Ball Bearing Material and Manufacture
Ball Bearings: The specification for ball bearing material is very demanding. In normal service the steel must withstand 300,000 psi compressive stresses and, in extreme service, compressive stresses of 500,000 psi.
The standard grade steel for ball bearings is high carbon, high chromium, vacuumed degassed AIS/SAE 52100. The high carbon content of 1% makes the steel responsive to heat treatment resulting in very high strength and hardness. The high chromium content of 1.35% further increases response to heat treatment and adds depth of hardness penetration. Vacuum degassing removes impurities making the steel extra clean for extremely critical applications. Consumable electrode vacuum melted steel is available for an even higher degree of cleanliness and uniformity.
Rings and balls are heat treated throughout to the RC60 hardness level for optimum toughness and strength at operating temperatures up to 300oF. For operating temperatures over 300oF, the steel softens and loses dimensional stability. A special stabilization heat treat procedure is available for continuous operation at temperatures up to 400oF. Stabilization tempers the steel at a temperature above what is encountered in service resulting in a slight decrease in hardness from the RC60 level.
Stainless steel is used for rings and balls for corrosion resistance and high temperature operation up to 550oF. For even higher temperatures up to 1,100oF, special tool steels and cobalt alloys are used.
Separator steel for most bearings is low carbon steel. Most angular contact bearings operating at high speed use a non-metallic separator material. Non-metallic combines low friction, light weight, and strength at temperatures up to 275oF. With higher temperatures and speeds, iron silicon bronze and phosphor bronze provide low friction and a high strength-to-weight ratio. For temperatures up to 1,000oF, S-Monel, special tool steel, and alloy steel are available. Figure 19 gives temperature limitations of the various bearing and separator materials.
