Comparative evaluation of several hydraulic fluids in operational equipment, a full-scale pump test stand, and the four-ball wear tester

A four-ball wear test has been designed and tested with a series of petroleum based hydraulic fluids. This test procedure comprises a sequence of three 30 minute test segments designed to evaluate "wear in," steady state wear and the effect of antiwear films produced in the first two parts of the test. Excellent repeatability of this sequential testing has been established. The wear properties of formulated fluids have been shown to be a function of system temperature and bearing load. A series of formulated mineral oil base lubricants that have been evaluated extensively in heavy-duty industrial hydraulic equipment have also been evaluated in a laboratory pump test system and the sequential four-ball wear test. A correlation developed for the heavy-duty industrial hydraulic systems with the laboratory pump test system has been extended to the four-ball wear tester sequential runs under specific load and temperatures.