Friction Coefficient of Grooved Rubber Disc Sliding Against Ceramics: I. Effect of Motion Direction

The present research investigates the effect of grooves on the rubber surface, direction of motion and elasticity of rubber on the static friction coefficient when sliding against ceramic surface. Rubber test specimens were prepared from two types of rubber of 2 and 8 MPa modulus of elasticity and 27 and 53 hardness Shore-A. The specimens had a cylindrical shape of 36 mm diameter and 10 mm high. Test specimens were prepared by introducing single groove of different lengths. The ceramic surface roughness was 0.14 µm Ra. Friction tests were carried out at different values of normal load. Tests were carried out at dry, water, sand contaminated, water contaminated by sand, water and detergent, water and detergent contaminated by sand, oil, oil contaminated by sand, oil/water dilution, oil/water dilution and contaminated by sand. Based on the experimental results, it was found that, introducing single groove in the rubber disc greatly influenced friction coefficient. At dry sliding friction coefficient decreased with decreasing contact area in presence of hard rubber while soft rubber showed an increase in friction coefficient. This behavior was attributed to the fact that friction displayed by hard rubber depended mainly on adhesion while that observed for soft rubber depended mainly on deformation. For water lubricated ceramics, the value of friction coefficient drastically decreased compared to dry sliding. Further decrease in friction coefficient was observed when water was diluted by detergent. In the presence of sand, water and detergent the values of friction coefficient showed significant increase due to the embedment of sand particles in rubber surface and consequently abraded ceramic surface. In the presence of water and oil, the sliding directions showed significant effect on friction coefficient, while for relatively soft rubber, sliding directions had slight effect on friction coefficient.