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Graphic element Research > Growth > Research projects > Previous projects > New Products and Materials > High-precision bearings deliver winning performance
Graphic element High-precision bearings deliver winning performance
The throughput of high-speed, high-precision machine tools such as metal cutters and grinders is limited by the performance of their bearings. The need to develop better bearings for such tools prompted an engineering school, a university, five companies and a technology research centre to launch EUROBEARING. The project has yielded a new, low-temperature process for coating steel bearing races, an innovative coating, and improved prediction of the behaviour of coated components.

Targeting performance

In a high-speed metal grinder or cutter, the grinding and cutting device must turn very quickly and bite with force and accuracy into the hard material, without causing the machine bearings to overheat or fail. It is crucial to minimise the friction between bearing components and the damage they inflict on each other through mechanical or chemical interactions. It is also important to minimise the use of lubricants, both for ecological reasons and to reduce power dissipation and the temperature of the revolving spindle.
Current bearings fall short of the performance criteria for some high-speed applications, which is the problem addressed in the Brite-Euram EUROBEARING project.

The European partners focused on improving ball bearings for high-speed grinding machines. Given the increase in rotating capacity brought about by the use of hybrid bearings with ceramic balls in steel races, they decided to tackle the primary limitation of these bearings: the unsatisfactory frictional and wear behaviour of the steel races. The idea was to enhance the race surface by depositing a thin hard coating on it, with the aim of reducing friction and wear and establishing a significant increase in spindle speed.

Close collaboration

The project initiators were two partners from Germany: the WZL (Werkzeugmaschinen Labor) of the Rheinisch-Westfalische Technische Hochschule (RWTH), an engineering school in Aachen, and Cemecon GmbH, specialists in coatings for high-speed bearings. Six more partners soon joined: the University of Thessaloniki (Greece), a technology research centre (Tekniker, Spain), a ball-bearing manufacturer (SNR Roulements, France), and makers of spindles, grinding machines and other machine components (Gamfior SpA. Italy; Meccanica Nova SpA, Italy; Minitek Feinmechanische Produkte, Austria). The teams worked together closely, each according to its specific expertise, to produce test specimens, coat them, test spindles and coatings, predict bearing component behaviour, and finally test the newly developed bearings.

Low-temperature coating process

Cemecon coated the metal races using a technique called physical vapour deposition-magnetron sputter ion plating (PVD). The company had a major problem to solve: usually, deposition on metal surfaces is carried out at temperatures around 450°C degrees Celsius. Here this was not possible, because the steel used for such bearings tends to soften if the coating temperature exceeds 160°C. Cemecon successfully developed a process operating below 160°C and yielding a high-quality coating. The system combines the latest in vacuum technology and plasma electronics with powerful process control facilities. It is also applicable to other fields, and Cemecon has already sold the process and process unit to a gear manufacturer.

Novel coating concept

Another task for the partners was to test and compare the performances of various coatings in order to determine and select the best. This involved both real tests and finite-element modelling (computer simulations). Tekniker studied coating behaviour on four different test devices, while the university team in Greece developed finite-element simulations for predicting component behaviour in real situations. The simulations were based on an impact test (hard balls repeatedly hitting target specimens) and validated by other tests. The resulting 'impact tester', including an improved impact test and the simulation hard- and software, is now on the market. Cemecon also developed a 'hard-soft' coating comprising an inner hard layer of titanium nitride and an outer, softer layer of carbon. In tests on ten different coatings, this new one ranked among the 'top three'.

Achievements and prospects

In final tests, coated bearings showed reduced wear and made possible a 40% increase in spindle speed. Any remaining problems are being tackled in REFINE, a follow-up project with an expanded scope including the definition of new applications and a new spindle concept.
The market for deposition coating of friction-bearing machine parts is increasing yearly by 15-20%. In automobiles, coated bearings may soon totally replace wet-lubricated ones. In a market previously dominated by Japan and the USA, Europe has been gaining ground. Projects such as EUROBEARING and REFINE will play a large part in EU progress in this sector.

Cordis RCN: 6657
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