Example of Bearing Mounting Errors

The correct installation of bearings is very important, but it is always easy to run off in the actual operation, and the problems are endless. The reason is that some details are not noticed, leading to bearing damage during installation, this article shares several error examples of bearing installation, and correct installation methods and tips.

Demonstration of common errors in bearing instalation

A. Loose fit between shaft and bearing bore

Sliding between the shaft and the surface of the bore is caused by the loose fit. The sliding friction will cause heat generation, causing the bearing to be damaged due to heat generation.

[Sliding mark between the shaft and the surface of the bore]

1) Cracks caused by friction heat between the end face of the inner ring and the shaft shoulder

When the inner ring and the shaft are under loose fit, the sliding friction between the end of ring and the shaft shoulder will cause higher temperature due to the small contact surface, then the thermal cracks will appear and extend, and finally lead the inner ring with fracture in operation.

2) Adhesion between shaft and bore surface caused by heat generation

Due to the loose fit of the shaft and bearing bore, sliding friction occurs between the surfaces of the two components, causing high temperatures that melt the surface metal and create adhesion.

B. Shell bore fits loosely with bearing out ring

Sliding between the bearing outer ring and the bore of mounting housing caused by the loosely fit. The sliding friction will cause heat generation, which will damage the bearing.

[Sliding mark between the shell aperture and the bearing outer diameter surface]

1) Hammer directly strikes the bearing

When Installing the inner ring (or outer ring) interference fit bearings, using a hammer to hit the bearing inner ring (or outer ring) end face are prohibited, because it is easy to hurt the edge of the rings.

2) Transferring mounting force by rolling elements

When installing a bearing with an interference fit on the inner ring, the force cannot be transmitted to the inner ring through the outer ring and rolling elements. Because knocking the bearing raceways and rolling element surfaces, will cause the bearing noisy and prematurely damaged during operation. The correct method should be to use the sleeve directly to the force on the inner ring end face.

C. Excessive heating temperature

Some users heat the bearing bore with an acetylene torch. When the heating temperature exceeds 727°C (the phase change temperature of bearing steel), the internal metallographic organisation of the bearing steel will change. When the bearing cools down, the bearing bore will not be able to return to its original size, which is usually larger than the size before heating.

[Bearing heated by acetylene torch, surface turns black]

Bearing correct instal method:

Mounting of bearings should be carried out as far as possible in a dry, dust-free area and away from equipment that generates metal shavings and dust. When mounting must be done in complex environments, contamination should be minimized.

Engineers should choose mechanical, thermal or hydraulic methods of installation depending on the type and size in the actual practice.

A. Cylindrical Ball Bearing mounting

1) Cold installation

When mounting small bearings with a fit that is not too tight, the bearing can be mounted in the proper position by means of a sleeve and hammering the bearing into place by gently tapping the sleeve. The hammering should be applied as evenly as possible to the bearing collar to prevent the bearing from tilting or skewing.

Most bearings are mounted using the press-in method. If the inner and outer rings of a bearing are to be fitted onto the shaft and into the housing at the same time, it must be ensured that the same pressure is applied to both the inner and outer rings at the same time and must be in the same plane as the contact surface of the fitting tool.

2) Thermal installation

As a rule, the mounting of larger bearings is not possible without heating the bearing or housing, since the force required for mounting increases with increasing size. The temperature difference between the bearing collar and the shaft or housing required for hot mounting depends mainly on the amount of interference and the diameter of the bearing fit.

Open bearings must not be heated to temperatures exceeding 120 °C. It is not recommended to heat bearings with seals and dust caps above 80 °C (it should be ensured that the temperature does not exceed the permissible temperature of the seals and grease). When heating the bearings, the heating should be uniform and there should never be localized overheating.

[Bearing induction heaters]

B. Tapered Roller Bearing mounting

Most of the inner rings of bearings with tapered bores are fitted with an interference fit. The amount of interference is determined by the inner ring in the conical shaft diameter, tightening sleeve or unloading sleeve on the axial push distance. The greater the advancement distance on the tapered mating surface, the smaller the radial internal clearance of the bearing can be determined by measuring the clearance reduction or axial advancement distance to determine the amount of interference.

Small and medium-sized bearings can be mounted using a bearing mounting tool or, preferably, a locknut to push the inner ring into the appropriate position on the tapered shaft diameter. In the case of tight sets, use a sleeve nut that can be locked with a hook spanner or impact spanner. For the withdrawal sleeve a bearing mounting tool or end plate can be used to push it into the bearing bore.

Larger bearings require more force for mounting and therefore hydraulic nuts should be used. Hydraulic nuts can be used to mount tapered bore bearings on tapered shaft diameters (Fig. 1), on tightening sleeves (Fig. 2), and on withdrawal sleeves (Fig. 3).