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8. Select a loading speed, with the "Load" NOTE valve, that will meet the following require- When conducting compression tests in ments: which the deformation is relatively a. Specifications generally designate the small, it is suggested that the piston is loading speed to be used when testing raised an additional inch above its specimens to that specification; in normal start position. Otherwise, to some cases it may be necessary to unload, it might be necessary to clear calculate the loading speed from the piston positioner switch by lifting known or given data. the activating mechanism. (Fig. 5-1). b. In the absence of a testing specifica- B. Run lower crosshead up or down on screws tion, a good rule to follow is: Select that the distance between the face of a loading speed that will allow the the compression plate and the weighing load pointer to move sufficiently slow table is slightly greater than the overall that its position may be accurately length of the specimen. read at any time. C. Set specimen on weighing table so the specimen is approximately concentric with 9. Apply load to specimen by actuating the the circular grooves in the compression "Load" valve. Load may be applied, removed, plate. or held constant by manipulating the "Load" NOTE and "Unload" valves. It is recommended that a block of steel 10. After the specimen fails, close "Load" be placed between the specimen and valve and open "Unload" valve to move down the weighing table to prevent damage to the piston positioner stop switch. to the weighing table. 11. Remove tested specimen from machine. D. Zero all load ranges with the zero adjust- ment controls. COMPRESSION TESTING E. Select a load range that is applicable to the size of the and to the type A. In conducting compression tests it is nec- of material being tested. essary to install the compression plate in F. Select a loading speed with the "Load" the lower crosshead as follows: value that will meet the following require- ments: 1. Check to be sure that all tension testing plates and tools have been removed from the lower crosshead. 1. Specifications generally designate the loading speed to be used when testing speci- 2. Position the compression plate to the mens to that specification; in some cases it underside of the lower crosshead, and posi- may be necessary to calculate the loading tion plate and wing nut to end of stud and speed from known or given data. tighten. 2. In the absence of a testing specification, 3. Depress "Start" button to begin oper- a good rule to follow is: Select a loading speed ation of the pump. that will allow the load pointer to move suf- ficiently slow SO that its position may be ac- 4. Make sure piston is in its start test posi- curately read at any time. tion. To check, open the "Load" valve and G. Apply load to specimen by actuating the raise piston about two inches. Then close the "Load" valve. "Load" valve and open the "Unload" valve. The piston will drop until the piston posi- H. As the test progreses, record all pertinent tioner valve closes and stops the piston data required by the specification. inch from the bottom of the stroke. Then I. Remove tested specimen from the ma- close the "Unload" valve. chine. 24