US1705702A - Concentric hot plate - Google Patents

Description

CONCNTRIC HOT PLATE' A.

' Filed oct.- 20, 1927v l www = v ATTORNEY v .l devices and Pateffed Mu.. 19,*i 1929. l

'UNlT-'ED STA i Application led ctober 20, 1927,`Serlal No. 227,445, and in GreatBritainJ'anuary 28, 1827.

I `My invention-relatesv to electrically heated units.. l

An object of my invention is to provide a I relatively simple,-highly eilicient,` flat elec-v 1 tric-heatin unit, the surface of which shall be-uniform y heated.

Another object of my invention is to pro- Vide a two-part heater that Vshall embody 10 means for maintaining the two parts in.

proper operative positions vrelatively to each other and for reducing the heatvilo'w therebetween.

In practicing mylinvention, I iprovideam inner heating unit-embodying a plurality of metal-encased tubular heatingA elements embedded lin -a substantially' circular-mass of cast metal having a i peripheral shoulder thereon and an outerV annular heatin unit 20 embodying a plurality o f metal-encase tubular elements embedded in an annulus of cast metal. A screw-threaded stud extends into the central mass of cast metal and cooperates with a metal spider to hold the'two units inJ 26 proper operative position in one plane,

In the single sheet of drawings: Figure 1 1s a-vie'w, in section on the line I--I of Fig. 2, of a device embodying myinvention, and v i 3 I Fig. 2 isa top plan view thereof.l

A two-part heater embodies an inner heating unit 11 and an outer heating unit 12, the two parts being concentrically located.`

The heating unit 11 embodies a pair of metal-encased tubular heatin` elements 13 i L and 14, each bent to substantlally U-shape,

as is shown moreparticularly in Fig. 2 of the drawing, the end`- portions thereofbeing bent down- 0 wardly out of the plane of the ,other part of the heatin elements. f

Each of bodies an outer metal casing 15, a helix -16 of resistor wire located therein and held'tight- 4,5 ly by a crystalline mass 17 of electric-insulating material consisting of magnesium hydroxide or oxide. The method of making these heating elements is more lparticularly disclosed and claimed in my Relssue Patent 5o No. 16,340.

Briefly, the method therein described comprises winding va resistor wire into helical particularly to electric-heating,

'sired shape,

j resistance,

and located. in a ysingle plane,`

.the heatlng units 13and-14 emcmusrIAN n. Maxim. or BRooxLYN, NEW Yonx. l

form, surrounding the hellx of resistor wlre p `or holds the resistor helix -within the metal.

tube, which tube may then be bent to any desuch as that shown in the drawings. As the mass 17 ofmagnesium hydroxide or oxide, is a crystalline mass that provides a heat-conduetin path from the resistor to the metal tube, '0

so that there is a relatively small temperature gradient only between the re'- sistor and the outer surface of the metal tube. -The two heating elements `13 and 14 are then located in a suitable mold and held by very low thermal I molding nails or othersuitable means, to per- V l mit of casting therearound a mass 18 of'metal which) is preferably made flat and circular.

A peripheral shoulder portionv 19 is provided 4 at the upper edge thereof, and the upper surface thereof is smoothed and polished, as may be considered necessary or desirable.

The outer annular heating element 12 embodies a plurality of heating elements 21 and 22 which are bent to substantially circular shape land which are located in the same plane. The end rtions thereof extend downwardly out of thls plane.

The vmethod of construction of the heating elements 21 and 22 is the same asV has been hereinbefore described for the heating elements 13 and 14. c l

An annulus-23 of cast metal is provided to embed the heating units 21 -a-nd`22, the method of supportingcfthe heating velements 21 and 22 during the casting operation being well known and, therefore, unnecessary to describe in detail.

The annulus 23 is provided with a plurality Y of peripherally spaced lugs 24 extending radia ly inward and located a slight distance metal-encased tubular '1 against the 430 The heating elements 45 irrespective of whether the two heatin below the upper surface ofthe annulus 23. The

" innerfaces of the lugs 24 arev adapted toengage the outer peripheral surface of the circu- 18 to cast metal, and the upper suri face-of the lugs 24 i`s adapted to -fit below the lar mass shoulder portion v19 of the mass 18 ofecast .metal. ,Y

A-screw threaded rod or stud 25 is located coaxially with the two heating units and more particularly with the screw threaded opening being provided in the masses of cast metal, -a

member 18 to receive the upper end ofthe stud.A Aspider or 'skeleton frame 26 is provided, having a central ,portion and a plural- 1 5 ity of 'arms extending radially outward therefrom. The central portion has the stud 25 ex-` tending therethrough, and the' outer ends of the arms operatively engage a portion of the lower surface of the annulus 12, being pressed 20 thereagainst by a nut 27 having screw threadv ed engagement on the stud and pressing central portion of the member- 26. In order to reduce the heat iow from the l mass 23 ofcast metal to the spider 26, I prefer 25 to cast the member23 withja recess 28 in its lower surface, providing-relatively narrow ridges of metal at theedge thereof, whereby the area of surfacelin actual engagement is reduced to a minimum.

inbefore described, are substantially standard articles 'and Iv have therefore,

any additional details of construction, lsuch as the terminals and the terminal construction f provided therefor.

' As has beenherembefore stated, the two heating elements13 and. 14 in the central member y11 shape and are thenlocated in; such position [40 that Vthey extend oppositely-to each other, as

is. shown more particularly in-Fi 2 of the drawing. This location permits o lobtaining a substantially uniform temperature ofthe entire'upper surface of the central heating unit,

ments 13 and 14 are connected in series-clrcuit relation and energized from a source of electric energy of a predetermined voltage to pro- I vide a low heat; whether only one ofthe heatl ing elements is energized, or'whether both heating elements are-energlzed while connected in parallel-circuit relation; Such connections and `method of control are well known inthe art and it is, therefore, considered unnecessary to describe these in greater detail.

' When itis desired to thus connect two heating elements indifferent relatlons to provide` aselective .plurality of temperatures, it is desirable, if not necessary, that the lengths ofthe resistor be the same, and the construction, shape and location of the heating elements 13 and 14 are such as to effect the desired result; namely, uniform heating of the operative surface of the unit 11 under all condi- I tionsof operation. l

13,14, 21 and 22 here- I not described v are each bent to .substantially U- ele- It is possible also to make the lengths of the heating elements 2l and`22 the same, so that they also may be connected in a plurality of relations, inthe manner described above.`

Itis, of course, obvious `that it is possible to energize the heating elements-13 and 14 either individu ally or simultaneouslywithout, at the same time, energizing the heating elements 21 l and 22, -This permits of adapting the heater lto the size ofthe cooking utensil being-employed at any time. y

v The cooperating shoulder and lugs'onl the inner and the outer heating units provide a very simple means, which in -combination l with the spider andscrew threaded stud', will maintain the two heating units in proper operative positions relatively to each other in both a radial plane andin a plane parallel to the operatingsurface ofthe heater. Simultaneously, the relatively small surface area of contact between the two-heating units and, 'more particularly between the masses of .cast

metal, tends to reduce the flow of heat therebetween to a-minimum.

Various modifications-may be made in the device embodying my invention without departing from the spiritandfscope thereof, and' e I. desire, therefore, that only suchlimitatins shall be 4placed thereon as are imposed vby the prior art or are specifically set forth in the appended claims.

I claim as my invention;

V1. A multi-unit heater comprising a central i circular mass ofcast metal having an outer over-hanging shoulder portion and a metalencased tubular heating element embedded in the castmetaL-and an outer annular mass of cast metal embodying a plurality of inwardly-extending portion to locate the annular mass in proper operative position both'axially and radially lugs fitting below said shoulder relatively to the central mass, and a metalencased tubular heating element embedded in said annular mass.

2. An electric heater comprising a central:

substantially circular mass of cast metal emmass of metal, and a nut on said rod for hold- 125 .i I

ing the skeleton frame in close operative engagement with the'annular mass of metal, the lugs of which are-thereby pressed against the shoulder on the central mass of metal.

3. An' electric heater comprising a central '180 l 1,705,702 v l -v 3v circular unit andan outer annular unit, each units apart andv reduce heat .ow therebe-v unit embodyingameta1-encased tubnlar heattween.` l A l' ing element, and a mass of cast metal em- Intestimony Wl1ereof,Ihave hereunto sub- 10 beddingthe same, and the annular unit hav-- scribed my name this 10th day of October, 5 ing a plurality of lugs integral with the cast 11927.

. metal and extendingradially inwardly to env gage' the circular unit to space the heating CHRISTIAN B. BACKER. Y

Images