MRO Today
 


MRO Today

False brinelling

Taking care of your bearings during storage

by Enrique Mora

Bearings have made huge contributions to the manufacturing industry. However, bearing failures still cause more than half of the problems in production machinery. Most of the failures result from bearing damage that is preventable or easily delayed.

The problem
Maintenance crews all over the world focus their efforts on keeping production machines going. One strategy to accomplish that is having spare motors, gearboxes and other rotative devices on hand. Storing these items usually is not considered a big deal. The belief is that any area is OK, as long as the spares are protected from rain and other harmful elements. Very rarely is vibration considered as one of those elements.

In many instances, spares are stored on racks near traffic or near pieces of equipment that produce moderate to high vibration. That vibration is an invisible enemy of bearings.

Think about it. When bearings are lubricated, a protective film covers the surface of the races and rotating elements, such as the balls, needles or rollers. While the bearings are in use, at whatever speed, the lubricant film is constantly renewed so no metal-to-metal contact takes place.

But when the rotation ceases, the weight of rotors, shafts and other equipment rests on the bearings, and the lubricant is eventually squeezed out until metal-to-metal contact occurs between the rolling elements and the races.

When that happens, any subsequent vibration will cause a dry hit on a particular point or line of a bearing’s surfaces. Just like a tiny hammer hitting steel, the surfaces (particularly on the races) are prone to denting. This is proved through microscopic analysis.

When the bearings go back to work, the surfaces are not in perfect condition. The bearings begin to heat up with each fall of a roller or steel ball in those microscopic grooves or slots, until the friction increases to the point of destruction.

The solution
If you have rotating spares in your plant, there is something you can do to prevent this effect, called “false brinelling.” Have the people responsible for the spare parts turn the shafts at least once a week. You can purchase colored target labels, or you can make your own, and attach them to the end of the shaft. These round stickers are divided into sectors, each with a different color. Have the person in charge rotate the shaft two or three turns until color “A” reaches the upper position (12 o’clock). The next week, have the turns end with color “B” in that upper position, then color “C” and finally color “D.”

Each time, all of the motors, gearboxes, fans, etc., will have the same color at the 12 o’clock position.

This action will keep bearing components lubricated and healthy.

The conclusion
Many spare elements are damaged after a few weeks of operation as the result of the false brinelling effect. Use of this maintenance method will increase the performance and reliability of your spares, saving you money and helping you avoid downtime.

Enrique Mora is president of Methods, Organization, Resources and Achievement, a consulting company that provides training for manufacturing plants. To learn more, call 866-589-6058, e-mail kaizen@tpmonline.com or visit www.tpmonline.com.

This article appeared in the April/May 2003 issue of MRO Today magazine. Copyright 2003.

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