US2765391A - Quick heat electric heating unit - Google Patents

Description

Oct 2, 1956 J. L sHRoYER QUICK HEAT ELECTRIC HEATING UNIT Filed Nov. 18, 1953 MMV nited States Patent O i QUICK HEAT ELECTRIC HEATING UNIT Jacob L. Shroyer, Oak Park, Ill., assignor to Tuttle & Kift, Inc., Chicago, Ill., a corporation of Illinois Application November 18, 1953, Serial No. 392,798

3 Claims. (Cl. 219-37) My invention relates to electric heating units of the metal sheathed type such as commonly employed in electric ranges for surface heating, and has reference more particularly to facilities for operating the unit temporarily at awattage suliiciently in excess of normal to heat up rapidly in starting.

Such units are made with one or more heating resistances embedded in insulation in a metal sheath, and because of the mass of insulating material and sheath which must be heated, considerable delay is experienced in bringing the unit to the desired operating temperature unless the heating unit is adapted to temporarily supply heat instarting, considerably in excess of that required in normal operation.

Water heaters have been made in which the entire heating resistance was made of a material having a high positive temperature coefiicient of resistance to protect the heater against damage if not submerged and these provide extra wattage during heating up periods, but such resistance was not acceptable for open heaters, such, for example, as employed in electric ranges, and accordingly it has been customary with such heaters to use standard resistances and merely provide controls therefor which are operable to provide temporary connections at starting to supply excess wattage for a short time after which.l the connections are changed to supply normal wattage.

Such controls, however, not only required extra connections but also instrumentalities of a precision nature to operate the connections, which appreciably increased the cost. Moreover, the instrumentalities were not directly responsive to the temperature of the heating elements and by reason thereof were not suiiiciently exact or certain to assure adequate preheating or interruption of the preheating before detrimental exposure of the heating elements to the high starting heat.

Furthermore, it has been customary to accomplish the preheating by impressing on the heating elements a higher voltage than that at which they are normally intended to operate and this high voltage is likely to shorten the life of the unit and may permanently impair the heating element if unduly prolonged. y

The principal objects of the present invention are to provide improved preheating facilities in which the preheating is accurately controlled by the temperature in the heating unit at the place where the heat is generated for heating the unit; to accomplish the preheating without subjecting the heating resistances to a higher voltage than that at which they are normally intended to operate; to avoid extra connections and changes of connections for controlling therpreheating; and in general to provide simple and reliable Vfacilities which insure rapid preheating and avoid the above mentioneddisadvantages of previous preheating facilities, these and other objects being accomplished as pointed out more particularly hereinafterA and as shown in the accompanying drawing, which shows a preferred embodiment of the invention, and in which: Fig. 1 is atop view of a range surface heating unit 2,763,391 Patented Oct. 2, 1956 made in accordance with the present invention and with parts broken away to show details of the construction and including a somewhat diagrammatic illustration of a control for selective regulation of the operating temperature of the unit;

Fig. 2 is an enlarged cross sectional view of the unit of Fig. 1 taken on the line 2-2 thereof;

Fig. 3 is an enlarged sectional view of the inner closed end of the unit of Fig. l taken on the line 3-3 thereof; and

Fig. 4 is a sectional view on the line 4-4 of Fig. 3 showing the connection of the resistances to a return conductor at the closed inner end of the heating unit.

In accordance with this invention, the heating unit is composed of a tubular metal sheath having a conventional or standard heating element extending lengthwise in the sheath and embedded in highly compacted heat conductive electrical insulating material by which the heating elements are electrically insulated from one another and from the sheath, and for preheating purposes, a special heating element which not only serves to supply the additional heat for preheating but also controls the extent and duration of preheating, extends lengthwise in the sheath alongside the conventional or standard heating element thereof and is electrically insulated throughout its length from the conventional heating element and the sheath, and this special heating element is connected in parallel with the conventional heating element so that the current supplied to the heating unit passes parallelly through both of the heating elements and are both simultaneously energized.

Only one conventional or standard heating element and one such special heating element are shown in the illustrated embodiment of the drawing, but it is to be understood that more than one conventional heating element and more than one special heating element may be employed if desired.

The heating unit shown in the drawing is similar to and may be made in a manner similar to the heating unit shown and described in Patent 2,643,317 to William R. Tuttle, and comprises a tubular metal sheath 10 containing two long heating elements 11 and 12 which extend lengthwise in the sheath 10 in side by side spaced apart relation and are embedded in and electrically insulated from one another and from the sheath by a compacted mass of heat conductive electrical insulating material 13. These heating elements may be of any desired type but preferably are and are shown in the conventional form of helices of resistance wire composed of a connected series of spaced apart coils or convolutions as are well known in the art.

In the illustrated embodiment, the sheath 10 and its contents are in a at spiral form, such as employed for range surface units, with a wide attened pan or utensil supporting top face 14, and the particular unit has the sheath closed at the inner end, as indicated at 15, and the other end open with terminals projecting therefrom through which current is supplied to the heating elements or resistances 11 and 12.

In this heating unit, which is somewhat triangular in shape, the resistances 11 and 12 are located side by side near the top of the unit directly under the flat top 14 and a common conductor 16 of low resistance extends lengthwise of the unit near the bottom thereof in the insulation 13 and at the closed inner end 12 of the unit is connected to the inner ends of both resistances 11 and 12, as indicated in Figs. 3 and 4, as for example, by the bent wire conductor member 17 which is permanently secured centrally to the end of the conductor 16 and has the two ends thereof inserted and secured in the respective inner ends of the resistances 11 and 12.

A terminal 18 leads from the otherend of the con.

duct 16 out through the open end of the sheath 10 and preferably. eachheating element or resistance 11 and 12 has, at its end remote from the connector 17, a separate terminal, indicated respectively at 19 band 20, which leadsY` Preferably the heating elements 11 and 12 areiof the.y same voltage rating and for ,operation of the unit current is supplied simultaneously to bothheating elements, either from a two wire power supply, by connecting ther two terminals 19 and 20 to one conductor of the two wire feed and the terminal 1S to the other-conductor of the two wire feed, or from a three wirepower supply having a neutral wire in which event the neutral wire is connected to theterminal 18 and the other-two power supply wires are connected respectively tothe terminals 19 and 20 so that `the same voltage is impressed on each of the heating elements 11 and'12.

Itis possible, however, to employ heating elements 11 and 12 of'different voltage ratings, for example, one for 110-120 voltage and the other for 220-240 voltage, in which event the neutral of the three wire feed would be connected to the terminal 19 or 20 of the low voltage heating element and the other two feed wires respectively to the other of said terminals 19 or 20 and the terminal Theheatingelement 11 is of conventional type, the re-N sistance of which is not appreciably aiected bychanges of temperature. The heating element 12, however, is made of an alloy which has a high temperature coefficient of resistance so that the resistance thereof increases with the temperature and by reason thereof the wattage cag;

heating element 12 immediately supplies excess heat toyy the unit for preheating and as the heat thus supplied is dissipated it continues to supply excess heat, the amount` of which diminishes, however, as the unit is heated until the operatingtemperature of the unit is reached, whereupon the wattage supply to the heating elementv 12 levels off at the low amount determined by the high resistanceof the heating element 12 at the temperature at which the unit operates and the low kwattage supply is continued so long as that operating temperature is maintained-- Theheating element 12 may be made, for example,

of anfalloy of -nickel and iron containing about 70% nickel'n and about 30% iron, which will .provide a resistance which has atV normal high operating temperature/of the unit about one fourth the wattage capacity of -the resistance at normal or room` temperature, this being' adesirable range of resistance varlatlon as 1t affords suffi-- cient extra heat for starting and at thesame ,time permits a heating element 11 of high wattage-to Vbe employed.-

It is to be noted particularly'that in view ofthe parallell Y connection of the elements 11 and 12 the heating element 11 operates` during the'preheating, but at its normal wattage capacity, and that the heating element 12 continues to operate after the preheating period, Vbut at the 1 reduced wattage thereof and that in normaloperation of the heating unit it is heated in part by the element -11 and in part by the elementv12, the initial temporary high wattage of the latter serving as a booster to contributev the necessary additionalvheat for preheating only in the starting operations of the unit. l

Preferably, the heating element'` 11 is of such wattage 'Y capacity to supply the larger proportion of the heat rre-j quired by the heatingrunit in normal operation thereof f and the heating element 12 is ofsuch wattagecapacity l' that after its preheating purpose isaccomplished, -it-sup 1 plies only a small amount of the heat required by the heating unit thereafter.

For example, in a heating unit of 1250 normal wattage capacity, it is preferred to employ a heating element 11 having a rated operating capacity of 1000 watts and a heating element 12 having a rated operating capacity of 1000 watts at normal or room temperature and which diminishes to 250 watts at the normal high operating temperature of the unit so that'the major portion of the heating load is imposed on the heating unit 11 in normal operation of the unit. t

Thus the inherent temperatureof the heating element.`

12 is relatively low in vnormal operation and its actual temperature at that time depends largely upon the heat contributed thereto from the heating element 11V. More-v over, this relative wattagecapacity of theL heating element 11 and parallel connection thereof is advantageous as the operation of the main heating element 11 is not affected by the auxiliary heating element 12, and accordingly the heating element 11 will continue to operate `and to heat the unit to a usable cooking temperature irrespective of impairment or failure of the heating element 12.

The above described heating unit may be employed for full heat only by merely providing conventional switch controlled or plug-in facilities to make and break the above described connections to the power supply feed wires, or it may be employed, for example, for high-low 'heating by switch or plug facilities whi-ch energize the elements 11 and 12 conjointly for high heat and the element 12 alone for low heat.

l prefer, however, to employ an infinite control of the type shown in Patent 2,294,573 to Paul H. Potter and Patent 2,503,082 to William R. Tuttle, yand as shown somewhat diagrammatically in the drawing hereof, wherein a shaft21 which operates at a constant rate of speed has cams 22 and 23 thereon which operate contacts 24 and 25 respectively to `and from other contacts 26 and 27 respectively which are connected respectively to the two lines 28 and 29 of a two wire current supply.

The contacts 24 and 25 are carried on spring arms 30 and 31 respectively which are biased to cause engagement of the contacts 24 and 25 with their mating contacts 26 and 27 and are moved away from their mating contacts 26 and 27 by the cams 22 and 23 against the tension of the spring arms 30 and 31 and the spring arm 30 is connected by the conductor 32 with the terminals 19 and 20 of the heating unit so that the corresponding ends of the 1 heating elements 11 and 12 are connected to the line wire 28 when the contacts 24 and 26 are engaged while the spring arm 31 is connected by the conductor 33 to the heating unit terminal `18 so that the other connected ends of the heating yelements 11 and 12 (which are at the` closed end 15 ofthe sheath 10) are connected with the other line wire 29 when the contacts 25 and 27 are engaged.

Thecams 22 and 23 are alike and correspondingly positioned on the shaft 21 so. that they impart simultaneous corresponding movement to the respective spring arms 30 and 31.

The contacts 26 and 27 are likewise carried by spring- 'arms 34 and 35 respectively which are biased to move said contacts away from their mating contacts 24 and 25 andV the spring Iarms 34 and 35 engage against corresponding cams 36 and 37 on a shaft 38 which is operable by a knob 39 to move the cams 36 and 37 in unison and correspondingly so as to adjust the contacts 26 andt27 correspondingly to and from thecontacts 24 and 25. y

Thus, by the adjustment of the knob 39, the contacts 26 and 27 can be adjusted out of range of the contacts 24 and 25 to completely interrupt the connection of both -line conductors 28 and29 with the heating unit or they can be adjusted Vso that-the contacts 24 and 25 are not separable from the contacts 426 and 27 and the connectionsoff the line conductors with the heating unit are constantly maintained, or said contacts 26 'and 27 can be adjusted by "the knob39to anyrintermediate position between such I constant engagement and constant disengagement of the contacts 26 and 27 with the contacts 24 and 25 so as to provide any desired length of time of engagement of the contacts 24 and 25 with the contacts 26 and 27 in each rotation of the shaft 21 and the cams 22 and 23 thereon.

Thus current may be supplied to the heating unit in. each rotation of the shaft 21 for any selected length of time or throughout complete rotation of the shaft 21 and thereby heat the unit to 'any desired intensity and at each occasion of intermittent engagement of the contacts 24 and 25 with lche contacts 26 and 27 and also on each occasion of full time engagement of said contact, both of the elements 11 and 12 are energized and accordingly the element 12 is effective upon starting to use the unit either Iat full heat or at any intermediate intensity of heat to heat the unit quickly to the particular intensity of heat for which the knob 39 is set.

While I have shown and described my invention in its application to a heating unit of range surface type and wherein the current supply terminals are all located at one end of the heating unit sheath, the invention is applicable to other types of heating units and other types of surface heating units and there are various other changes and modification may be made without departing from the principles of the invention, the scope of which is to be determined by the appended claims.

What is claimed is:

1. An electric range surface heating unit of a predetermined normal high wattage capacity for sustained heating and having excessive temporary wattage capacity substantially in excess of said normal wattage capacity for quick preheating of the unit, the said unit having an active portion comprising -a metal tube which is bent in the form of a at winding at one side of which the tube has a wide flat face providing 'at said side a substantially uniplanar surface on which a utensil is supportable for con ductivity of heat thereto directly from the aforesaid Wide flat face of the said metal tube, the said tube having therein a pair of corresponding, parallel connected, concurrently energizable helical resistances which extend lengthwise ofthe tube in laterally spaced apart side-byside relation and are embedded in compacted heat conductive electrical insulating material by which the resistances are separated and electrically insulated from one another and from the tube, one of the said resistances having such temperature coeilicient of resistance that the resistance thereof is substantially constant throughout the range of temperature to which it is subjected in the heating operation of the heating unit, and the other of said resistances having a high positive temperature coeicient of resistance providing a wide variation of increasing resistance from the low limit to the high limit of the range of temperature to which it is subjected in the operation of the heating unit and affording a wattage capacity at said low limit of temperature thereof greatly in excess of the wattage capacity at said high limit of temperature thereof, the resistances of said pair being located substantially closer to that side of the winding at which the tube has the wide flat face as aforesaid than they are to the opposite side of the winding and each said resistance being substantially the same distance as the other from said wide flat face and substantially uniformly distant throughout its length from said at face.

2. A heating unit according to claim 1 wherein the helical resistances of the pair are correspondingly attened in cross section in a direction perpendicular to the Wide flat face of the tube and are correspondingly elongated in cross section in a direction paralleling said wide at face.

3. A heating unit according to claim 1 wherein the resistances of the pair are connected in parallel to and simultaneously suppliable with current through la switch which is power operated to interrupt the current supply concurrently to said resistances at optional variable intervals.

References Cited in the le of this patent UNITED STATES PATENTS 1,276,589 Steinmetz Aug. 20, 1918 1,393,325 Smith Oct. 11, 1921 1,510,125 Woodford Sept. 30, 1924 1,767,249 Leckie et al June 24, 1930 2,110,727 Heinisch et al Mar. 8, 1938 2,400,672 Wiegand May 21, 1946 2,508,552 Tuttle May 23, 1950 2,575,113 Lennox Nov. 13, 1951

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