Table 1-3.—Portion of Conversion Table Furnished with Brinell
Tester
the microscope. After measuring the diameter of the
impression, the measurement is converted into the
Brinell hardness number on the conversion table
furnished with the tester. A portion of the conversion
table is shown in table 1-3.
ROCKWELL TESTER
The Rockwell hardness tester, shown in figure 1-27,
measures the resistance to penetration as does the
Brinell tester, but instead of measuring the diameter of
the impression, the Rockwell tester measures the depth,
and the hardness is indicated directly on a dial attached
to the machine. The more shallow the penetration, the
higher the hardness number.
Two types of penetrators are used with the Rockwell
tester–a diamond cone and a hardened steel ball. The
load that forces the penetrator into the metal is called the
“major load,” and is measured in kilograms. The results
of each penetrator and load combination are reported on
separate scales, designated by letters. The penetrator,
the major load, and the scale vary with the kind of metal
being tested.
For hardened steels, the diamond penetrator is used,
the major load is 150 kilograms, and the hardness is read
on the C scale. When this reading is recorded, the letter
C must precede the number indicated by the pointer. The
C-scale setup is used for testing metals ranging in
hardness from C-20 to the hardest steel (usually about
C-70). If the metal is softer than C-20, the B-scale setup
is used. With this setup, the 1/16-inch ball is used as a
penetrator, the major load is 100 kilograms, and the
hardness is read on the B scale.
In addition to the C and B scales, there are other
setups for special testing. The scales, penetrators, major
loads, and dial numbers are listed in table 1-4. The dial
Table 1-4.—Standard Rockwell Hardness Scales
1-37
