US3069526A

US3069526A - Electric hot plate

Info

Publication number: US3069526A
Application number: US828356A
Authority: US
Inventors: Robert D Bremer; George C Pearce
Original assignee: Motors Liquidation Co
Current assignee: Motors Liquidation Co
Priority date: 1959-07-20
Filing date: 1959-07-20
Publication date: 1962-12-18
Anticipated expiration: 1979-12-18

Description

Dec. 18, 1962 R. D. BREMER ETAL ELECTRIC HOT PLATE 3 Sheets-Sheet 1 Filed July 20, 1959 INVENTORS. Robert D. Breme'r Gorge C. Pearce Their iflorney 3 Sheets-Sheet 2 R. D. BREMER ETAL ELECTRIC HOT PLATE Dec. 18, 1962 Filed July 20. 1959 INVHVTORSZ D. Bremer z /eorge C. Pearce Their Attorney Robert 2 Fig.7

Dec. 18, 1962 R. D. BREMER ETAL 3,069,526

ELECTRIC HOT PLATE Filed July 20. 1959 3 Sheets-Sheet 3 INVENTORS, Robert D. Bremer George C. Pearce Their Attorney United States Patent Ofilice B,liii9,52fi Patented Dec. 18, 1952 This invention relates to a domestic appliance and more particularly, to an improved surface cooking unit for an electric range.

In the development of surface cooking units for electric ranges, the solid plate heater was the result of the earliest efforts in this field. However, these prior art plate heaters lacked durable. insulation, heated slowly, and included fragile resistance wires for heating the plate. Due to these disadvantages, the electric range art concentrated its efforts on sheathed tubular heaters which could be formed in spiral configurations and designed to Withstand the severe usage to which such structures are subjected. The problems of durability and rapid heat-up were overcome in the spirally formed tubular heaters. Still the spiral element does not have the advantage of cleanliness and smooth appearance which attends the use of solid plate heaters. Thus, the electric range art has sought solid plate heaters which heat as rapidly as their coiled counterparts and which possess the rugged durability required in electric range operation. It is to this end that the applicants invention is drawn.

Accordingly, it is an object of this invention to provide a solid plate heater having a metal casting with a sheathed tubular heater embedded therein.

It is also an object of this invention to provide a solid plate heater with means to heat the plate rapidly upon initial energization thereof.

Another object of this invention is to provide a means for flashing or rapid heating a solid plate cooking unit wherein the amount of flashing is proportioned to the mass of the solid plate.

Still another object of this invention is to provide a casting for a solid plate cooking unit which has an integral depending portion on the underside thereof to house in close heat conducting relationship a sheathed tubular heater provided with means for flashed heating, thereby to offset the mass of the casting during heat-up.

A further advantage of this invention lies in the provision of a casting of one material for a solid plate heater which is reinforced with another abrasion resistant material.

Another object of this invention is embodied in the provision for a solid cast plate heater wherein an aluminum casting is reinforced with stainless steel.

A still further object of this invention is the provision of a cast iron casting for a solid plate heater wherein the surface of the cast iron plate is metal flame sprayed with a stainless compound to guard against rust and corrosion of the casting.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein preferred embodiments of the present invention are clearly shown.

In the drawings:

FIGURE 1 is a top elevational View of a solid plate heater designed in accordance with one concept of this invention.

FIGURE 2 is a partial sectional view taken along line 2-2 of FIGURE 1.

FIGURE 3 is a fragmentary side elevational view taken in the direction of line 3-3 of FIGURE 1.

FIGURE 4 is a fragmentary top elevational View of a solid plate casting with a reinforcing grid in accordance with a second embodiment of this invention.

FIGURE 5 is a fragmentary sectional view taken along line 55 of FIGURE 4.

FIGURE 6 is a fragmentary top elevational View showing a solid plate casting with embedded metal particles in accordance with a third embodiment of this invention.

FIGURE 7 is a fragmentary sectional view taken along line 77 of FIGURE 6.

FIGURE 8 is a schematic wiring diagram showing one means of rapidly heating a solid plate surface cooking unit, the control circuit being in flash condition.

FIGURE 9 is a similar schematic wiring diagram wherein the solid plate surface cooking unit is energized for a high heat operation.

In accordance with this invention and with reference to FiGURES l, 2 and 3, a circular surface cooking unit It is shown which may be adapted for a surface cooking operation in an electric range. The cooking unit 10 is comprised of a casting 12 having a top surface 14 and an irregular integrally cast protuberance 16 depending from a bottom 18 of the casting. Within the protuberance 16 is embedded a sheathed tubular heater 2d. The heater 29 is comprised of an outer sheath 22 of stainless steel or other suitable material, an inner resistance element 24- and a quantity of a compacted dielectric 26, such as magnesium oxide, to insulate the resistance element 24 from the tubular sheath 22. The tubular heating element 20 is embedded in the cast protuberance 16 and is merely distributed along the bottom surface 18 of the casting in a manner to conduct the heat thereof in the most eflioient manner to the casting 12. Note that the tubular element 20 is encased and supported by the casting 12. This permits the sheath 22 to be formed of a less expensive grade of stainless steel, since oxidation is eliminated within the casting and the sheath doesnt require the high amount of hot strength which an exposed spirally coiled heater element would need. The cost savings in the sheath 22 is an important factor in offsetting the cost of the additional material in the casting 12.

The tubular heatin element 2i) includes terminal end portions 28 and St} to which may be attached

spades

32 and 34 respectively for engaging the electrical circuitry in accordance with the teachings of this invention. The heating element 20 is attached to a source of electricity through a suitable flash heat switch means, to be described more fully hereinafter. As aforesaid, the sheathed heater 2t? is adapted to be embedded in the casting protuberance in. For this purpose the casting is formed in a manner to terminate the protuberance l6 along a surface 3-6, 38 from which the

end portions

37, 39 of the heater 2t]? may project. When the heater 2d is clear of the casting 12, it should be understood that the end portions 37, 3? may be formed to accommodate the particular range application for which the solid plate heater if is to be used.

On the top surface 14 of the casting 12 a depression ii is formed. The depression will serve to eliminate the spinning of the pans or utensils placed on the cooking unit it Further, the depth of the depression it) may be designed to transfer a regulated amount of heat to any suitable temperature sensing element 42. disposed therebelow. For instance, the thinner the section of the casting is beneath the depression 40, the faster will be the transfer of heat from the cooking load to the sensing head 42, and the slower will be the transfer of heat from the heating element 20 to the sensing head 42. This will prevent premature cycling of the control circuit.

As aforesaid, one major advantage of the solid plate heater in is its durability. For this reason the casting 12 may be formed of any suitable metal such as cast iron, aluminum or an aluminum alloy. Metals, such as these,

however, do have certain dis come by the teachings of this i cation as follows.

conductor of heat the tubular units However, aluminum is not very 1 Where tie rapid h at con-" n minurn is desired, this invion conic the castiua, as shown in 4 and 5 steel grid is embedded in an al or stantl lly similar in overall co 'figc t metal cas ed in co wi- 1, 2 and 3. ing nctwor entire top su F integrally with to ca casting, as shown in FIGURE 5. recognized that the resistance to abrasion sils placed on the top surface 54 of ca ng 52 may accommodated with a grid which extends only slightly below the top surface of the casting. It should be not also that the grid 56' will serve also to strengthen and reinforce the casti g as wel as to provide the abrasion wear characteristics desired for solid plate cool ng units.

Another means for strengthening a casting of aluminum alloy or other non-abrasion resistant material is shown in FIGURES 6 and 7. this embodiment, metal particles 60 are embedded in the top surface 62 of a casting 6d. These particles, of stainless steel or other relatively abrasion resistant material, a e pre sed into the top of the casting a l along with n of a sufficient amount of eat to ermit the pr bination these particles will provide t. e abrasion resistance required whereas the aluminum casting will provide the rapid he t conducting characteristics so desirable in e coo. units for electric ranges. above two methods of acquiring additional ab asion resistance in a casting are merely by way of example and could take many other forms wi hin the purview of this invention. l

9 may be desig l'l;e elements to extend over to casting 52 e For instance, stainless steel close-messed screen could be applied or embedded in the castings upper surface. Further, the stainless steel grid 56 could take the form of a spiral element whose convolutions lie the plane of the top surface of the casting.

Where cast iron is utilized for a solid plate heater, there is generally no problem with regard to abrasion resistance to utensils placed on the heater. Ho ever, cast iron does tend to discolor, corrode, or rust with extended usage. For this reason the top surface of the casting should be metal flame sprayed with a stainless compound and may be rubbed smooth or fused to enhance the appearance of the cast iron casting. Thus, it should be seen that reinforcement techniques have been taught this invc on whereby good conducting materials such as aluminum be made abrasion resistant and whereby durable materials such as cast iron may be made corrosion resistant.

The primary difficulty with solid plate heaters for electric ranges has been their slowness to heat up upon initial energization. The user of the modern electric ra objects to this delay and demands that cooking op .tion commence rapidly. it is, therefore, here proposed to overcome this disadvantage of solid plate heaters throuol the application of a flash heat principle to a solid pl te heater. In prior art the spiral type tubular elements have been frequently controlled through a 1 h heat switch which connects spiral element for short pe- 1. c. 1. Y i al 8 are 9, mo e comp e novel appli ttion 0t FIGURE 8 stantially in a flash or .E 9 illustrates the flash heat and ;o the casting volt do provided mass of the pl temperature. of this invention, t

which 7 between nash he up to cooking '-up function 1116i; des latch bimetal 75 srer conduction switch Ii: and norma operation conatch bimetal '76 actuates switch o 013, o/ respectively for the solid plate .256 watt 118 volt unit which is swi h, shown in ELGURES 8 l ieating. The switch auton: itically connects the tubu or heating element 23 to 236 volt current (double vce) to develop four times the wattage (5986 watts) for limited time dependme on the heat setting selected by the user. For instance, may be Tigl rm, Simmer, Low,

ium Low and Medium i. hc-ut the flash heat principle, this is simply an finite heat switch of which there are many o 'able. The heating element 20 is flashed each time the switch 78 is turned from the Oil position to the On. Switch '73 closes whenever the user turns a switch to any dc heat setting. Contacts within the switch auton" v r tore the heating element to 118 volt operation tor the n CDClxlng period after the it 1 heat operation.

Ti e circuit includes a users knob (not shown) appropria el marked to pen. 1t selection of the desired average wattage input to the tubular element 23 in accordance with of the s ting" recited above. line Contact '7 to be closed each time the solid The flash transto change the voltwice normal dur- "2 is included to during normal he length and 9, to

operation which of time that the contact 'i in any given period deterr s anount of it the surface heater T he cycle-r 5'2 is d of a irnetallic actuator and a flat punched moduh ng or modifying the action of the etal o The latch biinctal '75 is self-heated by the passage of current theretlrough and cooperates with

switch blades

78, 84 an S6 to terminate t.e flash heat operator. in accordance v' 1 users heat Tl e switch of w O U ration, also includes c.-n (not shown) v the users heat selection to condition the internal conand 87 or" the switch for the desired M ore particularly, 1" cams would operate the contact switch blade 7,, the latched binieta contacts 3-5 to overcome the action of the latch bimetal and alter the setting of the cyc er "2 to pro duce the desired average wattage to the heating element 20. When the switch is turned to an Off position, the cams may also serve to reset the latch bimetal '76 to the position shown in FIGURE 8 for

switches

78, 8d and 86 to ready the switch for the next flash heat operation.

As aforesaid, one major concept of this invention is the application of a predetermined amount of flash heat to a surface cooking unit 10. This predetermined amount depends upon the mass and the material of the casting and thus must be adjustable for different castings. Some small flexibility is provided in the circuitry of FIGURE 8 by a resistance heater 92 which may be varied according to the casting or plate. By changing the resistance of the element 92, a longer or shorter flash heat operation will continue. For greater flash time change, however, it will be necessary to vary the latch bimetal 76 itself. A longer flash time will require a slower acting latch bimetal. For instance, the latch bimetal could have a lower resistance, a .greater mass or could be constructed of a material of lower resistivity. The reverse of the foregoing will produce a shorter flash time. In other words, the flash time depends on the proportions of bimetal cross-section, length and resistivity. Still another method of varying flash time is through the mechanism or linkage which is responsive to the latch bimetal and interconnects the latch bimetal with the cams and switches of the flasher control, namely switches 78, 84 and 86. Thus, this invention, through current responsive elements, compensates for castings such as iron which require a different flash time than castings such as aluminum or copper. The object of the invention is to provide a flash heat which will cause a solid plate heater litl to heat up as quickly as its counterpart, the conventional spiral tubular elements. For particular details with reference to the switches depicted representatively in FEGURES 8 and 9 reference may be had to the patent to Vogelsberg 2,666,124, issued January 12, 1954. In this patent a suitable switch is set forth which, when modified in accordance with this invention, will satisfactorily operate or energize the solid plate heater it? in accordance with the teachings of this invention.

By Way of example only, reference may be had to FIG- URES 8 and 9, wherein an explanation will be set forth for an initial flash heating period with the heating element 29 connected for High heat operation. As soon as any suitable users control knob (not shown) is rotated to the High position, the main line contact switch 70 will be closed. With reference to FIGURE 8, the flash heat operation will start immediately where a 1250 watt, 118 volt heating element 20 is used at 236 volts, 21.2 amperes to give 5,000 watts load at the heating element 20. The current will flow from L1 through main line switch 70, flash heat contact 80, transfer switch blade 78, line 100, the tubular heating element 20, line 102 and then through parallel paths to the other side of the line L2. One parallel path will be through the bimetal heater 90 of the cycler 72 and cycling contact 74 to L2. The other parallel path for current flow will be through the series resistance strip 92, the latch bimetal actuated switch 86, line 104, the cycler bimetal 88 and cycling contact 74 to L2. Current flow through the closed latch bimetal contact 84 and latch bimetal 76 is insignificant at this point. After a time interval, the cycler bimetal 88 moves to open cycling contact 74 thereby ending the flash heat cycle. By Way of example, the timing interval is approximately 26 seconds for High or Medium High settings. At other settings, the timing is reduced proportionately to prevent overshooting temperatures at the surface unit It When the cycling contact 74 is open, all line current must then pass through the latched bimetal 76 which is heated by the current. At this time current will flow from L1, main line switch 70, flash heat switch blade 78, line 103, tubular heating element 20, line 102 and parallel paths as follows: through the series resistance heater 92, latch bimetal contact switch 86, latch bimetal contact switch 84, through ii) the latch bimetal 76 to L and the parallel path through cycler bimetal heater 9t cycler bimetal 88 and cycling contact 74- to L With full current flow through the latch bimetal 76, the heated latch bimetal will release a detent for

switches

78, 84 and 86 in about five seconds. At this point transfer switch blade 78 will be moved to contact 82 thereby transferring the heating element 20 to a 118 volt, 1250 watt operation on the neutral line N. The total in terval of the flash heat will be the sum of the time taken by the cycler bimetal88 to open contact 74, plus the time the latch bimetal 76 takes to move the switch blade 78 toward the neutral line I. connects with contact 82. the circuitry is conditioned for normal operation at the heat selected. Where High heat has been selected, FIGURE 9 is representative of this circuitry. More particularly, a flow will be through the tubular heater 26* from N, contact 82., transfer switch blade 78, line 1%, line 162, heater 90, cycler bimetal 88, cycling contact 74 to L At the same time a parallel path will be connected through the series resistance strip 92, switch 86, line lib-t, cycler bimetal 88, cycling contact 74- and L At other heat settings the cycler will operate in the manner taught by the Vogelsberg patent. The contact 74 is opened and closed to regulate power to the tubular heating element 28 and the solid plate cooking unit 18 in accordance with the settings of Medium, High, Medium Low, Low, Simmer and Warm. When the user turns the control to Off, a cam resets the latch switches '78, 84, 86 ready for the next flash heat operation as in FIGURE 8.

Tests have shown that the end result of obtaining rapid heat-up of the plate heater it), may be accomplished in a number of ways. On any given heater with any given size heating element 28, the heating element may be flashed at a greater wattage for a lesser time to achieve substantially the same results as a lesser wattage for a longer tim The important thing to know is that the amount of flash heat applied to a solid plate heater iii, in accordance with the concepts of this invention, depends upon the material and the mass of the casting itself. Cast iron will, of course, take a longer flash period than will an aluminum alloy casting. These flash times are to be determined in accordance with the mass and material by varying the series resistance heater 92.

Operating temperatures for solid plate heaters are generally limited to a temperature of approximately 1000 to prevent cracking or warping the casting. A temperature range of from 850 to 950 F. has been believed most desirable as a calibration range for flash heat switches. It will be recognized that even though exposed spiral tubular heatin elements operate at higher surface temperatures, in the range of 1200 to 1400 F., the greater heated surface area of the solid plate heater or cooking unit Iitl, while operating at lower temperatures, will provide the same total Btu. output for the plate heater as with the tubular type.

It should now be seen that an improved solid plate heater has been designed wherein the slowness of the plate heater response is overcome by the application of a flash heat principle tailored to the particular requirements of the casting being used for the heater. Further, a plate has been designed which will conduct heat rapidly and which is reinforced by abrasion resistant material to facilitate long heater life.

While the embodiments of the present invention as herein disclosed, constitute preferred forms, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. A solid plate cooking unit comprising, a casting of one material, said casting having a substantially flat plate portion forming a. top side thereof, a depression in said top side, an irregular protuberance on the bottom of said casting, a sheathed tubular heating element embedded in said protuberance, and means for reinforcing said casting, said reinforcing means including a ribbonlike grid member of another material embedded in said At the instant switch blade 78.

flat plate portion, said grid member h thereof coplanar with said top side.

2. A solid plate cooking unit comprising, a casting of one material, said casting having a substantially fiat plate portion forming a top side thereof, an irregular protuberance on the bottom of said casting, a sheathed tubular heating element embedded in said protuberance, and means for reinforcing said casting, said reinforcing means inciuding a ribbon-like grid member of another material embedded in said fiat plate portion, said grid member having one edge thereof coplanar with said top side.

3. The combination of claim 2 wherein said grid mem- C ing one edge her is comprised of a network of intersecting elements substantially coextensive With said top side.

Refierences Cited in the file of this patent UNITED STATES PATENT S Andrews a- Dec. 14, Zublin Apr. 26, Jordan et al. Apr. 23, izard iune 13, Fry Oct. 10, Russell May 15, Fischer Dec. 29, McCormick Jan. 20, Turner Sept. 29,