As a rule, surface coatings of rolling bearings serve to expand the functional scope of the bearing or to give it properties that rolling bearing steel alone cannot reproduce. KRW offers a large number of technical coatings based on the application, which are most clearly classified according to their properties.
KRW offers current-insulated rolling bearings that reliably prevent current passages up to 3,000 V DC due to an aluminium oxide ceramic coating. The coating can be applied to either the outer ring or inner ring.
These coatings are usually applied galvanically and, depending on the design, prevent or retard a chemical reaction of the rolling bearing surface with the surrounding media. The bluing of rolling bearing components is relatively simple and widespread. This is not permanently resistant to abrasion in rolling contact and, if intact, provides basic protection against corrosion without the action of aggressive media. In addition, the separation of the metallic surfaces in the rolling bearing leads to partial wear protection if full lubrication is not provided. Zinc-iron coatings provide better protection against corrosion, which can significantly extend the service life of the rolling bearings in corrosive environments. These coatings are also not resistant to abrasion in rolling contact and are therefore expressly not suitable for media lubricated rolling bearings. A zinc or iron phosphate coating is suitable to retard or avoid fretting corrosion.
These functional coatings are not very common in the standard area of rolling bearing technology. Standard rolling bearing steel is not sufficiently resistant to tempering (heat stable) to enable the functional application of large series coatings from tool technology such as titanium nitride or titanium carbonitride. Nevertheless, there are modern PVD coatings that are applied at low temperatures and show very good wear resistance. These coatings are a more cost-effective replacement for expensive special materials, particularly in the case of large rolling bearings that are subject to inadequate lubrication or require media lubrication.