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How to choose the right fitting tool for your bearing

Bearings are an essential component in extending the service life of machinery by reducing the coefficient of friction between moving components and distributing rotating forces.

Bearing can be fitted in numerous ways, but the optimum methods fall into three categories: mechanical, heat and oil injection. Poor bearing fitting practices (often using brute force) are responsible for around 16% of premature bearing failures, so it’s easy to see why the choice of method for bearing mounting is so important.

Mechanical fitting methods

What is mechanical fitting?

Mechanical fitting (not to be confused with brute force) involves using controlled force to fit the bearing, whilst protecting the bearing components from damage using tools such as impact rings.

Mechanical methods are a quick, convenient and economical method of mounting bearings. However, if not done correctly, mechanical mounting can lead to internal bearing damage, causing misalignment and eventually premature failure of the bearing.

Where is it appropriate to use mechanical methods to mount a bearing?

Mechanical methods of fitting are appropriate for bearings with an inner diameter of between 10mm and 55mm, and an outer diameter of between 26mm and 120mm. Mechanical fitting can be useful where heat is not appropriate but should not be used on bearings outside of these diameters.

What products are available?

SKF’s bearing fitting toolkits are ideal for the mechanical mounting of bearings. TMFT 24 contains 24 impact rings, whilst TMFT 36 contains 36 impact rings. Both kits also contain 3 impact sleeves and a dead-blow hammer, presented in a lightweight carrycase for easy storage.

Heat fitting methods

What is heat fitting?

Applying controlled levels of heat to a bearing enables the bearing to expand sufficiently to slide onto the shaft with ease. Bearing fitting methods which use heat can reduce the risk of incorrect mounting, helping to prevent bearing damage and premature bearing failure.

Although still in use, the methods of oil baths and propane torches are fraught with problems, including the spread of contamination, accurate measurement of temperature and consistency of temperature.  Therefore, the recommended method of heat mounting is through the use of an induction heater.

Where is it appropriate to use heat to mount a bearing?

Heat is an appropriate method of mounting for a vast range of bearings, thanks to the wide selection of induction heaters available. Heat is often the method of choice for safely mounting medium to large sized bearings.

Heating methods may not be appropriate for certain bearings or sealing arrangements, as some seals and bearings can be particularly sensitive to high temperatures. Always check the temperature range of the bearing and sealing arrangement before selecting a fitting method.

What products are available?

SKF’s TWIM range of induction heaters provide the ideal tool for safely heating bearings ready for fitting. These bearing heaters are equipped with features to make them safer, more efficient and highly user friendly. For example, the bearing heaters come equipped with a remote control, to enable the operator to control the heater from a safe distance. Bearing support arms are also in place to reduce the risk of the bearing toppling during heating.

Hydraulic fitting methods

What is hydraulic fitting?

Fitting a bearing using hydraulics involves injecting a thin film of oil between the mating surfaces, under high pressure. This virtually eliminates the friction between the surfaces, allowing the bearing to slide easily into position.

This oil injection method reduces manual effort, as well as the risk of damage to the bearing and shaft.

Where is it appropriate to use hydraulic methods to mount a bearing?

Oil injection is appropriate for use on many bearing applications and is often the method of choice wherever using heat is inappropriate. Oil injection methods are frequently used on the largest bearings, where mechanical fitting methods are not possible and the size of the bearing would make it difficult to heat the bearing to a consistent temperature.

What products are available?

SKF manufactures a range of oil injection sets such as the THKI series. An oil injection set consists of an oil injector, high pressure pipe, pressure gauge and a range of connection nipples.