18. The Purpose of the test is to know the effect
of heat treatment, such as
hardening,tempering,etc and to check the
quality and uniformity of products. To resist
wearing away of the material certain
hardness is required in materials used for
rollers, tooth gear, sideways, for such uses is
given heat treatment for hardening. the test
can give us the idea of hardness of metals.
19. Hardness is defined as the resistance to local
penetration or scratching or abrasion .It
indicates the ability of material to withstand the
deformation under a locally applied load.
Various tests have been developed to test
resistance to either indention (i.e. local
penetration) or abrasion or scratching. But the
indentation test is the most widely used test. It
is a quick test and also a non- destructive test.
20. The various methods of hardness tests are:
(a) Brinell hardness test.
(b) Rockwell hardness test.
(c) Vicker’s hardness test.
(d) Dynamic indentation test.
(e) Rebound test, etc. out of these tests the
first three tests are very common.
21. Conical point or a hard steel ball of standard
dimensions is forced into the surface of the test
specimen in two consecutive loads, and the depth
of indentation is measured which is taken as
measure of hardness. Two scales, ’c’ scale ‘b’ scale
are used for measuring indentation. The ‘c’ scale is
used for diamond penetrator, and ‘b’ scale is used
in case of steel ball indentator. The scale reads
indentation in units of 0.002mm. Specimens for
testing should have smooth surface, the thickness
of the specimen being at least 8 times the
indentation.
22. i. Place the specimen on horizontal Platform so as to be in
contact with the indentater.
ii. Apply minor load of 10 kg by raising the platform.
iii. Set the dial of the indicator of death gauge of suitable
scale, at initial position. Apply major load without shack
within 2 to8 seconds value of load shall be 140 kg for
diamond cone 90 kg for ball, this is in addition to the initial
minor load of 10 kg.
iv. Maintain the load till the indicator stops moving.
v. Record the indentation ‘e’
vi. Of appropriate scale, and calculate the Rockwell hardness
number.
