The Brinell and Rockwell hardness tests can be used to evaluate the hardness of a wide range of metallic materials. When either test is performed accurately to procedure each will produce a reliable hardness rating to compare to other materials. While both the Brinell and Rockwell tests are consistent, they produce values of hardness on different scales from each other due to slightly different methods and analysis.

The Rockwell test measures hardness by using diamond cone indenter. The indentation is measured after a lighter initial load is applied and after a heavier load is applied. This test is carried out on a machine that records each depth and calculates the hardness factor. The evaluator must consider the fundamental properties of a sample before it is tested to ensure it is being evaluated using the proper loading. The hardness is reported on one of the scales A through G; depending on what material is being tested and which loading is used in the procedure.

The Brinell test is the predecessor to the Rockwell test. It reports a hardness factor that can be compared on a single scale but only factors can be compared that were tested using the same ball size and force. Despite it being a more primitive test, it is still used and considered accurate, especially for larger parts that have a coarse grain structure. Popular test samples are casted steel or iron that are not as easily evaluated with the Rockwell test. The Brinell test procedure can take a little bit longer than the Rockwell test. First a material sample has to be prepared to test. A steel or tungsten carbide ball (typically 1 cm in diameter) is then shot at the sample with a 29 kN force. The dent is measured optically with a microscope or by a mechanism in an electronic device. The two diagonals of the indentation are measured along with the diameter of the ball. These dimensional values are used to solve the Brinell hardness formula.

When comparing the two tests it is important to understand that one is not particularly better than the other. Each has its own benefits, but choosing one over the other depends on which material is being tested and what equipment is available. Automatic test machines are manufactured in the format of each test but are not always available. One may assess that optically measuring an indentation in the Brinell test is not as accurate as a Rockwell test because the indentation of the carbide ball is not as consistently finished as a diamond cone. However, the Brinell test does not destruct the test material. This is large advantage that the Brinell test has over the Rockwell test because it is easier to perform on steel or iron parts. These larger parts are heavier and inherently more expensive making it a crucial factor that they can still be used. It can be concluded that the Rockwell test is easier and more accurate for smaller samples of less coarse material.

Source by John Noriega

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