Machine Design

Bearings Made of Other Metals

Cadmium: Has high-temperature fatigue properties superior to those of babbitt. Cadmium has a low affinity for steel and excellent compatibility characteristics, so cadmium-base alloys are used in steel and bronze rolling mills for heavily loaded roll-neck bearings. Use of these alloys has dropped off, however, because of high cost and poor corrosion resistance.

Silver: These bearings are excellent for heavy-duty applications in aircraft engines and diesels. For reciprocating engines, silver bearings normally consist of electrodeposited silver on a steel backing, with an overlay of 0.001 to 0.005 in. of lead. The lead improves the embeddability and antiscoring properties of the silver. Indium is usually flashed on top of the lead overlay for corrosion protection.

The compatibility characteristics of silver can be used in other applications. A thin coating of silver plate frequently relieves any welding or seizing otherwise encountered under severe rubbing conditions in machine components.

Cast iron and steel: These materials are used in inexpensive bearings for operation under relatively light loads. Flake graphite in the cast iron develops a glazed surface which is useful at surface speeds up to 130 fpm and at loads up to about 150 psi. Frequently, the bearing surface is machined directly in a cast iron structure. Because of the poor conformability of cast iron, good alignment and cleanliness are essential. Guide bushings and lightly loaded journal bearings can also be machined directly in steel structural parts for loads up to 200 psi for operation at speeds up to 150 fpm.

TAGS: Bearings
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