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EuroAuto: Ceramics Build Better Bearings

There are a number of unsung heroes in the motorsport industry, those whose products are vital in keeping the cars on the track but whose presence you have to dig deep to discover.

There are a number of unsung heroes in the motorsport industry, those whose products are vital in keeping the cars on the track but whose presence you have to dig deep to discover. One such is German company Cerobear (www.cerobear.de), a leading manufacturer of ceramic and hybrid rolling bearings, whose products are used in Formula One, Le Mans, DTM and the World Rally Championship.

It could be said, of course, that if Cerobear did not exist, or was not interested in supplying the motorsport market, its products would be replaced by another. However, product manager Christian Klatt insists, no other company can bring the same high level of expertise when it comes to designing and manufacturing these products. "Other companies may manufacture silicon nitride rollers as well, but we know that ours have the best surface quality by far," says Klatt. "This is achieved by a special machining technique that has been developed by Cerobear."

The company has 18 years of experience from which to draw. It was founded in 1990 in the Aachen Technology Centre by Matthias Popp and Jens Wemhöner, two former research engineers from the Fraunhofer Institute in Germany. Initially, they were cashing in on the new-found craze in ceramics and its possible use in the oil-less engine that was undergoing quite an amount of research at the time. "The company was started at a time when there was a great deal of hype surrounding ceramics, when designers were dreaming of the adiabatic engine running at a very high temperature that would cause the oil to break down," says Klatt. "They therefore needed materials that could run in a dry state so huge amounts of money were being pumped into research in this area."

It turned out that for all its thermal properties, ceramic did not really provide the solution as it has a tendency to fail when used as a large and high loaded structural part, such as a con rod or piston. "So while it was found that it is a perfect material from a surface behavior point of view, it isn't from a structural one," says Klatt. "However, this is totally different in rolling bearings, because here the very high stressed volumes are extremely small and lying directly beneath the surface, which means that they can be inspected regarding structural errors which could cause the ceramic to fail"

Using this knowledge, Cerobear, blazed a trail in ceramic rolling bearing technology, supplying industries as diverse as the semiconductor, machine tool and beverage industries. However, it was the aerospace industry that made the toughest demands, with NASA, in particular, being extremely rigorous in its approach. The end result, though, was that Cerobear's ceramic rollers became part of the space program. "The driving force was NASA in the early 1990s when it approached Cerobear for ceramic rollers for the Space Shuttle's main engines," says Klatt. "The surface quality at that time wasn't on a level as it is today and the requirements were very tough to meet. It took 12 years for the bearing to be certified, but the end result is that where the original bearings had to be changed after every mission, now they are replaced after every 12 missions."

However, all these industries, which are serviced by Cerobear's industrial division, still do not exceed in terms of turnover that of motorsport, says Klatt. "Motorsport sales accounted for around 60% of the company's revenue last year. Of this, 80% is in Formula One with which we have been involved since 1999 supplying wheel, differential and gearbox bearings. We also used to supply engine bearings until ceramic was banned for all the oscillating and rotating parts of an engine in 2005. However, we still supply transmission and wheel bearings to the majority of the 10 teams. I think it is fair to say that we have the biggest market share in specialized or customized bearings in Formula One."

Customization is key, says Klatt, and is what his customers demand as it helps them to adapt and downsize their assemblies to the requirements of the specific-load situation, bringing the frictional losses to a lower level. "Where aircraft bearings used to be found in the gearbox, the teams were learning that if they wanted a customized design they were having to wait for at least 26 weeks and sometimes even 70 weeks, which is the standard delivery time in the aircraft industry," says Klatt. "However, our flexible production concept, which is optimized for working on small manufacturing lots, allows us to manufacture bespoke bearing designs or roller dimensions in a maximum of 12 weeks, even for the most complex of pieces, starting with a clean sheet of paper."

In Formula One gearboxes, hybrid bearings have generally replaced aircraft types. While the fixed bearing is either a four-point contact or a double-row angular contact ball bearing, the floating bearing is typically a cylindrical roller bearing that mostly runs direct on the hardened steel shaft. To prevent axial and rotation movement, the gearbox bearing races often feature complex flanges, notches or threads, which allow a compact design of the assembly.

Although the precision machining of ceramic is one of Cerobear's core competencies, steel still plays a key role in the company's business. "Complex flanges and threads cannot be machined onto ceramic parts with a hardness of 80 HRc," Klatt admits. This is the reason why 99% of bearings used in motorsport are hybrid bearings. In a hybrid bearing the rings are made from steel while the rolling elements are made of silicon nitride ceramic. This material provides superior mechanical properties, like a friction coefficient around 40% lower than that of conventional bearing steel. At a density of only 41%, silicon nitride ceramic offers twice the hardness of standard bearing steel, making sinter-hipped silicon nitride one of the hardest man-made materials in the world. Its excellent resistance to seizure and the minimum lubrication requirements are also important characteristics deriving from its extremely stable chemical structure. Besides this, the Young's modulus of silicon nitride is 50% higher than that of steel, resulting in less deflection in the rolling contact.

Klatt points out that friction reduction cannot only be achieved by downsizing or the use of ceramic but also by choosing a dedicated bearing type. "As the majority of racing differentials are designed to be used in a variety of cars, they contain tapered roller bearings that are appropriate for a number of applications and so are often over-sized for the job in hand. If these can be replaced by angular contact ball bearings, manufactured to the original main dimensions in order to guarantee that the mating parts can be used further, it leads to a dramatic decrease of the frictional losses as the sliding friction of the tapered rollers against the shoulder of the cone is replaced by the rolling friction of the balls in the ultra-precise raceway. However, the internal bearing layout is always adapted to the specific load case."

The other 20% of Cerobear's motorsport business mainly comes from the sports car teams that typically compete at the Le Mans 24 Hour race, Klatt proudly claiming that every winner of that race since 2000 has been equipped with his company's wheel bearings. Audi has also been a customer since the beginning of its Le Mans program as was Bentley when it was racing. Cerobear's bearings can also be found in the Porsche and Acura. "The complexity of the bearings in this series is more or less the same as it is in Formula One with its emphasis more on having a longer life than the most compact design," says Klatt. "This is why we utilize only the 'High Nitrogen Steels' in these applications. Due to their high content of nitrogen instead of carbon, these steels offer less and smaller carbides which leads to a more homogenous structure and increased over-rolling resistance." 

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