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Dismounting

Performance and operating conditionsBearing type and arrangementBearing sizeLubricationOperating temperature and speedBearing interfacesBearing executionSealing, mounting and dismounting

There are several reasons why bearings may need to be dismounted. For example, the bearings may need to be replaced or they may have to be removed to access other components. If bearings are to be used again after dismounting, the force used to dismount them must never be applied through the rolling elements.
With separable bearings, the ring with the rolling element and cage assembly can be removed independently of the other ring. With non-separable bearings, the ring having the looser fit should be withdrawn from its seat first. To dismount a bearing with an interference fit, the tools described in the following section can be used. The choice of tools depends on the bearing type, size and fit (→ SKF methods and tools [PDF]). Bearing sizes are categorized as follows:
  • small →  d ≤ 80 mm 
  • medium-sized →  80 mm < d < 200 mm 
  • large →  d ≥ 200 mm
Dismounting bearings fitted on a cylindrical shaft seat

Cold dismounting

Small bearings can be dismounted from a shaft by applying light hammer blows via a suitable drift to the ring side face, or preferably by using a mechanical puller. The claws must be applied to the inner ring or an adjacent component (fig. 1). Dismounting is made easier if slots for the claws of a puller are provided in the shaft and/or housing shoulders. Alternatively, tapped holes in the housing shoulder can be provided to accommodate push-out bolts (fig. 2).

Medium-sized and large bearings generally require greater force than a mechanical tool can provide. Therefore, SKF recommends using either hydraulically assisted tools or the oil injection method, or both. Using the oil injection method assumes that the necessary oil supply ducts and distribution grooves have been designed into the shaft (fig. 3).

Hot dismounting

Dismounting by heating is a suitable method when removing the inner rings of needle roller bearings or cylindrical roller bearings of the type NU, NJ and NUP. Two different tools for this purpose are common: heating rings and adjustable induction heaters.

Heating rings are typically used to mount and dismount the inner ring of small to medium-sized bearings that are all the same size. Heating rings are made of light alloy. They are radially slotted and equipped with insulated handles (fig. 4).

If inner rings with different diameters are dismounted frequently, SKF recommends using an adjustable induction heater. These heaters (fig. 5) heat the inner ring rapidly without heating the shaft. Read and follow the safety precautions below.

Special, fixed induction heaters have been developed to dismount the inner rings of large cylindrical roller bearings (fig. 6).

Induction heaters and heating rings are available from SKF. For additional information, refer to Maintenance products and the SKF bearing maintenance handbook.

WARNING

Fire hazard. Never use an open flame for hot dismounting.

Dismounting bearings fitted on a tapered shaft seat
Small bearings can be dismounted using a mechanical or hydraulically assisted puller that engages the inner ring. Self-centering pullers equipped with spring-operated arms should be used to simplify the procedure and avoid damage to the bearing seat. If it is not possible to apply the claws of the puller to the inner ring, withdraw the bearing via the outer ring or use a puller in combination with a pulling plate (fig. 7).

It is much easier and safer to dismount medium-sized and large bearings when the oil injection method is used. This method injects oil, under high pressure, between the two tapered mating surfaces, via a supply duct and a distribution groove. This significantly reduces the friction between the two surfaces and separates the bearing from its seat (fig. 8).

WARNING

To avoid the risk of serious injury, attach a provision such as a lock nut or end plate to the shaft end to limit the bearing travel when it suddenly comes loose.

Dismounting bearings fitted on an adapter sleeve
To dismount small bearings fitted on an adapter sleeve and a plain shaft, loosen the sleeve lock nut a few turns, then use a hammer of suitable size to tap a small steel block evenly around the bearing inner ring side face (fig. 9).

For small bearings fitted on an adapter sleeve and a stepped shaft with a spacing collar between the shoulder and the bearing side face, loosen the adapter sleeve lock nut a few turns and apply a couple of sharp hammer blows to a dolly abutting the sleeve lock nut (fig. 10).

Using a hydraulic nut for dismounting bearings fitted on an adapter sleeve and a stepped shaft with a spacing collar makes bearing dismounting easy. However, to use this method, you should mount a suitable stop that abuts the piston of the hydraulic nut (fig. 11). If the sleeves are provided with oil supply ducts and distribution grooves, dismounting becomes easier because the oil injection method can be used.

Dismounting bearings fitted on a withdrawal sleeve
When dismounting a bearing fitted on a withdrawal sleeve, the locking device (for example a lock nut or end plate) must be removed.

Small and medium-sized bearings can be dismounted with a lock nut and a hook or impact spanner (fig. 12).

Medium-sized and large bearings fitted on a withdrawal sleeve can be easily dismounted using a hydraulic nut.

Withdrawal sleeves with a bore diameter ≥ 200 mm are provided, as standard, with two oil supply ducts and distribution grooves in both the bore and outside surface. When using the oil injection method, two hydraulic pumps or oil injectors and appropriate extension pipes are needed (fig. 13).

WARNING

To avoid the risk of serious injury, attach a stop behind the hydraulic nut at the shaft end (fig. 14). The stop prevents the withdrawal sleeve and hydraulic nut from shooting off the shaft if the sleeve separates suddenly from its seat.

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