Reliability of turbomolecular vacuum pumps: A comparison of rolling element and magnetic bearing systems

Abstract

Turbomolecular pumps (TMP) are introduced as high‐vacuum pumps in a wide range of vacuum applications. High reliability, but also contamination‐free operation, low vibrations, and free choice of mounting position are customers demands that directly depend on the choice of the bearing system. Most of the infield TMPs use rolling element bearings that are lubricated by oil or grease. An increasing number of TMPs show active magnetic bearings. A new generation of TMPs use a passive magnetic bearing design. This paper compares the design and performance characteristics of the most common rolling element bearing systems to the more advanced magnetic bearing systems, considering in reliability, hydrocarbon contamination, vibration intensity, choice of mounting position, and costs. The comparison is based on design considerations and on relevant test results, i.e., lifetime tests and lubrication film measurements on TMPs with rolling element bearings. Based on this systematic and empirically founded comparison, this paper gives a guideline for chosing the appropriate TMP and bearing system for a certain range of applications. Furthermore, the paper tries to give a perspective by showing future lines of development of bearing systems for TMPs.