8. Procedure
8.1 When using the instrument shown in Fig. 1, level the
base plate of the apparatus and place it so that the weight
holder is toward the operator. This places the beam release on
the operator’s right and allows freedom to move the test
specimen manually under the weighted scraping element
(loop). Adjust the main bearing support so that the beam is
balanced in the horizontal plane when the loop is just touching
the specimen surface.
8.2 Raise the beam and lock it. Wipe the loop with clean
cloth or chamois. Place a test panel on the sliding platform so
that it may be moved away from the operator and the uncoated
portion is toward the main beam support. Place weights on the
weight support using an initial amount that is estimated to be
appropriate for the particular coating. Carefully lower the beam
until the loop rests on the uncoated portion of the test specimen
and the full load is applied, then slowly (1 to 2 s/in.) push the
sliding platform away from the operator for a distance of at
least 75 mm (3 in.). If the coating is removed, continue the
testing, using successively smaller loads (0.5-kg increments)
until the coating is not removed. If the coating is not removed
by the initial scrape, continue the testing, using successively
larger loads (0.5-kg increments) until the coating is removed or
until the maximum load of 10 kg has been applied. Use a new
area of the test surface each time a scrape is made.
8.3 When the critical load has been approximately located,
repeat the test five times at each of three loadings: above,
below, and at the load determined in the first trial. Use the
replicate specimen to apply different loads in random fashion
so the same load is not made in succession.
8.3.1 Periodically examine the loop to ensure that the
original smooth surface is intact. If the contacting surface is
worn, reverse the loop. When both sides are worn, replace with
a new loop.
8.4 For each applied load, tabulate the number of times the
coating was removed or adhered. The load where the scrape
results change from mainly adhering to mainly removed,
ignoring the first 13 mm (1⁄2 in.) of the scratch if the coating
was removed, is the adhesion failure end point.