Maintenance of bearings

Reasons for high bearing temperature

This may be due to

• Excessive quantity of grease causing churning
• Inadequate grease due to deterioration or leakage
• Misalignment, causing friction and excessive axial forces
• Loose fit of the bearing housing, causing both inner and outer races of the bearing to rotate inside the housing
• Corrosion or the presence of foreign matter in the bearing.

Any of the above reasons may result in noise and an increase in temperature and must be corrected. Critical installations such as a refinery, a petrochemical plant, a chemical plant or a petroleum pipeline may require special precautions and control to avert any excessive heating of the bearings, which may become fire hazards. For these installations, bearing temperature detectors with a relay and alarm facility may also be installed in the control circuit of the switching device to give warning or trip the motor if the temperature of the bearing exceeds the preset safe value.

Maintenance of bearings

Grease may leave skin effect on the races of the bearings if the motor is stored idle for a long period. This may cause noise during operation and overheating of the bearings. After a long period of storage grease may also dry and crack, and produce these effects. To detect this, bearing covers may be opened and the condition of the grease and any skin effects checked. If such marks are visible, the bearings must be taken out and washed thoroughly in petrol or benzene to which is added a few drops of oil, and then re-greased with a recommended grade and quantity of grease. Quantities of grease above recommended levels may cause heat the same way as quantities below recommended levels.

Cleaning bearings

For cleaning bearings and bearing housings, before applying the grease, only the following fluids should be used: benzene, white petrol and benzole (white petrol is the most recommended).