ALTANA Hoffman Scratch Hardness User Manual

Measure what you see.

Hoffman Scratch Hardness Tester

A member of

Manual

Additives & Instruments

Hoffman Scratch
Hardness Tester

Manual

Cat. No.: 1610

BYK - Gardner USA

9104 Guilford Road
Columbia, MD 21046
USA
Phone [phone]
301-483-6500
Fax [phone]
301-483-6555

www.byk.com/instruments

BYK-Gardner GmbH

Lausitzer Str. 8
D-82538 Geretsried
Germany
Tel. 0-800-gardner
(0-800-4273637)
[phone]
Fax [phone]

Description

Description

This instrument consists of an applicator blade
The Hoffman Scratch Hardness Tester was
developed by the National Paint, Varnish and
Lacquer Association and has been produced by
BYK-Gardner for many years. This instrument
was designed to ll the need for a simple portable
device to rate scratch resistance and adhesion of
industrial product nishes on a comparative basis.
It is an ideal tool for laboratory or eld use.

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General Information

General Information

The Hoffman Scratch Tester consists of a four­wheeled carriage, a balanced beam with a
scale of 0-20 arbitrary units and a scratching
tool with a sharp circular rim mounted at 450 to
the test surface. a counterweight, allen wrench
and movable weights (riders) both large (100 g)
and small (25 g) are also included. The overall
dimensions of this instrument are 11 x 1 x 1 inches
( 27.9 x 2.5 x 2.5 cm).

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Calibration Procedure

Calibration Procedure

Place the Hoffman Scratch Tester on a at, level
surface with the wheels of the roller carriage
contacting the surface and the scale arm
positioned to the left. The scale arm has no riders
attached.

1. Using the small allen wrench, loosen the

counter weight until it slides across the scale

arm.

2. The correct position for the counter weight is
when the scratching tool is in contact with

the surface with virtually no downward force.

A recommended starting position is the scale

arm protruding one or two millimeters to the

right of the counter weight. Adjust the position

of the counter weight on the scale arm and

tighten with the allen wrench.

3. Use the following procedure to check the
calibration:

• With one hand, hold down the roller carriage
so all the wheels remain in contact with the
surface.

• With the other hand, place one nger at the
very end of the scale arm and push down until
the scratching tool contacts the surface

(position 1).

• Remembering to keep downward pressure
on the roller carriage, slowly lift your nger off
the scale arm. The scale arm should stay in
position 1.

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Calibration Procedure

• At this point, a small upward tap on the scale
arm should cause it to settle in a higher
position; the scratching tool is not in contact
with the surface

(position 2).

The optimal calibration is reached when the
smallest amount of force is required to raise the
scale arm from position 1 to position 2. If the scale
arm will not stay in position 1 on its own and goes
directly to position 2, the counter weight needs to
be shifted to the left. If the lifting force required to
switch from position 1 to position 2 is too great,
the counter weight needs to be shifted to the right.
Once calibrated the counter weight should not
need further adjustment, but it is recommended to
check the calibration on a regular basis.

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Operation

Operation

Before initial setup, please remove protective lm
from the scale arm (balanced beam). In operation,
small and/or large riders are attached to this arm
at the numbered positions. These must be placed
on the scale very carefully so that the test surface
is not marred before actual testing is begun. The
large rider generates a load of 100 grams per
division, while the small rider generates a load of
25 grams per division. The small quarter rider may
be used for marking low range measurements
involving small increments of pressure, or it may
serve as a vernier in conjunction with the large
rider in making more precise medium range
measurements. Two large riders may be used
for making high range measurements. The sum
of all the rider settings represents the total load
in grams applied by the lever system to the
scratching tool. The scale arm is counterpoised
and its graduation marks can be used with any
combination of riders to create a reproducible load
on the pivoted lever system. In order to assist you
in selecting the correct rider for your application,
listed below are several examples:

• Small quarter rider at position
4: 4 x 25 = 100 grams

• Large standard rider at position
20: 20 x 100 = 2000 grams

• Large standard rider at position 6, plus small ...
quarter rider at 2: (6 x 100) + (2 x 25) =
600 + 50 = 650 grams

• Large standard rider at position 20, plus ..........

.............another large standard rider at position

10: (20 x 100) + (10 x 100) =
2000 + 1000 = 3000 grams

After attaching the rider(s), place the Hoffman
Scratch Tester on a at test surface that measures
at least 2 x 4 inches (5.1 x 10.2 cm). Place your

6

Operation

hand on the carriage platform directly over the
pair of wheels nearest to the scratching tool,
using suf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 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 magnication.

Adhesion: First, mark off a panel to form a painted
edge, or cut a line all the way through the paint
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 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 lm
removal made by the same load and scraping tool
from a series of test surfaces.

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Maintenance and Care

Maintenance and Care

The scratching tool should be rotated between
series of tests to equalize wear; and replaced
when the edge becomes dulled. It is made of
special tool steel and should give long service
on conventional nishes if used properly. Always
approach the nal reading from the lower end
of the scale to prevent overloading and dulling
the cutting edge against very hard substrates.
Do not lubricate the Hoffman Scratch Tester. To
maintain the tester in the best condition, keep it
free from dust and other foreign material. Handle
with reasonable care to prevent damage to the
pivotable beam and store the instrument in its
case when not in actual use.

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253 017 659 EDFIS 0408 Europe