Metal hardness testing is used to determine the rigidity of a metallic substance. What constitutes hardness is somewhat vague, though a common definition of hardness characterizes how resistant the material is to warping and deformation. This testing process is crucial to the manufacturing industry, among others, because it tells the metalworkers how compatible the material will be with their means of production. There are many forms of this examination process. In the early twentieth century, however, there were only four widespread assessment practices.
The first of these was known as Turner’s Sclerometer and it was developed in 1896. In this method, a carefully weighed diamond point is run across the surface of the metal being tested. The level of hardness is determined by the diamond weight needed to produce a substantial scratch to the metal’s surface. The scratch is only sufficient when it is visible as a dark line to the naked eye. Another quality to look for is whether or not the scratch can be felt from a quill edge drawn over its surface.
The next form of metal hardness testing was created in 1907 and is known as Shore’s Scleroscope. During this technique, the hardened point of a small cylinder made of steel is dropped on the surface of the metal. The height of the rebound determines the measurement of hardness. The height of the fall is about 10 inches.
Brinell’s test, created around 1900, involves a steel ball being pressed into the metal’s surface. The purpose is to form an indentation sizeable enough to be measured under a microscope. The hardness level is known by comparing the spherical indentation area, the pressure used and the stress per unit when the ball becomes rested.
The final method of metal hardness testing was implemented in 1893. Keep’s test involved a steel drill making a definite number of resolutions while it pressed against the metal being tested. The level of hardness is recorded automatically on a diagram. A soft material produces a horizontal line while a hard metal gives a vertical line. Intermediate hardness is shown by the angle corresponding to 0 and 90 degrees.
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