A Low Friction Bearing Based on Liquid Slip at the Wall

Abstract

In recent years it has been shown experimentally by a number of workers that simple, Newtonian liquids can slip against solid surfaces when the latter are both very smooth and lyophobic. It has also been shown theoretically how, based on a half-wetted bearing principle, this phenomenon may be used to significantly reduce friction in lubricated sliding contacts and thus make possible the hydrodynamic lubrication of very low load contacts. This paper describes the experimental validation of this concept. A low load bearing is constructed and the influence of surface roughness and the wetting properties of the surfaces on friction are investigated over a wide range of sliding speeds. It is shown that liquid slip can be used to considerably reduce friction in full film, hydrodynamic conditions.

The Effect of DLC Coating Thickness on Elstohydrodynamic Friction

“…Furthermore, many authors have concluded that for solid-liquid slip to take place, the surfaces have to be very smooth, generally below 6 nm RMS [12,41,42,50]. However, the present authors have presented an investigation in which friction reduction with DLC coatings was measured [7] in full film EHL even when the combined RMS roughness of the surfaces was in the range of 155-355 nm.…”

“…However, it is more uncertain if the friction reduction achieved with the coatings compared to the uncoated reference is only due to thermal insulation, or if a smaller part of the friction reduction is also due to solid-liquid slip. The influence of surface roughness on solid-liquid slip has been discussed by several authors, where many of them have concluded that for slip to occur, the surfaces have to be very smooth [12,39,41,42,49], typically 6-12 nm RMS. The critical roughness is most likely depending on the size of the molecules of the liquid used [24,36,38].…”

“…Several authors have experimentally observed a reduction in friction with DLC-coated surfaces in full film EHL [6,7,14,27,48]. The friction reduction has been explained by several authors as an effect of boundary slip, or solid-liquid interface slip [14,27,29] a phenomena thoroughly discussed in literature [12,25,37,38,41,42,46,47,49], where some of the work is based on atomically smooth surfaces. However, it is still not entirely clear how the mechanism of slip works, and several hypothesis can be found in the literature.…”

The beneficial effect of superhydropobic layer addition on lubrication behavior in bearing application

“…F + =0.037), the minimum value is achieved when HD = 0.25 in full slip condition. Slip can be used to reduce friction under full film, hydrodynamic lubrication Choo et al [1]. …”

“…The sliding step bearing is one example of texturing, leading to a high load support. Regarding slip, Choo et al [1] showed that liquid slip could be used to considerably reduce friction under full film, hydrodynamic lubrication. Tauviqirrahman et al [2] demonstrated that partial texturing gave even better results than full texturing.…”