US1949450A - Low voltage heating element - Google Patents

Description

March 6, 1934. H. 5. BROWN 1,949,450

LOW VOLTAGE HEATING ELEMENT Filed March 22, 1935 Hl VEH TOR, Howard 6. Brown 50 Att'orne i Patented Mar. 6, 1934 UNITED STATES PATENT QFFICE LOW VOLTAGE HEATING ELEMENT Howard S. Brown, Shelbyville, Ind.

Application March 2 2, 1933, Serial No. 662,119

2 Claims.

This invention relates to the art of electrical heating elements and particularly to that type of element over which utensils may be placed. A

unit producing the heat.

A further important element to the utensil thereover.

A still further important object of the invention is to provide a structure whereby the resistance unit producing the heat may be of sufiicient structural strength to support utensils or bodies to be heatedwithout the aid of intervening supports.

A still further important object of the invention is to provide a resistance unit as a part of the heating element of such nature that it may be supported through contact with a very small area of an insulating medium whereby an extremely small part of the heat is conducted away from the unit to that member.

I accomplish these and other objects which will become apparent to those versed in the art by employing a structure, one particular form of which is shown in the accompanying drawing,

in which Fig. 1 is a top plan view;

Fig. 2, a vertical transverse section on the line 2-2 in Fig. 1, and

Fig. 3, a vertical longitudinal section on the line 3-3 in Fig. 1.

Like characters of reference indicate like parts in the several views in the drawing.

I form a resistance unit to have a plurality of spaced apart parallel ribbons or bars 10 here shown as four in number, the ends of the bars being widened to connect with supporting plates 11 and 12.

The resistance unit is preferably an integral structure although the ends of the bars may be attached to the supporting plates as may be desirable in manufacture.

llhe plates 11 and 12 and the interconnecting bars 10 are made from a suitable resistance material, the exact composition of which is not essential to my invention, since there are many types of such material now commercially available on the market.

It is essential however that the material have sufiicient structural strength even when heated that the bars 10 do not sag any appreciable amount.

Also

there should be sufficient structural strength of the material to permit the bars 10 being made sulficiently narrow and thin to give the required resistance to flow of electrical current therethrough and at the same time support a body or utensil such as a pan 13, Fig. 2.

The plates 11 and 12 are vertically disposed in parallel relation to give structural strength to serve in elTect as girders carrying the respective ends or" the connecting bars 10. It is to be noted that the major lengths of the bars 10 are here shown as having uniform widths and thicknesses but that their ends are widened to appreciable Widths where they connect with the plates 11 and 12. By so widening the ends, only the narrow Widths of the bars offer suificient resistance to current passing therethrough to produce incandescence.

Preferably the bars 10 are turned upwardly sharply to lie in a plane above that including the wider ends which connect with the supporting plates. This formation is provided so as to carry the utensil entirely in contact with the incandescent portions only of the bars and to keep the utensil out of contact with the cooler widened ends.

One particular means for supporting the resistance unit is here shown in the form of a refractory block 14 having a central opening therethrough somewhat greater than the rectangle defined by the spaced apart bars 10. The block 14 is cut through by slots 15 and 16 back of opposing edges of this central opening so that the plates 11 and 12 may be inserted through such slots and allowed to extend downwardly therethrough to have their major portions hang from the under side of the block. Narrow ribs 17 and 18 of the block are left between the slots 15 and 16 and the central opening over which the heat ing element rests. Particular attention is directed to the fact that these ribs are in contact with parts only of the widened ends of the rear and front bars 10 and that the ribs are relieved so as to drop below the intervening ends of the bars. The element is thus supported at what amounts to four points only. Since the unit is supported in this manner, there can be but very little direct conduction of heat from the unit to the block.

The block 14 is provided with horizontally disposed siots along the inner faces of the ribs 1'? and 18, within which slots is fitted a reflecting plate 19. This plate 19 has its upper face highly polished and is spaced immediately below the bars 10. The spacing may be varied, in one instance being as close as onehalf inch away from the under side of the bars. It is preferable to keep this distance relatively small so that there may not be any great loss of heat. Preferably the block 14 has a slot cut through the front side through which the plate 19 may be inserted and carried on back to rest within the slots in the ribs 1'7 and 18. A tongue 20 is provided on the' front end of the plate 19 by which the plate may be withdrawn from the block for cleaning purposes. The block 14 is provided preferably with one or more ribs 21 therearound having an elevation equal to that of the upper surfaces of the bars 10. Preferably these ribs are formed to be triangular in cross section so as to present sharp upper edges in case the utensil 13 overlaps the bars 10 whereby there is but a line contact between the utensil and the rib so as to prevent any great amount of conduction of heat from the utensil to the block. These ribs also serve to protect the bars 10 when the utensil is being placed on or withdrawn from the supporting bars The cross sectional area of each of the bars 1G is made such that a current of very low voltage may be employed. The unit is intended to be operated on voltages not to exceed one and onehalf so that the difference in potential between any two points on a common bar or between adjacent bars is so slight that the utensil may be in direct contact with all of the bars without any danger of electrical shock to a person handling the utensil. The plates 11 and 12 are purposely made to have considerable area so that the low voltage of current may be employed without any great loss in these particular parts of the heating unit and also to keep the resistance down to such a point that there will be no heating of the plates by the current flow. Current is conducted from any suitable source (not shown) to the plates 11 and 12 by the conductors 22 and 23 respectively. Of course the widened ends of each bar 10 offer less resistance than the central and major portions of the bars so that these ends are not heated to incandescence as are the bars and therefore, those ends resting on the supporting ribs are relatively cool and do not conduct any great amount of heat to the block. Of course only those parts of the ribs 17 and 18 which are in direct contact with the bar ends need be made of electrical insulating material and the rest of the block can be made of metal as desired.

By reason of my invention, employing the very low voltage indicated and for which the resistance unit is designed, utensils may be placed directly in intimate contact with the current carrying bars 10 so that the heat may be conducted directly to the contacting surfaces of the utensil resting thereover. Also since the bars are heated to incandescence, heat is radiated therefrom to the under surface of the utensils and this is intensified by the reflector plate 19 thereunder which directs back upwardly such radiant heat tending to otherwise pass downwardly away from the utensil. Again since the utensil is supported in spaced relation from the plate 19 and that there are openings around the lower edge of the utensil, convection currents may be set up in addition to the direct conduction and radiation of the heat.

While I have here shown and described my invention in the one best form as now known to me it is obvious that structural variations may be employed without departing from the spirit of the invention and I therefore do not desire to be limited to this specific form beyond the limitations as may be imposed by the following claims.

I claim:

1. In a heating element, a refractory block having a central opening therethrough, a resistance unit comprising a plurality of spaced apart bars which also act as a support for a utensil to be heated, the ends of said bars being widened and connected with supporting plates which plates are passed through the block and are connected in circuit with a source of current and ribs on the block outside of the central opening of an elevation equal to the upper surface of the resistance unit.

2. In a heating element, a refractory block having a central opening therethrough and vertical slots back of opposing edges of the central opening leaving narrow ribs of the block between the slots and central opening, said block also having horizontally disposed slots along the inner face of .said ribs, 2. reflecting plate within the horizontal slots, a resistance unit comprising a plurality of spaced apart bars which also act as a support for a utensil to be heated, the ends of said bars being widened and connected with supporting plates, and said plates being passed through the vertical slots of the block and connected in circuit with a source of electric current.

HOWARD S. BROWN.

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