Patent GB-594158-A (GB)
Title: Improvements in and relating to apparatus for testing materials by magnetic or electrical analysis
IPC: G01N27/90
Filed: 1945-05-07
Abstract: 594,158. Magnetic tests; determining physical qualities of materials. SUPERHEATER CO., Ltd., and RUDORFF, D. W. May 7, 1945, No. 11552. [Class 37] In apparatus for testing materials such as metallic tube stock by magnetic or electrical analysis the energizing current or flux is applied peripherally to the stock, instead of with the operative lines disposed axially, so that longitudinal defects in the stock under test cause a major variation in the indicator circuit. In the construction shown in Fig. 2, three analysing elements of differential type are spaced symmetrically around the specimen tube 1 of magnetic material, each element comprising a double yoke 7 with a central A.C. energizing coil 5 and three poles 8, 9, 10. Two identical detector coils 11, 12 are wound in the same direction around the two outer branches of the core 7 and are connected in series to indicating means such as a cathode-ray tube or a telephone. If the sections of the specimen 1 between the pair of poles 8, 9 and the pair of poles 9, 10 are both without flaws, equal and opposite fluxes traverse the coils 11, 12 and no indication is given. If there is a fault in either section, the fluxes through the coils 11, 12 are unequal and a signal is given. Relative axial and rotary movements are imparted to the analyser and specimen, and a spray gun operated by a relay in the indicator circuit may be provided to mark the flaw. As shown in Fig. 3, the three cores 7 are housed in an annular insulating block 15 embracing the specimen 1 and journalled on ball bearings 16 within a stationary frame 17 assembled around it in two parts. The block 15 is rotated and is provided with slip-rings 18 co-operating with brushes 19 for connections to the coils 5, 11, 12. Insulating rollers 20 guide the specimen in its axial movement. The poles 8, 9, 10 may be set at an angle to the axis so that the stronger eddy currents as well as the flux are cut by an axial crack, and specimens of non-magnetic material may also be tested. The three analyser units may be supplied with three-phase currents so that they are rotated by the. squirrel-cage principle. In a modification for testing non- magnetic materials and employing peripheral induced currents, two arcuate energizing coils are arranged to form a differential system on the periphery of the specimen and induce opposite peripheral A.C. currents on the two covered arcs of the specimen which are equal in the absence of flaws. A detector coil surrounding the specimen and it may be also the energizing coils will not pick up any A.C. signal until a flaw causes the induced currents in the two arcuate portions of the specimen to be unbalanced. The indicator may be a cathoderay tube having a circular time base synchronized with the rotation of the specimen and such connections to the detector coil that an indication appears in the angular position corresponding to the position of the flaw. Instead of the 3-pole units 7, one or more U-shaped iron yokes may be employed, each having an A.C. energizing coil and a detecting coil connected to a network which compares its signals with a fixed standard.