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Bearing Failure Due to Over Lubrication

At many industrial facilities, the task of equipment lubrication is often assigned to a newly hired maintenance technician or mechanic with little or no lubrication training who is just learning the ins and outs of the plant. Often times these mechanics are handed a grease gun and told to lubricate the points on a particular line or maybe the entire plant. To the maintenance supervisor, this seems like a good way to familiarize the new mechanic with the plant’s equipment. To the new mechanic, he is performing an important task that is helping to increase bearing life. Both the maintenance supervisor and mechanic are right but they are also wrong.

Certainly, assigning a new mechanic the task of equipment lubrication will help familiarize him with the plant’s equipment, but at what cost? The new mechanic is correct in believing that he is performing an important task, but is the way he performs the task actually increasing bearing life? The answer depends upon how well the new mechanic has been trained. More than 35% of bearing failures can be attributed to improper lubrication. An enthusiastic but untrained lube tech with a grease gun is more than likely to cause premature bearing failures due to over greasing than he is due to under greasing.

Over greasing a bearing will cause the rollers or balls to slide along the race instead of turning, and the grease will actually churn. This churning action will eventually bleed the base oil from the grease and all that will be left to lubricate the bearing is a thickener system with little or no lubricating properties. The heat generated from the churning and insufficient lubricating oil will begin to harden the grease (see Fig. 1). This will prevent any new grease added to the bearing from reaching the rolling elements. The end result is bearing failure and equipment downtime. Ironically, an attempt to sufficiently lubricate a bearing by giving it several extra pumps from a grease gun will eventually result in its failure due to under lubrication.

Over lubricating the bearings in an electric motor causes an additional problem that will negatively effect the efficiency of the motor resulting in higher operating costs. The excess grease pumped into the bearing will eventually work its way into the stator body and the rotor assembly will distribute the grease throughout the windings (see Fig. 2). This will not only cause the motor to operate inefficiently because the grease will be insulating the windings, but it could also effect the operation of the fan and cause excessive heat within the motor.

The key to preventing the over lubrication of bearings is to ensure that all maintenance personnel are trained on proper lubrication techniques including how to determine the correct amount of grease to pump into a bearing (see Fig. 3). Establishing a sound overall maintenance program that includes lubrication intervals for each asset in your facility or even condition monitoring using ultrasonic technology will not only decrease maintenance costs; it will decrease downtime as well. Contact your Bel-Ray representative for suggestions.