Rolling wear of EPDM and SBR rubbers as a function of carbon black contents: correlation with microhardness

The rolling friction and wear of ethylene/propylene/ diene (EPDM) and styrene/butadiene rubbers (SBR) with different carbon black (CB) contents were studied against steel in orbital rolling ball (steel)-on-plate (rubber) test rig (Orbital-RBOP) and oscillating rolling ball (steel)- on-plate (rubber) set-up (Oscillating-RBOP). The universal hardness (H), coefficient of friction (COF), and specific wear rate (Ws) of EPDM and SBR were determined. Incorporation of CB increases the universal hardness and the COF (the latter marginally) and decreases the specific wear rate for both EPDM and SBR. The wear mechanisms were concluded by inspecting the worn surfaces in scanning electron microscope and discussed as a function of CB modification. An inverse relationship between the specific wear rate and universal hardness was proposed in form of Ws = kH-n, where k and n are constants for a given rubber and testing condition.