Installation

It’s okay to hammer a bearing into position – FALSE. Never strike a direct blow to a bearing. The rolling elements and raceway are hardened, but can still be damaged. If installation is difficult, 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 raceways and rolling elements.

Off-the-shelf TGP shafting is always the best option – FALSE. It’s more important to know the shaft’s tolerance range to be sure it meets your bearing manufacturer’s spec for diameter and roundness. Review manufacturer’s recommendations and measure/specify the correct shaft diameter.

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. Over tightening can distort the raceway or crack the inner ring. Tighten the first setscrew to half the recommended torque, the second setscrew to the full torque. Go back to the first setscrew and apply full torque. 

Application myths

Bearings should not be hot to the touch – FALSE. Normal bearing operating temperatures range from 80 to 150°F, but certain applications may run higher or lower. Most bearings are rated for -20 to 220°F, but can be supplied with special grease, seals or heat stabilising processes that allow them to operate at higher temperatures. Spikes 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. 

  

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 failure.

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.

  

Lubrication myths

Re-lubrication once a year is sufficient – FALSE. The bearing manufacturer’s lubrication recommendations will give amounts and intervals as suggested starting points, but actual lubrication intervals may vary, depending on load, speed, temperature, or environmental conditions. Applications with higher speeds, temperatures, or heavy contamination sometimes require frequent re-lubrication. By contrast, a mounted ball bearing in a lightly loaded, low-speed, clean environment may do fine with re-lubrication at 12 to 24 month intervals. Certain applications may need to be monitored and intervals/amounts adjusted accordingly.

Pumping new grease into a bearing helps flush away contamination. Many mounted bearings are designed to allow grease to enter the bearing cavity as close to the rolling elements as possible. As more grease is added, old grease is pushed out of the seals (if the seals are purgeable). The purged grease carries out contaminants and keeps dirt from the seals.

Always add grease until it purges from the seal – FALSE. If you pump grease into the bearing until it purges out the seal, you probably have completely filled the bearing cavity. Excess grease can increase operating temperature and may create enough pressure to blow the seal out. However, in low-speed or dirty conditions where contamination may easily enter the seals, filling a bearing with grease may help improve performance.

  

If a bearing makes noise, grease should be added – FALSE. If a bearing is making noise, internal damage has likely occurred. This increases over time, with the potential for catastrophic failure. Adding grease may provide temporary relief, but a noisy bearing should be monitored and replaced at the first opportunity. The root of the failure should be investigated either with independent or manufacturer failure analysis.

Any grease will do – FALSE. Greases DO differ. Some may be incompatible because of the different thickeners (soaps) used. When two incompatible greases are mixed, they may thicken and harden or become thin and leak. Grease types can also be incompatible based on viscosity or type of oil in the grease.

Just shoot grease through the fitting – FALSE. Always clean grease fittings and the grease gun tip. It’s good practice to put the grease gun tip in an oil bath or wrap it with a plastic cover to protect it.

 

Ian A. Rubin is director of marketing, mounted bearings, for Sealmaster, System Plast and Browning-branded products at Emerson Power Transmission Solutions.