Influence of ZnO concentration in rapeseed oil on tribological behavior

This paper presents results of testing the coarse rapeseed oil additivated with different concentrations of ZnO (0.25%wt, 0.50%wt and 1%wt, with 14 +/- 5 nm in size), on a four-ball machine. The test parameters were load on main shaft of the machine: 100 N, 200 N and 300 N and the rotational speed 1000 rpm, 1400 rpm and 1800 rpm. For the tested range of ZnO concentration, the value of 1%wt does not improve the friction coefficient, but the wear rate of wear scar diameter was lower than that obtained with the neat rapeseed oil and the values are less sensitive with load and sliding speed for the more severe regimes. The additivation of rapeseed oil with ZnO is still efficient for the tested range of load and speed as compared to neat rapeseed oil. The authors formulated lubricants using as dispersant (2-methoxyphenol) in the ratio 1:1 to the additive. The technology is at scale laboratory and implies mechanical stirring and sonication. The tribological behavior was analysed based on obtained results, by mapping the friction coefficient, the wear rate of the wear scar diameter and the final temperature in the oil bath. For the additivated lubricants the following conclusions could be drawn. Friction coefficient tends to reach 0.1 only for low speed and high load (v = 0.38 m/s and F = 300 N), wear rate of wear scar diameter decreases with the increase of load, for each tested speed, probably because of a full fluid film generation. For F = 250...300 N, the map reveals a poor dependence on the additive concentration. The final temperature in the lubricant bath depends on speed, but for the same speed, it depends less on load, having a maximum value for 0.75% nano additive. These conclusions underlined the necessity of testing the new formulated lubricants because additive concentration and regime parameters could have synergic influences on the tribological parameters.