Dakota-ultrasonics PR-82 Manuel d'utilisateur télécharger pdf (Page 15)

PR-8

Sonic Tester

Condition and Preparation of Surfaces

In any ultrasonic measurement scenario, the shape and roughness of

the test surface are of paramount importance. Rough, uneven surfaces

may limit the penetration of ultrasound through the material, and result in

unstable, and therefore unreliable, measurements. The surface being

measured should be clean, and free of any small particulate matter, rust, or

scale. The presence of such obstructions will prevent the transducer from

seating properly against the surface. Often, a wire brush or scraper will be

helpful in cleaning surfaces. In more extreme cases, rotary sanders or

grinding wheels may be used, though care must be taken to prevent

surface gouging, which will inhibit proper transducer coupling.

Extremely rough surfaces, such as the pebble-like finish of some cast

irons, will prove most difficult to measure. These kinds of surfaces act on

the sound beam like frosted glass on light, the beam becomes diffused and

scattered in all directions.

In addition to posing obstacles to measurement, rough surfaces

contribute to excessive wear of the transducer, particularly in situations

where the transducer is "scrubbed" along the surface. Transducers should

be inspected on a regular basis, for signs of uneven wear of the wearface.

If the wearface is worn on one side more than another, the sound beam

penetrating the test material may no longer be perpendicular to the material

surface. In this case, it will be difficult to exactly locate tiny irregularities in

the material being measured, as the focus of the soundbeam no longer lies

directly beneath the transducer.

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Dakota-ultrasonics PR-82 Manuel d'utilisateur Page 15