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Physical Properties Plastics Used in Gears

Engineering Materials
Gear Engineering and Design

Physical Properties Plastics Used in Gears

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
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