GB208708A - Improvements in and relating to electric heating units - Google Patents

Abstract

208,708. British Thomson-Houston Co., Ltd., (Assignees of Tang, B. G.). Dec. 20, 1922, [Convention date]. Wire and ribbon resistances mounted on flat or curved surfaces, encased, cored.-An electric heating unit is made by folding a metal blank shaped as shown in Fig. 2 along the line x, y, inserting a heating element between the folded portions and finally bending or rolling it so as to bring the opposite edges 15 adjacent, for example in the form of a tube having an open seam 11, Fig. 1. The heating element is preferably made by winding a ribbon conductor 22, Fig. 9, zig-zag upon two rectangular insulating sheets such as mica. Before the heating element is inserted within the folded metal sheath, sheets of insulating material are placed on each side of it and also between the two sets of ribbon. The metal sheath is rolled so that the part 16 becomes the inside and the edges 15 which project are turned over the edges of the heating element thus forming the open seam 11. Alternatively the blank may be so shaped that no projecting edges are formed and the edges of the heating element thereby left exposed. The ribbon is placed parallel with the fold in the blank so as to avoid the inner lengths of ribbon becoming crowded on rolling the sheath. In a modification shown in Fig. 13, the blank from which the sheath is made is rectangular and is so folded that when it is rolled after insertion of the heating element the edges of the latter are enclosed and the edges of the blank 35, 36 come in the inner wall. The blank may be of such shape that projections are formed at either or both ends of the heating unit thus enabling the latter to be sealed. The tube may be of circular, rectangular or triangular section.