Beware improper installation inssues

Modern rolling element bearings are quiet marvels of precision engineering. They are made from extraordinarily clean materials, machined to exceptional smoothness and dimensional accuracy, heat treated to create a finely tuned balance between strength and wear resistance, and assembled to tolerances measured in µm.

For many bearings, however, the first experience of life after manufacture is a traumatic one: beaten with hammers, roasted by blowtorches or seared in hot oil. Such brutal methods matter, because they can dramatically affect the ability of a bearing to do its job. Damage, distortion or misalignment during installation can lead to increased friction, noise and vibration in use, driving up energy consumption and reducing equipment performance. Poorly installed bearings fail faster too, leading to increased maintenance costs and unplanned stoppages. Our analysis suggests that improper installation is the underlying cause of 16% of bearing failures in service. In the worst cases, it isn’t just the bearings that need to be replaced when these problems occur: damage can extend to shafts, housings and connected equipment.

Most bearings are fitted to their shaft or housing with one component having an interference fit. The key to correct installation lies in achieving this fit without excessive effort or damage to the bearing. This can be done through mechanical, thermal or hydraulic methods.

Smaller bearings are often installed using mechanical force. The key here is to ensure that the mounting force is applied to the ring with the interference fit, and not transmitted through the raceways, where it can cause surface damage. Bearing manufacturers supply special tools to ensure mounting forces are applied evenly, and to the correct part of the bearing. The SKF Bearing Fitting Tool Kit TMFT 36, for example, comprises a range of different sized impact rings suitable for bearings with bore diameters of 10 to 55mm, three impact sleeves and a ‘dead blow’ hammer. It can also be used to mount other components such as bushings, seals and pulleys.

For larger bearings, thermal expansion of the bearing is sometimes used to reduce the force required to move the bearing into the correct position. One common approach is to heat the bearing in an oil bath prior to installation. Unfortunately, this can introduce contamination, shortening the life of the bearing, not to mention the safety hazards associated with handling a hot, slippery component prior to installation. A better approach is the use of dedicated induction heaters which, as well as avoiding contamination or damage due to excessive or uneven heating, also allow the bearing to be heated with greater efficiency, controllability and safety. The SKF TIH 030m induction heater, for example, is a compact, energy efficient device that can be used to quickly and evenly heat bearings up to a maximum weight of 40kg.

Recognising the importance of proper installation and removal techniques, bearing manufacturers have also developed a range of proprietary mounting methods. The SKF Oil Injection Method, for example, uses shafts manufactured with special oil ducts and grooves. During installation, oil is injected at high pressure through these ducts, creating a thin film between the shaft and bearing that significantly reduces the force required to push the bearing into position. 

The SKF Drive-up Method, meanwhile, controls the axial drive-up of tapered bore bearings from a predetermined position. Using a special hydraulic nut with a dial indicator, and an accurate digital pressure gauge mounted on a pump, the technique helps to reduce the use of feeler gauges and greatly reduces mounting time. The use of both these assembly techniques is further simplified by the availability of bespoke software to help maintenance teams calculate the right pressures and settings for their own specific applications.