GB864124A - Electric heating unit - Google Patents

Abstract

864,124. Electric heating units. ELECTROFILM Inc. Nov. 18, 1957, No. 35845/57. Class 39(3). An electric heating unit includes a heating element formed as a conductive mesh composed of interwoven longitudinal and transverse conductive strands, an insulating layer bonded to the mesh, and electrical connection means at spaced locations, the mesh being in elongated strip form having a number of parallel extents which occupy the greater part of the area of said insulating layer between the outermost edges of said extents. As shown, Fig. 3, a heating unit comprises an elongated woven wire mesh conductor 13, e.g. of nickel-chrome alloys, tungsten alloys, stainless steel and the like, sandwiched between and bonded to two insulating layers 12 and 14, e.g. of thermal setting plastic, the whole being bonded to a metallic or other rigid support 11. Each layer 12 and 14 may consist of one or more preformed sheets of reinforcing fibre, e.g. glass cloth, impregnated with non-conductive plastic. A flexible element, Fig. 4, comprises a conductive mesh 18 sandwiched between one fabric reinforced insulating layer 19 on one side and two similar layers 20 on the other side. Terminal arrangements for supplying current to the mesh may comprise terminals of the mesh itself extending out of the insulation as at 16, exposed areas of mesh to which lead wires are soldered or spot welded, terminal lugs in direct contact with the mesh, or insulated terminal posts extending through the laminations with a washer in electrical contact with the mesh (Fig. 8 not shown). Where the mesh has a reduced cross-sectional area, e.g. due to the provision of terminal posts or fixing studs as shown in Fig. 5, conductive patches 26, e.g. of mesh, or of a conductive coating on the mesh or of finely divided conductive particles in a non-conductive binder, are provided in contact with the mesh to compensate for the resulting increased resistance of the mesh. The laminations after being bonded may be coated with an insulating varnish. An element of the type shown in Fig. 4 may be given a metallic foil surface on one or both sides.