GB405611A - Electric heating elements and machine and process for producing same - Google Patents

Abstract

405,611. Electric hot - plates &c. SMITH, J. E., 95th Avenue, Belleville, Illinois, U.S.A. July 22, 1932, No. 20699. [Class 39 (iii).] A heating-element consisting of a coiled resistance wire located in a mass of material having electrical insulating but heat conducting properties is formed by simultaneously extruding the coiled wire and the insulating material, when the latter is in the plastic state, and forcing the turns of the coil apart during the extrusion of the plastic material, so that this is forced into the space between the turns. The coated coiled wire is then fashioned into the desired form and dried to set the formed unit. The plastic material may be an argillaceous material or may consist of aluminium or magnesium oxide with a binder such as vegetable gum or lignin. The coiled resistance wire 14, Fig. 1, is fed through a guide tube 20 into a hopper 10 containing the plastic material 12. Pressure is applied, for example by means of compressed air or a piston and cylinder, to the material 12, which causes the coils of the resistance wire 14 to be spread apart and coated with the material to a thickness determined by a nozzle 18 through which the coated resistance wire is extruded. The extruded resistance unit may be wound into any desired form, for example, as shown in Fig. 3 applied to an iron, three turns of the coated resistance wire 14 are coiled within a casing 24 having sloping sides 24b and an open bottom so that the unit is pressed directly against the sole plate 26. In a modification, a single or double turn of the resistance unit is similarly held in contact with the surface of a waffle iron. For a waterproof heating element, for example for use on the top of an electric stove, the coated resistance is coiled into a flat spiral, built up with additional plastic material, moulded into the form of a ribbed disc, coated with vitreous or porcelain enamel, and baked. In a further construction the coated resistance wire is extruded directly into a tubular casing much as a copper or steel tube, which may be bent into any form before the unit is cured and baked. Such a tube may, for instance, be brazed or welded through the wall of a tank &c. The unit may be coiled and held at spaced points, for instance by a spider.