Static friction of stainless steel wire rope–rubber contacts

• Static friction measurements were done on stainless steel cable-rubber pairs.
• LAT delivered about twice as high static friction as NIT or SIL.
• Cable size and structure had only minor effects on static friction.
• Friction theories should not be applied without considering interaction effects.
• Static friction is a minor factor in selecting cables for practical use on rubber.

Little is known about static friction of stainless-steel wire ropes (‘cables’) in contact with soft rubbers, an interface of potential importance for rigidifiable medical instruments. Although friction theories imply that the size and profile of the cables affect static friction, there are no confirmative data for stainless-steel cable-rubber contacts. Static friction was measured between five cable types (0.18, 0.27 and 0.45 mm diameter, twisted in 1×7, 1×19, or 7×7 strands) and latex, nitrile, and silicone rubber. Mean static friction coefficients of the cables ranged over 0.27–0.31, 0.25–0.27, and 0.44–0.53 for nitrile, silicone, and latex, respectively. Overall, the cable type had little effect on static friction. For all cables, friction was twice as high for latex as for nitrile rubber, which had slightly higher friction than silicone rubber. The higher static friction for nitrile compared to silicone rubber despite silicone rubber being significantly softer could be caused by the high polar surface free energy of nitrile rubber. Common friction theories were valuable in predicting the effect of cable profiles and rubber properties on static friction but should not be applied without considering interaction effects. Static friction seems to be a minor factor when selecting cables for practical applications involving cable-rubber contacts.