Bearing Materials And Failure Modes

Materials The most common material used for oil-lubricated fluid film bearings is babbitt. Tin- and lead-based babbitts are relatively soft materials and offer the best insurance against shaft damage. They also enable embedded dirt and contaminants without significant damage.

Two types of babbitts are in common use. One has a tin base (86 to 88 percent), with about three to eight percent copper and four to 14 percent antimony. The other has a lead base with a maximum of 20 percent tin and about 10 to 15 percent antimony. The remainder is principally lead. The physical properties of babbitt are shown in Table 5. The primary limitations of babbitt are operating temperature (300°F [140°C] max) and fatigue strength. The chemical composition of various babbitt alloys are indicated in Table 6.

Tin-based babbitts have better characteristics than lead-based babbitts; they have better corrosion resistance, are less likely to wipe under poor conditions of lubrication, and can be bonded more easily than lead-based materials. Because of cost considerations, however, lead-based babbitts are widely used. The more widely used is the SAE 15 alloy containing one percent arsenic (refer to Table 6).

TABLE 5 Properties of Bearing Alloys
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