ROCKWELL TESTER

Table 1-3.—Portion of Conversion Table Furnished with Brinell Tester the microscope. After measuring the diameter of the impression, the measurement is converted into the Brinell hardness number on the conversion table furnished with the tester. A portion of the conversion table is shown in table 1-3. ROCKWELL TESTER The Rockwell hardness tester, shown in figure 1-27, measures the resistance to penetration as does the Brinell tester, but instead of measuring the diameter of the impression, the Rockwell tester measures the depth, and the hardness is indicated directly on a dial attached to the machine. The more shallow the penetration, the higher the hardness number. Two types of penetrators are used with the Rockwell tester–a diamond cone and a hardened steel ball. The load that forces the penetrator into the metal is called the “major load,” and is measured in kilograms. The results of each penetrator and load combination are reported on separate scales, designated by letters. The penetrator, the major load, and the scale vary with the kind of metal being tested. For hardened steels, the diamond penetrator is used, the major load is 150 kilograms, and the hardness is read on the C scale. When this reading is recorded, the letter C must precede the number indicated by the pointer. The C-scale setup is used for testing metals ranging in hardness from C-20 to the hardest steel (usually about C-70). If the metal is softer than C-20, the B-scale setup is used. With this setup, the 1/16-inch ball is used as a penetrator, the major load is 100 kilograms, and the hardness is read on the B scale. In addition to the C and B scales, there are other setups for special testing. The scales, penetrators, major loads, and dial numbers are listed in table 1-4. The dial Table 1-4.—Standard Rockwell Hardness Scales 1-37