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HARDNESS TESTING
ROCKWELL TESTER

Aviation Structural Mechanic (H&S) 3&2 - How airplanes are built and how to maintain them
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Figure 1-25.—Brinell hardness tester. Figure 1-26.—Microscopic view of impression. BRINELL TESTER The Brinell hardness tester, shown in figure 1-25, uses a hardened spherical ball, which is forced into the surface of the metal. The ball is 10 millimeters (0.3937 Figure 1-27.—Rockwell hardness tester. inch) in diameter. A pressure of 3,000 kilograms (6,600 pounds) is used for ferrous metals and 500 kilograms for nonferrous metals. Normally, the load should be applied for 30 seconds. In order to produce equilibrium, this period may be increased to 1 minute for extremely hard steels. The load is applied by means of hydraulic pressure. The hydraulic pressure is built up by a hand pump or an electric motor, depending on the model of tester. A pressure gauge indicates the amount of pressure. There is a release mechanism for relieving the pressure after the test has been made, and a calibrated microscope is provided for measuring the diameter of the impression in millimeters. The machine has various shaped anvils for supporting the specimen and an elevating screw for bringing the specimen in contact with the ball penetrator. There are attachments for special tests. To determine the Brinell hardness number for a metal, the diameter of the impression is first measured, using the calibrated microscope furnished with the tester. Figure 1-26 shows an impression as seen through 1-36







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