US3132229A - Electric hot plate - Google Patents

Description

R. D. BREMER ETAL May 5, 1964 ELECTRIC HOT PLATE Original Filed July 20 3 Sheets-Sheet 1 IIIIIIII I I I I I I I INVENTORS. Robe/f 0. Bremer By George 6. Pearce Afforne y y 5, 1964 R. D. BREMER ETAL 3,132,229

ELECTRIC HOT PLATE Original Filed July 20, 1959 3 SheetsSheet 2 "i 52 z r 54 .6 1 //l I r I I I I 5 L 40 I I I I If I I f l L i a i l 5 52 I I I mmvrons. Robert D. Bremer By George 6. Pearce W$KM The/r Afro nay y 5, 1954 R. D. BREMER ETAL 3,132,229

ELECTRIC HOT PLATE 3 Sheets-Sheet 3 Original Filed July 20, 1959 n w m y M a M W5 4W 00 .v "w. A 8 MW M R T Y B E Fig. 9

United States Patent Office Patented May 5, 1964 3,132,229 ELECTRIC HOT PLATE Robert D. Bremer and George C. Pearce, Dayton, Ohio, .assignors to I General Motors Corporation, Detroit,

IMich., a corporation of Delaware Original application July 20, 1959, Ser. No. 828,356, now Patent No. 3,069,526, dated Dec. 18, 1962. Divided and this application Aug. 2l, 1961, Ser. No. 132,758

5 Claims. (Cl. 219-20) This invention relates to a domestic appliance'and more particularly to an improved surface cooking unit for an electric range.

Thisis a division of our copending application Serial No. 828,356, filed July 20, 1959, now Patent No. 3,069,- 526.

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 towhich 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 appearancewhich 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 possessthe rugged durability requiredin electric range operation. .It is to this end that the applicants invention is drawn.

Accordingly, it is anobject 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 uponv 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. I

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 materialfor a solid plate heater which is reinforced with another abrasion resistant material. j

Another object ofthis. invention is embodied in the provision for a solid castplate heater wherein an aluminum casting is reinforced with stainless steel.

A still further object of this invention is the provision of a cast ironcasting 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 apparentfrom the following description, reference being had to the accompanying drawings wherein preferred embodiments of the present invention are clearly shown. h a

In the drawings: i 6

FIGURE 1 is a topelevational view of a solid plate heater designed in accordance with one concept of this invention.

an irregular integrally cast protuberance 16 from which the end FIGURE 2 is a partial sectional view taken along line 22 of FIGURE 1.

FIGURE 3 is a fragmentary side elevational view taken the direction of line 33 of FIGURE 1. FIGURE 4 is a fragmentary top elevational view of a solid plate casting with a reinforcing grid in accordance 1 ing 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 flashcondition.

FIGURE 9 is a similar schematic wiring diagram wherein the solid for a high heat operation.

In accordance with this invention and with reference to FIGURES 1, 2 and 3, a circular surface cooking unit 10 is shown which may be adapted fora surface cooking operation in an electric range. comprised of a casting 12 having a top surface 14 and depending from a bottom 18 of the casting. Within the protuberance 16 is embedded a sheathed tubular heater 20. The heater 2% 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 eflicient 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 inthe sheath 22 is an important factor in offsetting the cost of the additional material in the casting 12.

The tubular heating element 20 includes terminal end portions 28 and 30 to which may be attached spades 32 and 34 respectively for engaging the electrical circuitry in accordance with the teachings of thisinvention. 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 21) is adapted to be embedded in the casting protuberance 16. For this purpose, the casting is formed in a manner to terminatethe protuberance 16 along a surface 36, 38

project. When the heater 20 is clearof the casting 12, it should be understood that the end be formed to accommodate the particular range applica- 10 is to be used.

On the top surface 14 of the casting 12 a depression 40 is formed. The depression will serve to eliminate the spinning of the pans or utensils placed on the cooking unit 10. Further, the depth of the depression 40 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 plate surface cooking unit is energized.

Thecooking unit 10 is portions 37, 39 of the heater 20 may.

portions 37, 39 may from the tubular units 20 at the top surface 14- of the casting. However, aluminum is not very resistant to abrasion wear. Wherethe rapid heat conducting charac-. teristics Ofaluminum is desired, this invention contem plates reinforcing the casting, as shown in FIGURES 4 and 5. A stainless steel grid 5% is embedded in an aluminum casting 52 substantially similar in overall configuration to the general metal casting 12 outlined in connection with FIGURES 1, 2 and 3. a The grid 56 may be, designed as a criss-crossing network of ribbon-like elements to extend overthe entire top surface .54 of the casting 52 and may be formed integrally with the casting throughout the depth of the casting; as shown in FIGURE 5.

However, it should be recognized that the resistance to abrasion wear from utensils placed on the top surface 54 ofcasting 52 may be accommodated with a grid which extends only slightly below the top surface 54' of the casting. Itshould be noted also that the grid 50 will serve also to strengthen and reinforce the casting as. well as to provide the abrasion wear characteristic desired for solid plate .cooking units.

Another means for strengthening a casting of aluminum alloy or other non-abrasion resistant material is shown in FIGURES 6 and 7. In this embodiment, metal particles 60'are embedded in the top surface 62 of a casting 64. These particles, of stainless steel or other relatively abrasion resistant material, are pressed into the top of the casing 64- along with the addition of a suflicient amount of heat to permit the proper penetration. In combination, these particles willprovide the abrasion resistance required whereas the aluminum casting will provide the rapid heat conducting characteristics so desirable in surface cooking units for electric ranges.

The above two methods of acquiring additional abrasion resistance in a casting are merely by way of example and could take many other forms within the purview of this invention. For instance, a stainless steel closemeshed screen could be applied or embedded in the castings upper surface. Further, the stainless steel grid 50 could take the form of a spiral element whose convolutions lie in the plane of the top surface of the casting.

Where cast iron is utilized for a solid plate heater, thereis generally no problem with regard to abrasion resistance to utensils placed 011 the heater. However, cast iron considerably less than that of a solid plate typecooking unit and the prior art fails to consider this fact in overcoming the slowness in heat response in place heaters.

This invention adapts a flash heat switch which will supply the desiredamount of additional wattage for a pre determined period of time in accordance with the mass of the casting. v i I With reference to FIGURES 8 and 9, a more complete description will'be set forth for the novel application of speed heat to the casing of this invention. FIGURE 8' illustrates thecooking unit substantially in a flash or rapid heat condition, while FIGURE 9 illustrates the circuitry at the conclusion of rapid or flash heat and with the surface cooking unit connected for high heat operation. The circuit isfed through a conventional 236 volt domestic power source including a power line L a neutral line N and a power line L In the line L a master On-Off or main line switch 70, 71 is placed. The circuit includes a bimetallic cycler element 72 which operates on a contact 74 to intermittently interrupt power to the tubular element 20 of the surface unit 10 in accordance with a heat selected by the operator. The methods of a connecting the power source L L N for achieving the different desired heat outputs at the surface unit 10 have not been set forth as they are believed conventional. Only that initial portion of each surface heater energization is illustrated to point out that rapid or flash heat is provided on any user temperature preselection where the does tend to discolor, corrode, or rust with extended usage. For this reason, the top surface ofthe casting should be metal flame sprayed with a stainless compound and may be rubbedsmooth or fused to enhance the appearance of the castiron casting. Thus, it should be seen that reinforcement techniques have been taught in'this invention whereby good conducting materials such as aluminum maybe madeabrasion resistant and whereby durable materials such as cast iron may be made corrosion resistant. I j

v 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 range objects to this delay and demands that any cooking operation commence rapidly. It is, therefore, here proposed to overcome this disadvantage of solid plate heaters through the application of'a flash heat principle to a solid plate heater. elements have been frequently controlled through a. flash heat switch which connects the spiral element for short periods of time at maximum voltage to cause rapid heatup. However, the massof the tubular cookingunit is In the prior art, the spiral type tubular mass of, the plate unit 10 must 'be brought up to cooking temperature. To accommodate the rapid heat-up function of this invention, the circuitry includes a latch bi- .metal '76 which operates a flash heat transfer conduction switch 7 8 between flash heat contact and normal operation contact 82. In addition, the latch bimetal 76 actuates switch blades 84 and 86 operating on contacts 85, 87 respectively in accordance with the users temperature selection.

One suitable tubular element 20 for the solid plate. heater 10 may be a 1250 watt 118 volt unit which is equipped with a flash heat switch, shown in FIGURES 8 and 9, to provide extremely fast initial heating. The switch automatically connects the tubular heating element 20 to 236 volt current (double voltage) to develop four times the wattage (5000 watts) for a limited time depending on the heat setting selected by the user. For instance, these heat settings may be High, Warm, Simmer, Low, Medium Low and Medium High; Without the flash heat principle, thisis simply an infinite heat switch of which there aremany available. The heating element 20 is flashed each time the switch 70 is turned from the Ofl position to the On. Switch 70 closeswhenever the user turns a switch to any desired heat setting. Contacts within the switch automatically restore the heating element 20' to 118 volt operation for thenormal cooking period after the flash heat operation. a

The circuit includes a users knob (not shown) appropriately marked to permit selection of the desired average wattage input to the tubular element 20 in accordance with one of the six heat settings recited above. The line contact 70 is adapted to be closed each time the solid plate cooking unit lt) is turned on. The flash heat trans,- fer contact switch blade 7 8 is adapted to change the voltage on the element 20-from normal to twice normal during the flash heat operation. The cycler 72 is included to regulate or pulse the amount of. current duringnormal 'operation which flows to the heater element 20- the length of time that the bimetallic'element 72. is engaged with contact 74 in any given period determines the amount of wattage output at the surface heater 10. The

heated by the passage of; current therethrough and 'co- 1 operates with switch blades 78, 84 and 86 to terminate setting.

The switch of which FIGURE isa graphic representation also includes cams (not shown) which respond to the users heat selection to condition the internal contacts 71, 74, 80, 8-5 and 87 of the switch for the desired amount of flash heat. More particularly, the cams would operate the main line contact switch blade 70, the latched bimetal contacts 84 and 86 to overcome the action of the latch bimetal and alter the setting of the cycler 72 to produce the desired average wattage to the heating element 20. When the switch is turned to an Off position, the camsmay also serve toreset the latch bimetal 76 to the position shown in FIGURE 8 for switches 78, 84 and 86 to readythe switch for the next flash heat operation.

7 As aforesaid, one major concept of this invention is the application of a predetermined amountof flash heat to a surface cooking unit This predetermined amount depends upon the mass and the material of the casting and thus must be adjustable for diflerent 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 timewill 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 10 to heat up as quickly as its counterpart, the conventional spiral tubular elements. For particular details with reference to the switches depicted represent'atively in FIGURES 8 and 9, reference may be had to the patent to Vogelsberg 2,666,124, issued January 1Q, 1954. In this patent a suitable switch is set forth which, when modified in accordance with this invention, will satisfactorilyoperate or energize the solid plate heater 10 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 Willbe set forth for aninitial flash heating period with the heating element 20connected for High heat operation. As soon as any suitable us-ers 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 235 volts, 21.2 amperes to give 5,000 watts load at the heating element 20. The current will flow from L 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 L One parallel path will be through the bimetal heater 90 of the cycler 72 and cycling contact 74 to L 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 L 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 10. 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 L main line switch 70, flash heat switch blade 78, line 1100, tubular heating element 20, line 102 and parallel paths as follows: through the series resist ance heater 92, latch bimetal contact switch 86, latch bimetal contact switch 84, through the latch bimetal 7 6 to L and the parallel path through cycler bimetalheater 90, 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 86 thereby transferring the heating element 20 to a 118 volt, 1250 watt operation on the neutral line N. The total interval of the flash heat will be the sum of the time taken by the cycler bimetal 88 to. open contact 74, plus the time the latch bimetal 76 takes to move the switch blade 78 toward the neutral line N. At the instant switch blade 78 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 20 from N, contact 82, transfer switch blade 78, line 100, line 102, 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 104, 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 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 heater10 may be accomplished in a number of ways. On any given heater with any given size heating elementy20, the heating element maybe flashed. at a greater wattage for a lesser time to achieve substantially the same results longer time. Theimport-ant thingto know is that the amount of flash heat applied to a solid plate heater 10, in accordance with the concepts of this invention, depends upon theymaterial 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 has been believed most desirable as a calibration range for flash heat switches. It will be recognized that even though exposed spiral tubular heating 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 10, while operating at lower temperatures, will provide the same total B.t.u. 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 as a lesser wattage for a high and lowtvoltage conductors, and means to control said power source to flash said heating means on high voltage for a time interval predetermined in accordance with the predetermined mass and material of said casting,

said control means including switch means for connecting said heating means in series with said high voltage conduci- V tor whensaid heating means is being flashed for, said time interval, latch meansloperatively, connected to said switch means and inseries therewith for operating said switch means to disconnect said heating means from said high voltage conductor at the end of said time interval, and resistance means in series with saidfsjwitch means, said heating means andtsaid latch means :for determining the duration of said'time interval. l i

'2. A solid platecooking u'nitfor an electric range comprising, a casting of predetermined mass, a heating means in heat transfer relationship to said casting, a power source for energizing said heating means andihaving high and low voltage conductors, and means to controlsaidpower source to flash said heating means on high voltagefor atime interval predetermined in accordance with the predetermined mass of said casting, said control means ineluding switch means for connecting said heating means in series with said highvoltage conductor when :said heating means is being'flashed for said time interval,

latch means operatively connected to said switch means and in seriestherewith for operating said switch means to disconnect said heating means from said high voltage con ductor at the end of said time interval, and resistance means in series with said switch means, "said heating time interval, means for operating said switch means to disconnect said heating means from said high voltage conductor at the end of said timeinterval, and resistance means in control relationship with said operating means and inzseries with said switch 'means for determining the duration of said time interval.

4. A solid plate cooking unit for an electric range comprising, a solid plate of predetermined mass, a heating means for heating said solid plate, a power source for energizing:said heating'means and having first and second voltage conductors, and means to control said-power source 7 to flash said heating means on said first voltage for a time interval predetermined in accordance with the predeter mined mass of said solid plate, said control means includ ing-switch means for connecting said heating means in series with said first voltage conductor when said heating means is being'flashed for said time interval, means for operating said switch means to disconnect said heating means from said first voltage conductor at the end of said time interval, and means in control relationship with said operating means "and operative concurrently 'with said switch means during said time interval for determining the duration of said time interval. a

5. A solid plate cooking unit foranelectric range comprising, a casting of predeterminedimass and material, a

sheathed tubular heating means integral with said casting,

V a power source for energizing said heating means and havmeans and said latch means' for determining the duration of said time interval. 7 V

' 3. A solid plate cooking unit for anele'ctric' range comprising, a solid plateof predetermined mass, aheating means in heat transfer relationship to said solidfplate,'a power source for energizing said heating means and having high and low voltage fconductor's,'and means to control said power source to flash said heating means on high voltage for atimeinterval predeterminedin accordance with the predetermined mass of said solid plate, said control means including switch means for connecting said heating means in series with said high voltage con ductor when said heating'means'is being flashed for said ing 236-volt and 1l8-volt conductors, and means to control said power source to flash said heating means on 236 volts for a time interval predetermined in accordance with the predetermined mass and material of said casting, said control means including switch means 'for connecting said heating means in series ;with said 236-volt conductor when said heating'means is being flashed for said time interval, latch means for operating said switch meansto disconnect said heating means from said 236-volt conductor at the end of said time interval, and current respon sive means'inseries'with said switch 'meansand incurrent flow control relationship to said latch means for determining the duration of said time interval, said current responsive means being preselectable in accordance with said predetermined mass and material,

References Cited in the file of this patent UNITED STATES PATENTS 1,663,810 Morse Mar. 27', 1928 1,696,684 Knopp Dec.'25, 1923 1,979,471 Knopp Nov; '6, 1934 Knopp Jan. 4, 1938

Claims (1)

1. A SOLID PLATE COOKING UNIT FOR AN ELECTRIC RANGE COMPRISING, A CASTING OF PREDETERMINED MASS AND MATERIAL A HEATING MEANS IN JUXTAPOSITION TO SAID CASTING, A POWER SOURCE FOR ENERGIZING SAID HEATING MEANS AND HAVING HIGH AND LOW VOLTAGE CONDUCTORS, AND MEANS TO CONTROL SAID POWER SOURCE TO FLASH SAID HEATING MEANS ON HIGH VOLTAGE FOR A TIME INTERVAL PREDETERMINED IN ACCORDANCE WITH THE PREDETERMINED MASS AND MATERIAL OF SAID CASTING, SAID CONTROL MEANS INCLUDING SWITCH MEANS FOR CONNECTING SAID HEATING MEANS IN SERIES WITH SAID HIGH VOLTAGE CONDUCTOR WHEN SAID HEATING MEANS IS BEING FLASHED FOR SAID TIME INTERVAL, LATCH MEANS OPERATIVELY CONNECTED TO SAID SWITCH MEANS AND IN SERIES THEREWITH FOR OPERATING SAID SWITCH MEANS TO DISCONNECT SAID HEATING MEANS FROM SAID HIGH VOLTAGE CONDUCTOR AT THE END OF SAID TIME INTERVAL, AND RESISTANCE MEANS IN SERIES WITH SAID SWITCH MEANS, SAID HEATING MEANS AND SAID LATCH MEANS FOR DETERMINING THE DURATION OF SAID TIME INTERVAL.

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