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Rockwell Hardness - ASTM D785 Plastic Test Standard

Rockwell Hardness - ASTM D785

Rockwell hardness is a measure of the indentation resistance of a material. Testing is performed by first forcing a steel ball indentor into the surface of a material using a specified minor load. The load is then increased to a specified major load and then decreased back to the original minor load. Rockwell hardness is a measure of the net increase in depth of the indentor. Each Rockwell scale division represents a 0.002 mm (0.00008 in) penetration of the indentor.

Rockwell Hardness Test Parameters
Scale Minor Load (kg) Major Load (kg) Indentor Diameter (in) Indentor Diameter (mm)
R 10 60 0.5 12.7
L 10 60 0.25 6.35
M 10 100 0.25 6.35
E 10 100 0.125 3.175
K 10 150 0.125 3.175

Rockwell hardness is calculated by subtracting the penetration divided by the scale division from 130. For example, if the indentor has a net depth increase of 0.12mm, the Rockwell hardness is 70.
Hardness = 130 - (penetration / scale division)
Hardness = 130 - (0.12mm / 0.002mm) = 70

Shown below is a hardness comparison chart. Hardness is a complex material property influenced by a variety of factors. Any conversions using this chart will be a rough estimate and should not be considered an exact conversion.

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