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    Factors Affecting Simulated Service Tests of Greases

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    There have been many attempts to establish a reliable means for predicting the service life of a grease. Greases have been selected on the basis of composition, physical characteristics, and operation in actual equipment. More recently, simulated-service tests have been used and have been accepted as a dependable means of evaluating greases. These tests are in most cases less time consuming than those in actual standard equipment. However, there is still a need for a means of accelerating testing to obtain results in a shorter time without reducing their reliability. This paper deals with our attempts to accomplish this objective. The initial work on the evaluation of greases by performance tests led to the development of the Navy Grease Machine. This work was described by Adams and Patten in 1941. This machine was abandoned when reports from the field indicated that the premises on which its evaluation of greases was based were invalid. It then was necessary to devise a test which would more nearly simulate service conditions. Simulated-service testing of greases under conditions of high temperature and high speed was started with an apparatus designed to rotate a No. 204, grease-lubricated ball-bearing at 10,000 rpm. while maintaining any desired temperature. A Specification for High Temperature Water Resistant Grease was subsequently written around this apparatus using as the criterion of acceptability a minimum of 300 hr. satisfactory bearing operation at a temperature of 300 F. This work was summarized last year by Adams and Collegeman. The information and experience gained with this apparatus were used to design and construct an improved tester which permits better control of more variables. This apparatus has been given the name of Universal Grease Tester, a single unit of which is illustrated in Fig. 1. This apparatus recognizes and provides control of four variables: temperature, speed, bearing size, and bearing load, both radial and axial. Permissible temperatures with this installation range up to 500 F., speeds up to 20,000 rpm., bearing sizes up to 60-mm. bore, and bearing loads up to 50 lb. The radial-load range can be extended readily by modification of accessories without changing the basic design of the unit. In order to obtain in a reasonable time sufficient replicate runs for appraisal of both the magnitude and the variability of the results, thirty units of this tester have been installed. Two views of the assembly are shown in Figs. 2 and 3.

    Author Information:

    Collegeman, Sidney M.
    Head of Grease Section and Chemical Engineer, U. S. N. Engineering Experiment Station, Annapolis, Md.

    Belt, John R.
    Head of Grease Section and Chemical Engineer, U. S. N. Engineering Experiment Station, Annapolis, Md.

    Committee/Subcommittee: D02.GO

    DOI: 10.1520/STP46229S