Rockwell Hardness - A common
method of testing a plastic material for resistance
to indentation in which a diamond or steel ball, under
pressure, is used to pierce the test specimen. The load
used is expressed in kilograms and a 10-kilometer weight
is first applied and the degree of penetration noted.
The so-called major load (60 to 150 kilograms) is next
applied and a second reading obtained. The hardness
is then calculated as the difference between the two
loads and expressed with nine different prefix letters
to denote the type of penetrator used and the weight
applied as the major load.
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