Design, Construction, and Evaluation of Rubber Friction Tester

Coeffcient of friction (COF) for rubber parts is one of the key parameters in their interaction with solid rough surfaces (micrometer to millimeter scales), such as tire-road interactions. COF of rubber depends on viscoelastic properties of rubber, roughness characteristics of the counter-part surface, and process variables such as contact nominal pressure and sliding speed. Due to the need for measuring COF for rubber, a new friction tester, with continuous variation of nominal pressure and sliding speed, was designed and constructed in order to assess the effect of above mentioned parameters. Tire tread compounds, as the most common rubber part in the feld of rubber tribology, was used for this purpose. Viscoelastic properties of compounds were varied by changing composition of styrene-butadiene rubber (SBR) and butadiene rubber (BR) in the blend. Effect of surface roughness was evaluated by using silicon-carbide papers with different roughness parameters. By statistical analysis it was shown that the designed friction tester has high accuracy in measuring the coeffcient of friction of rubber and differentiating the effective parameters. Increasing the nominal pressure led to reduction of COF and increase in sliding speed forced it through a maximum. In conclusion, the loss factor of the compound and asymmetry in roughness distribution of the counter-surface are considered as the most effective parameters on COF of rubber