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Practical Solutions to Machinery and Maintenance Vibration Problems

Chapter 8, Vibration in Bearings

Section 5, Use of IBF Units to Accurately Determine Bearing Lubrication

One of the challenges of maintenance departments worldwide is to develop effective lubrication programs for the many grease lubricated rolling element bearings. In an effort to ensure that a bearing is not lost due to lack of lubrication, there is a strong tendency to over-lubricate rolling element bearings. Over-lubrication is probably responsible for more bearing failures than under-lubrication. There have been several approaches over the years to solve lubrication problems of rolling element bearings. Some special instruments have built-in computers. Strong claims are made for their effectiveness. Others use certain features of their regular vibration instruments, such as measuring IBF units. However, none of these approaches address the question of how much grease the bearing needs. A fully sealed bearing does not require regreasing through the course of its life, which if correctly installed in a machine that is well balanced and well aligned, can run in excess of 10 years. Why is it, therefore, that relubricating bearings can be called for every few months? The usual answer is, "To flush the bearing of contaminants." However, if the bearing lip seals are in good condition, there should be no contaminants and, therefore, no requirement for regular lubrication.

This is not a section on bearing lubrication. Its focus is only on how some specialists use IBF units to accurately determine the quality and quantity of bearing lubrication in rolling element bearings. IBF measurements are made on a regular basis, watching for significant change. When significant change occurs, the technician verifies the initial data. Then, while monitoring the IBF reading, grease is applied. After applying two or three pumps of the grease gun, the technician pauses for a few seconds while observing the IBF reading. Typically, the reading decreases. Grease is applied until no further reduction in the IBF reading can be obtained. At that point, the bearing is considered to be properly lubricated. The bearing should be monitored for 10 to 15 minutes after the process to ensure that the IBF reading does not increase. If it does, the process is repeated. Sometimes overgreasing will show an IBF increase.

The bearing should then be checked 24 to 48 hours later to ensure no further increase has occurred. A return to previous levels probably means the bearing is starting to fail. It is possible to temporarily reduce the IBF readings on severely defective bearings by applying grease.


 

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