Evaluation of a novel UHMWPE bearing for applications in precision slideways

This paper presents a novel slideway bearing design comprised of a thin-film (0.1–0.2 mm) ultra-high molecular weight polyethylene (UHMWPE) bound to a rigid hemispherical substrate. Two prototype bearing designs were fabricated and tested to characterize the coefficient of friction (dynamic and static) and wear of the polymer. In addition, similar bearings were incorporated into a kinematically constrained rectilinear carriage to determine the repeatability of motion during multiple traverses. The first bearing had a radius of curvature on the order of 2.38 mm incorporating an UHMWPE film thickness between 0.1 and 0.2 mm. The friction coefficient was measured to be 0.16 at a normal load of 11.5 N while changing to 0.19 as the normal load is decreased to 2.2 N, at a surface speed of 4.2 mm s−1. This bearing failed after a traverse of approximately 700 m at a load of 11.5 N. A similar evaluation procedure was carried out on a bearing of radius 6.35 mm resulting in a friction coefficient of 0.13 at a normal load of 27.8 N while changing to 0.19 as the load is decreased to 2.2 N, and the bearing endured a traverse of over 2.2 km at a load of approximately 28 N (in both air and vacuum conditions) with a surface speed of 4.2 mm s−1. The second bearing prototype was further subjected to a repeatability test. In this set-up, a carriage incorporating five bearings was traversed in a nominally linear path while vertical deviations for multiple traverses were measured by a custom built displacement sensor. Deviations from a linear path were observed to repeat to within a few nanometers about nominal variations of less than 10 nm for a traverse distance of 10 mm. This system and other subsystems used to characterize the friction coefficient and noise of the polymer bearing are presented.