7 reasons bearings fail early, and how to prevent it

The maintenance trade reckons that fewer than one bearing in ten actually runs to its theoretical life. Every one of the rest fails for a reason that could have been prevented.

1. Incorrect lubrication

Too little grease and too much grease both cause damage. Too little leads to metal-to-metal contact; too much causes heat to build up until the grease degrades. Using the wrong type of grease, or mixing two different types, can also break down the soap structure.

2. Contamination getting into the bearing

Dust, metal particles and water are the real enemies. A particle only a few microns across passing through the contact surface leaves an indentation that can spread into spalling. Check the condition of the seals regularly and replace the oil seals every time the assembly is opened.

3. Fitting it the wrong way

Hammering directly on the ring, or driving the force through the rolling elements, leaves permanent marks in the raceway. The correct method is to apply force only through the ring that is an interference fit, or to heat the bearing with an induction heater to no more than 120 degrees Celsius.

4. Misalignment and shaft / housing tolerances

Shaft and housing tolerances have a direct effect on how load is distributed. If the shaft is worn or the housing bore is oversized, the bearing will creep in the housing and wear quickly. Always measure the shaft and the housing before fitting a new bearing.

5. Too much load, or too little

Overloading fatigues the contact surfaces quickly, but what many people do not realise is that too little load is dangerous too: the rolling elements skid instead of rolling, which generates heat and smearing — especially in cylindrical roller bearings at high speed.

6. Electrical current passing through the bearing

In inverter-driven motors, stray current can pass through the bearing to earth, leaving rows of tiny burn marks known as fluting. The remedy is an insulated or ceramic coated bearing, or a shaft earthing brush.

7. Poor storage

Keep bearings in their original packaging until the moment they are fitted, store them somewhere dry and off the floor, and keep them away from anywhere that vibrates continuously — vibration causes the indentations known as false brinelling even before the bearing has been used.