94-09 Mounting & Dismounting Cylindrical Bore Bearings

Proper mounting practices eliminate unnecessary bearing damage during installation. Bearings should never be struck directly with a hammer or a drift as damage may result. Only evenly distributed force should be applied over the entire bearing ring face. When fitting both rings simultaneously, pressure should be applied to both rings to avoid indentations in the raceway or rolling elements.

Cold Mounting
Interference fits require even more care during installation due to the bearing having a smaller bore or a larger outside diameter than the mating part. Bearings with relatively small interference fits can be press fit at room temperature by using a sleeve against the ring face as shown in figure 1. Bearings are frequently mounted by striking the sleeve with a hammer; however, if available, a mechanical or hydraulic press will apply a more uniform force.

When mounting a non-separable bearing on a shaft and in a housing at the same time, a pad that distributes the fitting pressure evenly over the inner and outer rings should be utilized as shown in
figure 2.

Heated Mounting
Bearings with large inner ring interference (and large bore bearings), require a considerable amount of force to mount at room temperature. Mounting in these cases is facilitated by heating and thus expanding the inner ring. The amount of heating required depends on the amount of interference and the shaft diameter.

A commonly used method to heat bearings is to immerse them in hot oil. To avoid overheating, the bearing should be suspended inside the heating tank on a wire grid. Never bring bearings in direct contact with the heating element or bottom of the heating tank.

Another commonly used method to heat bearings, including pre-lubricated sealed and shielded types, is by using a hot plate. Gaps between the inner ring and the abutment are avoided by holding the inner ring against the shaft abutment during cooling.

It is essential to apply heat uniformly throughout the entire bearing. It is recommended that a torch not be used to heat the inner ring during installation due to the very high localized heat torches produce. No matter what method is used: NTN Bearings should never be heated above 120°C (248°F)

Outer Ring Fitting
For outer ring interference fits, the outer rings of small type bearings can be pressed in at room temperature. Installation of large interference fits and large size bearings is assisted by heating the housing or cooling the outer ring before installation. When cooling the outer ring, extreme care must be taken to prevent corrosion due to moisture from the atmosphere condensing on the cooled parts. Parts should be dried after they have been mounted and should be coated with a suitable rust preventative compound.

Dismounting Cylindrical Bore Bearings
When dismounting bearings during maintenance and inspection procedures care must be taken not to damage any components of the bearing or accompanying machinery. When removing inner or outer rings that have been installed with interference fits, the dismounting force should be applied to that ring only.

For small bearings, bearing pullers or hydraulic presses as shown in figure 3 are commonly used for dismounting. Large bearings that have been in service for a long period of time and installed with interference fits require considerable dismounting force. In addition, fretting corrosion is likely to have formed on the mating surfaces, further complicating dismounting.

In some designs, consideration has been given to overcome this dismounting difficulty by injecting oil between the mating surfaces. If available, special induction heaters may also be used to expand the inner rings before disassembly.

A dismounted bearing should only be reused if it is not damaged and has not reached its fatigue life.