ALTANA Hoffman Scratch Hardness Tester Operating Instructions - Manual (Page 6)

5
platform directly over the pair of wheels nearest
to the scratching tool, using suffi cient downward
pressure to lift the counterpoised beam with the
selected rider at the 0 position. Pull the carriage in
the opposite direction from the scratching tool in
order to cause a trailing scratch. Move the tester
in a straight line making sure that the scratching
tool follows the rolling carriage in making both of
the following types of tests:
Cohesion: Start making tests for cohesion or
scratch resistance by moving the rider to
increase the load on the scratching tool until a
barely perceptible mark is made. Move the tester
(scratching tool) slightly before each new trial to
avoid marring the same surface more than once.
As an alternate procedure, compare the width
and character of the scratch made on a series
of test surfaces with the same load on the same
scratching tool. The scratch may be viewed either
with the unaided eye or measured under low
power magnifi cation.
Adhesion: First, mark off a panel to form a painted
edge, or cut a line all the way through the paint
fi lm to the substrate. Next, place the scratching
tool on the bare substrate at right angles to
the painted edge or cut. Start making tests for
adhesion or scrape resistance by moving the
selected rider to the left. Increase the load on the
scraping tool resting on the bare substrate until it
fails to ride up onto the test fi lm, but scrapes or
peels it away completely. Move the scraping tool
slightly before each new trial.
Another method is to compare the degree of fi lm
removal made by the same load and scraping tool
from a series of test surfaces.
Operation