A hardness tester sounds like something students use to select the courses they might want to avoid, but it is in fact a device for measuring the hardness of a material. Hardness is a characteristic of a given material defined as the resistance to indentation. We all have a conceptual definition of hardness, since we all understand when someone says that steel is harder than wood. A hardness tester allows the user to quantify this concept.
Using a hardness tester, a person can say that material A is twice as hard as material B. There are over 12 different accepted methods of testing for hardness. The most common method is known as the Rockwell Hardness Tester, and the results are given in terms of the Rockwell hardness scale. A Rockwell Hardness Tester is used to measure the hardness of metals. There is a strictly defined method for preforming a Rockwell Hardness Test and specifically built Rockwell Hardness Testers.
Metals are the most common materials for which a hardness tester is used. The reason for this is that the hardness of a metal is dependent upon its composition and state. Steel is the most common metal for which hardness testing is done, and steel is an alloy, meaning that it is a mixture of different elements. The degree to which these elements are mixed together in the steel will affect its hardness. In many steels, these mixtures separate slowly over time in a somewhat similar manner to oil and water.
You can use a hardness tester to determine how much the steel has started to separate, since the hardness will change as the elements separate. This is very important if the steel has been used to build a bridge, for instance. If the steel is becoming softer, then the bridge is no longer as sturdy and eventually may no longer be safe. Using a hardness tester, materials engineers can determine when an old steel bridge may need to be replaced by a new steel structure.
Hardness testers are also used to grade materials, particularly steels. A very hard steel may be required for one type of application, while a milder steel may be required for a different application. The difference may be small enough that you cannot tell which is best without using a hardness tester. However, this small difference can often be the difference between success or failure.