T-195
CELCON***. The physical and mechanical properties of these materials vary with regard
to strength, rigidity, dimensional stability, lubrication requirements, moisture absorption,
etc. Standardized tabular data is available from various manufacturers' catalogs.
Manufacturers in the U.S.A. provide this information in units customarily used in the U.S.A.
In general, the 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. Tables 18-1 through 18-9 are representative listings of physical
and mechanical properties of gear plastics taken from a variety of sources. All reprinted
tables are in their original units of measure.
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. For this reason, Table 18-10 is presented.
Other properties and features that enter into consideration for gearing are given in
Table 18-11 (Wear) and Table 18-12 (Poisson's Ratio).
Moisture has a significant impact on plastic properties as can be seen in Tables 18-1
thru 18-5. Ranking of plastics is given in Table 18-13. In this table, rate refers to
expansion from dry to full moist condition. Thus, a 0.20% rating means a dimensional
increase of 0.002 mm/mm. Note that this is only a rough guide, as exact values depend
upon factors of composition and processing, both the raw material and gear molding. For
example, it can be seen that the various types and grades of nylon can range from 0.07%
to 2.0%.
Table 18-14 lists safe stress values for a few basic plastics and the effect of glass
fiber reinforcement.
Table 18-1 Physical Properties of Plastics Used in Gears
Reprinted with the permission of Plastic Design and Processing Magazine; see Reference 8.
*** Registered trademark, Celanese Corporation, 26 Main St., Chatham, N.J. 07928.
Tensile
Strength
(psi x 103)
Material
Flexural
Strength
(psi x 103)
Compressive
Modulus
(psi x 103)
Heat Distortion
Temperature
(°F @ 264psi)
Water
Absorption
(% in 24 hrs)
Rockwell
Hardness
Mold
Shrinkage
(in./in.)
Acetal
ABS
Nylon 6/6
Nylon 6/10
Polycarbonate
High Impact
Polystyrene
Polyurethane
Polyvinyl
Chloride
Polysulfone
MoS2–Filled
Nylon
8.8 – 1.0
4.5 – 8.5
11.2 – 13.1
7 – 8.5
8 – 9.5
1.9 – 4
4.5 – 8
6 – 9
10.2
10.2
13 – 14
5 – 13.5
14.6
10.5
11 – 13
5.5 – 12.5
7.1
8 – 15
15.4
10
410
120 – 200
400
400
350
300 – 500
85
300 – 400
370
350
230 – 255
180 – 245
200
145
265 – 290
160 – 205
160 – 205
140 – 175
345
140
0.25
0.2 – 0.5
1.3
0.4
0.15
0.05 – 0.10
0.60 – 0.80
0.07 – 0.40
0.22
0.4
M94
R120
R80 – 120
R118 – 123
R111
M70
R112
M25 – 69
M29
R90
R100 – 120
M69
R120
D785
0.022
0.003
0.007
0.007
0.015
0.015
0.005
0.007
0.003
0.005
0.009
0.002
0.004
0.0076
0.012
