GB732780A - Method and apparatus employing induction heating for producing welded tubing - Google Patents

Abstract

732,780. Induction heating. CRAWFORD, T. J. Dec. 18, 1951 [Jan. 11, 1951], No. 29662/51. Class 39 (3). [Also in Group XXII] In producing welded tubing wherein opposed spaced edges of a longitudinally extending seam in a tubular metal blank are brought together and are heated by a high-frequency induced electric current flowing generally circumferentially in the blank in the region in advance of the initial point of junction of the edges, the point of junction lies beyond the effective limit of the current inducing field. In an embodiment metal strip S is passed through forming rolls 3 to a welder 5 incorporating a high-frequency coil 7. The coil 7 of rectangular section copper tube which may be silver plated for very high frequencies is water cooled. A field concentrating element which may also be silver plated is arranged within and insulated from the coil 7. The element comprises two longitudinally split tubes 53, 55, Fig. 6, brazed &c. together and having end walls to forma hollow C section coil cooled by water circulated by conduits 59, 60. A frusto-conical end 63 extends beyond the coil 7 and an insulating plug 61 in the other end has a guide hole 62 for the tube. A small portion 67 serves to concentrate current in this region. Frequencies of 2800-500,000 or even 10,000,000 may be employed. Specification 377,655, [Group XXII], is referred to.