In the present work, polymeric particles such as polymethyl methacrylate (PMMA), polyethylene (PE) and polystyrene (PS) were used as solid lubricants dispersed in paraffin oil in concentration of 5, 10, 15 and 20 wt. %. Tests were carried out using cross pin wear tester. Friction coefficient was investigated under application of an electric voltage of 1.5, 3, 4.5 and 6 volts.Test specimens were in the form of cylinders of 18 mm diameter and 150 mm length.
The experimental observations showed that for oil free of polymer friction coefficient displayed a value of 0.08 at no voltage. For both positive and negative voltage friction coefficient decreased with voltage increasing. Adding polymeric particles into the oil displayed slight friction increase at no voltage. Friction coefficient increased with increasing voltage regardless the charge. Adding polymeric particles into oil caused significant friction increase in the presence of applied voltage. This is because the polymeric particles strongly adhered to the steel surfaces and the contact will be between polymeric particles and steel. The highest friction values were displayed by PS followed by PE and PMMA.
Applying electric current on the lubricated contact of the tested steel specimens showed that wear significantly decreased. Adding polymeric particles into the oil caused significant wear decrease when the electric voltage was applied. In condition of no voltage, wear slightly decreased due to the direct adherence of polymeric particles into steel. The enhancement in wear was observed for positive and negative voltages. Further increase in polymer content dispersing oil showed significant wear decrease. At no voltage, wear displayed the highest values. When the rotating pin was anode or cathode, wear significantly decreased.