load of 10 kilograms is applied before the lever is
In addition to the C and B scales, there are other
tripped. This preliminary load is called the "minor
setups for special testing. The scales, penetrators, major
load." The minor load is 10 kilograms regardless of the
loads, and dial numbers are listed in table 2-4. The dial
scale setup. When the machine is set up properly, it
numbers in the outer circle are black, and the inner
automatically applies the 10-kilogram load.
numbers are red.
The metal to be tested in the Rockwell tester must
The Rockwell tester is equipped with a weight pan,
be ground smooth on two opposite sides and be free of
and two weights are supplied with the machine. One
scratches and foreign matter. The surface should be
weight is marked in red. The other weight is marked in
perpendicular to the axis of penetration, and the two
black. With no weight in the weight pan, the machine
opposite ground surfaces should be parallel. If the
applies a major load of 60 kilograms. If the scale setup
specimen is tapered, the amount of error will depend on
calls for a 100-kilogram load, the red weight is placed
the taper. A curved surface will also cause a slight error
in the pan. For a 150-kilogram load, the black weight is
in the hardness test. The amount of error depends on the
added to the red weight. The black weight is always
curvature-the smaller the radius of curvature, the
used in conjunction with the red weight; it is never used
greater the error. To eliminate such error, a small flat
alone.
should be ground on the curved surface if possible.
Practically all testing is done with either the
B-scale setup or the C-scale setup. For these scales, the
Riehle Tester
colors may be used as a guide in selecting the weight (or
weights) and in reading the dial. For the B-scale test,
The Riehle hardness tester is a portable unit that is
use the red weight and read the red numbers. For a
designed for making Rockwell tests comparable to the
C-scale test, add the black weight to the red weight and
bench-type machine. The instrument is quite universal
read the black numbers.
in its application, being readily adjustable to a wide
range of sizes and shapes that would be difficult, or
In setting up the Rockwell machine, use the
impossible, to test on a bench-type tester.
diamond penetrator for testing materials that are known
to be hard. If in doubt, try the diamond, since the steel
Figure 2-31 shows the tester and its proper use. It
ball may be deformed if used for testing hard materials.
may be noted that the adjusting screws and the
If the metal tests below C-22, then change to the steel
penetration indicator are set back some distance from
ball.
the penetrator end of the clamps. This makes it
practicable to use the tester on either the outside or
Use the steel ball for all soft materials--those
inside surface of tubing, as well as on many other
testing less than B-100. Should an overlap occur at the
applications where the clearance above the penetrator
top of the B scale and the bottom of the C scale, use the
or below the anvil is limited. The indicator brackets are
C-scale setup.
arranged so that it is possible to turn the indicators to
Before the major load is applied, the test specimen
any angle for greater convenience in a specific
must be securely locked in place to prevent slipping and
application, or to facilitate its use by a left-handed
to properly seat the anvil and penetrator. To do this, a
operator. Adjustment of the lower clamp is made by the
Table 2-4.--Standard Rockwell Hardness Scales
Scale symbol
Penetrator
Major load (kg.)
Dial number
A
Diamond
60
Black
B
1/16-inch ball
100
Red
C
Diamond
150
Black
D
Diamond
100
Black
E
1/8-inch ball
100
Red
F
1/16-inch ball
60
Red
G
1/16-inch ball
150
Red
H
1/8-inch ball
60
Red
K
1/8-inch ball
150
Red
2-36
