In fast spinning rotary systems Active Magnetic Bearings (AMBs), which work on the principle of magnetic levitation, are used to suspend shafts contactless and wear-free. AMBs operate in a wide range of applications, from very large turbo compressors to very small turbo molecular pumps, and in a lot of systems which are size-wise in-between, like blowers (e.g. for water aeration), gas expanders or machine tool spindles. CEROBEAR can offer aux bearing solutions for all these and further applications.
In case of an AMB failure or temporary electrical power loss, auxiliary bearings will catch the shaft before the rotor is touching the stator. In case of a shaft drop the auxiliary bearings are accelerated from zero to operating speed within a split second. CEROBEAR aux bearings have successfully proven their capabilities at speed factors (n x dm) of up to 3.6 Mio mm/min. Due to their customized geometry they can control shafts even at the highest radial and axial shock loads.
According to their preference, customers can choose from different aux bearing specifications. State- of-the-art are superduplex bearing designs, which feature a one-piece, double row inner ring in combination with an axially split outer race. The advantage of the superduplex configuration is the more uniform load distribution to both ball rows, which leads to lower Hertzian stress in the rolling contact. For less demanding applications CEROBEAR also offers pairs of single row angular contact ball bearings. Both specs are available for spring- or hard preload, for the latter one CEROBEAR offers anextremely precise bearing matching, the gap between the outer races is tolerated to +/- 2.5 microns.
On the material side CEROBEAR offers a variety of superior choices compared to standard bearing steel. Heart of every aux bearing are silicon nitride (Si3N4) balls. Si3N4 is an inert and very hard (1550 HV) ceramic material, which provides a 60% lower density and a 40% reduced coefficient of friction compared to standard bearing steel. Due to their low density it needs less energy to rotate ceramic balls, hence ball skidding is suppressed. And even in the case of skidding there is no adhesive wear between races and balls because of the inertness of Si3N4. CEROEAR matches the Si3N4 balls with bearing races made from High-Nitrogen-Steel (HNS) or M50 tool steel. In combination with a customized cross section and contact angle this leads to superior bearing load capacity and service life.
CEROBEAR auxiliary bearings featuring HNS races are especially qualified to operate in H2S (sour gas) environment, due to the excellent corrosion resistance of the High-Nitrogen-Steel.
CEROBEAR aux bearings normally operate cage-less, in full complement arrangement but are also available with a segmented cage. The segmented cage avoids the ball to ball contact and hence allows more drops at high speed without having wear on the balls.
In applications in which the bearings are directly exposed to process gases the aux bearings have to perform without oil or grease lubrication. For these conditions CEROBEAR offers coatings, e.g. silver or WS2, which act as a solid lubricant. The solid lubricant reduces not only the rolling friction but also the friction between the shaft and the inner ring, which helps to prevent shaft whirl situations.