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Mounting Bearings Using Heat
The force needed to mount a bearing
increases rapidly with bearing size. Because of the mounting force
required, larger bearings cannot easily be pressed onto a shaft or into
a housing. Therefore the bearing or the housing is heated before
mounting.
Principle of induction heating
An induction heater can be compared to a
transformer using the principle of a primary coil with a large number of
windings, and a secondary coil with a few windings, on a mutual iron
core. The input/output voltage ratio is equal to the ratio of the
windings, while the energy remains the same. Consequently, the secondary
coil will provide a low voltage at a high amperage. In the case of the
SKF induction heater, the bearing is a short circuited, single turn,
secondary coil through which a low A.C. voltage flows at high amperage,
thus generating high heat. The heater itself, as well as the yoke,
remains at ambient temperature. As this type of heating induces an
electric current, the bearing will become magnetised. It is important to
ensure that the bearing is then demagnetised so that it will not attract
metal particles during operation. All SKF induction heaters have
automatic demagnetising cycles.
Hot mounting
The temperature difference between the
bearing and seating depends on the magnitude of the interference fit and
the bearing size. Normally a bearing temperature of 80 to 90 °C (144 to
162 °F) above that of the shaft is sufficient for mounting. Never heat a
bearing to a temperature greater than 125 °C (257 °F), because the
material may change metallurgically and produce alterations in diameter
or hardness. Local overheating must be avoided and in particular never
heat a bearing using an open flame. Wear clean protective gloves when
mounting a hot bearing. Lifting (hoisting) gear can facilitate mounting.
Push the bearing along the shaft as far as the abutment and hold the
bearing in position, pressing until a tight fit is obtained.
Lifting gear
Never heat a bearing using an open flame
SKF supplies a full range of heating
tools, such as induction heaters and electric plates with an adjustable
thermostat and cover for all common mounting needs.
SKF m20 concept
“m20” represents the weight
(kg) of the heaviest SRB 231 bearing which can be heated from 20 to 110
°C (68 to 230 °F) in 20 minutes. This defines the heater’s power output
instead of its power consumption.
Selection guide
There are no totally restrictive guidelines to follow when choosing your
SKF bearing heater. It will depend upon the type and geometrical
dimensions of the components you want to heat. Nevertheless, SKF offers
the following helpful general selection guide.
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