THIS paper describes briefly why extreme-pressure lubricants are necessary and what machines most commonly have been used to evaluate them.
Examples of differences in test results caused by differences in operating conditions, by the type of machine used, and by the method of installation of the machine are presented.
The new S.A.E. Extreme-Pressure-Lubricants Tester is described, and the probable advantages of the machine are discussed.
Other requirements of commercial extreme-pressure lubricants are listed.
In conclusion, the statement is made that the new machine is believed to constitute an approach to the gear problem that is more sound fundamentally than that of any of the other machines that have been used. In the older machines one or more of the test surfaces was always stationary while, in the S.A.E. Tester, both surfaces are in motion and a combination of sliding and rolling friction approaching that of gearing may be achieved.
In spite of this progress, however, the problem is by no means solved and a true solution can be achieved only by correlating the S.A.E. Tester with actual service tests.