These high performance pumps offer a particularly unforgiving environment for bearings. They are used in semiconductor production, chemical analysis and SEM, working in the 10-6 to 10-9m mBar region.
Under vacuum conditions, the most important requirements for bearings are long, reliable life, reliability and high speed performance. They are expected to exceed 30,000 hours of life with just a single shot of lubricant and operate with very low vibration and noise.
To this end, special surface finish and harmonic limits are applied, while the geometry of the bearing is optimised to combat vibration and noise. Highly reliable, Barden bearings are designed to have infinite fatigue life where possible.
Whilst the speed requirements on the bearings for this application are often lower than for other pump types - at up to 800,000 ndm - factors including temperature, contamination and reliability mean that a special bearing is required to meet the application requirements. The bearing is designed to allow the rotor of the pump to drop over the front part, reducing the shaft length and improving the rotor dynamics. Laser drilled holes are added to allow direct oil lubrication and ceramic balls are used to improve the life and performance of the bearing.
Without the special design, a standard bearing used in this application would be difficult to lubricate, would cause the shaft to be too long for good rotor dynamics and could suffer from fretting corrosion.
Magnetic bearing systems are used to support many different systems. If a complete electronics failure occurs, mechanical bearings protect the system from a total crash. Successfully controlling a shaft will often require a bearing that can accelerate from zero to 2.7 or higher ndm virtually instantly, even after many years of inactivity. In addition, the bearing system must then control the rotor and the very high radial and axial loads and shock loads. This initial shock loading is very high due to the gyroscopic forces generated.
Barden has developed bearings for this application using ceramic balls and a full ball completment design, with Cronidur 30® materials to give exceptional performance and corrosion resistance. The bearing design is fully optimised for the maximum number of touchdowns.
Added value design features for pump applications include:
Cronidur 30® high-nitrogen steel for optimum performance and reliability
High performance ceramic bearing design chosen to meet the performance and corrosion-resistance requirements
High speed Small Ball Technology for improved pumping speeds
Shielded angular contact design to guard against contamination ingress and prolong lubricant life
Special internal design to maximise the in-application performance
Special Barden "TMP Standard" internal finish for quieter running, longer life and high reliability
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