Heat and surface treatment
Rolling bearing rings and rolling elements must:
be hard enough to cope with fatigue and plastic deformations
- be tough enough to cope with applied loads
- be sufficiently stable to experience only limited changes of dimensions over time
The required properties are achieved by heat and surface treatments.
There are three typical hardening methods that may be applied to bearing components:
This is the standard method for most bearings and provides good fatigue and wear-resistance, as hardening is applied over the full cross section.
Surface induction-hardening is used to selectively harden a component’s raceway to limit rolling contact fatigue, leaving the remainder of the component unaffected to maintain structural strength.
Case-hardening provides hardness to the surface. It is used, for example, where bearing rings are subjected to high impact loads causing structural deformations.
Heat treatment is used to limit dimensional changes caused by metallurgical effects at extreme temperatures. There is a standardized classification system for dimensional stability (table 1). The various SKF bearing types are stabilized to different classes as standard.
Coating is a well-established method for providing bearings with additional functional benefits to accommodate specific application conditions. Widely used coatings are zinc chromate and black oxide.
Two other methods developed by SKF have proven successful in many applications:
INSOCOAT bearings are standard bearings that have the external surfaces of their inner or outer ring coated with an aluminium oxide layer. This coating increases resistance to electric current through the bearing.
- NoWear enhances wear-resistance of the raceway or rolling element surfaces. It can help the bearing withstand long periods of operation under poor lubrication conditions and to reduce the risk for low load damage.