Heating Element For Flush Top Ranges

Abstract

A flush top range having replaceable heating units comprising a sandwich structure which includes a coiled heater element and heat conducting or infrared transmitting disc having a substantially planar surface, and cable means for easily connecting the unit into range circuitry with the planar surface of the disc being adapted to lie substantially in the plane of the adjoining surfaces of the range cooktop.

Description

BACKGROUND OF THE INVENTION

In electric ranges the so-called "flush top" design has become popular and is particularly desirable in countertop styling, although free-standing ranges can be incorporated with flush top features if desired.

By "flush top" it is meant that substantially the entire top of the cooking surface, including the cooking areas, lies in a single plane without openings such as normally contain heating elements.

Such range top constructions usually employ a cooktop comprising a large sheet of infrared transmitting material with a number of electric heating elements directly beneath it in the areas where heaters would normally be located. When the elements are operated they transmit heat through the sheet by conduction or radiation onto the bottoms of cooking utensils located directly over the elements. In such a structure hopefully a large part of the heat from the element will be transmitted through the sheet without much transmission laterally within the sheet, thereby keeping adjacent areas of the sheet relatively cool.

However, many problems exist in flush top ranges. For example, too much loss of heat may occur by lateral flow through the cooktop material, large sheets of cooktop material are relatively expensive to manufacture and replace, and relatively inefficient heat transfer into a supported pan or pot is often encountered. Furthermore, replacement of heating elements is rendered somewhat difficult because the large, fragile cooktop must be lifted or removed, with possible consequent chance of damage, and usually an electrical technician must be employed to replace the thus exposed heater elements. Also, heat in portions of the cooktop adjoining the portions overlying the heater elements will cause some burning of spilled foods and will thus stain. Additionally, since no means is specifically employed to prevent transconductance of heat laterally within the cooktop material, larger than desired areas of the cooktop become heated, thereby necessitating relatively long warmup periods before the cooking regions will attain cooking temperatures, and consequent undesirably lengthy cooldown times.

SUMMARY OF THE INVENTION

In accordance with the present invention there is provided a novel range top construction which overcomes many of the above and other disadvantages of flush top ranges by the provision of a novel replaceable heater unit which includes, as a part thereof, an efficient infrared transmitting or heat conducting portion which may be disposed in flush relation with adjacent portions of a flat cooktop.

The unit comprises a heater element which is sandwiched between a disc of selected infrared transmitting material and disclike insulator, the assembled unit being of a size and shape which will fit into an opening provided for it in a cooktop. Desirably, when the unit is in place the exposed surface of the disc will lie substantially flush with the adjacent surfaces of the cooktop and, because spacing between the adjacent edges is held to a minimum, will present a flush top which can be easily cleaned and is neat and attractive in appearance.

The disc is preferably provided with a flange portion which encircles the edge of the unit, and suitable retaining means is provided for supporting the insulator and the heater element with respect to the disc so that efficient transfer of heat will occur from the element to the disc by both radiation and conduction. The disc is, of course, made of electrical insulating material.

In such a unit, the ends of the heater element project from the underside as a cable which may be readily connected into the range circuitry, preferably as a "plug-in" connection.

Furthermore, a large temperature gradient is provided between the heater units and the adjoining portions of the cooktop, thereby achieving relatively fast warmup and cooldown cycles and permitting easy cleanup of cooktop surfaces and pyrolytic self-cleaning of heater unit surfaces.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention will become apparent from the following description taken in connection with the accompanying drawings, wherein:

FIG. 1 is an isometric view of a flush top range embodying the invention;

FIG. 2 is an isometric view of a heating unit for the range shown in FIG. 1;

FIG. 3 is an exploded view of the parts of the heating unit shown in FIG. 2;

FIG. 4 is an isometric view partly in section of a portion of the cooking top showing the means for supporting a heating unit;

FIG. 5 is a vertical sectional view of a heating unit and adjacent portions of a cooking top;

FIG. 6 is a diagrammatic view of the bottom side of a utensil supporting element having a photoetched heater element thereon; and

FIG. 7 is an enlarged fragmentary plan view of a portion of the bottom of the unit shown in FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring more particularly to the drawings wherein like characters of reference designate like parts throughout the views, there is shown in FIG. 1 a range 10 of the so-called built-in type, that is, it is built into an array of cabinets 12. It is to be understood, however, that the range may be of any suitable type such as free standing or countertop, for example.

Range 10 is provided with an oven to which access may be had through a hinged door 14 in the usual manner, and is also provided with a cooktop 16 which preferably comprises one sheetlike element having a substantially plane exposed surface defining what is commonly called a flush top. A backguard 18 may be provided as well as a front-located control panel 20 upon which are disposed a number of knobs or switches for controlling the operation of individual heating units to be described. The controls may be positioned in the backguard 18 or elsewhere, if desired, and may also include a timer, clock, light and oven control knobs if desired.

As is usual in flush top ranges, a number of heating elements are located beneath the cooktop 16 at selected locations so that, when operated, the heating units will create heat which will pass upwardly through the cooktop to utensils placed on the cooktop above the heating units. In known flush top ranges a large portion of the cooktop is formed of a one-piece sheet of material which is conductive to the heat from the heating units. Such material may be an opaque, fragile, glass-like material which has an attractive appearance.

However, such flush top sheets create many undesirable problems. For example, the sheet many times must be microfinished to provide good surface contact with the utensils in order to achieve efficient heat conduction to the utensils, when a heating unit must be replaced, it is necessary to lift the cooktop to obtain access to the heating units, with possible resultant damage to the cooktop during this operation. Furthermore, in such devices, and very important, is the heat loss sustained between the heating units and the cooktop because of spacing therebetween. an additional disadvantage is that heat will pass laterally within the material of the cooktop as well as vertically toward the utensils. Thus, localizing of heat is not satisfactorily achieved and possible undesirable heating of large areas of the cooktop occurs, with resultant straining when foods are spilled and burned on areas adjoining the cooking regions.

In accordance with the present invention, the cooktop 16 is provided with openings 22 in the areas where the heating units are to be located and within each opening 22 is located a respective heater unit 24. Each heater unit 24 is an independent assembled structure as shown in FIG. 2 which includes a hollow heat conducting or infrared transmitting utensil support element 26 (FIG. 3), a heater element 28, an insulator 30 and a disclike spring retainer 32.

The infrared transmitting or heat conducting element 26 is an inverted cup-shaped structure having a planar disclike base portion 34 and a peripheral flange or rim portion forming an annular side wall 36. Element 26 is made of electrically insulating ceramic or glass-like material having low thermal expension and high thermal shock resistance such as, for example, quartz or one of the ceramic or glass-like materials now being sold on the market by Raytheon Company under the tradename "Rayceram," by Corning Glass Co. under the tradename "Pyroceram," by Pittsburg Plate Glass Co. under the tradename "Hercuvit," or by General Electric Co. as "GE 725" glass, for example.

The base portion or bottom 34 of the cup 24 is used as the heating or infrared surface and is, of course, strong enough to support a filled cooking utensil when the unit 24 is inserted in one of the openings 22 in the cooktop. The unit 24 is of a diameter which will enable it to fit within the opening with only a minimum amount of clearance between it and the encircling peripheral edge of the opening, as shown in FIG. 5, so that spilled materials will not be able to easily penetrate into the intervening space.

Within the support element 26 is a heater element 28 which may be of any suitable shape such as a spiral pancake of coiled Nichrome wire having its ends extending as leads 40 externally of the support and forming an electric cable with a plug 42 at its end by which the heater element may be connected easily into the range circuitry. Heater element 28 is disposed between the support bottom 34 and the insulator disc 30, and the assembly is held in place by the disclike spring retainer 32 with the heater element being pressed firmly against the support base 34 for efficient transfer of heat thereto by conduction.

The insulator disc 30 is preferably an electrical insulating and low thermal conductivity material such as a disclike mass or pad of expanded alumina or ceramic fibers. An example is the material marketed as "Cerefelt" by Johns Manville Co. Disc 30 may be provided with one or more small openings 44 through which the heater leads may extend. Such an insulating material has a capability, when the heater element is operated, of itself becoming a reradiator of infrared when it becomes sufficiently hot.

The spring retainer 32 is a metal disc which is adapted by its own inherent resiliency to be snugly interfitted into the support 26 with its edges engaging the inner peripheral surface of the rim 36 thereof for retaining it and the insulator-heater assembly in place. To achieve this, the periphery of the retainer may be provided with a series of spring fingers 46 which are bent to some selected angle with respect to the plane of the retainer and to the inner surface of wall 36 so as to resiliently engage the wall and hold the assembly in place. To add to the resiliency of the retainer, annular convolutions may be provided, one 48 thereof being shown in FIG. 5 in the central area of the disc, and a second 50 in spaced encircling relation to the central bulge 48. Openings 45 may be provided for the electric cable if desired.

It is to be understood that although the heater element has been described as being a separate coil 28 of heater wire in close juxtaposition to the base 34 of support 26, it may take the form of a thin photoetched member 52 (FIGS. 6 and 7) which may be disposed adjacent the inner side of the support base 34. Such a heater element may be made by conventional photoetching processes from a sheet of, for example, 0.020 inch thick nickel-chromium-steel alloy. Such a heater is self-supporting when handled carefully and will perform adequately when held in place by the insulator disc 30.

It is to be understood that the foregoing description relates to a support 26 which is a good heat conducting material and, therefore, the heater element 28 will preferably engage the base 34. However, in cases where the support is a good heat transmitter, such as quartz, for example, the heater element 28 will preferably be spaced from the base 34 as by a spider or web (not shown).

In order that an assembled heater unit 24 may be retained properly in an opening 22 in the cooktop 16, the underside of the cooktop is provided with a support structure encircling each opening 22. The cooktop itself, as mentioned above, may be porcelainized metal or any of the other mentioned materials. The support structure may comprise a ring 54 of metal or other substantially rigid material bonded, welded or otherwise secured at one side to the cooktop in encircling spaced relation to the opening 22, as shown best in FIGS. 4 and 5. An annular shelf 56 extends inwardly from the lower side of ring 54 and carries on it an annular ceramic support 58. The inner diameter of the shelf and support are such as to slightly underlie the opening 22 whereby when a heater unit 24 is positioned in an opening 22 the lower annular edge of the side wall 36 will rest upon the ceramic support 58. The dimensions of the side wall 36 and of the cooktop heater unit support structure are controlled so that the exposed surface of the heater unit 24 lies in the plane of the upper surface of the cooktop 16. A ring 60 of insulating material such as ceramic may be located on the ceramic support 60 between the heater unit side wall 36 and the ring 54.

It will be seen that with a structure as described, a substantially large thermal gradient will be provided between the heater unit 24 and the cooktop 16. Thus, relatively little heat will be transmitted into the cooktop from the heater unit. This will, therefore, because of improved localized heating, provide fast warmup of the heating surfaces and will permit consequent faster cooldown. Furthermore, with the described structure, the heater unit 24 may be operated for a length of time without any utensil on it and will perform a self-cleaning operation by pyrolytic action. The adjoining areas of the cooktop, of course, may be easily wiped off for cleaning since food spilled on it will not burn because the cooktop remains relatively cool.

From the foregoing it will be apparent that all of the objectives of this invention have been achieved by the structure shown and described. It will be apparent to those skilled in the art, however, that various changes and modifications may be made within the scope of the appended claims. Accordingly, all matter shown and described should be interpreted as illustrative and not in a limiting sense.

Claims

We claim:

1. An electric heating unit for a range comrpising a disc of rigid dielectric material, an integral peripheral flange extending perpendicularly from one side of the disc and forming therewith a cuplike support, said flange being the outermost portion of the unit, an electrical heater element within the support adjacent the disc, an electrically and thermally nonconductive member within the support and having one side disposed adjacent the side of the heater element opposite the disc, spring retainer means engaging the opposite side of the nonconductive member for urging it toward said disc and connected with the inner side of said flange for retaining the cuplike support, heater and nonconductive member as an assembled unit, and electrical means connected with the heater element and extending externally of the unit for connecting the element to a source of electric current.

2. An electric heating unit as set forth in claim 1 wherein said spring retainer means is a disclike member having edge portions resiliently engaging the inner side of said flange.

3. An electric heating unit as set forth in claim 1 wherein said nonconductive member is a pad of low thermal conductivity ceramic capable of infrared radiation when heated.

4. An electric range comprising a substantially planar cooktop having at least one opening of predetermined size therein, an electrical circuit in the range having termination means adjacent said opening, and a replaceable heater unit in said opening, said unit comprising an electrical heating element and a support for said element, said support including a disc disposed within and in closing relation to said opening and having a planar surface disposed substantially flush with the cooktop, said support further including an integral peripheral flange extending from said disc perpendicularly thereto and of a size substantially equal to the size of said opening, said flange being the outermost portion of said unit, and electrical conducting means connected with said heater element for connection with said termination means in the range.

5. An electric range as set forth in claim 4 wherein means is provided between said support and cooktop for establishing a thermal gradient therebetween whereby the cooktop will remain cool relative to the disc when the unit is operated.

6. An electric range as set forth in claim 5 wherein said thermal gradient establishing means includes said flange extending from said disc peripherally thereof inwardly of the opening, and additionally a ceramic ring between the flange and adjacent portions of the cooktop.

7. An electric range comprising a cooktop having at least one opening therein, an electrical circuit in the range having termination means adjacent said opening, and a replaceable heating unit in said opening comprising a disc of rigid dielectric material, an integral peripheral flange extending from one side of the disc perpendicularly thereto and forming therewith a cuplike support, said flange being the outermost portion of said unit, an electrical heater element within the support adjacent one side of the disc, an electrically and thermally nonconductive member within the support and having one side disposed adjacent the side of the heater element opposite the disc, spring retaining means engaging the opposite side of the nonconductive member and yieldably connected with the inner side of said flange for retaining the cuplike support, heater element and nonconductive member as an assembled unit, and electrical means connected with the heater element and extending externally of the unit for connecting the element to a source of electric current.

8. An electric range as set forth in claim 7 wherein said flange is integral with said disc.

9. An electric range as set forth in claim 7 wherein said spring retaining means is a disclike member having edge portions resiliently engaging the inner side of said flange.

10. An electric range as set forth in claim 7 wherein said nonconductive member is a pad of low thermal conductivity ceramic capable of infrared radiation when heated.