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How to Lubricate a Bearing

How to Lubricate a Bearing


Lubrication plays a vital role in the performance and life expectancy of rolling bearing elements. To eliminate metal-to-metal contact, lubrication creates a thin oil film on both, the rolling and sliding surfaces of a bearing, eliminating friction, and increasing the performance of rolling element bearings.

Ball and roller bearings use extremely little lubricant; the concept of their structure, as well as the design of the spaces around them (grease cavities), is to lubricate the tracks and rolling parts with a very thin coating. This is provided by the oil that slowly bleeds from the grease in the cavities.

Therefore, it is not required to have the bearing and cavities entirely filled; in fact, for high-speed bearings, this might be detrimental. Filling bearings and cavities entirely can lead to over greasing. Overgreasing causes the rotating bearing elements to begin churning the grease, pushing it out of the way, resulting in energy loss and rising temperatures. This results in rapid oxidation of grease as well as an accelerated rate of oil bleed, eventually leading to premature failure.

The only times when bearings and housing should be completely filled and kept full are when –

  • Bearings are at a slow speed
  • Poor sealing
  • Dusty conditions

Initial Greasing

Initial Greasing, if done correctly, plays a key role in extending the life and performance of ball and roller bearings. Some of the key steps in Initial Greasing include:

  • After unpacking, the corrosion protection layer present in bearings should be rinsed off with a suitable solvent and dried.
  • After that, oil should be gently applied to the tracks, cage, and rolling components, and the bearing spun to disperse the grease.
  • The remaining grease should then be spread throughout the housing or grease cavities lying adjacent to the bearing.
  • It is important to ensure that all the parts are properly clean and free of grit.

The following table summarises the approximate initial grease fill quantities based on the shaft diameter of the bearing (these can vary dependent upon bearing and housing design) –

Shaft Diameter                            Relubrication Fill

25mm                                                 6 grams

50mm                                                 12 grams

75mm                                                 25 grams

100mm                                               40 grams

125mm                                               130 grams


Relubrication of rolling element bearings is required on a regular basis to replace grease that has deteriorated, seeped away, or become contaminated. Because the operating circumstances for rolling element bearings vary so much, determining optimum relubrication intervals — which might range from once a day to once a year — requires on-the-spot expertise. Conditions such as operating temperatures, environmental conditions, type of bearings also play an important part in determining the relubrication frequency of ball and roller bearings. Some of the key steps in relubrication include –

  • Wipe any accumulated dirt or grit off the grease nipple or fitting.
  • Pump in the required quantity of grease as detailed below (a standard cartridge gun applies 1gm of grease per shot), making allowance for any leakage at the nipple.
  • Wipe the nipple clean.

The following table summarises the approximate amount of grease to be pumped during relubrication based on the shaft diameter of the bearing –

 Shaft Diameter                            Relubrication Fill

25mm                                                 2-3 grams

50mm                                                 4-5 grams

75mm                                                 8-12 grams

100mm                                              12-20 grams

125mm                                              40-60 grams

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