2. Experimental apparatus and specimens
A slider bearing tester [19] capable of measuring lubricant film in a conformal slider-on-disc contact was used in this study. The schematic of the tester with a lubricated contact that consisted of a stationary slider and a rotating disc is shown in Fig. 1. A specific slider inclination angle α was set using the adjustment bolts. The disc was made of BK7 glass with 4 nm surface roughness (Ra). To facilitate interferometry measurements of film thickness, the glass disc was coated with a two-layer film (a bottom Cr layer and a SiO2 layer on top) which serves as the beam splitter. A monochromatic light beam of wavelength λ=635 nm that is projected perpendicular to the contact thereby forming a multi-beam Fizeau interference was used in the interferometry measurements [20]. The inclination angle of the slider was set accurately by controlling the number of fringes formed on the contact. When the surface of the glass disc moved at a speed ud and a load w, the rotating disc and the inclined slider were separated by a thin lubricating film. During the tests, film thickness was represented by the minimum film thickness h0 at the exit. In the present study, steel (AISI 52100) sliders were used, and their lubricated surfaces were polished with a surface finish of Ra=8 nm and flatness error of λ/4. The surface size was 4 mm×9 mm (length×width). Materials other than steel are currently used in advanced engineering designs, but steel is still the most common engineering material. The main focus of this paper is on the effect of BSA aqueous solution on slider bearings. Hence, the study was conducted mainly with steel sliders.