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Installing large diameter bearings on rotating equipment and oscillating applications

Many things can go wrong during and after installation of a large diameter bearing. Fortunately, there are steps you can take to prevent many of them.

The installation of a large bearing should be done in a clean, dry area. Mounting surfaces and housing pilots should be unpainted and wiped clean prior to assembly, as dirt or chips will cause high spots if trapped between the mounting surfaces. Inspect the mating surfaces and remove any nicks or burrs.

The protective wrapping applied by the manufacturer can now be removed and the bearing hoisted by the use of eye bolts in the mounting holes, or by non-metallic slings. This will prevent damage to the exposed gear teeth or mounting surfaces.

The bearing should be mounted so the loading plug is in an area of minimum load. If the plug is in the rotating race, it should be located 90 degrees from the maximum moment loading zone. If the plug is in the stationary ring, its location will depend on the position of the minimum load zone relative to the stationary part of the machine.

The manufacturer's recommendations for size and diameter of fasteners should be followed. Usually, SAE grade 5 bolts are specified, but in some cases higher strength bolts may be necessary. An increase to Grade 8 bolts will usually increase proof load by 40% and therefore decrease the number of bolts and bolt holes required. If rigidity factors are maintained, the use of Grade 8 bolts might create a considerable cost advantage due to the decreased amount of drilling required.

Applying the proper torque

It is critical that the proper torque be applied to each bolt during installation. Fatigue failure of a bolt can result if the bolt preload (resulting from applied torque) is not greater than the dynamic load on the bolt.

Hardened flat washers or preload-indicating washers should be used to distribute the bolt load under the bolt head and prevent crushing of the area surrounding the bolt hole.

Care must be taken when mounting bearings with weld hands, to ensure that the welding does not distort the bearing when cool. Changes in bearing clearance and out-of-roundness will affect performance and life. It is a good practice to tack the bearing down every six inches along the weld band before the final weld head is laid.

After the mounting, the bearing should be checked for torque level and evenness of torque during rotation. This level can be compared to the torque of the unmounted bearing, to give the assembler a final indication of the flatness of mounting surfaces. If excessive torque is developed, remove the bearing and check mounting surfaces.

Lubrication

Most large bearings are shipped from the manufacturer already lubricated. They should be kept in their shipping container and stored horizontally until ready for installation. Long-term storage may require re-greasing of the bearing before installation.

Regular lubrication and bolt torque checks will help maximize the life of your bearing operation. Find out more about large slewing ring bearing maintenance.