Damage occured on chain spreaders on track vehicles because of faulty welds.
Figure 1 shows a chain spreader with two micrographs of the ring-shaped weld
between the threaded rod and the eyes. The micrographs show pores, bonding flaws
and insufficient weld penetration. Owing to this a non-destructive method of testing
was needed to detect such flaws in a large number of chain spreaders.
On account of the complicated geometry of the weld an ultrasonic test
was not possible with just one probe. Detection was only successful with a "squint"
arrangement of two miniature probes (Krautkrämer type K5K, 5 MHz) under 70°.
Figure 2 shows the sound beams of such a probe arrangement.
A beam coming from the transmitter probe is reflected from the flaw,
situated vertically to the axis of the cylinder, back to the receiver probe.
Using trigonometry the value "p" in figure 13 (left)
can be calculated (1):
with a as the incidence angle of the probe.
The exact positioning of the probe was determined by
making tests on a flat-bottom hole positioned on the front
side of a cylindrical shaped test object and having a diameter of 1.5 mm (fig.3).
A holder for probe alignment was made by using a hot adhesive sprayed around
the probes (fig.3) using a spray gun.
Further flat-bottom holes in the test object, at different distances to the surface,
enable testing and optimization of the sensitivity range.
Testing of chain spreaders according to this method is shown in fig. 1.
Flaws shown in the micrographs are detected in this way.
Literature:
(1) H. Richter: Ein Ultraschallprüfverfahren für Spurstangen, Materialprüfung 25
(1983) Nr. 5, S 160
