Frictional properties of some additives for sliding guide way lubricants in a sliding speed range between 0.002 and 1.5 m/s with a thrust collar friction tester

Frictional properties of some additives used in sliding guide way lubricants were studied for a pair of mild steels under sliding speeds ranging from 0.002 to 1.5 m/s with a thrust collar type friction tester. As the sliding speed was decreased, the coefficient of friction first decreased, then after reaching the minimum value, it increased. The minimum friction coefficient μmin and the transition sliding speed Vmin showing μmin depended upon the additive. That is, μmin for the oil containing sulfurized lard was lower than those for the other oils tested and its Vmin was as low as 0.005–0.1 m/s compared with the transition speeds of 0.2–0.5 m/s for the other oils tested. Observations of the surface profile and surface analyses of the test specimen after the tests indicated that the unique phenomena for sulfurized lard were due to the formation of a boundary film containing a long carbon chain with a chemical bond between the sulfur and carbon.