Study on Rubber Tread Block Design for High Slip Resistance on Liquid-Contaminated Condition

This study analyzes the design criteria for obtaining high slip-resistant shoe sole tread pattern the by adept control of various design parameters such as the height, orientation, and hardness of rubber strips. In the typical process, specimens of natural rubber (NR) strip with a width of 3 mm, length of 25 mm, and height of 1, 2, 3, 4, or 5 mm were affixed onto the base rubber sheet (25 mm × 25 mm × 2 mm) at an interval of 2 mm. The Shore A hardness values of the rubber strips were 37, 47, and 61. The specimens thus obtained were slid against a stainless steel plate that was lubricated with 90 wt.% glycerol solution. Slid tests were performed to analyze the effects of hardness, height of the rubber strip, and the orientation angle of the rubber strip with respect to the sliding direction on the static coefficient of friction (SCOF) and dynamic coefficient of friction (DCOF) values. Results indicated that soft (Hs37) and thin rubber strip (height: 2 mm) with an orientation angle of 0° (parallel to the sliding direction) provided the highest SCOF (1.39) and DCOF (1.18) values. For rubber hardness values corresponding to 47 and 61, a thin rubber strip (height: 2 mm) with an orientation angle of 30° showed the highest SCOF and DCOF values. The contact area observed using the total reflection of light demonstrated a larger contact area for the thin rubber strip corresponding to the orientation angle of 0°, thereby resulting in high SCOF and DCOF values. Softer rubber tread block with high stiffness toward frictional force in the sliding direction is effective in facilitating high slip resistance under lubricated surfaces.