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Raising the bar for bearings

01 February 2012

Setting the scene on our bearings feature this month, Phil Burge discusses the challenges faced by bearing manufacturers and how advances in modern bearing technology can bring significant benefits to a wider group of users

It is estimated that in 75% of applications self-aligning bearings are operating, at best, under contaminated conditions and, at worst, excessively contaminated conditions. So, a key challenge (or opportunity) for manufacturers of self-aligning bearings is to develop products that offer significantly longer service or improved performance under less than ideal conditions.

The self-aligning bearing currently accounts for approximately one quarter of world-wide bearings sales and, while its design has remained virtually unchanged since it was launched in 1907, the introduction of electronics has brought additional functionality, reductions in weight have enabled significant efficiency gains, and performance has been improved by new bearing steels and innovations in component design.

The characteristics of bearing steels must include high levels of hardness as well as resistance to corrosion, wear and contamination. Get the steel right and you will achieve significant product enhancements even before you start to apply an intelligent component design regime. Its composition aside, the way bearing steel is heated and subsequently cooled during its production will also have a big impact on the final result. When steel is held at a fixed temperature for a long period, for example, it achieves excellent levels of hardness; the result is Bainite.

The exceptional strength of Bainite hardening attracted SKF, which adopted the process in the 1950s for the manufacture of bearing rings. By the 1990s, adjustments in the transformation stage of the Bainite hardening process added toughness, high dimensional stability, good wear resistance, positive surface compressive residual stresses and long fatigue life. SKF is currently working to enhance the Bainite process to achieve an upgrade of its Explorer class bearing.

But beyond the material processing considerations, there is always the potential to make refinements in design that also bring measurable improvements in performance and product life span. For example, the intelligent redesign of rolling elements, cages and guide rings can ensure correct alignment, increase load-bearing strength and minimise friction, while refined internal geometries and surface finishes can reduce stress on moving parts. All of these factors can result in the smoother, lower temperature operation of machinery, and bring improvements in terms of energy efficiency.

Now, thanks to continuing advances in high-precision manufacturing techniques, finer dimensional tolerances are achievable Higher contact interface tolerances have resulted in bearings that run more smoothly, while advances in internal roller and raceway geometries have enabled optimised geometric conformity (osculation) and thus improved load bearing capacity.

The use of a floating guide ring in the upgraded SKF Explorer bearings series serves to illustrate that there is always the potential for innovation – even when it comes to the venerable self-aligning bearing. The floating guide ring maintains the correct roller position under load, which in turn ensures a stable temperature within the bearing, also reducing both friction and wear. And there are further benefits, since the reduced vibration and noise levels enable safer, more efficient operation.

Of course, the effort to improve bearing performance through better bearing steels and component design does not stop there. These components can have a very significant impact on the reliability and efficiency of the machines that rely upon them, and so the demand for even higher performing bearings will continue to drive new developments. Watch this space…!

Phil Burge is with SKF (UK)

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