GB421641A - Improvements relating to the magnetic testing of materials for flaws - Google Patents

Abstract

421,641. Magnetic tests. BRITISH THOMSON - HOUSTON CO., Ltd., Crown House, Aldwych, London.-(Assignees of I. G. Farbenindustrie Akt.-Ges. ; Frankfort-on-Main, Germany) May 23, 1933, No. 14879. Convention date, May 23, 1932. [Class 37] In order to test materials for flaws by examining the normal components of a magnetic field set up at non-uniform points, a coil mounted in a plane parallel to the surface of the test piece is caused to oscillate in its own plane and is connected to head phones or a loud-speaker so that changes in the normal magnetic components are detected. A test piece W containing a weld R to be examined is magnetized by two bar magnets T, T1 excited by alternating or direct current. The upper ends of the cores of the magnets T, T1 are formed with large iron surfaces so as to lead the stray field outwards. A search coil S is mounted so as to vibrate in a plane parallel to the plane of the test piece and is connected through an amplifier V to headphones K. The coil S is vibrated by mechanical connection to the reed of a loudspeaker, the exciting coil E of which is connected through an amplifier U to a pick-up N, the needle of which contacts with an electromagnet excited by alternating current, so that the coil S is vibrated at the frequency of the supply. The currents or sounds received at the headphones K may be back-coupled electrically or acoustically with the primary oscillation circuit of the coil E or with the oscillating member of the coil S. The pick-up N may alternatively run on a recording disc of constant frequency. In a modification, the coil S is mounted on a vibrating metal spiral such as the first or second inner turn of a clock gong, which is set in oscillation by striking. Alternatively the coil may be fixed to the end of a tuning fork which is struck by a clock mechanism every 1 to 5 seconds. Specifications 153,748 and 296,303, [both in Class 37], are referred to. The Specification as open to inspection under Sect. 91 states also that the coil S may be held fast against the point to be examined, an iron core being vibrated axially. The core may be of a material having high initial permeability and a high demagnetizing factor, such as iron carbonyl powder. This subjectmatter does not appear in the Specification as accepted.