Materials for severe service bearings
03 December 2017
There are several different severe service industries that bearings are often used in and the main sectors include aerospace, automotive and industrial. Out of these three, aerospace is commonly acknowledged as being the most severe.
To determine whether a bearing would be suitable for a severe service end-use application, it is important to consider that materials that have been used in the bearings, that is the ‘bearing design.’ Three key materials that allow bearings to successfully work in severe service applications are ceramic rolling elements (silicon nitride), high nitrogen chromium (HNCR) for the bearings rings and polyether ether ketone (PEEK) as the cage material.
However, the manufacture of ceramic rollers is still not available as mass-produced components. There is still some degree of manufacturing development required. Ceramic rolling elements have several advantages but the most important one (in terms of severe service) is the ability to operate under marginal lubrication conditions.
HNCR stainless steel
This material offers greater material “cleanliness” than standard bearings steels, with almost no presence of sulfides, aluminates, silicates or globular oxides. The absence of these non-metallic contaminants contributes to extended bearing service life, as does the extremely homogeneous structure.
PEEK is a semi crystalline thermoplastic with excellent mechanical and chemical resistance properties that are retained to high temperatures. Using this material for cages is still relatively new.
One example of where these types of bearings can be used is in sour gas compressors. With sour gas, the H2S (the gas that makes natural gas “sour”), condenses in the compressor and contaminates the lubricating oil and forms sulfuric acid, which then corrodes the bearing.
The bearing would soon fail and the compressor would have to be rebuilt. The bearings were significantly more expensive than the standard, however the run time between failures stretched from months to years saving the user millions of dollars in avoidance of penalties. Therefore the use of sour service bearings has become the standard for certain compressor suppliers and users in the oil and gas industry in Alberta.
Image courtesy of SKF Canada