EP0250880B2 - Radiant heating element - Google Patents

Abstract

In a radiant heater unit (1) for heating through a hotplate (2), the periphery of the heating field is formed by an initial cooking marginal heating system (9), which is e.g. operated by a short-circuit connection (19), so that it passes much more rapidly from the cold state into the visible glowing state and also in the marginal region use is made of the faster heat transfer there to the bottom (3) of the cooking utensil. The increased radiant power density can also be obtained by other measures, namely by modified insulating conditions in the vicinity of the marginal heating system, by using a PTC resistor in the vicinity of the inner partial power system and similar measures.

Description

The invention relates to a radiant heater according to the preamble of claim 1. Such a radiant heater is known from GB-A-2 087 698.

With numerous cooking processes, it is desirable to achieve the shortest possible heating time, i.e. At the beginning of the cooking process, the food to be cooked must be gently heated to a predetermined temperature level for as short a time as possible, after which, when the power is reduced and controlled by a temperature switch or controlled by a power control unit, cooking is continued without the need for a separate actuation of the electrical actuation process for the hotplate. This automatic influencing of the heat output of the hotplate is so desirable that it does not automatically return to the state of the boiling phase after the single transition from the state of the boiling phase to the continued boiling phase, unless it has been completely switched off and cooled down again accordingly provided for the execution of a next parboiling phase.

In the case of radiant heaters, it is also desirable that after switching on a hotplate, radiant heat in the visible wave range is emitted as quickly as possible, so that the cook can quickly recognize the operational readiness or the operating state of the hotplate from the visible glow of the associated radiant heater, and thus as far as possible high radiation density or heat output is quickly available.

Attempts have already been made to achieve this thermal and optical behavior of a radiant heater by providing a separate radiant heating resistor on the periphery of the heating field. which is switched on during the heating or heating phase and remains switched off after the heating phase. Such an external, separately switchable heating resistor is also available for those hotplates which can be switched between two fixed heating field sizes in order to be able to selectively switch them to cooking vessels of different floor plan sizes. With such arrangements, quite good results can be achieved in some cases, but switching off the heating resistor that was switched on during the boil-up phase during cooking continues to result in a relatively uneven specific heat application to the bottom of the cooking vessel. Power control units with additional switches are also required for this.

According to GB-A-2 115 259, a radiant heater is known in which a separately switchable radiant heating resistor determines the edge heating and thus the fixed heating field size. The inner area of the radiant heater lies within the edge heating, of which the radially outermost part of the circle does not belong to the edge heating formed exclusively by the outermost heating resistor. All sections of the radiant heating resistors are approximately evenly distributed over the entire heating field, without a particular distribution of the radiation density being recognizable.

The invention has for its object to provide a radiant heater of the type described, in which the time from switching on until reaching visible glow and thus also the heating time compared to previously known radiant heaters, which in particular have at least one exposed heating resistor, can be significantly reduced.

This object is achieved in a radiant heater of the type described in the introduction according to the invention by claim 1.

Advantageously, the parboiler heating is not switched off at the end of the parboiling phase, but is possibly reduced to a smaller difference in its radiation density compared to the area of the radiant heater within it. Parboiling control means are created which, during the parboiling phase, at least temporarily result in faster heat development in the edge region of the radiant heater or wherever the best contact between this vessel bottom and the heating plate is generally given due to the usual shape of the bottom of cooking vessels. The increased power difference during the heating phase, with which the edge heating is operated compared to the rest of the partial power, can also be used to ensure that the edge heating described in this way glows visibly in an extremely short time after switching on the hotplate and thus visually indicates the full operational readiness of this hotplate .

The described heat emission behavior of the boil-on edge heating, which is continued to be operated at the same time in the continued boiling phase, can be achieved, for example, in a simple manner by providing or switching on the boil-up edge heating over the entire boil-up phase with relatively increased power.

Since, according to the invention, the boil-on edge heating is connected to the carrier with less heat-conducting coupling than the inner part of the radiant heater, the specific heat dissipation from the edge heating in the carrier is significantly lower than that of the inner part of the radiant heater and therefore the edge heating comes after switching on much faster to visible glow. This lower specific heat dissipation can be achieved by various, relatively simple measures, for example by a lower specific surface contact between the associated heating resistor and the carrier, by using a support material with a lower specific thermal conductivity in the area of the edge heating and by similar measures. In this case, the parboiler control device can also be formed exclusively by the heat-conducting connection between the jet heater and the carrier without using a separate control or regulating device, since only the characteristics of this heat-conducting connection are used to end the parboiling phase.

A particularly low specific thermal connection between the edge heating and the support can e.g. can be achieved in that longitudinal sections of the associated heating resistor are arranged essentially freely floating contact-free with respect to the carrier, that is to say they run in a contact-free or tensioned manner between suspension sections in the manner of suspension bridge sections.

The longitudinal sections of the heating resistor with a low thermal coupling to the support can also be created in that they are located in areas of the support which have different thermal conductivity due to its material and are formed, for example, by a thermal insulation or insulation material which is suitable for the immediate mounting of the heating resistor is unsuitable, but has very good insulation properties.

Such an insulation material is used in radiant heaters, for example, as underbedding of a cup-shaped or disk-shaped insulation support body, which has lower thermal insulation values, but is suitable for the reliable determination of the heating resistance by direct embedding. In this case, the relatively dimensionally stable insulation support body can be provided with openings in the area of the said longitudinal sections of the heating resistor, into which upward projections of the underbedding expediently project such that these projections are the openings Fill in substantially completely at least in plan view, wherein these projections can be set back at least partially in the vertical direction relative to the front side associated with the heating resistors and / or can be at least partially set ahead of it. The insulation support body can be, for example, a relatively solid molded body made of mineral fibers, made of a material such as is known, for example, under the trade name "Fiberfrax", while the underbedding is based on pyrogenic silica.

A temperature sensor designed as a strain rod sensor can be embedded in the insulation carrier in a simple manner by inserting it into the insulation carrier, and its switching head can lie outside the carrier. However, this switch, which operates in the manner of a temperature protection switch, can also be formed by a so-called Klixon thermostat which interacts with a heat conducting rod which transfers the heat from the sensing point to the temperature sensor in the switching head of the thermostat, for example a bimetallic sensor.

Fig. 1

einen Strahlheizkörper im Querschnitt und in vereinfachter Darstellung,

Fig. 2

den Strahlheizkörper gemäß Fig. 1 in Draufsicht,

Fig. 3

eine schematische Darstellung der Verteilung der Strahl-Leistungsdichte in der Ankochphase,

Fig. 4

eine weitere Ausführungsform eines Strahlheizkörpers in einer Darstellung entsprechend Fig. 2,

Fig. 5

einen Schnitt nach der Linie V-V in Fig. 4 in abgewickelter Darstellung,

Fig. 6

eine weitere Ausführungsform in einer Darstellung entsprechend Fig. 5,

Fig. 7

einen Schnitt nach der Linie VII-VII in Fig. 6.

These and further features of preferred developments of the invention are also apparent from the description and the drawings. Embodiments of the invention are shown in the drawings and are explained in more detail below. The drawings show:

Fig. 1

a radiant heater in cross section and in a simplified representation,

Fig. 2

1 in top view,

Fig. 3

1 shows a schematic representation of the distribution of the beam power density in the parboiling phase,

Fig. 4

2 shows a further embodiment of a radiant heater in a representation corresponding to FIG. 2,

Fig. 5

3 shows a section along the line VV in FIG. 4 in a developed representation,

Fig. 6

5 shows another embodiment in a representation corresponding to FIG. 5,

Fig. 7

a section along the line VII-VII in Fig. 6.

1 and 2 show, a radiant heater 1, which is intended to be arranged on the underside of a translucent heating plate 2 made of glass ceramic or the like, has a bowl-shaped or cup-shaped support 4. The carrier 4 consists essentially of a one-part or multi-part inner shell 5 made of at least one insulation material and a relatively thin-walled outer shell 6, which serves to protect and mount the inner shell 5, which preferably consists of sheet steel. The inner shell 5 carries on its substantially flat or parallel to the heating plate 2 floor a radiant heater 7 to be operated by electric current in the form of at least one encapsulated heating resistor 8, but it is conceivable that at least part of the power of the radiant heater 1 also with a encapsulated radiant heater, that is, a bulb lamp, such as a halogen lamp, can be operated. However, the preferred arrangement is that the radiant heater has only unencapsulated heating resistors.

The heating resistor 8 is laid in a double spiral approximately in such a way about the central axis of the radiant heater 1 that its two connection ends 14 lie on the periphery of the heating field 10 which is essentially delimited by the outermost, approximately annularly closed spiral winding. A predetermined number of outer turns of the heating resistor 8, namely about half of all turns or about three spiral turns in the exemplary embodiment shown, are provided as the heating-up edge heating 9 for operation with a relatively increased radiation density during the heating-up phase, while the rest lie within this heating edge 9 Windings of the same heating resistor form a remaining partial power 11, which can be operated in a variable power gradient with respect to the edge heating 9.

The entire jet heater 7, that is to say the only heating resistor 8 forming this, is operated during the entire heating operation by means of an adjustable control device or, for example, a clocking power control device, with the jet heater 7 being connected to the mains current with the interposition thereof. Appropriately, there is a temperature sensor 16 crossing the heating field 10 in the space between the radiant heater 7 and the heating plate 2, which in the case of using a control device 12 for the operation of the Jet heater 7 can influence this or can be assigned to a temperature limiter 15, the switching head of which is arranged directly on the outside of the carrier 4 penetrated by the temperature sensor 16.

An additional control device 13 is provided for the different operation of the radiant heater 7 in the parboiling phase, on the one hand, and in the boiling phase, on the other hand, whose temperature sensor 17 is exposed to the temperature inside or in the full cross section of the inner shell 5. The temperature sensor 17, which can be an expansion rod sensor with an outer tube and an inner rod arranged therein with different expansion coefficients, or a heat conducting rod, which supplies the heat from the sensing point to the switching head of the control device 13 below the switching head of the temperature limiter 15 on the outside of the carrier 4, is located also parallel to the heating plate 2, but below the bottom surface of the inner shell 5 receiving the radiant heater 7 and above its underside, i.e. on the side of the radiant heater 7 facing away from the heating plate 2 or the temperature sensor 16, embedded in the insulation material of the inner shell 5 and approximately radially to the central axis of the radiant heater 1, wherein this temperature sensor 17 can be shorter than half the width of the heating field 10 such that it essentially only on one side of its central axis in the area of the associated turns of the edge heating 9 l weighs. Arranged in the switch head of the control device 13 designed as a cut-off switch 18 in the form of, for example, a snap switch, which is not directly connected to the power supply for the radiant heater 7, is arranged in a short-circuit circuit of a short-circuit for the partial power 11, that is to say exclusively via its two connecting poles two points at a distance from each other of the heating resistor 8 so electrically connected that when the parboiler 11 is closed, the longitudinal section of the heating resistor 8 belonging to the partial power 11 and occupying the inner zone of the heating field 10 is essentially taken out of operation by short-circuiting. As a result, the remaining section of the heating resistor 8 associated with the parboiler heating and operating essentially up to the periphery of the heating field 10 is operated during the closed short-circuit circuit 19 with a relatively substantially increased radiation density and, after being switched on, is heated up very quickly to such an extent that the heating plate 2 a visible glow can be perceived. As soon as the temperature sensor 17, which can be embedded essentially in contact with the insulation material or in a cavity in the inner shell 5, has been heated to the switch-off temperature of the control device 13 with the time delay due to its thermally insulated arrangement, the parboiler switch 18 opens, so that now also the longitudinal section of the heating resistor 8 belonging to the partial power 11 goes into full power operation and thus the difference in radiation density between the area of the heating edge heating 9 and that of the partial power 11 is at least reduced. As a result, increased power should be available for as long as possible during the boil-up without switching back to the increased power again during continued cooking and after the temperature monitor forming the control device 13 has responded.

The shortening of the heating-up time to be achieved also results from the fact that the cooking vessel base 3 of cooking vessels is usually curved in such a way that the cooking vessel base 3 has the most direct contact with the heating plate 2 in the region of its outer edge and therefore a particularly rapid heat transfer is possible there . In Fig. 3, arrows, the length of which represent the radiation density, indicate that an operating arrangement is provided in the subject matter of the invention in such a way that the power density is greatest in this edge region in the boiling phase. In the continued cooking phase, either this external power density in the edge area 9 can be reduced, the power density in the area of the partial power 11 can be increased, or both processes can be carried out simultaneously.

The carrier 4 is stretched with the end face of the edge of the shell of the inner shell 5 under pressure over the entire surface against the inside or underside of the heating plate, so that the inner circumference of this contact edge essentially coincides with the periphery or outer boundary of the heating field 10. The heating resistor 8 can be immovably fixed to the inner shell 5 by at least partially embedding its coils in the insulating material. Furthermore, the radiant heater can also be round, rectangular or square, deviating from the circular shape, instead of being circular, the heating resistor then expediently following this outer contour in its spiral shape.

4 to 7 are the same reference numerals for corresponding parts as in Figs. 1 to 3, but in Figs. 4 and 5 with the index "a" and in Figs. 6 and 7 with the index " b "is used.

The radiant heater 1 a according to FIGS. 4 and 5 has as the parboiling edge heater 9 a one in only one operation, i.e. only in a single-strand loop or bifilar external heating resistor made of particularly thin, heavy-duty resistance wire, i.e. of a resistance wire that is thinner and is more resilient than the heating resistor belonging to the partial power 11a. The radiant heater of this radiant heater 1a is therefore basically of two circuits, but the two heating circuits are connected in parallel or in series, which is why they are always switched on and off simultaneously.

As shown in FIG. 5, the inner shell 5a consists of two superimposed support bodies 20, 21 of different insulating materials and thicknesses, the lower, panel-shaped support body 20 consisting of a powdery pressed mass, being relatively pressure-elastic, a greater thickness than the molded body 21 lying thereon over the entire surface has and above all has a thermal insulation value that is significantly higher than that of the support body 21. In contrast, the, for example, disk-shaped support body 21 is a relatively dimensionally stable molded body made of compressed mineral fibers, on which the heating resistors are held by embedding in places. This support body 21 has at the top upwards about its remaining thickness projecting to the central axis of the radiant heater 1a approximately radial and integrally formed with the rest of the support body 21 webs. The webs lying only in the radially outer region of the heating field are each formed between depressions 23, which extend from the periphery of the heating field only over part of the turns of the heating resistors. The windings lying radially inside the depressions 23, that is to say in the central region, are therefore in direct contact with the inner shell 5a. In the area of the webs 22, which in addition to the parboiler edge heating 9a also detect three further turns of the heating resistor 8a, these turns are held by embedding exclusively on the webs 22, while, according to FIG. 5, they float freely in the area of the depressions, that is to say opposite span or bridge the inner shell 5a without contact or only lie weakly. The distance of the longitudinal sections of the heating resistors bridging the depressions parallel to their bottom surfaces from these bottom surfaces can be smaller than the outside diameter of these heating resistors, in particular about half as large, while the heating resistors are embedded in the webs 22 by about half their outside diameter. The distance between adjacent webs can be approximately twice their width.

As shown in FIGS. 6 and 7, in the upper support body 21b, instead of the recesses 23, openings or openings 23b which are continuous over the thickness of the support body 21b and which are at least partially filled by projections 24 of the lower support body 20b can be provided. In the exemplary embodiment shown, the projections 24 extend slightly above the upper sides of the webs 22b, but are provided with channel-shaped receiving grooves 25 in the region of each longitudinal section crossing them, the bottom surfaces of which may be slightly lower than the upper side of the webs 21b. The depth of the receiving grooves 25, relative to which the associated longitudinal sections of the heating resistors can be provided in a contact-free manner or only loosely lying embedded, is expediently so great that the adjacent receiving grooves 25 separating webs of the support body 21b only extend approximately to the middle of the outer diameter of these longitudinal sections. Due to the design described, the heat dissipation from the above-mentioned longitudinal sections of the radiant heaters lying between the webs 21b into the inner shell 5b is particularly low, so that these longitudinal sections very quickly come to a visible glow after being switched on from the cold state. The fact that the support body 20b is thickened by the projections 24 at least in some, grid-like zones beyond the underside of the support body 21b, results in excellent additional thermal insulation. But it could also be.

1, the control device 13 can be similar to that according to DE-OS 32 47 028 or that according to EP-A-O1 14 307 may be formed, to which reference is made for further details. The parboiler heating is in the same space as the rest of the jet heater 7, which is enclosed by the support 4 and the heating plate 2, and is not separated from it in a ring shape by an intermediate web of the support.

The invention results in a higher specific power in the outdoor area, which may be as high as it could not be expected from the heating resistor and / or the glass ceramic plate in continuous operation. Due to its mostly temporary effect and the higher power consumption in this area, especially during the parboiling phase, it does not trigger any harmful effects. In general, a higher specific power could also be provided outdoors. It mainly has an effect during the heating-up time, in that the outer heating conductor glows faster, so that the desired optical effects are triggered and heat transfer to the cooking vessel begins earlier. During the continued cooking phase, this power distribution, which is advantageously maintained without switching, hardly plays out, preferably at least not negatively, because then the total power e.g. is reduced by switching the total power on and off. It has been shown that a higher specific load on the edge area and in particular on the outer heating conductor winding does not play an important role in their service life, since these do not burn out even with some overload.

Claims (8)

1. Radiant heater unit (1) for heating a glass ceramic hotplate (2) with at least one cooking point and a support (4) for an electric radiant heater (7) having at least one radiant heating resistor (8), such as a heater coil, the radiant heater (7) extending from a circular periphery of a heating field (10) determining a fixed heating field magnitude over a central zone to an inner zone of the heating field (10), with the area of the radiant heater (7) associated with a partial power system at the periphery of the heating field (10) forming a marginal heating system (9) around an inner area associated with a further partial power system and the marginal heating system (9) being provided with a higher radiation density than that of the inner area, characterized in that control means for the initial cooking operation of the marginal heating system (9) are formed by a heat conducting connection between the radiant heater (7a) and the support (4a), in that the marginal heating system (9a) with a lower thermal conduction coupling than the inner area of the radiant heater (7a) is connected to the support (4a).
2. Radiant heater unit according to claim 1, characterized in that the marginal heating system (9a) has a smaller specific surface contact with the support (4a) than the inner area.
3. Radiant heater unit according to claims 1 or 2, characterized in that the longitudinal portions of at least the heating resistor of the marginal heating system (9a) are arranged in substantially freely suspended, contact-free manner with respect to the support (4a).
4. Radiant heater unit according to any of claims 1 to 3, characterized in that the longitudinal portions of at least the heating resistor of the marginal heating system (9b) are arranged, in particular in alternating manner, in regions of the support (4b) having different thermal conductivity characteristics.
5. Radiant heater unit according to one of the preceding claims, characterized in that the marginal heating system (9) and the inner part of the radiant heater (7) are formed by a single radiant heating resistor.
6. Radiant heater unit according to any of claims 1 to 4, characterized in that the marginal heating system (9a) is formed by a separate heating circuit, which in particular extends in single-strand or bifilar manner over approximately 360°.
7. Radiant heater unit according to one of the preceding claims, characterized in that a side of said support (4b) receiving said radiant heater is provided by two superimposed support bodies (20b, 21b), the lower one of which having a minor specific thermal conductivity and penetrating openings (23b) in the upper support body (21b) at least in the vicinity of the marginal heating system (9b).
8. Radiant heater unit according to claim 7, characterized in that the support (4a) has a thick-walled inner shell (5a) made from insulating material for receiving the radiant heater (7a) and a thin-walled outer shell (6a) as a reinforcement and that preferably the upper support body (21) is made from fibrous insulating material and/or the lower support body (20) is made from substantially pulverulent insulating material.

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