ALTANA Hoffman Scratch Hardness Tester Manual - Manual (Page 8)

7
hand on the carriage platform directly over the
pair of wheels nearest to the scratching tool,
using sufficient 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 the left
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 magnification.
Adhesion: First, mark off a panel to form a painted
edge, or cut a line all the way through the paint
film 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 film, but scrapes or ....
peels it away completely. Move the scraping tool
slightly before each new trial.
Another method is to compare the degree of film
removal made by the same load and scraping tool
from a series of test surfaces.
Operation