Patent GB-571817-A (GB)
Title: Apparatus for ultra-sonic testing
IPC: G01M17/02
Filed: 1943-03-18
Abstract: 571,817. Detecting flaws by ultrasonic waves. WINGFOOT CORPORATION. March 18, 1943, No. 4436. Convention date, Sept. 2, 1942. [Class 118 (ii)] [Also in Groups XIX and XXXIX] In apparatus for detecting internal flaws and occlusions in articles or material, comprising means for creating high-frequency sound or ultra-sonic waves, for directing them against a portion of a wall of the article, for picking-up the waves from an opposed surface after passage through the article, and for giving an indication of the received waves, means are provided for holding liquid in contact with at least a portion of the article and the sound waves are directed on to the wall through the liquid. The invention is described as applied to the detection of flaws in pneumatic tyre covers. As shown in Fig. 1, the tyre is rotatably supported on rollers 72, 76 with its lower part immersed in water in a tank 64. Waves of a frequency of between about 10,000 and 50,000 cycles are generated by a magnetostrictive vibrator 30 and pass through the water in a tube 88 which directs them to a small area on the underside of the tyre. An air jacket between the tube 88 and a surrounding tube 90 prevents transmission of the vibrations to the water in the tank. The vibrator 30 comprises a nickel rod or tube 28 which dips into the water and is surrounded by two coils respectively coupled to the grid and plate circuits 01 a thermionic valve oscillator, the circuit of which is given in Fig. 20 (not shown). The oscillator contains a filter resonant at any desired frequency, and the rod or tube 28 vibrates owing to the magnetostrictive effect and forms the coupling between the grid and plate circuits of the oscillator. The vibrations passing through the tyre are received by a pick-up device 34 supported adjacent the inner face opposite to the end of the tube 88. This may comprise a piezo-electric pick-up 35, Fig. 21, of the usual phonograph type, mounted in a watertight casing 34 having a diaphragm 37 which picks up the vibration and transmits it through a rod 38<x> to the pick-up. Alternatively, an inertia type pick-up may be secured inside a watertight casing, the vibration being transmitted to it directly from the casing. The pick-up is connected to an amplifier containing a filter which removes frequencies due to the pick-up of extraneous vibration, and the amplifier output is connected to means such as an oscillograph, vacuum tube voltmeter, or a rectifier and D.C. ammeter, giving a visual indication of the received energy, or to an oscillator which gives an audible beat note with it. By rotating the tyre an annular portion of it may be examined for flaws, the position of the annulus on a transverse section of the cover being varied by adjustment of the position of the pick-up and of the end of the flexible tube 88. In a modification the tube 88 is not flexible, but is angularly adjustable about an axis passing horizontally through the centre of the bottom transverse section of the cover in order to direct the waves on to the desired portion of the transverse periphery. Fig. 8 shows a further modification in which the tube 88c is formed with a number of lateral extensions round the transverse periphery of the tyre, and the pickup is pivotally mounted so that it may be positioned opposite any one of them. In other forms a number of oscillators or pick-ups are used, operative at different points of the transverse periphery. Fig. 13 shows a form employing several pick-ups, and in which the waves are transmitted to all points of the transverse periphery of the cover by a bent metal bar 150 attached to a cup 148 containing liquid in which the magnetostrictive bar 28h dips. The pickup may be placed in contact with the inner surface of the cover, which then contains no water; alternatively, the pick-up may be in contact with the outer face, and the oscillator may operate through liquid held in the lower part of the cover.