7-6 Issue 03, 04/2005 Krautkramer DynaPOCKET
The rebound hardness testing method The treatment of test material
7.3 The treatment of test material
In order to obtain reliable and reproducible measure-
ment results, you have to observe a few notes on the
quality and treatment of the test material. Therefore,
please read the following information.
Surface quality
The surface must be clean, free of oil, grease and
dust. The peak-to-valley height or surface roughness
should not exceed 10 micrometers.
You should therefore grind off rougher surfaces, for
example using the battery-driven grinder MIC 1060
(ref. chapter 2).
Curved surfaces
In the case of surfaces showing a radius of curvature
< 30 mm (convex or concave), a correspondingly
shaped test attachment must be used for a firm and
secure positioning of the impact device.
Measurements on small objects
Due to the impact effect of the impact device, vibra-
tions liable to cause a corruption of the measurement
results may occur with smaller or more lightweight test
objects.
❚ Objects having a mass less than 2 kgs must always
be fixed to the support using couplant so that no
vibrations can occur.
❚ Test objects having a mass between 2 kgs and
5 kgs must be placed on a large metal support
(e.g. a table) so that they are not moved or do not
start to vibrate by to the impact. If necessary,
couple the test objects using our couplant ZG.
Minimum wall thicknesses
Similar problems occur with test objects having small
wall thicknesses. Walls, e.g. on tubes, can start to
vibrate due to the impact of the impact device in a
similar way as the membrane of a drum. This generally
results in indicating too low hardness values.
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