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Aviation History
1934
1934 - 1465.PDF
NOVEMBER I, 1934 77 THE AIRCRAFT ENGINEER SUPPLEMENT TOFLIGHT 1152f TESTING THE FILM STRENGTH OF LUBRICANTS A Machine Which Also Measures Friction and Wear ASIMPLE machine has been designed which, it isclaimed, gives accurate information on the load-carrying capacity of lubricants. The machine also measures friction and calculates the wear-resisting properties of materials. It is manufactured by British Timken, Ltd., the makers of tapered roller bearings. Until recently reliable information of this character had been obtainable only through complicated and expensive laboratory research. The new machine has therefore proved a boon, not only to manufacturers and users of lubricants, but also to producers of all kinds of materials. The Timken lubricant and wear-testing machine was developed during research work in the company's labora- tories. Originally it was used for obtaining measurements of the film strength of lubricants. Later it was improved and adapted to perform the three functions mentioned. The general appearance of the machine is as shown in Fig. 1. Fig. 2 shows the essential details of the load and testing lever system. The main features of the device are the lubricant container and return pump, the lever system, and the arrangements for direct or belt drive. The lubri- cant container holds about a gallon of lubricant, which can be raised to and maintained at any tempcraturo up to 210 deg. Fahr. by means of an electric hotplate. When the machine is in use the lubricant under test is constantly circulated by means of a pump in the base. The Lever System The lever system consists of two levers, one above the other. The upper lever, carrying the test block, is known as the "load lever" and is pivoted on a knife-edge mounted in the lower or "friction lever." The latter, which is also pivoted on a knife-edge, has a stop at the unloaded end, and is provided with a Vernier scale and a sliding weight for obtaining accurate measurements. , ' 1^T*^?I ^ 6 1 : The Timken lubricant and wear-testing machine. A tapered mandrel carries the testing cup, and a notch in the adapter carried on the load lever is provided to take the test piece Friction is measured between cup and test the P^u rom the container flows regularly the two contacting surfaces. The arrangement of the levers ensures that the test piece is always in the same position relative to the revolving cup and that the unit-loading over the length or surface of the two test pieces is always constant. Provision is made for either direct or belt drive by means of a 2 h.p. synchronous speed electric motor. An 8in. pulley with a 3m. face is mounted on an extension of the mandrel, and a key way is provided so that the motor may be coupled direct to the mandrel if desired. The oil pump is mounted in the base of the machine, and is driven from the testing mandrel. In operation the lubricant from the container flows over the test piece, the rate of flow being controlled by means of a valve in the pipe line. It then enters a sump, whence it is pumped back to the container. The mandrel is mounted on two Timken tapered roller bearings to preserve positive align- ment, and is tapered at the end opposite the drive to receive the test cup. Test Procedure for Lubricants In using the machine for testing the film strength of lubricants, both test pieces, that is the cup and the block, i;re usually made of carburised steel, hardened to 60 deg. C. Rockwell and ground. Four tests may be carried out with one test block, but each new test requires a new cup or a reground surface of the cup. Newly ground faces on both pieces are necessary to ensure accurate and uniform results. Assuming both test pieces are in position, and the lubri- cant is heated to the required temperature, the driving motor is brought up to the desired speed and the lubricant is allowed to flow over the test block. The loading lever is then loaded by means of weights until the desired unit pressure is obtained. The full load should be applied at once rather than gradually, because the first few seconds of operation determine the possibility of sustaining loads when near the scoring point. Breakdown tests are usually run for a period of ten minutes, and the surface of the block after test is tru- final check. If the surface is very scratchy or scored, then the load-carrying capacity of the lubricant has been ex ceeded. Rubbing speeds vary according to the type of test, and as an example it may be observed that lubricants for automobile rear axles are usually tested at 400 r.p.m. (800 r.p.m. of the spindle). Light oils, such as free-wheel ing lubricants and motor oils, are tested at 200 r.p.m. Greases may be tested by using a special chamber which surrounds the test pieces. The chamber is filled with grease before the tests begin, and is kept filled by adding grease from a screw-down container, which is inter- changeable with the oil container supplied with the machine. Care must be taken to add grease at a constant rate in order that tests may be truly comparative. Use of a Chart A chart provided with the machine shows the number of lb. avoirdupois placed on the loading lever in terms of 1,000 lb. of unit pressure on the test pieces. The chart also shows the turning speed necessary to produce any given rubbing speed, both by direct and belt drive. Standard formula- for use with the machine are given on the charts. Reference to Fig. 2 in conjunction with the following list of symbols used will make clear the method of taking readings and calculating results: A. Weight on the load lever. B. Weight on the friction lever.
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