The effect of sample spin on boundary lubrication by several oil blends based upon zinc dialkyldithiophosphates

A direct observation wear machine (DOWM), was modified to spin the ball sam ple around the point of contact on a rotating countersurface in order to si mulate aspects of reciprocating wear while retaining some observational cap ability. Four commercial zinc dialkyldithiophosphates (ZDDPs) with and with out dispersants or detergents were worn against the normal sapphire counter surface and also against steel. Wear constants averaged over the 60-min run s ranged from 0.01 to greater than 10 mu m(3)/N m. Wear behaviour could be followed with time when wearing against sapphire. Significant changes in ra te occurred in about half of these runs, with eight decreasing and 10 incre asing. Good performance was clearly associated with the presence of films o n wear scars. The addition of spin had a minor deleterious effect when the performance in both modes was good or bad: however, there were four instanc es when spinning changed poor protection to good and three instances when s pinning changed good protection to poor. Reciprocating wear therefore appea rs to be no more difficult to lubricate than other actions. However, as ble nds could behave very differently with only minor changes in the wearing co nditions the practise of rating oils in rigs matched to the application is justified. (C) 1999 Elsevier Science S.A. All rights reserved.