US 1287192 A
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F. BERRY. ELECTRH HEATING DEVICE.
APPLICATiON HLED JULY 8.1918.
1,287,1 92. Patented Dec. 10, 1918.
Inventor-z Arthur" Francis Berr g,
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UNITED STATES Parana ARTHUR FRANCIS BERRY, OF LONDON, ENGLAND, ASSIGNOR TO GENERAL ELECTRIE! COMPANY, A CORPORATION'OF NEVT YORK.
ELECTRIC HEATING DEVICE.
Specification of Letters Patent.
Patented Dec. 10, 1918.
Application filed July 8, 1918. Serial No. 243,764.
To all whom it may concern Be it known that I, ARTHUR FRANoIs BERRY, a subject of the King of Great Britain, residing at London, England, have invented certain new and useful Improyements in Electric Heating Devices, of which the following is a specification.
This invention has reference to that kind of electrical heating element suitable for cooking and similar heating apparatus, wherein a length of bare strip or wire of resistance metal or alloy (hereinafter referred to as a resistance strip) is arranged between sheet material of a refractory and insulating character, such as sheet mica, and inclosed within or backed by, it may be, sheet or plate metal, and particularly to a heating element of this kind, in which the resistance strip is arranged wholly or mainly at one side of refractory sheet insulating material of the kind referred to and hereinafter called for distinction the outer sheet and is separated from'the surface of the metal body to be heated by similar refractory sheet insulating material, hereinafter called for distinction the inner sheet. Adjacent to the outer sheet of refractory insulating material is or may be arranged one or more sheets of similar material. Example of heating elements of the kind referred to are described in the specification of my British Patents, Nos. 4672/09, 14699/18 and 12551/14.
In such heating elements the refractory sheet insulating material used has been clear sheet mica. While the use of this material is advantageous forthe inner sheet next to the surface of themetal body, to be heated, (hereinafter called for distinction the hot plate), because it admits of heat passing therethrough as radiant heat and by conduction to the hot plate against which it is'firmly pressed, the use of such clear sheet mica for the outer sheet is disadvantageous when it is not desired to transmit heat outward from the resistance strip to a metal back plate because owing to its being smooth and clear, it has a comparatively low emissivity for heat. Consequently, when the heating element is in action, although such outer sheet will be raised toa temperature approaching nearly to that of the resistance strip in contact'therewith, it will not radiate its acquired heat very rapidly to the hot plate and consequently will not readily take up and rapidly and usefully dissipate the heat of the resistance strip so as to enable such strip to be run at such high power as is usually desirable for efficient working in apparatus such as electrical cooking and like apparatus.
Now the present invention has for object to enable the outer sheet of refractory insulating material to rapidly acquire heat from the hot resistance strip and quickly radiate it from those parts of its surface that are not covered by the resistance strip through the inner strip to the hot plate and in this way enable the resistance strip to be Worked at a higher power and in a more economical manner than heretofore usual.
For this purpose the outer sheet of refractory insulating material is constructed of material adapted rapidly to radiate through the inner sheet of refractory mate rial the heat that it acquires from the hot resistance strip. To this end there is employed an outer sheet having a mat, roughened or dulled surface on the side next to the length of resistance strip so that it will rapidly radiate inward toward the hot plate, the heat which it takes up from the resistance strip. The opposite side or surface of such sheet, which will usually be of mica, and.is hereinafter referred to as mica, is smooth and clear so that it will have a low emissivity in a backward direction unless it is desired to also heat a back plate in which case the rear surface of the outer sheet may also be of a mat, roughened 0rdulled character. The sheet mica used for such outer sheet may have the mat, roughened or dull surface existing naturally thereon, or such a surface may be produced thereon artificially, as by treating one surface of clear sheet mica chemically, as with a suitable acid or other corroding agent. or mechanically, for example, by abrasion, as by rubbing it with powdered glass or emery.
In the accompanying illustrative drawings Figure 1 shows in section, a portion of one construction of electrical heating element of the kind herein referred to embodying the invention. Fig. 2 is a face View of a portion of an outer sheet of mica with resistance strip thereon.
Fig. 3 is a section showing the electrical heating element applied between a hot plate to be heated and a back or holding plate. Fig. 4: is a similar view to Fig. 3 but showresistance strip 1 designed to be heated by' the passage therethrough of an electriccur- 7 rent and two sheets 2 and 8 of mica between which the strip 1 is held. In Fig. 3 the heating element is held against one side of a metal plate 4 to be heated by a back plate 5 that may be of metal or refractory insulating material. according to circumstances, the sheet'2 being what is herein called the inner sheet and 3 the outer sheet. The resistance strip 1 in the example shown is mounted on the outer sheet 3 of mica after the manner described in the specification of former Letters Patent granted to me No. 8829 of 1915 so that it is mainly on the inner surface of the said outer sheet of mica. This inner surface of the outer sheet 3 of mica, which is pressed closely against the heating strip 1 has a mat, roughened or dull surface for the purpose hereinbefore explained. As the outer sheet 3 of mica will, by reason of its being in close contact with the re sistance strip 1, be heated to almost the same temperature as the resistance strip and as the portion of its mat, roughened or dulled surface not covered by the resistance strip forms a large proportion of such surface, say thereof, such portion, owing to its high emissivity, will act rapidly to transmit or dissipate the heat of the resistance strip 1 and outer sheet 3 through the inner sheet 2 of mica to the hot plate 4 and thus allow of the resistance strip being worked at a high power. The opposite or outer surface of the said outer sheet 3 is, in this example,
smooth or clear. The inner sheet 2 may be of clear or transparent mica so as to admit of radiant heat from the outer sheet 3 passing through it to the hot plate, and also of the passage by conduction, of heat directly received from the resistance strip 1 which is in direct contact therewith. To admit of this inner sheet absorbing and transmitting in a better or quicker manner heat obtained from the outer sheet 3 and resistance strip 1 to the hot plate l, its outer surface, namely that next the outer'sheet 3 and resistance strip 1,,mayalso be of a mat, roughened or dulled character.
Loss of heat from the outer side of the outer sheet 3 of mica may, when desired, be prevented in any known or suitable way. In Fig. 4 refractory nonconducting material 6, for instance slag woo-l, is for this purpose, arranged between the outer sheet 3 and a back plate 5.
7 What I claim as new and desire to secure by Letters Patent of the United States, is
1. An electrical heating element of the kind herein referred to, having an outer sheet of refractory insulating material with a mat, roughened 0r dulled surface facing toward the inner sheet and bearing directly against the resistance strip of the element, substantially as described.
2. An electrical heating element of the kind herein referred to, comprising inner and outer sheets of mica and a resistance strip clamped between and in direct contact with such sheets, the inner surface of the outer sheet having a mat, roughened or dull surface bearing against the resistance strip, substantially as described.
3. A heating element according to the preceding claims, wherein the opposite or outer surface of the outer sheet of mica is smooth and clear, substantially as described.
4:. An electrical heating element according to any of the preceding claims, wherein the outer surface of the inner sheet opposite the resistance strip and outer sheet has-a mat, roughened or dulled surface, substantially as described. 7 V
5. In electrical heating apparatus, electrical heating elements embodying sheet mica having mat, roughened or dulled surfaces, substantially as described for the pup poses set forth.
In witness whereof, I have hereunto set my hand this 19" day of June, 1918.
ARTHUR FRANCIS BERRY.
Copies of this patent may be obtained for five cents each, by addresslng the Commissioner-of ratente,
' Washington, D. G. I