Hardness is property of solid material, which allows it resist deformation brought about by an external force. A hardness tester is of great importance in modern day engineering scenario because it ensures safety and reliability in any manufactured product.
There are different types of hardness testing machines available in the market and they follow different hardness checking procedures. With advent of microprocessor technology in field of testing and calibration, one can see computer driven hardness testing machines in the market that eliminate manual errors and give precise meaurements.Following are major types of hardness testing machines that are employed by the material testing laboratories. They are:
Rockwell Hardness Tester
The Rockwell hardness tester applies the load on a selected point on the material surface and measures the net increase in the depth of impression. It is used basically to test hardness of steel, malleable iron and chilled iron castings on HRC scale. This testing methodology works well while testing the parts that manufactured on mass scale and is more suited to large production houses, where quick , accurate and reliable hardness testing can be done , piece by piece on semi-finished and finished goods.
Brinell hardness Tester
This type of hardness tester is used where a larger testing depression needs to be created to detect average harness of the surface in a fly. Brinell hardness is determined by forcing hardened Carbide sphere against the surface. The hemi-spherical impression created, indicates the hardness reading, which is also called as Brinell number, measured in HB. The Brinell hardness number is obtained by dividing the load used, in kilograms, by the actual surface area of the indentation, in square millimeters. This type of method offers a quick and precise hardness reading, with smaller dispersion of hardness values. It is an ideal hardness testing method for foundries. By Brinell hardness test one can easily calculate the tensile strength of surface through a conversion table.
Shore Hardness Tester
In this type of machine a diamond tipped hammer is impacted on the surface and the hardness reading that shows up on the dial is calculated after taking in account the rebound height. Harder surface will cause a higher rebound, which means that surface has a higher hardness number. This hardness tester is known as Durometer and is used to measure the hardness of polymers, rubbers and plastic. Because of the resilience of rubbers and plastics, the hardness reading may change over time. Hence the indentation time is sometimes reported along with the hardness number in the test report.
Vickers Hardness Tester
This type of hardness tester measures the hardness of the metal and ceramic by pressing a pyramid shaped indenter against the surface. The diamond shaped impression left on the surface is measured by the calibrated microscope and the hardness of the material is calculated on the basis of the size of the indent created on the surface. This is a reliable method of measuring hardness and devised by Vickers, Ltd., UK. The machine employs square-based pyramid that is slowly presses it against with load of 120 kilograms to create an impression. It is floor mounted machine with automated controls to ensure precise testing results.