The industry of wheels turn on bearings, so why do the wheels often vibrate, clatter, squeak, drag and overheat? Bearings can fail for lots of reasons. Most failures (as shown in Figure 1) are related to lubrication and contamination, but myths and misconceptions handed fromwheel bearings, one generation of maintenance engineers to the next help perpetuate many easily avoidable problems. These myths fall into three general areas of bearing use: installation, misapplication and lubrication.
Figure 1 – Sources of bearing wear or failures
Installation myth #1: It’s okay to hammer a bearing into position if needed – FALSE.
Never strike a direct blow to a bearing. The rolling elements and raceway are hardened, but can still be damaged. 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, look for burrs, dirt or corrosion on the shaft. If needed, use a press to slide the bearing on. Apply pressure equally on the face of the inner ring to avoid damaging the raceways and rolling elements.
Scratching, gouging and general wear
in the bore of an inner ring and on the OD of a shaft are indications of
loss of lock. Sometimes, the setscrew tips will also be worn. Fretting
wear can be present on the surfaces and is sometimes a precursor form of
wear prior to loss of lock.
This can be caused by improper tightening of the locking mechanism, undersized/worn/damaged shafting, frequent start/stop operation, or hardened or stainless steel shafting that prevents set screw penetration or holding.
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. Review the bearing manufacturer’s recommendations and measure/specify the correct shaft diameter.
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.