Heavy Duty Gear Oils

Abstract

The development of suitable laboratory methods for the evaluation of gear oils would be an important aid in the selection of gear lubricants. The tests should be such that they can be completed in a matter of hours rather than days and in which the test apparatus is of low cost. Test equipment such as the Timken, Falex Tester, Shell Four-Ball Lubricant Tester, and others of this type, though widely employed, did not, at first, appear to offer the solution to the present problem. Chief among the apparent shortcomings was the reputed fact that these machines did not rate any given series of lubricants in the same order, and that correlation with field performance characteristics had not always been established. However, the important advantages of these machines from the point of view of initial cost, cost of operation, volume of oil required, and extreme flexibility in the choice of test conditions suggested that these types of apparatus offered a logical starting point. Some time ago a program was inaugurated at Aluminum Research Laboratories directed to the development of satisfactory procedures employing the Falex, Timken, and Four-Ball machines for the preliminary evaluation of heavy duty gear oils. Many hundreds of commercial heavy duty extreme pressure gear oils were tested, involving some thousands of test runs. Gear oils with extensive and known field performance characteristics were included. As a result of that work, a system was developed which, we believe, has merit as a preliminary screening test for the classification of heavy-duty gear oils. In brief, this procedure involves testing a given lubricant with each of the three machines. The performance of the oil in each of the three machines is determined and the data combined by means of standard rating charts. The results are thus reduced to a single number, which is a measure of the utility of the lubricant. Experience to date strongly suggests that the over-all performance of a lubricant as indicated by the combined results obtained on the Four-Ball, Timken, and Falex is appreciably more significant than would be the case if the Falex, the Four-Ball, or the Timken data were to be considered singly.