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Extrusion

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For the process that creates volcanic rock, seeExtrusive (geology).

Extruded aluminium with several hollow cavities; slots allow bars to be joined with specialconnectors.

Extrusion is a process used to create objects of a fixedcross-sectionalprofile. A material ispushed or drawn through adieof the desired cross-section. The two main advantages of thisprocess over other manufacturing processes are its ability to create very complex cross-sections and work materials that are brittle, because the material only encounterscompressiveandshearstresses. It also forms finished parts with an excellent surface finish.[1]

Extrusion may be continuous (theoretically producing indefinitely long material) or semi-continuous (producing many pieces). The extrusion process can be done with the material hotor cold.

Commonly extruded materials includemetals,polymers,ceramics,concreteand foodstuffs.

Hollow cavities within extruded material cannot be produced using a simple flat extrusiondie, because there would be no way to support the center barrier of the die. Instead, the dieassumes the shape of a block with depth, beginning first with a shape profile that supports thecenter section. The die shape then internally changes along its length into the final shape,with the suspended center pieces supported from the back of the die.

Contents

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1 History 2 Process

o 2.1 Hot extrusiono 2.2 Cold extrusiono 2.3 Warm extrusiono 2.4 Equipment

2.4.1 Forming internal cavities 2.4.2 Direct extrusion 2.4.3 Indirect extrusion 2.4.4 Hydrostatic extrusion 2.4.5 Drives

o 2.5 Extrusion defects
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3 Materialso 3.1 Metalo 3.2 Plastico 3.3 Ceramico 3.4 Food

o 3.5 Drug carrierso 3.6 Biomass briquettes

4 Design 5 See also 6 References

o 6.1 Noteso 6.2 Bibliography

7 External links

[edit] HistoryIn 1797,Joseph Bramahpatented the first extrusion process for making lead pipe. It involvedpreheating the metal and then forcing it through a die via a hand driven plunger. The processwasn't developed until 1820 when Thomas Burr constructed the first hydraulic poweredpress. At this time the process was called squirting. In 1894, Alexander Dick expanded theextrusion process to copper and brass alloys.[2]

[edit] Process

Extrusion of a round blank through a die.

The process begins by heating the stock material (for hot or warm extrusion). It is then loadedinto the container in the press. A dummy block is placed behind it where the ram then presses
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on the material to push it out of the die. Afterward the extrusion is stretched in order tostraighten it. If better properties are required then it may beheat treatedorcold worked.[2]

The extrusion ratio is defined as the starting cross-sectional area divided by the cross-sectional area of the final extrusion. One of the main advantages of the extrusion process is

that this ratio can be very large while still producing quality parts.

[edit] Hot extrusion

Hot extrusion is ahot workingprocess, which means it is done above the material'srecrystallizationtemperature to keep the material fromwork hardeningand to make it easierto push the material through the die. Most hot extrusions are done on horizontal hydraulicpresses that range from 230 to 11,000 metric tons (250 to 12,000 short tons). Pressures rangefrom 30 to 700 MPa (4,400 to 100,000 psi), therefore lubrication is required, which can be oilor graphite for lower temperature extrusions, or glass powder for higher temperatureextrusions. The biggest disadvantage of this process is its cost for machinery and itsupkeep.[1]

Hot extrusion temperature for various metals[1]

Material Temperature [C (F)]

Magnesium 350-450 (650-850)

Aluminium 350-500 (650-900)

Copper 600-1100 (1200-2000)

Steel 1200-1300 (22002400)

Titanium 700-1200 (1300-2100)

Nickel 1000-1200 (19002200)

Refractory alloys up to 2000 (4000)

The extrusion process is generally economical when producing between several kilograms(pounds) and many tons, depending on the material being extruded. There is a crossover pointwhereroll formingbecomes more economical. For instance, some steels become moreeconomical to roll if producing more than 20,000 kg (50,000 lb).[2]

Aluminium hot extrusion die

Front side of a four family die. For reference, the die is 228 mm (9.0 in) in diameter.
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Close up of the shape cut into the die. Notice that the walls are drafted and that theback wall thickness varies.

Back side of die. The wall thickness of the extrusion is 3 mm (0.12 in).

[edit] Cold extrusion

Cold extrusion is done at room temperature or near room temperature. The advantages of this

over hot extrusion are the lack of oxidation, higher strength due tocold working, closertolerances, good surface finish, and fast extrusion speeds if the material is subject tohotshortness.[1]

Materials that are commonly cold extruded include: lead, tin, aluminum, copper, zirconium,titanium, molybdenum, beryllium, vanadium, niobium, and steel.

Examples of products produced by this process are: collapsible tubes, fire extinguishercases,shock absorbercylinders, automotive pistons, and gear blanks.

[edit] Warm extrusion

Warm extrusion is done above room temperature, but below the recrystallization temperatureof the material the temperatures ranges from 800 to 1800 F (424 to 975 C). It is usuallyused to achieve the proper balance of required forces, ductility and final extrusionproperties.[3]

[edit] Equipment

A horizontal hydraulic press for hot aluminum extrusion (loose dies and scrap visible inforeground)

There are many different variations of extrusion equipment. They vary by four majorcharacteristics:[1]
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1. Movement of the extrusion with relation to the ram. If the die is held stationary andthe ram moves towards it then its called "direct extrusion". If the ram is heldstationary and the die moves towards the ram its called "indirect extrusion".

2. The position of the press, either vertical or horizontal.3. The type of drive, either hydraulic or mechanical.

4. The type of load applied, either conventional (variable) orhydrostatic.

A single or twin screw auger, powered by an electric motor, or a ram, driven by hydraulicpressure (often used for steel and titanium alloys), oil pressure (for aluminum), or in otherspecialized processes such as rollers inside a perforated drum for the production of manysimultaneous streams of material.

Typical extrusion presses cost more than $100,000, whereas dies can cost up to $2000.

[edit] Forming internal cavities

Two-piece aluminum extrusion die set (parts shown separated.) The male part (at right) is forforming the internal cavity in the resulting round tube extrusion.

There are several methods for forming internal cavities in extrusions. One way is to use ahollow billet and then use a fixed or floatingmandrel. A fixed mandrel, also known as aGerman type, means it is integrated into the dummy block and stem. A floating mandrel, alsoknown as a French type, floats in slots in the dummy block and aligns itself in the die whenextruding. If a solid billet is used as the feed material then it must first be pierced by themandrel before extruding through the die. A special press is used in order to control themandrel independently from the ram.[1]The solid billet could also be used with a spider die,porthole die or bridge die. All of these types of dies incorporate the mandrel in the die andhave "legs" that hold the mandrel in place. During extrusion the metal divides and flowsaround the legs, leaving weld lines in the final product.[4]

[edit] Direct extrusion
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Plot of forces required by various extrusion processes.

Direct extrusion, also known as forward extrusion, is the most common extrusion process. Itworks by placing the billet in a heavy walled container. The billet is pushed through the dieby a ram or screw. There is a reusable dummy block between the ram and the billet to keepthem separated. The major disadvantage of this process is that the force required to extrudethe billet is greater than that need in the indirect extrusion process because of thefrictionalforces introduced by the need for the billet to travel the entire length of the container.Because of this the greatest force required is at the beginning of process and slowly decreasesas the billet is used up. At the end of the billet the force greatly increases because the billet isthin and the material must flow radially to exit the die. The end of the billet (called the buttend) is not used for this reason.[5]

[edit] Indirect extrusion

In indirect extrusion, also known as backwards extrusion, the billet and container movetogether while the die is stationary. The die is held in place by a "stem" which has to belonger than the container length. The maximum length of the extrusion is ultimately dictatedby the column strength of the stem. Because the billet moves with the container the frictionalforces are eliminated. This leads to the following advantages:[6]

A 25 to 30% reduction of friction, which allows for extruding larger billets, increasingspeed, and an increased ability to extrude smaller cross-sections

There is less of a tendency for extrusions to crack because there is no heat formedfrom friction

The container liner will last longer due to less wear The billet is used more uniformly so extrusion defects and coarse grained peripherals

zones are less likely.

The disadvantages are:[6]

Impurities and defects on the surface of the billet affect the surface of the extrusion.These defects ruin the piece if it needs to beanodizedor the aesthetics are important.

In order to get around this the billets may be wire brushed, machined or chemicallycleaned before being used.
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This process isn't as versatile as direct extrusions because the cross-sectional area islimited by the maximum size of the stem.

[edit] Hydrostatic extrusion

In the hydrostatic extrusion process the billet is completely surrounded by a pressurizedliquid, except where the billet contacts the die. This process can be done hot, warm, or cold,however the temperature is limited by the stability of the fluid used. The process must becarried out in a sealed cylinder to contain the hydrostatic medium. The fluid can bepressurized two ways:[6]

1. Constant-rate extrusion: A ram or plunger is used to pressurize the fluid inside thecontainer.

2. Constant-pressure extrusion: A pump is used, possibly with apressure intensifier, topressurize the fluid, which is then pumped to the container.

The advantages of this process include:[6]

No friction between the container and the billet reduces force requirements. Thisultimately allows for faster speeds, higher reduction ratios, and lower billettemperatures.

Usually the ductility of the material increases when high pressures are applied. An even flow of material. Large billets and large cross-sections can be extruded. No billet residue is left on the container walls.

The disadvantages are:[6]

The billets must be prepared by tapering one end to match the die entry angle. This isneeded to form a seal at the beginning of the cycle. Usually the entire billet needs tobe machined to remove any surface defects.

Containing the fluid under high pressures can be difficult.

[edit] Drives

Most modern direct or indirect extrusion presses are hydraulically driven, but there are somesmall mechanical presses still used. Of the hydraulic presses there are two types: direct-drive

oil presses and accumulator water drives.

Direct-drive oil presses are the most common because they are reliable and robust. They candeliver over 35 MPa (5000 psi). They supply a constant pressure throughout the whole billet.The disadvantage is that they are slow, between 50 and 200 mm/s (28 ips).[7]

Accumulator water drives are more expensive and larger than direct-drive oil presses, andthey lose about 10% of their pressure over the stroke, but they are much faster, up to380 mm/s (15 ips). Because of this they are used when extruding steel. They are also used onmaterials that must be heated to very hot temperatures for safety reasons.[7]

Hydrostatic extrusion presses usually usecastor oilat pressure up to 1400 MPa (200 ksi).Castor oil is used because it has good lubricity and high pressure properties.[8]
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[edit] Extrusion defects

Surface cracking - When the surface of an extrusion splits. This is often caused by theextrusion temperature, friction, or speed being too high. It can also happen at lowertemperatures if the extruded product temporarily sticks to the die.

Pipe - A flow pattern that draws the surface oxides and impurities to the center of theproduct. Such a pattern is often caused by high friction or cooling of the outer regionsof the billet.

Internal cracking - When the center of the extrusion develops cracks or voids. Thesecracks are attributed to a state of hydrostatic tensile stress at the centerline in thedeformation zone in the die. (A similar situation to the necked region in a tensilestress specimen)

Surface lines - When there are lines visible on the surface of the extruded profile. Thisdepends heavily on the quality of the die production and how well the die ismaintained, as some residues of the material extruded can stick to the die surface andproduce the embossed lines.

[edit] Materials

[edit] Metal

Metals that are commonly extruded include:[9]

Aluminiumis the most commonly extruded material. Aluminium can be hot or coldextruded. If it is hot extruded it is heated to 575 to 1100 F (300 to 600 C). Examplesof products includeprofilesfor tracks, frames, rails,mullions, andheat sinks.

Copper(1100 to 1825 F (600 to 1000 C)) pipe, wire, rods, bars, tubes, and weldingelectrodes. Often more than 100 ksi (690 MPa) is required to extrude copper.

Leadandtin(maximum 575 F (300 C)) pipes, wire, tubes, and cable sheathing.Molten lead may also be used in place of billets on vertical extrusion presses.

Magnesium(575 to 1100 F (300 to 600 C)) aircraft parts and nuclear industry parts.Magnesium is about as extrudable as aluminum.

Zinc(400 to 650 F (200 to 350 C)) rods, bar, tubes, hardware components, fitting,and handrails.

Steel(1825 to 2375 F (1000 to 1300 C)) rods and tracks. Usuallyplain carbon steelis extruded, but alloy steel andstainless steelcan also be extruded.

Titanium(1100 to 1825 F (600 to 1000 C)) aircraft components including seattracks, engine rings, and other structural parts.

Magnesium and aluminium alloys usually have a 0.75 m (30 in)RMSor better surfacefinish. Titanium and steel can achieve a 3 micrometres (120 in) RMS.[1]

In 1950, Ugine Sjournet, ofFrance, invented a process which uses glass as a lubricant forextruding steel.[10]The Ugine-Sejournet, or Sejournet, process is now used for other materialsthat have melting temperatures higher than steel or that require a narrow range oftemperatures to extrude. The process starts by heating the materials to the extrudingtemperature and then rolling it in glass powder. The glass melts and forms a thin film, 20 to

30mils(0.5 to 0.75 mm), in order to separate it from chamber walls and allow it to act as alubricant. A thick solid glass ring that is 0.25 to 0.75 in (6 to 18 mm) thick is placed in the
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chamber on the die to lubricate the extrusion as it is forced through the die. A secondadvantage of this glass ring is its ability to insulate the heat of the billet from the die. Theextrusion will have a 1 mil thick layer of glass, which can be easily removed once it cools.[3]

Another breakthrough in lubrication is the use of phosphate coatings. With this process, in

conjunction with glass lubrication, steel can be cold extruded. The phosphate coat absorbs theliquid glass to offer even better lubricating properties.[3]

[edit] Plastic

Sectional view of a plastic extruder showing the componentsMain article:Plastics extrusion

Plastics extrusioncommonly uses plastic chips or pellets, which are usually dried in a hopperbefore going to the feed screw. The polymer resin is heated to molten state by a combinationof heating elements and shear heating from the extrusion screw. The screw forces the resinthrough a die, forming the resin into the desired shape. The extrudate is cooled and solidifiedas it is pulled through the die or water tank. In some cases (such as fibre-reinforced tubes) theextrudate is pulled through a very long die, in a process called pultrusion.

A multitude of polymers are used in the production of plastic tubing, pipes, rods, rails, seals,and sheets or films.

[edit] Ceramic

Ceramic can also be formed into shapes via extrusion.Terracottaextrusion is used to producepipes. Many modern bricks are also manufactured using a brick extrusion process.[11]

[edit] Food

Macaroniis an extruded hollow pasta.

This section requiresexpansion.
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Extrusion has application in food processing. Products such as certainpastas, manybreakfastcereals,Fig Newtons, premadecookie dough,Murukku,Sevai,Idiappam,jalebi, somefrenchfries, certainbaby foods, drypet foodand ready-to-eat snacks are mostly manufactured byextrusion. In the extrusion process, raw materials are first ground to the correct particle size(usually the consistency of coarse flour). The dry mix is passed through a pre-conditioner,

where other ingredients are added (liquidsugar,fats,dyes,meatsand water depending on theproduct being made), steamis injected to start the cooking process. The preconditioned mixis then passed through an extruder, and then forced through a die where it is cut to the desiredlength. The cooking process takes place within the extruder where the product produces itsown friction and heat due to the pressure generated (1020 bar). The process can induce bothprotein denaturationandstarch gelatinization, depending on inputs and parameters. Extrudersusing this process have a capacity from 125 tonnes per hour depending on design.

As with other forms of cooking, extrusion achieves the following nutritionally:

Inactivation of raw foodenzymes Destruction of certain naturally occurringtoxins Diminishing ofmicroorganismsin the final product Slight increase of iron-bioavailability Creation of insulin-desensitizing starches, which are a risk-factor for developing

diabetes[12][13] Loss of the essentialamino:lysine, which is essential to developmental growth and

nitrogen management[14][15] Simplification of complex starches, increasing rates of tooth decay[16][17] Marked increase of processed foods'glycemic indexes[18][19] Destruction ofVitamin A(beta-carotene)[20][21]

Extrusion is also used tomodify starchand to pelletanimal feed.

[edit] Drug carriers

This section requiresexpansion.

Extrusion through nano-porous, polymeric filters is being used to manufacture suspensions oflipid vesiclesliposomesorTransfersomesfor use in pharmaceutical products. The anti-cancerdrugDoxorubicinin liposome delivery system is formulated by extrusion, for example.

[edit] Biomass briquettes

Main article:Biomass briquettes

The extrusion production technology of fuel briquettes is the process of extrusion screwwastes (straw, sunflower husks, buckwheat, etc.) or finely shredded wood waste (sawdust)under high pressure when heated from 160 to 350 C. The resulting fuelbriquettesdo notinclude any of the binders, but one natural - the lignin contained in the cells of plant wastes.The temperature during compression, causes melting of the surface of bricks, making it moresolid, which is important for the transportation of briquettes.

[edit] Design
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The design of an extrusion profile has a large impact on how readily it can be extruded. Themaximum size for an extrusion is determined by finding the smallest circle that will fitaround the cross-section, this is called the circumscribing circle. This diameter, in turn,controls the size of the die required, which ultimately determines if the part will fit in a givenpress. For example, a larger press can handle 60 cm (24 in) diameter circumscribing circles

for aluminium and 55 cm (22 in). diameter circles for steel and titanium.[1]

The complexity of an extruded profile can be roughly quantified by calculating the shapefactor, which is the amount of surface area generated per unit mass of extrusion. This affectsthe cost of tooling as well as the rate of production.[22]

Thicker sections generally need an increased section size. In order for the material to flowproperly legs should not be more than ten times longer than their thickness. If the cross-section is asymmetrical, adjacent sections should be as close to the same size as possible.Sharp corners should be avoided; for aluminium and magnesium the minimum radius shouldbe 0.4 mm (1/64 in) and for steel corners should be 0.75 mm (0.030 in) and filletsshould be

3 mm (0.12 in). The following table lists the minimum cross-section and thickness for variousmaterials.[1]

Material Minimum cross-section [cm (sq. in.)] Minimum thickness [mm (in.)]

Carbon steels 2.5 (0.40) 3.00 (0.120)

Stainless steel 3.0-4.5 (0.45-0.70) 3.00-4.75 (0.120-0.187)

Titanium 3.0 (0.50) 3.80 (0.150)

Aluminium


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What is Aluminum Extrusion?

Share

Aluminum extrusion is a technique used to transform aluminum alloy into objects with a definitive cross-sectional

profile for a wide range of uses. The extrusion process makes the most of aluminums unique combination of

physical characteristics. Its malleability allows it to be easily machined and cast, and yet aluminum is one third

the density and stiffness of steel so the resulting products offer strength and stability, particularly when alloyed

with other metals.

The Process of Aluminum Extrusion

The process of aluminum extrusion consists of the following steps:

After designing and creating the shape of the die, a cylindrical billet of aluminum alloy is heated to800F-925F. The aluminum billet is then transferred to a loader, where a lubricant is added to prevent it from sticking

to the extrusion machine, the ram or the handle.

Substantial pressure is applied to a dummy block using a ram, which pushes the aluminum billet into thecontainer, forcing it through the die.

To avoid the formation of oxides, nitrogen in liquid or gaseous form is introduced and allowed to flowthrough the sections of the die. This creates an inert atmosphere and increases the life of the die.

The extruded part passes onto a run-out table as an elongated piece that is now the same shape as thedie opening. It is then pulled to the cooling table where fans cool the newly created aluminum extrusion.

When the cooling is completed, the extruded aluminum is moved to a stretcher, for straightening andwork hardening.

The hardened extrusions are brought to the saw table and cut according to the required lengths.

The final step is to treat the extrusions with heat in age ovens, which hardens the aluminum by speedingthe aging process.

Additional complexities may be applied during this process to further customize the extruded parts. For example,

to create hollow sections, pins or piercing mandrels are placed inside the die. After the extrusion process, a

variety of options are available to adjust the colour, texture and brightness of the aluminums finish. This may

include aluminum anodizing or painting.

Today, aluminum extrusion is used for a wide range of purposes, including components of the International

Space Station. These diverse applications are possible due to the advantageous attributes of aluminum, from its

particular blend of strength and ductility to its conductivity, its non-magnetic properties and its ability to be

recycled repeatedly without loss of integrity. All of these capabilities make aluminum extrusion a viable and

adaptable solution for an growing number of manufacturing needs.

Check this link for more information:http://en.wikipedia.org/wiki/Extrusion

ALUMINUM EXTRUSIONO OVERVIEWFACILITYDIE CATALOGUEPROCESS FACTS & FIGURES FULL COLOUR ANODIZING

POLISHING & CUSTOM MECHANICAL FINISHING

WET PAINT & POWDER COATING

FABRICATION & ASSEMBLY

ARTICLES
http://void%280%29/http://void%280%29/http://en.wikipedia.org/wiki/Extrusionhttp://en.wikipedia.org/wiki/Extrusionhttp://en.wikipedia.org/wiki/Extrusionhttp://www.spectraaluminum.com/Aluminum-Extrusionhttp://www.spectraaluminum.com/Aluminum-Extrusionhttp://www.spectraaluminum.com/Facilityhttp://www.spectraaluminum.com/Die-Cataloguehttp://www.spectraaluminum.com/Process-Facts-Figureshttp://www.spectraaluminum.com/Full-Colour-Aluminum-Anodizinghttp://www.spectraaluminum.com/Polishing-and-Custom-Mechanicalhttp://www.spectraaluminum.com/Wet-paint-and-Powder-Coatinghttp://www.spectraaluminum.com/aluminum-fabrication-and-assemblyhttp://www.spectraaluminum.com/Articleshttp://www.spectraaluminum.com/Articleshttp://www.spectraaluminum.com/aluminum-fabrication-and-assemblyhttp://www.spectraaluminum.com/Wet-paint-and-Powder-Coatinghttp://www.spectraaluminum.com/Polishing-and-Custom-Mechanicalhttp://www.spectraaluminum.com/Full-Colour-Aluminum-Anodizinghttp://www.spectraaluminum.com/Process-Facts-Figureshttp://www.spectraaluminum.com/Die-Cataloguehttp://www.spectraaluminum.com/Facilityhttp://www.spectraaluminum.com/Aluminum-Extrusionhttp://www.spectraaluminum.com/Aluminum-Extrusionhttp://en.wikipedia.org/wiki/Extrusionhttp://void%280%29/


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O ALUMINUM EXTRUSION ARTICLES APPLICATIONS OF ALUMINUM EXTRUSIONALUMINUM

FINISHINGALUMINUM FABRICATIONALUMINUM EXTRUSION GLOSSARIES

THE SPECTRA ADVANTAGE
http://www.spectraaluminum.com/aluminum-extrusion-articleshttp://www.spectraaluminum.com/applications-of-aluminum-extrusion-articleshttp://www.spectraaluminum.com/aluminum-finishinghttp://www.spectraaluminum.com/aluminum-finishinghttp://www.spectraaluminum.com/aluminum-fabricationhttp://www.spectraaluminum.com/aluminum-extrusion-glossarieshttp://www.spectraaluminum.com/Spectra-Advantagehttp://www.spectraaluminum.com/Spectra-Advantagehttp://www.spectraaluminum.com/aluminum-extrusion-videohttp://www.spectraaluminum.com/Spectra-Advantagehttp://www.spectraaluminum.com/aluminum-extrusion-glossarieshttp://www.spectraaluminum.com/aluminum-fabricationhttp://www.spectraaluminum.com/aluminum-finishinghttp://www.spectraaluminum.com/aluminum-finishinghttp://www.spectraaluminum.com/applications-of-aluminum-extrusion-articleshttp://www.spectraaluminum.com/aluminum-extrusion-articles


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Waterproofing

From Wikipedia, the free encyclopedia

Jump to:navigation,search

"Waterproof" redirects here. For the town in Louisiana, USA, seeWaterproof, Louisiana.

This article does notciteanyreferences or sources.Please helpimprove this articleby adding citations toreliable sources. Unsourced material may bechallengedandremoved.(April 2007)

Waterproofor water-resistant describes objects relatively unaffected by water or resistingthe ingress of water under specified conditions. Such items may be used in wet environmentsorunder waterto specified depths. Waterproofing describes making an object waterproof orwater-resistant (such as acameraorwatch).

"Water resistant" and "waterproof" often refer to penetration of liquid water.Permeationofwater vaporis reported as awater vapor transmission rate. Also, water fromcondensationisusually separate from "water resistant".

The hulls of boats and ships were once waterproofed by applyingtarorpitch. Modern itemsmay be waterproofed by applying water-repellent coatings or by sealing seams withgasketsorO-rings.

In construction, a building or structure is waterproofed with the use of membranes andcoatings to protect contents underneath or within as well as protecting structural integrity.The waterproofing of thebuilding envelopein construction specifications is listed under '07 -

Thermal and Moisture Protection' withinMasterFormat2004, by theConstructionSpecifications Institute, and includes roofing material as well as waterproofingmaterials[citation needed].

Waterproofing is used in reference to building structures (basements, decks, wet areas, etc.),watercraft, canvas, clothing (raincoat,waders) and paper (e.g.,milk and juice cartons).

Waterproofing should not be confused withroofing, asroofingcannot withstand hydrostatichead, and waterproofing can.

The standards for waterproofing bathrooms in domestic construction have improved over theyears, due in large part to the general tightening of building codes. A very small portion ofthe population believe that this is due in part to the Japanese custom of over-filling their baths- these people are wrong.

Contents

[hide]

1 Construction waterproofingo 1.1 Basement waterproofing

2 Standard
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edia.org/wiki/Construction_Specifications_Institutehttp://en.wikipedia.org/wiki/Construction_Specifications_Institutehttp://en.wikipedia.org/wiki/MasterFormathttp://en.wikipedia.org/wiki/Building_envelopehttp://en.wikipedia.org/wiki/O-ringhttp://en.wikipedia.org/wiki/Gasketshttp://en.wikipedia.org/wiki/Pitch_(resin)http://en.wikipedia.org/wiki/Tarhttp://en.wikipedia.org/wiki/Condensationhttp://en.wikipedia.org/wiki/Water_vapor_transmission_ratehttp://en.wikipedia.org/wiki/Water_vaporhttp://en.wikipedia.org/wiki/Permeationhttp://en.wikipedia.org/wiki/Watchhttp://en.wikipedia.org/wiki/Camerahttp://en.wikipedia.org/wiki/Under_waterhttp://en.wikipedia.org/wiki/Wikipedia:Verifiability#Burden_of_evidencehttp://en.wikipedia.org/wiki/Template:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Identifying_reliable_sourceshttp://en.wikipedia.org/w/index.php?title=Waterproofing&action=edithttp://en.wikipedia.org/wiki/Wikipedia:Verifiabilityhttp://en.wikipedia.org/wiki/Wikipedia:Citing_sourceshttp://en.wikipedia.org/wiki/Waterproof,_Louisianahttp://en.wikipedia.org/wiki/Waterproofing#p-searchhttp://en.wikipedia.org/wiki/Waterproofing#mw-head


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3 References 4 See also

[edit] Construction waterproofingMain article:weatherization

In buildingconstruction, a structure needs waterproofing sinceconcreteitself will not bewatertight on its own (but note concrete is easily waterproofed with additives). Theconventional system of waterproofing involves 'membranes'. This relies on the application ofone or more layers of membrane (available in various materials: e.g.,bitumen,silicate,PVC,EPDMetc.) that act as a barrier between the water and the building structure, preventing thepassage of water. However, the membrane system relies on exacting application, presentingdifficulties. Problems with application or adherence to the substrate can lead to leakage. In

the UK these membranes are rarely allowed below ground below the water table.

Over the past two decades, the construction industry has had technological advances inwaterproofing materials, including integral waterproofing systems as well as more advancedmembrane materials.

Integral systems work within the matrix of a concrete structure, giving the concrete itself awaterproof quality. There are two main types of integral waterproofing systems: thehydrophilic and the hydrophobic systems. A hydrophilic system typically uses acrystallization technology that replaces the water in the concrete with insoluble crystals.Various brands available in the market claim similar properties, but not all can react with a

wide range of cement hydration by-products, and thus require caution. Hydrophobic systemsuse fatty acids to block pores within the concrete, preventing water passage.

New membrane materials seek to overcome shortcomings in older methods like PVC andHDPE. Generally, new technology in waterproof membranes relies on polymer basedmaterials that are extremely adhesive to create a seamless barrier around the outside of astructure.

[edit] Basement waterproofing

Basement waterproofing once completed becomes very difficult since the water pressure isfrom the negative side (from outside coming inside), the difficulty arises when a membranecannot withstand hydrostatic pressure from within the substrate and therefore fails. Watermay enter a basement through various means including through joints, walls, or floors.Various basement waterproofing systems address these problems. There are many systemsavailable of varying cost, effectiveness, and installation invasiveness. Specially usedmembranes in this field are protection board sheets. Basement waterproofing may be doneinternally and externally. Because basement foundations can be brick, block, concrete, andeven wood, it is important to pick the right waterproofing system for the right foundation.One effective way to waterproof cracks in poured concrete walls is byepoxyinjection.[1]
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Retaining wall

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Agravity-typestoneretaining wall

This article contains too muchjargonand may need simplification or furtherexplanation. Please discuss this issue on thetalk page, and/or remove or explain

jargon terms used in the article.Editing helpis available. (January 2011)

Retaining walls are built in order to hold back ground which would otherwise movedownwards. Their purpose is to stabilise slopes and provide useful areas at differentelevations, e.g. terraces for agriculture, buildings, roads and railways.

Contents

[hide]

1 Definition 2 Types

o 2.1 Gravityo 2.2 Cantileveredo 2.3 Sheet pilingo 2.4 Anchored

3 Alternative Retaining Techniqueso 3.1 Soil nailingo 3.2 Soil-strengthened

3.2.1 Gabion mesheso 3.3 Mechanical stabilization

4 See also 5 References

6 External links
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Definition

A retaining wall is a structure designed and constructed to resist the lateral pressure of soilwhen there is a desired change in ground elevation that exceeds theangle of reposeof thesoil.[1]

The basement wall is thus one form of retaining wall.

However, the term is most often used to refer to a cantilever retaining wall, which is afreestanding structure without lateral support at its top.[2]

Typically retaining walls are cantilevered from a footing extending up beyond the grade onone side and retaining a higher level grade on the opposite side. The walls must resist the

lateral pressures generated by loose soils or, in some cases, water pressures.[3]

The most important consideration in proper design and installation of retaining walls is torecognize and counteract the fact that the retained material is attempting to move forward anddownslope due to gravity. This createslateral earth pressurebehind the wall which dependson theangleof internalfriction(phi) and the cohesive strength (c) of the retained material, aswell as the direction and magnitude of movement the retaining structure undergoes.

Lateral earth pressures are zero at the top of the wall and - in homogenous ground - increaseproportionally to a maximum value at the lowest depth. Earth pressures will push the wallforward or overturn it if not properly addressed. Also, anygroundwaterbehind the wall that

is not dissipated by adrainagesystem causeshydrostatic pressureon the wall. The totalpressure or thrust may be assumed to act at one-third from the lowest depth for lengthwisestretches of uniform height.[4]

Unless the wall is designed to retain water, It is important to have proper drainage behind thewall in order to limit the pressure to the wall's design value. Drainage materials will reduce oreliminate the hydrostatic pressure and improve the stability of the material behind the wall.Drystoneretaining walls are normally self-draining.

As an example, theInternational Building Coderequires retaining walls to be designed toensure stability against overturning, sliding, excessivefoundationpressure and water uplift;and that they be designed for asafety factorof 1.5 against lateral sliding and overturning.[5]
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Types

Various types of retaining walls

Gravity

Construction types of gravity retaining walls

Gravity walls depend on the weight of their mass (stone, concrete or other heavy material) toresist pressures from behind and will often have a slight'batter' setback, to improve stabilityby leaning back into the retained soil. For short landscaping walls, they are often made frommortarlessstone or segmental concrete units (masonry units).[6]Dry-stacked gravity walls aresomewhat flexible and do not require a rigid footing infrostareas. Home owners who buildlarger gravity walls that do require a rigid concrete footing can make use of the services of aprofessional excavator, which will make digging a trench for the base of the gravity wallmuch easier.

Earlier in the 20th century, taller retaining walls were often gravity walls made from largemasses of concrete or stone. Today, taller retaining walls are increasingly built as compositegravity walls such as: geosynthetic or with precast facing;gabions(stacked steel wire basketsfilled with rocks); crib walls (cells built up log cabin style from precast concrete or timberand filled with soil); or soil-nailed walls (soil reinforced in place with steel and concreterods).[7]

Cantilevered
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