Patent GB-985942-A (GB)
Title: Means for ultrasonic inspection of rails
IPC: G01N29/265
Filed: 1962-04-02
Abstract: 985, 942. Measuring angular rotation electrically. I. L. JOY. April 2, 1962, No. 12566/62. Heading G1N. [Also in Division H4] In an arrangement for the progressive testing of track rails utilizing ultrasonic waves the emitter of the latter together with means in contact with the rail for establishing ultrasonic coupling between emitter and rail are carried by a detector car adapted to move along the rails and to improve such coupling, means mounted forwardly (in the direction of travel of the car) of the coupling means is provided for prewetting the rails by the application of a thin film of coupling liquid. The testing system utilizes the pulse echo technique and a single crystal transducer acting as emitter and receiver or separate transducers may be employed. In the progressive testing of both rails respective carriages 31 (Figs. 1 and 2) each containing a transducer gauge shoe and coupling means are carried by telescopic tubes 40, 41 supported by frame members 37 connected to axle 33 by rubber joints 38 the arrangement being such that under the control of motor 36, cable 43, limit switches 49, 51 and co-operating lugs 48, 50 the frame members 37 may be lowered from an inoperative position in which carriages 31 are above the rails to a position in which the coupling means together with portions 101 of a trailing gauge shoe 100 (Fig. 6) are in contact with the rail bead and with the side member 104 of the gauge shoe urged against the side of the rail under the action of a compression spring 42 associated with the telescopic bars 40, 41. Each carriages 31 comprises (in the case of a single transducer system) a crystal transducer T (Fig. 4) mounted in a block 118 with an air backing pocket 119 and supported by a hollow tube (of hard rubber or plastic) 120 which is in communication with an inflatable boot 121 the whole assembly being filled with a coupling liquid via inlet pipe 123. The boot 121 is guided in its travel along the rail (R) by means of an arm 122 secured to the vertical portion 102 of the gauge shoe. The block 118 is secured to a bar 107 by means of screws 117 and a resilient spacer 116 (to allow of longitudinal adjustment of the plane of the crystal) and the other end of bar 107 is formed with members 108 pivotally supported at 110 on the horizontal bar of a spider 109 such that a reciprocated rod 114 connected to bar 107 produces a "lateral roll" of the crystal housing 106. A further reciprocated rod 115 causes bar 107 to pivot about the vertical member 109 and produces movement of the crystal housing termed "vertical pivotal movement". In operation both movements are effected with a 90 degrees out of phase relationship so that the whole of the rail head is "scanned" by the ultrasonic beam. Figs. 11 and 12, show a further suspension system for the transducer coupling means and gauge shoe assembly 322 comprising a pair of members 333 pivotally supported at one end by the front axle 335 of a detector car 320 and the other ends of which are provided with the assemblies 322 urged apart by a spring loaded telescopic bar 336 as in the embodiment of Figs. 1 and 2. The detector car is a conventional road vehicle usually running on rubber tires 323 but is additionally provided with retractable flanged wheels 324, 325 the arrangement being such that when travelling on rail tracks the tires support the weight of the vehicle whilst the flanged wheels, when lowered serve to maintain the car on the rails. In operation, the rail 321 is pre-wetted by means of a sponge 330 supplied with coupling liquid from a tank 328 and a further improvement in the altrasonic coupling is produced by supplied coupling liquid via a pipe 349 immediately in advance of the assembly 322. Fig. 8 shows the arrangement for producing the reciprocating motion of the rods 114, 115 of Fig. 4. As shown the rods are reciprocated by hydraulic piston assemblies 225, 227 under the control of further pistons 224, 226 connected to operate 90 degrees out of phase and driven by a shaft 221 at 400 r.p.m. To ensure that the centre of the motion due to each rod coincides with the centre of the rail head the echoes from the base of the rail of each extremity of each of the two motions are supplied via a rotating contact arm 232 to memory devices 237...240 and any departure of the centre of either motions from the centre of the rail bead, which is manifest as an error voltage at the midpoint of networks 241, 244 is employed via known servo systems 242, 245 and pistons 230, 247 to vary the mean point of reciprocation of pistons 227, 225 to compensate for such departure. Fig. 8 also shows the ultrasonic testing system which comprises a rate generator 250 operating at 2000 c.p.s. and controlling the ultrasonic driving source 251 for the crystal transducer C the latter also functioning to receive echo signals for transmission via receiver 253 and gate 252 (controlled by generator 250) to an indicator 254. In the arrangement shown both the base echo signals (which are fed to the contact arm 232) and echoes from flaws in the rail are supplied to the indicator, but by employing a plurality of gates flaw echoes alone may be applied to the indicator. In order to compensate for changing contours of the rail (e.g. when going around curves) a feeler shoe 202 (Fig. 7) which follows such contours is utilized in a servo system arrangement comprising a potentiometer 204, control unit 209, servomotor 210 and compensating potentiometer 214 to produce a compensating movement of the transducer assembly. In the embodiment of Fig. 8 a direct mechanical drive of rods 114, 115 may be employed instead of the hydraulic system shown. If however, additional degrees of transducer movement are required control system utilizing a separate piston arrangement for each movement each piston being provided with a cam follower operated by a cam on a drive shaft is considered preferable to direct mechanical drives (Fig. 10, not shown).