Physical Properties Plastics Used in Gears

Related Resources: gears

Physical Properties Plastics Used in Gears

Engineering Materials
Gear Engineering and Design

Popular materials for Plastic Gears are acetal resins, nylon resins and acetal copolymers. The physical and mechanical properties of a these materials vary with regard to strength, rigidly, dimensional resistance, fabrication requirements, moisture absorption etc. Standardized tabular data is available from various manufacturers catalogs. In general, the information and data is less simplified and fixed than for the metals. This is because plastics are subject to wider formulation variations and are often regarded as proprietary compounds and mixtures.

It is common practice to use plastics in combination with different metals and materials other than plastics. Such is the case when gears have metal hubs, inserts, rims, spokes, etc. In these cases one must be cognizant of the fact that plastics have an order of magnitude different Coefficients of Thermal Expansion as well as Density and Modulus of Elasticity.

The table below lists safe stress values for a few basic plastics and the effect of glass fiber reinforcement

Plastic Gear Material	Tensile Strength (psi x 10³)	Flexural Strength (psi x 10³)	Compressive Modulus (psi x 10³)	Heat Distortion Temperature (°F @ 264 psi)	Water Absorption (% 24 hr)	Rockwell Hardness	Mold Shrinkage (in./in.)
Acetal	8.8-1.0	13-14	410	230-255	0.25	M94 R120	0.022/0.003
ABS	4.5-8.5	5-13.5	120-200	180-245	0.2-0.5	R80-120	0.007/ 0.007
Nylon 6/6	11.2-13.1	14.6	400	200	1.3	R115-123	0.015
Nylon6/1O	7-8.5	10.5	400	145	.4	R111 M70	0.015/0.005
Polycarbonate	8-9.5	11-13	350	285-290	0.15	R112	0.007/ 0.003
High Impact
Polystyrene	1.9-4	5.5-12.5	300-580	160-205	.05-.10	M25-69	0.005
Polyurethane
Polyvinyl	4.5-8	7.1	85	180-205	.60-.80	M29 R90	0.009/0.002
Chloride	6-9	8-15	300-400	140-175	07-.40	R100-120	0.004
Polysulflon
MoS2	10.2	16.4	370	345	0.22	M69-R120	0.0076
Filled Nylon	10.2	10	330	140	0.4	D785	0.012