US2400672A - Electric heater - Google Patents

Description

May 21, 194.6." E. WEGA@ 400,612

ELECTRIC HEATER original Enea nec. s, 1940 wfg n BTZJ/wuM-/MW atenied May 21, 194.6

ELECTRIC HEATER Edwin L. Wiegand, Pittsburgh, Pa., assigner to Edwin L. Wiegand Company, Pittsburgh, Pa., a corporation of Pennsylvania Original application December 3, 1940, Serial No. 368,347. Divided and this application July 24, 1941, Serial No. 403,79*?

(ci. 21e- 37) 3 Claims.

My invention relates to electric heaters, and nore particularly to electric range units embodyng one or more electrical resistance heating elenents of desired types comprising a resistor disiosed Within and insulated from a metal sheath. ihe principal object of my invention is to profide new and improved electric heaters and new ind improved electric range units of these types. i'his lapplication is a division of my application Serial Number 368,347, i'lled December 3, i940,

In the drawing accompanying this specifica'- tion, and forming a part of this application, I have shown, for purposes of illustration, one form which my invention may assume, and in this drawing:

Figure 1 is a fragmentary plan view of an elec-v tric range unit illustrating an embodiment of the invention, parts being broken away to more clearly illustrate the construction, y

Figure 2 is a fragmentary vertical sectional view corresponding substantially to the line 2-2 of Figure l, showing the unit in position on the top of a stove,

Figure 3 is a fragmentary transverse sectional view corresponding substantially to the line 3 3 or Figure 2, and

Figure 4 is an enlarged transverse section corresponding substantially to the line :1 4 of Figure l.

The embodiment disclosed in the drawing includes a range unit il@ which may comprise one or more heating elements, in this instance two elements lil, il; of ring shape which are concentrcally arranged. The elements iii, H2 are carried by spaced-apart supporting frames M3, the latter being secured toheat directing means, such as a reflector iid. The supporting frames i lil are detachably connected to an adaptor ring als, which rests on a stove tot Ht, the reector' and some oi the parts oi the rangeI unit liti extending through an aperture il formed in the stove top.

The heating elements iii and H2 are here shown as similar, each being oi generally trapezoidal cross-sectional outline, and in this ine1 stance of isosceles trapezoidal outline. A detailed description of the member iii is sufficient to describe both elements. Referring to Figure 4,

the heating element lll comprises a sheet-metal trough or channe1 ile having side walls H9 and a generally plane wall i2@ connecting the side walls H9. The side walls H9 are inclined so that each forms an obtuse angle with the con-a necting wall E20. Disposed within the channel dit is electrical-insulating heat-conducting .material I2i which may be'in the form of suitable granular, comminuted or powdered refractory material, preferably compacted to a dense hard condition. If desired a bonding or cementing material may be mixed with the refractory material.

An electrical-resistance heating means is embedded in the insulating material IZI, and this heating means may assume various forms. As shown in the drawing, the heating means cornprises ve connected helical coils 22 of electrical resistance' wire. The end coils, referring to Figure' 4, are preferably dropped slightly below the plane of the intermediate coils, so that these end coils are properly spaced from the adjacent walls of the trough lit. A plate lit is positioned within the trough lla to overlie the insulating material i2i, the plate lit being generally parallel to the wall im, and being of a width to extend substantially from one of the sides H9 to the other. The terminal portion oi each side H9 is bent or crimped, as shown at S24 to overlie the plate 23, so as to hold this plate in assembled relation with the trough tit. As best seen in Figure 4, the plate i2@ may be bowed in a direction inwardly of the trough liti, and the plate lit and crimped portions lt close ofi the open side of the trough.

In the embodiment herein shown, the heating element lit is termed' with inclined sides ili, a generally plane connecting Wall 26, and a closure plate lil-the parte being substantially similar to the parts ile, tilt, and 523, respectively, of the heating element i i i. However, in this particular case, the heating element H2 is of a smaller transverse size than the heating element iii, and accommodates only three coils lt of resistance wire, although it is entirely within the' invention to change the sm ci the heating element i i2, or oi the heating element i l i, or of both.

The method of forming the heating elements iii and iii comprises the provision of a sheet metal channel er trough, such as the trough lit hereinbeore referred to, having sides inclining away from each other in a direction tov/'ard the open end of the trough. Asshown in dotted lines at tilt, in Figure e, the terminal portions of the sides are originally in an extended position to give unobstructed access to the interior of the trough, The refractory material and the heating means may be positioned within the trough in any suitable manner, one manner, :for example, consisting oi placing a certain amount of refractory material, in a granular, comminuted or powderedstate, within the trough, and positioning the heating resistance in this material. if desired, a suitable bonding or cementing material may' be mixed with the refractory material. The refractory material maybe compacted to a degree wherein it retains its form. and then additional refractory may be added to 'overlie the material originally disposed within the trough. The entire mass of refractory material may then be compacted to a rather dense hard condition,

this compacting force being generally perpendicular to the wall |20 of the trough. The inclined sides ||3 redirect this compacting force. so as to urge the refractory material to closely form about the coils |22, and also to closely form along the inside surfaces of the sides H9, the Wall |20,

and the bends forming the junctions therebetween. The plate |23 may then be positioned to overlie the refractory material, and the terminal portions of the sides ||9 may be bent or crimped to overlie the plate |23. Preferably, the refractory material is so compacted as to have a concave outwardly directed surface, and the plate |23 is bent to concave form before being assembled with the trough H3. The concave form of the plate |23 tends to stiffen this plate, and therefore tends to maintain intimate contact between the inner surface of the plate and the adjacent surface of the refractory material.

Desirably, the heating element is subjected to a final pressing or squeezing action, to cause the walls of the trough and the plate to closely contact the refractory material, to highly densify the refractory material, and to close up any discontinuities or voids that may have been formed or left in the refractory material for any reason. This is particularly desirable where the heating element is designed so that the energy input is such that the element operates at elevated temperatures suitable for electric ranges. It is of course understood that the sheath of the element may be made of nickel, or a metal alloy, for example, nickel chrome, or inconel, or of any material capable of withstanding such elevated temperatures or whatever temperature of operation may be selected. The final pressing or squeezing may be effected by placing the heating element in a'die having a recess receiving at least part of the heating member, and pressing or squeezing the heating member by means of other suitable die means, such as by a die having a convex surface fitting the concave formation of the plate |23. In certain cases it may be desirable to effect the bowed formation of the plate |23 during the final pressing or squeezing formation.

In some instances, some or all of the steps of compacting the refractory material Within the trough may be omitted, and this compacting may be effected when the plate |23 is assembled with the trough, or by the nal squeezing or pressing action, or by both.

The plates |23 and |21 of the heating elements and ||2 are respectively formed with spacedapart local depressions |30 and |3|, each depression accommodating the head of a rivet |32, the rivet having a split shank passing 'through an aperture in the bottom of the depression. The depressions |30 and |3| are spaced in pairs along common radial lines, four pairs of depressions being provided in the embodiment shown.

Referring to Figures 2 and 3, the shanks of the rivets |32 also pass through apertures formed in generally inverted cup-shaped portions |34, |35 of the supporting frames ||3, the lattercorresponding in number to the four pairs of depressions, and washers |38 are positioned on the shanks of the rivets. The split ends of the rivets are bent to overlie the washers |36 and secure the heating elements and ||2 to the supporting frames ||3. The cup-shaped portions |34 and |33 are integrally connected by legs |31,

and the extremities of the legs |31 are formed with spaced-apart feet |38 which bear against one surface of the reector |4, the ends of the alledem feet |33 passing th the reflector fill opposite surface cA Each of the .cuf- |40, formed by l; tions of the cu legs |31. Each .gc a hook portion lili data margin of a respectif tures |42 in a resi ,ably latching with the ne ci' ,a plurality of apertly-distortable wall |43 of the adaptor ring: tiki. e wail |43 merges with a top wall M4, and 4top wall in turn merges with a downwardly extending wall |45 the terminating margin of which is adapted to rest on the stove tcp i it as shown in Figure 2.

The reflector li4 is provided with a curved lower edge |48 extending below the feet |38, and the reflector is inclined upwardly toward the center of the range unit, where it is provided with an aperture |41.

The heating elements lli and ||2 are provided with terminals i49 and |50, and certain of these terminals are connected by a connector strip |5|, as shown in Figure l, and these terminals lead into a terminal box |52 formed to receive conductors leading from a suitable source of current supply.

Referring to Figure 2, the heating elements I i and I2 are carried in side-by-side relation, that is, one side ||9 of the heating element is adjacent a side |25 of the heating element II2.

In this relation the adjacent sides ||9 and |25 incline away from each other, so that the distance between the sides is gradually increased in a direction toward the top of the range unit H0, the inclination of the sides preferably being such that the normal lines of radiation from one surface do not strike the adjacent surface, thereby diminishing the inter-radiation between the inclined sides. It has been found that by the use of such heating elements greater efliciency is obtained, in that a greater amount of heat is conducted or radiated, or both, away from the elements in a useful direction. It is of course evident that when an object, such asa cooking vessel, is seated on the elements ill, |i2, heat is adapted to be transmitted to the cooking vessel by direct conduction from the top walls |20, |26 and by radiation from the inclined walls i I9, |25. Also, under all circumstances of operation, because inter-radiation between the elements is materially reduced, the elements, at their adjacent surfaces, will not become overheated, and therefore the life of each heating element is greatly prolonged. Additionally, the inclined sides present a greater amount of surface radiating in a direction upward with reference to Figure 2, while at the same time the top wall, such as the wall |20 or |26, is actually reduced in width, therefore diminishing the possibility of distortion or buckling of this wall.

It will of course be apparent that what has been hereinbefore stated with respect to reduced inter-radiation between adjacent portions of two ring form elements such as the elements ||2, applies also with respect to adjacent portions of separate elements whether the longitudinal axes of the elements are circular, rectilinear, or any other form, and applies also with respect to adjacent portions of a single element the longitudinal axis of which 'is such that the forcing or embossing the top wall may be omitted if desired. The plate |23, because of its connection with the trough l I8, and because of its particular shape, will assist in maintaining the sheath against any buckling action. Accordingly, the material at all times will closely encompass the refractory material, and thus materially assist in preventing cracks or discontinuities from forming in the refractory material.

Thelower end of the wall |43 and the adjacent edge |46 of the directing member |I4 define an annulaiport through which air or low velocity may enter, and becoming heated, flows in an upward direction, and escapes through the spaces between the element ||2 and the wall H3, the elements and Ill, and between the element II I and the top of the heat directing member H4. It will be appreciated that the frames H3 offer very little resistance to such flow of air, and the construction' of this unit is such that transverse obstruction to the flow of airis materially diminished.

In some instances, it is preferable to provid the directing member Il with al rather dull surface, instead of a -bright reilecting surface. In such instances the air entering the annular port becomes heated to a greater extent by contact with the member IIJ, and flows with increased velocity toward the center of the unit, where it escapes, in somewhat chimney fashion, through the space between the element Il I and the upper part of the member ||4, when no receptacle is positioned on the range unit I l0. Additionally, air along the lower outer surface of the directing member I Il becomes heated, and flows upwardly through the central opening |41, thereby inducing an air flow through the annular air-inlet port formed by the lower` -end of the wall |43 and the adjacent edge |46 of the directing member I I4.

It has been found that a range unit, designed in accordance with the foregoing, maintains a relatively low temperature when a receptacle and its contents are removed from the unit, therefore making unnecessary the extreme care ordinarily required to prevent burning up of the unit. Since the air-inlet port of the range unit is preferably below the top l I8 of the stove, as shown in Figure 2, the flow of air into this inlet port induces movement of air along the bottom of the top IIB, thereby preventing excessive heating of the stove top.

'I'he radially positioned frames Il) are preferably stamped of sheet-metal, so that the overall weight of the unit is reduced. Also, the time-required to heat up the unit is reduced, because the sheet-metal frames store very little heat. The frames I3 have been so constructed and arranged that air entering the annular port may flow over and in contact with the inner and outer surfaces of the legs |31, whereby additional heat is picked up by the air, and overheating of the frames is prevented.

It will be understood that the resistor may be made of erw desired mutable material, and or any desired suitable form; that the refractory lnsulating material may be, or may include, for

example, silica, or silicates, or magnesium oxide,

or aluminum oxide, or any refractory -oxide or combination of refractory oxides, or any other suitable refractory material, desirably o: s, mmeral character: that such refractory material may be mixed, if desired, with a bonding or cementother suitable binder; that a sheath of desired suitable initial form, a resistor and insulating material may be assembled in any desired suitable way and in any desired .suitable sequence; and that such assembly may be brought to nal form in any desired suitable way.

From the foregoing it will be apparent to those skilled in the art that the illustrated embodiment of my invention provides new and. improved electric heaters and new and improved electric range units, and accordingly, accomplishes the principal object of my invention. 0n the other hand, it also will be obvious to those skilled in the art that electric heaters and electric range units embodying my invention may be variously changed and modied, or features thereof, singly or collectively, embodied in electric heaters or electric range units or combinations other than those illustrated, all without departing from the spirit of my invention or sacricing all of the advantages thereof, and that, accordingly, the disclosure herein is illustrative only, and my invention is not. limited thereto.

` I claim:

l. An electric heater., comprising: heating means; heat-directing means, underlying said heating means; and a plurality of spaced-apart sheet-metal elements, each comprising an inverted U-shaped part extending between and secured to said heating means and to said directing member, and holding said heating means and said directing means together as a unit, said heating means and said U-shaped parts being secured to each other by means including studs carried by said heating means and extending downwardly through apertures in the bights of the respective U-shaped parts.

2. An electric range or hot-plate unit comprising: heating means indicating an approximately flat annular plate; wall means circumstant said heating means; heat directing means disposed below said heating means and in spaced relation to said wall means and constructed andarranged to facilitate flow of air in' through the space between f said heat directing means and said wall and out through said heating means; and a plurality of spaced peripheral supporting means each connecting said heat directing means and said heating means and engaging said wall means, together supporting said heating means and said heat directing means from said wall means removable as a unit.

3. An electric range or hot-plate unit comprising: heating means indicating an approximately nat annular plate; wall means circumstant said heating means, supported from the topot the range or hot-plate; heat directing means disposed below said heating means and in spaced relation to said wall means and constructed and arranged to facilitate flow of air in through the space between said heat directing means and said wall and out through said heating means; and a plurality of spaced peripheral supporting means each connecting said heat directing means and said heating means and engaging said wall means, together supporting said heating means and said heat directing means from said wall means removable aS a unit. g

' EDWIN L. WIEGAND.

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