Continuous lubrication assists in preventing damage caused by vibration to both moving and stationary bearings.
Separation of the rolling elements of a ball or roller bearing depends on hydrodynamic lubrication – the maintenance of a continuous presence of a very thin – micron sized – elastohydrodynamic film of lubricant between rolling elements and raceways.
This oil film that protects the surfaces from damage is formed as the bearing rotates. When the bearing is stationary and is in the presence of vibration, this film will be lost and vibration will cause raceway wear. This can also occur in certain vibration and rotational conditions in rotating bearings.
Vibration-caused wear that occurs in boundary friction conditions results in small particles breaking away from the surfaces in contact with each other, causing damage known as fretting or false brinelling. Bearings and races appear smooth however they are microscopically rough.
High points on the contact surfaces break off under concentrated load in the absence of lubrication. This wear leads to the formation of depressions in the raceways at intervals corresponding to the pitch of the rolling elements – sphered cavities for ball bearings and fluted rectangular shaped cavities for roller bearings. Rust may also be present from the oxidation of the small detached particles.
The damage is directly proportional to the severity of the vibration and the time period. It mainly occurs on the races, not the balls or rollers.
Roller bearings are more affected than ball bearings. The most damage occurs to roller bearings as the balls in ball bearings can roll in every direction and are thereby able to offset some vibration induced movements that otherwise would result in sliding, as occurs with the unidirectional rollers, cylindrical rollers being the most affected.
Machinery that is not in operation and is close to vibration sources will be susceptible to vibration induced bearing damage. Standby equipment such as pumps, motors, fans, generators and similar, or process equipment that is idle because of reduced production volumes, or stopped due to an extended maintenance requirement, is potentially at risk from this type of damage.
The onset of vibration-induced bearing damage will occur more quickly if the bearing is not correctly lubricated prior to being stopped. Continuous automatic lubrication will provide the best outcome in this regard.
Vibration also causes fretting damage in moving bearings where inadequate lubrication allows surface contact. If the lubrication is poor and the effect of vibration is severe enough, contact between the surfaces may result, even though the rolling elements are rotating. Because this damage is directly related to inadequate lubrication, continuous lubrication, with the correct lubricant, will provide a solution to the problem
Excessive bearing vibration can also cause lubricant problems which have the same wear effect as irregular regreasing of bearing contact surfaces. It may cause the grease to be broken down into the oil and the thickener; that is, the oil separates from the thickener.
GreaseMax lubricators provide continuous grease replacement that will assist in preventing problems cause by vibration.