US 3359524 A
Description (OCR text may contain errors)
Dec. 19, 1967 D. GALLAGHER ET AL 3,359,524
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United States Patent Oflice 3,359,524 FLEXIBLE HEATING ELEMENTS Daniel Galiacher, Glasgow, and Thomas W. McGill, Bishopton, Renfrewshire, Scotland, assignors to Ioco Limited, Glasgow, Scotland, a British company Filed Sept. 2, 1964, Ser. No. 393,937 Claims priority, application Great Britain, Nov. 11, 1963, 44,493/63 2 Claims. (Cl. 338-212) This invention relates to flexible heating elements and is concerned with the provision of such elements having a greater degree of flexibility than is provided with conventional elements.
According to the invention, there is provided an electrical heating element including two spaced conductors, respectively incorporating a coiled length of conductive material, secured to a flexible sheet of material incorporating or consisting of a film or layer of conductive rubber or resin which provides a current path between the two conductors.
In order that the invention may be more fully understood, one construction of heating element in accordance with the invention will now be described, by way of example, with reference to the accompanying drawing, in which,
FIGURE 1 illustrates the element in perspective,
FIGURE 2 shows a length of conductor incorporated in the element of FIGURE 1, and
FIGURE 3 shows an enlarged View of one strand of the conductor.
Referring now to the drawings, the element comprises a rectangular sheet 1 of terylene fabric provided with a coating 7 of conductive silicone. For the purposes of illustration, the coating 7 is shown as extending over a zone 8, although in practice the whole of the sheet of fabric is coated. To one face of the sheet 1 are secured two spaced conductors 2 lying adjacent opposite edges of the sheet. The silicone is an 1.01. conductive grade of silicone rubber known as ER 567.
Each conductor 2 comprises eight strands 3 and each individual strand consists of two strips 4 of high conductivity copper (0.001" x 0.01") wound helically onto a 250 denier terylene yarn 5. The individual strands are then spun together with four yarns 6 of 250 denier terylene yarn to form the completed so-called metal tinsel conductor. The conductors 2 are secured to the sheet 1 by stitching 9 which is preferably in the form of a cross-locking stitch.
Each conductor may, however, consist of any conductive metal coiled without any central core or wound around a central core of cotton, synthetic (e.g. polyester) or other yarn. The conductor may be used in this single strand form or a number of such single conductors may be built up into a multistrand conductor, which may itself be built up with a central core of cotton, synthetic (e.g., polyester) or other yarn.
In operation of the element, conductor to a suitable supply,
upon connection of the heat is generated by the 3,359,524 Patented Dec. 19, 1967 passage of electric current through the conductive coating, the conductors merely assisting in the conveyance of current to the coating.
It has been found that the element provides a heated surface of more uniform temperature than that of conventional flexible elements and the form of conductor used results in a greater degree of flexibility than is provided by previously known elements. The stitching of the conductors to the fabric has been found to provide (1) a satisfactory contact area between the conductor and the conductive sheet surface with suflicient contiguity to eliminate discharge between the conductor and the sheet; (2) a firm location of the conductors along their total length without possibility of displacement by normal mechanical stresses such as would result from flexing; and (3) an accurate and industrially practical method of spacing and positioning the conductors to provide the required degree of heating.
Applications of the heating element include heated blankets, heating floor heaters and tube and We claim:
1. An electrical heating element including a flexible sheet of material consisting of a woven fabric coated with electrically conductive rubber, two spaced substantially parallel and elongated conductors disposed on said coated flexible sheet, each conductor extending along an opposite edge of the flexible sheet, said conductors and coated sheet providing a current path such that the current passes from one conductor through the portion of the flexible sheet extending between the two conductors to the second conductor, each said conductor comprising a plurality of strands of conductive material wound around a core of textile material and each said strand comprising a plurality of lengths of electrically conductive material wound around a core of textile material, and stitching passing over the respective conductors securing the conductors to the surface of said flexible woven fabric sheet coated with electrically conductive rubber.
2. A heating element as claimed in claim 1, wherein the stitching is in the form of a cross-locking stitch.
References Cited UNITED STATES PATENTS electrically pads, bags and sheets, underpipe heaters.
2,277,772 3/ 1942 Marick 219-527 X 2,299,162 10/1942 Marick 219-527 2,575,987 11/1951 York et al. 219-549 X 1,275,469 8/1918 Pruessman 174-131 2,013,211 9/1935 Herkenberg 174-69 X 2,406,367 8/1946 Griffith et al. 244-134 2,473,183 6/1949 Watson 338-212 X 2,515,294 7/1950 Cowgill 338-212 X 2,669,646 2/1954 Ford 338-208 3,060,303 10/ 1962 Skoglund et a1. 338-208 X 3,092,685 6/1963 Argento 174-128 X 3,100,240 8/1963 McKirdy 174-113 X RICHARD M. WOOD, Primary Examiner. V. Y. MAYEWSKY, Examiner.