Schaeffler has supplied a special purpose induction heating device for large workpieces to TAKRAF GmbH, a manufacturer of bucket wheel excavators, stackers, crushers and conveyors for mining applications. The heater has cut the heating time for a typical two-tonne gear from 6 hours to just 20 minutes.
One of TAKRAF’s new product introductions is the development of roll crushers and associated gearboxes. The roll crushers can weigh up to 160 tonnes. The gearboxes comprise large, heavy components such as gears, the heaviest of which weighs 5000kg with an outside diameter of 1700mm. Although TAKRAF has always used conventional FAG inductive heating devices from Schaeffler, these are only suitable for workpieces weighing up to 1200kg. The roll crusher gears typically weigh between 2000kg and 5000kg each. TAKRAF therefore needed a new more powerful heating device to heat these larger components and approached Schaeffler for help.
In response to this request, Schaeffler engineers developed an induction heating device that can generate sufficient electrical power required to heat the large components quickly. The result is the FAG HEATER5000, the largest inductive heating device ever built by Schaeffler. The heater can heat workpieces up to a maximum weight of 5000kg, including gears heated to 200degC and rolling bearings to 100degC.
The need for uniform heating
Prior to mounting, large workpieces such as bearings and gears must be heated uniformly. If heat output is too high, this can cause temperature differences between the inside and outside of the workpiece, which in turn, can lead to cracks or distortions in the material. To ensure the heating process is carried out safely and evenly, the HEATER5000 is fitted with a Delta T control system. Two magnetic sensors simultaneously measure the temperature of the inside and outside of the workpiece. By monitoring the temperature levels at two different measuring points, the temperature of the workpiece is reduced automatically if the maximum permitted temperature difference is exceeded. The heater is equipped with various features, including temperature-time (ramp) controls, which prevent overheating of the workpiece.
Since purchasing the HEATER5000, TAKRAF can heat large workpieces such as gears and bearings much more quickly. The cost and time savings, as well as the reduction in labour costs, varies depending on the application and the workpiece. However, for a typical medium size gear weighing 2000kg, the heating time is reduced from 6 hours to 20 minutes using the HEATER5000.
Benefits of induction heating
Induction heating is superior to traditional heating methods such as oil baths or gas flame burners, as it is faster, cleaner and more suitable for batch heating. Heat is generated within the workpiece and unlike alternative heating methods, does not need to be transmitted via convection, radiation or thermal conduction. As induction heating is uniform across the workpiece, local overheating is prevented.
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.
Schaeffler’s HEATER range includes seven induction heater models, which are suitable for the mounting of bearings – or other circular steel components such as gears, couplings, pulleys and bushings – with a minimum bore diameter of 10mm, up to bearings with outside diameters of 1500mm, with a maximum weight of 1200kg.
For more information about Schaeffler’s HEATER range please visit www.schaeffler.co.uk.