Wear in Roller Bearings

Wear in roller bearings is usually caused by the introduction of foreign particles, inadequate lubrication, or vibrations in the bearing.

Foreign particles, such as grit, can cause wear of the raceways, rolling elements and cage, if they enter the bearing for whatever reason.

If the problem is not dealt with quickly, the amount of abrasive particles increases, as material is worn away from the surface of the machinery. If this problem is allowed to escalate, the bearing can become worn to such an extent that it is unserviceable.

Abrasive particles can enter the bearing if the sealing arrangement is not adequate for the bearing's application. Other causes include using contaminated lubricant, or lack of care during the mounting operation.

One can usually spot the presence of dirt by examining the bearing. Signs of wear include small indentations around the raceways and rolling element, dull or worn surfaces, and discoloured grease, that usually takes a green appearance.

In order to avoid contaminating the bearing with grit or other abrasive particles, make sure you do not unpack the bearing until it is due to be mounted. Keep your tools and surroundings clean and free of dirt, and always use clean lubricant.

Lubricants can play a big part in preventing wear inside a roller bearing, and one should be aware that insufficient lubrication ultimately leads to problems.

The surfaces of the bearing can become worn, almost mirror-like, later colouring from blue to brown. These are tell-tale signs of inadequate lubrication.

When left untreated, the temperature within the bearing begins to rocket, and in some cases may cause the bearing to seize up completely.

If, after regular lubrication, the appearance of the bearing does not change, you should double-check that the lubrication is actually reaching the bearing itself.

Finally, if a bearing is not running, there is no lubricant film between the rolling element and the raceways, leading to metal on metal contact. Vibrations can then cause small movements of these two components, causing small particles to break away from the surfaces. This causes depressions to form within the raceways, sometimes referred to as false brinelling. Obviously the greater the energy of the vibration, the more severe the damage.

The detached particles often oxidise, often giving them a red colour.

It is therefore important to make sure that bearings securely fastened during transportation and provide a vibration-dampening base. Wherever possible you should look to use an oil bath to lubricate the bearing.