12.08.2010 | Author / Editor: E. Pickel and W. Schleyer / Marcel Dröttboom
Belt conveyor pulley bearings are some of the most important parts of a belt conveyor system, as they are responsible for a low resistance movement of belt and material. To ensure proper functioning, bearing arrangements and sealing must be carefully selected.
Belt conveyors have a large number of rolling bearing positions, e.g. idler rollers and the different pulleys are equipped with rolling bearings (Fig. 1). The following elaboration, however, is focused on the self-aligning bearing arrangements, the lubrication and the sealing of drive-, tail-, bend- and tension-pulleys. When talking about different bearing variants of belt conveyor pulleys, a distinction is drawn between inner and outer bearing arrangements.
At inner bearing arrangements, bearings are located inside the pulleys. They are generally used in non-driven pulleys. The bearing seat in the pulley housing is designed with a tight fit to realize a secure interference to the bearing outer ring which is subjected to rotating load condition. The non-rotating axis is connected to the surrounding construction. Bearing combinations typically used are (Fig. 2):
These two bearing arrangement variants are used where high loads in combination with angular deviations e.g. due to misalignment or deflection of the shaft occur. Permissible misalignment of the bearings is limited to ca. 0.2 degree due to rotating outer ring.
Outer bearing arrangements are preferable used for drive pulleys. The bearing inner rings are fixed tightly on the shaft, while the outer rings are located in the housings with a loose fit.
Most common is a combination of two spherical roller bearings (Fig. 3, top). The outer ring of the non-locating bearing is axially free. So the required axial movement due to shaft elongation as result of temperature differences can be realized. Depending on bearing series and size, the permissible misalignment is between 1.5 to 3.5 degree. If the maximum values shall be used, of course also housings and sealings have to be designed accordingly. A second alternative is the combination of spherical roller bearing and toroidal CARB (Fig. 3, bottom). Both housings are designed as locating arrangements (axial fixation). The axial movement takes place friction-optimized inside the CARB. Maximum permissible misalignment for the compact aligning roller bearing is 0.5 degree.
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