Ultrasonic Probe for Testing the Material of Slotted or Hollow Pieces of the Material

FIG. 1 shows an example of an ultrasound probe for testing a slotted guide pin of guide support tubes for fuel rods of a nuclear reactor.

FIG. 2 diagrammatically illustrates the general sound way for the piezo-electric elements at the tip of the ultrasonic probe of FIG. 1.

FIG. 3 is an enlarged detail of the ultrasonic probe according to FIG. 1 as seen from one side.

FIGS. 4 and 5 show the same detail seen from another side and top respectively.

FIG. 6 shows a modified embodiment of an ultrasonic probe of the type shown in FIG. 1, and

FIG. 7 shows and ultrasonic probe according to the invention intended for testing the material of test pieces formed with cylindric bores.

FIG. 1 shows a chisel formed ultrasonic probe 1 for testing a slotted pin, for instance a guide pin. The probe comprises a carrier 3 and a chisel part 4 adjacent the tip of which two "round scanning" piezo-electric crystals 5 are mounted. At the end of the carrier part 3 the probe may also be formed with two "straight scanning" crystals 6.

The slotted pin 2 is formed with threads 7, a web part 8, a flange 9 and the very slotted guide part 10 with the slot 11. In this type of pin it may be expected that defects like fissures or cracks appear both in the transition section between the web 8 and the flange 9 and also at the root of the slot 11. Of course there may be some defects internally in the material. In order to firstly observe the first mentioned defects two piezo-electric crystals adjacent the ends of the chisel part 4 are used, which crystals are mounted so as to give a round scanning or angle scanning substantially as shown with the arrows 12 of FIG. 2. Each crystal scans at least half the periphery of the pin 2.

The probe rod with the piezo-electric crystals should have such dimensions as to fit the slot or bore in which the probe is to be introduced for the material testing with only some few tenth of a millimiter play.

As a supplemental part for the round scanning crystals 5 the probe also may have a couple of straight scanning crystals 6 scanning the bolt in the axial direction substantially shown with the arrows 13 of FIG. 2.

Each "round" scanning crystal 5A and 5B in FIGS. 3, 4 and 5 is generally rectangular in configuration and has a thickness to dictate its frequency (smaller thicknesses providing higher frequencies and thick crystals lower frequencies). This thickness is constant throughout the crystal as suggested in these views, and each crystal further includes planar exterior surfaces that are parallel to one another and to a major element axis oriented at an angle (a) relative to the longitudinal axis 14 of the chisel part 4. The two parallel longer edges or edge surfaces are oriented parallel this major axis. The two shorter edges of the crystal are not parallel to one another although one edge adjacent the edge of an associated or adjacent crystal is oriented in alignment with the associated shorter edge of the adjacent crystal as suggested in FIG. 3 and also in FIG. 5. These shorter edges are referred to as the "near" shorter edges while the more remote shorter edges are generally perpendicular to the longer edges of the crystals and as illustrated in FIG. 4 these shorter edges are parallel to a minor axis of each crystal oriented perpendicular to its major axis. More particularly this minor axis is oriented at an angle (b) relative to the parallel faces of the chisel part 4 again as best shown in FIG. 4.

The angle (a) is preferably on the order of 46.degree. relative the longitudinal axis of the probe or chisel part 4 and the angle (b) of the minor element axis is preferably oriented at 46.5.degree. relative to the line normal to the faces of the chisel part 4.

The locating and positioning of the piezo-electric round scanning crystals 5 is critical and is shown diagrammatically in the enlarged picture of FIGS. 3 and 4. The crystals are mounted isolated in a damping block, and they are localized in an angle a of between 40.degree. and 70.degree. or preferably between 40.degree. and 50.degree. in relation to the longitudinal axis 14 of the chisel part 4, and they are also rotated in an angle b around its own axis of between 45 and 50.degree.. Practical tests have shown that the optimum angles vary for different crystals. For instance a crystal of 4 MHz gives the best values at an angle a of about 50.degree. and an angle b of about 45.degree., whereas a crystal of 2 MHz frequency gives the best result at an angle a of 46.degree. and an angle b of about 46.5.degree.. The two crystals 5a and 5b are isolated from each other, and each is connected to a mixing box 15 over a (not illustrated) conduit, and the mixing box 15 in turn is connected to an ultrasonic apparatus 16 having an oscilloscope like reading instrument 17. A computer or a tape registering unit 18 also may be connected to the ultrasonic apparatus 16. With the assistance of the mixing box 15 each of the piezo-electric crystals can in turn be connected and be read whereby a cumulated total sound picture is obtained of the four illustrated units, which picture is compared with corresponding reference pictures over fault free reference objects or reference objects having known defects thereby giving a clear conception of the character of the test object. Any fissures, cavities or similar defects given an echo which is observed as a peak on the oscilloscope 17.

As previously mentioned the ultrasonic probe can be formed with a circular cylindrical probe part 19 as shown in FIG. 7 and at the tip of said cylindrical part 19 the probe is formed with one or several piezo-electric crystals. Irrespective of the number of crystals which are used said crystals ought to be placed as mentioned above at an angle a to the longitudinal axis of 40.degree.-70.degree. or preferably 45.degree.-50.degree. and rotated an angle b around its own longitudinal axis of about 45.degree.. In case the probe has only one crystal this is provided centrally in the cylindric part and close to the tip thereof, and when making tests with such a probe it is rotated into several test steps, for instance 180.degree., 90.degree. or any other angle, whereby a test is made in each such angular position. In case the probe is formed with two or several crystals they are mounted symmetrically according to the above mentioned guide lines.