GB994171A - Improvements relating to methods of and apparatus for the detection of flaws in members of elongated form - Google Patents

Abstract

994,171. Detecting flaws in metal. D. KARO. Aug. 4, 1961 [May 4, 1960; Jan. 18, 1961], Nos. 15658/60 and 1988/61. Heading G1N. In a method and apparatus for detecting flaws, in an elongated member 10 such as a cable wire, rope, tube or rod in which the member is magnetized longitudinally and a signal is generated by the movement of the member relative to the field, the output of the pick up arrangement is applied to means responsive to a selected frequency or amplitude, or to a combination of these factors in order to discriminate against changes in permeability and dimension. In the arrangement Fig. 1 (prove) the energizing coils 14, 15 which are used also as detecting coils are connected with resistors R 1 R 2 in a.D.C. bridge and impulses resulting from the leading and trailing edges of flux changes arising from the passage of flaws are selected by wave analyser, and rectifier and filter units 16, 17 and recorded on a recorder 20 driven in synchronism with the passage of the member. A similar arrangement described with reference to Fig. 1 (complete) (not shown) includes a transformer having a characteristic as described with reference to Fig. 13 (not shown) whereby signal pulses within a predetermined amplitude range only, are efficiently passed. The energizing and delecting coils may be provided with yokes to complete the magnetic circuit which yokes may be divisible through the aperture for the passage of the member. A hinged arrangement may be used. The turns of the coils may be arranged to lay in a plane at right angles to the axis of the member, or may be in planes parallel to or at right angles to the lay of strands in a cable under test. A single coil may be divisible along a diametral plane by plugs and sockets at each end of the diameter or half coils for assembly around the periphery as in Fig. 2, may be used. Recessed circular yokes having a single recess or two recesses for the energizing and/or detection coils are described with reference to Figs. 7 and 9 (not shown) and magnetization by permanent magnets is also referred to. Magnetic anomalies may be detected by toroidal coils which may be on a rigid core or wound on a flexible material which is subsequently bent into segmental form.