Measuring Castings - REED R7900 Manuel D'utilisation

Measuring Castings

Castings will cause large attenuations in sound energy due to coarse
crystal particles and a not-so-dense structure. The attenuation is due to
the material's scatter and absorption of sound energy. Coarse out-phase
structures and coarse crystal particles will cause abnormal reflection
(i.e. a grass-shaped or tree-shaped echo) resulting in error readings.
When the crystal particle is coarse, the anisotropy in flexibility in metal's
crystallizing direction will be obvious. This results in difference in sound
velocities in different directions, with the maximum difference being up to
5.5%. The compactness in different positions of the workpiece is different,
which will also cause difference in sound velocity. All of these will produce
inaccuracy in measurement.
While measuring castings pay attention to the following:
• When measuring casting with an un-machined surface use engine
oil, consistent grease, or water glass as a coupling agent
• Calibrate the sound velocity for the object with a standard test
piece having the same material and measuring direction as that
for the object to be measured
• If necessary, take a 2-point calibration
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