The correct procedures for using the Ernst tester are
Each tester is supplied with a test disc for checking
as follows:
the condition of the point. To check the condition of the
point, press the instrument down on the test disc. When
1. Solidly support the metal being tested by
the downward pressure brings the end of the lower
placing a bucking bar behind the metal. This will
plunger guide against the surface of the disc, the
minimize flexing of the metal and yield a more accurate
indicator reading should be within the range shown on
reading of hardness.
the test disc.
2. The handgrip must be pressed down with a
To replace the point, remove the two screws that
steady, even force to ensure accurate readings.
hold the halves of the case together. Lift out the frame,
3. Press down until the fluid column has stopped
remove the spring sleeve, loosen the locknut, and
moving. The hardness value is given at the point where
unscrew the lower plunger guide, holding the point
the fluid column has stopped moving on the scale.
upward so that the spring and plunger will not fall out of
place. Insert the new point and replace the lower
As with other portable testers of similar type, the
plunger guide, screwing it back into the frame. Adjust
material must be smooth and backed up so there will be
the lower plunger guide with the wrench that is
no tendency to sag under the load applied on the tester.
furnished until the indicator reading and the test disc
The test block supplied with each tester should be used
average number are identical. After the lower plunger
frequently to check its performance.
guide is properly set, tighten the locknut to keep the
Q2-38.
What measurement must be taken to
lower plunger guide in place. This adjustment should
determine the Brinell number of a metal?
be made only after installing a new point; any
readjustment on a worn or damaged point give
Q2-39.
How does a Rockwell tester measure the
erroneous readings.
hardness of a metal?
Q2-40.
The Riehle tester is designed for making tests
Ernst Tester
comparable to what bench type machine?
The Ernst tester is a small versatile tool that
Q2-41.
What hardness tester is used for testing
requires access to only one side of the material being
aluminum alloys, copper, brass, and other
tested. There are two models of the tester--one for
soft metals?
testing hardened steels and hard alloys and one for
testing unhardened steels and most nonferrous metals.
NONMETALLIC MATERIALS
It has a diamond point penetrator, and it is read directly
from the Rockwell A or B or the Brinell scales,
LEARNING OBJECTIVES: Identify the
depending on the model used. Figure 2-34 shows the
properties of nonmetallic materials used in
Ernst portable hardness tester and its proper use.
aircraft construction. Identify the properties of
composite materials used in aircraft con-
struction.
Figure 2-34.--Ernst portable hardness tester.
2-39
