The Rockwell Hardness Test Method, Part 2
As a general guide to selecting a Rockwell scale, the operator should select the scale that specifies
the largest load and smallest indenter possible to do the job without exceeding defined operating
conditions and accounting for conditions that influence the test result.
These influencing conditions
include test specimens which are below the minimum thickness for the depth of indentation (see chart);
a test impression that falls too close to the edge of a specimen or another impression (indentations
should be spaced greater than 3x indentation diameter and greater than 2-1/2x diameter from the edge
of the specimen); or testing on cylindrical test specimens (see chart).
Some important operating conditions
are: the axis of test must be within 2 degrees of perpendicular; there should be no deflection of the test sample
or tester during the load application (from conditions such as dirt under the test specimen or on the
elevating screw; surface finish should be kept ; surface conditions such as decarburization from heat
treatment should be removed. Also refer to the General Hardness Training Guide:
Hardness Testers Part 1 Part 2 Part 3.
To purchase a copy of the complete Rockwell test method standard, designated E18,
contact ASTM
Books describing hardness testing are available from a number of organization
such as ASTM and NIST
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