GB791650A - Improvements relating to magnetic crack detection - Google Patents

Abstract

791,650. Magnetic tests. METROPOLITANVICKERS ELECTRICAL CO., Ltd. Dec. 14, 1954 [Dec. 21, 1953], No. 35524/53. Class 37. For dipping articles to be tested in a bath of magnetic fluid a pair of cranks are provided, so coupled as to rotate together with the article under test clamped between their ends to immerse the article in the bath during part of the revolution. As shown, the article to be tested is clamped between faces 10, 11 of cranks 8, 9 which are attached to shafts 1, 2 journalled in bearings 2, 3. At the lower part of their throw the cranks dip the article in bath 23 containing magnetic fluid. A coupling shaft 14 and chain drives 12, 13 are provided so that the cranks rotate together. Shafts 1, 2 each consist of an inner part 16, 20 and an outer part 15, 19. In the case of shaft 1 the inner part is axially movable under the action of a spring 17 which thus clamps the article between the faces. Relative angular rotation of the two parts is prevented by handle 18 which is pivoted at 19 in the outer part and passes through the inner. This handle serves to compress spring 17 to enable the article under test to be withdrawn. The inner part of shaft 6 is adjustable by means of a set screw in the outer part engaging a slot 22 in the inner. Coils 24 provide an axial magnetizing field which passes through the cranks, the article, frame 5, 6 and shaft 28, while a circumferential field is derived by applying A.C. to terminals 25, 26. Cams rotating with the crank shafts may serve to switch on and off the magnetizing currents or, if desired, to insert permanent magnets in the magnetic circuit and to short-circuit them. In Fig. 3 the crank positions are represented by the radii and the article position by the ends of these radii. At position I the article is inserted, at II the axial field is applied, at III the axial field is removed, at IV the A.C. field is applied, at V the A.C. field is removed, and at VI observation of the article leaving the bath commences and continues to I. A mirror 38 is provided to facilitate the observation. In the embodiment of Fig. 2 (not shown) the two cranks are coupled by a central non- magnetic shaft splined in the left-hand crankshaft and projecting therefrom to engage the face of the right-hand crankshaft.