AU7616198A - Heating conductor for radiant heating bodies of a cooking hob - Google Patents

Description

P/00/011 Reguiation 3.2

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

.TO BE COMPLETED BY APPLICANT Name of Applicant: AKO-WERKE GmbH CO KG Actual Inventors: Norbert M6rsch; J6rg Meyer Address for Service: CALLINAN LAWRIE, 711 High Street, Kew, 3101, Victoria, Australia Invention Title: ."HEATING CONDUCTOR FOR RADIANT HEATING BODIES OF A COOKING HOB" The following statement is a full description of this invention, including the best method of performing it known to me:- The invention concerns a heating conductor for radiant heating bodies of a cooking hob as set forth in the classifying portion of claim 1.

Heating conductors comprising a flat strip or band are already disclosed in DE 42 29 375 Al and [P 0 585 538 A2. In those two publications the desired geometrical pattern of the heating conductor is formed by the flat strip being laid in :uitab-e:turns or windings on an insulating bottom of the radiant heating body. The large surfaces of the adjacent flat strip portions face towards each other while only the narrow edges of the flat strip are directed towards the cooking hob itself. That means that such a flat strip which is laid in a geometrical pattern is disposed upright in an on-edge pdsition ard is to be fixed on the insulating bottom of the radiant heating body by a particular clipping arrangement. The clips which are fitted in succession at short spacings form portions of low electrical resistances, which make themselves perceptible in a negative fashion in terms of the incandescent configuration or image produced on the hob. As heat radiation occurs substantially laterally from the flat strip, no direct radiant heating effect occurs. For, the narrow edges which are towards the cooking hob cover only a very small part of the area thereof.

EP 0 175 662 Bl discloses a heating conductor with a geometrical pattern which is formed by stamping out of a metal foil or sheet. That heating conductor however is only suitable for temperatures up to a I maximum of 400°C and for that reason alone cannot be used for a radiant heating body. Such a heating conductor is installed in vehicle seats S 25 where bendability of the heating conductor is not wanted.

SHeating conductor tracks using a flat conductor technology, preferably a thick-film paste technology, are also already known from EP 0 229 928 A2 for heating elements of cooking appliances. Such thick-film paste conductor tracks are applied to a carrier element which is stable in 30 respect of shape. That publication does not describe a radiant heating body in which incandescence of the heating conductor track is the important consideration.

The object of the invention is to provide a heating conductor for a radiant heating body of a cooking hob of the kind set forth in the 35 opening part of this specification, which can be easily mounted over the insulating bottom of the radiant heating body by simple means which reliably ensure that the temperature expansion effects of the heating conductor are absorbed.

In accordance with the invention that object is attained by the features of claim 1. Advantageous developments and configurations of this concept of the invention are set forth in appendant claims 2 to 27.

The individual features of the structure in accordance with the invention provide heating conductors having heating limbs in various arrangements and configurations. There is also provided a plurality of holding plate portions or tongues for the heating limbs, which make it possible for such he'ating limbs to be fixed in accurate position in the radiant heating body in a technically simple manner. In that respect an essential feature of the constructions according to the invention is that the novel heating conductors with the holding tongues formed thereon can be industrially manufactured in mass-production and fitted into radiant neating bodies.

The technical details are set forth and described in the specific description hereinafter. The drawing shows a numbe' of examples. In the drawing: Figure 1 is a plan view of a heating limb with a holding plate portion or tongue formed thereon, Figure 2 shows the holding tongues taken along line II-II in Figure 1, Figure 3 shows a holding tongue of another kind, Figure 4 shows the holding tongue of Figure 3 in the fully fitted condition, Figure 5 is a diagrammatically simple view of yet another holding tongue, Figure 6 shows the holding tongue of Figure 5 in use in an insulating bottom, Figure 7 is a plan view of heating limbs with holding tongues of yet another shape in use, .Figure 8 shows a plan view of a further variation of heating limbs with holding tongues formed thereon, Figure 9 shows yet another variant of a holding tongue-for a heating limb, i 9 c-nu~rI Figure 10 is a view in section of a heating limb when fitted into an insulating bottom with a support portion, Figure 11 is a 'view in section shbwing a heating limb with a fixing mode using cip ,technology, Figure 12 is a view in section of a heating limb with a fixing mode using rivet tcthnology, Figure 13': 'a-view in section of a heating limb with holdin-otongues at the end and'l sing clip technology, Figure 14 is a plan view of a holding tongue with a normal turn portion, Figure 15 is a plan view of a holding tongue with a modified turn portion, SFigure 16 is a plan view of a holding tongue with a further modified turn portion, Figure 17 shows a holding tongue with a turn portion in yet a further variation, Figure 18 %shows a holding tongue with a turn portion in a structure with two current flow paths, Figure 19 shows a holding tongue with a reduced end portion, Figure 20 is a plan view of a holding tongue with side incisions, Figure 21 is a plan view of a holding tongue with openings, Figure 22 is a plan view of a heating limb with impressed grooves, Figure 23 shows a heating limb with openings, .Figure 24 shows a heating limb with openings in a new arrangement, Figure 25 is a plan view of a heating limb with recesses, Figure 26 shows a heating limb with bent-away incisions, Figure 27 is a plan view of a heating limb with cooling lugs, Figure 28 is a plan view of a heating limb arrangement, Figure 29 shows a heating limb arrangement with connecting limbs, Figure 30 shows a contact lug of a heating limb with profiling, •Figure 31 shows a contact lug of a heating limb with another profiling, Figure 32 shows a contact lug of a heating limb with yet another profiling, Figure 33 shows a contact lug- of a heating limb with another new profiling, and la~ura~ar 4 Figure 34 shows a contact lug of a heating limb with still another new profiling.

In regard to a heating conductor for a radiant heating body of a cooking hob whichcomprises individual heating limbs which are or were separated or severed out of a metal foil or sheet, particular attention is to be paid to fixing and handling in oroduction and in assembly. The heating limbs are cut out of the metal foil or sheet in such a way that different variations in terms geometrical patterns are produced in plan view, depending on the respective circumstances involved. Those heating limbs are directed towards the cooking hob with their wide surfaces, that is to say in a plan view on to the geometrycal pattern, thereby providing for optimum direct radiant heating. The high temperatures which occur in the heating limbs cause thermal expansion of the heating limbs, which is to be absorbed and accommodated by particular fixing modes in a technically simple and effective manner. If the end points are rigidly connected to the underlying structure, longitudinal expansion manifests itself in terms of the foils or sheets sagging downwardly or bowing.

Referring to Figure 1 shown therein is a plan view of the holding plate portion or tongue 1 for two heating limbs 2 which are disposed in parallel mutually juxtaposed relationship. A fixing tag or lug 3 is stamped free out of the holding tongue 1 in such a way that it can be S bent away out of the plane of the holding tongue 1 by bending about a bend edge 4. Disposed beneath the holding tongue 1 is a holding portion 5. The fixing of fixing lugs 3 to the holding portion 5 is effected by a procedure whereby a stamp or punch 6 with three cutting edges and a rounded edge cuts the fixing lug 3 out of the holding tongue 1 and at the same time also severs three edges out of the subjacent holding portion A suitably shaped bending-over stamp or punch 7 which is moved from below against the fixing lug 3 with the cut-out holding portion 5 causes the holding portion 5-to be bent over, together with the fixing lug 3, in the manner shown in Figure 2. The bent-over fixing lug includes an angle of 90°. Consequently the fixing lug 3 embraces the resulting edge of the window 8 with an angle of between 0' and 90°. By virtue of that configuration the holding tongue 1 is fixed to prevent it from being FIC~i~: lifted off. The fixing lug 3 can be of any selected contour and that contour can already be produced upon production of the geometry of the metal foil or sheet. Alternatively the contour cf the fi:xing lug 6 can be identical to the external contour of the holding tongue 1.

Referring to Figure 3, a drawn-through collar portion 9 is integrally formed on the holding tongue 1. The collar portion 9 substantially comprises a hollow-cylindrical body of any cross-section but in particular a circular cross-section, which is fitted into a corresponding opening 10 in the holding portion 5. The collar portion 9 is flanged-over by suitable tools on the rear side of the holding portion so that the holding tongue I is firmly secured with the heating limbs 2 in the holding portion 5 (Figure 4).

Figure 5 is a view in section through an insulating ring 13 which can be fitted on to an:insulating bottom 20 (Figure 10) in a conventional known structural configuration. Provided in the underside of the insulating ring 13 is an annular groove 20 which is of a substantially rectangular cross-section. The wall of the annular groove 12, which is at the outward side of the annular configuration thereof, can preferably extend inclinedly, whereby the bottom of the groove is narrower than the opening thereof. A holding tongue 1 of a heating limb 2 is fitted into the annular groove 12. The holding tongue 1 is of a substantially Zshaped form and as a result self-lockingly engages .into the annular Sgroove 12. It will be appreciated that the holding tongue 1 may also be S.:2 of different shapes, instead of the Z-shaped configuration illustrated.

In addition, as an alternative to the annular groove 12, it is also possible to adopt an individual recess or a-plurality of recesses which S. are arranged in series in mutually juxtaposed relationship and into which the end portion 11 of the holding tongue 1 is inserted. The end portion 11 of the holding tongue can be shaped prior to-the assembly operation; S 30 however, the operation of shaping the end portion 11 of the holdina tongue may also be implemented in the assembly procedure by virtue of pressing the holding tongues 1 into the annular groove 12 (recess) by means of a suitable annular punch or stamp.

Tf 1 iloa linb or ln 14(iure 6) which connects th e ins lat ng in(, 13 is Forf),ideA th t ihsulajirno .ttO rl 20 i d i i n t the insulatiflo ri'nq 13, the holding tongue I'which terrminates in that diagonal limb or land 14 will also be of a Z-I' oed -conficuration anod a engage into a aroove or recess, as is sho~j-W in ~uiva~lnt form in FigSire 6.

Referring to Fiur proviJdd therein are 2 7,t n c imb s 2 which are fitted between an insujlatino rino 13 and -a diagonal limb or -land 14> of an insulating bottom. in thisZ Case the hold 4nga tongues are of a dovetail confliguration in Plan and enqace into corresponding recesses or openings in the insulating ring 13 and the diaoonal limb or land i14 respectively. Instead of the dovetail shape the holding tongues 1 may also be of a rectangular or other shape and may have an opening therethrough. Thus the holding tongues 1 may be angled vith their ends.

(or upwardly), ,qhereby( they hokiclwie naoent i the material, just like the illustrated dovetaifl configuration. The holding tongues are desirably iniserted into, the initial material inH powder form, which is then pressed by a bottom tOOl and a top tool. Ths in the shaping procedure, the ends of the holdina toncues 1 are fitted in position and then enclosed by the material.

Figure 8 shows another mode of fixing. In this. cse the holId ingr tongues l have at their ends so-called push-in or_ pluc-a-' n to rig'es 16 which in the left-hand embodiment in Figure 8 arecut out. in the form ofI a trapezium and in the right-hand embodiment in Fioure 8 larc- cut out -in a half-round shape. The'push-ini tongues 16 are secured to prevent them from beino released from the holding portion 5 insofar as they,,are of a substantially arrow-like configuration with' an inclined insertion portion and a barb confiouration. The neck 17 of the push-in tongues 16 is the same width as or na=rrower. than- a corresponding window 18 in tne holding crbr5. n cotrs thL ietpr of the push-in tongue- 6 iss a:hly fo mple 0.2 to I rmn wider than the window 18. In the pushinu.-procedure there-fore then push-in tonque cuts somnewhat into the holding ior tion 5 and is thereby sligq.h tly deformed. In the pushed-in cordition che eniarcEd-wit portion acting as barb means prevents the pus-h-In tongues i16 from ccrninc loose 0 Ut Of the Wi;ndcw 13, in the holding portion S. The enlar-oed-width portion or the ba-rb means of the push-in tongues 16 canals beanaed verafer beino: insert'ed -into the -wndow 18, which utmtely results in themc teino positivel lockingly held in position- D i~n Ficure 9 the hn o1dr tOn QUeaS 1 are prolonged in line with the hEatino liallbs 2 and ar-e fitted thrcugh Openings 19 in the holding portion and are angled irY.>a direction back towards the heating l imbs 2. That construction pro',fdts an ;!Cci'tionai heatinc conductor surface. As a result the heatinoi conductor temoperature is reduced f or the entire 0heati..a conductor so that the radiant heatina body ci-n overall be Fprovided with a higher level o f electrical Output power. The ends of the Fholding tongues, which are Fitted through the openings 19 and bent back, have current. flowing therethrough, as far as the end or to close to the outer end, and are incandescent when the heating body is in the condition of beinq switched on.

Figure 10 shows that a heatina limb 2 of a heatino conductor is taken from the integral annular portion of an insulating bottom 20 to the integral diagonal limb or land 14. The holding tongues 1 are fixed in the hoidino portion! 5 and -in the insulating ring 13 respectively by one or more of the above-described fixing structures. [n order to reduce the extent of bowing of the freely hanging ,heatino limbs 2, the heating limbs 2 are Eupbor~ted in the hot region by a suitable support portion 211. If that suppor7t portion is8 formed by a part of' the -insulation- or- 'by a which is a poor therm.-al conductor, then* the cantact surfacae wit ''ich hot heating limb r :sts onte pot port4o 2 ad':an7-age-6' iL smal I in order not substantially to interfer6 w nth tnhe h eat, e ri i o of- the. heating li-m b 2. A small contact surface is a, orded soort portion 21 is formied from a miatrial eJoys good thermal conductivity. The Isupport portion 21 carries awa th hat r. th hat~nuconductor by way of-hccn actsur7: .G ,ifl thusproect theheaingconductor 7ofrom ov e rhe=-a ti ra at the upr ioctin. '4 i-tE O-asuita:ble des-in confiouration for the suoco.-rt portion 21, it gives off the received energy to the internal space of the heating body. In particular quartz glass or ceramic can be used as preferred materials for the support portion.

A further fixing mode is afforded by a clip 22 which is bent in a U-shape and which, as shown in Figure 11, is shot through the holding tongue 1 and the holding portion 5 which is disposed therebeneath, and which is bent over at the respective ends where they issue therefrom. If the holding portion 5 is annular or is formed with a diagonal limb or land 14 then the outer and inner holding tongues 1 can also be fixed in the insulating ring 13 in the same manner.

Instead of the clip or staple 22, as shown in Figure 12 the holding limb can also be joined to the holding portion 5 by a rivet 23. It is further also possible to use nails, screws or the like fixing means for mounting the holding tongue 1 on the holding portion Figure 13 shows the fixing of the holding tongues 1 by clips or staples 22 directly on to the annular edge or insulating ring 13 and the diagonal limb or land 14 of the insulating bottom of the radiant heating body.

The holding tongues 1 form in known manner and, as described above, the one-sided connection of at least two heating limbs 2 which extend in mutually parallel relationship. The region of the holding tongue 1 which represents the electrical connection of the two adjacent heating limbs involves a critical region, in the case of most possible incandescent patterns. As the electron flux endeavours to follow a flow path of the.; lowest electrical resistance, a point of local overheating of the heating conductor occurs at the inner region of a turn portion or return loop portion 24, due to concentration of the current flow. Such overheating can have a damaging effecton the heating conductor material structure.

The large thermal gradient within the holding tongue 1 also causes thermal stresses which can result in crack formation in the heating limb 2 or in the holding tongue 1.

Figure 14 shows an example of a simple holding tongue 1 with two connected heating limbs 2 without particular measures to prevent overheating.

I I~ I- Fioure 15 now shows an enlarged surface area for the holding tongue 1 by virtue of the heating limbs 2 being increased in width on one side from approximately the transition from the heating limbs 2 to the holding tongue 1. That increase in width as indicated at 25 in a radial outward direction from the turn portion 24 provides that the current flow from the heating limbs 2 is displaced somewhat outwardly in the region of the holding tongue 1. In addition those increased-width portions 25 have the effect of dissipating heat.

An enlarged-width portion 24 with an increase in the radius thereof, as shown in Figure 16, reduces the difference in resistance between the innermost notional current flow path and a further outwardly disposed notional current flow path, around the holding tongue 1. The concentration of the flow of current at the inner edge of the portion 24 thereby markedly falls. The embodiment shown in Figure 16 is of particular advantage in combination with the enlargement configuration as indicated at 25 in Figure Suitable stamping-out or etching produces in the region of the portion 24 of the holding tongue 1 a cooling tag or lug 26 which does not have the current flowing therethrough or which has only a very small amount of current flowing therethrough and which carries heat directly away from the region of the highest level of energy density. Instead of such an individual cooling lug 26 it will be appreciated that it is also possible to provide a plurality of cooling lugs along the inside contour of the turn portion 24. Such a cooling lug 26 can remain in the plane of the holding tongue or however it can be angled upwardly or downwardly.

Figure 18 shows that the portion 24 of the holding tongue 1 is geometrically divided into an inner current flow path 27 and an outer current flow path 28. In that arrangement the inner current flow path 27 is also artificially prolonged by. an additional meander configuration.

These features provide for an increase in the resistance of that inner current flow path, the current flow itself decreases and as a result the level of thermal loading is not higher than that of the other regions, for example of the heating limbs 2. Any change in the direction of the j «i current flow at another location, for example also a change in direction through 900 to a connecting path, can be toned down or alleviated by such a measure.

The reduction in the dissipation of heat within a holding tongue 1 overall provides for a homogeneous temperature distribution in the region of the portion 24. The temperature gradient decreases and there are scarcely any temperature-induced stresses in the entire heating conductor with heating limbs 2 and holding tongues 1. In order to reduce the dissipation of heat the holding tongue 1, as shown in Figure 19, is provided at its end with a reduced or narrowed end lug portion 29.

Instead of such a reduced or tapered end lug portion 29 the conduction of heat is also reduced by cut-in incisions 30 or by a row of holes 31 with a plurality of successively arranged perforations. It will be appreciated that the holding tongue geometry may also be afforded by a combination of the arrangenments described with reference to Figures 19, 20 and 21.

If heating limbs 2 with holding tongues 1 are made from a metal foil or sheet by etching on both sides, there is then in principl(. the possibility of making such heating limbs 2 thinner than the ho-4ing tongues 1 with the portions 24. For that purpose the metal foil or sheet is etched over an area in the region of the heating limbs 2 froT' one side. By virtue of embossing or stamping the heating limbs 2 or by partially thinner rolling of the metal foil or sheet in the region of the heating limbs 2, a difference in thickness is achieved between the heating limbs 2 and the holding tongues 1i. The holding tongues 1 then 2 5 remain in the original material thickness of for example 0.12 mm of the metal foil or sheet. The heating limbs 2 on the other hand are reduced to a material thickness of about 0.06 mm. Such heating limbs 2 are more stable at their end at which the greatest flexural loading also occurs.

The above-discussed problem of overheated points in the turn portions is alleviated for the turn portions now involve a relatively thick gauge of material.

The positive effect referred to above can also be achieved by the portions 24 being increased in cross-section by a suitable application of material, for example galvanically or by laser build-up welding.

III

*Il The surface of the heating limbs 2, which radiates heat in the direction of the cooking hob, is increased as shown in Figure22 by virtue of the fact that longitudinal grooves 32are etched or impressed on the surface which is towards the cooking hob, with the grooves 32 terminating before the end region, that is to say before the turn portions 24. As a result the turn portion region is of a thicker material cross-section and the points in the portion 24 heat up to a substantially lesser degree, whereby the durability of the heating conductor generally is increased.

Figures 23 to 26 describe an increase in the resistance of the l9 heating limbs 2 by a reduction in the resulting cross-section, which is afforded for example by introducing a pattern of holes. That generally produces an increase in the length of the current flow paths in the heating limbs 2. In addition the heat-radiating surface area is increased by virtue of such perforations. The heating limbs 2 are wider than usual and the overall heating conductor length decreases. As a result the entire heating conductor geometry comprises only a few limbs, and that also signifies less dead area which is required for safety spacings. That arrangement in turn affords an enlarged heatable surface which reduces the heating conductor temperature. As shown in Figure 23 approximately 20 oval holes 33 or openings are provided in the heating limb 2. The holes 34 in the heating limb 2 shown in Figure 24 on the other hand are of a substa6ftially rectangular cross-section. As shown in Figure 25, larger circular recesses or blind holes 35 are provided in the heating limb 2.

In Figure 26 the heating limb 2 has incisions 36, the cut edges 37 of which are bent slightly upwardly or downwardly. It will be appreciated that the holes and recesses in the heating limbs may also be of other cross-sections,, for example square, rhomboidal or. the like suitable Sshapes. It is also possible to implement other arrangements of the holes or recesses 33, 34, 35 and 36 in the heating conductor 2. As the Figures show the holes can be in the form of through holes extending through the heating limb or they may also form recesses or depressions 35 which for example are etched therein only halfway through same. In the case of the Sheating limb 2 shown in Figure 26, the original heating conductor crosssection is retained, with an enlarged radiating surface area.

12 Small cooling lugs or tags 38 which do not have current flowing therethrough and which are provided along the outside edges of the heating limbs 2 reduce the heating conductor temperature. In order to increase the safety spacing relative to adjacent heating limbs 2 the cooling lugs 38 are advantageously bent or angled upwardly or downwardly, as is shown in Figure 27.

In the case of a dual-circuit radiant heating body with a central small cooking area or cooking zone and an outer cooking area or cooking zone which can be additionally switched on, the current connections of the inner heating zone necessarily extend through the region of the outer heating zone. By virtue of a suitable design in respect of width of the heating limbs 2 it can be provided that in operation of only the inner zone, the current connections remain below the incandescent temperature.

Upon operation of the two heating circuits, the heating limbs 2, due to the increased internal space temperature in the outer zone, assume a temperature which is perceived as incandescent. That provides that the outer heating zone has a highly homogeneous incandescence image or configuration, without dark locationswhich usually occur by virtue of the inner zone connections necessarily passing therethrough.

Optimisation in regard to the increase in size of the radiating surface of the heating limbs and at the same time a reduction in the number of fixing locations or holding tongues 1 is achieved if the heating limbs 2 rest on the peripherally extending insulating ring 13 with their holding limbs 1 without reversal points in the inner region, for example due to the use of a diagonal limb or land 14, as is shown in Figure 28. if it is found to be necessary, the heating limbs 2 are supported at one or more locations by support portions 21. The heating limbs 2 can be slightly enlarged in their cross-section in the support region in order to reduce the heat output in that region and therewith the temperature of the metal foil or sheet.

The state of the art and the previously described illustrations only ever show that the heating limbs 2 which are etched or stamped out :of a metal foil or sheet or the corresponding geometrical pattern of the heating conductor is arranged in a plane under the cooking hob. It is -I

I

13 however also possible, and this is embraced by the scope of protection of the invention, for the heating limbs 2 to be arranged at different heights one above or one below the other. In order to take up less space for fixing of the heating limbs 2, the holding tongues 1 are disposed for example at different heights for the purposes of fixing to the dilagonal limb or land 14. As a result there is more space available for the actual heat radiation surface and the heating element temperature falls. The heating limbs 2 which are arranged at different heights generally do not form such a dense surface as in the case of a simple flat arrangement. As a result convection in the internal space of the radiant heating body is promoted, and that also signifies that the heat produced at the heating limb 2 is transported away in a better fashion. The different heightwise arrangement can involve the fixing positions of the holding tongues 1 both in the edge region 13 and also in the inner region 14. This arrangement at different heights can also be combined with the abovedescribed advantageous possible arrangements of the heating limbs 2.

An arrangement of the heating limbs 2 at different heights can also be implemented by arranging two or more heating limbs in two or more different heating conductor planes. In that case the directions of the heating limbs 2 of the different metal foils or sheets may be parallel, iperpendicular or at another angle to each other. Such a structure affords substantial advantages in terms of radiant heating bodies with a high level of output power and a high level of power density. The arrangement of for example three metal foils or sheets or heating limbs in mutually superposed relationship affords the possibility of constructing a sevenstage radiant heating body of known kind by a combination of individual, parallel and series connections.

By virtue of the fact that the temperature of a heating limb 2 or a portion of heating limbs 2 falls with an increasing width of the heating limbs 2, there is the possibility as shown in Figure 28 of producing a so-called light-dark pattern on the heating conductor foil. That technology is utilised in order to provide that feed line and fixing portions are non-incandescent. In an incandescence pattern which covers a L

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14 surface area, with for example parallel interconnection of all heating limbs 2, the desired light-dark pattern is then afforded by local dark locations in the heating limbs 2 (enlargement portions). With a suitable arrangement of such local dark locations it is possible to represent letters, logos and the like patterns in the incandescence image or configuration, for example the word 'HOT', thereby at the same time expressing a warning that the cooking hob is hot.

Usually thin transverse connections are provided between the individual holding tongues 1, which serve to increase the stability of the heating conductor during the production procedure and assembly. Such connections are mechanically severed or electrically burnt away, after completion. A feature of the invention now involves glueing a stable, self-adhesive and heat-resistant cloth or.fabric laminate on to the holding tongues 1 and thereby interconnectig, the holding tongues 1. As the connections by way of the laminate are electrically insulating the laminate can remain on the holding tongues 1 and also provides for stability during operation of the assembly. It prevents holding tongues 1 which are in mutually closely adjacent relationship from moving towards each other or touching each other. As a result the heating conductor, even after operation, forms a stable unit which can be handled. if required.

In the case of a heating conductor structure which is produced by an etching procedure, a self-adhesive and etching-resistant plastic foil .or sheet is advantageously already laminated on one side of the metal foil or sheet, prior to the etching operation. The metal foil or sheet for the subsequent heating conductor is then coated only on one side with etching resist and is etched only on one side thereof. The holding foil or sheet which is laminated thereon remains on the etched foil or sheet until it is securely mounted in the radiant heating body by fixing arrangements.

An alternative to that construction is shown in Figure 29.

*Thin transverse connecting limbs 39 at the outwardly disposed holding tongues 1 extend to the initial strip material 40 for production of the heating conductors from a metal foil or sheet. In the case of this production process the heating conductor geometry remains, :in the initial 'strip until stability and positional security of the heating conductor are guaranteed, by completion. This means that the metal foils or sheets can be handled after the etching or stamping operation in the interconnected strip 40 or in suitably cut sheet portions. During or after the completion operation, such connections to the strip 40 are cut mechanically, chemically, by laser beam or electrically, and the strip waste is removed.

For connecting the heating limbs 2 to the electrical connecting paths for electrical contacting of the heating limbs 2, it has been found .when using resistance welding that the quality of the weld between the S contact lug 41 of the connecting base portion and the heating conductor Sconnection 45 cannot be controlled or can only be controlled with i difficulty, when using conventional flat welding lugs in combination with 15 flat or slightly spherical electrodes. Therefore, as shown in Figures to 34, in accordance with the invention, the contact lug 41 is provided with an impressed profile from below. That provides zones involving a different current flow and zones involving a different contact pressure, during the welding procedure. During the welding procedure with the flat 20 electrode,-zones with a strong to a weak fusion flux and a desired different weld quality are produced.

.The profiling which projects on the contact lug 41 can be in the form of a bead or corrugation or a plurality of beads or corrugations as indicated at 42. The profiling can be in the form of one or more pimples or bosses 43 in different arrangements relative to each other or can be formed by other cross-sectional shapes, for example triangular or rectangular impressed portions 44. The profiles each project about 0.1 to mm above the surface of the contact lug 41. The profile--edges can extend parallel to the surface of the contact lugs 41. It is-,however advantageous to provide for an inclined configuration which falls away S- towards the heating body or different heights in order to acquire the desired zones involving a different fusion flux.

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IWIP

Where the terms "comprise", "comprises", "comprised" or "comprising" are used in this specification, they are to be interpreted as specifying the Spresence of the stated features, integers, steps or components referred to, but not to preclude the presence or addition of one or more other feature, integer, step, component or group thereof.

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Claims (22)

1. A heating conductor for a radiant heating body of a cooking hob, substantially comprising a metal foil or sheet which is fitted forming heating limbs between the cooking hob and an insulating bottom, characterised in that the heating limbs are directed with their wide surface towards the cooking hob and have holding tongues for fixing the heating limbs in holding portions of the radiant heating body or portions of the radiant heating body.

2. A heating conductor according to claim 1 characterised in that integrated in the holding tongue is a fixing lug which is bent over out of the plane of the holding tongue around the holding portion

3. A heating conductor according to claim 1 or claim 2 characterised in that the holding portion is at least partially bent over together with the fixing lug

4. A heating conductor according to claim 1 characterised in that integrated in the holding tongue is a drawn-through collar portion (9) which extends in a tubular configuration from the plane of the holding tongue through an opening in the holding portion and is flanged over under the holding portion 1 5. A heating conductor according to claim 1 characterised in that the holding tongue has a Z-shaped or S-shaped end portion (11) or the like which self-lockingly engages into a suitable recess, groove or the like (12) of a holding portion 14, 13). S6. A heating conductor according to claim 1 characterised in that the holding tongue has an end portion of a geometrical configuration, S which is fitted flat or in an angled condition into a suitable opening of the holding portion or into holding portions, of the insulating bottom (13, 14). IC~--L~ 17

7. A heating conductor according to claim i characterised in that the holding tongue is provided with an end portion in the form of a push-in tongue (16) which is provided at its head with lateral inclined insertion portions and has a constricted neck (17) which latches into suitable openings (18) in the holding portion

8. A heating. conductor according to one of the preceding claims characterised in that the holding tongue is provided with an elongated turn portion which is disposed in the surrounded region of the holding tongue

9. A heating conductor according to one of the preceding claims characterised in that the central part of the heating conductor which hangs freely between two end portions rests floatingly on a support portion (21) formed from a material which is a good thermal conductor. A heating conductor according to one of the preceding claims characterised in that the end portions of the holding tongues are connected to the holding portions by mechanical fixing means, in particular by clips or staples rivets pins, nails, screws or the like.

11. A heating conductor according to one of the preceding claims .characterised in that the holdina tongue as a turn portion (24) oios: two heating limbs together.

12. A heating conduetor according to one of claims 1 to 11; characterised in that the holding tongue- is increased: -inu dth approximately from the region of the turn portion (24) outwardly beyond the S side edges of the heating limbs

13. A heating conductor according to one of claims 1 to 11 characterised in that the holding tongue is increased in width in the region of the turn portion outwardly beyond the heating limbs (2) and/or has an inner turn portion radius which is larger than the lateral spacing of the heating limbs

14. A heating conductor according to one of claims 1 to 12 characterised in that the holding tongue has a cooling lug (24) in the region of the portion (24). A heating conductor according to one of claims 1 to 14 characterised in that the holding tongue has an inner and an outer current flow path (27, 28) in the region of the portion (24).

16. A heating conductor according to one of claims 1 to characterised in that the heating limbs are of a greater material thickness in the region of the turn portions than in the remainder thereof.

17. A heating conductor according to one of claims 1 to 16 characterised in that the end porticn (29) of the holding tongue is centrally reduced or has cut-in incisions (30) or one or more holes-(31).

18. A heating conductor according to one of the preceding claims characterised in that the heating limbs are provided with surface area- enlarging portions which are selectively provided in the form of longitudinal grooves or longitudinal channels openings (33, 34, of any cross-sectional area and in any arrangement, or incisiions (36).

19. A heating conductor according to one of the preceding claims characterised in that the heating limbs are provided with cooling lugs (38). A heating conductor according to claim'19 characterised in that the cooling lugs are selectively angled with their- end portions downwardly or upwardly.

21. A heating conductor according to one of the preceding claims characterised in that the heating limbs have narrower or wider limb surfaces at predetermined locations. 19

22. A heating conductor according to one of the preceding claims characterised in that the heating limbs are integral in a continuous structure and are fixed only to the externally peripherally extending insulating ring (13) of the insulating bottom.

23. A heating conductor according to one of the preceding claims characterised in that there are provided two or more heating limb arrangements at a spacing in mutually superposed relationship.

24. A heating conductor according to one of the preceding claims characterised in that the holding tongues are fixed at different heights in the holding portions A heating conductor according to one of the preceding claims characterised in that the holding tongues are connected together by a heat-resistant cloth laminate, a holding foil or the like means applied by adhesive.

26. A heating conductor according to one of the preceding claims characterised in that the holding tongues and the entire heating limb are covered in such a way as to cover the surface area thereof by a self-adhesive plastic foil which is applied on one side.

27. A heating conductor according to one of the preceding claims characterised .in that the holding tongues have mechanically or electrically severable holding limbs (39) for.ing a connection with the S initial strip material (40) which surrounds the holding tongues

28. A heating conductor according to one of the preceding claims characterised in that the heating limbs are connected at their ends to contact lugs (41) which are provided in their contact iug surface with profiling means in the form of beads or corrugations, pimples or the like means (42, 43, 44). 4 29, A heating conductor according to one of the preceding claims characterised in. that, in a dual-circuit radiant heating body, the heating limbs are of a width by virtue of which the current connections remain below the incandescent temperature upon operation only of the inner zone of the cooking hob, while upon operation of the inner and outer zones of the cooking hob the current connections assume such a temperature that it is perceived as incandescent. DATED this 15' day of July, 1998. AKO-WERKE GmbH CO KG By Their Patent Attorneys: CALLINAN LAWRIE Vt we