Ceramic bearings for corrosive condition

Bearings can be attacked by exposure to water and moisture, marine climate, and various chemicals (gases and liquids).

In food processing plants, for example, bearings are pressure-washed daily with a mixture of water and a disinfectant or antibacterial agent. Likewise, submersible pumps in irrigation systems are also exposed to water containing sediment and fertilizer. Conveying equipment in an automated paint line is affected by many different chemicals during the cleaning cycle, and of course the paint itself is also affected by various chemicals. These environments can damage bearings and lubricants.

Rings and components are usually made of stainless steel. AISI 440C or similar is the most commonly used alloy because it provides moderate corrosion protection and has properties that benefit fatigue life. Special nitrogen-strengthened martensitic stainless steels are also an option. When tested in salt spray, the material is five times more resistant to corrosion than 440C. Other advantages include high resistance to blood and other substances, fine microstructure providing lower noise levels, and extended fatigue life.

Other stainless steel options are AISI 304 and 316. These austenitic steels have excellent corrosion resistance compared to the 400 series. However, due to their low hardness, their load capacity is greatly reduced compared to 440C, which has a hardness of Rc 60 after heat treatment.

The precipitation hardening resistant AISI 630 stainless steel has an RC 40 hardness and increased load-carrying capacity compared to the 300 series. However, AISI 630 does not provide the same level of corrosion resistance. Compared to 400 series martensitic steels, AISI 630 is more suitable for highly corrosive environments but has poorer load carrying capacity.

Rolling elements made of ceramic materials should be considered for corrosive environments. There are various grades and types of ceramic materials, but silicon nitride is the most common.

Bearings composed of ceramic balls and steel rings are called hybrid bearings. In hybrid bearings, ceramic rolling elements increase durability. The ceramic material is resistant to almost all chemicals, so it won't deteriorate the ball or roller due to corrosion. Also, since ceramic is a different material than steel rims, there will be no cold welding and wear debris in the raceways (or elsewhere). As a result, raceway pitting and degradation are reduced. This, in turn, helps maintain the condition and longevity of the lubricant.