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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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