EP0714223B1 - Radiant heater - Google Patents

Abstract

The appts. includes a basic heating zone (21) which, in operation, is continually heated. It also has at least one additional heating zone (22) which can be switched on as required. The additional zone (22) is adapted to form an extension of the basic zone (21) providing a larger total heating surface (23). The heating zones (21, 22) are provided in a carrier with an insulator (13) on which heat conductors (18) are arranged. The insulator surrounds the total heating surface (23) in the form of an insulating outer edge (15). The basic zone and the additional zone (21, 22), when combined, have a greater total power than the basic heating zone (21) alone. A temperature limiter (30) has a temperature probe (36) which extends over the basic zone (21). The flat basic and additional zones (21, 22) are arranged such that they provide overlapping radiation. When combined, the basic and additional zones preferably are connected in parallel. The boundary (19) of the total heating surface (21, 22) is formed by a rib whose height is at most half, but preferably not less than an quarter of the distance between the surface of the insulator (13) and the underside of the cooking surface (16).

Description

APPLICATION AREA AND PRIOR ART

The invention relates to a radiant heater for stoves, including cooktops or other cooking facilities are, with a flat, plate-shaped cooking surface, e.g. a glass ceramic cooktop. The radiant heater has a heated basic heating zone during operation and at least an optional switch-on heating zone, which for Creation of a larger total heating zone of the basic heating zone is formally adapted. Such radiant heaters are commonly referred to as a two-circuit radiator. The heating zones are provided in a support with insulation, are arranged on the heating conductor. The total heating zone is surrounded by a thermally insulating outer edge. Base- and auxiliary heating zone have a when interconnected greater total output than the basic heating zone alone. On Temperature limiter protrudes with an essentially rod-shaped one Sensor over at least one of the heating zones. GB-A-2 087 698 discloses a radiant heater according to the preamble of claim 1.

DE 27 29 930 A describes a radiant heater, in which several troughs in a larger insulating body with heating conductors arranged therein are provided. The later, revoked DE 30 04 187 C describes one Radiant radiators with an auxiliary heating zone by a basic heating zone through an insulating partition is thermally completely delimited.

EP 0 103 741 B also describes a radiant heater two concentric heating zones, from which the middle is intended as a parboil. she will turned on for parboiling alone and has one essential greater output than the radiator in continued cooking, if both zones are connected in series.

With all dual-circuit radiators, it was previously considered essential an insulating, thermal between the two heating zones provide as tight a partition as possible, which ensures that the basic heating zone clearly and thermally limited Has outer edge.

TASK AND SOLUTION

The object of the invention is to provide a radiant heater improved thermal uniformity of the heating zones create.

This object is achieved in that both heating zones delimited from one another in terms of area are arranged radially overlapping.

This delimitation of both heating zones from each other can e.g. by be a rib, the height of which is at most half the distance between the insulation and the cooking surface. You could but also through a more or less wide demarcation zone be formed without any particular increase in insulation. This measure will make the base heating zone, which is mostly on the inside not clearly delimited in the direction of the auxiliary heating zone, but gets a relatively soft thermal Crossing. Above all, however, a cold zone in the area of the so far reaching up to or shortly before the glass ceramic plate Avoid webs.

After the development of the two-circuit radiators clear separation by an insulating partition wall is essential was held, especially with regard to the Efficiency when operating the basic heating zone alone, it is astonishing that these disadvantages do not occur and themselves even give benefits.

If the basic heating zone is operated alone and a very small cooking vessel is used, then there are some Loss of efficiency due to blasting or convective drainage in the auxiliary heating zone. In-depth investigations have shown, however, that these losses can be neglected are when you look at normal cooking practice. Already that Switch-on times of the smaller basic heating zone alone are in the Very low compared to the operating times of the entire heating zone. If you then take into account how few cases in practice the cooking vessels are actually so small that they cannot use the co-heated edge area, so is the practical impact of the theoretical reduction in efficiency to neglect.

This is counteracted by uniform heating and avoidance cold places the heat transfer to the cooking vessel improved when operating the entire heating zone. The cold ring zone with earlier dual-circuit radiators with an intermediate web exactly at the point where the usually hollow ones The bottom of the saucepan has the best thermal contact with the hotplate, namely on its edge. In contrast, the invention also this area is evenly heated, which is the heat transfer improved and also on the thermal load of the Cookware has a positive effect.

Also due to the lower insulating body mass and the heat flow In the area of the intermediate margin, the parboiling values are also shown (Efficiency) of the entire radiant heater improved. This is partly due to the fact that the partition between the two heating zones made of a mechanically stronger insulating material had to be, the larger mass and smaller has thermal insulating properties than that in the field of Heat conductor used, now continuously formed insulation surface. The total heating zone can therefore be switched on the auxiliary heating zone continuously and essentially without gaps be heated.

Such two-circuit radiant heaters are available in different Surface arrangements of their heating zones made. There are those e.g. a circular base heating zone and one-sided or have additional heating zones attached on both sides, to create an elongated total heating zone. Frequently but the two heating zones are also concentric with each other arranged, with the basic heating zone occupying the center. In the latter case in particular, a rod-shaped temperature sensor protrudes a temperature limiter at least on one side across both heating zones. Because the temperature limiter serves to prevent the glass ceramic plate from overheating To protect, care must be taken to ensure that both when operating the basic heating zone alone as well as during operation the overall heating zone without sacrificing performance by switching off at too low a temperature.

A temperature limiter is already known from EP 0 141 923 B2 has become known, the sensor is so compensated that the Basic heating zone alone determines the sensor effect. To this The purpose of the sensor is in the area of the auxiliary heating zone. the thermal expansion differences ineffective by for an expansion sleeve and the rod materials inside it same or slightly higher expansion coefficients be used.

In the arrangement of radiation overlapping each other Heating zones, it is advantageous if special measures are taken to complete this compensation. Due to the smooth transition from the basic heating zone to the auxiliary heating zone the temperature sensor is now larger Section heated and provides as that of the pure basic heating zone for an early shutdown. This can be compensated i.e. mutual coordination of the stretch materials on the sensor or by shielding or additional Heating of the sensor can be counteracted. The shift path, to open the contact of the temperature limiter, yes both operating states (single and dual circuit operation) as be viewed constantly. The sections of the route of the sensor are not in relation to the respective one Heat application. To compensate for this, now not only compensated for zero amount, but by means of of an inner rod with slightly higher expansion slightly overcompensated. Here are the masses of the casing tube and inner rod taken into account with regard to the expansion path. This Overcompensation causes a switch-off delay. This is already at the due to the flowing radiation transition Operation of only the basic heating zone effective. As a result, must the same single-circuit radiator (without connection zone) the cold adjustment is lowered (smaller switching path = earlier shutdown). If the additional heating zone is now switched on, is also the contribution of the switch-off delay the direct application of heat increases and the switch-off point is raised to the normal level. In the operation of the basic heater or basic heating zone plus additional heating zone almost the same switch-off values achieved. Another measure creation can replace and / or complement this one not to the same extent as the rest of the area with heating conductors occupied zone under the temperature sensor.

An embodiment in which the heating conductor is particularly advantageous are thin corrugated ribbons, preferably with the Corrugated spade-shaped feet in the insulation are embedded. This makes it possible without any special Fasteners such as brackets or the like. Very quickly glowing radiator immediately in a highly effective To attach insulation, for example made of pressed Silicic acid gel exists, which are made pyrolytically can. The advantages brought about by the invention have an effect with such highly effective insulation and quickly glowing Radiant radiators especially.

These and other features go beyond the claims also from the description and the drawings, wherein the individual characteristics individually or in groups in the form of sub-combinations in one embodiment of the invention and in other fields and advantageous as well as protective designs can represent, for which protection is claimed here.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1

eine schematische Draufsicht auf einen Strahlungsheizkörper,

Fig. 2

einen diametralen Schnitt nach der Linie II in Fig. 1,

Fig. 3

eine schematische Draufsicht auf einen weiteren Strahlungsheizkörper und

Fig. 4

einen Schnitt nach der Linie IV in Fig. 3.

Embodiments of the invention are shown in the drawings and are explained in more detail below. The drawings show:

Fig. 1

1 shows a schematic top view of a radiant heater,

Fig. 2

2 shows a diametrical section along line II in FIG. 1,

Fig. 3

a schematic plan view of a further radiant heater and

Fig. 4

a section along the line IV in Fig. 3rd

DETAILED DESCRIPTION OF THE EMBODIMENTS

1 and 2 show an electric radiant heater 11, which is arranged below a glass ceramic cooktop 16 and to this by means of spring means, not shown is pressed down below. It lies at the bottom of the Cooking surface 16 with an edge made of insulating material 15 on.

The radiant heater 11 contains in a flat bowl-shaped Sheet metal shell 12 an insulation 13, which is made of a generally plate-shaped body 14 and the edge 15 is composed.

The molded insulation body consists of a heat-resistant, thermally excellent insulating compressed bulk material from fumed silica. On a slightly raised edge 17 lies the outer edge 15 of the insulation 13, which consists of a Ring made of mechanically stronger insulating material, for example a pressed mineral fiber mass. The higher strength is necessary because this edge is due to its attachment the underside of the glass ceramic hob 16 also mechanically is claimed. The inner surface 50 of the edge 15 can be optical be dark, e.g. by a coating or equivalent Treatment. This could not be more visible in the area Infrared radiation reflective and only in the wavelength range visible light and absorb it as a longer wave Radiate infrared again. The edge of the tin bowl 12 does not reach up to the glass ceramic plate 16.

The molded body 14 contains two flat, horizontal surface areas, which are provided with heating conductors 18. Between them is a delimitation 19 in the form of a circumferential projection or web provided that is as high as the edge 17 of the Insulation molded body 14 is sufficient, but overall over the Surface 20 of the molded insulating body or the heating in heated area no more than half of the total distance between this surface 20 and the bottom of the Glass ceramic plate 16 protrudes upwards. Its height can be beneficial between a quarter and a half of the distance mentioned be.

The delimitation 19 delimits, as can be seen from FIG. 1 central base heating zone 21 of a ring surrounding this Switch-on heating zone 22 from. Both are represented by a switch manually operated switch so that either only the basic heating zone or the basic and additional heating zone are switched on together. This will in the illustrated concentric arrangement of both heating zones 21, 22 heating surfaces of different diameters created, however, both are essentially the same power density have and are intended to be like each independent heating zone operated and regulated or controlled become. The control is usually done via a clocked circuit breaker, which is either only the basic heating zone 21 or the total heating zone 23, which from the heating conductors 18 connected in parallel in both heating zones is.

The heating conductors consist of a thin corrugated band Heating conductor material and are free-radiating, i.e. without any Sheathing or shielding against the atmosphere the surface 20 of the molded insulating body 15. They have projections pointing downwards at intervals from one another or feet that are in the material of the molded body 15 penetration. These feet are at least partially in the area the wave curvature arranged and according to the corrugation bent so that they have an arched spade shape that despite the small thickness and rigidity of the heating conductor material in penetrate the surface 20 and can fix it. The heating conductor tape is otherwise perpendicular from the surface in front. Due to the relatively large surface and small Mass of the heating conductor material together with the good radiation conditions can at a given surface temperature the heating time of the heating conductors can be shortened very much and in of the order of three seconds. This heating conductor arrangement is described in detail in DE 93 13 218 U, to which reference is made here by reference in the disclosure of the present application is incorporated.

Connection and arrangement of the heating conductor 18 are as follows: The Heating conductors of the auxiliary heating zone 22 run from a connecting lug 24 of a connecting block 25 to a turning point 26 on one of the main axes 27 of the circular radiator, reverse there by 180 ° and run over half a degree Circumference back until it is on the other side of this The main axis in turn reach a turning point. After five to each other The heating conductor crosses parallel semicircular paths 18 the main axis to on the other side (in Fig. 1 below) also lay five parallel tracks. Then he is with a contact 28 connected to the switch head 29 a Temperature limiter 30 belongs. The heating conductor runs from there on a path 31 parallel to the axis 27 to innermost heating conductor 32, which has a central projection 33 of the Insulating molded body 14 surrounds. In the basic heating zone 21 are the loop-shaped turns are placed so that they almost the embrace the entire circumference before turning around at turning points 26. There they leave an area around axis 27 one side of the basic heating zone largely free of heating conductors. However, the heating conductor track 31 runs in this area parallel to axis 27.

The outer turn adjacent to the delimitation 19 Heating conductor 18 runs parallel to axis 27 and the heating conductor track 31 over the auxiliary heating zone 22 and from there parallel to the outer edge 15 to a second contact tab 34 of the connecting block 25. The connections are therefore in the area the outer edge 15 or the molded body edge 17 is provided and the heating conductors are led directly to them. If it it is not desirable that e.g. in the area of the heating conductor 31 heat is generated, the heating conductor could run out there thicker or better conductive material or without Be formed corrugation. The delimitation rib 19 has in the area the axis 27 on the switch head 29 facing Side an exit gate 35 to pass through the heating conductor to let.

The temperature limiter 30 has a rod-shaped sensor 36, that of the switch head along axis 27 via the auxiliary heating zone and the basic heating zone protrudes. It ends in the area the demarcation 19 before entering the auxiliary heating zone for the second time would cross. In the area of the auxiliary heating zone 22 and in the area of the base heating zone 21 near the switch head it runs between the respective turning points 26 in one, apart from the parallel heating conductor tracks 31, heating conductors free areas 37, 38.

The temperature limiter consists of a metallic sensor tube, e.g. stainless steel, which is a larger specific Thermal expansion has as a rod 39 therein, e.g. made of ceramic (steatite) or the like. The differences in elongation between these materials cause two to operate contacts housed in switch head 29, one of which the actual temperature limiter contact is that at a Temperature in the order of 600 ° to 700 ° Celsius the underside of the glass ceramic hob 16 the heating switches off to avoid damage to the glass ceramic. On further contact is at much lower temperatures (below 100 ° Celsius) set to over a signal lamp or the like. To indicate the hot state of the hotplate.

The sensor is at a distance from the surface 20 of the molded insulating body and the heating conductors. He is lying on the Center projection 33, and preferably under one certain preload, so that he thereby his exact location to Heating as fixed to the glass ceramic and on the other hand the middle region of the molded insulating body is also held down by it becomes. At the end of the sensor 16 there is one Adjustment by a screw or a fixed point Pin 40, the pressure connection between the expansion sleeve and Manufactures inner rod 39.

To ensure that the glass ceramic plate 16 in all Operating conditions of the radiant heater to the same extent is protected against temperature, but also reached the maximum possible damage-free temperature that has a sufficient energy throughput through the Ensures glass ceramic plate, the temperature sensor is like this compensates that it is essentially in the area of the basic heating zone 21 is temperature sensitive. For this purpose is the ceramic rod 39, which as a standard of comparison against the expanding Outer sleeve 41 is used on the area of the basic heating zone 21 limited. It ends at a point 42 that approximately over the boundary 19, possibly a little towards the auxiliary heating zone offset, is to avoid that in the edge area of the Base heating zone slightly less due to radiation to the side Temperature level a shutdown when operating the basic heating zone alone at a higher temperature than at Operation of both heating zones together. At this end point 42 of the Ceramic rod 39 is followed by an inner rod 43 which a material that is related to the sleeve material the thermal expansion corresponds under the given circumstances and preferably slightly higher thermal expansion behavior has, for example, a stainless steel rod. This transmits the result of the relative expansion Movement to the switches located in the switch head 29.

This compensation can therefore be counter or over compensation cause rod 43 to expand, than the corresponding section of the sleeve. Through the The fact that the heating conductor 31 in the area of the sensor can also run across the auxiliary heating zone achieved that the conditions for the temperature sensor when alone as with interconnection are similar. That too partial suspension of the heating of the auxiliary heating zone in the Area 38 which the temperature sensor crosses can do this contribute. It would also be possible e.g. through breakthroughs in Outer tube 41 the effectiveness of the counter-compensation section 43 to accelerate.

From Fig. 2 it can be seen that the molded insulating body 14 on its underside has recesses that the projections on correspond approximately to the opposite side. This will not only help ensuring the most uniform density possible, but also a cheap stacking option at Shipping and storage of the preformed insulating body 14 created.

3 and 4 corresponds to that previously described in every detail with the only difference that the delimitation 19 is not by an upward directed projection is formed, but by a more or less wide, flat, unheated zone or a largely smooth transition between the two heating zones 21, 22, i.e. possibly also without an unheated intermediate area. The based 1 and 2 description applies otherwise also for this version.

FUNCTION

The radiant heater 11 works as follows:

The user chooses the radiator size, e.g. through a Adjustment knob, in front, according to the size of a Cooking vessel 44, which stands on the glass ceramic plate 16 and provides the desired one, if necessary using the same setting element Power (relative duty cycle) on the clocking power control device on.

As always with cooking processes, the cooking vessel should be slightly larger than the actual heating zone. Here comes the for the heat transfer most important area 45 in the area of The outer circumference of the cooking vessel is usually approximately above the boundary 19 to stand. When the middle basic heating zone is switched on is, the heating conductor 18 glows very quickly and irradiates and through the underside of the glass ceramic plate through the cooking vessel 44. Although the glass ceramic plate a certain permeability for the radiation that occurs has, however, a part is also in the glass ceramic plate in Heat implemented as contact heat in the cooking vessel 44th penetrates. It can now be seen that in the explanations 1 to 4 in the area of delimitation 19 none cold zone occurs on the glass ceramic plate 16, which otherwise especially in the area 45, where due to the usual negatively convex shape of the cooking vessel the best heat transfer would be expected.

As a result of the optically dark inner surface 50 of the edge 15 avoided that a glowing ring by reflection at the edge shimmering through the plate 16 and another heating surface limitation mirrors.

Now the additional heating zone 22 is switched on and a corresponding larger cooking vessel 44a (dash-dotted lines) put on, so the entire enclosed by the outer edge 15 Total heating zone 23 without gaps and without "cold spots" heated.

When the base heating zone 21 is operated alone, it is above this Base heating zone lying part of the temperature sensor heated. in the Area of low relative thermal expansion Rod 39 affects the greater elongation of the outer sleeve 21 of the temperature sensor 36 in a corresponding expansion difference off, so that at the set limit temperature the heating is switched off.

When the activation heating zone 22 is switched on, this changes not because the corresponding area protrudes beyond it of the temperature sensor remains practically ineffective. As a result of the concentrated over the central part of the base heating zone 21 temperature sensitive area (displacement the separation 42 from the boundary 19 towards the center) there is also a smooth transition in the area of demarcation for this not distracting. It could also be a shorter advantage Sensor are used, which also ends with the Adjustment 40 still distance from the boundary 19 to the center of the radiant heater. Also an extension which is usually made of a stainless steel pin Adjustment bolt would have the same compensation effect like the displacement of the interface 42.

An advantage of the invention is that the temperature limit due to the soft transition less sensitive to the Power distribution is basic / additional heating zone. Sensor for the pot detection, i.e. one from setting up a cooking vessel 44 switch-on and switch-off device dependent on the hotplate, could be arranged on protrusions in the delimitation zone be without the thermally balanced total heating surface to interrupt.

Claims (16)

1. Radiant heater for cookers with a planar, platelike cooking surface, such as a glass ceramic cooking surface, comprising a basic heating zone (21), which is always heated in operation of the cooker and at least one additional heating zone (22), which can be connected additionally as desired, and which for creating a larger total heating zone (23) is shape adapted to the basic heating zone (21), the heating zones (21, 22) being provided in a support having an insulation (13), on which heating conductors (18) being located, and which insulation surrounds the total heating zone (23) in the form of an insulating outer rim (15), the basic and the additional heating zones (21, 22) having in connection with each other a higher total power than the basic heating zone (21) alone, further comprising a thermal cutout (30), whose preferably rod-like temperature sensor (36) projects over at least part of the basic heating zone (21), characterized in that the basic and the additional heating zone each covering a separate surface area are in overlapping arrangement one to the other in relation to radiation.
2. Radiant heater according to claim 1, characterized in that the basic and the additional heating zones (21, 22) are connected in parallel connection with each other.
3. Radiant heater according to claim 1 or 2, characterized in that the boundary (19) of both heating zones (21, 22) is formed by a rib, whose height at most takes up 1/2 the spacing and preferably no less than 1/4 of the spacing between the surface (20) of the insulation (13) and the underside of the cooking surface (16).
4. Radiant heater according to claim 1 or 2, characterized in that the boundary (19) is comprised of a boundary zone of the insulating surface (20) free from heating conductors (18).
5. Radiant heater according to any of the preceding claims, characterized in that the sensor (36) of the thermal cutout (30) at least partly projects over and beyond both heating zones (21, 22) and in the vicinity of the additional heating zone (22) is compensated by reducing, disconnecting or reversing its temperature activity.
6. Radiant heater according to claim 5, characterized in that the temperature sensor comprises a thermally expanding, metal sleeve (41) and at least one inner rod (39, 43), which in the temperature-active area (39) is made from a material with a limited thermal expansion, such as ceramic, and in the compensated area (43) is formed from a material with a similar, but preferably somewhat higher thermal expansion than the material of the sleeve (41).
7. Radiant heater according to claim 6, characterized in that the sleeve (41) has means for improving or accelerating a heat transfer to the compensated area, preferably openings in the sleeve (41).
8. Radiant heater according to any of the preceding claims, characterized in that the heating conductors of both heating zones (21, 22) have connections, which project from the outer rim (15) into the total heating zone (23) and are directly connected there to the heating conductors (18).
9. Radiant heater according to any of the preceding claims, characterized in that the additional heating zone (22) surrounds the basic heating zone (21) in ring-like manner.
10. Radiant heater according to any of the preceding claims, characterized in that at least one heating conductor (18) of the basic heating zone (21) passes from the outer rim (15), over the additional heating zone (22) and substantially under the sensor (36) of the thermal cutout (30).
11. Radiant heater according to any of the preceding claims, characterized in that in the basic heating zone (21) is formed an unheated or less heated area (37), over which extends the temperature sensor (36) of the thermal cutout (30), preferably by heating conductors (18) adjacent to this area (37) having 180° turning points (26).
12. Radiant heater according to any of the preceding claims, characterized in that in the additional heating zone (22) is formed an area (38) which is unheated or less heated by the heating conductors (18) of the additional heating zone (22), and over which extends the temperature sensor (36) of the thermal cutout (30), preferably by heating conductors (18) adjacent to this area (38) having 180° turning points (26).
13. Radiant heater according to any of the preceding claims, characterized in that the heating conductors (18) are thin, corrugated strips, which comprise spade-shaped feet preferably accommodated to the corrugation and embedded in the insulation (13).
14. Radiant heater according to any of the preceding claims, characterized in that the temperature sensor (36) projects in diametral manner over the radiant heater (11) and preferably ends after partly traversing the basic heating zone (21) before passing beyond the boundary for the second traversing of the additional heating zone (22), in particular shortly after traversing a projection (33) projecting out of the insulation (13) and on which rests the temperature sensor (36).
15. Radiant heater according to any of the preceding claims, characterized in that the overlapping in relation to radiation of the basic and the additional heating zones (21, 22) uniformly projects over the entire boundary between the heating zones and/or the total heating zone (23) is free from areas which are covered against radiation.
16. Radiant heater according to any of the preceding claims, characterized in that the inner face (50) of the outer rim (15) is provided with a dark surface, preferably formed by a visible light absorbing coating or treatment.

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