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Bearings have been, no doubt, one of
the key elements of the progress that we enjoy today. Their failure though, cause more
than 50% of the problems in the industrial world. The causes for those failures or damages
in bearings, can be prevented or at least delayed in several ways. Of course lubrication
is a very important resource and the most commonly known, applied and some times ignored.
Maintenance crews all over the world focus most of their efforts on the best way to keep
machines going. One of the strategies to accomplish that responsibility consists of having
spare motors, gearboxes and some other rotative devices. The storage of such, is usually
not considered a big deal. Any area will be OK, as long as they are protected from the
rain and other calamities, but not very often is vibration considered one of those. In
many cases, they are stored on racks near traffic or pieces of equipment that produce
moderate to high vibration. That vibration is an invisible enemy of bearings.
Think about it. When a ball bearing
is lubricated, a protective lubricant film covers the surface of the races and rotating
elements such as balls, needles or rollers. While they are running, whatever the 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, etc., rests on the bearings, and the lubricant is eventually
squeezed out of the way until metal-to-metal contact is reached between the rolling
elements and the races. Not only that, but any vibration that may happen, will cause a dry
hit on a particular point or line of their surfaces. Just like a tiny hammer hitting on
steel, the surfaces (more likely the races' surfaces) will be dented. This has been proven
through microscopic analysis. Then, later on, when the bearings go back to work, those
surfaces are not as perfect as they used to be, the bearings start warming up with each
"fall" of a roller or steel ball in those microscopic groves or slots, until the
friction increases to the point of destruction.
If you happen to have some 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 per week. There are some colored target labels, or you can make your
own, that you can put at the end of the shaft. These round stickers are divided in sectors
each sector has a different color. Have the person in charge rotate the shaft two or three
turns until color "A" reaches the upper position (12:00 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 the motors, gearboxes, fans,
etc. will have the same color pointing the 12:00 o'clock position. You will be saving a
lot of downtime and money by doing that. Many spare elements are damaged just after a few
weeks of operation just because of the False Brinelling effect.
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