US2518807A - Electrical heating element - Google Patents

Description

Aug. 15, 1950 J. L. MUSGRAVE HAL ELECTRICAL HEATING ELEMENT Filed April 16, 1947 A b Ii i i I I 2 Sheets-Sheet 1 A g- 1950 J. L. MUSGRAVE ET AL ,80

ELECTRICAL HEATING ELEMENT 2 Sheets-Sheet 2 Filed April 16, 1947 z lTi z iTlTl T iT T L u T u uT f li Ti l| T L Ti l 1| i'l 1 Ti 1 Ti 1 Ti Patented Aug. 15, 1950 ELECTRICAL HEATING ELEMENT Joseph Leslie Musgrave and Douglas Gastrell Lewis, London, England, assignors, by mesne assignments, to Dulrae Limited, London, England, a British Company Application April 16, 1947, Serial No. 741,774 In Great Britain August 22, 1946 The present invention relates to electrical heating elements employing resistance wire or tape (referred to throughout this specification comprehensively as wire) and made in the form of sheets or strips which may be either plane or curved. Such elements are especially suitable for the heating of buildings, being for this purpose made up in the form of panels adapted to be incorporated in walls and/or ceilings. The main object of the invention is to simplify the construction and manufacture of electrical heating elements of the kind referred to.

According to the invention, an electrical heating element of the type set forth comprises a sheet or strip of material having a number of perforations through which resistance wire is threaded, the lengths of the wire extending between those sections of the wire located in the perforations lying substantially against one face or other of the sheet or strip. The resistance wire employed may be bare or insulated and may be applied to the sheet or strip either by hand or by a suitable mechanical device. If bare wire be employed, the sheet must be of insulating material and this is the form of construction chiefly referred to in the specification, it being understood, however, that if insulated wire be used it it not essential that the sheet or strip be insulating. The sheet with its incorporated conductor or conductors may be encased in any suitable manner, for instance by embedding it in insulating compound or covering it with material in sheet form with or without the interposition of appropriate adhesive or embedding compound.

Generally the perforations will be arranged in rows, and in the simplest case they consist of round holes equispaced in each row and each of a diameter somewhat greater than that of the outside diameter of the resistance wire whether bare or insulated. Alternatively the perforations may take the form of slots, or, according to another construction, slits are formed in the sheet, the wire being threaded through the slots or slits as the case may be.

In a convenient construction there extend, in proximity to opposite edges of the insulating sheet or strip, two conductors constituting busbars connected to the power circuit, and these are suitably respectively threaded in and out through the rows of perforations nearest to the above opposite edges. Any number of lengths of resistance wire may then be connected between these bus-bars, and normally, in order to accommodate the required length of resistance wire, it will be applied to the insulating sheet or strip in Claims. (01. 219-19) the form of a zigzag. In other cases terminals mounted on the sheet or strip are employed instead of bus-bars.

In order that the invention may be clearly understood and readily carried into effect, it will now be described more fully with reference to the accompanying drawings, which illustrate by way of example various forms of heating elements and the manner in which such elements may be made up in the form of a panel. In the drawings:

Figure 1 is a plan view of a portion of a heating element wherein the perforations in the supporting sheet or strip consist of round holes,

Figure 2 is a section on the line IIII of Figure 1 to an enlarged scale,

Figure 3 is a view similar to Figure l, the perforations being in the form of slots,

Figure 4 is a section on the line IVIV of Figure 3 to an enlarged scale,

t Figure 5 is a view similar to Figure 1, the perforations being in the form of slits,

Figures 6 and 7 are respectively sections on the lines VI-VI and VII-VII of Figure 5 to an enlarged scale, and

Figure 8 is a perspectiveview of a heating element made up into the form of a panel, certain parts being shown as broken away for the sake of clearness in illustration.

Referring to Figures 1 and 2, the sheet or strip of material I which serves to support a length of resistance wire 2 which constitutes the heating element proper may be made of insulating material, such as plywood, paper, cardboard, a plastic substance or asbestos, in which case the resistance wire 2 may be bare; alternatively, the sheet or strip I may be of metal or other conductive material, in which case it is necessary that the resistance wire 2 shall be covered with insulating material.

Formed in the sheet I is a series of perforations 3 in the form of round holes, through which the wire 2 is threaded as indicated so that a portion of this wire lies on each side of the sheet I. For the purpose of connecting the wire 2 to a power circuit, there are provided in proximity to opposite edges of the sheet I conductors 4 and 5 which serve as bus-bars between which any number of resistance wires 2 may be connected by soldering or by any appropriate clip or corre sponding device. The bus- bars 4 and 5 are conveniently supported by threading them through a series of perforations 8. Normally the length of a single resistance wire 2 to be connected between the bus- bars 4 and 5 will exceed the distance between the latter, and, accordingly, as indicated in the drawing, the resistance wire 2 is usually disposed in the form of a zigzag. It is convenient to arrange that the spaces between the perforations 3 shall be equal, and under such conditions approximately half of thetoteil'length of the resistance'wire -2 will lie on each side of the sheet I. However, if it be desired that a greater proportion of this total length shall lie on one side than on the other, this resultis readi- 1y secured by varying the spaces between the perforations 3.

Figures 3 and 4 illustrate a construction Wherein the perforations in the sheet I are in the-form of slots '1 which extend in substantially the same direction as that of each arm 'in'the zigzag into which the wire 2 is formed, this feature being clearly seen in Figure 3. As indicated in Figure 4, the result of employing slots is that the greater part of each length of resistance Wire 2 is exposed-on both sidesof the'sheetl, and further, since-in. each arm-of the zigzag each of the slots lies in the general direction of thewire'and, as seen in Figure 4, the wire extends diagonally through each slot, it followsthat the bending to which the wireZ is subjected'is-nscesearily much less'sharp than is the-case if the perforations'be in'the form of round'holesas'in the construction depicted in Figures'l and 2. It is also to be noted from Fig. 4 that the gauge of the wire 2 is substantially lessthan'the thickness of thesheet. 'Thus',-a substantial part of the length ofwire2'in the respective slots 7 lies inwardly-of the outersurfacesof the sheet! and is protected against injury bythe slot walls, as when the sheet I is being assembled in-a panel.

For" the purpose of connecting the wires 2 to the power circuit, :bus barssuch as those illustrated in Figure 1, might be employed, but, for the sake of illustration-an alternative means'of connection is shown inFigure'3, comprisingtterrninals 8, mounted on the sheet I, to whichthe ends of the zwire 2 are led, such terminals ser-ving as means of connectionfor leads to a power circuit. It will be appreciated that, in any of the constructions described and illustrated in this specification as employing bus bars, terminal connections, as shown/in Figure 3, might besubstituted.

Referring to Figures-5, 6-and 7,'the perforations in the sheet l-throughzwhich'the resistance conductor? is threaded take the form of-slits fl, that "is "to say that, as illustrated, there is no removal of material from the sheet and between these slits there remain'tongues ll] of the material of whichthe 'sheet :1 is 'formed. As seen in Figuresrfi and 7, these tongues are prefera'bly raised from'the general plane of the sheet I :by the amount'suiiicient to allow the Wire -ZEtopass under each tongue with little or 'no deviation, with ithe-result'ithat, 'as indicated 'in Figure 7, each farm into which'ith zigzagged' conductor 2 is divided takes a 'form approximating to a' straight line. s

Convenientlyth'e slits i9 are locatd in the sheet I in pairs, with :the result :that the tongues fll are comparativelyinarrow and the greater part of "the wire'2 is therefore exposed on one: side of the sheet LI only. Such an arrangement isnot, however, essentiaLsince'the slits might be other wise disposed;ffor instance, they might beequally spaced, in whichlcase half the length f the wire would be exposed :on .each side .of the sheet]; V f

LSDIIle-Of the materials suitable-fo the-sheet 1 are conveniently packed in roll form, and in the manufacture of heating elements as above described sheet or strip material in such form may be employed, a length of the roll being unwound and the operation of forming the perforations and-.threading-the conductors through them beingthen performed and the strip or sheet again rolled up for storage or transport purposes, being ultimately cut into lengths as required. Particularly in cases in which the elements are to be employed in the heating of buildings, it is usual to apply an embedding compound to the sheet or:strip,whereby the conductors are retained in position, and also covering material in sheet form. In that case the embedding and/or covering material may be-applied to the insulating sheet or-strip before it is re-rolled, but in other instances, if such materials be of a comparatively rigid nature for example, it may be more suitabel to apply either or both of them after the insulating sheet has been again unrolled fo the purpose of cutting it'into the lengths required in use. In'an alternative mode of production, thelengths required for use are cutimmediately after-the perforations have-been formed and .the resistance conductor applied, or even before-these operations. Again, the perforations might be cut-before'the sheet or strip is :rolled, the latter being then ready for application of the conductorsimmediately on unrolling.

-In thepanel illustratedinFigure 8, a sheet 1.- wherein the perforations .3 are in the form of round 'holes as depicted inFigures 1 and is employed. In addition, however, to the resistance wire 2 there is a second'resistance wire 1.! connected in-parallel with the wire2 and threaded through the same seriesof perforations 3. Asiindicated, howeventhe-direction of threading of theconductor H through ,each'perforation is opposite to that of, the conductor 2, with the result that alength of resistance wire is exposed on both sides of the sheet I over the'whole zigzag-into .whichthe-1esistancewires 2 and H are formed. It is :tobe'understood-thatthis arrangem'ent'of :two resistance wires in parallel 'might beemployedin connection witha construction of sheet other than that depicted'in Figuresl, 2 and 8, forwinstance, suchiapair of resistance conductors might be applied to a sheetwherein the perforations are constituted by slots, as depicted in Figures 3 and 4;

In building up a heating panel as illustrated in Figure 8, to asheetor strip i of finite or of indefinitelength as above mentioned, with which one-or more resistance wires ,2 have been previously incorporated, there is-applied on .one or the sheet I inrany appropriate manner,-such,- foi" instance, as stapling, eyeleting, riveting, stitching:

orila'cing, or' the cement, adhesive or the like I-2,-if suchT:be-used,:with or without theapplica tiono'f pressure andyorheat, maybe relied upon for securingthe covering "sheets- :As a "further alternative, the-insulating sheet with its resist ance wires 7 may i-beiiincorporate'dwiii- :a' laminated' plastic material, or in a plastic or moulded heatresisting or refractory material; or the insulating sheet might be placed between layers of dielectric material, such as mica or micanite, and then encased in metal or heat-resisting material.

Certain of the adhesives referred to above as appropriate for attaching covering plates to the insulating sheet, when in the solid condition, are themselves suitable for constituting the latter; thus the resistance wire might be wound in perforaticns cut in a sheet of uncured phenol formaldehyde resin and the covering plates applied and secured to this insulating sheet by means of pressure and heat.

Obviously, many different ways of covering the insulating sheet or strip bearing the resistance Wires might be adopted according to the particular purpose for which the heating element is to be used and having regard to the decorative or other conditions with which it is desired to comply. Also the element may be fashioned to.

any appropriate form, for instance, fiat, corrugated, or curved to any required shape to suit local conditions. Such elements, either alone or made up into panels, may be used for any purpose where heat is required at a temperature within the working temperature limits of the elements. They may be used for drying, heating, cooking or in processing tunnels or compartments; for warming compartments or surfaces in ships, aeroplanes, trains, automobiles, as well as for warming rooms of buildings. They may be applied as independent units, stationary or portable, or attached to or form part of the structure they serve.

What we claim and desire to secure by Letters Patent of the United States is:

1. An electrical heating element for wall panels and the like comprising a sheet of material having perforations in the form of slots, said slots being arranged in rows and each slot being located lengthwise in its row, resistance wire lying in said slots in a row and being of a gauge less than the thickness of said sheet of material whereby a substantial part of the wire in a slot between the ends of the latter will be protected by the side walls of the slot, said wire extending progressively from one face of said sheet to the opposite face of said sheet through said slots.

2. The structure of claim 1, characterized by the space between adjacent slots in a row being less than the length of one slot.

3. The structure of claim 1, wherein the resistance wire in extending through each slot lies diagonally relatively to the surface of the sheet and lengthwise of the slot.

4. In the art of electrically heated panels for room walls, ceilings and the like, a sheet-form heating element for such panels comprising a sheet of material having perforations in the form of slots, said slots being arranged in laterally spaced rows and each slot being located lengthwise in its row, resistance-wire-provided heating means of a cross-section substantially less than the thickness of said sheet of material, said resistance-wire-providing heating means threaded successively and lengthwise through the slots of each row and alternately from oppositesurfaces of said sheet, a substantial part of each portion of the Wire between ends of a slot lying inwardly of the plane of the opposite surfaces of the sheet and at an angle inclined from one surface of the sheet to the other whereby to be protected by the side walls of the slot, said wire-providedheating means lying in close proximity to the surface of the sheet between slots in each row, the sheet portions between slots of each row causing the heating means to partake of a bend of but a few degrees at the exit and entry ends of the slots whereby to avoid liability of breakage of the heating means in service or when the sheet is being installed in a heating panel.

5. The structure of claim 4, characterized by the space between adjacent slots in a row being less than the length of one slot.

JOSEPH LESLIE MUSGRAV'E. DOUGLAS GASTRELL LEWIS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 853,784 Heath May 14, 1907 1,077,635 Ovington Nov. 4, 1913 1,119,838 Kuhn Dec. 8, 1914 1,123,225 Bernecker Jan. 5, 1915 1,153,703 Phelps Sept. 14, 1915 1,241,578 Thornton, Jr Oct. 2, 1917 1,996,522 Norris Apr. 2, 1935 FOREIGN PATENTS Number Country Date 432,057 Germany July 24, 1926

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