The wheels of industry turn on bearings, so why do the wheels often vibrate, clatter, squeak, drag, and overheat? Bearings for your vehicles and other plant equipment fail for many reasons. Most failures are related to lubrication and contamination, but myths and misconceptions help perpetuate many easily avoidable problems. These myths fall into three general areas of bearing use: installation, misapplication, and lubrication.
No. 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.
No. 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.
No. 3: It’s fine to hand-tighten setscrews one at a time–False.
Setscrews should be tightened to the manufacturer’s recommended torque. Undertightening can allow the bearing to slip on the shaft. Overtightening 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.
No. 1: Bearings should not be hot to the touch–False.
Normal bearing operating temperatures can range from 80° F to 150° F, but certain applications may run higher or lower. Most bearings are rated for -20° F to 220° F, 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 start up or right after re-lubrication because excess grease increases drag and friction in the bearing. Spikes up to 50° F are normal at start-up, and 30° F after re-lubrication. As the rolling elements purge excess grease through the seals, the bearings return to steady-state temperatures.
No. 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.
No. 3: Sealed/lubed-for-life bearings will last forever–False.
Bearing life depends on grease life, which is affected by the operating conditions (speed and load) and environment (temperature and contamination). Grease life can be improved with enhanced seals, proper installation and proper grease selection. Ultimately, the best bearing is the properly lubricated bearing.