EP0585831B9 - Heater, especially for kitchen appliances - Google Patents

Abstract

Heating and/or bias resistors (10) are curved into an undulating shape from flat strip and are pressed into the base (7) of insulation (3) such that they are in consequence secured only against lifting off from the base (7), namely by friction. The respective resistor (10) has edge surfaces (14,15) which are continuous without any interruptions and without any steps. In consequence, an area-specific high power density can be achieved with a very simple construction. <IMAGE>

Description

The invention relates to a heater according to the preamble of claim 1. A heater, in particular for kitchen appliances, e.g. a radiant heater or other radiator for heating a hotplate, an oven muffle or other. Such radiators usually form a self-contained unit, which as such is then connected to the corresponding device, e.g. a hob, a muffle wall or the like is to be attached. A heating side of the radiator then forms the correspondingly large-area output for the thermal output of the radiator. Resistors, such as heating resistors, series resistors or similar components, can be provided in a plane which is approximately parallel or set back from the plane of the thermal output.

The respective resistor is expediently assigned insulation which can simultaneously form the only support for mechanically holding one or all of the resistors and expediently has a continuous surface area which is approximately in the order of magnitude of the thermal output, for which a particularly flat or only a few millimeters thick insulation is suitable. The insulation is primarily electrically insulating and can also be thermally insulating, but does not have to be impermeable to visible thermal radiation, for example infrared radiation, at least in the region of the intervention of the respective resistor. At least in these areas, the insulation can also be designed such that as much heat or at least the majority of it is dissipated from the engaging section of the resistor not only in the first phase of commissioning, but also in continuous operation, as from the non-engaging section.

On insulation that e.g. Resistance to lifting is relatively difficult to secure from a slurry poured into the form of mineral fiber, granules, binders or the like. It is then pressed into shape and then dried or hardened, while securing against lateral movements by engaging in depressions or between projections of the insulation is less difficult. Fastening elements can be used for securing against lifting, which can be formed in one piece with the resistor in the form of staples, adhesive spots or similar separate components or in the form of angled projections and are both connected to the resistor and engage in the insulation.

In the case of flat resistors in particular, such fastening members then form resistance-inactive components insofar as they do not contribute to the electrical resistance value, namely rather in the manner of blind branches of the current or only a significantly reduced flow through them compared to the sections with maximum flow density. These fasteners increase in the case of certain training the complexity and possibly not negligible the weight of the radiator and are essentially only heated by heat conduction or radiation from the resistive areas of the heating resistor, but not by your own resistance work. Round wire resistance coils, on the other hand, can be embedded tightly enclosed in the insulation with resistance-active fastening sections. This also applies to flat resistors, which are attached to the insulation at least partially lying or completely embedded between insulating layers, for example as a non-inherently stable evaporated layer. Compared to such resistors, flat resistors, whose resistance-active cross-sections are at least partially not parallel to the heating side or heating level, but instead inclined to right-angled, have significant advantages because they take up less space even with high resistance power transversely to their longitudinal direction and approximately parallel to the heating level and therefore in higher power density and can be better insulated against leakage currents. Securing against taking off, however, is more difficult and more complex for the reasons mentioned above.

DE-A-2 551 137 shows a support leg which is continuously flat until after it has been inserted into the base body and only then is angled around a zone parallel to the heating plane.

The US-A-600 057 shows for a flat resistor a support leg which is curved back and forth in the elastic range, so that it would return to its flat, elongated shape when relaxed.

The invention is further based on the object of creating a radiator with which disadvantages are known Training or disadvantages of the type described can be avoided. Preferably, a resistor with flat cross sections in the area or outside of these cross sections should be secured in a simple manner on the insulation, in particular against being lifted off, even if at least parts of the respective flat cross section lie transversely to the heating plane. Furthermore, thermal overloads of the insulation should possibly be avoided and / or as many conductive or metal elements that are electrically conductively connected to the resistor should be included in the electrical resistance work.

According to the features of claim 1 are provided.

Means are proposed by means of which the respective resistance is secured against lifting off through direct engagement connection of a resistance-active area with the insulation. The resistance expediently has in the region of this fastening section and / or subsequent to or in the longitudinal distance from this fastening section at least one elongated longitudinal section with full flat cross sections which are at least partially transverse to the heating plane.

If the resistor or the fastening section does not have any protruding protruding fastening element on the edge surface facing the core of the insulation or on the other edge surface and engages in the insulation in a manner similar to a blind branch, the respective fastening section or the resistor can have only resistance-active cross-sections over its entire one-part longitudinal extension. Furthermore, the overall height of the insulation, the resistance and the entire radiator can be reduced in particular if the longitudinal edge surface mentioned in essentially all of the longitudinal sections of the resistor lie essentially in a single plane. Or if there are no longitudinal sections of the resistor which are spaced apart and adjoin one another via an arc of curvature and which engage in the insulation to different depths or whose longitudinal direction is at an angle to one another. The central longitudinal axis of all fastening sections or all longitudinal sections can be provided in a single plane, through which the heating plane can be defined.

The heating resistor is also supported directly over the surface of the insulation to secure it against lateral movements parallel to the heating plane, its two side surfaces being able to bear closely against approximately parallel supporting surfaces of the insulation, essentially under all operating conditions, at approximately the same or different heights. In contrast to a support only in the area of a sharp edge of an edge surface and not also at a distance from this edge surface, very good lateral support is achieved as a result. The resistance can also be well secured against movements to the core of the insulation if it is supported on the insulation over at least half of its length or its entire length with the associated edge surface at least in one operating state. Is the respective mounting section spring back z. B. biased in that it engages curved approximately parallel to the heating level in the insulation, so an additional securing jamming against the insulation takes place by the expanding and / or narrowing spring force.

The respective fastening section or the entire resistor is formed by a flat wire or a flat strip, the respective longitudinal edge of which is approximately straight in the stretched, that is to say the longest, state and / or the lateral surfaces of which can also be free of any projections or openings. The material thickness of the flat cross section can be well below half a millimeter and, depending on the requirements, any integer multiple of a tenth of a millimeter or a hundredth of a millimeter, e.g. seven hundredths of a millimeter. The material width or height of the flat cross section is expediently several millimeters, in particular less than 5 mm, and, depending on the requirements in these areas, can be any integer multiple of a half and / or a millimeter, e.g. 3 mm. The greatest depth of engagement of this flat cross-section in the insulation is expediently at least a quarter of the material width or the width between the edge surfaces and at most a fraction more than this width, the depth of penetration being any integer multiple of half a millimeter and / or one millimeter, depending on the requirements can.

Irrespective of the features described, there is a very advantageous embodiment of the radiator if the insulation is at least partially designed as a light guide and / or on at least one surface as a light exit window within its cross sections and is thus connected to at least one light source. The light source can easily be the resistance emitting infrared radiation during operation, e.g. is arranged over a large area or approximately uniformly distributed over the insulation and its radiation then propagates over a large area within the insulation and also emerges to the heating side. As a result, the entire insulation can be used in whole or in part as a light plate, which can be recognized by the covering, translucent and / or transparent cover plate made of glass ceramic or the like as an indication of the operating state. By partially darkening and / or cross-sectional mixing with an opacifier, the light guide and / or the light exit function can be changed so that certain desired patterns are achieved. No opacifier can be provided in light-guiding areas or areas intended for the light exit, but rather by means of a translucent admixture, e.g. Quartz powder, or another grain can be replaced. The remaining components of the insulation are expediently light-colored to white and / or translucent in these areas.

Corresponding components have been added so that the insulation does not tend to sinter or brittle hardening, even under high operating temperatures, but remains elastic or elastic. As a result, the insulation remains reversibly deformable and / or resiliently elastic without tearing and can adapt to its own thermal expansions or to those of the resistance or fastening section.

Fig. 1

einen Ausschnitt eines erfindungsgemäßen Heizkörpers in perspektivischer Ansicht,

Fig. 2

einen Ausschnitt einer weiteren Ausführungsform in vergrößerter Darstellung,

Fig. 3

eine weitere Ausführungsform eines Heizkörpers im Schnitt.

These and further features emerge from the claims and also from the description and the drawings, the individual features being implemented individually or in groups in the form of sub-combinations in one embodiment of the invention and in other fields, and being advantageous and protectable per se Can represent designs for which protection is claimed here. Embodiments of the invention are shown in the drawings and are explained in more detail below. The drawings show:

Fig. 1

a section of a radiator according to the invention in a perspective view,

Fig. 2

a section of another embodiment in an enlarged view,

Fig. 3

another embodiment of a radiator in section.

The heater 1 has an essentially dimensionally stable, multi-part and cup-shaped base body 2, the cup opening of which essentially forms the thermal output. The largest material volume of the base body 2 forms an essentially two-part or three-part insulation 3 consisting of a supporting body 4 and an insulating body 5. The supporting body 4 has, in particular, electrically insulating properties and forms the essentially flat and / or smooth bowl bottom which is exposed for thermal output , The supporting body 4 is supported flat on an approximately plate-shaped insulating body 5, which has better thermal insulating properties than the supporting body 4 and can only rest on this in the edge and / or at least one ring area, so that a large-area free between the two bodies 4, 5 Gap gap exists. The mechanical strengths, such as compressive, bending, tensile and / or shear strength of the insulating body 5 can be lower than that of the supporting body 4, and both are arranged in a socket 6 made of material with a higher strength, e.g. in a sheet metal shell, which secures the insulation 3 axially and / or radially essentially without play.

Axially beyond the bottom 7 of the insulation 3 is a ring-shaped continuous edge 8 which forms the cup opening and is made of insulating material which, according to FIG. 1, is formed in one piece with the supporting body 4 and consists of an insulating material which corresponds to that of the supporting body 4 and / or the insulating body 5 is similar. This edge 8, the radial thickness of which is greater than the thickness of the supporting body 4, is closely surrounded by a jacket-shaped edge 9 of the holder 6, which here projects axially beyond the free end face of the edge 8, but does not bear directly against the cover plate in the installed state, eg by an insulating ring placed on the edge 8, which protrudes beyond the edge 9.

At the bottom 7 several elongated strand-like resistors 10 are attached so that they are parallel to movements against Floor 7 or to their longitudinal direction or against lifting movements transversely from the floor 7 are secured substantially free of play. The resistors 10, which are provided here as heating resistors lying at least partially freely within the cup space, can be arranged approximately parallel to the edge 8 in single or multiple spiral windings or spirals which are located one inside the other. The resistors 10 are preferably distributed substantially uniformly over a field which approximately adjoins the inner circumference of the edge 8 over the entire circumference and extends to the center of the base 7.

Each resistor 10 has exactly the same, approximately rectangular, flat cross-sections throughout its entire length in that it is made from a flat strip which is not cut or further processed to remove material components in order to produce the heating resistor.

Rather, the flat strip is only deformed in a bending manner. It has two side surfaces 12, 13 which are parallel in cross section and two very narrow edge surfaces 14, 15 connecting them, its thickness 29, for. B. about 0.07 mm and its largest cross-sectional width or width 28 z. B. can be about 3 mm. The respective band end of the resistor 10 can be formed directly and without additional intermediate elements as an electrical connection end 16 and can be brought into a position by bending or interleaving with the rest of the resistor 10, in which it is contact-free with respect to the insulation 3 and is particularly suitable for the electrical connection well suited.

A one-piece, continuous flat strip can also form two mutually adjacent, separately switchable resistors if they end at one end in one piece via a cross section and / or these individual resistors connecting cross section is integrally formed with a corresponding connection end.

The respective resistor 10 forms a fastening section 17 which is continuous over most of its length or its entire length by virtue of the fact that it is continuously in engagement with the support body 4 over this length in such a way that it is secured against movement in the directions mentioned is. For this purpose, an engagement section 18, which adjoins an edge surface 14 in the form of a strip, is continuously embedded in a correspondingly groove-shaped depression 19 of the supporting body 4. The flat cross section 11 continuously forms resistance-active cross sections between the two edge surfaces 14, 15, which is why the engagement section 18 is also resistant to the same extent as the sections of the flat cross section 11 projecting freely above the bottom 7.

The depth of engagement of the engaging portion 18 may e.g. about 2 mm or two thirds of the total width of the flat band. The two side surfaces 12, 13 can rest in the area of the respective common longitudinal section at different heights on the insulating material of the support body 4 or at the same height, depending on which radiation conditions or coupling effects are to be achieved. Depending on whether the respective spiral section is elastically prestressed in an area by widening or narrowing, it rests under spring tension with the inner or outer side surface 13 or 12.

The resistors 10 are located on the heating side 20 of the base 7 or the base body 2 facing the cup opening and determine, for example, with their edge surfaces 15 closer to the thermal output, a heating plane approximately parallel to the base 7 21. The radiator 1 has a central axis 22, perpendicular to this heating plane 21, about which the resistors 10 are curved. In addition to its large elastic curvature, each resistor 10 has a course which changes in its longitudinal direction, for example a sinusoidal curve, in that, in view of the heating plane 21, it is alternately provided with opposite, but essentially the same curvatures 23 and adjacent curvatures with their approximately straight or planar legs 24 merge into one another.

Correspondingly, the engagement section 18 and the groove-shaped recess 19 are curved permanently or intrinsically stiff, the legs 24 diverge from the respective curvature 23, expediently at an angle of more than 30 °, 60 ° or 90 °. As a result, thermal elongations of the resistor are transmitted to the support body 4 in a relatively unproblematic manner, namely mainly in the longitudinal direction of the depression 19. The fastening section can also be biased in the longitudinal direction by stretching and / or compressing the corrugation or the resistance 10 in individual partial or all longitudinal sections, so that it resiliently rests with tension on corresponding transverse flanks of one or both side surfaces of the recess 19. The two legs 24 of a wave arc can each form a correspondingly narrowed or widened pretensioned clamp, which rests with the prestress on the associated side surface of the recess 19. At least in the area of these side surfaces, the support body 4 is resiliently resilient under these tensioning forces, so that there is a very secure clawing of the resistor 10. In contrast, the compressive strength of the material of the resistor 10 is significantly higher.

The inner circumference 27 of the edge 8, which according to FIG. 3 can also form a component separate from the supporting body 4, practically limits the thermal output of the heating element 1 on the outer circumference. According to FIG. 3, the free end face 25 of the edge 8 projects a small amount beyond the end face of the edge 9, so that a radiation-permeable cover plate 26 made of glass ceramic or the like is prestressed with its flat back or underside under pressure on this end face 25 can concern. The measure of leadership, e.g. about the sheet thickness of the socket 6 can be so large that there is only a gap distance between the back of the cover plate 26 and the edge 9. If the end face 25 diverts to the heating plane 21 under the pressure or due to the aging of the edge 8, the edge 9 cannot thereby come into direct contact with the cover plate 26, but the gap distance can at most be reduced to a minimum of e.g. Reduce 1 mm or the like.

The heating plane 21 is set back at a distance from the end face 25 or the cover plate 26. However, the respective heating resistor or separate heating resistors can protrude freely to different degrees from the bottom 7 to the heating side 20, engage in the support body 4 at different depths, have different bandwidths and / or different strip thicknesses, as a result of which areas of the heating field with different power density or different sensitivity the heating effect and the glow can be created.

The corrugated resistance can be pressed into the dry prefabricated support body 4 without prior production of the recess 19. When pressed into the supporting body 4, the insulating material diverts in a compressive manner, after which it springs back or flows back against the engagement section 18, so that the resistance 10 then against lifting off from the floor 7 is secured very positively. The resistor 10 can be pressed in until its edge surface 14 or the fastening projections on the insulating body 5 and / or until the edge surface 14 stops on the support body 4.

All described configurations, components, units or spaces can only be provided once or in a plurality of two or more, e.g. to be able to switch several heating fields and / or heating circuits in different power levels.

Claims (15)

1. Radiant heater for heating a cooking point, which is to be positioned below a cover plate and is formed by at least one base member (2), which has a support body (5) made from insulating material, as well as several components (10, 17, 18), whereof at least two are interconnected to form a subassembly in an unassembled fitting state of the heater (1), one component being a resistor (10), which is formed from a flat strip, whose material thickness is below 0.5 mm and whose material width is below 5 mm, which has a prefabricated wavy path and is fixed with an engagement portion (18) connected in strip-like manner to an edge (14) by pressing into the dry, prefabricated support body (5).
2. Radiant heater according to claim 1, characterized in that the engagement portion (18) is free from resistance-inactive fastening members.
3. Radiant heater according to claim 1 or 2, characterized in that the resistor (10) has a maximum material thickness of approximately 0.1 mm and/or a maximum material width (28) of approximately 30 to 50 times the material thickness (29).
4. Radiant heater according to one of the preceding claims, characterized in that the resistor (10) engages in the support body forming an insulation (3) over a height which is at least approximately 20 to 30 times the material thickness (29).
5. Radiant heater according to one of the preceding claims, characterized in that the resistor (10) engages approximately uniformly in the support body (5) over a length which is between one tenth of its linear, stress-free, stretched operating length and its total operating length, the engagement portions (18) having a smaller cross-sectional height compared with the length thereof and the resistor (10) is secured exclusively by friction contact on at least one of its lateral faces (12, 13) against lifting transverse to the heating plane (21) and in its right-angled cross-sections to the heating plane (21) is free from bends and/or openings.
6. Radiant heater according to one of the preceding claims, characterized in that at least in the vicinity of the engagement portion (18) the support body (5) contains for its visible thermal radiation at least partly unfiltered, permeable and preferably substantially opacifier-free radiotransparent granular material or quartz resistant to the operating temperatures of the support device (17).
7. Radiant heater according to one of the preceding claims, characterized in that at least in the vicinity of the engagement portion (18) in the direction of the thermal expansion-caused shape changes of the component, the support body (5) is substantially temperature-neutral, resilient and in particular rebound elastic or unsinterable under the operating conditions.
8. Radiant heater according to one of the preceding claims, characterized in that the engagement portion (18) of the resistor (10) is resistance-active.
9. Radiant heater according to one of the preceding claims, characterized in that the wavy path of the resistor (10) forms a bent profiling resulting from permanent and non-resilient deformation of the starting material, but forms a resilient, stretchable compensating profile for stresses.
10. Radiant heater according to one of the preceding claims, characterized in that the engagement portion (18) is constructed in one piece with the resistor (10).
11. Radiant heater according to one of the preceding claims, characterized in that the engagement portion (18) forms a projection.
12. Radiant heater according to one of the preceding claims, characterized in that the engagement portion (18) has cross-sections, whose extension in two directions at right angles to one another is greater than the material thickness (29) of the starting material and in particular the profiling is curved in groove-like manner over the entire longitudinal extension and/or that the longitudinal extension of the particular support leg (18) exceeds the residual height of the member (10).
13. Radiant heater according to one of the preceding claims, characterized in that with its end apex (14) the engagement portion (18) forms a plug-in edge projecting at right angles to the operating length extension and is in particular plate-like.
14. Radiant heater according to one of the preceding claims, characterized in that the engagement portions (18) are substantially uniformly distributed over the heating field (20) or resistor (10).
15. Radiant heater according to one of the preceding claims, characterized in that two legs (24) of the engagement portion (18) of the resistor (20) form a clip engaging with pretension on a lateral face of a depression (19) formed by pressing into the support body (5).