Optimized Cage Design for Increasing the Life of Solid Lubricated Roller Bearings

Abstract

Roller bearings rank among the most used machine elements. Depending on the applications a lifetime of thousands of hours (e.g. machine tools: 15000h) can be realized as long as standard lubrications can be used. Nevertheless some applications only provide special environments, like high temperatures or vacuum, where oil or grease cannot be used. In these areas solid lubrication might be a choice. However solid lubricated roller bearing cannot offer similar lifetimes nor is a universally valid lifetime prediction available for such systems. Currently the friction work of a tribologically stressed surface offers a possibility for estimating the life. For doing so the paper gives an introduction. Further a test rig designed to examine roller bearings under high temperatures up to 300°C and high vacuum will be presented. In various experiments the influence of roller bearing cage design on its possible lifetime could be proven, especially if the cage has been used as a lubricant depot. On this basis a multibody simulation (mbs) model was built to get an understanding of the inner dynamics of roller bearings and its parts, e.g. rolling bodies and cage. While the geometry was built in commercial software the calculation of contacts, e.g. rolling body to raceway, and loads as well as friction is done in user written subroutines developed at the Institute of Machine Elements, Gears, and Transmissions at the University of Kaiserslautern. This model allows for an investigation of the effects resulting due to a parameter study of the geometry of the different parts a common roller bearing consists of: inner race, outer race, rolling bodies and cage. By using this tool the weak points in cage design could be determined as well as options for increasing the functionality of a cage as lubricant depot were shown. Combining experimental with simulated results, a new cage design for solid lubricated roller bearings could be developed. This new cage design increases the lifetime of the used test bearings from 2.5 million revolutions to more than 40 million revolutions. A further benefit of the new cage design is the ability to run at much higher rotational speeds than bearing systems that are available on the market nowadays.