Protecting Shaft with Heat Dismounting

Bearing removal usually receives less attention to detail than mounting operations. That's because most dismounted bearings are not reused. In the field, mechanics often pound used bearings off with a hammer or cut them off with a torch.

Bearing dismounting may become necessary when a machine functions improperly or is being overhauled. At these times, heating devices can play an important role in bearing dismounting. They are especially useful in situations where mechanical dismounting is difficult.

Even if the dismounted bearing will not be used again, it's important to exercise care. The shaft, housing and adjacent components are often reusable and can be damaged by careless dismounting. For example, if you use a hammer to dismount a slightly cocked bearing, the shaft can be smeared and gouged in the process.

Two of the most common heating devices designed for dismounting the inner rings of cylindrical roller bearings are aluminum heating rings and adjustable induction heaters. Heating rings are equipped with handles to make positioning on the shaft easier and facilitate bearing removal. For larger bearings with bores of 200 mm (7.87 in.) and more, a special locking device eases the task of tightening the ring around the bearing.

When dismounting with a heating ring, first remove the bearing's outer ring and cage assembly, then couat the inner ring with an oxidation-resistant oil. Heat the aluminum heating ring to about 280C (536F) by means of a hot plate and place it around the bearing's inner ring. Press the heating ring handles together and rotate the tool until the bearing's inner ring comes loose from the shaft.

Adjustable induction heaters are recommended for frequent dismounting of various sizes of cylindrical roller bearings. These heaters raise the temperature of inner rings by inducing electric currents. The heaters generally consist of a circular yoke on which movable yokes made of laminated iron are attached. By pressing handles on both sides of the heater, a technician can adjust the yokes to accommodate different bearing sizes. The heaters are available off the shelf for inner ring diameters ranging from 80 to 170 mm (3.15 10 6.7 in.). Heaters for larger bearing sizes usually have to be made to order.