FI67988C - FOERFARANDE FOER TILLVERKNING AV ETT ELEKTRISKT STFOERFARANDE FOER TILLVERKNING AV ETT ELEKTRISK STRRAOLNINGSVAERMEELEMENT AOLNINGSVAERMEELEMENT - Google Patents

Description

1 67988

A method of manufacturing an electric radiant heating element

The invention relates to a method for manufacturing an electric radiation heating element, in which an electric heating resistor formed as a wire coil is attached to an insulating support.

It has become known from U.S. Patent No. 2,913,695 to place massive heating elements partially immersed in a layer of granular material. This is not usually possible with heating coils, as they could move due to thermal expansion and shaking and cause short circuits. DE-A-15 23 39 768 discloses a method for attaching heating coils to an insulating support, in which needles in the shape of a hairpin are inserted into the insulating support. This method is time consuming and the needles may come off as the body expands thermally.

It is further known that the heating coils are fitted in the slots of the fixed insulating supports and in part also puttyed into them (DE-A-21 65 569). In this case, however, the heating coil is largely covered by its circumference and must be brought to very high temperatures in order for it to dissipate sufficient radiant heat. Therefore, it has a short lifespan.

The object of the invention is to provide a method for manufacturing a radiant heating element, which method enables the secure attachment of electric heating resistors to the insulation support at low cost and largely without additional fastening parts, and in which the electric heating resistors have good radiant heating properties and a long service life.

This object is solved by the invention in that the wire coil is pressed into a prefabricated, plastically deformable insulating support with a substantially plate-like surface only to a part so high that the insulating material penetrates only to a small extent between the wire coils its largely free of insulating material.

Thus, the wire coil is attached directly to the insulating support without additional fixing agents, such as putty or wire studs or the like, so that the method can be performed quickly. Nevertheless, the wire coil is in perfect condition and also in place with regard to the effects of thermal expansion.

The printing of the wire coil on the insulating support can advantageously be performed in the pressing step of the insulating support.

10 This further saves one method step. It is particularly advisable to press the wire coil only part of its height into the insulating support so that the insulating material penetrates only to a small extent into the spaces between the wire coil conductor threads, largely surrounds only the wires and leaves the free interior of the wire coil largely free of insulating material. The individual threads of the yarns thus act like a lattice, which largely retains fibrous materials, so that only the binder or short fibers can penetrate when the Ruka is pressed into the empty interior. The coils are thus only surrounded by the insulating material in the lower area, but also in this area the interior of the coil remains free, so that a recess is formed in the insulating support in this area. Thus, the interior of the wire coil is not prevented from radiating and the reflective surface is covered only to a very small extent relative to the non-immersed wire coil and only from the surface away from the side to be heated.

It is advantageous to immerse only a small part of the threads of the wire coils and leave the rest of their circumference free.

The insulating material of which the insulating support consists comprises fibers, preferably provided with a binder. The wire spool is pressed into the insulating support as long as the insulating support is still soft or malleable, followed by drying or curing 35 or a burning operation to permanently secure the wire spool.

Embodiments of the invention will now be described in more detail with reference to the accompanying drawing, in which 67988 Fig. 1 shows a partially cut-away central section through a laser heating stove, Fig. 2 shows similarly to a variation, Fig. 5 shows a top view of a heating unit, with an alternative embodiment being marked with a breakpoint line, Fig. 6 shows a section along the line VI-VI in Fig. 5,

Fig. 7 shows a section on the line VII-VII in Fig. 5

Fig. 8 shows an enlarged section corresponding to the section of Fig. 7, Fig. 9 shows an enlarged section of a variant as a section according to Fig. 6, Fig. 10 shows a top view of a detail of another embodiment 20, and Fig. 11 shows an enlarged detail section along the line XI-XI in Fig. 10. along.

Figure 1 shows a glass-ceramic plate 11 which forms the cooking surface of an otherwise unexplored electric hob 25. A heating unit is arranged under the glass-ceramic plate, which in particular is preferably printed by means of spring parts (not shown) for the lower surface of the glass-ceramic plate. The heating unit 12 has a support shell 13 made of a plate, which consists of a lower plate 14, 30 consisting of a flat-bottomed flat plate and an upper plate part 15, which consists of a ring of z-cross section. The two plate parts are connected to each other by their overlapping ring flanges.

The support shell 13 is covered with an insulation formed by two insulation layers or plates 17, 18 and an insulation ring 19 parallel to the base 16 of the support shell. The insulation layers can be made of a wide variety of materials 4 67988. Since the thermal insulation properties of the high heat resistant insulations used herein usually deteriorate as the mechanical strength improves, a material having relatively low mechanical strength but good thermal insulation can be used in the insulating layers 17, 18 because these layers are relatively unloaded in terms of strength. In this case, the lower layer 17 may, for example, be an uncompressed or slightly compressed fluffy substance (e.g. finely divided silicic acid) or a substance which does not have such good heat resistance, since this is the "coldest" point of the heating unit. In contrast, the insulating ring 19, which has a specific support function, must be slightly more mechanically loaded. It may be a fibrous insulating material, e.g. alumina fiber, which acquires a cardboard-like structure when molded by the addition of a corresponding binder. Such a substance is marketed under the trade name "Fiberfrax". However, other mineral fibers can also be used as a basis for insulation.

On the insulating layer 18 and inside the insulating ring 19, but still in the annular opening of the insulating ring, an insulating support 20 in the shape of a round plate is located. The standard heating element of a glass-ceramic stove has a diameter of 15 cm and a thickness of 5 mm. This insulating support is likewise a compressed fibrous insulating material with very good heat resistance and having tongue-and-groove, wire coil-shaped heating resistors 21 on the upper surface, forming an annular heating zone which leaves only the unheated central zone 22 free.

The heating resistors 21 are located for the most part 30 on or slightly above the upper surface of the insulating support 20. Protrusions 24, 25 protrude radially from a substantially flat surface 23. The protrusions 24 extend from the outer edge to the unheated central zone, while the protrusions 25 terminate approximately between this half-35. This ensures that the distances between the protrusions remain within a certain range. These protrusions are made by embossing from an insulating support, the latter 5 67988 being made by pressing from a binder pulp. In this case, the heating resistors are pressed in at the same time so that they penetrate through the protrusions and remain attached to them. As can be seen in particular from Figures 5 2 and 3, the heating resistors are embedded in the region of the protrusions slightly over the middle of their helix, however, their upper threads and almost the entire upper half as well as the inside of the helix remain free.

As a result, the heating resistors remain excellently in place, but their heat radiation is hardly blocked. In the entire area between the protrusions, the heating resistors can radiate outwards without hindrance and in the area of the protrusions only the radiation of the lower thread is blocked.

This results in a very efficient heating element which guarantees the best possible radiation conditions upwards.

The insulating support 20 should have better mechanical strength than other insulation. This is achieved, for example, by a corresponding choice of substance or by compressing the substance more. The support thus forms a plate which, although still having a certain cardboard-like structure, can still be easily handled during manufacture, installation and repair. The heating resistors are so strong in this plate that it is not to be feared that they could in any way become detached due to vibrations or thermal expansions.

The heel patterns forming the protrusions 24, 25 provide recesses 26 in the lower surface of the insulating support. Preferably, recesses 27 are also provided in the upper surface of the upper insulating layer 18, so that these potentially intersecting recesses form an air space which contributes to improving the insulation. The electrical connection of the coils preferably leads downwards through the insulating support, so that the connecting conductors can, for example, pass in one recess 26. The corresponding connecting pins or tongues can already be pressed through the still soft material of the insulating support already under pressure. After compression, the insulation support is normally subjected to the drying and incineration stage.

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The installation of the heating unit is carried out in such a way that the lower plate part 14 is first filled with insulating layers 17 and 18 and / or placed inside it in the case of pre-compressed plates, after which the insulation support 20 is placed in place. The connecting conductors 28 are passed laterally through the recess 29 in the region of the dividing line between the plate parts 14, 15. The insulating ring 19 is then placed in place and the heating unit is completed by placing and fixing the upper plate part 15 in place. The cover 19 of the insulating grate-10 also has an upwardly projecting annular area 30 which abuts the lower surface of the glass-ceramic plate.

Figure 1 shows an embodiment in which the temperature limiter or temperature controller 31 is arranged so that its rod-like temperature sensor 32 passes diametrically through the heating space 33 formed between the heating resistors 21 and the lower surface of the glass-ceramic plate 11. The temperature sensor then passes through the opening of the plate part 15 and the insulating ring 19. In this embodiment, however, the temperature sensor is electrically insulated, for example coated with a quartz tube, in the event of a breakage of the glass-ceramic plate for safety reasons. Therefore, in the otherwise similar embodiment of Fig. 4, the temperature controller 31 may be arranged to pass through the separation line of the two plate parts 14, 15 into a recess in the lower surface 25 of the insulating ring 19 'and located on the upper surface of the insulating layer 18'. The insulating support 20 also has a diametrical recess 34 for the temperature sensor 32, so that this can detect the heating temperature relatively well, because the insulating support absorbs the heating temperature very quickly due to its higher mechanical strength and the consequent slightly lower thermal insulation effect.

Due to this structure, the radiation space 33 remains largely free and can be connected to a grounding grid 35 located on the shoulder of the insulating ring 19 'and forming 35 immediately under the glass-ceramic plate a contact shield against live heating resistors 21.

7 67988

Since the entire insulation 17, 18, 19 and also the insulation support 20 should be compressed only to the extent that mechanical strength necessarily requires, there may still be some friction on the surface of the insulation parts during contact. Due to this, the surfaces of the insulating parts can be treated separately, in which case, for example, more binder can be added to them or they can be sprayed with a heat-resistant varnish. In addition, it is advantageous to provide the surface of the insulating support with a varnish acting as black as possible with respect to heat radiation in order to improve the heat radiation upwards.

Normally, the heating units have a round shape, in which case it is expedient to make the insulation support round as well. However, it may be advantageous to use rectangular or square heating units that better adapt to the hob in a normal four-wire arrangement. In this case, the insulating ring could have a rectangular shape on the outside and a circular shape on the inside when a round insulating support is used.

When a ne-20 angled insulating support and an insulating ring are used in the circular heating ring region, monitoring and sensor devices for temperature control can be fitted to the resulting unheated corners. When the heating element is placed on a mechanically very durable and airtight insulating support, a very advantageous possibility is obtained to use a fluffy insulating material in the area of the insulating layers 17, 18, which has a very good thermal insulation capacity. When the mains voltages and heating capacities vary, only a second insulation bracket with its heating resistors has to be manufactured in each case, while the other heating unit remains the same and can be manufactured in series. This is also important for stocking and spare parts. The helical arrangement of the heating resistors can be two-wire, i.e. both ends of the heating resistor are located on the circumference and the helical heating-35 resistor runs with two mutually parallel wires to the center. The insulation bracket can be connected particularly well with radially extending supply lines, which means that it is also easily stackable thanks to them, which simplifies transport.

The heating resistors on the insulating support are usually helically arranged round wire-5 coils. However, it may also be advantageous to make the wire coils oval, with their smallest dimension in the direction of the glass-ceramic plate. Thanks to this, the radiation can also be used to obtain a sufficient size when using larger coils, which is necessary e.g. in terms of electrical strength. Whenever 10 he finds it very difficult, despite good insulation and the required electrical strength, to manufacture very thin heating units which at the same time still have a sufficiently low temperature on their lower surface to be confined to the flammable parts of kitchen furniture.

15 In another variant not shown, the coils could be placed slightly deeper in individual parts of the insulation support in order to make room for, for example, a rod temperature sensor. Thanks to this deepening, the required insulation gap can be maintained without having to place the entire radiating surface deeper.

In the described embodiment, each heating unit has a special support shell which is pressed for a glass-ceramic plate. Advantageously, it is also possible to use only one support shell 10 for the multi-unit hob, in which insulation is located, which limits the number of cup-shaped recesses in which the insulation support is placed.

The heating unit 111 shown in Figs. The surface 115 of the base 113 facing the interior 116 of the cup has a zigzag shape, as shown in particular in Figures 7 and 8. It consists of mutually parallel undulating ridges and descents, the 9 67988 ridges 117 of which, however, are made relatively sharp. The zigzag form is otherwise relatively flat.

A heating resistor 118 is formed in the interior 116 and on the surface 115, which consists of a helical resistor 5 which is arranged to be reciprocating (meander-shaped), the successive parts 119 of the heating resistor running relatively close to each other back and forth. They are connected to each other by U-shaped areas 120 which are made smooth and unthreaded, e.g. by stretching (smoothing) the heated 10 coils. These joints are embedded in the protrusions 124 of the insulating support, i.e., pressed into them preferably before the insulating support cures. The protrusions may have the shape of one or more zigzag waves, so that the immersed area, despite sufficient attachment, is kept to a minimum.

It should be noted that the zigzag protrusions and the recesses 122 between them run transversely with respect to the dimension of the heating resistor parts 119, it being seen from Fig. 8 that the heating resistors are embedded in the ridge 117 in each case. In this case, only a small part of each thread, which is turned towards the surface 115, is embedded, while the thread is located free in the rest of its circumference.

Fig. 9 shows a modification in which another corrugation is made transversely to the protrusions 121 'and the recesses 122', so that the heating coils are embedded in the tip 123 formed by the intersections of the protrusions.

It is found that thanks to this measure 30, despite sufficient attachment to the insulating support, which thus forms an easy-to-install and commercial unit, the heating coils are embedded only in very small areas, so as to avoid the risk of local overheating at these points, which could lead to burn-in. This is also due in part to the fact that the helices, if they expand, can adapt to an approximately zigzag-shaped upper surface, so that they are located on the upper surface 10 67988 without having to bend to the side due to compression. Above all, however, the entire upper side of the heating coils is free and can radiate freely. The meander-shaped structure allows a fairly good 5% load on the heating surface, which is also due to the fact that the heating coils can be relatively close, as the zigzag structure and anti-bending reduce the risk of short circuits and possible short circuits have no significant consequences. very small.

The joints 120 release little thermal energy because they use untwisted wire. This is particularly important because, due to the U-arc, there is a risk of overheating, which would also be affected by the extension required.

On both sides of the heating resistors 119 are temperature sensors 125 of temperature switch members 126, which may be either temperature limiters or temperature controllers. These may be rod-like temperature sensors, which are sensors consisting of an expansion sleeve and a relatively low-expansion rod located therein, extending along the entire inner edge of the insulating support and extending in the plane of the heating resistors between the edge 25 114 and the outer part 119. They extend through the opening 127 in the edge 114 so that their coupling support end is located outside the heated area. A connection of a heating resistor 118 is also passed through this area, which can be connected directly to the connection of the coupling head, so that this at the same time forms the connecting part of the heating resistor. When the temperature sensor is fitted on both sides, both connections are thus made by means of temperature switch elements, so that special connection parts can be omitted. The temperature switch members are thus connected in series with the heating resistor 35, so that the wake-up of the temperature sensor switches off the heating resistor 118.

11 67988

A variation is the temperature switch member 26 'shown in Figures 5 and 6, which may be similar in structure to the members described above. Its temperature sensor 125 'is located slightly below the level of the heating resistors in the recess 128 of the insulating base-5 which passes through the ribs 121. Here again, the temperature sensor is arranged in parallel with the parts 119 and, more specifically, in the immediate vicinity of the two parts, so that it has good contact with the temperature of the heating elements. The described temperature sensor arrangement in parallel with the heating resistors 10 ensures efficient control and temperature limitation, which prevents overtemperatures in the glass-ceramic plate. In this way, as the heating resistors and thus the temperature of the glass-ceramic material rise, the formation of temperature peaks which could damage the glass-ceramic surface is prevented. Thus, the heating can be set to a higher average, which in turn promotes power throughput.

The heating unit 111 'according to Fig. 10 corresponds to the structure according to Fig. 5 with respect to the structure of the scanner and the structure and arrangement of the heating resistors. The arrangement of the temperature-20 switch member 126a is only different. As shown in Fig. 11, the temperature sensor 125a, which is likewise a rod sensor, is located in a deep recess 130 in the bottom 113a of the insulating support 112a. . Since the sensor 125a is located quite close below the heating resistors, the recess 130 is provided with a cover 131 formed by a quartz glass plate.

The embodiment shown and described can be modified in many different ways within the scope of the invention. Thus, for example, a zigzag-shaped structure could be chosen in which a flatter body was interconnected in the region of the recesses 122. When attaching the heating resistors, it should first be noted that the tips 17 are relatively sharp so that the embedded area of the heating coils becomes quite small. In addition to heating the glass-ceramic hob, the heating unit can also be used to heat other objects, e.g. in industrial ovens for heating metal plates or walls or for heating dishes.

Claims (3)

13 6 7988 A method of manufacturing an electric radiant heating element, wherein an electric heating resistor (21, 118) formed as a wire coil is immersed in an insulating support (20, 112) containing fibrous insulating material and then the insulating support (20, 112) is cured, characterized in that the wire coil is pressed to a prefabricated, substantially plate-like, plastic-deformable insulation support (20, 112) only partially so high that the insulating material only incinerates to a small extent in the spaces between the wire coil conductor threads, largely surrounds only the wires and leaves the wire coil material largely free . Method according to Claim 1, characterized in that the printing is carried out in connection with the pressing of the insulating support (20, 112). Method according to one of the preceding claims, characterized in that only a small part of the threads of the wire coil is immersed and the rest of its circumferential area is left free.