED is defined as the ratio of the load duration t to the total cycle time T inpercent.

For thermoplastic friction bearings, the total cycle time is defined as T = 60 min. The total of all individualloads during these 60 minutes forms the load dura-tion.

This calculated value can then be used to determine thecorrection factor f from Diagram 7. It should be notedthat every load duration t, over and above 60 min. (regardless of whether this only happens once), is to beevaluated as continuous loading.

3.3 Determining sliding abrasionIt is a very complex matter to determine the sliding abrasion beforehand in order to determinethe expected life of a friction bearing. Generally it is not possible to record the external conditionsadequately, or conditions change during operation in a manner that cannot be predetermined.However, it is possible to calculate the expected sliding abrasion sufficiently accurately to providea rough estimate of the life of a bearing. Roughness, pressure and temperature proportions areaggregated to form an equation based on simplified assumptions.

tED = . 100 [%]

T

0% 50% 100%

Relative duty cycle ED

1,2

1,0

0,8

0,6

0,4

0,2

0Co

rrec

tio

n f

acto

r f

Diagram 7: Correction factor f


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Hence sliding abrasion ∆ S is

r cF cF–c0 i

∆ S = 10pN (S0 + S1 . RV

. + S2 . R2

V ) . e1 - ––– + 400 d0 e. r2g [µm/km]q c0 t

whereS0 = measured and experience valueS1 = measured and experience valueS2 = measured and experience valuec0 = measured and experience valuecF = sliding surface temperature in °CRV = average depth of roughness in µmpN = maximum compression in MPar2 = grooving direction factorg = smoothing factor

The grooving direction factor r2 is only used in the equation if the sliding direction corresponds tothe direction of the processing grooves of the metallic mating component. This takes account ofthe influence of the different degrees of roughness during the relative movement of the metallicmating component in the same direction and vertically to the direction of the processing grooves.

The smoothing factor g describes the smoothing of the metallic mating component through theabrasion of rough tips and/or the filling of roughness troughs with abraded plastic material.

Using an approximation equation the maximum compression pN is

16 FpN = –––– . ––––––––– [MPa]

3p dw . L

whereF = bearing load in NdW = shaft diameter in mmL = bearing width in mm

where pN 6 (0,8 bis 1,0) may not exceed jD (compressive strength of the respective plastic).

The measured and experience values can be seen in Table 5, the grooving direction factors in Table 6. We do not have any measured or experience values for materials other than those listedbelow.

Material S0 S1 S2 c0 g

PA 6 0,267 0,134 0 120 0,7PA 66 0,375 0,043 0 120 0,7PA 12 0,102 0,270 0,076 110 0,7POM-C 0,042 0,465 0,049 120 0,8PE-UHMW 1,085 - 4,160 4,133 60 0,7PET 0,020 0,201 - 0,007 110 0,8PTFE 1,353 -19,43 117,5 200 0,6

Table 5: Measured and experience values for individual plastics


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Rv vertical to the direction of the processing grooves in µm PA POM-C PET PE-UHMW

> 0,5 1,0 0,9 0,8 0,80,5 – 1 0,9 0,6 0,6 0,41 – 2 0,8 0,3 0,4 0,22 – 4 0,8 0,2 0,3 —4 – 6 0,8 0,2 0,3 —

3.4 Determining the service life of a bearingAs a rule, a plastic friction bearing has reached the end of its service life when the bearing playhas reached an unacceptably high level. Bearing play is made up of several factors. On the onehand there is some deformation due to the bearing load, and on the other hand the operatingplay and the wear resulting from use must be considered. As these can only be arithmetically calculated in advance and since the sliding abrasion calculated approximately at 3.3 is used to calculate the service life, the service life itself should only be regarded as an approximate value fora rough estimate.

Under these prerequisites and in combination with the running speed, the expected service life His

r h0i

eDhper - Dh - eq 2 t

H = ––––––––––––––––––– . 103 [h]DS . v . 3,6

whereDhper = permissible journal hollow in mmDh = journal hollow in mmh0 = operating play in mmDS = wear rate in µmv = running speed in m/sec

To obtain a rough approximation of the actual service life, it is acceptable to leave the journal hollow Dh out of the calculation, as in realistic conditions this is very small and is often within themanufacturing tolerance range.

Table 6: Groove direction factors for plastics


Thermoplastic sliding pads


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1. Thermoplastic sliding pads

In the same way that friction bearing bushes are used to arrange the bea-rings of a shaft for rotational and up and down movements, the sameplastics can of course be used for linear movements in the form of slidingpads. Basically all the plastics listed in the “Friction bearings” chapter aresuitable for use as sliding pads. However, several are especially suitable.These will be described in the following with their advantages.

1.1 MaterialsPlastics that are used as sliding pads require good sliding properties aswell as high stability and elasticity and creep resistance. These require-ments are fulfilled especially well by Polyamide 6 cast. The high stabilitycompared to other thermoplastics allows higher loads. The good elasti-city ensures that deformation is reversed when the material is subjectedto impact load peaks. Assuming that the load remains below the permis-sible limit, this ensures that permanent deformation is avoided to a greatextent.

The oil-filled modification OILAMID is available for highly stressed sliding pads. The oil which is embedded in the molecular structure reduces sliding friction by around 50% and also considerably reduces sliding abrasion.

PET is best suited for applications where a high level of moisture is ex-pected. The material has high mechanical stability, creep resistance, dimensional stability and good sliding properties. Water absorption islow and has virtually no effect on the mechanical or electrical properties.

However, PET is not as wear resistant as polyamides. But PET-GL is available as a modified grade with a solid lubricant. This has improvedsliding properties and much better wear resistance.

2. Design information

2.1 Friction heatAs opposed to friction bearings that operate continuously at highspeeds, most sliding pads and guide rails usually work under conditionsthat minimise the evolution of friction heat. The running speeds are relatively slow and operation is more intermittent than continuous. Under these conditions, it is unlikely that friction heat builds up to a levelthat could cause increased wear or a breakdown in the component.

Plastic sliding pads


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2.2 Pressure and running speedAs a rule, when dimensioning and designing sliding elements, the design engineers consider thepressure and speed ratio. If the pressure and speed ratios are unfavourable, the resulting frictionheat leads to excess wear and even to a premature breakdown of the component. However, experience in the design and operation of guide pads has shown that it is generally unnecessaryto calculate the pressure and speed values due to the favourable operating conditions of slidingpads. Instead of this, the following limiting pressure values can be used as a basis for most guiderail applications. The values apply at a standard temperature of 23°C.

2.3 LubricationAgain the statements regarding dry running and the use of lubricants from the “Friction bearings” chapter apply. Basically it must be said that installation lubrication considerably impro-ves the service life and running behaviour. The materials that have been modified with lubricant,such as Oilamid, have much longer service lives than all other plastics.

2.4 MountingPolyamide sliding pads or guide railswith a mechanical sliding function aregenerally mounted on steel construc-tions.

Countersunk screws or machine screwscan be used without any problem forapplications at room temperature andnormal climatic conditions (50% RH).For operating conditions with high humidity, we recommend that you con-sider using PET / PET-GL.

If a higher ambient temperature is expected, the approx.10 times higher linear expansion of plastic compared to steel must be considered. Firmly screwed plastic rails cancorrugate due to linear expansion. To prevent this from happening, the mounting points shouldbe less than 100mm apart. In the case of longer sliding rails, one single fixed point screw is advised. The other screws in oblong holes should be able to absorb the thermal expansion. Instead of oblong holes, the rails can also be held in grooves, T-slots or similar. Changes in lengthcaused by extreme ambient conditions have no effect on the fixing or function.

For polyamide sliding pads in high performance applications such as telescopic booms on mobilecranes, we recommend special nuts that are pressed into hexagonal holes on the sliding panels. Bypressing the nut into the hexagonal hole it cannot fall out or loosen. The bottom of the slide plateshould be absolutely flush.

PA PET Load Movement Lubrication

28 MPa 21 MPa interrupted interrupted periodic

14 MPa 10 MPa continuous interrupted periodic

3,5 MPa 2,5 MPa continuous continuous none

Figure 1: Example of threaded inserts


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Under full torque, the polyamide is held under pressure by the threaded insert and the insert sitson the steel support. For mountings such as this, pad thicknesses of 12 – 25mm are adequate foroptimum performance.

2.5 Applications and examples of shapesSlide and guide pads in telescopic cranes, garbage presses, car body presses, road and rail vehicles,timber processing machines and plants, packaging and filling plants, transport and conveyor systems,chain guides, etc.


Plastic castors


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1. Plastics as castor materials

Plastic wheels and castors are increasingly used in plants and material flow systems, replacing conventional materials.

This is because of advantages such as

• Cost-effective manufacturing• Very quiet running• High wear resistance• Good vibration and noise damping• Low weight• Protection of the tracks• Corrosion resistance

In addition to the soft-elastic wheels made from polyurethanes, hard elastic wheels and castorsmade from cast polyamide, POM and PET are popular for higher loads. However, compared toconventional metal wheel and castor materials, several plastic-specific properties must be consi-dered when calculating and dimensioning.

1.1 1.1 MaterialsPA 6 G, PA 6/12 G and PA 12 G have proved to be ideal materials. POM and PET can also be used.However, experience has shown that although these have a similar load bearing capacity to thecast polyamides, they are subject to much more wear. The recovery capacity of these materials islower than that of polyamides. In dynamic operation, flattening that occurs under static loadingdoes not form back as easily as with polyamide castors.

1.2 1.2 Differences between steel and plasticPlastic has a much lower modulus of elasticity than steel, which leads to a relatively greater de-formation of plastic wheels when they are subjected to loads. But at the same time, this producesa larger pressure area and consequently a lower specific surface pressure, which protects thetrack. If the loading of the wheel remains within the permissible range, the deformation quicklydisappears due to the elastic properties of the plastics.

In spite of the larger pressure area, plastic wheels are not as loadable as steel wheels with the same dimensions. One reason for this is that plastic wheels can only withstand much smaller compressive strain (compression) in the contact area, another reason is the transverse strain thatoccurs due to the very different degrees of rigidity of the castor and track materials. These hinderthe wheel from deforming and have a negative influence on the compressive strain distribution inthe wheel.

1.3 ManufactureThere are several production processes that can be used to manufacture plastic castors. If high volumes of wheels with small dimensions are to be produced, injection moulding is a suitable method. As a rule, for production-engineering reasons, larger dimensions can only beproduced by injection moulding as recessed and ribbed profile castors. It must also be noted thatthese only have half the load bearing capacity of a solid castor with the same dimensions. It is alsoa very complex procedure to calculate a castor such as this compared to a solid castor, and rollingspeeds of more than 3m/s are not recommended because of production-related eccentricity.An economic and technical alternative to injection moulding is to machine semi-finished pro-ducts. In the small dimensional range up to Ø 100mm, the castors are manufactured on automaticlathes from rods. Sizes above this are produced on CNC lathes from blanks.

Another alternative is the centrifugal moulding process. In this process, the outer contours of thecastor are moulded to size and then only the bearing seat and axis holes are machined to the re-quired finished size. This allows large quantities of larger dimensions to be manufactured econo-mically.

Plastic castors


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With this process, running truths are achieved that allow speeds of up to 5 m/s.

1.4 Castor designIn addition to the four basic castor body shapes, castors differ mainly in the type and design oftheir bearings. Like rope pulleys, solid castors can also be fitted with friction bearings. A prere-quisite is that the material-specific max. loading parameters are not exceeded. How to calculatefriction bearings and the significant factors for safe operation of the bearing are contained in thechapter on »Friction bearings«. If it is not possible to use a friction bearing because the load is toohigh or because of other factors, the use of antifriction bearings is recommended.The chapter on »Tolerances«, sec-tion 2.5.2 deals with the material-related design of bearing seats indetail.Compression-set antifriction bea-rings used at temperatures above50°C can loosen. This can be coun-teracted by design measures such aspressing the bearing into a steelflange sleeve screwed to the body ofthe castor. Alternatively we recom-mend the use of our Calaumid-Fematerials (PA with a metal core),which combines the advantages ofplastic as a castor material and steelas a bearing seat material. Because of its form and frictional connection of the steel core with theplastic, this material is also recommended for applications where driving torque has to be trans-ferred.For castor diameters > 250 mm, a lined castor design is advantageous. The plastic lining is fixed tothe metallic core of the castor through shrinkage. Details of this design alternative will be described in a separate section.

2. Calculation

When calculating plastic castors, several important points must be remembered. The material hasvisco-elastic properties, which become visible through decrease in rigidity as the load duration increases. The result of this is that when the contact area of the static wheel is continuously loa-ded, it becomes larger the longer this load continues. However, as a rule because of the materials’elastic properties, they are quickly able to return to their original shape when they begin rolling.Hence, no negative behaviour is to be expected during operation. But if the permissible yieldstress of the material is exceeded the material can »flow« and lead to permanent deformation.This causes increased start-up forces when the castor or wheel is restarted and eccentricity in therolling movement. High ambient temperatures and, especially for polyamides, high humidity promote this behaviour, as they reduce the maximum yield stress. An exception to this are the PA 12 G polyamides, as they have less tendency to absorb water. It should also be noted that because of the material’s good damping properties, the body of thecastor can heat up as a result of high running speeds or other loading factors. In extreme cases,temperatures can occur that cause the plastic wheel to malfunction. However, if the loads remainwithin the permissible limits, plastic castors and wheels will operate safely and reliably.

2.1 Calculation basicsIt would appear practical to apply the Hertzian relationships when calculating castors. But plasticwheels do not fulfil all the conditions for this approach. For example, there is no linear connection

Figure 1: Basic castor shapes


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between stress and expansion, and because of the elasticity of the material, shear stresses occur inthe contact area while the wheel is rolling. Nevertheless, it is possible to make an adequately precise calculation on the basis of Hertz’ theory. The compression parameter p’ is determined withthe following calculations. This parameter is generally calculated with short-time modulus of elasticity determined at room temperature and therefore does not reflect the actual compressionin the contact area. Because of this, the determined values are only expressive in combinationwith Diagrams 1 to 4. The calculated values are usually rather higher than those that actually occur during operationand therefore contain a certain degree of safety. Still, castors or wheels can malfunction as it isnot possible to consider all the unknown parameters that can occur during operation to an adequate extent in the calculation.For castors with friction bearings, the load limit of the friction bearing is decisive. As a rule, thefull load bearing capacity of the running surface cannot be utilised, as the load limit of the frictionbearing is reached beforehand (see chapter »Friction bearings«).

2.2 Cylindrical castor/flat track Under load, a projected contact area is formed with length 2a and width B, with compression distributed over the area in a hemiellipsoidal form. Noticeable is that the stress increases at theedges of the castor. This stress increase is generated by shear stresses that occur across the runningdirection. These have their origins in the elastic behaviour of the castor material. The stress increa-ses become larger the greater the differences in rigidity between the track and the castor mate-rials. As stress increase in a castor made from hard-elastic plastic is quite small and can thereforebe ignored for operating purposes and as the shear stresses cannot be calculated with Hertz’theory, these are not considered.

Assuming that the track material has a much higher modulus of elasticity than the castor materialand that the radii in the principal curvature level (PCL) 2 are infinite, the compression parameterp’ is

where:F = wheel load in Nr11 = castor radius in mm from PCL 1B = wheel width in mmfw = material factor

PA 6 G = 25.4PA 6 = 38POM = 33.7

If the moduli of elasticity of the castor and track materials are known, the following equationscan be used:

and

1 1 1 - v21 1 - v2

2–– = –– –––– + –––––Ee 2 E1 E2

p’ = fwF

r11. B

[MPa]

p’ = F . Ee

2 . p . r11. B

[MPa]

r11

F

2a

p’

B

Principal curvature level1 2


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For identical track and castor materials Ee is

EEe = ––––––

1 - v2

whereF = wheel load in NEe = replacement module in MPar11 = castor radius in mm from PCL 1B = wheel width in mmE1 = modulus of elasticity of the castor body in MPav1 = transversal contraction coefficient of the castor body from Table 1E2 = modulus of elasticity of the track material in MPav2 = transversal contraction coefficient of the track material from Table 1

Table 1: Transversal contraction coefficients for various materials

PA 6 Cast ironPA 6 G Steel withPOM Ferritic approx. Austenitic GG GG GG GGG 38 Aluminium TitaniumPET steels 12% Cr steels 20 30 40 to 72 alloys alloys

Transversal con- 0,4 up 0,25 0,24 0,24 0,28 0,23traction coeffi- to 0,3 0,3 0,3 up to up to up to up to 0,33 up tocient µ at 20° C 0,44 0,26 0,26 0,26 0,29 0,38

The half contact area length required to estimate flattening is calculated from

8 . F . r11a = ––––––––– [mm]p . Ee

. B

whereF = wheel load in NEe = replacement module in MPar11 = castor radius in mm from PCL 1B = wheel width in mm

2.3 Cylindrical castor/curved track

Also in this system a projected contactarea is formed with length 2a and widthB, with compression distributed over thearea in a hemiellipsoidal form. The pre-viously described stress increases alsoform in the edge zones.The calculation is carried out in the sameway as for the “cylindrical castor/flattrack” from section 2.2. However, be-cause of the second radius in PCL 1, a replacement radius re is formed from theradii r11 and r21. This is used in the equa-tion corresponding to relationships ofthe moduli of elasticity to calculate thecompression parameter.If the castor runs on a curved track the replacement radius is

F

p’

r11

r21

2a

B



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r11. r21re = ––––––– [mm]

r11 + r21

For castors running on a curved track the replacement radius is

r11. r21re = ––––––– [mm]

r11 - r21

wherer11 = castor radius in mm from PCL 1r21 = track radius in mm from PCL 1

The replacement radius re is also used in the equation to calculate half the contact area length a.

2.4 Curved castor/ flat track castor systemThe phenomenon described in section 2.2, where stress increases at the edges, can be reducedwith design changes of the shape of the wheel. If the track is furthermore slightly curved acrossthe rolling direction, only minor stress increases are observed. It has proven practical to use thediameter of the wheel as the radius of the curvature. This measure also counteracts the evolutionof excess edge pressure that could arise from alignment errors during assembly. A castor with curves in PCL 1 and 2 forms an elliptical contact area with axes 2a and 2b acrosswhich the compression is distributed in the form of an ellipsoid. The semi axis of the ellipticalcontact area are calculated from

1 1a = s . 3 3 . F . re

. ––– [mm] and b = l . 3 3 . F . re. ––– [mm]

Ee Ee

and

r11. r12re = ––––––– [mm]

r11 + r12

whereF = wheel load in NEe = replacement module in MPas = Hertz correction value from Table 2re = substitute radiusl = Hertz correction value from Table 2

The replacement module is determined as described in section 2.2. To determine the Hertz correction values s and l the value cos t must be determined mathmatically.

r1 1 ie––- - ------ eqr11 r12 t

cos t = ––––––––––––r1 1 ie–– - + ------eqr11 r12 t

wherer11 = castor radius in mm from PCL 1r12 = Rcastor radius in mm from PCL 2

The Hertz correction values in relation to cos t can be taken from Table 2. Intermediate valuesmust be interpolated.

Table 2: Hertz correction values in relation to cos t

cos t 1 0,985 0,940 0,866 0,766 0,643 0,500 0,342 0,174 0

s ∞ 6,612 3,778 2,731 2,136 1,754 1,486 1,284 1,128 1

l 0 0,319 0,408 0,493 0,567 0,641 0,717 0,802 0,893 1

w ∞ 2,80 2,30 1,98 1,74 1,55 1,39 1,25 1,12 1

r11

F

B

2a

p’ r12

2b



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With these calculated values the compression parameter can be determined as follows:

3 . Fp’ = ––––––––––––––––– [MPa]

2 . p . a . b

whereF = wheel load in Na = semi axis of the contact area longitudinally to the running directionb = semi axis of the contact area transversely to the running direction

2.5 Curved castor/curved track castor systemBoth the shape of the contact area and the calculation correspond to section 2.3. However, whenthe replacement radius r and the value for cos t are being calculated, it should be considered thatthe track also has curvature radii in PCL 1 and 2.Consequently the replacement radius for castors that roll on a curved track is

1 1 1 1 1––– = –––– + –––– + –––– + –––– [mm]re r11 r12 r21 r22

and for castors that roll in a curved track

1 1 1 1 1––– = –––– + –––– + –––– + –––– [mm]re r11 r12 -r21 -r22

wherer11 = castor radius in mm from PCL 1r12 = castor radius in mm from PCL 2r21 = track radius in mm from PCL 1r22 = track radius in mm from PCL 2

When determining cos t it should be remembered that the value should be con-sidered independently of whether the castor runs on or in a track. Therefore in theequation a positive value is always used forthe radii.

r 1 1 i r 1 1 ie–– - –– e +e–– - –– eq r11 r12 t q r21 r22 t

cos t = –––––––––––––––––––––––––––––r 1 1 i r1 1 ie–– + ––e +e–– + –– eq r11 r12 t q r21 r22 t

To calculate the semi axis a and b and the compression parameter the method described in section 2.4 can be applied.

2.6 Cylindrical plastic castor lining2.6.1 CalculationCastor linings can only be calculated according to the equations in sections 2.2 to 2.5 if specific ratios between the half contact area length a, the wheel width B and the height of the lining hare fulfilled.The ratios h/a ≥ 5 and B/a ≥ 10 must be fulfilled as a condition. As soon as these limiting values arenot met, the evolving contact area is reduced despite the same load and outer wheel dimensions.The result is that the compression of the contact area increases and becomes greater, the smallerthe lining thickness. In spite of this, it is possible to determine the compression ratios approxi-mately.

F

r11

r21

2a

B

p’

2br12

r22



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The half contact area length a becomes

F E’1 . h2 + E’2 . h1a = 3 1,5 . re. –––. ––––––––––––––––––––– [mm]

B E’1 . E’2

For castor linings that run on a flat trackre = r1. For castor linings that run on or in a curved track, the replacement radiusre is determined as described in section2.3.

The compression parameter then becomes

9 1 r F i2E’1 . E’2p’ = 3 ––– . ––– . e – e . –––– –––––––––––––– [MPa]

32 re

q Bt E’1. h

2+ E’

2. h

1

whereF = wheel load in N re = replacement radius in mmE1 = calculation module of wheel material in MPa h1 = castor lining thickness in mmE2 = calculation module of track material in MPa h2 = track thickness in mm

B = wheel width in mmThe calculation moduli of the materials must be determined taking account of the transversalcontraction coefficients.

E1 (1 - v1)2 E2 (1 - v1)2

E’1 = –––––––. –––––––––– und E’2 = –––––––. –––––––––– [MPa] 1 - v2

1 1 - 2v1 1 - v22 1 - 2v2

whereE1= modulus of elasticity of the castor material in MPav1 = transversal contraction coefficient of the castor material from Table 1E2 = modulus of elasticity of the track material in MPav2 = transversal contraction coefficient of the track material from Table 1

2.6.2 Design and assembly informationThe shape of the plastic castor linings and the metallic core is generally dependent on the type of load that the castor will be subjected to. For castors with alow load where no axial shear isexpected and where the diameteris < 400mm, it is possible to choosea core shape with no side support.The operating temperatures maynot exceed 40°C. If it is expectedthat axial forces may affect the castor, that the lining will be subjected to high pressures orthat operating temperatures willexceed 40°C for short or long periods, the linings must be se-cured against sliding down by a side collar on the core or with aflange. The same applies for cas-tor diameters ≥ 400mm.

h1

F

2a

p’

r11

B

Bar

e sn

ap-b

ack

size

Axi

al p

lay

40 60 80 100

Operating temperature

°C

Aufschrumpfuntermaß in Abhängigkeit zur Betriebstemperatur

0,25

0,45

0,65

0,85

%

0,25

0,45

0,65

0,85

%

0,05 0,05

Diagram 1: Bare snap-back size and axial play in relation to operating temperature



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No special demands are placed on themetal core in the area of support for thelining in regard to surface quality anddimensional stability. A cleanly ma-chined surface and a diameter toleranceof d ± 0.05mm are adequate. Grooves inthe axial direction (e.g. knurls withgrooves parallel to the axis and brokentips) are permissible. Approximately 1.0to 1.5% of d has proven to be a suitableheight for the plastic lining. The lining is generally fixed to the metalcore by heating it and then shrinking iton to the cold core. The lining can beheated either with circulating hot air(approx. 120 to 140°C) or in a water bath(approx. 90 to 100°C). The lining is heated to an extent that it can be easilydrawn on to the cold core with a gap between the core and the lining all the way around. Thisprocess should be carried out quickly so that the lining does not become cold before it sits properly on the core. Rapid or uneven cooling should be avoided at all costs, as otherwise stresseswill form in the lining. The bare snap-back size for manufacturing the lining depends on the operating temperature and the diameter of the metal core. Diagram 1 shows the proportional bare size in relation to the diameter of the metal core for castors with a diameter of > 250mm. Forcastors with a securing collar/flange a slight axial play must be considered to absorb the changesin width resulting from thermal expansion. The proportional axial play in relation to the width ofthe lining can also be seen in Diagram 1.

2.7 Maximum permissible compression parametersDiagrams 2 to 5 show the limit loads of castor materials for various temperatures and in relationto the rolling speed. The results for compression parameters gained from the calculations have tobe compared with these limits and may not exceed the maximum values. The curves in relation tothe rolling speed reflect the load limits in continuous use. In intermittent operation, higher valuesmay be permitted. Unallowable high loads must be avoided when the castor is stationary, as thesecould cause irreversible deformation (flattening) of the contact area.

Load

lim

it p

’ max

0 1 2

20

10

30

43 5

40

50

60

70

80

20°C

50°C

75°C

100°C

m/s

90

Load limit for ball bearing solid castors made from PA 6 G

Rolling speed

MPa

Load

lim

it p

’ max

0 1 2

20

10

30

43 5

40

50

60

70

80

m/s

90

Load limit for ball bearing solid castors made from POM

Rolling speed

MPa

20°C

50°C

75°C

100°C

Diagram 2 Diagram 3

h

ø D

ø d

a


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3. Estimating the elastic deformation of the castor body

Often the function of castors and wheels is dependent on the deformation of the running surface(flattening) while the wheel or castor is stationary. This is determined immediately after the loadhas taken effect with the modulus of elasticity of the material. However, because of the visco-elastic behaviour of the plastic, the time-related deformation behaviour must be determined withthe part-specific creep modulus. The creep modulus is determined by carrying out creep expe-riments with castors and can be seen in Diagrams 6 and 7. On the basis of the values determinedin experiments, the time-related flattening can only be estimated with the following equations. Itis virtually impossible to make an exact calculation due to the often unknown operating para-meters and the special properties of the plastic. But the values obtained from the equations allowthe flattening to be determined approximately enough to assess the functioning efficiency.The following is used to estimate the cylindrical castor/cylindrical track

1,5 . w . FoA = –––––––––––––– [mm]

Ee. a

and the cylindrical castor/flat track

F r r 2 . r11 i ioA = --––––––––––––– . e2 . ln e–––––– e+ 0,386e [mm]

p . Ee. B q q a t t

where

Load

lim

it p

’ max

20

20

40

60

40

80

100

60 80 100°C

Load limit for PA 6 G castors with static loading

MPa

Ambient temperature vu

Load

lim

it p

’ max

20

20

40

60

40

80

100

60 80 100°C

Load limit for POM castors with static loading

MPa

Ambient temperature vu

Diagram 4

Diagram 5


F = wheel load in NW = Hertz correction value from Table 2Ee = modulus of elasticity or creep modulus in MPaa = semi axis of the contact area longitudinal to the running directionB = wheel width in mmr11 = castor radius in mm from PCL 1

As in castor systems with curvature radii quite considerable shear stresses occur in the PCL 2, it isnot possible to analytically estimate the systems with curvature radii in the PCL 2. These can onlybe determined numerically with a three-dimensional FE model.

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Cre

ep m

od

ulu

s

Load time

10-4 10-3 10-2 10-1 10-0 101 102 103h

Creep modulus of PA 6 G at 20 °C

500

1000

1500

2000

2500

3000

MPa

Cre

ep m

od

ulu

s

Load time

10-4 10-3 10-2 10-1 10-0 101 102 103

Creep modulus of POM at 20 °C

500

1000

1500

2000

2500

3000

MPa

h

Diagram 6

Diagram 7


Plastic sheaves


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Plastic sheaves

1. Use of PA 6 G as a sheave material

Steel wire ropes are important and highly stressed machine elements in conveying technology. Inmany cases, large plants depends on their functioning not only for efficiency but also safety. Asopposed to other machine elements, they must be replaced before they are completely damaged.

The surface pressure that occurs at the point of contact between the sheave and the rope is decisive for the service life and loadability of ropes that run over sheaves. Sheave materials with alow modulus of elasticity lead to low surface pressures and consequently to a longer service life ofthe rope. For this reason, thermoplastics are used to manufacture sheaves.

The plasticvs need to offer the following properties:

• Rope conserving elasticity • Adequate compression fatigue strength• High wear resistance• Adequate toughness, also at low temperatures• Resistance to lubricants• High resistance to weathering effects

Experience has shown that cast polyamide (PA 6 G) fulfils these requirements more than ade-quately. Other plastics such as PE-UHMW or PVC as shock-resistant modifications are only used inspecial cases due to their low degree of loadability and lower wear resistance. Because of this, wewill only deal with PA 6 G as a sheave material in the following.

1.1 Advantages of sheaves made from PA 6 G

1.1.1 Low rope wearRopes that run over sheaves made from metallic materials are subject to high stress due to the surface pressure that occurs between the rope and the groove. When the rope rolls over the sheave, only the outer strands lie on the groove. The result of this is wear in the form of individualstrands breaking or, more serious, rope breakage.

Sheaves made from PA 6 G prevent this due to their elastic behaviour. The pressure between therope and the roller in the combination steel rope/polyamide roller is around 1:10 compared tosteel rope/steel roller. This can be attributed to the visco-elastic behaviour of polyamide. It is notjust the outer strands that lie in the groove, but almost the whole projected strand width. This reduces surface pressure between the rope and the roller and considerably extends the life of therope.

1.1.2 Weight reductionPolyamides are around seven times lighter than steel. Because of the weight advantage, a con-siderable weight reduction can be achieved by using polyamide sheaves with a similar load bearing capacity. A mobile crane with up to 18 polyamide sheaves can save approx. 1,000kg andthus reduce the axle load. The lighter sheave weight also has a positive effect on the crane boomand considerably eases the handling and assembly of the sheaves.


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1.1.3 DampingThe good damping properties of PA 6 G reduce vibration that metallic sheaves transfer from therope via the sheave to the shaft and bearings. This conserves the rope, shaft and bearings and alsoreduces running noise.

1.2 Lubricating the ropeThe use of viscous and adhesive rope lubricants can cause the rope to stick to the sheave groove.In combination with a dusty environment or dirt particles that are introduced to the sheave system, this forms an abrasive paste that can cause increased wear on the rope and the sheave.Therefore we recommend that the rope is lubricated with a low viscous corrosion protection oil,which keeps the rope and the sheave relatively clean.

1.3 Wear on sheaves made from PA 6 GEssentially, wear is caused on polyamide sheaves through excess mechanical stress or wheel slip,whereby the sheave groove is the most stressed point. The sheave groove is subjected to pulsatingstresses as the rope rolls over it and it becomes warm at high speeds.

Basically, wear on idler sheaves or sheaves that run over a taut rope is less than on driven sheaves.If stranded ropes are used, the individual strands can press into the base of the groove in highlystressed applications. For highly stressed, non-slipping sheaves in combination with an open stranded rope, the circumference of the groove base must not be an integral multiple of the wirestrand. Thus, like the combing teeth of a cog wheel, it is prevented that the same points of thegroove base are constantly in contact with a rope summit or valley. When closed ropes are used incombination with lubricants, pits can form, which are probably caused in the same way as pitsform with gear wheels. As a rule, under normal environmental conditions and when the limit loadvalues are not exceeded, one can expect groove base wear of ≤ 0.1µm/km.

2. Construction Design information

2.1 Sheave groove profileThe radius of the sheave groove should be approx. 5 – 10% larger than half the diameter of therope. This ensures that rope tolerances are adequately considered and that the rope sits well inthe groove. The sheave groove depth h is given in DIN 15061 part 1 for steel sheaves as at least hmin = da2. We recommend a sheave groove depth of h ≥ 1.5d for polyamide sheaves.The V angle b is dependent on the lateral fleet angle (max. permissible fleet angle in the groovedirection = 4.0°).

The following groove angles in combination with the fleet angle have stood the test:

Fleet angle 0° - 2.5° c b = 45°Fleet angle >2.5° - 4.0° c b = 52°

A groove angle of < 45° should be avoided.DIN 15061 part 1 recommends the dimensions in Table 1 as guiding values for sheave groove profiles.As a guiding value for the diameter of the rope groove base of rope disks made from cast polyamide, we recommend:

D1 = 22 · d1 [mm]

Groove angle b

Rounded

Rope ø d1

mm

h

Groove radius rD1


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Ø d1 r1 h m Ø d1 r1 h m Ø d1 r1 h m

3 1,6 8 2 21 11 35 7 39 21 60 11

4 2,2 10 2 22 12 35 7 40 21 60 11

5 2,7 12,5 2 23 12,5 35 7 41 23 60 11

6 3,2 12,5 3 24 13 37,5 8 42 23 65 11

7 3,7 15 4 25 13,5 40 8 43 23 65 11

8 4,2 15 4 26 14 40 8 44 24 65 12,5

9 4,8 17,5 4,5 27 15 40 8 45 24 65 12,5

10 5,3 17,5 4,5 28 15 40 8 46 25 67,5 12,5

11 6,0 20 5 29 16 45 8 47 25 70 12,5

12 6,5 20 5 30 16 45 8 48 26 70 12,5

13 7,0 22,5 5 31 17 45 8 49 26 72,5 12,5

14 7,5 25 6 32 17 45 8 50 27 72,5 12,5

15 8,0 25 6 33 18 50 10 52 28 75 12,5

16 8,5 27,5 6 34 19 50 10 54 29 77,5 12,5

17 9,0 30 6 35 19 55 10 56 30 80 12,5

18 9,5 30 6 36 19 55 10 58 31 82,5 12,5

19 10,0 32,5 7 37 20 55 11 60 32 85 12,5

20 10,5 35 7 38 20 55 11 – – – –

2.2 BearingsDue to the good sliding properties of PA 6 G, when sheaves are not subjected to undue stress, fric-tion bearings can be used. Decisive is the pv limiting value. If high degrees of wear are expectedon the bearing with an intact sheave groove, the use of a replaceable bearing bush can preventthe sheave having to be replaced prematurely.

For highly stressed sheaves, whose maximum load values are above those for a friction bearing,we recommend the installation of anti-friction bearings. These can be mounted by pressing theminto a bearing seat produced according to the dimensions in Diagrams 1 and 2. If axial loads areexpected on the anti-friction bearings, we recommend that the bearing is secured against fallingout by securing elements commonly used in machine engineering, such as circlips according toDIN 472.

The following diagram shows several possible sheave designs.

1 2 3 4 5

Design with bearing seat for antifriction bearings Design with friction bearings

Table 1: Guiding values for rope groove profiles in mm according to DIN 15061 Part 1


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When calculating and dimensioning the bearings, especially friction bearings, attention should bepaid that the bearing load for idler sheaves corresponds to the rope tension, but for fixed sheavesthe angle of contact forms a force equal to twice the cable tension at 180°. Section 3 »Calculatingsheaves« provides more information on this subject.

0,0

0,1

1,0

0,9

0,8

0,7

0,6

0,5

0,4

0,3

0,2

0 10 30 50 100 150 200 225175125754020

0,007

0,006

0,005

0,004

0,003

0,002

0,001

0 60 100 160 200 250180140804020 120

Internal diameter of bearing (mm)

Outer diameter of the antifriction bearing (mm)

Op

erat

ing

bea

rin

g p

lay

in %

Bo

re se

ttin

g si

ze p

er m

m o

ute

r dia

met

er

Diagram 1: Recommended bore setting size for antifriction bearing seats

Diagram 2: Recommended operating bearing play for friction bearings


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3. Calculating rope pulleys sheavesFor the calculation of sheaves, distinctions must be made regarding the load case, the rope usedand the type of operation.

A distinction is made between

• Point loading on the sheave • Circumferential loading on the sheave (the sheave runs on a taut rope) (rope encircles the sheave)

• The type of rope • The type of operationOpen wire rope (stranded rope) Loose sheave (e.g. sheave on a cableway)Closed wire rope Fixed sheave (e.g. deflection sheaves)

These criteria lead to different calculation procedures and force considerations for the individualload cases, rope types and types of operation.

3.1 Calculating the bearing compressionIf the roller bearing is to be executed as a friction bearing, the pv values in the bearing must becalculated and compared with the permissible values for PA 6 G. The friction bearing should beconsidered in the same way as a press fit bearing bush. In other words, the calculation is the sameas for dynamically loaded friction bearings. The expected bearing load is dependent on the typeof operation of the sheave. For idler sheaves, the rope tension Fs can be used as the bearing loadto calculate the pv value of the rope tension.

Thus the average surface pressure for radial bearings in idler sheaves is

FSp = ––––––– [MPa] dW

. L

whereFS = rope tension in NdW = shaft diameter in mmL = bearing width in mm

and the average sliding speed is

dW. p .n

v = –––––––––– [m/s] 60000

wheredW = shaft diameter in mmn = speed in min-1


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Aggregated pvduration for idler sheaves with dynamic loading becomes

r FSi r dW

. p . n ipvduration =u––––––––u . u––––––––––– u [MPa . m/s]

q dW . L t q 60000 t

In intermittent operation it is possible to correct pvduration by the process described in the section3.2 of the chapter on »Friction bearings«.

For fixed rollers, the bearing load is dependent on the angle of contact that the rope forms withthe sheave. If the sheave is completely encircled (180°), the rope tension is doubled in the calcu-lations. For an angle of contact a < 180°, a resulting force Fres must be calculated with the help ofthe angle and the cable tension.

This is calculated from the triangular relationship and is

Fres = FS 2 - 2 . cos a [N]

whereFS = cable tension in Na = angle of contact

For sheaves made from PA 6 G, the determined pv values may not exceed 0.13 Mpa · m/s in dryrunning applications or 0.5 Mpa · m/s with lubrication. If the calculated values exceed these maximum values, an antifriction bearing would be advisable.

3.2 Calculating the compression between the rope and the sheave grooveThe main criterion for the load bearing capacity of sheaves is the compression between the ropeand the sheave. To calculate the compression, the Hertz’ equations that have been modified forthis case are used. The results of the calculations must be compared with the permissible valuesfor PA 6 G shown in Diagrams 3 and 4. They must be considered in combination with the speed ofthe rope and may not exceed these values.

3.2.1 Point contact of closed wire ropesIf closed wire ropes with a small fleet angle are used (a < 10°), such as is the case with cableways,this causes concentrated loading. The area of pressure is elliptical.

Under these conditions the compression parameter p’ for sheaves made from PA 6 G is calculatedfrom the equation

a

FS

Fres

FS

a

Fres

FSFS

FS FS

2FS

180°


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63,5 r 1ip’ = –––––– . 3 eS ––e

2

. F [MPa]y . h q Rt

wherey = correction valueh = Hcorrection valueS 1

R = total of the principle curvatures in mm -1

F = sheave load in N

The sum of the principle curvatures of the bodies that are in contact with one another is calculated from

1 2 1 1 2S ––– =––– - ––– - ––– + ––– [mm –1]

R d r r D

From the sum of the principle curvatures, the correction angle c can be used to determine the correction values y and h according to the following formula:

2 1 1 2–– + –– - –– - ––d r r D

cos c = –––––––––––––––1

S ––R

whered = rope diameter in mmr = rope curvature radius (generally negligible as it is very large compared to other radii)r = groove radius in mmD = groove base diameter

The correction values y and h can be found in Table 1. If c lies between the table values, the correction values must be interpolated.

3.2.2 Point contact of open wire ropesIt can be assumed for sheaves made from PA 6 G that because of the elasticity of the sheave incombination with an open stranded rope, that not one single wire from the strand lies in thegroove but rather several wires and that these participate in the transmission of power. There-fore, the entire strand is regarded as a single wire and it is assumed that all loaded strands trans-mit the same power. In the calculation, a correcting factor is introduced that takes account of thepower transmission of several strands (maximum 40%).With this consideration the compression parameter p‘ becomes

Xp’ = p’e

. 3 ––– [MPa]Z

and the compression parameter p‘e e for one single wire in combination with a PA 6 G sheave is

r d1 d1i2 F

p’e = 42 . 3 e1 - –––– + ––––e. ––– [MPa]q 2r D t d 2

1

where

Table 1: Correction values y and h for different values of c

c 90° 80° 70° 60° 50° 40° 30° 20° 10° 0°

y 1,0 1,128 1,284 1,486 1,754 2,136 2,731 3,778 6,612 ∞h 1,0 0,893 0,802 0,717 0,641 0,567 0,493 0,408 0,319 0

Sheave load F

Sheave load F


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X = correction factor in relation to p’e, from Table 2

Z = number of outer strandsd1 = strand diameter in mmr = groove radius in mmD = groove base diameter in mmF = sheave load in N

3.2.3 Peripheral load with open wire ropesIn regard to the power transmission between the rope and the sheave, the same applies as to concentrated loading as described in item 3.2.2. The only difference is that the load on a com-pletely encircled pulley is not a point load but a uniform load.

Hence, the compression parameter p’ becomes

Xp’ = p’e

. ––– [MPa]Z

and the compression parameter p’e for a single wire in combination with a PA 6 G sheave is

(2r - d1) . FSp’ = 55 . ––––––––––––– [MPa]

2r . d1. D

X = correction factor in relation to p’efrom Table 2

Z = number of outer strandsd1 = strand diameter in mmr = groove radius in mmD = groove base diameter in mmFS = cable tension in N

When determining the correction factor, it should be considered that when X > Z, Z = X must beinserted in the radicand of the correction factor so that the radicand is 1. If the value of p’e is between the values given in the table, the value for X must be interpolated accordingly.

Strand

d d1

Idler

FS FS

FS FS

Fixed sheave

Surface pressure p’e Correction factor in MPa X

≤ 50 Z

150 6

300 4

≥ 450 2,5

Table 2: Correction factor X


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3.3 Maximum permissible surface pressuresThe results from the calculations must be compared with the maximum permissible load para-meters from Diagrams 3 and 4. It is not permissible to exceed these values.

20°C

50°C

75°C

100°C

0

80

40

120

140

160

200

240

280

0 1 2 3 4 5 6m/s

Diagram 3: Load limit in relation to the rope speed and ambient temperature for sheaves made from PA 6 G under peripheral loading

Max

. p’ i

n M

Pa

Diagram 4:Load limit parameter p‘max in relation to the rope speed and ambient temperature for sheaves made from PA 6 G underconcentrated loading.

20°C

50°C

0 0,5 1 2 3m/s2,51,5

40

80

20

100

60

120

0


Plastic gear wheels


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Plastic gear wheels

1. Use of plastics as a gear material

Although thermoplastic gears are unsuitable for applications in high performance gears and fortransmitting high power, they have opened up a broad field of application. The specific materialproperties allow use under conditions where even high quality metallic materials fail. For instance, plastic gears must be used if the following are the key requirements:

• Maintenance-free• High wear resistance when used in a dry-running application• Low noise• Vibration damping• Corrosion resistance• Low mass moment of inertia through low weight• Cost-effective manufacture

For a plastic to be able to satisfy these requirements, it is absolutely vital that the right material ischosen and that the design is carried out in a material-related manner.

1.1 MaterialsOnly a few thermoplastics are significant for the manufacture of gears. The plastics are describedin detail in the previous chapters, so here we will only describe them in regard to tooth forming.

• PA 6Universal gear material for machine engineering; it is wear resistant and impact absorbing evenwhen used in rough conditions, less suitable for small gear wheels with high dimensionalrequirements.

• PA 66Is more wear resistant than PA 6 apart from when it is used with very smooth mating com-ponents, more dimensionally stable than PA 6 as it absorbs less moisture, also less suitable forsmall gear wheels with high dimensional requirements.

• PA 6 GEssentially like PA 6 and PA 66, however, it is especially wear resistant due to its high degree ofcrystallinity.

• Calaumid® 612 / 612 – Fe (PA 6/12 G)Tough modified polyamide, suitable for use in areas with impact-like load peaks, wear resistancecomparable to PA 6 G.

• Calaumid® 1200 / 1200 – Fe (PA 12 G)Tough-hard polyamide with relatively low tendency to absorb water, hence, better dimensionalstability than other polyamides, especially suitable for use in areas with impact-like load peaks,excellent wear resistance.

• Oilamid®

Self-lubricating properties due to oil in the plastic, hence, excellent for dry running applicationsand especially wear resistant.

• POM – CBecause of its low moisture absorbing tendency it is especially suitable for small gears with highdimensional stability demands, not so loadable in dry running applications due to its hardness,however, if permanently lubricated, POM–C gears are more loadable than polyamide ones.

87


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• PE – UHMWBecause of its low stability, it can only be used for gears that are not subjected to high loads, gooddamping properties and chemical resistance, hence mainly suitable for use in applications withmechanical vibration and in chemically aggressive environments.

1.2 CounterpartsHardened steel is the most suitable counterpart regarding wear and utilisation of the load carrying capacity, as it ensures very good dissipation of friction heat. In regard to surface pro-perties, the same applies as with friction bearings: the harder the steel the less wear on the wheeland pinions. As a guiding value, we recommend a maximum roughness depth of Rt = 8 to 10 µmboth in lubricated operation and in dry running applications.For gears that are not subject to heavy loads, it is possible to mate plastic/plastic. The surface roughnesses are insignificant for wear.When choosing a material, it should be remembered that the driving pinions are always subjectedto a higher level of wear. Consequently, the more wear resistant material should always be chosenfor the pinions (r pinion: steel, wheel: plastic or pinion: PA, wheel: POM).

1.3 LubricationThe statements made in the chapter on »Friction bearings« regarding dry running and the use oflubricants also apply here. Basically it should be noted that installation lubrication considerablyimproves the service life and the running-in behaviour. Materials that are modified with a lubricant, such as Oilamid, have much longer service lives than all other plastics, even without lubrication. Continuous lubrication with oil leads to better heat dissipation and consequently to alonger life and higher levels of transmitted power.When the component is lubricated with grease, the circumferential speed should not exceed 5m/sec, as otherwise there is a danger that the grease will be cast off. Due to polyamide’s tendencyto absorb moisture, water lubrica-tion is not recommended for po-lyamide components.

1.4 Noise developmentPlastics in general have gooddamping properties. This consi-derably reduces noise on plastic gears compared to metal ones. Thediagram opposite shows the soundintensity curves of gear matessteel/steel (a) and steel/plastic (b). Itshows maximum differences of 9dB. Hence, steel/steel is up to threetimes as loud as steel/plastic.

1.5 ManufacturePlastic gears are manufactured with the same machining process as metal gears (usually shapingby the generating method and automatic hobbing). As the cutting forces are very low, the profile can be manufactured in one cycle with high forwardfeed rates, which in turn reduces manufacturing costs.When manufacturing with high forward feed rates, corrugated surfaces can be produced. At firstthese give an unfavourable impression. However, in dry running applications the faces of the

dB

80

70

60

500 1000 2000 2900U/min

a

b

Steel CK 45

Polyamide 6 G


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teeth are quickly smoothed after a short running-in period. In lubricated applications, thecorrugated form acts as a lubrication pocket where the lubricant can collect – to the advantage ofthe gear. In other words, this corrugation is no reduction in quality.Basically when machining plastic gears, depending on the module, qualities of 9 to 10 can beachieved. Regarding the tooth quality that can be achieved, it should be noted that the rollingtooth flanks of plastic gears easily fit one another. Therefore, greater tolerances are allowed thanwould be the case with metal gears. This especially applies to power transmitting pinions. For thegrade that is exclusively related to tangential composite error Fi" and tangential tooth-to-tootherror fi" this means that up to two grades more are permitted than for similar gears made frommetal. The tooth play is increased by one to two grades compared to steel to compensate for temperature and moisture effects.

2. Design information

The following design information is intended to assist when dimensioning new gear components.Existing data should be used for gear designs that are in use and which have been tried and tested.

2.1 Width of the tooth faceFor plastic gears there is basically no problem in extending their width to the same size as the diameter. Determining the smallest width is dependent upon the axial stability of the gear. No testresults are available in regard to the connection between the life of the component and the widthof the tooth face or regarding a determination of the optimum width of tooth face.Practical experience has, however, shown that the width of the tooth face should be at least six toeight times the module.For the mating components steel/plastic it is better to design the plastic gear slightly smaller thanthe steel pinion to make sure that the plastic gear is loaded across the entire width of the tooth face. A similar situation arises with the mating components plastic/plastic, where the dimensions ofthe gear on which the higher wear is expected should be slightly narrower. This prevents wear onthe edges of the teeth, which could affect the running behaviour.

2.2 Module, angle of pressure and number of teethThe load bearing capacity of plastic gears can be directly affected by the choice of module andangle of pressure. If, while maintaining the same peripheral force, the module/angle of pressure isincreased, the root-strength of the teeth increases. However, compared to steel gears, the actualincrease is less, as the effective contact ratio factor decreases and it is no longer possible for several teeth to engage simultaneously. A higher contact ratio factor, however, can be better forthe load bearing capacity than increasing the root-strength of an individual tooth. We can derivethe following connection from this (applies mainly to slow running or impact loaded gears):

• Preferably a small module for tough elastic thermoplastics (increase in the contact ratio factor, rseveral teeth engaged simultaneously)

• Preferably a large module for hard thermoplastics (increase in the root-strength of the teeth, asa higher contact ratio factor is not possible due to the inferior deformation behaviour)

In the case of gears with a high peripheral speed, attention must be paid that the movement isnot affected by the effective contact ratio factor.

The angle of pressure for involute teeth is defined at 20°. Nevertheless, it can occasionally be necessary to change the angle of pressure (e.g. to decrease the number of teeth or reduce


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running noise). Angles of pressure < 20° lead to thinner and hence less loadable teeth with steeptooth profiles but low running noise.Angles of pressure > 20° produce sharper, thicker teeth with a greater root-strength and flatterprofiles.In regard to the number of teeth, it should be noted for higher peripheral speeds that the ratiobetween the number of teeth may not be an integer multiple. If this is the case, the same teeth always engage, which encourages wear.

2.3 Helical gearingExperience has shown that helical plastic gears run quieter with a small helix angle than spur toothed types. However, the expected increase in the load bearing ability is smaller than is the case with steel gears. Although the length of the face contact line increases and the load is distributed among several teeth, the load is uneven and the teeth are deformed. This negates theadvantage of helical gearing to a certain degree.As with metal gears, helical toothed plastic gears are calculated via a spur toothed spare wheel.b ≈ 10° – 20° is regarded as being a favourable helix angle.

2.4 Profile correctionProfile corrections are generally necessary when

• a gear pair has to be adapted to suit a specified axle base(positive or negative profile correction)

• the number of teeth is not reached and this causes undercut(positive profile correction)

In the application, attention should be paid that in the case of negative profile correction theundercut is not too great. This would result in a greatly minimised root-strength of the teeth,which could reduce the life and load bearing capacity of the gear.Vice versa, in the case of positive profile correction, the thicker tooth root could cause a loss in thedeformation capability and a subsequent reduction in the contact ratio factor.

2.5 Flank clearance and crest clearanceBecause of the high thermal expansion factors of plastics when dimensioning gears, attentionmust be paid to the material-related fitting of the flank and crest clearances so that a minimumflank clearance is guaranteed. When plastic gears are used, it has proven practical to maintain aminimum flank clearance of ≈ 0.04 · modulus.The built-in flank clearance is thus

Se = Seo + 2l . sin a (ka. kF) [mm]

whereSeo = minimum flank clearance in mml = total distance consisting of plastic between the two rotational axes in mma = angle of pressureka = coefficient of elongationkF = correction factor for moisture absorption (to be used for polyamides, can be found in the

chapter on »Friction bearings«)

For the inbuilt crest clearance, a measure of 0.3 · module has proven to be practical. This takes account of temperature fluctuations of up to ± 20°C and also makes adequate consideration forany inaccuracies in the toothed gears.


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2.6 Power transmissionThe feather key and groove type of connection that is generally used in machine engineering is also used forplastic gears. For a connection such as this, the flank ofthe key groove must be examined to ensure that it doesnot exceed the permissible surface pressure. The surfacepressure is

Md. 103

pF =i . rm

. h . b [MPa]

whereMd = transmitted torque in Nmi = number of groove flanksrm = radius from the centre of the shaft to the

centre of the bearing flank in mmh = height of the bearing flank in mmb = width of the bearing flank in mm

The value produced from the calculation is compared with Diagram 1 and may not exceedthe maximum permissible values.

However, it should be noted that this value contains no safety factor for shock-type loads orsafety reserves. Depending on the load, we recommend a safety factor of 1.5 to 4.

Because of the notch sensitivity of plastics whenkey grooves are being manufactured, attention should be paid that the edges are designed with aradius. However, this is generally not possible because the usual cutting tools and feather keys aresharp edged. When larger torques are being transmitted this can also cause deformation in thehub.

If the calculation of the flank pressureshould produce high pressure values thatare not permissible, or if hub deformationis feared, there are several possibilities ofpower transmission available.

One possibility is the non-positive connec-tion of the wheel body with a steel insert.This is screwed to the wheel body. The diagram opposite shows one possible design solution.

For fixing the steel insert we recommendhexagon socket screws according to DIN912, property class 8.8 or better in the following dimensions.

rm

b

h

PA 6 G/POM30

20

10

00 20 40 60 80 100

MPa

Ambient temperature

Diagram 1: Guiding value for permissible surface pressure

Tip Number Screw diameter of screws size

up to 100 mm 3 M 6

up to 200 mm 4 M 8

above 200 mm 6 M 8 / M 10


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For gears with relatively thin walls, it is advis-able to use hexagon socket screws with a lowhead according to DIN 6912, property class 8.8or better.

One alternative to the use of a screwed steelfitting is to design the gears in Calaumid 612Fe or Calaumid 1200 Fe. The metallic corewhich is connected to the plastic both in aform-fit and non-positive manner enables theshaft-hub connection to be calculated and di-mensioned like a metallic component asusual. The form-fit and non-positive connec-tion between the plastic casing and the metallic core is created with a knurl.

3. Calculating thermoplastic gears wheels

The reasons for the premature breakdown of thermoplastic gears are generally the same damageaspects and principles that occur in metallic gears. This is why the calculation of plastic gears doesnot differ in principle from the known methods. The only difference is that the material-specificproperties of plastics are included in the calculations in the form of correction factors.

3.1 Torque Md, peripheral force FU and peripheral speed vThe torque is The peripheral force is The peripheral speed

is calculated as

P Md d0 . p . n

Md = 9550 . –– [Nm] FU = 2 . 103 . ––– [N] v = –––––––––– [m/s]n d0 60 . 103

where where whereP = power in kW Md = torque in Nm d0 = reference diameter in mmn = speed in min-1 d0 = reference diameter n = speed in min-1

in mm

3.2 Tooth body temperature cZ and tooth flank temperature cFin continuous operation

As with all designs made from thermoplastic materials, temperature also plays a major role for gears in regard to the load bearing capacity of the component. A distinction is made between thetooth body temperature cZ and the tooth flank temperature cF.

The tooth body temperature is responsible for the permissible tooth root loading and tooth deformation, whereas the tooth flank temperature is used to roughly estimate the level of wear.

However, it is very difficult to determine these two temperatures accurately, as on a rotating gearwheel the heat transmission coefficient can only be estimated roughly. Consequently, any arith-metical determination of the temperatures is liable to have a certain amount of error. In parti-cular, when the tooth flank temperature is being calculated, quite often high values are producedwhich, in some cases, are even above the melting temperatures of the plastics. However, in prac-tice no melting of the tooth profile has been observed. Nevertheless, the values can be regardedas characteristic and comparison temperature values.

It can be assumed that the excessive calculated values would guarantee a design which is on thesafe side in any case.

Calaumid

Steel

Knur DIN 82 – RKE 2,0


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For the thermal calculation of the gears, the friction heat, the heat dissipated from the gearwheel in the gear room and the heat that is dissipated from the gear room to the outside must beconsidered.

Under these conditions, we get the following:

i + 1 r k2 . 17100 k3

ic1,2 = cU + P . m. 136 . –––––––––––– . e ––––––––––––––––– + 7,33 . ––– e [°C]

z1,2 + 5i q b . z1,2. (v . m) 3

4 A t

where

Index 1 for the pinionIndex 2 for the wheelcU= ambient temperature in °C b = width of the tooth face in mmP = power in kW v = peripheral speed in m/secµ = coefficient of friction m = module in mmz = teeth A = surface of the gear casing in m2

i = transmission ratio z1/z2 with k2 = material-related factorz1 = number of teeth in pinion k3 = gear-related factor in m2 K/W

For factor k2 the following must be included depending on the temperature to be calculated:

Calculation of flank temperature: Calculation of root temperature:

k2 = 7 for mating components steel/plastic k2 = 1.0 for mating components steel/plastick2 = 10 for mating components plastic/plastic k2 = 2.4 for mating components plastic/plastick2 = 0 in the case of oil lubrication k2 = 0 in the case of oil lubrication k2 = 0 at v 1 m/sec k2 = 0 at v ≤ 1 m/sec

For factor k3 and the coefficient of friction µ, the following must be included independent of thetemperature to be calculated:

k3 = 0 for completely open gear m2 K/Wk3 = 0.043 to 0.129 for partially open gear in m2 K/Wk3 = 0.172 for closed gear in m2 K/W

µ = 0.04 for gears with permanent lubrication µ = 0.4 PA/PAµ = 0.07 for gears with oil mist lubrication µ = 0.25 PA/POMµ = 0.09 for gears with assembly lubrication µ = 0.18 POM/Stahlµ = 0.2 PA/steel µ = 0.2 POM/POM

3.2.1 Tooth body temperature cZ and tooth flank temperature cFin intermittent operation

Analogous to friction bearings, because of the lower amount of heat caused by friction, gears inintermittent operation are increasingly loadable the lower the duty cycle. The relative duty cycleED is considered in the equation in section 3.2 by introducing a correction factor f.

The relative duty cycle is defined as the ratio between the load duration t and the overall cycle timeT as a percentage.

tED = –– . 100 [%]

T

wheret = total of all load times within the cycle time T in minT = cycle time in min


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For thermoplastic gears, the overall cycle time isdefined as T = 75 min. The total of all individualload times occurring within this 75 min formsthe load duration t.

With the value that has been calculated in thismanner it is now possible to determine the correction factor f from Diagram 2. Attentionshould be paid that each load duration whichexceeds 75 min (regardless of whether this is only once) is evaluated as a continuous load.

Taking account of the correction factor, the tooth flank temperature and tooth body temperatureis

i + 1 r k2 . 17100 k3

ic1,2 = cU + P . f . m . 136 . –––––––––––– . e ––––––––––––––––– + 7,33 . ––– e [°C]

z1,2 + 5i q b . z1,2. (v . m) 3

4 A t

The values given in section 3.2 can be used for the factors k2, k3 and the coefficient of friction µ.

3.3 Calculating the root strength of teethIf the tooth root stress jF exceeds the permissible stress jFper under loading, it must be assumedthat the teeth will break. For this reason the tooth root stress must be calculated and comparedwith the permissible values. If the pinion and gear are constructed from plastic, the calculationsmust be carried out separately for each of them.

The tooth root stress is

FUjF = –––––– . KB. YF

. Yb. Ye [MPa]

b . m

whereFU = peripheral force in Nb = gear width in mm (where the width of the pinion and gear differ: use the smaller width + m

as a calculation value for the wider gear)m = module in mmKB = operating factor for different types of drive operation, from Table 2YF = tooth shape factor from Diagram 3Yb = helix factor to take account of the increase in load bearing capacity in helical gearing, as

this is the case with plastic gears, this value is to be set as 1.0Ye = contact ratio factor from Table 1, where Ye = 1/ea und ea = ea z1 + ea z2

1,0

20 40 60 80 100

0,8

0,6

0,4

0,2

Diagram 2: Correction factor for ED

Co

rrec

tio

n f

acto

r f

Relative duty cycle (%)


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z 14 15 16 17 18 19 20 21 22 23 24

eaz 0,731 0,740 0,749 0,757 0,765 0,771 0,778 0,784 0,790 0,796 0,801

z 25 26 27 28 29 30 31 32 33 34 35

eaz 0,805 0,810 0,815 0,819 0,822 0,827 0,830 0,833 0,837 0,840 0,843

z 36 37 38 39 40 41 42 43 44 45 46

eaz 0,846 0,849 0,851 0,854 0,857 0,859 0,861 0,863 0,866 0,868 0,870

z 47 48 49 50 51 52 53 54 55 56 57

eaz 0,872 0,873 0,875 0,877 0,879 0,880 0,882 0,883 0,885 0,887 0,888

z 58 59 60 61 62 63 64 65 66 67 68

eaz 0,889 0,891 0,892 0,893 0,895 0,896 0,897 0,898 0,899 0,900 0,901

z 69 70 71 72 73 74 75 76 77 78 79

eaz 0,903 0,903 0,904 0,906 0,906 0,907 0,909 0,909 0,910 0,911 0,912

z 80 81 82 83 84 85 86 87 88 89 90

eaz 0,913 0,913 0,914 0,915 0,916 0,917 0,917 0,918 0,919 0,919 0,920

z 91 92 93 94 95 96 97 98 99 100 101

eaz 0,920 0,921 0,922 0,922 0,923 0,924 0,924 0,925 0,925 0,926 0,927

2,0

2,2

2,4

2,6

2,8

YF

3,0

3,2

3,4

3,6

x=0,0

-0,05 -0,1

-0,2

-0,3

-0,4-0,5

-0,6

0,05

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

15 16 18 19 20 25 30 40 50 60 80 100 200 4001735 45 70 90 150 300

Z

x = Profile correction

Mode of operation Mode of operation of the driven machineof the driving machine Even Moderate Average Strong

impact impact impact

Even 1,0 1,25 1,5 1,75

Moderate impact 1,1 1,35 1,6 1,85

Average impact 1,25 1,5 1,75 2,0

Strong impact 1,5 1,75 2,0 2,25

Table 1: Partial transverse contact ratio for gears without profile correction

Table 2: Operating factor KB

Diagram 3: Tooth formation factor YF as a function of the number of teeth


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In the case of profile corrected toothed gears the factor Ye must be adjusted accordingly.The following applies:

z1r z2

i z2ea = –––––– . (tanaE1 - tanaA1) and tanaA1 = tanatw. e1 + ––– e- –––tanaA22 . p q z1 t z1

The value tanaE1 is dependent on the The value tanaA2 is dependent on the correction value correction value

dK1 dK1D1 = –––– D2 = ––– dG2 dG2

where wheredK1 = outside diameter of pinion dK2 = outside diameter of large wheeldG2 = base diameter of large wheel dG1 = base diameter of pinion

The values for tanaE1 and tanaA2 can be taken from Diagram 5. The effective pressure angles atwand tan atw are calculated from the profile correction x1,2 and the number of teeth z1,2 where Index 1 stands for the pinion and Index 2 for the large gear. The effective pressure angles for spurgears are shown in Diagram 4.

3.4 Calculating tooth profile strengthExcessive pressure on the tooth profile can cause pitting or excessive wear. The wear is particularlyobvious in the root and crest of the tooth, which changes the tooth formation and consequentlyleads to uneven transmission of motion.

In order to prevent premature failure due to excessive wear or pitting, the tooth flank pressure jHmust be determined. The pressure occurring on the tooth flank is

FU. (z1 + z2)jH = –––––––––––––– . KB

. Ze. ZH

. ZM [MPa]b . d0

. z2

whereFU = peripheral force in N d0 = reference diameter in mmz1 = number of teeth in pinion KB = operating factor for different z2 = number of teeth in large gear types of drive operation, from b = gear width in mm (where the width of Table 2

the pinion and gear differ: use the Ze = contact ratio factorthe smaller width + m as a calculation ZH = zone factorvalue for the wider gear) ZM = material factor

35

0 0,02 0,04 0,06 0,08

30

25

20

15

Diagram 4: Effective pressure angle atw, tanatw

atw

(x1 + x2 )/(z1 + z2 )

tanatw

100,10

0,7

0,6

0,5

0,4

0,3

0,2

tanatwatw,

1,0 1,1 1,2 1,3 1,4

Diagram 5: Correction diagram for transverse contact ratio

D1, D2

tana

A2

,tan

aE1

1,0

0,8

0,6

0,4

0,2

0


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The contact ratio of several teeth acts like a widening of the tooth. This apparent widening is taken account of with the contact ratio factor Ze and equated for spur and helical gears.

The contact ratio factor becomes

4 - (eaz1 + eaz2)Ze = –––––––––––––––– 3

whereeaz1 = partial transverse contact ratio of pinion

from Table 1eaz2 = partial transverse contact ratio of large wheel

from Table 1

The tooth formation factor ZH takes account of thetooth flank distortion. In the case of non-profile correc-ted spur teeth with an angle of pressure of a = 20° thezone factor can be approximated with ZH = 1.76. Forprofile corrected spur teeth ZH can be taken from thediagram opposite.For angles of pressure other than 20° the following applies:

1 1ZH = ––––––– . –––––––

cosa tanatw

wherea = normal angle of pressuretan atw = effective pressure angle from Diagram 4

The elasticity of the plastic and consequently the effective contact surface of the tooth profile areconsidered with the material factor ZM.

It can be said with sufficient accuracy that

E1. E2ZM = 0,38 . E’ and E’ = ––––––––

E1 + E

whereE1 = dynamic modulus of elasticity of the pinionE2 = dynamic modulus of elasticity of the gear

The different moduli of different materials for the pinion and gear have been taken into account.

For the mating components plastic/steel the corresponding factor for ZM can be taken from Diagram 8.

For the mating components of gears made from the same plastic the following applies:

1Z M(K/K) = –––– . ZM(K/St)M2

If the gear and pinion are made from different plastics, the factor ZM (K/St) for the softer plasticshould be used.

The tooth flank temperature is determined with the help of the formula in sections 3.2 or 3.2.1.

Diagram 6: Zone factor ZHwith profile correction and a = 20°

Z H

( x1 + x2 )/(z1 + z2 )

2,0

1,9

1,8

1,7

1,6

1,5

1,4

1,3

1,2

1,10 0,02 0,04 0,06 0,08 0,1


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-20

Diagram 7: Dynamic modulus of elasticity

Tooth flank temperature

Dyn

amic

mo

du

lus

of

elas

tici

ty

00 20 40 60 80 100 120 140 °C

POM

PA 6 G500

MPa

4500

4000

3500

3000

2500

2000

1500

1000

Diagram 8: Material factor for mating components K/St.

Tooth flank temperature

Z M

POM

PA 6 G

4

8

12

16

20

24

28

32

36

40

44

MNmm

-20 0 20 40 60 80 100 120 140 °C

3.5 Safety factor SThe results for jF and jH from the calculations must be compared with the permissible values. As arule a minimum safety factor of 1.2 to 2 is advisable.The following applies:

jFmax jHmaxjFzul = –––––– and jHzul = –––––– S S

whereS = advisable safety factorjFmax = permissible tooth root stress from Diagrams 9 and 10 in combination with the tooth

temperature

orS = advisable safety factorjHmax = permissible flank pressure from Diagrams 11 to 14 in combination with the tooth

temperature

The following table contains several minimum safety factors in relation to operating conditions.

Type of operation Minimum safety factor

Normal operation 1,2

High stress reversal 1,4

Continuous operation with stress reversals ≥ 108 ≥ 2

The permissible tooth root stresses and flank pressures are shown in the following diagrams.


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105 106 107 108

70

60

50

40

30

20

10

0

20 °C

60 °C

80 °C

100 °C

Tooth temperature

Diagram 9: Root strength of teeth jFmax für POM

Load alternations

Ro

ot

stre

ss j

Fmax

MPa

105 106 107 108 109

60

50

40

30

20

10

0

60 °C

120 °C

Tooth temperature

20 °C

40 °C

80 °C

100 °C

Diagram 10: Root strength of teeth jFmax for PA 6 G

Load alternations

Ro

ot

stre

ss j

Fmax

MPa

Flank temperature (°C)

20

40

60

80

100

120

140

Diagram 11: Contact surface pressure jHmax ,PA 6 G, dry running

Co

nta

ct s

urf

ace

pre

ssu

re j

Hm

ax

105 106 107 108 109

70

60

50

40

30

20

10

0

MPa

Load alternations


40

80

100

120

Diagram 14: Contact surface pressure jHmax ,POM, dry running

Co

nta

ct s

urf

ace

pre

ssu

re j

Hm

ax

140

120

100

80

60

40

20

0105 106 107 108 109

20

Load alternations

MPa

Load alternations

Co

nta

ct s

urf

ace

pre

ssu

re j

Hm

ax

MPa

105 106 107 108 109

140

120

100

80

60

40

20

0

Diagram 13: Contact surface pressure jHmax ,PA 6 G, oil lubrication

20

40

60

80

120

140

100


Diagram 12 : Contact surface pressure jHmax , PA 6 G, grease lubrication


Co

nta

ct s

urf

ace

pre

ssu

re j

Hm

ax

MPa140

120

100

80

60

40

20

20

40

60

80

100

120

140

Load alternations105 106 107 108 109

0


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3.6 Calculating tooth distortionThe tooth distortion that occurs when a load is applied acts like a pitch error during the transitionfrom the loaded to the unloaded condition of the tooth. As excessive deformation could causethe gear to break down, plastic gears must be examined in regards to their compliance with themaximum permissible tooth distortion.

Tooth distortion fK as a correction of the crest of the tooth in the peripheral direction becomes

3 . FUrw1 w2

ifK = –––––––––––– . J . e––– + –––e [mm]

2 . b . cos a0 q E1 E2twhereJF = correction value from Diagram 15w1,2 = correction values from Diagram 16E1,2 = modulus of elasticity from Diagram 7

For the mating components plastic/steel the following applies:

wST_____ = 0EST

The permissible tooth distortion is generally determined by the requirements that are placed onthe gears in regard to running noise and life. Practice has shown that the running noises increaseconsiderably from a tooth distortion fK = 0.4mm. Another parameter is the ratio between toothdistortion and module.

In the form of an equation, the permissible limiting values become

fKzul ≤ 0,4 [mm]

or

fKper ≤ 0,1 . m [mm]

The calculated values should not exceed the limiting values. If, however, this is the case one wouldhave to accept increased running noises and a shorter life.

Diagram 15: Correction value J

Co

rrec

tio

n v

alu

e J

14 16 18 20 25 30 40 50 100

Number of teeth z1,2

8,6

8,2

7,8

7,4

7,0

6,6

6,2

5,8

z1/z2 = 1,00,8

0,6

0,4

0,2

0

Diagram 16: Correction value w1,2

Co

rrec

tio

n v

alu

e w

1,2

14 16 18 20 25 30 40 50 100

Number of teeth z1,2

2,0x1,2 = - 0,6

1,6

1,2

0,8

0,4

- 0,4

- 0,2

0

0,2

0,4 0,6

0,81,0


Plastic spindle nuts


102

Plas

tic

spin

dle

nu

ts

102

1. Plastic as a material for spindle nuts

Spindle nuts, in combination with a threaded spindle, transform a turning motion into a linearmotion. Good stability of the nut material, a large thread bearing area and high surface qualityare advantages for power transmission. A trapezoidal screw thread design according to DIN 103 isadvantageous and practical.Loading of the thread flanks is the same as on a sliding element which means that in regard tochoosing a suitable material for the spindle nut, the main considerations are sliding and wear properties. The stability of the chosen material is decisive for safe power transmission.It should be noted that glass fibre reinforced plastics are unsuitable for the manufacture of spindlenuts. Compared to other thermoplastics, they exhibit inferior sliding and wear values. In addition,the glass fibres can cause increased wear in the mating component. The relatively high modulus ofelasticity of these materials also hinders deformation of the thread during stress peaks, so that the load can distribute evenly over all the threads. This results in tears in the threadand a much shorter service life compared to plastics that are not reinforced.

1.1 MaterialsFor the manufacture of spindle nuts, cast polyamides with and without sliding additives, as well asPOM, PET and PET with sliding additives have proven their worth.In regard to service life, like all other sliding applications, the use of materials with built-in lubrication (such as Oilamid and PET-GL) is an advantage. Compared to other plastics, they exhibitless wear and thus achieve a longer service life.

1.2 LubricationAs with all other slide applications, lubrication is not absolutely necessary, but among other thingsit does considerably prolong the service life of the components. It also counteracts the danger ofstick-slip occurring.An initial installation lubrication is practical, as recommended for friction bearings and slidingpads, with a subsequent empirical lubrication. This especially applies to highly stressed spindlenuts where attention has to be paid that the friction heat is dissipated.However, graphite should not be used as a lubricant in combination with polyamide spindle nuts,as with this combination stick-slip becomes more likely.

2. Manufacture and design

The threads of spindle nuts can be machined on suitable machine tools. We recommend that theybe produced on a lathe with the use of a lathe thread chisel. In this way, it can be ensured thatthere is enough play on the flanks of the thread to balance out the effects of heat expansion andmoisture absorption.Generally the spindle nut and housing are connected via a feather key. The load bearing capacityof plastic nuts in this case is oriented to the admissible compression in the feather key groove.To fully utilise the load bearing capacity of the plastic thread, a form-fit connection between theouter steel housing and the plastic nut is required.

Plastic spindle nuts


103

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spin

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3. Calculating the load bearing capacity

3.1 Surface pressure in the key grooveFor a feather key connection, the side of the key groove must be checked to ensure that it doesnot exceed the permissible surface pressure. The surface pressure is

Md. 103

PF = –––––––––––––– [MPa]i . rm

. h . b

whereMd = transmitted torque in Nmi = number of groove flanksrm = radius from the middle of the shaft to

the middle of the bearing flank in mmh = height of the bearing flank in mmb = width of the bearing flank in mm

The value from the calculation is compared with Diagram 1 and may not exceed the maximum value.

3.2 Surface pressure on the thread flankIf we assume that all thread flanks bear the load equally, the surface pressure on the flanks is

Fp = –––––––––––––––––––––––– [MPa]

r l i 2

z . H . ed2. p . –– e + l2

q P t

whereF = axial load of the spindle in NP = lead in mmd2 = flank diameter in mml = length of nut in mmH = depth for ISO metric trapezoidal screw

thread in mm according to Table 1z = number of screw flights

(in case of multiple-flights)

In the case of static loading for spindle nuts made from PA, POM or PET, at 20°C approx. 12 MPaand at 80°C approx. 8 MPa can be permitted as the maximum compression.

103

PA 6 G/POM30

20

10

0

MPa

0 20 40 60 80 100

Ambient temperature

Diagram 1: Guiding values for permissible surface pressure

Surf

ace

pre

ssu

re

P

30°

d d2

= D

2

d3

H


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Plas

tic

spin

dle

nu

ts

104

Table 1: ISO metric trapezoidal screw thread according to DIN 103

Thread Thread Threaddiameter P H d2 diameter P H d2 diameter P H d2

d = 0,5 . P = d - H d = 0,5 . P = d - H = 0,5 . P = d - H

8 1,5 0,75 7,25 36 6 3 33 75 10 5 70

10 2 1 9 40 7 3,5 36,5 80 10 5 75

12 3 1,5 10,5 44 7 3,5 40,5 85 12 6 79

16 4 2 14 48 8 4 44 90 12 6 84

20 4 2 18 52 8 4 48 95 12 6 89

24 5 2,5 21,5 60 9 4,5 55,5 100 12 6 94

28 5 2,5 25,5 65 10 5 60 110 12 6 104

32 6 3 29 70 10 5 65 120 14 7 113

3.3 Sliding friction on the thread flankAs the thread flanks can be considered, as a sliding element, the pv value can also be used as aguiding value for sliding friction loads for spindle nuts.For the thread flank this is

n . (d2. p)2 + s2

pv = p . –––––––––––––––––– [MPa . m/s]60000

wheren = number of strokes in 1/min –1

d2 = flank diameter in mms = stroke length in mm

As with friction bearings, the question regarding the permissible sliding friction load is a problemcaused by the heat that occurs due to friction. If it can be ensured that the plastic nuts have sufficient time to cool down in intermittent operation, higher values can be permitted than in thecase of continuous operation.

However, the determined values may not exceed the maximum values given in Table 2.

Table 2: pv – limiting values for spindle nuts

PA 6

G

Oila

mid

POM

– C

PET

PET

– G

L

PA 6

G

Oila

mid

POM

– C

PET

PET

– G

L

Continuous operation Intermittent operation

Dry running 0,15 0,23 0,15 0,15 0,25 0,23 0,34 0,23 0,23 0,37

Continuous lubrication 0,30 0,30 0,30 0,30 0,50 0,45 0,45 0,45 0,45 0,50


Tolerances


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Tolerances

1. Material-related tolerances for machined plastic construction parts

Plastics are often integrated into existing assemblies to replace conventional materials. As a rule,however, the production drawing is only altered in respect to the new material. Often the tolerances that have been specified for the steel component are not adapted to suit the new material. But even in the case of new designs where plastic is planned as a material, the tolerancefields that are normal for steel are still used.However, the special features of plastics extensively preclude the choice of the narrow productiontolerances required for steel parts.

The decisive factor is not the possibility of manufacturing the parts, since this is virtually no problem with the use of modern CNC machine tools, but rather the permanent compliance withthe tolerances after the manufacturing process. This applies especially to dimensions in a class oftolerances with very narrow fields (< 0.1mm). These can change immediately after the part is taken from the machine table due to the visco-elastic behaviour of the plastics. In particular, thehigher level of thermal expansion, volume changes due to the absorption of moisture as well asform and dimensional changes caused by the relaxation of production-related residual stressesare just some of the possible causes.

Another problem is the fact that there is no general standard for machined plastic components.The lack of a common basis for material-related tolerance for parts such as this often leads to disagreement between the customer and the supplier in regard to the classification of rejectsand/or defects in delivery. Choosing a tolerance field that is suitable for the respective materialcan avoid disputes and also ensure that the plastic components function and operate safely as in-tended.

The following sections of this chapter are based on our many years of experience with differentplastics and are intended to assist design engineers in defining tolerances. The aim is to create astandard basis and to avoid unnecessary costs caused by rejects due to off-spec tolerances.

The tolerance fields that we recommend can be achieved with conventional production methodsand without any additional expenditure. In general, the functioning and operating safety of thecomponents were not limited because of the increased tolerance. Narrower tolerances than thosestated here are possible to a certain extent, but would necessitate unjustifiably high processingexpenditure, and the materials would also require intermediate treatment (annealing) during theproduction process. If component parts require tolerance fields of < 0.1mm or ISO series IT 9 fitsand smaller, we will be happy to advise you in the choice of a technically/economically practicaland sustainable tolerance field.

2. Plastic-related tolerances

2.1 General tolerancesThe general tolerances for untoleranced dimensions can be chosen according to DIN ISO 2768 T1,tolerance class »m«.In this standard, the tolerances are defined as follows:


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Table 1: Limiting dimensions in mm for linear measures (DIN ISO 2768 T1)

Nominal size range in mmTolerance 0,5 above 3 above 6class up to 3 up to 6

f (fine)

m (medium) ± 0,2 ± 0,5 ± 1,0

g (rough)

v (very rough) ± 0,4 ± 1,0 ± 2,0

Nominal size range in mm

Tolerance 0,5 above 3 above 6 above 30 above 120 above 400 above 1000 above 2000class up to 3 up to 6 up to 30 up to 120 up to 400 up to 1000 up to 2000 up to 4000

f (fine) ± 0,05 ± 0,05 ± 0,1 ± 0,15 ± 0,2 ± 0,3 ± 0,5 -

m (medium) ± 0,1 ± 0,1 ± 0,2 ± 0,3 ± 0,5 ± 0,8 ± 1,2 ± 2,0

g (rough) ± 0,15 ± 0,2 ± 0,5 ± 0,8 ± 1,2 ± 2,0 ± 3,0 ± 4,0

v (very rough) - ± 0,5 ± 1,0 ± 1,5 ± 2,5 ± 4,0 ± 6,0 ± 8,0

Table 2: Limiting dimensions in mm for radius of curvature and height of bevel (DIN ISO 2768 T1)

Table 3: Limiting dimensions in degrees for angle measurements (DIN ISO 2768 T1)

Nominal size range of the shorter leg in mm

Tolerance up to 10 above 10 above 50 above 120 above 400class up to 50 up to 120 up to 400

f (fine)± 1° ± 30’ ± 20’ ± 10’ ± 5’

m (medium)

g (rough) ± 1° 30’ ± 1° ± 30’ ± 15’ ± 10’

v (very rough) ± 3° ± 2° ± 1° ± 30’ ± 20’

In special cases, for longitudinal dimensions it is possible to choose the tolerance class »f«. However, it is important that permanent compliance with the tolerance in regard to componentgeometry is checked in agreement with the manufacturer.

2.2 Shape and positionThe general tolerances for untoleranced dimensions can be selected according to DIN ISO 2768 T2,tolerance class »K«.In this standard the tolerances are defined as follows:

Table 4: General tolerances for straightness and evenness (DIN ISO 2768 T2)


Tolerance above 10 above 30 above 100 above 300 above 1000class up to 10 up to 30 up to 100 up to 300 up to 1000 up to 3000

H 0,02 0,05 0,1 0,2 0,3 0,4

K 0,05 0,1 0,2 0,4 0,6 0,8

L 0,1 0,2 0,4 0,8 1,2 1,6


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Dimension category Plastics Comments

A POM, PET, PTFE+glass, PTFE+bronze, Thermoplastics with or

PTFE+coal,PC,PVC-U, PVDF, PP-H, or without reinforcement/

PEEK, PEI, PSU, HGW (laminated fillers

fabric) (with low moisture

absorption)

B PE-HD, PE-HMW, PE-UHMW, PTFE, Soft thermoplastics and

PA 6, PA 6 G, PA 66, PA 12 polyamides with

moisture absorption

Table 5: General tolerances for rectangularity (DIN ISO 2768 T2)


Tolerance above 100 above 300 above 1000class up to 100 up to 300 up to 1000 up to 3000

H 0,2 0,3 0,4 0,5

K 0,4 0,6 0,8 1,0

L 0,6 1,0 1,5 2,0


Tolerance above 100 above 300 above 1000class up to 100 up to 300 up to 1000 up to 3000

H 0,5

K 0,6 0,8 1,0

L 0,6 1,0 1,5 2,0

Table 6: General tolerances for symmetry (DIN ISO 2768 T2)

The general tolerance for run-out and concentricity for class »K« is 0.2mm.

In special cases for shape and position it is possible to choose tolerance class »H«. The general tolerance for run-out and concentricity for class »H« is 0.1mm.However, it is important that permanent compliance with the tolerance in regard to componentgeometry is checked in agreement with the manufacturer.

2.3 FitsAs described above, it is not possible to apply the ISO tolerance system that is usually applied tosteel components. Accordingly, the tolerance series IT 01 – 9 should not be used. In addition, todetermine the correct tolerance series, the processing method and the type of plastic being usedmust be considered.

2.3.1 Dimensional categoriesThe different plastics can be classified into two categories according to their dimensional stability.These are shown in Table 7.

Table 7: Dimension categories for plastics


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2.3.2 Classification of tolerance series for milled partsClassification for milled parts with tolerances

Dimension A IT 10 - 12

category: B IT 11 - 13

Table 8: ISO basic tolerances in µm according to DIN ISO 286

Nominal size ISO tolerance series (IT)range in mm 6 7 8 9 10 11 12 13 14 15 16

From up to 1-3 6 10 14 25 40 60 100 140 250 400 600

Above up to 3-6 8 12 18 30 48 75 120 180 300 480 750

Above up to 6-10 9 15 22 36 58 90 150 220 360 580 900

Above up to 10-18 11 18 27 43 70 110 180 270 430 700 1100

Above up to 18-30 13 21 33 52 84 130 210 330 520 840 1300

Above up to 30-50 16 25 39 62 100 160 250 390 620 1000 1600

Above up to 50-80 19 30 46 74 120 190 300 460 740 1200 1900

Above up to 80-120 22 35 54 87 140 220 350 540 870 1400 2200

Above up to 120-180 25 40 63 100 160 250 400 630 1000 1600 2500

Above up to 180-250 29 46 72 115 185 290 460 720 1150 1850 2900

Above up to 250-315 32 52 81 130 210 320 520 810 1300 2100 3200

Above up to 315-400 36 57 89 140 230 360 570 890 1400 2300 3600

Above up to 400-500 40 63 97 155 250 400 630 970 1550 2500 4000

2.3.3 Classification of tolerance series for turned partsClassification for turned parts with tolerances

Dimension A IT 10 - 11

category: B IT 11 - 12

Table 8: ISO basic tolerances in µm according to DIN ISO 286

Nominal size ISO tolerance series (IT)range in mm 6 7 8 9 10 11 12 13 14 15 16

From up to 1-3 6 10 14 25 40 60 100 140 250 400 600

Above up to 3-6 8 12 18 30 48 75 120 180 300 480 750

Above up to 6-10 9 15 22 36 58 90 150 220 360 580 900

Above up to 10-18 11 18 27 43 70 110 180 270 430 700 1100

Above up to 18-30 13 21 33 52 84 130 210 330 520 840 1300

Above up to 30-50 16 25 39 62 100 160 250 390 620 1000 1600

Above up to 50-80 19 30 46 74 120 190 300 460 740 1200 1900

Above up to 80-120 22 35 54 87 140 220 350 540 870 1400 2200

Above up to 120-180 25 40 63 100 160 250 400 630 1000 1600 2500

Above up to 180-250 29 46 72 115 185 290 460 720 1150 1850 2900

Above up to 250-315 32 52 81 130 210 320 520 810 1300 2100 3200

Above up to 315-400 36 57 89 140 230 360 570 890 1400 2300 3600

Above up to 400-500 40 63 97 155 250 400 630 970 1550 2500 4000


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2.4 Surface qualityThe degree of surface quality that can be achieved depends on the processing method. Table 9shows the surface qualities that can be achieved without any additional expenditure for the indi-vidual processes.

Table 9: Achievable surface qualities for various machining processes

Form of machining Max. achievable Average roughness Averaged depth of degree of roughness value Ra (µm) roughness Rz(µm)

Milling N7 1,6 8

Turning N7 1,6 8

Planing N8 3,2 12,5

Sawing N8 3,2 16

It is possible to achieve better surface qualities than those shown in Table 9 in conjunction withhigher production expenditure. However, the production possibilities must be discussed with themanufacturer of the component part in regard to the respective plastic and the processing method.

2.5 Tolerances for press fits

2.5.1 Oversize for bushesTo ensure that friction bearing bushes sit properly in thebearing bore, the insertion of an oversized componenthas proved to be good method. The oversize for plastic bushes is very large compared to metal bearingbushes. However, due to the visco-elastic behaviour ofthe plastics, this is especially important because of theeffects of heat, as otherwise the bearing bush would become loose in the bore. If the maximum service tem-perature is 50°C, it is possible to do without an additi-onal securing device for the bearing bush if the oversizesfrom Diagram 1 are complied with. In the case of tem-peratures above 50°C, we recommend that the bush besecured with a device commonly used in machine en-gineering (e.g. a retaining ring according to DIN 472, seealso the chapter on »Friction bearings« section 2.5).

It should also be considered that when the bearingbush is being inserted, its oversize leads to it beingcompressed. Consequently the oversize must beconsidered as an excess to the operating bearingplay, and the internal diameter of the bearingmust be dimensioned accordingly. Diagram 2 shows the required bearing play in relation to theinternal diameter of the bearing. To prevent thebearing from sticking at temperatures above 50°C,it is necessary to correct the bearing play by thefactors shown in the chapter on »Friction bearings« section 2.3.

0,007

0,006

0,005

0,004

0,003

0,002

0,001

20 40 60 80 100 120 140 160 1800

Outer diameter of the friction bearing in mm

Pres

s-fi

t o

vers

ize

per

mm

ou

ter

dia

met

er in

mm

Diagram 1: Press-fit oversize for friction bearings

0 10 30 50 100 150 200

0,1

1,0

0,9

0,8

0,7

0,6

0,5

0,4

0,3

0,2

0

Internal diameter of bearing in mm

Op

erat

ing

bea

rin

g p

lay

in %

Diagram 2: Operating bearing play


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In regard to dimensioning thin walledbearing bushes, rings and similar components, it must be noted that themeasuring forces that are applied andthe deformation that this causes can result in incorrect measurements. Hence, the tolerances for the outer diameter and wall thickness shown in Figure1 are recommended.

2.5.2 Press-fit undersize for antifriction bearingsAntifriction bearings can be inserted directly into the undersized bearing seat for maximum operating temperatures of up to 50°C. If low stress and low operating temperatures are expected,no additional security is required for the bearing, but this is, however, recommended for higherstresses and operating temperatures. Again this is because of the visco-elastic behaviour of theplastics which can result in a reduction in the compression force and bearing migration. The bearing can also be securedwith devices commonly used in machine engineering (e.g. re-taining ring according to DIN472). If the bearing is to be usedin areas where high temperatu-res or loads are expected, it is al-so possible to place a steel slee-ve in the bearing bore. This steel sleeve is fixed in the bearing bore with additional securingelements, and the bearing ispressed in to this ring.

Diagram 3 shows the requiredtemperature-related undersizesfor fixing the bearing in thebearing seat by compression.

For bearing seats into which an-tifriction bearings are inserted for operation at normal temperature and load conditions, we re-commend the following press-fit undersizes and tolerances:

Bearing seat diameter up to 50 mm c – 0.15 / – 0.25 mmBearing seat diameter above 50 up to 120 mm c – 0.25 / – 0.35 mm

Bearing seat diameter above 120 mm c – 0.40 / – 0.50 mm

In our many years of experience, bearing seats manufactured according to the above exhibit noexcessive decrease in compression force and are able to keep the antifriction bearings in positionsafely and securely.

However, if this recommendation is taken, it should be noted that in the case of extremely smallratios between the bearing seat diameter and the outer diameter it is possible that the bearingsloosen despite compliance with our recommendations. This can be attributed to the fact that thestresses caused by insertion can result in elongation of the residual material. As a result of this,the bearing seat diameter becomes larger and the compression force needed to fix the bearingcan no longer be maintained. This behaviour is exacerbated by high temperatures and/or flexingthat occurs during operation. This can be negated to a certain extent by the securing measures described above.

70 0-0,2

2,5

-0,1

0-0

,15

Ø 4

5

(Ø 4

0)+0,

25+

0,15

Figure 1: Example of tolerance for a bearing bush

0,1

0,7

0,6

0,5

0,4

0,3

0,2

0,020 40 60 80 100 120

Operating temperature 50 °C

Operating temperature 20 °C

Antifriction bearing diameter in (mm)

Bo

re s

etti

ng

siz

e in

mm

Diagram 3: Bore setting sizes for bearing seats


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3. General information

The basic tolerances and dimensions stated above can only be sustainably maintained under normal climatic conditions (23°C/50% rel. humidity). If the environmental conditions differ, theymust be considered by applying the respective correction factors. These can be found for the specific cases in the previous chapters.

3.1 Dimensional and volume changes under the influence of temperatureIn general it can be said that elongation caused by temperature is approx. 0.1% per 10 K tempe-rature change. In addition, in the case of polyamides, due to the absorption of moisture a changein volume of 0.15 – 0.20% per 1% water absorbed must be considered.

Considering the material-specific coefficient of elongation, the expected elongation and volumechanges due to fluctuating temperatures can be calculated approximately.Hence, the expected elongation is

Dl = I . a . (u1 – u2) [mm]

whereDI = expected elongationl = original length in mma = material-specific coefficient of elongationu1 = installation temperature in °Cu2 = operating temperature in °C

The expected change in volume is calculated – with the assumption that the elongation is not hindered in any direction – from:

DV = V . b . (u2 – u1) [mm3]

and

b = 3 . a

whereDV = expected change in volumeV = original volume in mm3

a = material-specific coefficient of elongationb = material-specific coefficient of volume expansionu1 = installation temperature in °Cu2 = operating temperature in °C

The material-specific coefficients of elongation can be found in Table 10.


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Material Abbreviation Coefficient of elongation a 10-5 . K-1

Polyamide 6 cast PA 6 G 7

Polyamide 6 cast CC PA 6 G-CC 8

Oilamid PA 6 G + Öl 7

Calaumid 612 PA 6/12 G 8

Calaumid 1200 PA 12 G 10

Polyamide 6 PA 6 9

Polyamide 6 + 30% glass fibre PA 6 GF30 3

Polyamide 66 PA 66 10

Polyamide 12 PA 12 12

Polyacetal POM -C 10

Polyacetal GF-filled POM -C-GF30 2,5

Polyethylene terephthalate PET 7

Polyethylene terephthalate + lubricant additive PET -GL 8

Polytetrafluoroethylene PTFE 19

Polytetrafluoroethylene + 25% glass fibre PTFE -GF25 13

Polytetrafluoroethylene + 25% coal PTFE -K25 11

Polytetrafluoroethylene + 40% bronze PTFE -B40 10

Polyethylene 500 PE-HMW 18

Polyethylene 1000 PE-UHMW 18

Polyetheretherketone PEEK 4

Polyetheretherketone modified PEEK-GL 3

Polysulphone PSU 6

Polyether imide PEI 6

Table 10: Linear coefficients of elongation of various plastics

3.2 Geometric shapesThe geometric relationships of a workpiece can cause changes in dimensions and shape after the machining process. Therefore, either the geometric shape has to be changed or the recom-mended tolerance series for workpieces with extreme geometric shape and wall thickness relati-onships, e.g. extreme one-sided machining, extremely thin walls, extreme wall thickness differen-ces, must be adapted accordingly. If there is any uncertainty in regard to the definition of shape,dimension or position tolerances, we would be pleased to assist.

3.3 Measuring technologyIt is very difficult to measure narrow tolerances in plastic workpieces, especially in thin-walledparts. The pressure exerted on the workpiece by the measuring instrument can deform the plasticpart, or the low coefficient of friction of plastics can distort the starting torque of micrometergauges. This inevitably leads to incorrect measured values. Therefore it is recommended thatcontactless measuring systems are used.


Machining guidelines


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Machining guidelines

1. Machining of thermoplastics

With the increasing variety of engineering plastics andthe resulting applications, design engineers now havemany new horizons that were previously unthinkablewith conventional materials. In many cases, in additionto material limitations, the only other limit to designpossibilities are the restrictions imposed by the manu-facturing process. Particularly if large volume parts arerequired from cast polyamides and polyacetal (POM) orpolyethylene terephthalate (PET), manufacturing processes such as injection moulding cannot be used.This applies equally to complex parts that require machining from all sides with narrow tolerances.

In this area, machining has proven to be the best method. Highly precise parts and large components canbe manufactured especially economically in small andmedium batches by machining.

For the manufacture of high quality products, certainspecific features of plastics must be considered whenmachines and tools are being chosen and used.

1.1 Machining equipment/toolsNo special machines or processes are required for machining. The machines that are normally usedin the woodworking and metal industries with HSS tools (high performance superspeed steel) orhard metal tools can be used. The only thing to consider is that when a circular saw is used to cutplastic, hard metallic saw blades must be used.

The group of glass fibre reinforced plastics is a special case. While it is possible to machine themwith hard metal tools, it is very difficult to achieve economic results due to the short service life ofthe tools. In this case it is advisable to use diamond tipped tools, which are much more expensivethan conventional tools but have a much longer service life.

1.2 Machining and clamping the workpiecePlastics have lower thermal conductance properties than metals, as well as a lower modulus of elasticity. If not handled properly, the workpiece can become extremely warm and thermal expansion can occur. High clamping pressures and blunt tools cause deformation during machining. Dimensional and shape deviations outside the tolerance range are the consequence.

Satisfactory results are only achievable if several material-specific guidelines are considered whenmachining plastics.

In detail, these guidelines are:• The highest possible cutting speed should be chosen.• Optimum chip removal must be ensured so that the chips are not drawn in by the tool.• The tools that are used must be very sharp. Blunt tools can cause extreme heat, which results in

deformation and thermal expansion.• The clamping pressures must not be too high as this would result in deformation of the work-

piece and the clamping tool would leave marks in the workpiece.• Because of the low degree of stiffness, the workpiece must be adequately supported on the

machine table and should lie as flat as possible.

Fig. 1: Complex component made from POM

115


• Perfect, high-quality surfaces can only be obtained when the machines operate with low vibration.

If these guidelines are complied with, it is possible to obtain narrow, plastic-oriented toleranceswith a high level of reproducibility without difficulty.

1.3 Cooling during machiningAs a rule it is not absolutely necessary to cool the workpiece during machining. If cooling is to beapplied it is recommended that compressed air is used. This has the advantage that in addition tothe cooling effect, the chips are removed from the working area and cannot be drawn into theworkpiece or tool.

Conventional drilling emulsions can also be used for cooling and are especially recommended fordeep bores and cutting threads. In addition, it is possible to achieve higher rates of forward feedand consequently, shorter running times.

However, if using drilling emulsions, attention should be paid that these are completely removedafter machining. This prevents oily components causing problems in subsequent processes such asbonding or painting, especially in the case of polyamides where the water in the emulsion cancause changes in the components through absorption.

2. Parameters for the individual machining processes

2.1 SawingPlastics can be sawn with a band saw or a circular saw. The choice depends on the shape of the semi-finished product. The use of a band saw is particularly recommended when a “support groove” (prism) is used to cut rods and tubes and also has the advantage that the built up heat isdissipated via the long saw blade. However, the teeth of the blade must be set adequately so thatthe blade cannot jam.

Circular saws, on the other hand, are mainly used for cutting sheets and blocks with straight edges. Here, attention should be paid that the feed rate is adequate so that chips are removed,that the saw blade does not jam and that the plastic does not overheat at the point where it isbeing cut. Table 1 contains guiding values for the cutting geometry of the saw blades.

PA, PE, POM, PET, PVDF, PVC

Band saw Circular saw

a = Clearance angle (°) 30 - 40 10 - 15

g = Effective cutting angle (°) 0 - 8 0 - 10

v = Cutting speed m/min 200 - 1000 1000 - 3500

t = Number of teeth 3 - 5 per inch 24 - 80

t

α

γ

Table 1: Tool geometry for saw blades

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2.2 MillingMilling on conventional machining centres is unproblematic. With a high cutting speed and medium feed rate it is possible to achieve high levels of machining performance with good surface quality and accuracy. In regard to the cutter geometry, we recommend the values given inTable 2.

2.3 Turning on a latheSince most plastics produce unbroken chips, it is important to ensure that the chips are removed,as they would otherwise catch and revolve with the part being turned on the lathe. In addition,because of the low degree of stiffness of plastics, there is a great danger of longer parts sagging,and it is thus advisable to use a steady rest. The values given in Table 3 apply to the cutter geometry.

2.4 DrillingDrill holes can be made with a conventional HSS drill. If deep holes are being drilled, it must beensured that the chips are removed, as otherwise the plastic on the walls of the hole will heat tothe point of melting and the drill will “clog”. This especially applies to deep holes.For drilled holes in thin-walled workpieces, it is advisable to choose a high drilling speed and, ifapplicable, a neutral (0°) effective cutting angle. This prevents the drill from sticking in the work-piece and hinders the associated stripping of the hole or the workpiece being drawn up by thedrill.

Table 4 contains the recommended values for cutting edge geometry.

PA, PE PTFE POM, PET

PVDF, PVC

a = Clearance angle (°) 5 - 15 10 - 15 5 - 10

g = Effective cutting angle (°) 0 - 15 15 - 20 0 - 10

v = Cutting speed m/min up to 1000 up to 600 up to 1000

s2 = Forward feed/tooth up to 0,5 up to 0,5 up to 0,5

Angle of twist in ° 0 - 40 0 - 40 0 - 40

α

γ

PA, PE PTFE POM,PETPVDF, PVC


g = Effective cutting angle (°) 0 - 10 15 - 20 0 - 5

x = Setting angle (°) 0 - 45 0 - 45 0 - 45

v = Cutting speed m/min 200 - 500 100 - 300 200 - 500

s = Forward feed mm/rev. 0,05 - 0,5 0,05 - 0,3 0,05 - 0,5

a = Rate of cut mm up to 15 up to 15 up to 15

The point radius should be at least 0.5mm

α

γ

χ

a

Table 2: Tool geometry for milling cutters

Table 3: Tool geometry for lathe chisels


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2.5 Drilling large diameters in sections of round rodWhen drilling, high temperatures build up on the cutting edges, especially with highly crystallinematerials such as PA 6 G, which cannot be adequately dissipated because of the good insulationproperties of the plastics. The heat causes an internal expansion in the material, which in turn causes compressive stress in the inside of the rod section. This stress can be so high that the rodtears and splits.

This can be avoided to a great extent if the material is machined correctly.

It is advisable to pre-drill the hole and complete it with a right side tool. The pre-drilled holesshould not exceed 35 mm in diameter.

Drilled holes in long sections of rod must only be made from one side, as otherwise an unfavou-rable stress relationship is created when the drilled holes meet in the middle of the blank rod,which can lead to the rod section cracking.

In extreme cases it may be necessary to heat the blank to approx. 120 – 150°C and pre-drill it inthis condition. The hole can then be completed when the rod has cooled down and when an eventemperature has set in throughout the blank.

If these machining guidelines are complied with, it is quite possible to manufacture complex products from engineering plastics using machining processes even when the highest demandsare placed on quality, accuracy and functionality.

γ1

α

ϕ

PA, PE PTFE POM,PETPVDF, PVC


g1 = Effective cutting angle (°) 3 - 5 3 - 5 3 - 5

J = Point angle (°) 60 - 90 130 60 - 90

v = Cutting speed m/min 50 - 100 100 - 300 50 - 100

s = Forward feed mm/rev. 0,1 - 0,5 0,1 - 0,3 0,1 - 0,3

The angle of twist of the drill should be at least 12 - 16°

Table 4: Tool geometry for drills


Mechanical values and chemical resistances

of plastics


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Parameter Condition Footnote

Impact resistance DIN 53 453 Measured with an impact pendulum testing machine 0.1 DIN 51 222 1

Creep stress DIN 53 444 Stress that leads to 1% overall expansion after 1,000 h 2

Coefficient of sliding friction Hardened and ground against steel, P = 0.05 MPa,

V = 0.6 m/s, t = 60° in vicinity of running area 3

Linear coefficient of elongation For temperature range from +23°C up to +60°C 4

Temperature range Experience values, determined on finished

parts without load in warmed air, dependent on the type

and form of heat,

short-term = max. 1 h, long-term = months 5

Dielectric strength DIN 53 483 at 106 Hz 6

Colours POM-C natural = white

PET-natural = white

PVDF-natural = white to ivory (translucent)

PE-natural = white

PP-H natural = white (translucent)

PP-H grey ≈ RAL 7032

PVC-grey ≈ RAL 7011

PEEK-natural ≈ RAL 7032

PSU-natural = honey yellow (translucent)

PEI-natural = amber (translucent) 7

Units and abbreviations o.B. = without breakage

1 MPa = 1 N/mm2

1 g/cm3 = 1,000kg/m3

1 kV/mm = 1MV/m none

Information and conditions concerning the table “Mechanical values”

The information in the list is intended to provide an overview of the properties of our productsand to allow a quick comparison of materials. They represent our present standard of knowledgeand do not claim to be complete. Because of the high level of dependence on environmental influences and processing methods, the values given here should only be regarded as standard values. In no way do they represent a legally binding assurance in regard to the properties of ourproducts nor to their suitability for specific applications. All the values stated here were deter-mined from average values resulting from many individual measurements and refer to a tempe-rature of 23°C and 50% RH.For specific applications, we recommend that the suitability of the materials be first tested by practical experiments.

The conditions under which the individual values were determined, and any special features in regard to these values, are contained in the following list with the respective footnotes:


122

Physical MaterialGuiding Values

Den

sity

DIN

53

479

Yie

ld s

tres

sD

IN 5

3 45

5

Elo

ng

atio

n a

t b

reak

DIN

53

455

Mo

du

lus

of

elas

tici

ty r

esu

ltin

g

fro

m t

ensi

le t

est

DIN

53

457

Mo

du

lus

of

elas

tici

ty r

esu

ltin

g

fro

m b

end

ing

tes

t D

IN 5

3 45

7

Flex

ura

l str

eng

thD

IN 5

3 45

2

Imp

act

stre

ng

thD

IN 5

3 45

3

No

tch

ed-b

ar im

pac

t st

ren

gth

DIN

53

453

Bal

l in

den

tati

on

har

dn

ess

H35

8/30

DIN

53

456

Cre

ep r

ate

stre

ss a

t 1%

el

on

gat

ion

DIN

53

4442)

No. Material Abbrev. Colours Test specimen(standard) condition

1 Polyamide 6 Cast PA 6 Gnatural/black/ dry

blue humid

2 Polyamide 6 Cast + MoS2 PA 6 G + MoS2 blackdry

humid

3 Polyamid 6 Cast-CC PA 6 G-CC natural/black dry

4Polyamide 6 Cast

PA 6 G-WS blackdry

Heat stabilised humid

5 Oilamid® PA 6 G + Ölyellow/black/ dry

natural humid

6 Calaumid® 612PA 6 / 12 G

naturaldry

(impact resistant) humid

7 Calaumid® 1200 PA 12 G naturaldry

humid

8 Polyamide 6 PA 6 natural/blackdry

humid

9 Polyamide 66 PA 66 natural/blackdry

humid

10 Polyamide 6 + Glass fibre PA 6 + GF 30 blackdry

humid

11 Polyamid 66 + Glass fibre PA 66 + GF 30 blackdry

humid

12 Polyamide 12 PA 12 natural dry

13Polyacetal

POM - C natural7)/black dryCopolymer

14Polyacetal

POM - C GF 30 black dryCopolymer + Glass fibre

15Polyethylen-

PET natural7) dryterephtalat

16Polyethylenterephtalat/

PET-GL lightgrey drylubricant additive

17Polytetrafluoro-

PTFE white dryethylen

18Polytetrafluoro- PTFE + 25%

grey dryethylen / Glass fibre Glass fibre


black dryethylen / Carbon Carbon


brown dryethylen / Brass Brass

21Polyvinyl-

PVDF natural7) drydifluorid

22 Polyethylene 300 PE - HDnatural7)

dryblack

23 Polyethylene 500 PE - HMWnatural7)

dryblack/green

24 Polyethylene 1000 PE - UHMWnatural7)

dryblack/green

25 Polypropylene PP - H natural7)/grey7) dry

26 Polyvinylchloride PVC - Ugrey7)/black/

dryred/white

27 Polycarbonate PC transparent dry

28Polyether-

PEEKnatural7)

dryketone black

29Polyetherketone

PEEK - GL black dry(modified)

30 Polysulfone PSU natural7) dry

31 Polyether amide PEI natural7) dry

1 2 3 4 5 6 7 8 9 10r jzS ezR Et EB3 jbB acU acN HK j1/1000

g/cm3 MPa % MPa MPa MPa kJ/m2 kJ/m2 MPa MPa

1,1580 40 3.100 3.400 140

o. B.1 4 160

1 760 100 1.800 2.000 60 1 15 125

1,1585 40 3.100 3.300 130

o. B.1 5 150

1 760 100 1.800 2.000 50 1 15 115

1,15 71 1 40 2.800 2.700 97 o. B. - 125 -

1,1590 30 2.500 3.000 120

o. B.1 4 170

1 760 80 2.000 2.300 40 1 12 130

1,1480 50 2.500 2.800 135

o. B.1 5 140

1 755 120 1.500 1.800 55 1 15 100

1,1280 55 2.500 2.800 135

o. B.1 12 140

1 1555 120 1.500 1.800 55 o. B. 100

1,0360 55 2.200 2.400 90

o. B. 1 15-

1 1150 120 1.800 - - 100

1,1470 50 2.700 2.500 130

o. B.1 3 160

1 845 180 1.800 1.400 40 o. B. 70

1,1485 30 3.000 2.900 135

o. B.1 3 170

1 865 150 1.900 1.200 60 1 15 100

1,40180 4 9.000 8.300 240

556 220

35120 7 6.400 4.800 40 15 150

1,29 160 5 11.000 - - 50 6 240 40

1,02 50 1 200 1.800 1.500 60 o. B. 1 15 100 1 4

1,41 65 40 3.000 2.900 115 o. B. 1 10 150 13

1,59 125 3 9.300 9.000 150 30 5 210 40

1,38 80 40 3.000 2.600 125 o. B. 1 4 140 13

1,43 75 5 2.200 - - 30 2 - -

2,18 25 380 750 540 6 o. B. 16 30 1,5

2,23 15 280 1.500 1.320 4 o. B. 12 31 -

2,12 15 180 - 1.275 9 - 8 38 -

3,74 14 140 1.400 1.375 8 - 11 39 -

1,78 56 22 2.000 2.000 75 o. B. 1 15 120 3

0,95 22 300 800 800 32 o. B. 12 40 3

0,95 28 300 850 850 40 o. B. 50 45 3

0,94 22 350 800 800 27 o. B. o. B. 40 -

0,91 32 70 1.400 1.400 45 o. B. 7 70 4

1,42 58 15 3.000 - 82 o. B. 4 130 -

1,20 60 80 2.300 2.200 95 o. B. 1 25 100 40

1,32 95 45 3.600 4.100 160 o. B. 7 230 -

1,48 118 3 8.100 10.000 210 25 2,5 270 -

1,24 75 1 50 2.500 2.700 106 o. B. 4 150 22

1,27 105 1 50 3.100 3.300 145 o. B. - 165 -

All listed values were obtained as average values from a multitude of individual measures, and are related to a temperature of 23 °C and 50% RF.

Mechanical values

As of 9/2004


123

Slid

ing

fri

ctio

n c

oef

fici

ent

agai

nis

t st

eel3)

Slid

ing

wea

r ag

ain

st

stee

l (d

ry r

un

nin

g)3)

Mel

tin

g t

emp

erat

ure

DIN

53

736

Ther

mal

co

nd

uct

ivit

yD

IN 5

2 61

2

Spec

ific

th

erm

al c

apac

ity

Co

effi

cien

t o

f lin

ear

exp

ansi

on

4)

Op

erat

ing

tem

per

atu

re r

ang

e,lo

ng

-ter

m5)

Op

erat

ing

tem

per

atu

re r

ang

e,sh

ort

-ter

m5)

Fire

beh

avio

ur

afte

r U

L

Die

lect

ric

con

stan

t6)

DIN

53

483

Die

lect

ric

loss

fac

tor6)

DIN

53

483

Spec

ific

vo

lum

e re

sist

ance

DIN

53

482

Surf

ace

resi

stan

ceD

IN 5

3 48

2

Die

lect

ric

stre

ng

thD

IN 5

3 48

1

Cre

ep c

urr

ent

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stan

ceD

IN 5

3 48

0

Mo

istu

re a

bso

rpti

on

in n

atu

ral

rub

ber

un

til s

atu

rate

d D

IN 5

3 71

5

Wat

er a

bso

rpti

on

un

til

satu

rate

d D

IN 5

3 49

5

11 12 13 14 150 m V Tm l c

- mm/km °C W/(K·m) J/(g·K)

0,360,10 + 220 0,23 1,70,42

0,320,10 + 220 0,23 1,70,37

0,36- + 220 0,23 1,70,42

0,360,10 + 220 0,23 1,70,42

0,180,05 + 220 0,23 1,70,23

0,360,12 + 220 0,23 1,70,42

0,40 - + 190 0,23 1,7

0,380,23 + 218 0,23 1,70,42

0,350,10 + 265 0,23 1,70,42

0,46- + 220 0,25 1,50,52

0,45 - + 255 0,30 1,5

0,320,80 + 178 0,30 2,090,38

0,32 8,90 + 168 0,31 1,45

0,50 - + 168 0,40 1,21

0,25 0,35 + 255 0,24 1,1

0,20 0,10 + 255 0,23 -

0,08 21,0 + 327 0,23 1

0,14 1,30 + 327 0,41 -

0,12 1,0 + 327 0,70 -

0,14 0,50 + 327 0,70 -

0,30 - + 178 0,19 0,96

0,29 7,4 + 128 0,38 1,86

0,29 1,0 + 133 0,38 1,88

0,29 0,45 + 133 0,38 1,84

0,35 11,0 + 162 0,22 1,7

0,60 56,0 - 0,159 1,05

0,55 22,0 + 230 0,21 1,17

0,34 - + 340 0,25 1,06

0,11 - + 340 0,24 -

0,40 - - 0,26 1

- - - 0,22 -

16 17 18 19 20 21 22 23 24 25 26 27 28a - - - eR tand rD Ro Ed - w(H2O) WS -

10-5·K-1 °C °C - - - Ω· cm Ω kV/mm - % %

7 - 8- 40

+ 170 HB 3,7 0,031015 1013 50 KA 3c

2,2 6,5hard, pressure and abrasion resistant

+ 105 1012 1012 20 KA 3b can be produced in largest dimensions

7 - 8- 40

+ 160 HB 3,7 0,031015 1013 50 KA 3c

2,2 6,5as PA 6 G, except

+ 105 1012 1012 20 KA 3b increased cristallinity

8 - 9- 40

+ 150 HB 3,7 0,031015 1013 50 KA 3c

2,5 7,5 higher impact strength than PA 6 G+ 90 1012 1012 20 KA 3b

7 - 8- 40

+180 HB 3,7 0,031015 1013 50 KA 3c

2,2 7as PA 6 G, except heat

+ 105 1012 1012 20 KA 3b ageing resistant

7 - 8- 40

+ 160 HB 3,7 0,031015 1013 50 KA 3c

1,8 5,5 highest abrasion resistance,

+ 105 1012 1012 20 KA 3b low sliding friction

7 - 8- 40

+ 160 HB 3,7 0,031015 1013 50 KA 3c

2,2 7as PA 6G, except set for

+ 105 1012 1012 20 KA 3b high impact strength

10 - 11- 60

+ 150 HB 3,7 0,031015 1013 50 KA 3c

0,9 1,4low water absorption, very good

+110 1012 1012 20 KA 3b long-term rupture strength

8 - 9-30

+ 140 HB3,7 0,031 1015 1013 50 KA 3c

3,0 10,0tough, good

+ 100 7 0,3 1012 1010 20 KA 3b vibration damping

9 - 10- 30

+ 150 HB3,2 0,025 1015 1012 50 KA 3b

2,5 9,0high abrasion resistance

+ 100 5,0 0,2 1012 1010 20 CTI 600 (similar to PA 6 G)

2 - 3- 30

+ 180 HB3,7 0,021 1015 1014 60 KA 3c

2,1 6,3high strength, low

+ 120 7,0 0,2 1013 1012 30 KA 3a thermal expansion

2 - 3- 30

+180 HB 3,7 0,02 1014 1013 60 CTI 475 1,7 5,5high strength, low

+ 120 thermal expansion

11 - 12- 70

+ 140 HB3,1 0,03

2 x 1015 1013 30KA 3b

0,8 1,5tough, hydrolysis resistance

+ 70 3,6 0,06 CTI 600 negligible moisture absorption

9 - 10- 30

+ 140 HB 3,9 0,003 1015 1013 70KA 3c

0,2 0,8high strength, impact resistance

+ 100 KC1 600 low creep behaviour

3 - 4- 30

+ 140 HB 4,8 0,005 1015 1013 65KA 3c

0,17 0,6high strength,

+ 110 KC1 600 low thermal expansion

7 - 8- 20

+ 160 HB 3,6 0,008 1016 1014 60 KC 350 0,25 0,5tough, hard, negligible cold flow,

+ 100 dimensionally stable

7 - 8- 20

+ 160 HB 3,6 0,008 1016 1014 - - 0,2 0,4as PET, plus highest

+ 110 wear resistance

18 - 20- 200

+ 280 V - 0 2,1 0,0005 1018 1017 40KA 3c

!0,01 !0,01high chemical resistance,

+ 260 KB1 600 low strength

12 - 13- 200

+ 280 V - 0 2,85 0,0028 1016 1016 13 - !0,01 !0,01as PTFE, except

+ 260 higher strength

10 - 11- 200

+ 280 V - 0 - - 103 103 2,8 - !0,01 !0,01as PTFE, except

+ 260 lower wear due to sliding friction

9 - 10- 200

+ 280 V - 0 - - 108 108 - - !0,01 !0,01higher strength than PTFE,

+ 260 but chemically less resistant

13- 40

+ 160 V - 0 8,0 0,165 5 x 1014 1013 25 CTI 600 !0,04 !0,04resistant to UV-, b- and

+ 140 g-Radiation, resistant to abrasion

18- 50

+ 80 HB 2,4 0,004 1 1016 1014 47 KA 3c !0,01 !0,01high chemical resistance

+ 50 low density, high abrasion

18- 100

+ 80 HB 2,9 0,0002 1 1016 1014 44KA 3c

!0,01 !0,01as PE-HD, but far more

+ 50 KC1 600 abrasion resistant

18- 260

+ 80 HB 3,0 0,0004 1 1016 1014 44KA 3c

!0,01 !0,01as PE-HMW, but more abrasion

+ 50 KC1 600 resistant at low friction values

160

+ 100 HB 2,25 0,00033 1 1016 1014 52 KA 3c !0,01 !0,01as PE-HD, but higher

+ 80 thermal strength

80

+ 70 V - 0 3,3 0,025 1016 1013 39 KA 3b !0,01 !0,01good chemical resistance

+ 50 hard and brittle

6 - 7- 40

+ 140 V - 2 3,0 0,006 1017 1015 32 KA 1 0,20 0,36transparent, impact resistance,

+ 110 low cold flow

4 - 5-40

+ 310 V - 0 3,2 0,002 1016 1016 24 CTI 150 0,20 0,45high temperature resistance, hydrolisis

+ 250 dimensionally stable

3-40

+ 310 V - 0 - - 105 - 24,5 - 0,14 0,3as PEEK, except higher pv-values

+ 250 better sliding properties

5 - 6- 40

+ 180 V - 0 3,0 0,002 1017 1017 30KA 1

0,40 0,80can be sterilised in steam

+ 160 CTI 150 hydrolisis resistant, radiation resistant

5 - 6-40

+ 200 V - 0 3,0 0,003 1018 1017 33 CTI 175 0,75 1,35high strength and rigidity

+ 170 high thermal resistance

Specific properties

Thermal values Electrical values Miscellaneous data

All calculations, designs and technical specifications are merely for information and advice. Legally binding assurances of properties and/or results cannot be taken from this information. We recom-mend carrying out practical tests to establish the suitability of a product for a given application. Subject to errors and changes!


124

Mec

han

ical

val

ues

PA 6 GPA 12 GOilamid

PA 6 PA 66PA 12

POM - CPET

PET - GLPE - HMW

PE - UHMWPTFEPEEK

Steel St. 37Stainless steel 1.4301Stainless steel 1.4571

Brass

PA 6 G

PA 12 G

Oilamid

PA 6

PA 66

PA 12

POM - C

PET

PET - GL

PE - HMW

PE - UHMW

PTFE

PEEK

Comparison of material costs (volume prices)

E-modulus from tensile test in MPa (short-term value)

Permissible yield stress in MPa (short-term value)

0 500 1000 1500 2000 2500 3000 3500 4000

PA 6 G

PA 12 G

Oilamid

PA 6

PA 66

PA 12

POM - C

PET

PET - GL

PE - HMW

PE - UHMW

PTFE

PEEK0 10 20 30 40 50 60 70 80 90 100

3600

750

850

800

2200

3000

3000

1800

3000

2700

2500

2200

3100

95

25

22

28

75

80

65

50

85

70

80

60

80


125

Mec

han

ical

val

ues

Flexural strength in MPa (short-term value)

PA 6 G

PA 12 G

Oilamid

PA 6

PA 66

PA 12

POM - C

PET

PET - GL

PE - HMW

PE - UHMW

PTFE

PEEK0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170

Long term service temperature in °C (in air without static stress)

PA 6 G

PA 12 G

Oilamid

PA 6

PA 66

PA 12

POM - C

PET

PET - GL

PE - HMW

PE - UHMW

PTFE

PEEK0 25 50 75 100 125 150 175 200 225 250 275

Coefficient of sliding friction against steel(hardened and ground, P = 0,05 MPa, v = 0,6 m/s, t = 60 °C (in the vicinity of the running surface)

PA 6 G

PA 12 G

Oilamid

PA 6

PA 66

PA 12

POM - C

PET

PET - GL

PE - HMW

PE - UHMW

PTFE

PEEK0 0,05 0,10 0,15 0,20 0,25 0,30 0,35 0,40 0,45

160

6

27

40

115

125

115

60

135

130

140

90

140

0,34

0,08

0,29

0,29

0,2

0,25

0,32

0,32

0,35

0,38

0,18

0,4

0,36

250

260

80

80

110

100

100

70

100

100

105

110

105


126

Mec

han

ical

val

ues

Coefficient of linear expansion

PA 6 G

PA 12 G

Oilamid

PA 6

PA 66

PA 12

POM - C

PET

PET - GL

PE - HMW

PE - UHMW

PTFE

PEEK0 1 2 3 4 5 6 7 8 9 10 11 12 13 18 19

(10-5 · K-1)

pv guiding values in MPa · m/s (dry running with integrated lubrication v = 0,1 m/s)

PA 6 G

PA 12 G

Oilamid

PA 6

PA 66

PA 12

POM - C

PET

PET - GL

PE - HMW

PE - UHMW

PTFE

PEEK0 0,05 0,10 0,15 0,20 0,25 0,30 0,35 0,40

Water absorption until saturated in %

PA 6 G

PA 12 G

Oilamid

PA 6

PA 66

PA 12

POM - C

PET

PET - GL

PE - HMW

PE - UHMW

PTFE

PEEK0 1 2 3 4 5 6 7 8 9 10 11

19

18

18

4

8

7

10

10

9

7

10

7

12

0,34

0,05

0,08

0,08

0,25

0,15

0,15

0,08

0,13

0,11

0,23

0,13

0,45

<0,01

<0,01

<0,01

0,4

0,5

0,8

1,5

9

10

7

6,5

1,4

0,10


127

Ch

emic

al r

esis

tan

ce

Information on how to use the list “Chemical resistance”

The information regarding chemical resistance in the following list relates to experiments inwhich the samples were subjected to the respective media free of external stress and loading. Thisis supplemented by our practical experience and, in most cases, many years of using plastics incontact with these media. Due to the variety of media, this list is just an excerpt of the data that isavailable to us. If the list does not contain the medium that you use, we would be happy to provide information on the resistance of our plastics on request.

When using the list, please remember that factors such as:

• deviating degrees of purity of the medium• deviating concentration of the medium• temperatures different to those stated• fluctuating temperatures• mechanical stress• part geometries, especially those that lead to thin walls or extreme differences in wall thickness• stresses that are created by machining• mixtures that are made up of different media• combinations of the above factors

can have an effect on the chemical resistance.

Nevertheless, in spite of being rated as a component with »limited resistance«, a plastic component can still be superior to a metal part and can also be more practical from an economicaspect.

In the case of oxidising materials such as nitric acid and polar organic solvents, despite a chemicalresistance against the medium, in many thermoplastics there is still a danger of stress cracking.Therefore for the manufacture of parts that come into contact with such media, a process shouldbe chosen that creates as little mechanical stress as possible in the workpiece. An alternative is todecrease the stress by annealing the semi-finished products before and during the manufacturingprocess.

Generally it is not possible to forecast the level of resistance against mixtures of different media,even if the plastic is resistant to the individual components of the mixture.Therefore in such a case we recommend that the material is stored and aged with the respectivemixed medium under the expected environmental conditions. It is also important to rememberthat where parts are to be subjected to two or more media there could be an additional tempe-rature load in the area of immediate contact due to the evolving reaction heat.

In spite of the rating »resistant«, in certain cases the surfaces of plastics can become matte or discoloured, and transparent plastics can become opaque when they come into contact with themedia. However, the resistance remains intact even after these surface changes.

The information contained in the lists corresponds to our present standard of knowledge andshould be regarded as standard values. If in doubt, or in the case of specific applications, we recommend that the material be aged under the expected environmental conditions to test itsresistance.


128

Chemical resistance

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29

1 Acetal aldehyde 40 20 + + + + + + + + + + + + + + +

2 Acetamide 50 20 + + + + + + + + + + + + / / +

3 Acetone UV RT + + + + + + + + + + + + o o +

4 Acrylnitrile UV RT + + + + + + + + + + / / / / +

5 Alkyl alkohol UV RT o o o o o o o o o o / / + + +

6 Aluminium chloride 10 RT + + + + + + + + + + o o + + +

7 Formic acid 2 RT o o o o o o o o o o + + + + +

8 Formic acid UV RT L L L L o L L L L o - - o o +

9 Ammonia 10 RT + + + + + + + + + + + + - - +

10 Ammonium hydroxide 30 RT + + + + + + + + + + - - - - +

11 Ammoniumnitrate UV RT + + + + + + + + + + + + + + +

12 Aniline UV RT - - - - o - - - - o o o + + +

13 Anone 100 20 + + + + + + + + + + + / / / +

14 Antimontrichloride 10 RT - - - - - - - - - - / / / / +

15 Benzaldehyde UV RT o o o o o o o o o o + + + + +

16 Petrol, normal HÜ 40 + + + + + + + + + + + + + + +

17 Petrol, super HÜ 40 + + + + + + + + + + + + / / +

18 Benzene UV RT + + + + + + + + + + o o + + +

19 Benzene acid UV RT - - - - + - - - - + o o + + +

20 Benzyl alcohol UV RT o o o o o o o o o o + + + + +

21 Bleaching lye (12,5% AC) HÜ RT - - - - o - - - - o - - + + +

22 Borax WL RT + + + + + + + + + + + + + + +

23 Boric acid 10 RT + + + + + + + + + + + + + + +

24 Hydrobromic acid 10 RT - - - - - - - - - - - o o - +

25 Hydrobromic acid 50 RT - - - - - - - - - - - - - - +

26 Butanol UV RT + + + + + + + + + + + + + + +

27 Butyl acetate UV RT + + + + + + + + + + + + + + +

/ / / - + + + + - - + + - +

/ / / - + + + + / / + + / +

/ / / - + + + + - - + + - -

/ / / + + + + + / / + + - /

/ / / / + + + + - + + + o /

/ / / + + + + + + + + + + +

/ / / + + + + + + / + + / +

/ / / + + + + + + - o o - /

/ / / + + + + + + / o o - -

/ / / - + + + + / - + + + -

/ / / + + + + + + + + + - -

/ / / + + + + o - - + + - /

/ / / + + + + / / / + + - /

/ / / + + + + + + / + + / /

/ / / o + + + + - - + + - -

+ + + + + + + o + o + + o -

+ + + + o o o o - o + + o -

/ / / + o o o o - - + + - -

/ / / + + + + + + - + + / /

/ / / + + + + + / - + + o -

/ / / + + + + + + - + + - +

/ / / + + + + / / + + + / /

/ / / + + + + + + + + + + +

/ / / + + + + + + / + + + /

/ / / + + + + + + / o o / /

/ / / + + + + + + + + + o +

/ / / + + + + / / - + + - o

Co

nce

ntr

atio

n %

Tem

per

atu

re °

C

Poly

amid

e 6

Cas

tPA

6 G

Poly

amid

e 6

Cas

t, h

eat

stab

ilise

dPA

6 G

- W

S

Poly

amid

e 6

Cas

t / M

OS

PA 6

G +

Mo

S 2

Cal

aum

id®

612

PA 6

/ 12

G

Cal

aum

id®

1200

PA 1

2 G

Oila

mid

®PA

6 G

+ Ö

l

Poly

amid

e 6

PA 6

Poly

amid

e 6/

Gla

ss f

ibre

PA 6

+ G

F 30

Poly

amid

e 66

PA 6

6

Poly

amid

e 12

PA 1

2

Poly

acet

al C

op

oly

mer

POM

- C

Poly

acet

al C

op

oly

mer

/Gla

ss f

ibre

POM

- C

- G

F 30

Poly

eth

ylen

eter

eph

tala

tPE

T

Poly

ethy

lene

tere

phta

late

/lubr

ican

t add

.PE

T - G

L

Poly

tetr

aflu

oro

eth

ylen

PTFE

Poly

tetr

aflu

oro

eth

ylen

/Gla

ss f

ibre

PTFE

+ G

F 25

% G

lass

fib

re

Poly

tetr

aflu

oro

eth

ylen

/Car

bo

nPT

FE +

25

% C

arb

on

Poly

tetr

aflu

oro

eth

ylen

/Bra

ssPT

FE +

40

% B

rass

Poly

vin

yl d

iflu

ori

dPV

DF

Poly

eth

ylen

e 30

0PE

- H

D

Poly

eth

ylen

e 50

0PE

- H

MW

Poly

eth

ylen

e 10

00PE

- U

HM

W

Poly

pro

pyl

ene

PP -

H

Poly

vin

ylch

lori

de

PVC

- U

Poly

carb

on

ate

PC

Poly

eth

erke

ton

ePE

EK

Poly

eth

erke

ton

e m

od

ifie

dPE

EK -

GL

Poly

sulf

on

ePS

U

Poly

eth

er a

mid

ePE

I

UV = undiluted

WL = aqueous solution

GL = saturated solution

HÜ = commercial quality

RT = room temperature

+ = resistant

o = limited resistant

- = not resistant

L = soluble

/ = not tested

As of 9/2004


129

Chemical resistance

29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1

+ o + + + + + + + + + / / /

+ o + + / / + + + + + / / /

/ / + + + + + + + + + / / /

- L + + L - o o o o + / / /

/ / + + / / + + + + + / / /

- L + + L - o o o o + / / /

+ o + + + + + + + + + / / /

/ o + + / + o o o o + / / /

/ o + + o + + + + + + / / /

- o + + o + + + + + + / / /

/ L + + - + + + + + o / / /

o + + + - / / o o o o / / /

- L + + - - o o o o + / / /

/ / + + / - o - - - + / / /

+ - + + + + + + + + + / / /

+ - + + + + + + + + + / / /

/ / + + / + + + + + o / / /

+ + + + + + + + + + + / / /

+ + + + + + + + + + + / / /

+ + + + o + + + + + + / / /

- - + + - o + + + + + / / /

- - + + - - o o o o o / / /

+ o + + - - o o o o + / / /

o - L L - + + + + + + / / /

- - + + + + + + + + + / / /

+ o + + - + + + + + + / / /

+ + + + - + + + + + / / / /

Poly

eth

er a

mid

ePE

I

Poly

sulf

on

ePS

U

Poly

eth

erke

ton

e/m

od

ifie

dPE

EK -

GL

Poly

eth

erke

ton

ePE

EK

Poly

carb

on

ate

PC

Poly

vin

ylch

lori

de

PVC

- U

Poly

pro

pyl

ene

PP -

H

Poly

eth

ylen

e 10

00PE

- U

HM

W

Poly

eth

ylen

e 50

0PE

- H

MW

Poly

eth

ylen

e 30

0PE

- H

D

Poly

vin

y ld

iflu

ori

de

PVD

F

Poly

tetr

aflu

oro

eth

ylen

e/B

rass

PTFE

+ 4

0 %

Bra

ss

Poly

tetr

aflu

oro

eth

ylen

e/C

arb

on

PTFE

+ 2

5 %

Car

bo

n

Poly

tetr

aflu

oro

eth

ylen

e/G

lass

fib

rePT

FE +

GF

25 %

Gla

ss f

ibre

Poly

tetr

aflu

oro

eth

ylen

ePT

FE

Poly

ethy

lene

tere

phta

late

/lubr

ican

t add

.PE

T - G

L

Poly

eth

ylen

eter

eph

tala

tPE

T

Poly

acet

al C

op

oly

mer

/Gla

ss f

ibre

POM

- C

- G

F 30

Poly

acet

al-C

op

oly

mer

POM

- C

Poly

amid

e 12

PA 1

2

Poly

amid

e 66

PA 6

6

Poly

amid

e 6/

Gla

ss f

ibre

PA 6

+ G

F 30

Poly

amid

6PA

6

Oila

mid

®PA

6 G

+ Ö

l

Cal

aum

id®

1200

PA 1

2 G

Cal

aum

id®

612

PA 6

/ 12

G

Poly

amid

e 6

Cas

t / M

OS

PA 6

G +

Mo

S 2

Poly

amid

e 6

Cas

t, h

eat

stab

ilise

dPA

6 G

- W

S

Poly

amid

e 6

Cas

tPA

6 G

Tem

per

atu

re °

C

Co

nce

ntr

atio

n %

L = soluble

/ = not tested


+ = resistant


- = not resistant

UV = undiluted




As of 9/2004

+ + + o o + + + + + + + + + + RT 5 Calcium chloride 28

+ + + - - - L L L - - - - - - RT 20 ‘’ ‘’ in alcohol 29

+ o o - - - - - - - - - - - - RT GL Calcium hypochloride 30

+ + + o + + + + + + + + + + + RT UV Chlorbenzene 31

+ - - - - - - - - - - - - - - RT UV Chloroacetic acid 32

+ - - - - o o o o o o o o o o RT UV Chloroform 33

+ + + o o o o o o o o o o o o RT 1 Chromic acid 34

+ + + - - - - - - - - - - - - RT 50 Chromic acid 35

+ + + + + + + + + + + + + + + RT UV Cyclohexane 36

+ + + + + + + + + + + + + + + RT UV Cyclohexanol 37

+ - - + + + + + + + + + + + + RT UV Cyclohexanone 38

+ + + + + + + + + + + + + + + RT UV Dibutyl phtalate 39

+ - - + + + + + + + + + + + + RT UV Dichlorethane 40

+ L L L L + + + + + + + + + + RT UV Dichlorethylene 41

+ / / o o - - - - - - - - - - RT GL Iron(II)chlorid 42

+ / / o o - - - - - - - - - - RT GL Iron(III)chlorid 43

+ + + + + + - - - - + - - - - RT HÜ Vinegar 44

+ + + + + + + + + + + + + + + RT 5 Acetic acid 45

+ + + o o + o o o o + o o o o RT 10 Acetic acid 46

+ + + - - o - - - - o - - - - 50 10 Acetic acid 47

+ - - - - - - - - - - - - - - RT 95 Acetic acid 48

+ - - - - - - - - - - - - - - 50 95 Acetic acid 49

+ + + + + + + + + + + + + + + RT UV Ethylether 50

+ - - - - L L L L L L L L L L RT WL Hydrofluoric acid 51

+ + + + + o o o o o o o o o o RT UV Formaldehyde 52

+ + + + + + + + + + + + + + + RT UV Glycerine 53

+ + + + + + + + + + + + + + + RT HÜ Fuel 54


130

Chemical resistance

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29

55 Heptanol UV RT + + + + + + + + + + + + + + +

56 Hexane UV RT + + + + + + + + + + + + + + +

57 Isopropanol UV RT + + + + + + + + + + + + o o +

58 Potash lye 10 RT + + + + + + + + + + + + - - +

59 Potash lye 10 80 + + + + + + + + + + + + - - +

60 Potash lye 50 RT o o o o + o o o o + + + - - +

61 Ketone (aliphatic) UV RT o o o o o o o o o o + + - - +

62 Methanol 50 RT + + + + + + + + + + + o o + +

63 Methanol UV RT + + + + + + + + + + + o o + +

64 Methylene chlorid UV RT - - - - o - - - - o - - - - +

65 Mineral oil HÜ RT + + + + + + + + + + + + + + +

66 Sodium hypochloride 10 RT - - - - - - - - - - - - o o +

67 Sodium lye 10 RT + + + + + + + + + + + + o o +

68 Sodium lye 10 80 - - - - - - - - - - + + - - +

69 Sodium lye 50 RT o o o o o o o o o o + + - - +

70 Sodium lye 50 80 - - - - - - - - - - + + - - +

71 Nitrobenzene UV RT - - - - - - - - - - o o o o +

72 Nitrotoluene UV RT o o o o o o o o o o o o + + +

73 Oxalic acid 10 RT o o o o o o o o o o - - + + +

74 Phenol 90 RT L L L L L L L L L L - - - - +

75 Phenol UV 40 L L L L L L L L L L - - - - +



78 Phosphoric acid 10 RT - - - - - - - - - - + + + + +

79 Phosphoric acid 25 RT - - - - - - - - - - o o + + +

80 Phosphoric acid 85 RT L L L L L L L L L L - - + + +

81 Propanol UV RT + + + + + + + + + + + + + + +

/ / / + + + + o + + + + o +

/ / / + + + + + + - + + o +

/ / / + + + + + + - + + o /

/ / / + + + + + + - + + o +

/ / / o - - - + - - + + o -

/ / / + + + + + + - + + o -

/ / / / + + + / / / + + / /

/ / / + + + + + + - + + o +

/ / / + + + + + + - + + o +

/ / / + o o o o L - + + L L

+ + + + + + + + + + + + + +

/ / / + + + + o + + + + + /

/ / / o + + + + + o + + + o

/ / / o o o o + o - + + + -

/ / / o + + + + + - + + + -

/ / / o o o o + o - + + + -

/ / / + + + + + - L + + - -

/ / / / + + + + - - + + / /

/ / / + + + + + + + + + + +

/ / / + + + + + o L + + - -

/ / / + + + + + - L + + - -

/ / / o - - - - - L + + - -

/ / / o - - - - - L + + - -

/ / / + + + + + + + + + + +

/ / / + + + + + + + + + + +

/ / / + + + + + + + + + o -

/ / / + + + + + + + + + + +

Co

nze

ntr

atio

n %

Tem

per

atu

re °

C

Poly

amid

e 6

Cas

tPA

6 G

Poly

amid

e 6

Cas

t, h

eat

stab

ilise

dPA

6 G

- W

S

Poly

amid

e 6

Cas

t / M

OS

PA 6

G +

Mo

S 2

Cal

aum

id®

612

PA 6

/ 12

G

Cal

aum

id®

1200

PA 1

2 G

Oila

mid

®PA

6 G

+ Ö

l

Poly

amid

e 6

PA 6

Poly

amid

e 6/

Gla

ss f

ibre

PA 6

- G

F 30

Poly

amid

e 66

PA 6

6

Poly

amid

e 12

PA 1

2

Poly

acet

al C

op

oly

mer

POM

- C

Poly

acet

al C

op

oly

mer

/Gla

ss f

ibre

POM

- C

- G

F 30

Poly

eth

ylen

tere

ph

tala

tePE

T

Poly

ethy

lene

tere

phta

late

/lubr

ican

t add

.PE

T - G

L

Poly

tetr

aflu

oro

eth

ylen

ePT

FE

Poly

tetr

aflu

oro

eth

ylen

e/G

lass

fib

rePT

FE +

GF

25 %

Gla

ss f

ibre

Poly

tetr

aflu

oro

eth

ylen

e/C

arb

on

PTFE

+ 2

5 %

Car

bo

n

Poly

tetr

aflu

oro

eth

ylen

e/B

rass

PTFE

+ 4

0 %

Bra

ss

Poly

vin

yl id

iflu

ori

de

PVD

F

Poly

eth

ylen

e 30

0PE

- H

D

Poly

eth

ylen

e 50

0PE

- H

MW

Poly

eth

ylen

e 10

00PE

- U

HM

W

Poly

pro

pyl

ene

PP -

H

Poly

vin

ylch

lori

de

PVC

- U

Poly

carb

on

ate

PC

Poly

eeth

erke

ton

ePE

EK

Poly

eth

erke

ton

e/m

od

ifie

dPE

EK -

GL

Poly

sulf

on

ePS

U

Poly

eth

er a

mid

ePE

I

UV = undiluted





+ = resistant


- = not resistant

L = soluble

/ = not tested

As of 9/2004


131

Chemical resistance

29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1

+ + + - - - - - - - - - - - - RT 10 Nitric acid 82

+ - - - - - - - - - - - - - - RT 80 Nitric acid 83

+ - - - - L L L L L L L L L L RT 50 Nitric acid 84

+ - - - - L L L L L L L L L L RT 80 Nitric acid 85

+ o o - - - - - - - - - - - - RT 10 Hydrochloric acid 86

+ o o - - - - - - - - - - - - RT 20 Hydrochloric acid 87

+ - - - - L L L L L L L L L L RT 30 Hydrochloric acid 88

+ o o - - - - - - - - - - - - RT 40 Sulphuric acid 89

+ o o - - - - - - - - - - - - 60 40 Sulphuric acid 90

+ - - - - L L L L L L L L L L RT 96 Sulphuric acid 91

+ - - - - L L L L L L L L L L 60 96 Sulphuric acid 92

+ + + o o + + + + + + + + + + RT UV Carbon tetrachloride 93

+ + + + + + + + + + + + + + + RT UV Tolual 94

+ o o o o o o o o o o o o o o RT UV Trichlorethylene 95

+ + + + + + + + + + + + + + + RT 10 Hydrogen peroxide 96

+ + + + + o - - - - o - - - - RT 20 Hydrogen peroxide 97

+ + + o o - - - - - - - - - - RT 30 Hydrogen peroxide 98

+ + + - - - - - - - - - - - - 60 30 Hydrogen peroxide 99

+ + + + + + + + + + + + + + + RT UV Xylene 100

+ + + + + + o o o o + o o o o RT 10 Citric acid 101

+ + + - - o o o o o o o o o o 50 10 Citric acid 102

+ + + + - + + + + + + / / /

/ / + + - - - - - - + / / /

/ + o o - - - - - - + / / /

/ + o o - - - - - - o / / /

+ + + + + + + + + + + / / /

+ + + + + + + + + + + / / /

+ o + + o + + + + + + / / /

+ + o o + + + + + + + / / /

o o - - o o + + + + + / / /

- L L L - + o o o o + / / /

- L L L - o - - - - + / / /

+ + + + - - - - - - + / / /

- - + + - - o o o o + / / /

- L + + - - o o o o + / / /

+ + + + + + + + + + + / / /

+ + + + + + + + + + + / / /

+ + + + + + + + + + + / / /

/ / + + / o o o o o / / / /

o o + + - - o o o o + / / /

+ o + + + + + + + + + / / /

+ o + + / + + + + + + / / /

Poly

eth

er a

mid

ePE

I

Poly

sulf

on

ePS

U

Poly

eeth

erke

ton

e m

od

ifie

dPE

EK -

GL

Poly

reth

erke

ton

ePE

EK

Poly

carb

on

ate

PC

Poly

vin

ylch

lori

de

PVC

- U

Poly

pro

pyl

ene

PP -

H

Poly

eth

ylen

e 10

00PE

- U

HM

W

Poly

eth

ylen

e 50

0PE

- H

MW

Poly

eth

ylen

e 30

0PE

- H

D

Poly

vin

yl id

iflu

ori

dPV

DF

Poly

tetr

aflu

oro

eth

ylen

e/B

rass

PTFE

+ 4

0 %

Bra

ss

Poly

tetr

aflu

oro

eth

ylen

e/C

arb

on

PTFE

+ 2

5 %

Car

bo

n

Poly

tetr

aflu

oro

eth

ylen

e/G

lass

fib

rePT

FE +

GF

25 %

Gla

ss f

ibre

Poly

tetr

aflu

oro

eth

ylen

ePT

FE

Poly

ethy

lene

tere

phta

late

/lubr

ican

t add

.PE

T - G

L

Poly

eth

ylen

eter

eph

tala

tePE

T

Poly

acet

al-C

op

oly

mer

/Gla

ss f

ibre

POM

- C

- G

F 30

Poly

acet

al-C

op

oly

mer

ePO

M -

C

Poly

amid

e 12

PA 1

2

Poly

amid

e 66

PA 6

6

Poly

amid

e 6

/ Gla

ss f

ibre

PA 6

+ G

F 30

Poly

amid

e 6

PA 6

Oila

mid

®PA

6 G

+ Ö

l

Cal

aum

id®

1200

PA 1

2 G

Cal

aum

id®

612

PA 6

/ 12

G

Poly

amid

e 6

Cas

t / M

OS

PA 6

G +

Mo

S 2

Poly

amid

e 6

Cas

t, h

eat

stab

ilise

dPA

6 G

- W

S

Poly

amid

e 6

Cas

tPA

6 G

Tem

per

atu

re °

C

Co

nce

ntr

atio

n %

L = soluble

/ = not tested


+ = resistant


- = not resistant

UV = undiluted




As of 9/2004


Our machining capabilities:• CNC milling machines, workpiece capacity up to max. 2000 x 1000mm• 5-axis CNC milling machines• CNC lathes, chucking capacity up to max. 1560 mm diameter and 2000 mm long• Screw machine lathes up to 100mm diameter spindle swing• CNC automatic lathes up to 100mm diameter spindle swing• Gear cutting machines for gears starting at Module 0,5• Profile milling (shaping and molding)• Circular saws up to 170mm cutting thickness and 3100mm cutting length• Four-sided planers up to 125mm thickness and 225mm width• Thickness planers up to 230mm thickness and 1000mm width


We process:• Polyamide PA• Polyacetal POM• Polyethylene terephthalate PET• Polyethylene 1000 PE-UHMW• Polyethylene 500 PE-HMW• Polyethylene 300 PE-HD• Polypropylene PP-H• Polyvinyl chloride (hard) PVC-U• Polyvinylidene fluoride PVDF• Polytetrafluoroethylene PTFE• Polyetheretherketone PEEK• Polysulphone PSU• Polyether imide PEI

Examples of parts:• Rope sheaves and castors• Guide rollers• Deflection sheaves• Friction bearings• Slider pads• Guide rails• Gear wheels• Sprocket wheels• Spindle nuts• Curved feed tables• Feed tables• Feed screws

• Curved guides• Metering disks• Curved disks• Threaded joints• Seals• Inspection glasses• Valve seats• Equipment casings• Bobbins• Vacuum rails/panels• Stripper rails• Punch supports


134

Info

rmat

ion

on

ho

w t

o u

se t

his

do

cum

enta

tio

n/B

iblio

gra

ph

y

Information on how to use this documentation

All calculations, designs and technical details are only intended as information and advice and donot replace tests by the users in regard to the suitability of the materials for specific applications.No legally binding assurance of properties and/or results from the calculations can be deducedfrom this document. The material parameters stated here are not binding minimum values, ratherthey should be regarded as guiding values. If not otherwise stated, they were determined withstandardised samples at room temperature and 50% relative humidity. The user is responsible forthe decision as to which material is used for which application and for the parts manufacturedfrom the material. Hence, we recommend that practical tests are carried out to determine the suitability before producing any parts in series.

We expressly reserve the right to make changes to this document. Errors excepted.You can download the latest version containing all changes and supplements as a pdf file atwww.licharz.de.

© Copyright by Licharz GmbH, Germany

Bibliography

The following literature was used to compile “Designing with plastics”:

Ebeling, F.W. / Lüpke, G. Kunststoffverarbeitung; Vogel VerlagSchelter, W. / Schwarz, O.

Biederbick, K. Kunststoffe; Vogel Verlag

Carlowitz, B. Kunststofftabellen; Hanser Verlag

Böge, A. Das Techniker Handbuch; Vieweg Verlag

Ehrenstein, Gottfried W. Mit Kunststoffen Konstruieren; Hanser Verlag

Strickle, E. / Erhard G. Maschinenelemente aus thermoplastischen KunststoffenGrundlagen und Verbindungselemente; VDI Verlag

Strickle, E. / Erhard G. Maschinenelemente aus thermoplastischen KunststoffenLager und Antriebselemente; VDI Verlag

Erhard, G. Konstruieren mit Kunststoffen; Hanser Verlag

Severin, D. Die Besonderheiten von Rädern aus PolymerMaterialen;Specialist report, Berlin Technical University

Severin, D. / Liu, X. Zum Rad-Schiene-System in der Fördertechnik,Specialist report, Berlin Technical University

Severin, D. Teaching material Nr. 701, Pressungen

Liu, X. Personal information

Becker, R. Personal information

VDI 2545 Zahnräder aus thermoplastischen Kunststoffen; VDI Verlag

DIN 15061 Part 1 Groove profiles for wire rope sheaves; Beuth Verlag

DIN ISO 286 ISO coding system for tolerances and fits; Beuth Verlag

DIN ISO 2768 Part 1 General tolerances; Beuth Verlag

DIN ISO 2768 Part 2 General tolerances for features; Beuth Verlag


Licharz GmbHIndustriepark NordD-53567 BuchholzGermanyTelefon: ++49 (0) 26 83-977 0Telefax: ++49 (0) 26 83-977 111Internet: www.licharz.deE-Mail: [email protected]

TU 0

1. 0

1. 0

9. 0

4. E

For further information, detailed catalogs are available:

• Information on Licharz machining capabilities of component parts• Brochure „Material Guiding Values / chemical Resistance“• Product information on semi-finished products of PA, POM und PET• Delivery programme

Visit us on the internet at www.licharz.de

ZL Engineering PlasticsPO Box 227012 John Walsh BoulevardPeekskill, NY 10566USAPhone: ++1 914 – 736 6066Fax: ++1 914 – 736 2154E-Mail: [email protected]

ZL Engineering Plastics8485 Unit DArtesia BoulevardBuena Park, CA 90621USAPhone: ++1 714 – 523 0555Fax: ++1 714 – 523 4555E-Mail: [email protected]

Headquarters:

Branch offices:

Licharz Ltd.Daimler CloseRoyal Oak Industrial EstateDaventry, NN11 8QJGreat BritainPhone: ++44 (0) 1327 877 500Fax: ++44 (0) 1327 877 333Internet: www.licharz.co.ukE-Mail: [email protected]

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Documents

Designing with engineering Plastics - Tecno Plastic … · Engineering plastics are becoming increasingly popular in machine and plant construction as design engineers recognise their