US1142939A - Electrically-heated oven. - Google Patents

Description

R. W. 1L \VEI IPORT.

ELECTRICALLY HEATED oven.

APPLICATION HLED OCT. i0, 19M.

1,1 %21939. Patented June 15, 1915.

Jlllllll IIIIIII WITNESSES: [NI/EH70? m yiafzzport I W W L Mam ATTORNEYS UNITED STATES PATENT OFFICE.

Ransom w. DAVENPORT, or DETROIT, MIomGaN, ASSIGNQB To DETBQI s'rovn worms, or DETROIT, ronrsan, A oopronnrrou ,or' MICHIGAN.

ELEGTRIGALLY- HEA TED OVEN.

Specification of Letters Patent.

Patented June 15, 1915.

Application filed October 10, 191.4. Serial No. 866,076.

To all whom it may concern Be it known that I, Ransom WV. DAVEN- roar, a citizen of the United States of America, residing at Detroit, in the county of Wayne and State of Michigan, have invented certain new and useful Improvements in Electrically-Heated fivens, of which the following is a specification, reference being had therein to the accompanying drawings.

The invention relates to electrically heated ovens and has for its object: first, the obtaining of a simple construction of electric heater for said oven; second, a construction by which the heat is distributed partly by radiation and partly by convection, to secure the most favorable heating effect within the oven chamber; and further the obtaining of various advantages as hereinafter set forth.

In the drawings, Figure l is a cross section through the oven showing the arrangement and distribution of the heaters therein; 2 is a plan View; Fig. 3 is an enlarged section through the lower heating unit; Fig. 4 is a similar section through the upper heating unit; and Fig. 5 is a diagram showing the arrangement of the circuit.

ln the heating of an oven where the heat is distributed by radiation either from the bottom or the top, there is diliiculty in properly heating the central portion of the chamber. This is particularly so where there are one more intermediate shelves which serve as screens for the directly radiated heat. Thus where electrical heating units are employed which dissipate heat largely by radiation there is danger of uneven heating of the oven space which is undesirable. To avoid this result, I have devised a construction of electrical heating unit where the heat generated may be distributed by radiation or bv convection and in any proportion desirable. l have also so arranged the heating unit within the oven chamber as to obtain a uniform distribution in all portions thereof.

My improved construction of unit comprises a metallic strip A having a marginal portion thereof folded at B to embrace an insulated ribbon O forming the electrical resistor. This resistor is preferably insulated by mica or other suitable insulating I material which may be laid upon the strip A before folding, and bent as the strip is folded to embrace the resistor ribbon. Prererably both edges of the strip A are thus folded to embrace resistors. while the intermediate portion of the strip forms a heatconducting and radiatidn surface for the dissipation of the heat. The strip having the insulated resistors is then bent into a zigzag form as indicated at l), the edges of the bent portions being in the same plane while the sides of the strip are parallel to each other. This will expose only a limited surface of the ed e of the strip to direct radiation, while the heat which is conducted in the central portion of the strip will be effective for heating the air which is distributed by convection.

l preferably arrange heaters at both the bottom and the top oi the oven chamber, out form the heater at the top or" a relatively narrow strip, whereas the heater at the -ottom is formed of a wider strip. This reduces the convection and increases the radiation of the upper heater. while the lower heater is increased in convection and re duced in radiation. The purpose of this arrangement is to heat the air at the bottom where it will be distributed by a gravity circulation, while the air heated at the top is limited, and most of the heat generated is dissipated by downward radiation. The heat generation of the two heaters is not the same, but that of the lower heater is sufiiciently greater than that of the upper heater, so that the radiating effect of the two will be substantially the same, but the convective effect of the bottom heater is greatly in excess.

With the construction as described the electric circuits are preferably so arranged that the resistors in the folds of the opposite edges of the strip are in independent circuits, and the resistors of the corresponding edges of the bottom and top heaters are in series with each other. This balances the resistance of the two circuits, while at the same time the heat generation of the lower heater is in excess of that of the upper one. In operation, the heat generated in the lower element will be distributed by conduction into the central portion or" the strip, where it is in contact with the air between parallel portions of the strip. This will produce a heating and a convective eilect which will cause the hot air to rise and distribute through the central portion of the oven same manner the heat developed in the up- -heater is in series with the resistor per element will be partly distributed by radiation and partly by convection, but the reduced width of this upper strip will limit the heat distributed by convection, and the lesser length of the upper element will reduce the radiated heat to an amount substantially equal to that of ,the lower strip.

As shown in the diagram Fig. 5, the resistor G of the upper edge of the u peg o the upper edge of the lower heater, and the resistor I of the loweredge' of the upper heater is in series with the resistor J of the loweredge of thelower heater. The currents may be controlled by independent switches K and L.

What I claim as my invention is 1. The combination with an oven or chamber to be heated, of a heating element therefor, comprising a resistor and a strip in heat-conducting contact therewith, the edge of said strip being exposed for direct radiation into said chamber and the side dissipating heat to be distributed by convection. i

2. The combination with an oven or chamber to be heated, of heating elements arranged at the top and bottom of said chamber, said elements being adapted to distribute substantially equal quantities of heat by direct radiation into the chamber, and the lower element distributing an excess of heat by convection.

3. The combination with an oven or chamber to be heated, of a heating element therefor, comprising ametallic strip hav ing a folded edge with an insulated resistor clamped in the fold, said strip being returnbent to expose the edge portion thereof for direct radiation into said chamber, with the sides distributing their heat by convective air currents.

4-. The combination with an oven or chamber to be heated, of electrical heating units arranged at the top and bottom of said chamber, each comprising a metallic strip having a folded edge with an insulated resistor clamped in the fold, the strips being bent into zigzag form and having their edge portions exposed for direct radiation into the chamber, the sides of said strips being exposed to convective air currents, and the strip of the lower heater being of greater width than that of the upper one.

5. An electrical heating element, comprising .a metallic strip having a comparatively narrow folded edge, and a resistor clamped wholly within said fold.

6. The combination with an oven, or chamber to be heated, of electrical heating units arranged at the top and bottom of said chamber, each comprising a corresponding plurality of resistors and a strip in heat conducting contact therewith, the .strip at the bottom of the chamber being of greater width than the strip at the top, and means for electrically connecting the corresponding pairs of resistors of said units.

In testimony whereof I ailix my signature I in presence of two witnesses. i RANSOM DAVENPORT.

l/Vitnessesz JAMES P. BARRY, HENnI E. BOWNAN.

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