An Overview of Bearing Lubrication
Proper lubrication and lubrication procedures are key components to ensuring that a bearing reaches its expected life-span.

Lubrication is needed to reduce friction and wear inside the bearing. Proper lubrication and lubrication procedures are key components to ensuring that a bearing reaches its expected life-span.

Lubrication serves the following purposes:

  • As already mentioned, it reduces friction and wear between the direct metallic contact between the bearing rings, rolling elements, and cage.
  • It extends the bearing life.
  • It cools the bearing by circulating heat away.
  • It prevents foreign materials from entering the bearing – including water, which can cause rusting.

Lubricating a bearing can be done using either oil or grease. Generally, oil is superior in lubricating efficiency. However, grease lubrication allows for a simpler structure around the bearings.

The housing structure and sealing method of grease is simple. However, using grease limits bearing speed by about 65% to 80% when compared to oil. The cooling effect of grease is poor, as is its fluidity, and removing particles from grease is simply impossible. One advantage to grease, however, is that a bearing’s surroundings are hardly ever contaminated by grease leakage.

Compared to grease, oil has a number of advantages to offer. Replacing oil is easy, as is removing particles from it. It has good fluidity and circulates heat away from a bearing efficiently. It also has a high limiting speed, especially compared to grease. Some disadvantages of oil are that it often leaks without proper countermeasures. This requires a complex housing structure and sealing method.

The quantity of grease to use depends on a number of factors, including housing design, rotational speed of the bearing, characteristics of the grease selected, and the ambient temperature. As a rule of thumb, grease should never be used if the operating speed exceeds the grease’s limited speed listed for the bearing. Once packed, grease usually doesn’t need to be replenished for a long time, unless the operating conditions are quite severe.

If the operating speed exceeds grease’s limiting speed, oil should be used. Oil lubrication application can be achieved through a number of methods: oil bath lubrication, drip feed lubrication, splash lubrication, circulating system, oil mist lubrication, jet lubrication, and the oil/air lubricating method. Which method used depends on a variety of factors, including bearing speed and application.

How often oil is replaced depends entirely on operating conditions and oil quality. In most cases where the operating temperature is less than 50 degrees Celcius, and the environmental conditions are good, oil should be replaced roughly once a year. However, in cases where the oil temperature is about 100 degrees Celsius, the oil must be changed at least once every three months.

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