Design of an experimental setup to determine the coefficient of static friction of the inner rings in contact with the outer rings of radial spherical plain bearings

In this study, a new experimental setup was designed and manufactured to determine the coefficient of static friction (COFs) for polyoxymethylene (POM)/steel spherical contact surfaces in radial spherical plain bearings. The experimental setup can measure the frictional moment. The POM/steel COFs equations from the frictional moment measurements were obtained. A sequence of tests changing the normal force under dry sliding condition for three different axis angles was performed. The calculated POM/steel COFs decreased with increasing normal force until adequate tightness was observed for all axis angles. Then, the POM/steel COFs remained stable. The static and dynamic coefficients of friction for the spherical contact of different material couples may be further investigated using a methodology similar to this study.