EP0176063B1 - Radiative heating body for cooking apparatuses - Google Patents

Description

The invention relates to a radiant heater for cooking appliances with a glass ceramic plate, with electric bright radiator heating elements, which operate as intended at an elevated temperature above 1500 K (approx. 1200 degrees Celsius) and whose radiation spectrum extends considerably into the visible range.

Such radiant heaters are known for example from GB-PS 1 273 023. As a light source heating element, they have halogen lamps that emit their energy in the visible and infrared range and thus shine through a glass ceramic plate. Due to the low thermal mass, the heating-up times are quite short and the operator also has good control over the function due to the light emission. The light source is arranged there in the form of a circle. These light emitters are difficult to manufacture and regulate and have a short lifespan.

It is an object of the invention to provide radiant heaters that work with good controllability and economic costs with a good service life.

According to the invention, this object is achieved in that the straight light emitters are arranged in the form of a polygon in the edge region of the radiant heater.

The heating elements, referred to as light emitters, reach permissible maximum temperatures that exceed 2000K (approx. 1700 degrees Celsius). However, it may well be that the temperature is below the specified temperature limit in the down-regulated state. The use of halogen lamps in a straight rod shape with connections on both sides is particularly preferred. These light emitters can be produced economically and have good controllability and a long service life, particularly in the arrangement described.

Although the glass-ceramic plate is no longer heated as strongly when using light emitters, especially if it is made of a material that is well permeable to the specific radiation area, a temperature limitation should be provided for the glass-ceramic due to the risk of thermal damage. A rod-shaped temperature sensor can be used for this.

However, it is also quite possible to control the output of the radiant heater with a plurality of bright radiators via a multi-cycle circuit, preferably a seven-cycle circuit, in parallel, single and series connection of the radiators.

In order to provide a good optical glow plug with good thermal insulation. To provide the luminous image of the radiant heater in the cooking appliance, radiation shielding can be provided in the edge area. It can be formed by an annular insulating cover plate which, lying on the edge, is pressed onto the cooking surface and, because it preferably consists of a denser but temperature-resistant insulating material, has a relatively sharp cut. If it protrudes somewhat beyond the actual edge, which is made of highly insulating but less rigid material, then it alone determines the visual effect of the hob, and it is avoided that the cooking surface looks "frayed" due to a blurred interior boundary.

The radiation shielding can additionally or instead of the cover panel consist of a light-absorbing or reflecting layer on the connection ends of the light emitter. This prevents light from penetrating from the ends of the light emitter into the area of the cooking appliance outside the cooking zones and illuminating the glass ceramic plate in this area, usually unevenly, from below, which is visually disturbing and would also lead to undesired heating of the cooking appliance .

The radiation shielding can also be provided as a cover for a connection end of the light heater element, which can be part of the insulation and particularly preferably part of the cover panel. A combination of these measures is particularly preferred.

• Fig. 1 und 3 je einen vertikalen Teilschnitt durch eine Glaskeramikplatte mit darunter angeordnetem Strahlheizkörper, Fig. 2 und 4 eine schematische Draufsicht auf die Strahlheizkörper nach Fig. 1 und 3,
• Fig. 5 und 6 die Schaltung von jeweils vier in einem Strahlheizkörper vorgesehenen Heizelementen mittels eines üblichen, nicht dargestellten Siebentaktschalters in den sechs verschiedenen Leistungsstufen (a bis f),
• Fig. 7, 9, 10 und 12 vertikale Teilschnitte durch zwei Varianten eines Strahlheizkörpers nach der Erfindung und
• Fig. 8 und 11 Teildraufsichten auf diese Strahlheizkörper.

These and further features of preferred developments of the invention also emerge from the subclaims of the description and drawing, the individual features being able to be implemented individually or in groups in the form of subcombinations in one embodiment of the invention. Embodiments of the invention are shown in the drawing and are explained in more detail below. The drawing shows:

• 1 and 3 each a vertical partial section through a glass ceramic plate with a radiant heater arranged underneath, FIGS. 2 and 4 a schematic plan view of the radiant heater according to FIGS. 1 and 3,
• 5 and 6 the circuit of four heating elements provided in a radiant heater by means of a conventional seven-stroke switch, not shown, in the six different power levels (a to f),
• 7, 9, 10 and 12 vertical partial sections through two variants of a radiant heater according to the invention and
• 8 and 11 partial top views of these radiant heaters.

In the embodiments, the following elements are present: an insulation 13 is arranged in a flat sheet metal shell 12, onto which a ring 14 made of somewhat stronger insulating material than that of the layer 13, which bears against the underside of the glass ceramic plate, is placed in the edge region. The radiant heater 11 heats a standing cooking vessel through this glass ceramic plate 15. A temperature limiter 17 with a rod-shaped temperature sensor 18 protrudes over the heated area of the radiant heater and contains switches 19 in its switch head arranged outside the area of the shell 12, which supply the power to the radiant heater influence the body and possibly switch off partial heating elements.

In both embodiments, these elements are provided with the same reference symbols and are not described again.

In the embodiment according to FIGS. 1 and 2, light emitters 20 are present which are designed as straight halogen incandescent lamps which contain, for example, a tungsten filament which is contained in a quartz glass tube in a halogen atmosphere and is supported by intermediate webs. Such radiators are described in GB-PS 173 023, to which reference is made. Its filament works at temperatures in the order of 2400 K (2100 degrees Celsius) and, in addition to an infrared component, also generates a high proportion of visible light in the white area. The glass ceramic plate 15 is set up to at least partially let this spectral range pass, while a part of the heat is converted in the glass ceramic plate and is released from there to the cooking vessel 16 by contact etc. The light emitters 20 have connections 21 on both sides, which protrude beyond the edge 22 of the sheet metal shell 12 and are connected there with corresponding connecting lines. The ends of the four light emitters 20 protrude through the edge 14 and their radiant area is located inside the circular heated surface 23 of the radiant heater, which is formed in the bowl-shaped interior of the radiant heater.

1 and 2 show an embodiment in which four straight, rod-shaped light emitters 20 in the form of a square are arranged such that their radiating areas lie within the heated area 23 of the circular radiant heater. Adjacent light emitters are offset in height so that they cross each other in the area of the connection ends and are so easy to connect. However, they can also be arranged in one plane. The rectangular, preferably square, enclosed central region is designed as a dark radiator zone 27 and is zigzagged with conventional heating resistance coils. The dark radiators 25 consist of heating coils made of resistance wire, for example an iron / chrome / aluminum alloy, which is used up to temperatures of approximately 1500 K (1200 degrees Celsius). They are partially embedded in the surface of the insulating support 24 by the lower part of their turns being pressed into the insulating support at intervals from one another or also over the entire length before it hardens. But there are also other attachment options, for example using metal needles, putty or the like. conceivable. The light emitters form a light emitter heating zone 28 surrounding the dark emitter heating zone 27.

2 and 3, an arrangement is shown in which three straight rod-shaped light emitters 20 in the form of an equilateral triangle are arranged in a similar manner as in FIGS. 1 and 2. In the triangular central zone you enclosed, there may be a dark emitter heating zone 27 , in which a dark radiator heating element 25 is arranged in the form of a spiral from a resistance coil. Under the light emitters 20, a coating 59 made of titanium dioxide is applied to the insulating layer 13, which gives a good reflection of the radiation from the light emitters.

5 and 6 show two rows of a radiant heater design, each of which has four heating resistors and is switched by a known seven-cycle switch, not shown, which is connected to the radiant heater via four connecting lines. The letters a to f for the individual partial figures denote the switching stages from full power (a) to the lowest partial power (f). The design power of each heating resistor in watts is given in the partial figure a and the total power resulting from the circuit next to the figure. This is expressly referred to. The heating resistors in operation are identified by hatching, which is indicated by the hatching width if they are operated at a lower power by series connection.

6, a dark radiator 25 and three bright radiators 20 are provided in the exemplary embodiment. This arrangement can also be different. With full power (a), all are operated in parallel, while in stages b, c and d only three, two or one light source with its design power is in operation. At stage e, two light sources connected in parallel are connected in series with a light source, while in the lowest position f of this circuit e, the dark source 25 is also connected in series. The advantage here is that at least one light emitter is in operation in all positions and the operator can read the power level from the configuration and light intensity. In addition, a conventional seven-stroke switch can be used, as it is commercially available for other hot plates.

Figure 6 uses the same seven-stroke switch in the same switching stages, which can also be seen from the connection ends shown filled. The difference is that only two light emitters 20 and two partial resistors 34, 35 are used for the dark emitter 25. In addition, a diode 55 is provided, which is bridged by a switch 56 in the positions a to e. This circuit operates according to FIG. 5 with the difference that none of the light emitters, but only the conventional heating resistor 34, is switched on in the power stage d. Compared to FIG. 6, only one of the light emitters 20 has to be replaced by the resistor 34. In the lowest position f, the switch 56 is opened and the diode 55 halves the power again, so that the lowest level with 93 watts is only about 5 percent of the total installed power and a warming level is thus possible.

If it is not a question of using a commercially available seven-stroke switch, then with the configuration according to FIG. 6 with five independent connections to be created a version in which the diode is superfluous, because then by connecting all four emitters in series a very low power can be generated. The "dark" position d would also be omitted there. The alternative possibility to use dark emitters in addition to light emitters saves expensive light emitters and a further improved control option, but also ensures that the light appearance of the light emitters does not become too glaring and that, especially with clocked outputs, the power surges are somewhat dampened in their effect on the food to be cooked, which would otherwise be annoying due to the low heat replenishment with light emitters.

FIGS. 7 to 9 show a radiant heater 11 which is arranged below a cooking surface 15 made of glass ceramic. It heats the cooking surface 15 from below and thus forms a hotplate on which cooking vessels can be heated.

The radiant heater 11 contains an insulating support 24 which is bowl-shaped and lies in a sheet metal shell 12. On the edge 22 of the insulating support, which consists of a highly heat-resistant and relatively good insulating material, a cover panel 114 is arranged in the form of a ring made of a material that is denser and stronger than the insulating support 24, but also high-temperature resistant and insulating material, which has its inner edge 81 over the inner edge 80 of the edge 22 protrudes somewhat inwards. The upper face of the cover panel lies against the underside of the cooking surface 15 and is usually pressed against it by a spring force acting on the sheet metal shell 12.

Since a material with high thermal insulation capacity is normally used for the insulating support 24, but is not mechanically very high-strength, it could easily lead to minor crumbling in the area of the unprotected inner edge 80, particularly in the edge area, which is particularly stressed during manufacture and assembly Edge 22 come, which could lead to an optical image with a frayed edge deviating from the basic shape (in particular circular shape) of the cooking surface when using bright heater elements 20, which will be described below. This is prevented by the sharp edge boundary, in particular when the inner edge 81 projects inwards. The penetration of visible radiation through depressions formed in the soft edge and the consequent illumination of the area of the overall cooking appliance 100 lying outside the cooking surface is thereby also prevented. Furthermore, the cover 114 protects the edge of the insulating body from other mechanical influences.

In the exemplary embodiment, bright radiator heating elements 20 are provided, which can also be referred to as high-temperature radiant heaters and, as already described, consist of high-temperature heating filaments 83 enclosed in quartz pistons 82, which emit radiation far in the visible range and at temperatures well above 1500 K (approx. 1200 ° C) work. They are in the form of elongated rods or couches, which have a flattened section 84 at both ends, from which the connecting ends 21 protrude and are welded there to connecting lines.

Dark heater elements 25 can be arranged between the light emitters and in the circular section area formed between them and the edge 22 of the heated area 23 formed in the interior of the radiant heater. which consist of heating coils of conventional resistance materials used for radiant heaters, for example an iron / chrome / aluminum alloy, which are used up to temperatures of approx. 1500 K (1200 ° C) without encapsulation or protective gas atmosphere. These heating coils are arranged essentially spirally in a shape adapted to the shape of the respective dark radiator heating zone 27 and are partially embedded in the material of the insulating support, e.g. according to DE-PS 27 29 929 attached. Under the light radiator 20, the insulating support at a distance from the light radiator 20 can have the shape of a flat, arc-shaped groove 85 in order to achieve a targeted reflection of the radiation. The light emitters and dark emitters are switched on in parallel, in series or individually using selector switches, power or temperature controls or controls, the light emitters being switched on especially in the parboiling range or in the higher power range, because there they can best exploit their advantages of the relatively low-inertia rapid heating.

8 and 9 show that the ends of the light emitters 20 lie in edge recesses 86 which are adapted to the shape of the light emitter tube and narrow towards an outer opening 87 which are designed to receive the flattened connection end 84 of the light emitter. This flattened end is vertical therein, so that the light radiator is guided in the transverse and longitudinal directions in the edge recess 86, 87.

The edge recess is provided in FIGS. 7 to 9 in the edge 22 and is open at the top. The cover 81 covers the opening of the edge recess and shields it from the top, so that it is not visible from above. A part of the end sections 90 of the light radiator 20, which comprise the flattened section 84 and also an adjoining part of the untapered tube of the light radiator, partially protrude, with the flattened section 84, from the outer opening 87 and are electrically connected there. Through these flattened or flat-squeezed end sections 84, a relatively large amount of light emerges in the area 88 of the cooking appliance 100 lying outside the radiant heater and would increase the interior of the glass ceramic recess len. Since this is not only visually unattractive, but can also lead to inadmissible heating of the outer area 88 and to thermal damage to connecting lines or switching devices, the end section, and in particular the flattened section 84, is coated with a light-absorbing or reflecting layer 89 which in particular also covers the end faces 91 of the section 84. This layer could, for example, reflect inwards and outwards black for the radiation affected here and possibly consist of two layers arranged one above the other, for example a vapor-deposited metal layer and a layer of a highly heat-resistant lacquer applied above it, as is also used for coloring hotplates finds. At least the area that protrudes from the outer opening 87 into the space 88 should be covered with the layer 89, but other areas of the end section 90 can also be coated in order to protect the area of the edge recess 86, 87 from direct radiation as far as possible. As a very desirable side effect, the temperature in section 84 can thereby be lowered, which is very desirable because a critical point of halogen spotlights is the temperature at the pinch point through which the connection 21 is led to the outside. If this temperature rises too high, the tightness of the lamp could be jeopardized by oxidation processes at the lead-through point.

The embodiment according to FIGS. 10 to 12 is the same as that according to FIGS. 7 to 9 except for the following differences: The cover panel 114a consists of a relatively thick ring which has an almost square cross section. It too projects inwards with its inner edge 81 over the inner edge 80 of the edge 22 of the insulating support 24. However, the edge recesses for the two end sections of the light radiator 20 are each divided into two sections, of which the section 86a lies in the region of the insulating support 24, while the section 86b is arranged in the region of the cover panel 114a. The same, essentially central division into two applies to the outer opening 87 for the flattened section 84, so that the light radiator 20 is securely fixed by placing the cover panel 114a on the edge 22. Here too, the flattened section 84 protrudes from the outer opening 87 with most of its length. In this area there is a cover 92, which is formed as a projection on the cover panel 114 and partially surrounds the end section at a good distance upwards, on both sides and in the area of the end face. The shielding of the end face 91 is particularly important because the radiation exits there particularly intensively, as from a light guide. In the example shown, the edges 93 of the cover 92 surrounding the end section 84 extend to the lower level of the cover panel 114a and thus to the central plane of the light radiator. However, this division plane can also be set further up or preferably down with respect to the light emitter, in order to be able to encompass the end section 90 even further with the edge 93. The distance at which the end of the light emitter is surrounded is important, so that heat can be dissipated from there and overheating of the end is prevented. A combination of the two embodiments with the cover 92 and the layer 89 is particularly preferred.

In the manufacture of the cover panel with cover 92, care should be taken that in particular the cover 92 is largely opaque, which can be done on the one hand by a special compression of the material, for example a ceramic fiber made of aluminum dioxide, which is known under the trade name Fiberfrax appropriate opaque coating or both. Since the opacity is also desired for the cover panel, this purpose can also be achieved by appropriate coloring or choice of an absorbent binder. The material of the cover plate should be hardened by mineral binders in order to obtain the exact edge on the inner edge that determines the optical edge of the cooking surface. Due to the arrangement, in which only the flattened end section protrudes through the outer opening 87, a large part of the emerging light is already shielded in the area of the edge recess 86. However, it would also be possible to have the entire flattened section 84 protrude, although its inclusion in the edge recess enables the halogen lamp to be guided securely, also against rotation, which is important, for example, if the light emitter itself has a reflective layer on it Has the outside or inside of its piston 82. Above all, it is also advantageous that complex end bases can be avoided by the arrangement according to the invention. Because of the radiation conditions from the light emitter end sections 90, the edge 93 of the cover 92 is particularly important because it retains the majority of the undesired radiation. It would also be possible to form the cover from the material of the insulating support 24, if one provides for an appropriate compression and opacity with adequate ventilation of the end. It would also be possible to provide cover parts on the ring and insulating support which differ, for example, in the size of their edge so that they overlap in height, but leave a sufficient gap between them for ventilation. This would form a labyrinth-like cover that practically does not let light escape. In practice, for example, a cover of the basic shape of the cover 92 shown in FIG. 11 could be provided on the insulating support, while the cover provided on the cover panel 114a is in particular made larger with its edge and overlaps the cover provided underneath.

Claims (10)

1. Radiant heater for cookers with a cooking surface in particular constructed as a glass ceramic plate (15) and having electric heating radiator heating elements (20), which operate at high temperatures above 1500 K (approx. 1200°C) and whose radiation spectrum extends well into the visible range, characterized in that the straight light radiators (20) are arranged in the form of a polygon in the marginal area of the radiant heater (11

2. Radiant heater according to claim 1, characterized in that the three light radiators (20) are arranged in the form of a substantially equilateral triangle.

3. Radiant heater according to one of the preceding claims, characterized in that the light radiators (20) are halogen lamps in rod form with connections (21) on both sides.

4. Radiant heater according to one of the preceding claims, characterized in that the end regions of the light radiators (20) are at least partly covered with respect to the cooking surface (15).

5. Radiant heater according to claim 4, characterized in that the covering is formed by a border (14) of an insulation (13) of the radiant heater (11).

6. Radiant heater according to one of the preceding claims, characterized in that the radiation- emitting area of the light radiators (20) is located within the rim (14) and advantageously the radiant heater has a circular basic shape.

7. Radiant heater, particularly according to one of the preceding claims, characterized by a radiation shield (89, 92, 93, 114, 114a) in the marginal area of the radiant heater (11).

8. Radiant heater according to claim 7, characterized in that the radiation shield (89, 92, 93) shields the end portions of the light radiator (20) against the area of the cooker (100) located outside the radiant heater (11) and advantageously the rim (22) of an insulator (24) of the radiant heater (11) is covered by a radiation shield preferably constructed as a substantially circular insulating cover member (114, 114a) and which faces the cooking surface (15), the cover member (114, 114a) more particularly comprising an insulating material with a higher strength and possibility density than the underlying insulator (24) and which is preferably made from a high temperature-resistant, thermal insulating material provided with mineral binders and advantageously projects inwards at its preferably sharply defined inner circumference (81) over the corresponding inner circumference (80) of rim (22) of insulator (24) and in particular has a relatively small height compared with the ring width.

9. Radiant heater according to one of the preceding claims, characterized in that the at least one end portion of the light radiator heating element (20) located in the marginal recess is provided with a light-absorbing and/or reflecting layer (89) forming a radiation shield and in particular the end face (91) of the light radiator is substantially covered by the layer and/or the at least one end portion (90) of the light radiator heating element (20) is surrounded by a covering (92) forming a heat shield and connected to the marginal recess (86, 87) in the upwards direction, as well as at least in part laterally and in the vicinity of the end face (91) of end portion (90) and preferably the covering (92) is part of the thermal insulation (24, 114, 114a) of the radiant heater (11) and preferably on the cover member (114a) are provided at least parts of the covering (92) and the cover member (114a) can contain at least part of the marginal recess (86b) and the covering (92) facing the cooking surface (15) and optionally also covering part of the end portion (90) of the light radiator heating element (20) preferably has an all round rim (93) and is open to the bottom.

10. Radiant heater according to one of the preceding claims, characterized in that the marginal recess (86, 87) is provided in a rim (22) of an insulator (24) and is preferably open to the top, preferably the covering (92) at least partly spacedly surrounds the portion (84) of the light radiator heating element located therein and in particular a cross-sectionally reduced and in particular flattened portion (84) at the end of the light radiator heating element (20) projects through a matching slot-like outer opening (87) of marginal recess (86).

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