Power Transmission
Fig. 1. Schaeffler’s low-friction ball roller bearings offer the load capacity of ball bearings in a package that is around 20 per cent narrower and lighter.
Rotary bearings are integral to most power transmission systems and are therefore an area on which design engineers should focus when attempting to reduce product costs, minimise maintenance requirements and enhance reliability. Paul Stevens reports.
Bearing technologies offer benefits for power transmission designs
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Fig. 2. The NNF double-row, full-complement cylindrical roller bearings from NKE.
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otary bearings are often considered as commodity items, especially when the commonly used sizes are available from stock for what can seem very low prices. Of course,
buyers have to take care if purchasing low-cost bearings, as imports from outside Europe can sometimes be manufactured from poor-quality materials and to tolerances that are somewhat slack, and even bearings that are boxed and branded as coming from one of the major European manufacturers sometimes turn out to be counterfeit. While specifiers and buyers can do a certain amount to ensure that the right bearing is purchased for a particular power transmission system, design engineers have the most important role to play in the overall process. Indeed, engineers today have a wider choice of bearings than ever before, enabling them to influence the design in such a way as to reduce costs, enhance performance, extend product lifetime and minimise maintenance requirements. Broadly speaking there are three main aspects
of a bearing’s design that manufacturers can fine-tune: geometry, materials and finishes. Needless to say, there are other areas to consider beyond the bearing if a product’s performance is to be maximised; these range from the design and precision manufacture of the mating components, bearing seals, lubricants, installation
techniques, correct maintenance and, to avoid unplanned stoppages, condition monitoring is very useful. It is also worth considering whether a rolling element bearing is still the right answer, now that plain bearing materials are so highly developed Given the long history of rolling element
bearings, it might seem surprising that there are still significant new developments in something as basic as bearing geometry. On the other hand, it has to be recognised that modern computational, simulation and analysis techniques are providing new opportunities for bearing manufacturers to optimise their designs and try more radical alternatives than would have been feasible in the days when all testing had to be undertaken with physical prototypes. One of the most dramatic developments in recent years is Schaeffler’s ‘ball roller’ energy- efficient bearings that utilise truncated spherical elements. This unusual design also necessitated the implementation of new assembly methods. The result is a range of ball
roller bearings that offer the load handling capabilities of fully spherical ball bearings yet they
enable the overall bearing width and mass to be reduced by around
20 per cent, plus friction is lower (Fig. 1). In essence, the ball roller design removes the
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