US2569340A - Electric warming element - Google Patents

Description

Sept. 25, 1951 E() SRN ET AL 2,569,340

ELECTRIC WARMING ELEMENT Filed Nov. 10. 1949 H/Avgnor 50 Sarno and /7//\6 Lzndber f @mmm Patented Sept. 25, 1951 ELECTRIC WARMING ELEMENT Bo Srn and Arne Lindberg, Stockholm, Sweden, assignors to Allmanna Svenska Elektriska Aktiebolaget, Vasteras, Sweden, a Swedish corporation Application November 10, 1949, Serial No. 126,454 In Sweden February 21, 1949 2 Claims. (Cl. 219-46) This invention relates to an improved design of electric warming elements the warming body of which is made from a semi-conducting vinylsheet or other plastic material protected on the outside by an insulating plastic covering.

It is difficult to manufacture semi-conducting vinyl sheets having exactly the volume resistivity desired. The semi-conducting vinyl compound is prepared in batches, certain divergences from batch to batch thus being unavoidable. In manufacturing elements for warming Ipads, for instance, it is therefore necessary to calibrate the resistance of the warming body. It is an object of the present invention to facilitate this operation and to solve, at the same time, the power control problem. This is achieved by punching the warming body in the shape of a comb, so that it forms a plurality of parallel iiaps of substantially equal width extending from a part oi the original sheeting untouched by the punching operation.

The invention will be described more clearly reference being made to the accompanying drawing showing one embodiment of the invention. Fig. 1 is a front view of a warming body and Fig. 2 is a cross-section taken along the line A-A in Fig. 1.

The warming body is punched in the shape of a comb from a sheet of semi-conducting vinyl material. The comb consists of a plurality of teeth or flaps I, 2, 3, 4, 5, 6, 1, 8, 9, I0, extending from a part II of the original sheeting untouched by punching. The resistance of the sheet is measured lprior to the punching of the slots I2 which form the ilaps. For the punching a die is used having such a construction that the width of the slots may be varied and adjusted in order to compensate the deviation of the resistance from its normal value. A strip of insulating vinyl sheet I3 is inserted between the free ends of the flaps in such a manner that every even-numbered flap of the warming body will lie, for instance, on one side of the strip and every odd-numbered flap on the other side thereof. A stranded lead I4 is pressed into the warming body on one side to make contact with the flaps I, 3, 5, 'I, 9. Another lead I5 is pressed into the other side thus making contact with the aps 2, 4, 6, 8, I0. The leads I4 and I5 are insulated from each other. A third lead I6 is pressed into the back of the comb, i. e. into the part Il which is untouched by punching. After attaching the stranded leads a warming body is obtained, the resistance of which corresponds closely to the desired resistance.

With the embodiment shown three control positions are obtained. The lowest heating power is achieved when the voltage is supplied between the leads I4 and I5, the current will then flow in series through pairs of adjacent teeth, such pairs being connected in parallel. Medium heating power is obtained by supplying the voltage between the leads I4 and I6. Thereby only the teeth connected to the lead I4 will be warmed, whilst the current does not iiow to the teeth" connected to the lead I5. Maximum heating power is obtained when the voltage is supplied between the lead I6 and the joined leads I4 and I5, whereby all teeth will be warmed.

Thermostats may be inserted in a conventional manner, but care must be taken that they are connected to such teeth which are loaded in a control position for medium heating power. In order to insulate electrically the thermostats and the conductors from the warming body, the element may be covered entirely or partly by an insulating sheet, the thermostats and conductors being laid on that side of the sheet which is turned away from the element.

We claim as our invention:

1. An electric warming element, comprising a warming body of semi-conducting single ply nonrigid vinyl material in the shape of a comb with a plurality of parallel iiaps of substantially equal width extending from the integral lpart of the comb and forming the teeth, an insulating strip of sheet material interposed between the ends of the flaps with said ends alternately located at opposite sides of said strip, a common lead connected to the ends of the iiaps at one side of said strip, and a common lead connected to the ends of the iiaps at the other side of said strip.

2. An electric warming element, comprising a warming body of semi-conducting single ply nonrigid vinyl sheet material in the shape of a comb with a plurality of parallel flaps forming the teeth, an insulating strip of sheet material interposed between the free ends of said naps with the iiaps alternately located at opposite sides of said strip, a lead connecting the free ends of the iiaps at one side of the strip, a lead connecting the free ends of the flaps at the other side of said strip, and a lead connected to the integral part of the comb.

Bo sRN. ARNE LINDBERG.

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

UNITED STATES PATENTS Number Name Date 1,071,843 Wiegand Sept. 2, 1913 1,719,179 Hayden, Jr. July 2, 1929 1,962,673 Wilms June 12, 1934 2,382,312 Heinrich Aug. 14, 1945 2,386,095 Edgar et al. Oct. 2, 1945 2,404,736 Marick July 23, 1946 2,473,183 Watson June 14, 1949 2,513,415 Larsen et al July 4, 1950 FOREIGN PATENTS Number Country Date 224,648 Great Britain Nov. 20, 1924 294,452 Great Britain July 26, 1928

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