US3300621A - Electric hotplate and method of making same - Google Patents

Description

Jm, Z4, 957 K. FISCHER ELECTRIC HOTPLATE AND METHOD OF MAKING SAME Filed April 22, 1964 Kid United States Patent O 3,300,621 ELECTRIC HOTPLATE AND METHOD v F MAKING SAMFJ Karl Fischer, Am Gansherg 1, Gherderdingen- Wurttemberg, Germany Filed Apr. 22, 1964, Ser. No. 361,644 6 Claims. V(Cl. 219-457) This invention relates to electric hotplates and particu larly to electric hotplates having grooves on thev underside of the plate body, which are adapted to receive Wire coil heating elements embedded in insulating compound material, and to methods of making same.

Conventionally known electric hotplates are the kind referred to having heating elements equipped with comparatively long cable ends passing through the insulating compound into which the heating elements are embedded. Outside the insulation, the cable ends usually pass through another insulating member which is fitted into the cover shell underneath the hotplate. The free ends of the cables projecting over the latter insulating member are protected by covering same with insulating heatproof glassbeads or the like, and are either connected to a terminal bar mounted below the hotplate assembly, or are arranged as free connecting ends onto which further extensions are attached by soldering or welding.

The long flexible cable ends of the heating elements have been found extremely cumbersome during the manufacturing of the hotplate. They start to give rise to diiculties during the placing of the heating elements into the grooves of the plate where a first layer of insulating material had been pressed. The heating elements then may be forced out of their seat during the transportation of the hotplates to the next following manufacturing step due to movements of the connecting ends. Furthermore, the presence of the long free ends of the cable ends also are undesirable when the heating elements are covered with the nal insulating compound to be pressed into the grooves, particularly by obstructing the smoothing of the loosely poured insulating compound material. The long free hanging connecting ends must be laboriously threaded through bores lof the heavy die press head for the subsequent pressing-in of the loose insulating compound into the grooves of the hotplate. Furthermore, these ends are in the way during the subsequent processing stages, such as drying, testing and machining. Eventually there is the danger that the heating elements may be torn out of their embedding material by accident or by careless handling after the final pressing.

According to the present invention, which consists in such novel features, construction arrangements, combinations of parts and improvements as may be shown and described in connection with the apparatus herein disclosed by way of example only and as illustrative of a preferred example, the heating elements are equipped with relatively rigid connecting ends, which ends are dimensioned in such manner that they are covered entirely by the loosely poured insulating compound material. There are several possibilities of rendering the connecting ends of the heating elements accessible for connecting after the nal pressing of the insulating material. It is, for example, possible to provide for connecting ends which are bent-off at a right angle, so that they protrude over the insulating material, ready for connecting, by having entering of same into frontside clearances in the press die during the pressing operation of the insulating material. Furthermore, the. connecting ends could be shaped in such manner that they would remain within the confinement of the insulating material after the pressing of the insulating material. In this case, the connecting ends must be rendered accessible for the connecting by subsequent ICC machining of small grooves in the compressed insulating material. It could be also feasible to insert a low-temperature melting plug on the corresponding places.

The above-mentioned problems are being eliminated by this. The short, rigid connecting parts, preferably consisting of pins which are of light weight and constitute only a small lever arm in the bent-off design, do` not iniiuen'ce during transportation the heating `element which is looselyV positioned in the grooves. Since they are entirely'covered within the insulating compound material after this material has been poured on over the grooves, they will not be in the way whenthis material is smoothed fiat. If the connecting ends are bent oli and if they are dimensioned in such manner that they protrude over the linally pressed insulating material, they can enter without diliiculties into cut-outs provided on the pressing die at the time of compressing of the insulating material. Since the connecting ends only protrude very little, for example 7 mm., over the insulating material, they are not obstructing during the subsequent manufacturing operations. There also is no hazard of ripping out of the heating elements of finally pressed insulating material by careless handling. The hotplates can be packed and stacked in a space-saving manner, similarly to the plate blanks, for transporting of same to other manufacturing departments or to the assembly lines, since the connecting parts which only protrude little over the insulating material, are protected by the higher peripheral border of the hotplate body. Conductor pieces can be soldered or welded onto the connecting ends which protrude over the insulating material -or which have been rendered accessible by machining of grooves in this material. These conductor pieces are laid out to the outside of the hotplate assembly leading through the insulating member in the cover shell underneath the hotplate for being connected to the power lines, as in the case with the conventionally known long cable ends.

There is a further considerably advantage of this structure for the manufacturing of the hotplates. Since the connecting parts are joined immediately to the last coils of the heating element, so that it is no longer necessary for the heating elements having long uncoiled, stranded ends, the heating element coils can be cut off currently of a continuously produced endless spiralling coil emenating from a coiling machine in increments of suitable length. Thus, these heating elements may be produced fully automatically.

The connecting parts of the heating elements are preferably made of pins. As it is known from tubular heating elements, the connecting parts may be made of solid metal pins which are pushed into the coils and are welded or soldered thereto. In a yet more simple manner, the connecting pins may be made of small tubes which are pushed over the short, extended ends of the heating element coils and which are squeezed on to same for forming a rm joint or of sheet metal strips which are rolled about the extended ends of the heating element coils and are pressed thereon. The necessary straightening of short lengths of the ends of the heating element coils (approximately 10 to 15 mm.) is compensated by eliminating welding or soldering.

Various further and more specific advantages and features will clearly appear from the detailed description given below taken in connection with the accompanying drawing which forms part of this specification and illustrates merely -by way of example one embodiment of the device of the invention. In the following description and in the claims, parts will be identified by specific names for convenience, but such names are intended to be as generic in their application to similar parts as the art will permit. Like reference characters denote like parts in the several figures of the drawing, in which:

FIG. 1 shows a heating element coil end having a bentoff connecting pin;

FIG. 2 shows a radially taken partial section of the hotplate, illustrating the first step of placing the heating element coil in the hotplate body;

FIG. 3 shows the same radially taken partial section of the hotplate, as shown in FIG. 2, illustrating the loose filling of the insulating compound material over the heating element coils;

FIG. 4 shows the same' radially taken partial section of the hotplate as shown in FIG. 3, illustrating the pressing and compacting of the insulating compound material;

FIG. 5 shows the same radially taken partial section of the hotplate as shown in FIG. 4, after the pressing of the insulating compound m-aterial has been finished;

FIG. 6 shows a partial section of a hotplate having three heating elements;

FIG. 7 shows a circuit Vdiagram of the heating elements of t-he hotplate illustrated in FIG. 6;

FIG. 8 shows a connecting pin soldered or welded a heating element coil end;

FIG. 9 shows a heating element coil end, straightened out over a short length, having a tu-bular connecting pin fastened to same; and i FIG. 10 shows a heating element coil end, straightened out over ashort length, having a sheet metal strip rolled on said short length and pressed onto same;

Referring now inv more detail to the drawing illustrating a preferred embodiment by which the invention maybe realized, there is shown in FIG. 6 an electrichotplate body 10 which may be made of cast iron -or of any suitable metal having a conventionally known recessed unheated center portion 11 having a center screw bolt 12 for mounting of same in -an electric cooking range (not shown in the drawing) and having heated annular portion for receiving the heating element coils 14 embedded in insulating compound material 16 and 17 in grooves 13.I A short, rigid connecting part 15, shaped as a pin, is attached to each end of every heating element coil 14, as shown in FIG. l, and as illustrated in an enlarged scale in FIGS. 8 to lOshowing various modes of fastening. The connecting parts have bent-off ends 15. y

The. straight length, measured from the end o the coil, amounts to 10-15 mm. The bent-offends 15 are dimensioned in such manner that they protrude approximately 7 mm. over the .finally pressed insulating compound materi al on the underside of the plate body.

The assembling of the heating element coils 14 is performed as follows:

The rst step is to place the heating element coils 14 having the connecting parts 15 into the grooves 13 of the hotplate Ibody 11i, turned upside down, after said grooves 13 had `been lined with a pressed-in layer 16 of insulating material (FIG. 2). The bent-off ends 15 of the connecting parts 15 of the inserted heating element coils 14 extend upwardly beyond the grooves 13. Hereafter the insulating compound material 17 which is to be pressed into the grooves 13 is loosely poured over the grooves and the surface of the material is evened smoothly. The upright ends 15 of the connecting parts 15 are made so long that they are entirely covered by the loosely poured and smoothly evened layer 17 of the insulating compound material when'the dosage of the amount of this material has just been made right. The ends 15 of the connecting parts 15 will emerge from the insulating compound material after compressing the layer 17 of the insulating compound material by a die press head 18 (FIG. 4). They enter during this process step into cavities 19 of the die press head 18. The ends 15 of the connecting parts 15 protrude approximately 7 mm. over the finally pressed layer 17 of the insulating compound material, as shown in FIG. 5.

into

Conductor pieces 20 may -be welded or soldered to the ends 15 of the connecting parts 15, which protrude over the surface of the layer 17 of the insulating compound material. These conductor pieces 20 are led in a conventional manner t-hrough slots of an insulating member 21 which is inserted into the cover shell 22 which is located underneath theA hotplate 1t) `and which is fastened there by the center screw bolt 12.. rI`he conductor pieces 20 may be led to a terminal for the power line (not shown in the drawing) which is fastened in the conventional manner to the underside of the hotplate. However, they also may `be led to the outside of the insulating member 21, shaped as at bar plugs. -f

FIG. 6 shows a hotplatev having three heating elements N1, N2 and N3 `which are connected with four terminal elements designated by the numerals 1, 2, 3, 4 inthe circuit diagram, FIG. 7, lby Way of conductor pieces 20 which are welded or soldered to the connecting parts 15 of these heating elements. The ends of heating elements are schematically indicated in the insulating compound material 17.

FIGS. 8 to l() illustrate various possibilities of attaching connecting parts 15 to the ends of the heating element coils 14. According to FIG. 8 a solid metal pin havingan outside diameter correspond-ing to the inside diameter of the coil, is inserted into the coil and is welded therewith at 25. In both alternatives, shown in FIGS. 9 and 1U, a short end 26 of the heating element coil 14, corresponding to the length of the connecting part 15. According to FIG. 9, a small tube representing the pin, having a length of approximately l5 mm. and anoutside diameterof approximately 1.2 mm., is pushed on the straightened end 26 of the heating element coil 14 andis pressed or crimped togetherwith the wire 2.6 at the point 28. In FIG. l0 is shown that the connecting part 15 is formed by a sheet metal strip folded to a U- shape, which is rolled about the wire end 26 inserted into it, *forming a sort of sleeve, which is pressed together with the wire end 25 at the same instant.

The operation of bending oft .the connecting parts is preferably performed after the connection with the heating element coil wire end has been made.

Obviously the connecting parts 15 also can be dimensioned in such manner that they do not protrude over the pressed insulating compound material. In this case, the connecting parts 15 do not have to be bent off. They rather may bel laid bare for welding or soldering contacting pieces by machining away a corresponding portion of the insulation, for example, by using a milling tool. v

While the invention has been described and illustrated with respect to a certain preferred example which gives satisfactory results, it will be understood by those skilled in the art, after understanding the principle of the invention, that various other changes and modifications may be made without departing from the spirit and scope of the invention and it is intended therefore in the appended claims to cover all such changes and modifications.

'I claim:

1. An electric hotplate for an electric cooking range or the like, comprising a plate body having grooves in the underside thereof, heating ele-ments .embedded in an insulating compound material adapted to be received in said grooves, said heating elements consisting of wire coils having terminal windings, short connecting parts attached directly to the ends of said heating elements, said connecting parts consisting of solid pins being pushed into said terminal windings of said wire coils and being secured thereto, each one of said connecting parts having a bent-off end portion projecting from said insulating compound material, a second insulating member underneath said plate body, a cover shell of said plate body fitting over said second insulating member, and noninsulated conductor pieces secured to said bent-olf end 5 portions, said conductor pieces passing through said second insulating member fitted into said cover shell of said plate body, said conductor pieces providing for connections with power lines of an electric current source.

2. An electric hotplate according to claim 1, and each one of said connecting parts being substantially l0 to 15 mm. long.

3. An electric hotplate according to claim 2, and each one of said bent-off portions projecting from said insulating compound material by substantially 7 mm.

4. An electric hotplate according to claim 1, and said connecting parts consisting of tubes being pushed over straightened end portions of said Wire coils and being squeezed therearound.

5. An electric hotplate according to claim 1, and said 15 6 6. An electric hotplate according to claim 1, and having a terminal bar attached underneath said hotplate at a distance from said heating elements embedded in said grooves, and said conductor pieces passing through said second insulating member fitted in said cover shell and being connected with said terminal bar.

References Cited by the Examiner UNITED STATES PATENTS 2,042,203 5/1936 Baker 219-457 2,354,808 8/1944 Ganci 338-253 FOREIGN PATENTS 199,949 9/ 193 8 Switzerland.

RICHARD M, WOOD, Primary Examiner. L. H. BENDER, Assistant Examiner.

Claims (1)

1. AN ELECTRIC HOTPLATE FOR AN ELECTRIC COOKING RANGE OR THE LIKE, COMPRISING A PLATE BODY HAVING GROOVES IN THE UNDERSIDE THEREOF, HEATING ELEMENTS EMBEDDED IN AN INSULATING COMPOUND MATERIAL ADAPTED TO BE RECEIVED IN SAID GROOVES, SAID HEATING ELEMENTS CONSISTING OF WIRE COILS HAVING TERMINAL WINDINGS, SHORT CONNECTING PARTS ATTACHED DIRECTLY TO THE ENDS OF SAID HEATING ELEMENTS, SAID CONNECTING PARTS CONSISTING OF SOLID PINS BEING PUSHED INTO SAID TERMINAL WINDINGS OF SAID WIRE COILS AND BEING SECURED THERETO, EACH ONE OF SAID CONNECTING PARTS HAVING A BEND-OFF END PORTION PROJECTING FROM SAID INSULATING COMPOUND MATERIAL, A SECOND INSULATING MEMBER UNDERNEATH SAID PLATE BODY, A COVER SHELL OF SAID PLATE BODY FITTING OVER SAID SECOND INSULATING MEMBER, AND NONINSULATED CONDUCTOR PIECES SECURED TO SAID BENT-OFF END PORTIONS, SAID CONDUCTOR PIECES PASSING THROUGH SAID SECOND INSULATING MEMBER FITTED INTO SAID COVER SHELL OF SAID PLATE BODY, SAID CONDUCTOR PIECES PROVIDING FOR CONNECTIONS WITH POWER LINES OF AN ELECTRIC CURRENT SOURCE.

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