Plastic Gear Materials
|Plastic Gear Materials|
Under certain operating conditions, the tolerances for plastic gears may
be less critical than for metal gears for smooth and quiet performance.
Ordinarily, however, the same care in manufacturing, testing, measuring,
and quality level specifications should be utilized in plastic gearing
as in metal gearing. The inherent resiliency of some of the plastic used
may result in better conjugate action. The resiliency of many plastic
gears gives them the ability to better dampen moderate shock or impact
type loads within the capabilities of the particular plastics materials.
- Operating Characteristics.
gearing materials are noted for low coefficient of
friction, high efficiency performance, and quiet operation.
Many plastic gearing materials have inherent lubricity
so that gears require little or no external
They can perform satisfactorily when exposed
to many chemicals which have a corrosive effect
on metal gears.
gearing, when operating at low stress levels
in certain environments, have been known to outwear
equivalent metal gears.
- Load Carrying Capacity.
The maximum load
carrying capacity of most plastic gears decreases as
the temperature increases more than with metal
gears. The upper temperature limit of most thermoplastic
gears is 250_F(121_C) at which point they
lose approximately 50 percent of their rated
strength. The upper operating temperature limit of
thermosetting gears now exceeds 400_F(250_C).
Very little degradation of mechanical properties in
certain thermosetting materials occurs at temperatures
up to 450_F(232_C).
- Plastic Materials.
Many different plastics are
now used for
gearing. Both thermosetting and thermoplastic
material are used, with the latter being by
far the most prevalent.
- Phenolic(T/S - indicates thermosetting).
Phenolics are invariably compounded with various
fillers such as woodflour, mineral, glass, sisal,
chopped cloth, and such lubricants as PTFE (polytetrafluorethylene)
and graphite. Phenolics are generally
used in applications requiring stability, and when
higher temperatures are encountered.
- Polyimide (T/S).
Polyimide is usually
40-65 percent fiber glass reinforced and has good
strength retention when used at high operating temperatures.
- Nylon(T/P - indicates thermoplastic).
is a family of thermoplastic polymers. The most
widely used of any molded
gearing material is nylonbr>
6/6, but nylon 6 and nylon 12 are also used. Some nylons
absorb moisture which may cause dimensional
instability. Nylon may be compounded with various
types and amounts of glass reinforcing materials,
mineral fillers, and such lubricants as PTFE and
MoS2 (molybdenum disulfide).
- Acetal (T/P).
Acetal has a lower water absorption
rate than nylon and, therefore, is more
stable after molding or machining. Acetal polymers
are used unfilled or filled, with glass and minerals
with and without lubricants, such as PTFE and
MoS2, as well as one version with fibrous PTFE.
- Polycarbonate (T/P).
Polycarbonate is generally
used with the addition of glass fiber and/or
PTFE lubricant and is a fine, low shrinkage material
for producing consistently accurate molded gears.
- Polyester (T/P).
Polyesters are both unfilled
and with glass fiber, and are finding their way
into more markets as a molded
gearing material in
competition with nylon and acetal.
- Polyurethane (T/P).
Polyurethane is generally
noted for its flexibility and, therefore, has the
ability to absorb shock and deaden sound.
- SAN(Styreneacrylonitrile) (T/P).
SAN is a
stable, low shrinkage material and is used in some
lightly loaded gear applications.
- Polyphenylene Sulfid (T/P).
with 40 percent glass fiber with or without
internal lubricants, it has been found in certain gear
applications to have much greater strength, even at
elevated temperatures, than most materials previously
- Polymer Elastomer (T/P).
is a newcomer to the gearing field, and has excellent
sound deadening qualities and resistance to
flex fatigue, impact, and creep, among other advantageous
- Part Combinations.
Several plastic gears can be
molded together as a
gear cluster. Combinations of
gears, pulleys, sprockets, and cams can also be produced
as a single part.
- Gear Blanks.
Many of these plastic materials, notably
unfilled nylon and acetal, are available in standard
extruded shapes, such as rounds, squares, and
rectangles of various sizes from which gears can be
machined. Gears can be molded at less cost if large
quantity warrants the cost of the mold.
- Machined Plastics Gears.
The quality of machined
gears may be generally better than their
molded counterparts, but the molded tooth surface is
superior to the machined surface in smoothness and
toughness. Final tooth strength is generally better inr>
a molded gear, than an equivalent machined gear,
because of the flow of the material into the tooth cavity
of the mold. Gear cutting is done on standard machines
and with standard tools. The following considerations
will assist in obtaining higher quality machined
The modulus of elasticity is so
low in plastics that errors in measurements are very
difficult to control. The use of controlled load checking
equipment is almost mandatory to avoid errors in
Sharp cutting tools are necessary to
avoid tooth profile and size variation due to deflection.
Feather edge burrs, if not eliminated
by back up discs or subsequent removal by other means,
will impair inspection of gearing and possibly
contribute to noise during operation.
- Laminated Phenolics Plastics.
- Industrial Laminated Thermosetting
These products, whether in sheet or rod
form, contain laminations or plies of fibrous sheet
materials such as cellulose, paper, asbestos, cotton
fabric, glass fabric, or mat. These materials are impregnated
or coated with a enolic resin and consolidated
under high pressures and temperatures
into various grades which have properties useful for
Fabric base grades are chosen to withstand severe
shock loads and repeated bending stresses, and
to resist wear. Fabric base grades are tougher and
less brittle than paper base grades. The linen grades
made with finer textured lightweight fabrics will machine
with less trouble.
Gears of linen base phenolic
are abrasive, and thus may require a hardened steel
mate and adequate lubrication.
Asbestos-phenolic grades have excellent thermal
and dimensional stability.
The glass fabric base grades have good heat resistance
and very high tensile and impact strength.
- Performance Characteristics.
Phenolics are used for fine pitch gears due to economy,
high resiliency, and high wear resistance. Lower
density than metals often provides higher strength to
weight ratios. It should be noted that all grades have
some dimensional change due to humidity.
- Chopped Fabric Molding Compound.
Chopped fabric impregnated with phenolic resin is
capable of being molded as a
gear but may require
finish machining to meet most commercial quality
Cylindrical Gears |
Bevel Gears |
Worm and Worm Gears |
Non Circular Gears
Special Application Gears |
Read Before Inquire |
Gear Info |
Tel: 86-10-6492-5308 | Fax: 86-10-6492-5744 |
Remember to bookmark this web site for your future convenience!
Copyright by Beijing GEARX Limited. All rights reserved.