GB631988A - Improvements in and relating to apparatus for testing materials by magnetic or electrical analysis - Google Patents

Abstract

631,988. Magnetic tests; determining physical qualities of materials. SUPERHEATER CO., Ltd., SMALL ELECTRIC MOTORS, Ltd., and RUDORFF, D. W. A. F. July 25, 1947, No. 20034. [Class 37] Apparatus for detecting flaws in metal tubes by electroinductive exploration of their inner surface includes a device adapted to be inserted into the tube and to apply current or flux to an arc of the tube, means for maintaining the device at a constant minimum distance from the tube wall, and electrical connections to external indicating means. Two electro-inductive exploring units are mounted in diametrically opposite positions on a hub 1 journalled in ball-bearings 2, 3 on a central axle 4 of insulating material. The hub 1 carries a brush 7 for cleaning the tube 6 and a set of propeller blades 8. Compressed air fed through a flexible hose 9 attached to the rear end of the axle 4 drives the propeller to rotate the hub 1, with the brush 7 and the analyzing units, while also expelling any foreign matter dislodged by the brush. The axle 4 is located concentrically in the bore of the tube 6 by two spiders 5, each having three arms 10 provided with wheels 11, which may have resilient tyres. Alternatively, the arms 10 may be telescopic and outwardly spring-urged, their extensions being rendered uniform by links. The axle 4 carries at its rear end an air funnel 13, to which the hose 9 is attached. The hose can be pushed into the tube so that its inner end with the instrument can be traversed along the tube, the hose being calibrated to indicate the position of a flaw. The exploring units each comprise a pair of laminated U-shaped soft iron cores 20 bridged by bars 21, each outer core limb 22 being surrounded by an energizing winding 23 and each inner limb 24 carrying a search coil 25. Each exploring unit is slidably mounted on a pair of parallel spigots 27 fast with the hub 1, while the outer core limbs 22 carry rollers 28 which ride on the inner periphery of the tube 6. The exploring units are thus outwardly urged by centrifugal force and follow the tube bore with a fixed minimum air gap. Stip-rings 31 are connected to the analyzer coils, and brushes 32 and a four-core cable 34 carried in the hose 9 make connection with an external indicator and current source. The search coils of each unit are connected in series opposed and the two pairs are connected in parallel to two of the slip-rings, the remaining two being connected to the energizing coils. Where relative rotation is not required the device may be arranged to explore simultaneously one or more longitudinal zones of the tube while being traversed along the tube without rotation. The energizing field may be alternating or continuous. The apparatus may be self-propelled during operation and stop automatically on the detection of a fault. Specifications 594,158 and 631,987 are referred to.