Flat Plate Surface Heating Unit

Abstract

A flat plate surface heating unit with a recessed pan filled with thermal and electrical insulation. A closely wound, sinuous, electrical resistance heater wire of flattened cross section is arranged in a spiral formation and supported by the insulation. A glass-ceramic disk covers the pan. An insulating spacer is sandwiched between the disk and the heater wire in the interstices between adjacent turns of the spiral, and the spacer slightly overlies the spiral edges of the heater wire. A removable trim ring is capable of being fastened to a peripheral flange of the unit pan with a turning action of the ring for locking the ring in place and applying a clamping force on the peripheral edge of the disk.

Description

BACKGROUND OF THE INVENTION

Today the standard surface-heating unit for an electric range is a metal sheathed resistance-heating element of spiral formation which is generally mounted over an opening in the cooktop of the range and provided with a reflector pan positioned therebeneath for reflecting the heat from beneath the heating element in an upward direction for improving the efficiency of cooking. With the continuing improvement in the characteristics of high-temperature crystalline glass, the advent of a high-efficiency glass-ceramic plate surface heating unit is quickly approaching. Some problem areas are inherent when using the glass-ceramic material such as mechanical strength or the brittleness of the plate material when it is subjected to sharp mechanical blows or the heavy concentration of weight. Another problem to consider is a means of clamping the glass-ceramic plate to the heating unit in a manner that will not exert undue stresses on the plate during the variations of temperature of the heating up and cooling down cycles of the unit. Moreover, this type of glass has greatly reduced electrical resistivity at elevated temperatures so it is well to separate the glass plate from any uninsulated heating element.

The principal object of the present invention is to provide a solid plate surface-heating unit with an electrical resistance heating means such that the heat generated will be directed upwardly, there being a glass-ceramic disk mounted over the heating means in a spaced relation to avoid current leakage problems at elevated temperatures, while a removable trim ring is fastened to the heating unit with a quick-connect turning action to apply a clamping force to the periphery of the disk.

A further object of the present invention is to provide an insulating spacer member between the heating means and the glass-ceramic disk to serve as a positive holddown means for the heating means as well as added support means for the disk.

A further object of the present invention is to provide a solid plate surface-heating unit of the class described with a removable trim ring that is adapted to slip onto the outside of the surface unit with a slight turning action for locking the ring in place and supplying a compressive force on the peripheral edge of the disk.

SUMMARY OF THE INVENTION

The present invention, in accordance with one form thereof, relates to a surface-heating unit having a recessed pan supporting a layer of thermal and electrical insulation. An electrical resistance heating element of generally spiral configuration is supported by the layer of insulation. An insulating spacer member generally fills the interstices between adjacent turns of the spiral heating element as well as separates the adjacent turns to prevent shorting. A glass-ceramic disk covers the pan. The pan has a peripheral flange on which the disk is supported. A removable trim ring encircles the unit and has a top flange overlapping the peripheral edge of the disk and a bottom flange that is capable of tight-locking engagement with the peripheral flange of the unit pan so that the unit is held firmly together.

BRIEF DESCRIPTION OF THE DRAWINGS

My invention will be better understood from the following description taken in conjunction with the accompanying drawings and its scope will be pointed out in the appended claims.

FIG. 1 is a top plan view on a reduced scale of a flat plate surface-heating unit of the present invention mounted in a cooktop with a part of the glass-ceramic disk broken away to uncover the spiral heating means and the spacer member that substantially fills the interstices between adjacent turns of heating unit.

FIG. 2 is a fragmentary cross-sectional elevational view taken on the line 2--2 of FIG. 1, but on a larger scale, to show the construction of the surface-heating unit and especially the heavy layer of thermal and electrical insulation supported in a recessed pan and the fact that the heating means is spaced from the glass-ceramic disk rather than being in direct contact therewith.

FIG. 3 is a fragmentary exploded view of the recessed pan which is adapted to be substantially filled by the insulation, and which comprises a peripheral flange with an alternate series of vertically offset ledges, while a removable trim ring is furnished with a top flange for engaging the periphery of the glass-ceramic disk and a bottom flange that is notched to form widely spaced ears which are capable of being dropped between an adjacent pair of the uppermost offset ledges of the pan so that the trim ring may be rotated in place to engage beneath the uppermost ledges to effect a tight locking action.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Turning now to a consideration of the drawings and in particular to FIG. 2 there is shown a solid plate surface-heating unit 10 of the present invention having a recessed metal pan 12 which is substantially filled by a thick layer of thermal and electrical insulation 14 such as is made from molded fibers of silica and alumina to withstand temperatures as high as 2,000.degree. F.

Positioned on the top of the insulation 14 is an electrical resistance heating element 16 which is shown in plan view in FIG. 1 as a flattened wire of closely wound sinuous configuration that is formed in a spiral with a plurality of turns 18, 19, 20 and 21. This uninsulated heater wire 16 may be a resistance element that is sold commercially as Kanthan A-1 by the Kanthal Corp. of Stamford, Connecticut. It has about 5.5 percent aluminum, 2.2 percent of chromium, 0.5 percent of cobalt and the remainder is iron. The aluminum oxides upon use of the heater, and a layer of Al.sub.2 O.sub.3 is formed on the surface of the heater wire. While I have chosen as my preferred embodiment an uninsulated heater wire 16, it should be understood that an alternate construction could use a standard metal sheathed resistance heating element (not shown), but it of course would increase the total cost of the unit. The illustrated embodiment of the heater wire of the present invention would have elongated cold terminals (not shown) that would extend out through the pan 12 through suitable openings that are insulated with grommets through which the terminals extend for making an electrical connection therewith, and connecting the heater wire 16 in a suitable power circuit.

As is clear from both FIGS. 2 and 3, the recessed pan 12 is formed with an annular step 23 at the midheight of the sides of the pan and this is to provide a seat upon which the pan is supported from a recessed annular ledge 25 of a cooktop 26 for a range or a cooktop that is built into a kitchen counter. This cooktop 26 is furnished with a suitable large opening (oftentimes they are four in number) and the edge of the opening is formed with this recessed ledge 25 such that the pan 12 may be lowered through the opening until the step 23 of the pan comes to rest on the recessed ledge 25 of the cooktop. A series of radially spaced screw openings 27 are formed in the step 23 of the pan so that sheet metal screws 29 may be inserted therethrough and through suitable openings 31 in the recessed ledge 25 of the cooktop for fastening the surface-heating unit 10 in the cooktop. It should be understood that the surface-heating unit is in a semifinished condition when the pan 12 is fastened in the cooktop. In other words, the heating unit does not come as a complete subassembly that is assembled to the cooktop, but it is assembled directly to the cooktop in various assembly steps.

The pan 12 has a top edge with a peripheral flange 35 which extends outwardly therefrom. This flange 35 is adapted to overlie the top surface of the cooktop 26, as is best seen in FIG. 2. This peripheral flange 35 is formed with a plurality of widely spaced radial slots 37, which slots also extend down slightly into the vertical sides of the pan 12. The segments of the flange 35 are then formed into an alternate series of ledges that are vertically offset from each other, there being lowermost ledges 40 and uppermost ledges 42. Thus, it is the lowermost ledges 40 that actually engage the top surface of the cooktop 26, as is best seen in FIG. 2.

Positioned on top of the uppermost ledges 42 is a crystalline glass or glass-ceramic disk 45 of the type that is sold commercially by various companies under the trademarks "Pyroceram," "Cer-Vit," "Heatron" and "Hercuvit." This material is an opaque crystalline glass which may be molded into form and it has a flat polished top surface 46 that is adapted to make good thermal contact with the underside of a cooking vessel (not shown). It has been found important to space the disk 45 away from the heater wire 16 because the electrical resistivity of the disk drops substantially at elevated temperatures such that the current leakage might build up to a point where the housewife might inadvertently touch the disk or a metal pan on the disk and become startled by experiencing an electrical sensation in addition to a high-temperature sensation. Thus, there is an air space maintained between the heater wire 16 and the glass-ceramic disk 45. However, it is also well to provide mechanical support or reinforcement beneath the disk 45 so as to strengthen and cushion the disk against breakage upon heavy loading. Sandwiched between the heater wire 16 and the disk 45 is a spacer member 48 of insulating material that could be of the same material as the insulation layer 14. This spacer member 48 is not a solid member, but it is die-cut to fit around the spiral heating element 16. Thus it fills the interstices between adjacent turns 18-21 of the heating element 16 as well as fills the center of the spiral. This spacer member is allowed to overlap the spiral edges of the heating element 16 a slight amount so that the spacer applies a downward force on the heating element and tends to hold the heating element in place. Thus, the heating element is permitted to radiate heat energy upwardly without interference from the insulating spacer member 48. Admittedly, the layer of insulation 14 could be combined with the spacer 48 into a single member.

Now turning to the method of fastening the various elements of the surface heating unit 10 together, attention is directed to FIg. 3. A removable trim ring 47 is provided to encircle the unit. It is a sheet metal member having a generally hairpin transverse cross section in that it is folded at a reentrant angle as at 50 to provide a top flange 51 and a bottom flange 52. This top flange 51 is adapted to overlie the peripheral edge of the glass-ceramic disk 45, as is best seen in FIG. 2. For this purpose the peripheral edge of the disk is beveled as at 54 to obtain a better matching relationship with the inclined top flange 51. The bottom flange 52 of the trim ring is provided with wide notches 56 thereby forming or leaving widely spaced ears 58 which are capable of slipping down between adjacent pairs of the uppermost ledges 42, 42 of the peripheral flange 35 of the recessed pan 12. Thus the trim ring 45 is designed so that it may be turned or rotated in place to slip each bottom ear 58 of the trim ring 45 beneath an uppermost offset ledge 42 to effect a tight locking action. These ears 58 of the trim ring 45 are formed with inclined tabs 60 at each end to facilitate movement of the ears 58 beneath the corresponding uppermost ledge 42. In order to limit the amount of turning action of the trim ring 45 with respect to the pan 12, stops are formed in the uppermost ledges 42 in the form of lanced fingers 62. One inclined tab 61' is made longer than the others so that when the ear 58 underlies the uppermost ledge 42 this inclined tab 60' bears down upon the cooktop 26. This tab 61' is a rocking tab such that it is necessary for the disassembly of the trim ring to insert the blade of a screwdriver beneath the trim ring and beneath the tab 61' to raise it so that the trim ring may then be rotated in a clockwise direction for lifting the trim ring out of place.

MOdifications of this invention will occur to those skilled in this art; therefore, it is to be understood that this invention is not limited to the particular embodiments disclosed but that it is intended to cover all modifications which are in the true spirit and scope of this invention as claimed.

Claims

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A flat plate surface-heating unit comprising a recessed pan supporting a layer of thermal and electrical insulation, an electrical resistance heating element of generally spiral configuration supported in place on the layer of insulation, an insulating spacer member generally filling the spaces between adjacent turns of the spiral heating element, and a flat plate of high-temperature, high-resistivity dielectric material such as crystalline glass supported on the spacer member, the height of the spacer member being greater than the height of the heating element so that the heating element is spaced away from the flat plate, the said pan having a peripheral flange extending outwardly therefrom, the peripheral edge of the flat crystalline glass plate overlapping a portion of the peripheral flange of the pan, and a top-serviceable quick-connect trim ring encircling the unit, said trim ring having a top flange overlapping the peripheral edge of the flat plate and a bottom flange that is capable of tight locking engagement by means of a twisting action with the peripheral flange of the unit pan so that the unit is held firmly together.

2. A flat plate surface-heating unit as recited in claim 1, wherein the electrical resistance heating element is formed of closely wound sinuous wire of flattened cross section, and the spacer member has slight portions which bear down on the spiral edges of the heating element to hold the element firmly in place.

3. A flat plate surface-heating unit as recited in claim 1, wherein the peripheral flange of the unit pan is formed with a plurality of widely spaced slots to form an alternate series of vertically offset ledges, the bottom flange of the trim ring being notched to form widely spaced ears which are capable of slipping between adjacent pairs of the uppermost offset ledges of the peripheral flange of the unit pan, whereby the quick-connect trim ring may be turned in place to slip each bottom ear of the trim ring beneath an uppermost offset ledge of the unit pan to render a tight clamping action.

4. A flat plate surface-heating unit as recited in claim 3, wherein the electrical resistance-heating element is formed of closely wound sinuous wire of flattened cross section, and the spacer member has slight portions which bear down upon the spiral edges of the heating element to hold the heating element firmly in place.

5. A surface-heating unit comprising a body of thermal and electrical insulation supported in a recessed pan, the pan having a peripheral flange extending outwardly therefrom, a spiral groove formed in the top surface of the insulation, an electrical resistance-heating wire of flattened configuration and of spiral form held within and supported in place on the bottoms of the said spiral groove, the insulation normally rising above the said peripheral flange, a glass-ceramic disk seated on the insulation and spaced from the heating wire, while the said glass-ceramic disk is seated on the peripheral flange and compresses the said insulation, the peripheral flange having a plurality of widely spaced slots whereby the peripheral flange is formed into a series of alternate ledges that are vertically offset from each other, the said removable trim ring also having a bottom flange with a series of wide notches formed therein to form widely spaced ears which are each capable of dropping between an adjacent pair of the uppermost ledges of the peripheral flange, and a removable trim ring fastened on the unit and having a top flange overlapping the periphery of the disk for clamping the disk in place whereby the trim ring may be turned to force the ears of the ring to underlie the uppermost ledges of the peripheral flange so as to force the top flange of the ring into tight clamping action with the peripheral edge of the glass-ceramic disk.

6. A surface-heating unit as recited in claim 5 wherein the ears of the bottom flange of the trim ring are formed with downwardly inclined tabs on the sides thereof to facilitate movement of the ring into its locking position, the said uppermost ledges are slightly inclined downwardly in the manner of a partial thread to force the trim ring down as it is twisted into its clamping position.

7. A surface-heating unit comprising a recessed pan supporting a layer of thermal and electrical insulation, an electrical resistance-heater wire of closely wound sinuous configuration of flattened cross section formed into a spiral and supported in place on the said insulation, the said pan having a peripheral flange extending outwardly therefrom, a glass-ceramic disk covering the unit pan and spaced a distance above the said heater wire, the spiral formation of the electrical resistance-heater wire is spaced from the glass-ceramic disk by a thick spacer member of insulating material that fills the interstices between adjacent turns and only slightly engages the spiral edges of the sinuous heater wire, the glass-ceramic disk resting upon the spacer and compressing the same, and a removable trim ring fastened on the unit and having a top flange overlapping the peripheral edge of the disk for clamping the disk in place, the peripheral flange being formed with a series of alternate ledges that are offset vertically from each other, the said removable trim ring also having a bottom flange with a series of wide notches to form widely spaced ears which are capable of dropping over the lowermost ledges of the said peripheral flange, whereby the trim ring may be rotated through a small angle to force the ears of the ring beneath the said uppermost ledges so as to force the top flange of the trim ring into tight clamping action with the glass-ceramic disk.