EP0204185B1 - Radiant-heating unit - Google Patents

Abstract

In a radiant heating unit, an insulating support for carrying a radiant heating resistor is molded or pressed using a granulation of expanded clay materials, particularly expanded mica or vermiculite. The granulation is compressed and bound in a blank by a mineral binder, particularly water glass, and the heating resistor is positively secured in the moulded granulation by embedding parts of the resistance wire forming the resistor, in such a way that the resistor is in part free of the insulating support on the front. The heating resistor can be embedded during production of the insulating support or can subsequently be pressed into the support. The insulating support of the heating unit is low in weight and easy to manufacture, has optimum electrical and thermal insulating properties and has very good strength, whereby the heating unit has a long service life.

Description

The invention relates to a radiation heating unit and a method for producing a radiation heating unit, which is provided in particular for heating a plate, such as a glass ceramic hotplate, and has an insulating support which is essentially made of high-temperature-resistant material bound with a binder, at least partly based on clay minerals, at least one radiation heating resistor is preferably attached partially exposed to the front of the insulating support.

In a radiation heating unit of this type known from EP-A2-35 280, the insulating support consists of high-temperature-resistant material, for example aluminum silicate bonded with organic adhesive, and it absorbs the heating resistor in the recesses. This material is relatively difficult to process and expensive. This document also discloses a method for producing a radiation heating unit, in which an insulating support made of high-temperature-resistant material is produced essentially on the basis of clay minerals and at least one radiation heating resistor is attached to it by partial embedding.

From DE-PS 27 29 929 a radiation heating unit has also become known, in which the insulating support is pressed from an insulating material that contains fibrous materials. This design brings advantageous results, especially when using the heating unit on a glass ceramic plate. However, with regard to the simplicity of processing, the further improvement of the insulating properties and the increase in the efficiency of the heating unit, there is a need to find even more economical solutions.

EP-A1-105 968 also discloses a method for producing a radiation heating unit, in which adhesive is applied to a pre-shaped groove profile of the insulating support with a correspondingly profiled rubber stamp, after which the heating resistor is inserted into the groove profile. This results in an extremely complex process, and a permanent hold of the heating resistor is not guaranteed because the adhesive can become brittle over time.

The invention is based on the object of providing a radiation heating unit of the type described which, with simple manufacture, good mechanical strength, low weight and a long service life, ensures a high degree of efficiency with regard to the radiated heat.

This object is achieved according to the invention in a radiation heating unit of the type described at the outset in that the insulating support consists essentially of a pressed granule of expanded mica, such as vermiculite, the granule being bound in the compact by the binder, such as a mineral binder. Expanded mica of this type is generally used in construction as well as in technology for relatively large-sized thermal insulation. Surprisingly, it has been shown that this material can be used in a particularly advantageous manner for the production of an insulating support of the type according to the invention, although this is generally relatively small in size and finely structured and the heating resistors are mostly heating coils made of thin wire and therefore problems with Attachment of the heating resistor to the insulating support can occur. Due to the relatively bright and reflective surface of the finished compressed expanded mica, there is also an extremely good reflector effect with regard to the heat radiation emitted by the heating resistor, and at the same time the compressed expanded mica creates alternating reflective and heat-insulating particles, so that even with a relatively thin-walled design an extremely good insulation in the manner of superinsulation is achieved. Although other mica, exfoliated under the influence of heat, can also be used to produce the insulating substrate, the silicates of the vermiculite series, in particular the trioctahedral vermiculite, are particularly suitable as clay mineral for this purpose.

Numerous different materials are used as binders, including for example, cement or silica sol can be used. However, a water glass solution is particularly suitable as a binder for the production of the insulating support, since this binder on the one hand ensures high strength with a relatively tightly closed surface and low degree of compression and on the other hand can have such a low proportion by weight in the finished insulating support that the insulating support is very close 100% sufficient consists of expanded mica and possibly other admixtures. In order to nevertheless promote good and quick processing, the binder in the mixture with the expanded mica in the uncompressed state takes up between about 10 and 40% by weight, preferably about 30% by weight, so that it also penetrates between the fine-scaled structure of the expanded mica and Adjacent particles of the grain are pushed together in a tooth-like manner during pressing and can be bonded to one another in this toothed area.

Experiments have also shown that the binder, in particular at a density of about 37 to 40 ° Be, advantageously has at most about two thirds by weight of water, the other portion preferably consisting of about 8% sodium oxide and 27% silicon oxide, so that there is one Sodium water glass solution in the weight ratio of solids of about 1: 3.35 results. This solution is sufficiently low-viscosity to ensure thorough mixing with the swelling at a relatively low mixing energy to ensure mica. Very good strength and surface properties of the insulating support, on the one hand, and nevertheless highly effective insulating properties, on the other hand, have resulted when the expanded mica is pressed with the binder to about a fifth of its uncompressed volume to the insulating support, with very good results with a degree of compression of 5.3: 1 have been achieved.

In particular, when using at least one heating coil as a heating resistor, it is essential in a radiation heating unit that the heating resistor on the one hand is held sufficiently securely on the insulating support and on the other hand is arranged such that the heat can radiate from it as freely as possible. It can be assumed here that the heating resistor, due to the alternating load due to glowing and cooling, carries out movements in itself which can cause loosening. In itself, the heating resistor can also be fastened to the insulating support by means of separate fastening means, for example brackets or the like located at a distance from one another, which engage in or pass through the insulating support.

A particularly advantageous design for the operational safety of the heating unit is obtained, however, if the heating resistor is attached to the insulating support by being directly embedded in the pressed grain. Surprisingly, it has been shown that this pressed grain can also hold the heating resistor very well and reliably in comparison with a fibrous press material. When embedding the heating resistor, which usually consists of wire with a circular cross-section, the individual, intrinsically layered particles of expanded mica shift with increasing pressure on the surface of the heating resistor and with shape adjustment to this surface so that they are also in one another Interlock the area in the manner described and ensure a secure hold of the heating resistor without additional fasteners, even with a low embedding depth and relatively large embedding intervals. Here it plays a role that the binder, as a thin skin, also bonds to the surface of the heating resistor and, in particular after hardening, stiffens the particles of expanded mica adjacent to this surface in the manner of form-locking members, which at least partially cover the cross-section of the heating resistor in a manner that is permanent and dimensionally stable. At the same time, the alkali silicate acts as a corrosion inhibitor, so that the heating resistor is protected, at least in the embedded area. The adhesive power of the binder is extremely good both with respect to the metal of the heating resistor and to the inorganic silicon compound forming the grain. It is conceivable to fix the fastening means or sections of the heating resistor provided for engaging in the insulating carrier or essentially the entire heating resistor prior to mounting on the insulating carrier by means of a dipping process, spraying or the like. to be wetted with the binder and, if possible, to embed it immediately afterwards, as a result of which the effects described can be further improved.

In order on the one hand to ensure that the heating resistor is held as securely as possible and on the other hand to keep the surface provided for heat radiation as large as possible,. it is advantageous if the heating resistor is embedded at different depths in the area of adjacent longitudinal sections, in particular alternating successive sections each being approximately the same depth. However, it is also possible, in particular alternately, to provide longitudinal sections of the heating resistor which are completely exposed, that is to say are neither embedded, nor touch the insulating support directly or lie a short distance from the latter. However, it has surprisingly been found that even if the heating resistor is relatively densely clogged with the grain, for example if the inside of the filament is essentially filled over the entire length of the heating resistor when using a heating coil, the heating resistor exhibits an extraordinarily good glow pattern excellent heat radiation can result, especially if the filling in the heating coil is not pressed very hard or is held loose loose almost unpressed.

To further simplify the structure of the heating unit, the heating resistor is embedded in the grain with at least one turn in the region of the respective longitudinal section, so that the heating resistor does not have to be designed with separate fastening members which are formed in one piece with it and towards the core of the Insulation carrier protrude above him; such fasteners could be individual turns pulled out of the otherwise aligned turn formation, shaped hairpin-shaped supports or similar configurations that can be produced from wire by bending.

The described embedding in the grain ensures a sufficiently secure hold for most cross sections of the heating resistors commonly used, if at least one turn of the heating resistor is embedded in the grain at most up to its inner circumference, i.e. if the arc angle on which the turn is embedded is less than or at most 90 ° and the inner circumference of the winding is practically completely exposed. This can apply to all turns of the heating resistor or only to individual turns, for example successive turns in sections. Correspondingly, at least one turn of the heating resistor can be enclosed at least on a part of its inner circumference by the pressed grain, this also for all turns of the heating resistor or only for successive turns in sections what is possible depends in particular on the cross-sectional shape and size of the heating resistor.

Regardless of the type of embedding described, or in addition to this, it is advantageous if at least one turn of the heating resistor engages in the pressed grain at most up to its center, that is, when it is filled with the grain at most up to its axial plane which is approximately parallel to the front of the insulating support is. As a result, at least one half of the turn or all the turns engaging in this way is then completely exposed, which results in a very advantageous glow pattern. However, individual or all turns can also engage in the grain beyond this center or be filled with the grain and thereby form zones of particularly secure fastening. The grain of this filling also forms numerous small reflectors in a wide variety of directions due to its shiny metallic surfaces, which results in a diffuse radiation of the heat rays and a very uniform temperature pattern over the radiation surface.

In particular if the heating resistor is uniform throughout its length, for example not with molded-out fasteners, a very secure attachment is achieved with a simple structure in that longitudinal sections of the heating resistor are embedded in elevations of the insulating support, which are preferably in an otherwise in one Project the flat surface of the insulating support. These elevations are expediently transverse to the longitudinal sections of the heating resistor or webs that intersect them, which are preferably arranged in a radiation pattern around a central axis of the insulating support and in the configuration in which the heating resistor is laid. The heating resistor can therefore be laid in a single plane and is covered in sections by the elevations in such a way that it is embedded deepest in them and thus securely holding them. The holding force exerted by the elevations on the heating resistor is practically not reduced if the elevations decrease in cross-section to their apex in width, in particular are approximately semicircular, whereby on the one hand a high mechanical strength of the elevations in itself and on the other hand that a A larger proportion of the surface of the heating resistor is exposed than would be the case if the elevations did not decrease in width. In contrast to a shape that decreases, for example, in a trapezoidal shape, the rounded decrease in this width is more expedient for the strength of the elevations.

Despite very good insulation properties, the insulating support can be made relatively smooth and tightly closed on the surface if the grain is pressed closer to the surface boundary layers at least in the areas adjacent to the heating resistor than in the core, as a result of which the abrasion on the surface of the insulating support is also proportionate can be kept low. Instead of or in addition to this, it can be advantageous to provide the outer surfaces of the insulating support with a varnish which is as black as possible in relation to thermal radiation or a similar surface treatment. The mechanically denser and, if necessary, better heat-conducting surface layer of the insulating support can also be produced by means of an appropriate composition of the grain without post-treatment. However, it is particularly advantageous to treat the surface with a material that brings about the desired properties after the compact has been removed from the mold. For example, a silica sol or a silicon oxide in a coloidal form can be sprayed in uniformly. A targeted treatment in the vicinity of the embedding of the heating resistor could also take place instead or in addition, for example by arranging spray nozzles in the region of the corresponding fastening points on the pressing tool. It is therefore possible to achieve increased mechanical strength and better heat dissipation in the fastening areas between the heating resistor and the insulating support, without otherwise significantly influencing the insulating properties of the insulating support. Since the grain has a hydrophobic effect after pressing, for example by heat treatment, such as annealing, it can be achieved that a surface treatment or coating does not penetrate deeply and therefore does not reduce the thermal insulation capacity. The hydrophobic properties can be improved with a silicone treatment.

To further increase the thermal insulation properties, the grain is pressed with the release of air chambers between the individual grain particles, so that there is not only air between the lamellar or scale-like layers of the individual grain, but also between neighboring grains, the size of which is then roughly the same The order of magnitude of at least part of the grain is in the compressed state. The grain size is therefore expediently compressed just as much as is necessary to achieve the desired strength properties.

The heating resistor can be attached in a simple manner with the compression of the grain on the insulating support in one operation, in which case the turns or coils of the heating resistor are filled more or less in the manner described with a corresponding design of the pressing tool receiving the heating resistor. It has also been found that the insulating support can also be pressed into its shape in a previous operation and the heating resistor can then be embedded in that it is pressed into the corresponding surface of the insulating support, particularly before it dries, at the points where it should be embedded. Here, the grain size in the range of Portions of the heating resistor which enter the insulating carrier are further compacted by this and partially with the build-up of a resilient voltage so that the grain resiliently closes at least partially again after a sufficiently deep penetration of the associated cross section of the heating resistor and thereby the heating resistor at each associated one Section engages positively. The surface of the insulating carrier remains essentially in the form before being pressed in, ie the respective winding of the heating resistor is only filled by the amount by which the heating resistor has been pressed into the surface of the insulating carrier.

It has proven to be advantageous if the grain of the insulating support in the uncompressed state has particles which are in the order of the clear spiral spacings of the heating resistor, since the penetration of the grain into the inside of the turns of the heating resistor can thereby be significantly reduced or achieved that the penetration of the filling in the windings is relatively loose and at best weakly pressed. Instead of or in addition to this, the grain of the insulating support can consist of particles of different, preferably several times different, grain size. For example, a grain size between 1 and 2 mm has proven to be advantageous. The particles of different grain sizes can be mixed together and then pressed. However, it is also conceivable in an advantageous manner to construct the insulating support from layers with different grain sizes or to provide zones of different grain sizes over the surface boundary layer supporting the heating resistor such that, for example, a different grain size is provided in the embedding areas than between these embedding areas. In a preferred embodiment, the grain size in the region of the surface boundary layer carrying the heating resistor is selected to be finer than in the adjacent layer or layers, so that the grain size becomes coarser from the front side of the insulating support to its rear side. In addition to the advantage that the heating resistor already holds securely when it is fastened by pressing in even at a relatively small penetration depth, this also has the advantage that the insulating properties of the insulating support increase continuously or in stages from its front to its rear. In addition to being a substantially flat, card-like shape, the insulating support can also have a rim protruding beyond its front side and / or its rear side in the manner of a cup wheel, which edge is then expediently less compressed and / or constructed from coarser grains than the base supporting the heating resistor .

In the area of the heating resistor, the insulating support is expediently designed to be as thin as possible, in such a way that it protrudes from the back of the heating resistor only as far as is necessary for perfect electrical insulation. This can e.g. be achieved when the smallest distance of the heating resistor from the back of the insulating support is at most as large as its diameter, in particular smaller. As a result, the electrical lines used to connect the heating resistor can also be guided in the shortest possible way through the insulating support to the rear of the latter and from there into an area in which they are easily accessible for connection to electrical connection elements.

In order to significantly increase the thermal insulation on the back of the insulating support, particularly in the case of a relatively thin design of the area carrying the heating resistor, and to secure the insulating support against local mechanical overloads, the back of the insulating support is attached to a soft, in particular elastically deformable, insulating bedding made of at least one layer created. If the heating unit is provided for heating a plate, for example a glass ceramic hotplate, then it is expediently clamped against the underside of this plate with the pot edge of the insulating support, with the elastically deformable insulating bed on the side of the insulating support facing away from this plate being large and uniform adjacent spring member forms, which presses the insulating carrier against the plate under prestress. The insulating bed expediently consists of a pourable insulating material, for example as the base material pyrogenic silica, as e.g. sold under the trade name 'Aerosil' by Degussa. Furthermore, ceramic fibers, e.g. Aluminum silicate fibers are used. If the insulating support is formed in one piece with the insulating bedding, these components and possibly an opacifying agent can be added directly to the expanded mica grain to be pressed.

A particularly easy-to-use, namely easy to store, transport and assemble heating unit results if the insulating support and possibly the insulating bed are arranged in a thin-walled support shell, in particular made of sheet metal, and preferably by engaging in a connection block attached to it Heating resistor is secured against rotation against the carrier shell. As a rule, the heating unit is circular when viewed from the front and is provided with a single heating resistor. But it is also conceivable to give the heating unit a view of the front of any other shape, for example a rectangular or square basic shape, so that it is particularly well suited for a cooking unit which has several hotplates next to and / or in a row. Also, two or more independently connectable heating resistors can be arranged, preferably in interlocking spiral form, so that the heating unit has very different outputs can be driven. In any case, it is advantageous if the carrier shell is in one piece and therefore very simple in construction.

If it is advantageous to axially secure the insulating support with respect to the support shell before installing the heating unit, this does not need to take place, as possible, directly by engaging the support shell in the insulating support, but can be achieved by providing a temperature sensor that aligns the openings interspersed in the edge of the shell of the carrier shell and in the insulating carrier. The openings in the insulating support can be produced in a very simple manner by drilling after pressing the insulating support, so that no complex compression mold is required and instead of grooves, openings can also be provided with openings that are closed over the circumference.

In addition to the method steps described, the invention further relates to a method for producing a radiation heating unit, in which an insulating support made of high-temperature-resistant material is produced essentially on the basis of clay minerals and at least one radiation heating resistor is attached to it by partial embedding. According to the invention, this method is characterized in that a expanded mica, such as vermiculite, is first mixed with a binder as the press material and then pressed into the form of the insulating support in a pourable grain size, after which the heating resistor with partial zones of the circumference of its cross sections is pressed into the associated one Surface of the insulating support is pressed to the embedment depth and then the insulating support is dried with the pressed-in heating resistor or is further solidified by burning or annealing instead or in addition. As a result, the insulating support can first be compressed very strongly on the surface provided for receiving the heating resistor and forming its front side in such a way that the compressed grain does not tend to expand again when the heating resistor penetrates and penetrate the heating resistor substantially via the indentation depth . The heating resistor, with its parts penetrating into the grain, forms a press ram which partially and elastically compresses the grain in the area of these parts up to deeper layers of the insulating support in such a way that those areas of the grain, which cross-sectional sections of the heating resistor run past when penetrating and the then lie on the side of these cross-sectional sections facing the associated surface of the insulating support, spring back and thus grip these cross-sectional sections at least partially in a form-fitting and close-fitting manner with pretension. The further compaction of the grain when the heating resistor penetrates thus takes place not only in the penetration direction, but also laterally parallel to the associated surface of the insulating support. In addition to this or instead of this, it is also conceivable to arrange the heating resistor in the associated mold prior to pressing the insulating support and then to embed it in the compacting grain during the pressing, with the penetration of parts of the heating resistor, so that the insulating support can be carried out in practically the same operation Pressed form and the heating resistor is connected to the insulation support to form a structural unit by partially embedding. It can also be done in such a way that the heating resistor is first embedded in the last-mentioned procedure to a predetermined depth that is less than its final embedding depth, and then in the first-described procedure after pressing the insulating support a little deeper into its final embedding -Depth is pressed in, so that a particularly high compression of the grain is achieved in the area of the embedded parts of the heating resistor and a relatively small embedding depth is sufficient to hold the heating resistor. However, if several heating resistors are arranged, it is also possible to embed at least one heating resistor with the pressing of the insulating support and to attach at least one further heating resistor subsequently by pressing in in the manner described. In all cases, a very secure connection of the heating resistor made of bare or non-insulated resistance wire to the insulating support can be achieved.

In particular, in the procedure in which the heating resistor is embedded with the pressing of the insulating support, a filling of the turns of the heating resistor with the grain can be achieved, it being possible to proceed in such a way that this filling is not or not as much compressed as that zones of the insulating support adjacent to the heating resistor. If it is expedient to partially or completely remove this filling in order to achieve a certain glow pattern, this can be done after pressing and in particular after drying, in a simple manner e.g. in that the grain of this filling is caused to fall out by vibrating or shaking movements of the insulating support or is stripped out by brushing. In the area of the heating resistor, this results in a non-tightly closed surface of the insulating carrier, which surface is substantially rougher than in the areas adjacent to the heating resistor, and which can have an advantageous effect on the radiation behavior.

If a particularly tightly closed surface of the insulating support is also expedient in the area of the heating resistor, a device can be provided according to the invention for the manufacture of the radiation heating unit, which has an at least two-part pressing tool for pressing the granulate of expanded mica mixed with the binder, one of which the press die of the press tool is assigned to the front of the insulating support and this press die press projections for the engagement between the turns of the heating resistor. Here, the arrangement can be made such that press projections intervene essentially between all turns of the heating resistor or between all those turns that come to lie outside the elevations of the insulating support, or longitudinal sections of the heating resistor can be provided, between whose turns none Press-in projections engage, while such press-in projections engage in adjacent longitudinal sections, so that numerous different glow patterns and radiation effects can be achieved. With their pressing surfaces, the pressing projections expediently lie at least approximately in the plane of those pressing surfaces which compress the surface zones of the insulating carrier which are adjacent to the heating resistor. However, they can also stand back or protrude from it, in the first case an embedding of the heating resistor along a web projecting in its longitudinal direction on the associated surface of the insulating support and in the second case an embedding along a recessed groove or groove in the associated surface of the insulating support , which results in different reflection angles for the radiation.

• Fig. 1 eine erfindungsgemäße Strahlungs-Heizeinheit in Ansicht auf die Vorder- bzw. Oberseite,
• Fig. 2 ein Ausschnitt der Fig. 1 in vergrößertem Axialschnitt und bei aus der Trägerschale herausgehobenem Isolierträger,
• Fig. 3 ein Ausschnitt des Isolierträgers in vereinfachtem Querschnitt durch den Heizwiderstand,
• Fig. 4 ein vereinfachter Schnitt nach der Linie IV-IV in Fig. 3 in weiter vergrößerter Darstellung,
• Fig. 5 bis Fig. 8 zwei weitere Ausführungsformen in Darstellungen entsprechend den Fig. 3 und 4

These and further features of preferred developments of the invention are also apparent from the description and the drawings, the individual features being able to be implemented individually or in groups in the form of sub-combinations in one embodiment of the invention and in other fields. Embodiments of the invention are shown in the drawings and are explained in more detail below. The drawings show:

• 1 is a radiation heating unit according to the invention in a view of the front or top,
• 2 shows a detail of FIG. 1 in an enlarged axial section and with the insulating carrier lifted out of the carrier shell,
• 3 shows a section of the insulating support in a simplified cross section through the heating resistor,
• 4 is a simplified section along the line IV-IV in FIG. 3 in a further enlarged view,
• 5 to 8 show two further embodiments in representations corresponding to FIGS. 3 and 4

9 to 11 show three further embodiments of heating units in axial section.

As shown in FIGS. 1 and 2, a radiation heating unit 1 according to the invention has a card-like thin and essentially flat insulating support 2 with a heating resistor 5 attached to its front side and a pot rim 6 projecting beyond this front side on the outer circumference, the insulating support 2 in a support shell 7 made of sheet metal is provided on part of its height with an insulating bed 8. This carrier shell 7 receives in a cutout on its peripheral wall a connection block 9 made of insulating material, for example ceramic material, which protrudes both over the inner circumference and over the outer circumference of the peripheral wall and into a cutout 10 on the outer circumference of the insulating support 2 or the pot edge 6 engages in such a way that the insulating support 2 can occupy only a single position with respect to its central axis relative to the support shell 7 or the connection block 9 and is secured against rotation in this position in the assembled state. The top edge 6 of the insulating support 2, which has continuous, shoulder-free surface lines on the inner and outer circumference, projects beyond the open end face of the support shell 7 at least approximately by the thickness of the thin base 11 which receives the heating resistor 5, so that the heating unit 1 also the annular flat end face 12 of the pot rim 6, which extends over the entire thickness of the pot rim 6, can be clamped against the inside or underside of a plate, such as a glass ceramic hotplate. The pot edge 6, which is formed in one piece with the bottom 11 as a pressing body, is expediently less densely compressed than the bottom 11, in such a way that it has little elastic suspension properties in its pressing direction against the plate and, as a result, the pressing force is essentially uniform over the entire end face 12 acts. Opposite the front 3 of the bottom 11 of the insulating support 2 is the rod-shaped temperature sensor 13 of a temperature limiter 14, temperature regulator or the like. provided, the temperature sensor 13 engages in openings 15 in the pot edge 6 of the insulating support 2 and in the peripheral wall of the support shell 7, so that the insulating support 2 is secured in its axial position relative to the support shell 7. The temperature limiter 14 or the like. lies immediately adjacent to the connection block 9, which has outwardly directed tabs for the electrical connection, such that the heating resistor 5 and the temperature limiter 14 or the like. can be connected to electrical lines in close proximity.

The heating resistor 5 is formed by a wire helix having a continuous pitch and constant diameter essentially over its entire length, the windings of which lie closely together at the two ends for receiving wire-shaped connecting pins 16. The helix forming the heating resistor 5 is laid in a spiral parallel to the bottom 11, the height of which corresponds to the outer diameter of the helical turns 17 and which is on a part of it, in an outer circumference of the heating field, that is to say the inner circumference of the pot edge 6, with substantially constant spacings Height is embedded in the front of the insulating base 11 in such a way that it is exposed on a further part of its height at least on numerous longitudinal sections 18 of the heating resistor 5 on the front side 3 of the insulating support 2. The windings 17 can be circular or have a different, for example oval, shape.

On the front 3, the insulating support base 11 has a plurality of web-shaped elevations 20, 21, which are arranged radially in a radial manner around the central axis of the insulating support 2 and protrude beyond the otherwise flat associated surface 22 of the insulating support base 11 by an amount that approximately is equal to the thickness of the bottom 11 between the elevations 20, 21. The elevations 20, 21 extending from the pot edge 6 or from the outer circumference of the base 11 alternately extend radially inward to different extents, such that they are spaced apart from one another in the region of their radially inner ends. On the longitudinal sections 19, on which the heating resistor 5 passes through these elevations 20, 21 essentially at right angles, the heating resistor 5 is embedded deeper, corresponding to the height of the elevations, than in the area of the sections 18 between them, in the area of which the heating resistor 5 is also located can be completely free without embedding and, for example, with a clear distance from the surface 22. The or the like on the connecting pins 16. of the heating resistor 5 to be connected, electrical lines, not shown, are expediently immediately adjacent to the associated pin 16 through the insulating base 11 on its rear side 4 and between this rear side 4 and the insulating bed 8 adjacent to it to the terminal block 9 or the temperature limiter 14 o . Like. performed, for which purpose the insulating bed 8 expediently has a corresponding depression on the side facing the insulating support 2.

The insulating bed 8, which is expediently formed by a bed molded into the carrier shell 2 and softer than the insulating carrier 2 or its pot edge 6, i.e. is in particular easier to deform elastically, is supported on the bottom of the carrier shell 7 and forms a narrow annular contact surface 23 for the rear side 4 of the insulating carrier 2 with a small ring spacing adjacent to the peripheral wall thereof; on the outer circumference, this contact surface 23 is delimited by a recessed ring surface, so that there is a precisely defined contact of the insulating support 2 with the insulating bed 8. The contact surface 23 is also delimited on the inner circumference by a recessed recess in the insulating bed 8.

The insulating support 2 is produced in a two-part pressing tool, not shown, the two tool parts of which, namely a pressing die and a pressing die, enclose a shape in the closed state which corresponds to that of the finished insulating support 2. When the pressing tool is open, a pre-weighed amount of a expanded mica mixed with binder is poured into a pressing tool part, in particular the pressing tool part forming the front side 3 of the insulating support 2, and this is then pressed waste-free into the insulating support 2 by closing the pressing tool and without any reworking being necessary; In the pressing tool part forming the front of the insulating support 2, the heating resistor 5 can be inserted beforehand, for example into a corresponding spiral groove or into pressing projections arranged on a spiral ring, after which pouring onto the heating resistor is carried out. Furthermore, the filling can be carried out in succession in different grain sizes, for example in such a way that first finer grain size is poured in an approximately uniformly thick layer and then coarser grain size. When pressing, the insulating body is essentially compressed to its final shape and the sections of the heating resistor protruding beyond the associated pressing surface of the pressing tool part receiving the heating resistor are embedded within the compacting grain or pressed around it in such a way that they are at least partially securely held. With a multi-layer structure, which is achieved by pouring two or more layers of different grain sizes, the insulating support 2 can be finished pressed in a single operation. However, it is also possible to carry out layer-by-layer pressing if, for example, different layers are to be pressed to different extents, the respective layers lying inside the finished insulating support for better connection to the layers to be built thereon by appropriate shaping of the pressing surface of the pressing tool part or by mechanical processing can be roughened after the intermediate pressing. In any case, the design according to the invention enables the use of completely fiber-free materials for the production of the insulating body, although the addition of fibrous, for example mineral, components is also conceivable. There is practically no loss of material in the production of the insulating support 2 and after a possible annealing treatment the insulating support is also hydrophobic. A mineral glue is particularly suitable as a binder, with water glass having proven to be particularly advantageous.

3 to 8, three examples of numerous anchoring of the heating resistor in the insulating support are shown, with each of these examples applying to the entire anchoring of the heating resistor on an insulating support or can be combined in particular with one or more of the further examples that different anchors are alternately provided on different longitudinal sections of the heating resistor. 3 to 8 are the same reference numerals for corresponding parts as in the other figures, but in FIGS. 3 and 4 with the index "a", in FIGS. 5 and 6 with the index "b" 7 in FIGS. 7 and 8 with the index "c", in FIG. 9 with the index "d", in FIG. 10 with the index "e" and in FIG. 11 with the index "f".

In the embodiment according to FIGS. 3 and 4, the respective turns 17a of the heater are 1a, in particular the turns 17a lying in the region of the sections 18 according to FIG. 1 are embedded at a depth in the bottom 11a of the insulating support 2a, the highest being as large as or, in the exemplary embodiment shown, even slightly smaller than the associated cross-sectional dimension of the heating resistor 5a forming resistance wire, that is when using round wire as its wire diameter. 4, the individual particles of the pressed grain, from which the insulating carrier 2a is made, are indicated. The individual particles are flake-like layered particles and can therefore, in a manner not shown in detail, penetrate one another slightly in their adjoining regions with mutual interlocking. At the same time, however, the grain size is only compressed to such an extent that cavities in the form of air chambers 24 are enclosed between the individual particles, one of which is indicated in FIG. 4, and which can be both smaller and approximately the same size compared to the particles of the grain size . In the area of the part 25 of the respective winding 17a which engages in the insulating support in the manner of a ring segment, the individual particles of the grain nestle against the surface of this part 25 with particularly high compression and surface-fitting deformation, to which they are also connected in a form-fitting manner, that they receive this part 25 in a practically undercut opening and thereby clasp like a claw. In the case of the embodiment according to FIGS. 3 and 4, the inner circumference 26 of the turns 17a remains completely exposed. However, it is also conceivable to fill the interior of the heating resistor 5a, which is delimited by this inner circumference 26 and is outside the compressed surface 22a, more or less high and / or tightly with particles of the grain during the production of the insulating support 2a, these particles then expediently essential are less dense than the other areas of the insulating support or just so tightly pressed that they do not fall out by themselves.

In the embodiment according to FIGS. 5 and 6, the engaging part 25b of the respective turns 17b is enclosed by the material of the insulating support 2b over the entire cross section of the resistance wire, such that part of the inner circumference 26b is covered. However, the surface 22b does not extend in the region of the turn 17b to the middle of its height, that is to say not to that axial plane 28 of the turn 17b which is parallel to the surface 22b or to the insulation support base 11b. This arrangement can be produced particularly easily if the heating resistor 5b is produced simultaneously with the pressing of the insulating support 2b. When subsequently embedding by pressing the heating resistor 5b into the insulating support 2b, a slot-shaped groove 27, which penetrates the surface 22b and is indicated by dash-dotted lines in FIG. 6 and whose width is smaller than the wire diameter of the heating resistor 5b, can be formed in the area of the respectively embedded part 25b , however, a partial zone of the peripheral surface of the embedded part 25b is exposed to the front of the insulating substrate.

7 and 8 show an embedding of the respective winding 17c, as is expedient in particular in the region of the elevations 20c. The elevation 20c is approximately semicircular in cross-section and has a width such that it can accommodate at least two successive turns 17c or their associated parts 25c. The elevation 20c extends beyond the center of the height of the respective winding 17c in such a way that it also surrounds it on the largest part of its inner circumference 26c. 7 and 8, a portion of the circumference of the respective windings 17c also projects freely to the front of the insulating support in the region of the elevations 20c, although it can also be provided that the windings 17c enclose almost the entire outer circumference in the region of the elevations 20c, are embedded over their entire height or their entire outer diameter. 2, the pins 16 are also advantageously embedded in the insulating support 2 and thereby anchored in their position, and like the rest of the heating resistor they can be anchored either by pressing the insulating support or by subsequent pressing.

For axial and / or for securing in the direction of rotation of the insulating support 2 relative to the support shell 7, fastening members in the form of, for example, bending members 29 can also be provided in the peripheral wall of the support shell 7, which engage in the pot edge 6 of the insulating support 2. In the exemplary embodiment shown, the bending members 29 are formed by U-shaped slot punchings, in such a way that upward bending tongues are formed which, according to FIG. 9, are pressed into the outer circumference between the end faces of the insulating support 2d after its insertion. The bending tongues 29d according to FIG. 9 create their receiving recesses in the insulating support 2d by displacing the compressed press material, so that these recesses do not have to be formed in the insulating support 2d beforehand. At least two, in particular three bending tongues 29d evenly distributed over the circumference are expediently provided.

In the embodiment according to FIG. 9, the center of the bottom 11d of the insulating support 2d is also positively secured by a fastening member 30 directly opposite the support shell 7d or the insulating bed 8d, so that there is no danger even with an extremely thin base 11d it bulges upwards when the temperature rises accordingly. In the illustrated embodiment, the fastening member 30 is formed by a threaded screw lying in the central axis of the heating unit, which screw into the internal thread from the Engages the bottom of the shell 7d shaped sleeve and whose head is supported with the interposition of a washer 31 on the surface 22d of the insulating support 2d. It is also conceivable to dispense with a screw and to form the fastening member in one piece with the carrier shell 7d, for example in such a way that the sleeve formed upward from the bottom of the carrier shell 7d passes through the bottom 11 of the insulating carrier 2d and forms a molded-on surface 22d thereof Supports hollow rivet head or radially outwardly bent retaining tabs, which can be designed so that they can be bent into their upright position for non-destructive release of the insulating support 2d. In order to avoid bulging of the bottom 11d of the insulating support 2d under thermal stresses, it is also possible to provide the bottom 11d in the central area with, for example, continuous expansion slots over its thickness in such a way that thermal stresses are equalized; these slots can be radial, arc-shaped around the central axis of the insulating support 2d and / or tangential to a circle intended around this central axis.

According to FIG. 10, the bottom 11e of the insulating support 2e can also replace the insulating bed by a correspondingly thicker construction, it being conceivable that the bottom 11e is more densely compacted in the boundary layer adjacent to the surface 22e than in the area below which replaces the insulating bed. The bottom 11e of the insulating support 2e thus extends to the inside of the bottom of the support shell 7e. In the center, the bottom of the carrier shell 7e has a knob-shaped, upwardly projecting elevation 30e lying in its central axis, which engages in a corresponding recess on the underside of the bottom 11e of the insulating carrier 2e and which on the top of the insulating carrier 2e has a corresponding, Corresponding knob-shaped elevation protruding over the surface 22e. On the one hand, a possibly adhesive connection between the insulating carrier 2e and the carrier shell 7e can thereby be enlarged and it is also conceivable to absorb thermal stresses by means of such or a similar link 30e.

As shown in Fig. 11, the heating unit If can not only do without a separate insulating bed, but even without a carrier shell or without a base plate if a correspondingly high strength of the insulating support 2f is set by a suitable mixture of the press material and a corresponding choice of cross sections and compression. Such a heating unit If without a shell is particularly suitable for heating large-scale ovens, such as those used in commercial kitchens. In this case, the heating unit can also be arranged with a central axis deviating from the vertical position, for example with a horizontal central axis, on a side wall of the oven muffle. In each of the embodiments described, a mixture of pyrogenic silica, opacifying agent and fiber material with a weight fraction of approximately 15% can be added with a weight fraction of approximately 40% of mica and approximately 30% water glass before pressing, whereby the thermal insulation can also be influenced favorably .

Claims (11)

1. Radiant heating unit, particularly for heating a plate, such as a glass ceramic hotplate, with an insulating support (2), which substantially comprises high temperature-resistant material bound with a binder and based on clay materials, at least one radiant heating resistor being fixed to the insulating support (2), characterized in that the insulating support (2) substantially comprises a pressed granular material formed from expanded mica, such as vermiculite, the granular material being bound in the blank by the binder, such as a mineral binder.

2. Heating unit according to claim 1, characterized in that the expanded mica granular material is bound by a thorough mixing with a water glass solution or the like and that in particular the binder in the mixture with the expanded mica in the unpressed state represents between approximately 10 and 40%, preferably approximately 30% by weight and a few percentages by weight less in the pressed insulating support (2).

3. Heating unit according to claims 1 or 2, characterized in that in the unmixed state and in particular at a density of approximately 37 to 40° Bé, the binder represents approximately two thirds of the water weight proportion and preferably the other proportion comprises approximately 8% sodium oxide and 27% silicon oxide.

4. Heating unit according to one of the preceding claims, characterized in that the expanded mica is pressed with the binder to approximately one fifth of its unpressed volume to the insulating support (2).

5. Heating unit according to one of the preceding claims, characterized in that the pressed granular material of the insulating support (2) bound to the binder receives in fixed form the heating resistor (5), such as a heating coil, by direct embedding, that in particular the pressed granular material receives in varyingly deep form the heating resistor (5) in the vicinity of adjacent length portions, that in particular the pressed granular material receives the heating resistor (5) in the vicinity of the particular length portion (18, 19) with at least one turn (17), that in particular the granular material receives at least one turn (17a) of the heating resistor (5a) at the most up to the inner circumference (26) thereof, that in particular the pressed granular material encloses at least one turn (17b) of the heating resistor (5b) at least on part of its inner circumference (26b), that in particular the pressed granular material receives at least one turn (17b) of the heating resistor (5b) at the most up to its centre and that in particular the pressed granular material receives at least one turn (17c) of the heating resistor (5c) over and beyond its centre.

6. Heating unit according to one of the preceding claims, characterized in that the pressed granular material receives length portions (19) of the heating resistor (5) in protuberances (20, 21) projecting preferably over a surface (22) of insulating support (2) which is otherwise in one plane, that in particular the protuberances (20, 21) of the pressed granular material are webs at right angles to the length portions (19) of heating resistor (5), which are preferably radially arranged about a centre axis of the insulating support (2) and in particular protuberances (20, 21) decrease in width cross-sectionally towards the top thereof and are in particular approximately semicircular, and that in particular the pressed granular material fills at least one turn (17) of the heating resistor (5) at least partly with reduced pressing compared with the areas outside the heating resistor (5).

7. Heating unit according to one of the preceding claims, characterized in that the pressed granular material at least in the areas adjacent to the heating resistor (5) on the surface boundary layers is pressed more densely than in the core, that in particular the pressed granular material is pressed leaving free air chambers (24), whose size is preferably of the same order of magnitude as at least part of the granular material, that in particular the pressed granular material of the insulating support (2) has particles having the same order of magnitude as the inside coil spacings of the heating resistor (5) and that in particular the pressed granular material of the insulating support (2) has particles which are smaller than the order of magnitude of the inside coil spacings of the heating resistor (5).

8. Heating unit according to one of the preceding claims, characterized in that the pressed granular material of the insulating support (2) comprises particles of different particle sizes and which preferably differ considerably, which are in particular mixed and/or that in particular the pressed granular material of the insulating support (2) is thoroughly mixed with pyrogenic silicic acid and/or opacifying agents and/or fibre reinforcements and that these admixing components represent less than one third of the granular material.

9. Method for producing a radiant heating unit according to claim 1, in which an insulating support is. made from high temperature resistant material substantially based on clay materials and to same is fixed at least one radiant heating resistor by partial embedding, characterized in that the pressing material is binder-mixed expanded mica, such as vermiculite, which is pressed in a pourable granular material in the form of the insulating support (2), at least one heating resistor (5) being arranged prior to pressing in the associated pressing mould and then during pressing and accompanied by the penetration of parts of the heating resistor (5) is embedded over at least part of the embedding depth in the compressing granular material or at least one heating resistor (5) after pressing is pressed to the embedding depth partly into the associated pressed side of the insulating support and that then the insulating support (2) with the embedded heating resistor (5) is dried and optionally further solidified by stoving or baking.

10. Method according to claim 9, characterized in that components of the granular material are removed from the turns (17) of heating resistor (5) following the pressing of the insulating support (2) and the embedding of parts of the heating resistor (5), particularly by brushing out, shaking out or the like.

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