3.4 Coefficient of Friction vs. Load for Various Materials

The coefficient of friction varies with the bearing unit load. The following graph depicts this relationship for various plastic materials.

(A) Oilon Pv®–80—Class I
(B) Oilon Pv®–80—Class II
(C) Acetal—Class I
(D) Nylon MoS2—Class II
(E) Nylon MoS2—Class I
(F) PTFE glass filled—Class II
(G) Oil Impregnated Sintered Copper Alloy— Class II
(H) White Metal—Class I
Class I: Grease applied externally, prior to start-up.
Class II: No grease applied prior to start-up.

Test conditions:
Velocity: 46 ft/min (350 rpm)
Load: 140 lbs/in2, addition applied at 10 min. intervals
Dimensions of Test Specimen: 5/8" OD x 3/8" ID x 3/8" long
Mating Material: Steel 113° F HR-B 90

A comparison of frictional characteristics of various metallic and plastic materials is given in Figure 3-1. In some plastic materials the coefficient of friction decreases with load, thereby greatly reducing or eliminating the stick-slip in the start-up of machinery.

In recent years the properties of plastic bearing materials have been materially enhanced by the addition of fillers (such as fiber, powder, graphite and molybdenum disulfide) and composites (metal or other backings). If the cost is warranted the mechanical properties of such bearings can be dramatically improved.

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