GB711521A - Improvements relating to magnetic crack-detecting apparatus - Google Patents

Abstract

711,521. Magnetic tests. METROPOLITAN-VICKERS ELECTRICAL CO., Ltd. March 30, 1953, [April 2, 1952; June 4, 1952.] Nos. 8423/52 and 14099/52. Class 37. Apparatus for examining ferrous metal parts for cracks by magnetizing the part and painting with a magnetic powder of fluid to make the cracks visible is characterized by the use of two adjustable head stocks for locating the metal part, at least one of which has a magnet whose position relative to the test part is adjustable to a position where it induces magnetism in the test piece, or to a position where its poles are bridged by a keeper. As shown (Fig. I) two aligned mild steel head stocks 1, 2 are adjustable mounted on a base plate 3 with one head stock electrically insulated from the base plate by suitable insulation 4. The left hand member I comprises a steel cylinder 6, a non-magnetic metal ring 7 and a steel end cover 8 having an annular ring 9. A permanent magnet I2 with pole pieces I3 is located inside the rings, and is attached to a rod I6 having a handle I4 whereby the magnet may be moved axially inside the rings 6, 7, 9. The other headstock 2 carries a cylindrical block I8 spring- loaded by a spring 20 to hold the test piece between the end faces of the headstocks which are covered by copper braid pads I0, IO<SP>1</SP> to give good electrical contact. The position of the magnet I2 determines the strength of longitudinal magnetization of the test piece, to enable transverse cracks to be shown, and may be indicated by a scale on the extreme part of the rod I6, a running nut 22 on a threaded portion of the rod facilitating the exact repetition of the position of the, magnet I2 by limiting the movement of the magnet to the right. Circumferential magnetization, to locate longitudinal cracks, may be obtained by passing current directly through the test piece. In an alternative arrangement the magnet I2 moves in a cylinder which is spring-biased axially to hold the test piece, movement of the handle I4 in one direction causing withdrawal of the outer cylinder against the spring to allow the test piece to be inserted, and movement of the handle I4 in the other direction causing the magnet to go forward to the test position. Both headstocks may contain magnets, and the magnetic powder may be used with the residual magnetism after magnetization. Specification 668,73<SP>2</SP> is referred to.