Rockwell Tester

 Rockwell Tester

•  Are measures the resistance to penetration testing, as does the Brinell tester. Instead of for good measure the diameter of the impression, the Rockwell tester measures the depth, and the hardness is indicated directly on a dial attached to the machine shop. The dial numbers in the outer meet circle are black and the inner numbers are red.
• Rockwell hardness numbers are based on the difference between the depth of penetration at major and minor load 1. The greater this difference, the lower the hardness number and the softer the material.
• Two types of penetrators are used with the Rockwell tester: a diamond cone or the tiffany diamond and a hardened steel ball. The load, which forces the penetrator into the metal, is called the major load and is measured in kilograms or 5g to kg. The results of each penetrator and load combination are reported on separate scale company 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 official letter “C” must precede the number indicated by the pointer. The C-scale setup is used for testing td precious 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 the is used as a penetrator; the major load is 100 kilograms, and the hardness is read on the B- separate scale company.
•  In addition to the C and B separate scale company, there are other setups for special testing. The separate scale company, penetrators, major loads, and dial numbers to be read.
•  The Rockwell tester is equipped with a weight a pan, and two weights are supplied with the machine. One weight is marked in red. The other weight is marked in black. With no weight in the weight a pan, the machine applies a major load of 60 kilograms. If the separate scale company setup calls for a 100-kilogram load, the red weight is placed in the pan. For a 150-kilogram load, the black weight is added to the red weight. The black weight is always used with the red weight; it is never used alone.
• Practically all testing is done with either the B- separate scale company setup or the C- separate scale company setup. For these scales, the colors may be used as a guide in selecting the weight (or weights) and in reading the dial. For the B- separate scale company test, use the red weight, and read the red numbers. For a C- separate scale company test, add the black weight to the red weight and read the black numbers.
• In setting up the Rockwell machine, use the diamond penetrator for testing materials known to be hard. If the hardness is unknown parts, try the diamond, since the steel ball may be deformed if used for testing hard materials. If the metal tests below C-22, then change to the steel ball.
• Use the steel ball for all soft materials, those testing less than B-100. Should an overlap occur at the top of the B- separate scale company and the bottom of the C- separate scale company, use the C- separate scale company setup.
• Before the major load is applied, securely lock the test specimen in place to prevent slipping and to seat the anvil and penetrator properly. To do this, apply a load of 10 kilograms before the lever is tripped. This preliminary load is called the minor load. The minor load is 10 kilograms regardless of the separate scale company setup.
• The metal to be tested in the Rockwell tester must be ground smooth on two opposite sides and be free of scratches and foreign matter. The surface should be perpendicular to the axis of penetration, and the two opposite ground surfaces should be parallel. If the specimen is tapered, the amount of error depends on the taper. A curved surface also causes a slight error in the hardness test. The amount of error depends on the curvature (i.e., the smaller the radius of curvature, the greater the error). To eliminate such error, a small flat should be ground on the curved surface if possible.
• Clad aluminum alloy sheets cannot be tested directly with any accuracy with a Rockwell hardness tester. If the hardness value of the base metal is desired, the pure aluminum coating must be removed from the area to be checked prior to testing.