The Rockwell hardness test is a static type hardness test that slowly forces a standardized indenter into the test material with a standardized load. The relationship between load and depth of penetration determines the hardness value for a given scale.
There exist thirty different Rockwell hardness scales each of which use a different combination of indenter size, indenter shape, and indentation load. Each scale is optimized for material hardness and material thickness. For example, thin test material like hard steel sheet or a case hardened layer of steel, or even a hard coating requires a scale that produces a relatively shallow indentation which is not influenced by the softer underlying material. Rockwell "superficial" scales are used for this purpose. Fifteen of the thirty Rockwell scales are for superficial type measurements.
The conventional Rockwell hardness tester is generally destined to sit on a laboratory bench, that is, they are not portable. Smaller, handheld instruments are offered for field-testing situations. The smaller units are convenient to use but require additional operator skill to produce accurate and repeatable hardness measurements.
Measurement accuracy and precision depends more on the test specimen and less with the test instrument. When taking Rockwell hardness measurements, it is imperative to consider the surface condition of the test-piece.
The following precautions should be observed:
The remaining static type hardness scales will be discussed in the following articles.