Effect of Long Used Machine Oil on the Tribological Behaviour of Cu-Based Gear Materials

Abstract

A wear test was performed under the long-used machine oil sliding environment on Cu-based alloys Al-bronze and α-brass. A pin-on-disc wear testing method was applied where normal pressure of 0.255 to 2.55 MPa and a constant sliding speed of 0.641 m/s were considered. For the assessment dry and fresh machine oil sliding environments were also conducted. The results from the experiment demonstrated that the wear rate and friction coefficient in dry sliding condition were much greater for their direct contact but lower under machine oil due to the reduced roughness by the sealing effect as oil forms a thin lubricating film between the contact surfaces. Used oil displayed some degree of higher wear rate along with friction coefficient due to heavy and harmful chemical compounds in it. Al-bronze performed the better wear properties with lower wear rate and coefficient of friction for all the environments as it achieved the strength through different intermetallic formations. In case of α-brass, it had little effect on wear characteristics. Examined by optical microscopy and SEM analysis, worn surfaces showed that Al-bronze improved wear resistance through mild and smooth abrasive grooves filled with oxides in dry sliding conditions. In case of oil sliding environment, smooth surfaces were created by the resistance of the oil film to the direct contact between the surfaces. Used oil sliding conditions reduced the surface smoothness of the Cu and Cu-based alloys for the presence of damaging chemical compounds.