Mounting Bearings

Bearing manufacturers estimate that more than 15% of bearings, that don’t meet their expected lifetime, fail due to damage caused during the mounting process. These bearings are damaged before they have even begun to work.

Ball bearings are commonly held in their intended position by friction. The shaft onto which a bearing is to be fitted will be machined so that it is intentionally slightly larger than the bearing’s bore diameter. If the bearing is to be fitted into a housing, then the bore in the housing will be machined to be slightly smaller than the outside diameter of the bearing. The resulting ‘interference fit’ holds the bearing in place during use but also provides a lot of resistance during mounting.

Unless due care is taken, the relatively high mounting forces needed to overcome this resistance is often transferred through the rolling elements in ways that they were not designed to tolerate. Common mounting methods such as hammering directly around the outer ring of a bearing to mount it on a shaft, with or without using a length of wood or a pipe to spread the force can force the hardened balls of the bearing into the hardened face of the running groove. In the worst cases actual visible dents inside the groove may be made which can be heard and felt when the bearing is turned. More often the damage is not immediately visible but micro-cracking forms beneath the surface and these tiny cracks spread and grow under the normal operating stresses until they reach the surface and cause hard metal chips to detach and further damage the moving parts.

 The simatherm range of induction heaters is one way of avoiding this damage, by precisely heating either the bearing (to be fitted over a shaft), or the housing (for the bearing to be fitted into) so that they expand enough to be mounted with zero force. Once in place they cool and resume their normal dimensions without any undue stress on the rolling elements. This is quick, clean and the best way to mount bearings in many circumstances. The simatherm range includes precisely-controlled hot plates that can heat multiple small bearings and are therefore ideal for serial production tasks. The Volcano is a portable unit that weighs only 3.5 kg but can heat parts of up to 10 kg. The more conventional induction heaters in the range cover bearings of up to 120 kg.

There are circumstances where an induction heater cannot be used. Obviously if power is not available then the heater will not work, but also in circumstances where e.g. a bearing supports a shaft as it passes through the wall of a housing. In this latter case it may be necessary to position the bearing while the other parts are already in position.

For these applications simatec offer the FT-33 fitting set. This is a kit that does use a hammer and a pipe but adds a set of precisely moulded rings that ensure that mounting forces are only applied to a bearings inner and outer ring and never via the rolling elements. Each ring has an inner and outer diameter that matches a bearing size and an impact face flat to within 0.1mm across the whole surface. The hammer in the set is a sturdy metal deadfall type with plastic faces on the head – a useful tool in its own right. The set contains 3 different diameter anodised aluminium impact sleeves ribbed longitudinally for good radial grip but longitudinal slip.

The 33 rings suit bearings with a maximum internal diameter of 50 mm. They are moulded in a fibre reinforced polymer to very tight tolerances to provide an ideal mix of stiffness and toughness and will not distort over time. We consider this 50 mm ID the practical limit of what is comfortable and practical with this type of impact assembly.

Recognising that bearings of 55 mm and 60 mm are still relatively common sizes we decided to add another option to our mounting methods. The brand new FT-P kit allows the mounting of these larger sized bearings using a mechanical press. Following analysis of the mounting forces and deflection characteristics of various materials it was decided to produce the new larger rings in anodised aluminium. The supplied short sleeve is a press fit into the rings and has a flat cap to make use with a press straightforward. The cap has a central hole and a grub screw, allowing an easy way for a permanent mount on the press if required.

To provide users of the FT-33 with more flexibility an adaptor for the larger C-rings from this kit is also included so that a press may be used instead of a hammer for the larger sizes where this makes sense.

Simatec have more than 30 years’ experience ensuring that bearings reach their performance potential. For users of our heaters and tools this means the elimination of premature failure and unexpected breakdowns. Ensuring that bearings survive the mounting process in good condition is critical. FT-P adds another unique way to do this.