Current Research in Plastic Gears

7/27/2019 Current Research in Plastic Gears

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AVINASH BHARDWAJENROLMENT NO: 100520123027SEMESTER 6

PLASTIC ENGINEERINGCIPET AHMEDABAD


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Plastic gears developed only in past 50 yearsfrom curiosity to industrial mainstay

Everyday , they are growing:

more precise

more complex in geometry

more powerful

larger

Because of :High-performance resins

long-fiber compounds


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Plastic gears employed today in: Cars

Watches

Sewing machines

Building controls

Missiles.

Strongest growth arena : automobiles

Even with all the ground theyve gained, theirevolution is still far from over.


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Higher-end materials like PPS are findingbroader use in gear applications like thisstart-up section of an ignition switch madeby Delphi Saginaw Steering Systems.

start-up section of an ignition switch
http://d2n4wb9orp1vta.cloudfront.net/resources/images/cdn/cms/start-up%20section%20of%20an%20ignition%20switch%20.jpg


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This is a variable-ratio geared drive used incranes and theatrical stages provides safety-related interruption of mains or controlpower.(material : acetal)

differential geared drive made by Stromag AG in Germany
http://d2n4wb9orp1vta.cloudfront.net/resources/images/cdn/cms/precision%20gears%20such%20as%20this%20differential%20geared%20drive.jpg


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A gear is a rotatingmachine part havingcut teeth, or cogs, which meshwith anothertoothed part in order to transmit torque.
http://en.wikipedia.org/wiki/Rotatinghttp://en.wikipedia.org/wiki/Machine_(mechanical)http://en.wikipedia.org/wiki/Torquehttp://en.wikipedia.org/wiki/Torquehttp://en.wikipedia.org/wiki/Machine_(mechanical)http://en.wikipedia.org/wiki/Rotating


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Numerous nonferrous alloys cast irons

powder-metallurgy

Plastics

Steels are most commonly used because oftheir high strength-to-weight ratio and lowcost.

Plastic is commonly used where cost or

weight is a concern


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Plastics today can replace steel because ofproperties like,

dirt tolerance

low speed meshing

the ability to "skip" quite well and the ability to be made with materials not needing

additional lubrication


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Plastic offers many cost, design, processing,and performance advantages over metal

Manufacturers have employed plastic gearsfor reduce costs in consumer items copy machines,

optical storage devices,

VCRs,

cheap dynamos,

consumer audio equipment,

servo motors, and printers


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Plastic gears allow 50% to 90% cost reductionversus stamped or machined metal gearsbecause they usually need no secondaryfinishing.

Plastic gears weigh less than metal gears

Plastic gears are relatively inert . So they donot corrode in water pumps and chemical

plant controls


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Plastic gears offer better gear geometries. Internal gears, cluster gears, and worm gears

are cheaper to mould in plastics than metals.

Plastic gears enable greater load-bearingcapacity and more power transfer in a singlestage as they can be wider.

Plastic gears are quieter because of high

precision, novel tooth shapes, and lubriciousor flexible materials.


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Plastic gears are more forgiving than thosemade of metal because plastic deflects toabsorb impact loads and also betterdistributes localized loads caused by

misalignment and tooth errors.

Plastic gears are internally lubricated andthus ideal for computer printers, toys, andother low-load situations where lubricantsare excluded.

Plastics can be lubricated by grease or oil.


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Among the characteristics responsible for thelarge increase in plastic gear usage, the followingare probably the most significant :

1. Cost effectiveness of the injection-moldingprocess.

2. Elimination of machining operations; capabilityof fabrication with inserts and integral designs.

3. Low density: lightweight, low inertia.

4. Uniformity of parts.

5. Capability to absorb shock and vibration as aresult of elastic compliance.


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6. Ability to operate with minimum or nolubrication, due to inherent lubricity.

7. Relatively low coefficient of friction. 8. Corrosion-resistance; elimination of

plating, or protective coatings. 9. Quietness of operation. 10. Tolerances often less critical than for

metal gears, due in part to their greater

resilience. 11. Consistency with trend to greater use of

plastic housings and other components.


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1. Less load-carrying capacity, due to lowermaximum allowable stress; the greater compliance ofplastic gears may also produce stress concentrations.

2. Plastic gears cannot generally be molded to thesame accuracy as high-precision machined metal

gears. 3. Plastic gears are subject to greater dimensional

instabilities, due to their larger coefficient of thermalexpansion and moisture absorption.

4. Reduced ability to operate at elevatedtemperatures; as an approximate figure, operation islimited to less than 120C. Also, limited coldtemperature operations.


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5. Initial high mold cost in developing correcttooth form and dimensions.

6. Can be negatively affected by certainchemicals and even some lubricants.

7. Improper molding tools and process canproduce residual internal stresses at thetooth roots, resulting in over stressing and/ordistortion with aging.

8. Costs of plastics track petrochemicalpricing, and thus are more volatile andsubject to increases in comparison to metals.


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Popular materials for plastic gears are

Acetal resins such as DELRIN*, Duracon M90;

Nylon resins such as ZYTEL*, NYLATRON**, MC901 and

Acetal copolymers such as CELCON***.

* Registered trademark, E.I. du Pont de Nemours and Co., Wilmington, Delaware, 19898.

** Registered trademark, The Polymer Corporation, P.O. Box 422, Reading, Pennsylvania, 19603.

*** Registered trademark, Celanese Corporation, 26 Main St., Chatham, N.J. 07928


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Both thermosetting andthermoplastic material are used,with the latter being by far themost prevalent.

Phenolic(thermosetting). invariably compounded with various fillers such as wood

flour, mineral, glass, sisal, chopped cloth, lubricants as PTFE (polytetrafluorethylene) and graphite. generally used in applications requiring stability, when higher temperatures are encountered.


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Polyimide (thermoset) Polyimide is usually 40-65 percent fiber glass

reinforced

has good strength retention when used at high

operating


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Nylon( thermoplastic). Nylon 6,6

Nylon 12

Nylon 6

Some nylons absorb moisture which may causedimensional instability.

may be compounded with various types and amountsof glass reinforcing materials, mineral fillers, and suchlubricants as PTFE and MoS2 (molybdenum disulfide).


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Acetal (thermoplastic).

lower water absorption rate than nylon and

is more stable after molding or machining.

used unfilled or filled, with glass and minerals withand without lubricants, such as PTFE and MoS2, as wellas one version with fibrous PTFE.


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Polycarbonate (thermoplastic). Used in addition of glass fiber

and/or PTFE lubricant

is a fine, low shrinkage material

Accurate. Polyester (thermoplastic).

unfilled and with glass fiber,

competing with nylon and acetal.

Polyurethane (thermoplastic). flexible and therefore, has the ability to absorb shock

and deaden sound


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SAN(Styreneacrylonitrile) (thermoplastic). stable, low shrinkage material

is used in some lightly loaded gear applications.

Polyphenylene Sulfid (thermoplastic). When compounded with 40 percent glass fiber with or

without internal lubricants, it has been found in certaingear applications to have much greater strength, evenat elevated temperatures, than most materialspreviously available.


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Polymer Elastomer (thermoplastic). Polymer elastomer is a newcomer to the gearing

field,

has excellent sound deadening qualities

resistance to flex fatigue resistance to Impact

resistance to creep


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The physical and mechanical properties ofthese materials vary with regard to strength,rigidity, dimensional stability, lubricationrequirements, moisture absorption, etc.

Depend on applications.


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www.Akgears.com www.gearsolutions.com

www.google.com

www.wikipedia.org
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Documents

Current Research in Plastic Gears