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Graphic element Research > Growth > Research projects > Previous projects > Industrial Processes > Ceramic bearings on a roll
Graphic element Ceramic bearings on a roll
     
 
Research into silicon nitride ceramics has led to the production of more reliable pumps for use in the chemical processing industry, thereby significantly reducing maintenance costs. The work has also resulted in a number of spin-off applications, including use in Formula 1 racing cars and in a new gas laser machine. One of the project partners, Cerobear, is now global market leader in the serial production of silicon nitride rollers and raceways with close tolerances and high-quality surface finishes.
 

In the past, chemical processing plants have used pumps that incorporate silicon carbon sliding bearings which have a good resistance to chemicals but poor abrasion resistance. As a result they have a very low tolerance when running under dry conditions, for example during start-up operations, and often fail earlier than is desirable as a result of chipping and cracking. Silicon nitride ceramics were known to have better mechanical properties but this benefit was offset by the fact they were only available in formulations with poor chemical resistance. In 1993, a group of interested companies came together in a three-year Brite-Euram project in a bid to develop high-performance, low-cost silicon nitride bearings suitable for use with pumps in chemical processing plant where the chemicals involved are corrosive or abrasive.

Raw materials and machinery

Co-ordinated by the German bearing manufacturer, Cerobear, the project essentially had two strands of work. One part involved research into the raw materials required for the ceramic bearings, while the other concentrated on the machinery needed for production. Consequently the project attracted a complete cross-section of interested companies. Three raw material suppliers became involved in the work: Tioxide Specialities in the UK (which was part of ICI but has now been split between two smaller companies), the French company Ceramiques et Composites, and the German supplier SHM Werkstofftechnologie. On the machinery side was Cerobear, and on the material inspection side was SKF, the Netherlands arm of the biggest bearing manufacturer in the world.
The skills and expertise of these partners were complemented by the Institute für Keramische Technologien under Sinterwerksroffe (IKTS), part of the Fraunhofer Institute in Dresden, and Feodor Burgmann Dichtungswerke, also from Germany. IKTS carried out research into powder processing, while Feodor tested trial bearings in its acid production works.

Improved knowledge and new technology

The project let to three specific advances. First, knowledge of the relationship between performance of a ceramic and its formulation, forming and sintering technology was greatly improved. As a result a grading system for silicon nitride ceramics with specific physical, mechanical and chemical properties for pump applications was developed. This means that corrosion-resistant grades of ceramics can be tailor-made for exposure to a range of acids, bases and hydrothermal environments. For example, a ceramic produced from a silicon nitride powder with a low amount of aluminium and yttrium and using hot isostatic pressing as the production method exhibited good corrosion resistance to hydrochloric acid and other strong acids.
Secondly, a canned pump was designed to incorporate the newly developed corrosion resistant bearings. The pump had magnetic couplings and was hermetically sealed to prevent loss of the process liquids; it was used to demonstrate the very low wear of the ceramic rolling bearing under unlubricated operation. It has been estimated that chemical plant operators can realise maintenance cost reductions of up to 5% by switching to pumps with the new bearings.
A third major achievement was the development of machining and finishing technology that enables series-scale production. This is particularly important because it opens up high-volume markets to silicon nitride rollers. For example, machine tool operators can replace the steel rollers on their high-speed cutting machines with silicon nitride rollers, allowing them to achieve higher outputs. Also, because the technology allows the bearings and traces to be produced to a very high tolerance and with excellent surface finishes, they can be used in applications where high reliability is essential, such as in the aerospace industry.

Spin-off technology and competitiveness

The lessons learned during the development of the chemical plant pump have since been applied to a fan for a new design of gas laser machine where similar mechanical properties, chemical resistance and tolerance to dry running were required. Cerobear also recognised the potential of the technology in high-tech sports, and has now introduced it to the engineers of Formula 1 racing car teams.
In fact, thanks to this project, Cerobear is the only source of series-produced silicon nitride rollers and raceways that are tolerant to dry running, giving them a major advantage in the global industry. For Cerobear this has been translated into 30-35% growth per year and has also helped the company to obtain venture capital backing for further development work.

Cordis RCN: 6679
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