Bearing Corrosion and its Causes
Do you know the two types of corrosion that can affect bearings?
There are two types of corrosion that affect bearing performance: deep seated rust and fretting corrosion. Both types of corrosion will form if water or corrosive agents reach inside of the bearing in such quantities that the lubricant cannot provide protection for the steel surfaces.
Deep seated rust forms when water or corrosive elements make contact with the steel surfaces of a bearing. It can initiate flaking and cracks, which are exacerbated if the liquid penetrating to the steel is an alkaline solution. This causes greyish black streaks across the raceways. Pitting occurs over time, further damaging the bearing.
Fretting corrosion occurs with the thin oxide film covering the clean steel surface of the bearing is penetrated. Oxidation then proceeds deeper into the material. What causes this is loose fitting between the bearing ring and shaft or housing. Fretting corrosion will cause areas of rust on the outside surface of the outer ring or in the bore of the inner ring.
Luckily, preventative measures can be taken to lessen the impact of corrosion. Performance requirements must be considered in case design modifications need to be made to reduce exposure to corrosive elements. It is also important to identify contaminants – water, salts, and acids. Depending on what environmental contaminants are present, it’s possible to take preventative measures. For example, if there is salt spray, you can use electro-deposited chromium plating as a barrier.