Machinery Bearings Best Practices: Facts & Fiction
By Ian A. Rubin | Posted: 03/27/2014 1:11PM
The wheels of industry turn on bearings, so why do the wheels often vibrate, clatter, squeak, drag and overheat? Bearings can fail for lots of reasons. Most failures are related to lubrication and contamination, but myths and misconceptions help perpetuate many easily avoidable problems.
Installation Myth 1
It’s okay to hammer a bearing into position if needed – FALSE. Never strike a direct blow to bearing. A hammer blow can leave dents in the raceway that can cause noise and dramatically reduce bearing life. If installation is difficult, first check the shaft diameter and look for burrs, dirt or corrosion. If needed, use a press to slide the bearing on; apply pressure equally on the face of the inner ring.
Installation Myth 2
Off-the-shelf TGP shafting is the best option – FALSE. It’s much more important to know the shaft’s tolerance range to be sure it meets your bearing manufacturer’s spec for diameter and roundness.
Installation Myth 3
It’s fine to hand-tighten setscrews one at a time – FALSE. Setscrews should be tightened to the manufacturer’s recommended torque. Under tightening can allow the bearing to slip on the shaft. Over tightening can distort the raceway or crack the inner ring.
Use the “half-full/full” rule for tightening setscrews: tighten the first setscrew to half the recommended torque, the second setscrew to the full torque, then go back to the first setscrew and apply full torque.
Application Myth 1
Bearings should not be hot to the touch – FALSE. Normal bearing operating temperatures can range from 80F to 150F, but certain applications may run higher or lower. Most bearings are rated for -20F to 220F, but can be supplied with special grease, seals or heat stabilizing processes that allow them to operate at higher temperatures.
Bearings normally run hotter at startup or right after re-lubrication because excess grease increases drag and friction. Spikes up to 50F are normal at startup, and 30F after re-lubrication. As the rolling elements purge excess grease through the seals, the bearings return to steady-state temperatures.
Application Myth 2
Bigger bearings are always better – FALSE. Bigger bearings with a higher load capacity may show a higher fatigue life, but if the load does not achieve the minimum requirement, the rolling elements can skid along the raceway instead of rolling. This can cause high temperatures, excessive wear, lubrication breakdown and bearing failure.
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