EP0490289B1 - Electric heater particularly radiant heater - Google Patents

Abstract

The rim of an electric radiant heater is formed by a multilayer body (13). It can have the cross-sectional shape of a U, whose interior is filled with a good insulating material. In the interior (23) is placed a sensor coil (23) for a pot detection system, where it is well shielded against heat and mechanical influences.

Description

The invention relates to an electric radiator, in particular a radiant heater, with thermal lateral boundary insulation.

The unpublished EP 0 442 275 A2 (corresponding to USA patent application 650 489 of February 5, 1991) discloses a radiant heater in the outer edge of which a sensor coil of a pot detection system is inserted into a groove that is open to the outside.

DE 37 35 179 A1 shows a multilayer edge structure of a radiant heater.

The object of the invention is to provide an electric radiator, the lateral limitation is easy to manufacture with good strength and thermal insulation.

An induction coil running around the radiant heater is embedded in the edge. This can be done, for example, inside a U-shaped edge cross section, which is then filled with other insulating material behind it, or the coil can also be pressed in. It is thus possible to insulate this coil against the main heat influence, but close to the glass ceramic plate, with simultaneous electrical insulation. Their supply lines and the other heating element supply lines can also be led out in the region of cutouts of the edge, which can be pressed directly into the molded body. A connecting block can also extend directly into the area of an edge cutout. The fixing can take place by snap-in or bending-in connection as well as by clawing out a punched-out tab of a carrier shell.

The lateral boundary insulation, that is to say the insulation of the edge region of the radiator, which is usually ring-shaped, can be divided into several layers which are staggered according to the desired properties. For example, the mechanically more stressed sides, for example the inside facing the radiant heating chamber, could consist of a mechanically stronger layer, and a somewhat firmer layer could also be provided on the outer circumference, so that the ring can be handled and assembled easily. On the other hand, a mechanically less strong, but thermally well insulating layer could be attached inside. The individual layers could also have a reflective coating or have interposed reflective foils. The coating can be metallic and / or by other reflection means happen, for example metal oxides, which have a reflective effect in the mainly existing wavelength range.

The edge could, for example, be a vermiculite molded body with a U-shaped cross section, which is closed on the upper side facing a glass ceramic plate and rests with its two legs on the rest of the insulation of the radiant heater. The interior can be an air space or can be lined with a well-insulating bulk material or the like. It is also possible to manufacture from pipe sections of sandwich-like design. A horizontal layer formation can be provided if the main concern is to mechanically form the layer lying towards the radiation side.

This can create an edge which combines excellent insulation with good surface strength. The rest of the insulation can be made largely flat and thus relatively inexpensive and with good thermal insulation properties. The arrangement of the layers makes it possible to influence the thermal profile. For example, a bridge between the layers, for example the U-leg of a profile, can be arranged near the glass ceramic plate, so that the heat transferred there can preferably be dissipated through the glass ceramic plate. The dimensional stability and dimensional stability make it possible to attach the edge in the carrier shell without special adaptation measures. It can also hold the rest of the radiator insulation in the carrier shell. Production with smooth transitions between the insulating layers is also possible. For example, by correspondingly blowing or foaming the insulating material in the form, a structure similar to an integral foam can be achieved in which the The surface is denser and the densities decrease towards the center and thus the insulation capacity increases.

Advantageously, the insulating body can be partially or completely provided with an outer layer made of mechanically stronger material, for example vermiculite, which may even replace the otherwise customary sheet metal carrier shell and thus a self-supporting, relatively wear-resistant shell that also forms the base for connections, temperature sensors, etc. his. This can be a separate molded body into which other insulating materials are pressed, but the pressing can also take place at the same time as the rest of the insulating material, with the desired penetrations or intermixing of the insulating materials taking place in the interfaces between the insulating materials. This creates a largely seamless transition between these materials, which ensures good interlocking of the layers.

It is also possible to use mixtures of insulating materials, in particular vermiculite with pyrogenic silica airgel, which can both be pressed dry and form a thermally well-insulating but mechanically stronger material than the airgel alone. A carrier layer which carries the heating resistors could then also be formed from this material, preferably in one piece with an edge layer. They can be attached to it in any manner, a method which is derived from EP 0 355 388 A1 being particularly preferred. This document is referred to for the details.

Fig. 1 bis 7

mehrere Varianten von Heizkörpern, jeweils in einem Teilschnitt,

Fig. 8

einen Teilschnitt durch die Ausführungsform nach Fig. 7 im Anschlußbereich,

Fig. 9

ein Detail aus Fig. 7,

Fig. 10

eine andere Ausführung einer Festlegung der Begrenzungsisolierung,

Fig. 11

die schematische Draufsicht auf einen Zweikreis-Heizkörper,

Fig. 12

einen Teilschnitt durch einen Zweikreis-Heizkörper.

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

1 to 7

several variants of radiators, each in a partial section,

Fig. 8

7 shows a partial section through the embodiment according to FIG. 7 in the connection area,

Fig. 9

7 shows a detail from FIG. 7,

Fig. 10

another version of defining the boundary insulation,

Fig. 11

the schematic plan view of a two-circuit radiator,

Fig. 12

a partial section through a two-circuit radiator.

Fig. 1 shows an electric radiant heater 11, which is attached under a glass ceramic hotplate 12 and is pressed with a boundary insulation 13 on the underside. Arranged in a carrier shell 14 is a lower insulating layer 15, which is formed by pyrogenic silica airgel poured into the sheet metal carrier shell 14 and then compressed. With good temperature resistance, this insulating material is extremely heat-insulating, but mechanical not very firm. On the insulating layer 15 there is another insulating layer 16 made of a mechanically stronger insulating material, for example of a fiber material, such as that sold under the trade name "Fiberfrax", or another ceramic fiber material, which is pressed with binders. In this layer 16, heating coils 17 made of electrical resistance material are embedded with their lower vertices, namely at a clear distance from the glass ceramic plate 12 on which the cooking vessels can be placed. However, the radiator is also suitable for other heating purposes, for example for radiant heating of ovens or for heating other objects, for example metal hot plates.

The radiation space 18 formed above the heating resistors 17 is surrounded by the boundary insulation 13. It forms an edge running around the radiator, which protrudes somewhat beyond the edge 19 of the sheet metal carrier shell and thus makes contact with the glass ceramic plate.

The boundary insulation 13 has a horizontal stratification. It consists of an annular shaped body, which has a firmer layer 22 of compressed vermiculite on its upper side facing the radiation side, ie, for example, on the glass ceramic plate, while the remaining part 26 of the shaped body, which takes up most of the ring height, consists of one Mixture of vermiculite, pyrogenic silica airgel and reinforcing fibers can exist. Pressed into it, in the area of the interface between the layers 22 and 26, is a sensor coil 27 made of an oxidation-insulated aluminum wire, which runs around the edge and is therefore relatively close under the glass ceramic plate, but is thermally shielded. It is the sensor of a pot detection device that changes the induction recognizes this in the coil 27 by an attached or pushed pot and switches on the radiant heater.

The boundary insulation can be produced by first introducing vermiculite with the appropriate binder into a trough-shaped recess, then placing the coil on top and finally inserting the material forming part 26 and compressing the whole.

It can be seen that a sheet metal tab 30 is punched out of the material of the edge 19 of the carrier shell 14 and bent slightly inward, which yields resiliently when the ring is inserted, but digs barb-like into the material of the boundary insulation with its downward-pointing free edge and thus securely holds it in the carrier shell (see Fig. 10).

The boundary insulation 13 in FIG. 2 consists of a molded body made of pressed vermiculite (expanded mica). This is pressed in granular form, mixed with a binder, as is also described in DE-U-87 02 714, to which reference is made here. The cross section of the molded body is reversely U-shaped, so that the boundary insulation 13 has an inner leg 20, an outer leg 21, an upper connecting section 22 and an inner annular recess 23 which is elongated in the vertical direction. The sensor coil 27 is arranged in its upper part. There, too, it is close to the glass ceramic plate. The remaining part of the ring recess 23 is in turn filled with insulating material. The sensor coil 27 consists of a spiral-shaped winding made of flat band-shaped oxide-insulated line material, similar to a tightly tensioned clock spring. The conductor strips are vertical. This type of winding allows a high density of the coil body with low losses. The walls, in particular in the interior of the ring recess 23, can be coated with a reflective coating, for example by metal vapor deposition or by applying reflective metal oxides, so that radiation heat transfer through the annular space 23 is impeded. The ring recess 23 in the boundary insulation 13 is filled with an insulating material filling 24, the material of which differs from that of the U-shaped molded body. It can in particular be the same material as the lower insulating layer 15 or an even lighter and better insulating material can be used, which is filled into the ring recess and, if necessary, pressed in a little there to make the ring easier to handle. In Fig. 2, a cord made of ceramic fibers is used. The insulation is much better than would be the case with a solid molded body. The only place where the molded body passes from the inside to the outside is in the area of the connecting section 22, where, however, the heat can easily be dissipated through the glass ceramic plate 12.

It can be seen that the shaped body forming the boundary insulation is a stable shaped body which can be produced with sharp boundary surfaces, but which contains a fiber 53 on the upper inner side in order to form an optical boundary surface secured against nicks.

The annular boundary insulation also secures the insulating layers 15, 16 and presses them into the carrier shell 14.

The radiant heater is also ideal for the use of quartz-encapsulated high-temperature radiant heaters, such as halogen incandescent lamps. The single-layer insulation version can also be selected for this, in which the upper insulating layer 16 is dispensed with. The heating coils 17 and the boundary insulation 13 are arranged there directly on the insulating layer 15, they lie on the surface thereof and can be fastened there, for example by metal clips.

FIG. 3 shows an edge design with a shaped body as in FIG. 2, but with a round wire coil 27 and a pressed-in insulation 24 made of bulk material filling the recess 23. The insulating layer 16 has an elevated edge region 28, which lies approximately at the height of the top of the heating coils 17. As a result, the insulating layer 16 can be produced more easily because it can be placed flat on a drying plate with the pressed-in heating coils without fear of deformation.

The connecting lines of the heating resistors 17 can also be led out in the interface 29 between the insulating layer 16 and the boundary insulation 13, as shown in FIG. 4. There, however, the U cross-section of the boundary insulation corresponding to FIG. 3 is unequal leg, in that the inner leg 20 is longer than the outer leg. Accordingly, the inner leg 20 has pressed-in recesses 31 on its underside, through which the connecting lines 32 can reach.

Fig. 5 shows an annular edge 26 made of insulating material without an internal recess. On top of it lies a flat ring 22 made of mechanically stronger insulating material, for example vermiculite, in which a flat ring-shaped sensor coil made of wires arranged next to one another is embedded. It not only ideally protects the coil, but also the upper surface of the edge 26.

In Fig. 6 a similar ring 22 is provided with a recess 23 in which a common coil lies on the surface of the rim 26, i.e. is embedded or enclosed in the boundary surface of edge 26 and ring 22.

Fig. 7 shows an embodiment with a boundary insulation corresponding to FIGS. 3 and 4. A snap connection 33 is provided between the shell edge 19 and the boundary insulation 13, which consists of a resilient tab 30 which projects obliquely downwards and inwards and which presses in the boundary insulation 13 is pushed back and then falls into grooves 34 formed on the outer circumference of the leg 21, which extend only over part of the height. (For details see Fig. 9)

FIG. 8 shows the embodiment according to FIG. 7 at the point at which the connecting lines for the heating coils 17 and the sensor coil 27 are led to the outside. It can be seen that there the two legs 20, 21 of the molded body have cutouts 35 through which the connecting lines 32 of the heating coils 17 and the sensor coil connecting lines 36 project outwards. They lead to a connector body 37 which has tabs 38 for the leads. The connector body is attached to the carrier shell, but can also engage in a recess 35 in the boundary insulation 13. Any temperature sensors of temperature limiting and regulating devices reaching through the radiation space 18 can also be passed through cutouts in the limiting insulation. It can be seen that the relatively dimensionally stable and nevertheless well-insulating edge creates an ideal possibility for leading the connections to the outside, the cutouts being able to be worked in when the edge is formed. Together with a total good dimensional and dimensional stability, this makes installation considerably easier.

Fig. 11 shows the top view of a two-circuit radiator, in which two optionally separately controllable or adjustable circular heating zones are combined to form an oval or slot-shaped plate. The two zones 40, 41 are separated from one another by a central section 43 which, like the oval outer edge 13, can be constructed in multiple layers in the manner of the boundary insulation described above. For example, the double-concave central section 43 can have a single or double U-shaped profile, in which sensors other than pot detection sensors may also be incorporated, for example temperature sensors or the like.

Regarding the manufacturing process, it should also be noted that the sensor coil 27, for example in the embodiment according to FIGS. 2 to 4, can already be molded in during the manufacture of the shaped body. For example, the coil can be wound on the front edge of a mandrel, which is introduced into a trough-shaped shape and forms the recess 23. After pressing, it is pulled out and leaves the coil in the recess. This preferred manufacturing method creates a particularly good embedding of the sensor coil 27 just below the glass ceramic plate.

FIG. 12 shows a section through a two-circuit heating element 11 corresponding to FIG. 11. It can be seen there that the central web 43 can also carry an arm of a sensor coil 27, which is designed here according to FIG. 2. If the heating zones 40, 41 are arranged concentrically, only the edge forming the boundary insulation 13 of the inner heating zone can be provided with the sensor coil 27.

The sensor coil is connected to a pot detection system that works with an induction measuring principle. If the damping of the induction coil changes when the pot is put on, the radiant heater is switched on. As the coil inductance values change with temperature changes, the best possible temperature shielding of the coil is important, also for the selection of a cheap coil material. Good pot detection systems, e.g. according to EP 0 442 275 A2 (corresponding to USA s.n. 650 489) a compensation for the temperature-related drift of the coil values, but the good thermal shielding improves the function.

When the pot is removed, the induction values are changed again and the pot detection system acts on the radiator control to switch it off.

Claims (14)

1. Electric heater, particularly radiant heater, with a thermal boundary insulation (13), characterized in that a sensor coil (27) for a pot detection system is embedded on all sides in the boundary insulation (13).
2. Heater according to claim 1, characterized in that the boundary insulation (13) comprises a separate ring surrounding a heater interior (18) and which is located on an insulating layer and/or itself comprises several insulating layers (20 to 24, 26).
3. Heater according to claim 1 or 2, characterized in that the boundary insulation (13) has a substantially U-shaped cross-section, whose annular space (23) located between the U-legs (20, 21) contains the sensor coil and optionally an insulating medium (24), the annular space (23) preferably being closed to the emission side (25) of the radiant heater (11).
4. Heater according to one of the preceding claims, characterized in that the boundary insulation (13) contains a shaped body, preferably of pressed vermiculite and in said shaped body are optionally shaped recesses (35) for electric lines (32, 36) to the radiant heater and/or a sensor coil (27), as well as optionally for a connecting body (37).
5. Heater according to one of the preceding claims, characterized in that an insulating layer (21) on the side directed towards the exterior of the radiant heater (11) projects less far downwards and optionally rests there on a raised marginal area (28) of an insulating layer (16) and in said height are provided line recesses (35) in said boundary insulation (13) and/or said insulating layer (16).
6. Heater according to one of the preceding claims, characterized in that the boundary insulation is connected to one rim (19) of a support tray (14) of the radiant heater (11) by snapping in, bending in or barb-like clawing over marginal portions.
7. Heater according to one of the preceding claims, characterized in that the boundary insulation (13) is bevelled on its edge (53) facing the emission side and towards the radiation zone (18).
8. Heater according to one of the preceding claims, characterized in that the boundary insulation (13) comprises pressed together insulating layers with a shaped in sensor coil (27) and preferably the layer (22) towards the emission side is mechanically stronger and is made from a material such as vermiculite, whereas the layer (26) connected thereto is made from a less strong, but firmly better insulating material, such as pyrogenic silica aerogel mixed with additives and optionally vermiculite and preferably the insulating layers (22, 26) made from different insulating materials, preferably by joint pressing, in their boundary areas form a transition zone in which the insulating materials of both layers are present.
9. Heater according to one of the preceding claims, characterized in that the boundary installation (13) incorporates a control portion (43) between two optionally separately controllable or regulatable heater portions (40, 41).
10. Heater according to one of the preceding claims, characterized in that an insulating layer (23) of the boundary insulation (13) is constructed in one piece with a carrier layer (16) carrying heating resistors.
11. Heater according to one of the claims 2 to 10, characterized in that at least two and preferably all the insulating layers are jointly dry pressed, heating resistor coils (17) being partly pressed in therewith and optionally heater coils during the embedding process are partly filled with a filler removable following the embedding process.
12. Heater according to one of the preceding claims, characterized in that the sensor coil (27) comprises a flat conductor band winding.
13. Heater according to one of the preceding claims, characterized in that the sensor coil is enclosed in a flat ring mounted on a marginal portion (26), or in the vicinity of a separating face between the latter and a marginal portion (26) and/or comprises a flat coil with juxtaposed conductor wires.
14. Method for the manufacture of a heater with a thermal boundary insulation, characterized in that a sensor coil is wound onto a mould core or is fitted thereon and around it is pressed on all sides a shaped body forming the boundary insulation (13).

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