Plain bearings are renowned for their ability to operate for many years under heavy loads and in extremely harsh operating conditions with little wear or need for attention. This makes them a good choice for intense applications. However, in order to get the most out of them over the long term, it is important to pair these types of bearings with the correct lubrication solutions.
Some of the common reasons for plain bearings failures include misalignment, trapped dirt forming grooves in the bearing components, metal fatigue and localised rapid wear.
Misalignment and dirt build up
Misalignment is a common cause of failure. Although bearings can become disfigured and the source of the fault difficult to identify, misalignment between a journal and shaft is usually easy to see. The wear pattern, if carefully studied, will show an unbalanced or skewed pattern. Sometimes a thrust load is also indicated. This can be mitigated by using the correct lubrication to support any oscillation without it turning into long-term misalignment.
When it comes to dirt or foreign material, bearing failure can happen when large, hard particles plough grooves in the softer bearing alloy. The tracks are plainly visible either as large, long straight grooves, or as smaller particle tracks that wander. Numerous small, hard particles will cause many small, straight scratches, often resulting in excessive wear. If the foreign material is large or hard, it may become embedded. Lubrication is an excellent solution for preventing this problem because it by nature traps and removes dirt from a bearing system.
Callum Ford, national marketing manager at Lubrication Engineers (LE) South Africa explains that even though plain bearings don’t necessarily have complex lubrication requirements, the use of quality lubricants can prevent many of the common causes of bearing failures.
“The proprietary Almasol and Monolec additives that we use in LE products are particularly helpful in lubricating plain bearings, because they reduce operating temperatures considerably in the bearings while extending bearing life. They are very effective in reducing wear during the critical start-up and shutdown periods of operation,” he says.
Getting lubrication right
Lack of lubrication, or poor lubrication will show in a plain bearing as rapid wear, often in one spot, until a complete breakdown of the surface takes place. “An experienced lubrication consultant can help identify the correct lubrication solution for an application and plain bearing component to prevent this,” says Ford.
“Plain bearings of proper size and with proper clearances, supported by good lubrication, are better than antifriction bearings for carrying heavy loads or shock loads. Plain bearings can carry extremely high loads because of their large bearing area. But to get the most out of them, bearing surfaces should be completely separated by a film of lubricant. If this film wears out, most plain bearings will quickly get ruined. When the bearing is moving and correctly lubricated, friction decreases to almost the low point of antifriction bearings,” he adds.
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