When machining, it is necessary to know the hardness of workpiece material beforehand. There are a number of methods in which hardness can be calibrated. When machining, it is necessary to know the hardness of workpiece material beforehand.
There are a number of methods in which hardness can be calibrated. Each method varies slightly, the main factors that varies is the force that is applied to a penetrating device that is pressed into the workpiece surface, and the geometry of the penetrating device.
Below is an example of the 3 main calibration methods.
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Rockwell hard (HR)
The Rockwell hardness is determined by the depth of an impression left in the surface of a material after subjecting the penetrating device to a specific load. The units for the hardness is given as HRC (in the case of a C scale). Rockwell hardness is the scale that is most often used in machine workshops.
Vickers (HR)
The Vickers hardness is determined by the size of a surface area of an impression left in a material after pressing the tip of a diamond square pyramid penetrating device into a test material. The hardness value is shown as OOOHV.
Vickers (HR)
The Brinell hardness is determined by the size of a surface area of an impression left in a material after pressing a steel or cemented carbide ball into the test material. Generally a 10mm diameter ball is used, the load applied is 3,000kgf (29,400N). The Brinell hardness is shown as OOOHBS (10/3,000). More often than not the S(10/3,000) is omitted.
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