BEARING fatigue and failure is an all too common cause of machine shutdown and lost productivity, and is often attributed to problems with lubrication. Constant inspection of lubricated bearings is essential to realising a bearing’s full life as well as getting the most out of both oil and grease lubricants.
CBC Bearings National Engineering Manager Ross Lee, says the provision of correct and clean oil or grease lubrication is a core element in achieving satisfactory rolling element bearing performance.
“Correct grease or oil lubrication separates rolling element and raceway surfaces, preventing metal to metal contact, reduces rolling and sliding contact friction, controls wear and inhibits corrosion damage,” Lee said.
“By periodically gauging the condition of lubricant, any abnormalities or deficiencies are identified, permitting corrective action to be taken in a timely manner.
“Contaminated lubricant can cause distress such as abrasive wear, lubricating film penetration and breakdown, resulting in surface initiated fatigue, undesirable skidding of rollers or balls, corrosion and of course lubricant degradation,” Lee told Manufacturers’ Monthly.
“Very small solid particle contaminants have proven to be the most damaging as they are not detected by looking at the lubricant.
“In gearbox applications, metallic wear contaminants act as a catalyst with moisture, causing oil oxidation. This results in an oil acidity increase which can deplete the additive package, increase viscosity and ultimately generate sludge and varnish,” Lee said.
Bearing fatigue and failure frequently occurs before potential service life is achieved and industry evidence shows that in over 80% of cases, improper lubrication coupled with contamination of the lubricant is the cause.
Focusing specifically on oil lubrication, CBC offers an oil analysis program to determine if oil is dirty, contaminated, diluted or fit for continued use.
CBC Product Specialist Glenn Herpich says a detailed analysis will tell you the life expectancy of the oil before it needs to be changed as well as showing any alignment or potential mechanical problems.
“The oil analysis program helps to extend equipment life, prevent faults and improve safety control among other things.
“When taking samples, it’s important to ensure the fluid is well circulated, is at normal operating temperature and takes place at regular intervals to give a true indication of the fluids over time,” Herpich said.
“Most rolling bearings applications use grease lubrication rather than oil because grease is simple to apply, is retained in the bearing enclosure and does not require special shaft and joint face sealing to control leakage.
Lee adds that oil lubrication of rolling bearings is usually applied only when applications demand it.
“Oil is used with high speed bearings, where mating components such as gears must also be lubricated and where frictional heat must be dissipated. It also permits easy lubricant replacement and also allows effective filtration processes.”
An important consideration for end-users is the correct selection of lubricating oil which provides the recommended viscosity at various machine operating temperatures.
“Generally mineral oils and grease deliver good lubrication properties for rolling bearings. Mineral oils can also contain supplementary additive packages such as extreme pressure, anti-wear and anti-foam to meet specific application requirements,” Lee said.
Lee also points out that the lubricating oil’s chemical compatibility with shaft oil seal compounds is critical at higher operating temperatures as oil seals provide oil retention and are the first line defence against contaminants.
Quality breathers, and good sampling and filling procedures are recommended to minimise dirt and dust contamination of lubricants while water contamination can be curbed by installing desiccant breathers and ensuring oil stores are not affected by water condensation.