When you go to purchase certain types of materials such as metal sheets, you might notice that they come with specific numbers. To some, these numbers might seem like a mystery. Within these numbers is likely to be a hardness rating telling you how hard the metal is. In order to determine the hardness, tests had to be performed on that type of metal. One method of such testing is known as the Rockwell hardness testing method.
Rockwell hardness testing is the most common method for testing the hardness of metals. It is simple to do, accurate, and there are fairly strict guidelines put out by the American Society for Testing and Materials (ASTM) that explain how to properly test material hardness using the Rockwell method. Following these guidelines gives the most accurate results.
This method measures the depth an indenter makes on the material. This is done by testing a preload using a diamond indenter. This indenter may be either a ball or conical. A measurement is taken, representing the zero measurement for the test. The force for this preload usually ranges from 3 kgf (kilograms-force) to 15 kgf. A major load is then applied where the force of the indenter is held for a specified length of time. The force for the major load usually falls in the range of 15 kgf to 150 kgf. When this load is released, another measurement is taken and compared to the preload. The distance between the preload and the final depth is then changed to a number representing hardness.
When using the Rockwell hardness testing method, it is important to keep in mind that materials that are too thin, such as sheet metal below the minimum thickness requirement, has the potential to produce flawed results or even damage the testing equipment. It is important that you have the proper testing equipment, the right type and thickness of materials, and use the guidelines as specified by ASTM E18 for the most accurate results.
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