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Schaeffler’s Ian Pledger explains why flexible induction heaters for the mounting and dismounting of large-sized bearings and components are preferable to more traditional approaches.

The correct mounting and dismounting of rolling-element bearings can save companies time and increase the life of the bearings, as well as maximise the availability of critical plant and machinery by avoiding breakdowns.

But, in order to correctly mount or dismount bearings, it is usually necessary to heat the bearing first.

There are a variety of heating methods available to do this, each with its own advantages and disadvantages.

Heating methods include thermal mounting and dismounting tools (ie heating plates), induction heating devices, mounting paste and heating rings.

Selecting the most appropriate heating method will ensure that the bearings (or similar circular steel components) are mounted and removed easily and quickly, in a safe, reliable manner, without causing any damage to the bearings or surrounding equipment.

When it comes to heating large-sized bearings (1,500mm outside diameter and above), there are several options available: using an oil bath, a gas-flame burner, or a medium-frequency induction heater.

Using an oil bath requires the customer to have a large enough bath for the bearings to be heated in.

If such a bath does not exist, one will need to be constructed, which will require welding work, large quantities of steel and one to two days of manpower.

Hundreds of litres of oil are also required, which must then be disposed of in the appropriate way and can be expensive.

Compared to oil-bath heating, using gas-flame burners is a much easier method in terms of preparation, as it requires nothing more than a couple of gas cylinders and a burner.

However, heating the rolling bearing and the housing may tie up three to four people for up to four hours per component.

With gas burners, there is also a risk of local overheating, which can cause changes to the structure of the component being heated.

In addition, after heating is completed, the bearing itself may need to be cleaned or the housing painted, as these parts often become discoloured with black soot from the flames.

Induction heating is superior to traditional heating methods, as it is faster, cleaner and more suitable for batch heating.

Heat is transferred directly to the workpiece and, unlike alternative heating methods, does not need to be transmitted via convection, radiation or thermal conduction.

Fixed and mobile induction heaters are available for this.

As induction heating is uniform across the bearings, local overheating is prevented.

During the heating process, rolling bearing steels are automatically de-magnetised.

Due to their increased energy efficiency, induction heaters can reduce heating times by up to 50 per cent, keeping maintenance costs to a minimum.

Also, as the systems do not require oil, they have the added advantage of being both clean and environmentally friendly.

While induction heaters are suitable for many types of rolling element bearings, they are not always effective with large-sized bearings and housings.

The availability of an induction heater that is large enough to cope with the job in hand not only causes problems because of its physical size, but is also likely to cost tens of thousands of pounds – making it uneconomical for a one-off mounting or dismounting task.

In addition, the housings for large-sized bearings usually have an unusual shape, which makes it difficult to fit the component in the heater, or again means that the heater itself has to be very large.

However, using flexible induction heaters solves these types of issues.

Here, medium-frequency induction heaters are fitted with flexible inductors, which offer complete flexibility when it comes to the size and geometry of the workpiece or bearings.

The heating cable is flexible, enabling it to be placed in and around the workpiece, or in areas of a component that would normally be inaccessible.

This method is also ideally suited to mountings that do not take place at regular intervals.

The workpiece itself does not necessarily have to be a bearing; it could be any large, circular, ring-shaped steel structure that requires heating.

Examples here include the heating of bearing seats in a machine carrier such as a wind turbine.

Other applications include the preheating of welds in pipeline construction, as well as the dismantling of bearing inner rings and other shrink connections.

Preparation time with flexible induction heaters is relatively fast and heating time is one to two hours, depending on the size and mass of the bearings.

The heating process itself is automatic, which means resources are not tied up and the bearings do not require cleaning post-heating.

A sensor is mounted to the bearing in order to monitor the temperature during heating.

Once the bearings have been heated to the required temperature, the heater is stopped automatically.

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