Patent GB-1055423-A (GB)
Title: Method and apparatus for ultrasonic flaw testing
IPC: G01N29/06
Filed: 1963-06-12
Abstract: 1,055,423. Ultrasonic flaw testing. CHEMETRON CORPORATION. June 12, 1963 [June 27, 1962], No. 23309/63. Heading H4D. In an arrangement for testing a solid body, e.g. a rail R<SP>1</SP> (Fig. 1, not shown), for internal flaws ultrasonic energy generated by means of a crystal E is directed into the rail at an angle I such that shear waves are produced which travel at " flat " angles, i.e., almost parallel to the entrant surface, so that, as the crystal is moved along the rail in progressive testing flaws such as TF are effective to return echo signals for an appreciably longer period than the use of vertically injected energy would allow. However, because of the flat angle of travel, surface waves are inevitably produced and in accordance with the invention reflections of such surface waves are damped by means of the rail shoe 15E (forming part of the carriage for the crystal assembly) the application of echo signals to the cathode-ray tube indicator T, additionally, being delayed by means of a gate 34 controlled by a delay device 38, until after the time for the return of surface wave reflections from the near end of the shoe so that " noise " &c. produced at the interface between the coupling liquid and the rail is not reproduced. Fig. 2 shows the general arrangement for progressive rail testing comprising for the rails R, R<SP>1</SP> a crystal assembly 27, 27<SP>1</SP> including crystals V, V<SP>1</SP> utilized for both transmission and reception and crystals 20 and 30 R, R<SP>1</SP> and S, S<SP>1</SP> (R=receiving, S = transmitting) grouped as shown and connected to ultrasonic control circuitry U 1  . . . U 6  (also Fig. 4, not shown) operating in sequence under the control of a rate generator RG the arrangement being such that each circuit U 1  . . . U 6  operates for a predetermined interval and then triggers the next circuit whilst the triggering of the circuits U 1 , U 3  and U 5  operates via delays D to initiate the fly-back of the vertical sweep generator 45 for the memory display tube T. Thus, for each pulse output of rate generator RG (repetition frequency = 400 cps.) three vertical sweeps (Fig. 2B, not shown) are initiated during each of which received echo signals are applied to the tube gun 40 from the operative circuit U 1  . . . U 6  each of which incorporates delayed gate means (equivalent to 34, 38, Fig. 1) to eliminate surface reflection &c. in the immediate vicinity of the crystals as explained above. During the first trace echoes appertaining to crystals V<SP>1</SP>, V are displayed, these crystals, which have vertically directed axes (see Fig. 3) giving rise to echoes from the rail head and base H<SP>1</SP>, H, B<SP>1</SP>, B (Fig. 2B, not shown) and any intermediate flaws whilst during the second and third traces echoes appertaining to the crystals 30 and 20 respectively are displayed the former being orientated at angles such as to produce shear waves travelling at angles of about 85 degrees whilst the latter produce shear waves at about 55 degrees to 60 degrees the accompanying surface waves in each case being damped out by the member 55 comprising a thin sheet of rubber or plastic in contact with the rail surface. The surface waves may also be damped out by means of a film of water and the rail car (Fig. 2A, not shown) for transporting the equipment is provided with means at the forward end for applying a pre-wetting film of water which also serves to provide a coupling medium for the ultrasonic waves. The assembly of the crystals together with the water coupling supply system (distinct from the prewetting system) is described with reference to Figs. 5 to 8 (not shown). In another embodiment the crystals for producing the shear waves each comprise a composite set of 10 crystals maintained in flat relationship with the rail by means of springs, each crystal of such set being operated with a time delay related to the speed of travel along the rail (Figs. 9 to 13, not shown) and in a further embodiment the shear wave producing crystals are coupled via plastic wedges spring-urged against the rail (Figs. 14 to 22, not shown), coupling devices alternative to the plastic wedges being described with reference to Figs. 23 to 25 (not shown).