Page 178 - Know and Understand Centrifugal Pumps

Bearings

practices are very important. They must be stored correctly and
handled correctly to give good service life. The shaft and housing
dimensions must be within limits specified by the bearing
manufacturer. Shaft to motor alignment is also critical.
You should strictly follow correct and acceptable practices when
removing the old bearing and installing the new one. Cleanliness is
the order of the day. You’ll need a clean work area, clean hands, and
cleaning cloths without fuzz, lint, or strings. So much of premature
bearing failure is the direct result of not observing these basic
concepts.
2. Vibration Brinelling
Maintenance people are not normally familiar with vibration
brinelling, but this is also a common cause of failure. The brine11
marks themselves are small, even invisible indentions in the bearing
raceway. They result fiom vibrations or shocks originating outside
the bearing. Common sources would be cavitation, bent shafts, un-
balanced rotary assemblies; shock thrust loads, slapping v-belts, etc.
These vibrations cause the balls and rollers to jam into the raceways
causing the imperceptible indentations. The races eventually take on
the appearance of corduroy cloth or a washboard effect. It’s like
driving a car at high speed over a rough roadway. The surfaces of
the balls and rollers begin breaking away, thus destroying the
bearing. All bearings coming out of service should be disassembled
to examine the internal rotary and stationary surfaces.
3. Dirt and Abrasion
Careless handling during storage and assembly damages a lot of
bearings and lets dirt get in, thus leading to premature failure. Dirt,
sand and dust contamination between the balls and races of a new
bearing can start a round of ‘false brinelling’, ruining the bearing
even before it goes into service. Dirty sweaty hands, damp cloths,
humid air and even the morning dew can start a rusting process that
will destroy a new bearing. Bearings should be kept clean. Some
studies indicate that more than 90% of all bearing failure is
attributable to abrasive dirt entering the bearing before and during
its installation. A grain of dirt or sand trapped between the ball and
race of a precision bearing has the same effect as running a race with
a rock stuck in your shoe.
Sleeve bearings on some older, slower, larger pump shafts can
withstand dirt contamination better than ball and roller bearings.
This is because the tolerances are not so strict with sleeve bearings,
the surface area of contact is greater, and the lubricant flushing
action is better. The sleeve bearing material of construction is

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