EP1672958B1 - Thickfilm heating tube - Google Patents

Abstract

Electrical heating device has heat conductive layer for converting electrical energy into heat and is located on surface of base plate within heating range in form of structured resistance heating conducting layer in connection area. In between the base plate and heat conducting layer, dielectric layer (710) is arranged. The resistance coating electrically isolates the heating conductor path with opposite dielectric layer. The heating device in the heating range is coated in such a manner that the open pores in heat conducting layer and opposite dielectric layer are sealed. The surface of heating device in the heating area opposite the medium possess anti-adhesive coating. An independent claim is also included for the method for producing heating device.

Description

The present invention relates to the field of electrical heating devices, namely heating devices for heating liquid or gaseous media, in particular a thick-film pipe heater gem. Claim 1 and a manufacturing method according to claim 12 for such a thick-film pipe heater.

In household electric appliances, especially those for washing and drying items of laundry or dishes, electric heaters are used to heat the cleaning water. In the development of these household appliances is aimed on the one hand to reduce the electrical energy consumption of the devices, in the case of washing machines, for example, by reducing the amount of water, on the other hand, the manufacturing costs should be kept low, but still ensure a low failure rate of the devices during their life cycle. Finally, a compact design of the heater itself is desirable, on the one hand a design with the least possible space required for heat output and on the other hand, the electrical connections of the heater due to their sensitivity to damage should be particularly considered.

Another aspect is the modern detergents which contain not only "wash-active substances" such as soap, anionic and non-ionic surfactants. The major contributors include water softening aids such as zeolites, foam regulators, bleaches, and fillers. Enzymes are present in almost all detergents, so proteases, lipases and amylases promote soil removal, cellulases cleave cellulose chains and serve to remove split fibers from tissue to be cleaned. Therefore, the outer surface of the heating elements in contact with the medium to be heated are exposed to thermal and strong chemical stresses in addition to the thermal. Thus, this outer surface should have corresponding material properties. In the past, numerous attempts have been made with non-stick protective layers such as Teflon, thermoplastics, thermosets or polypropylene, which, however, have not led to good results. Thus, a Teflon coating can not effectively prevent the buildup of lime.

For use in laundry washing machines is therefore a stability to alkalis with a pH greater than 7 to a pH of 10 (slightly alkaline), with simultaneous chemical resistance to oxidizing or bleaching agents such. As hydrogen peroxide or chlorine bleaching necessary. For use in dishwashers, the chemical resistance with respect to the pH value of the washing solutions used should range from a pH of 5 to 10, since the detergent used, in particular by the use of acids in rinse aids, the pH value in the acidic Move the area.

The Fig. 1 shows an example z. B. from the EP 0 551 914 B1 Known heating module 100 with a pipe heater 110 of the prior art, as it is currently used in the aforementioned household electrical appliances. The tubular heating element 110 consists in principle of a corrosion-resistant tube 111 with two ends 112, 114, in which in the interior 116 in an insulating material z. B. magnesium oxide - as a filler and for electrical insulation - embedded high-resistance heating wire, ie the heating element are included. The tube 111 serves essentially to protect this electrically insulating filler and the heating conductor relative to the heated and for heat to the medium to be heated. The heating conductor can be contacted from the outside via electrical connections 122, 124 at the respective pipe ends 112, 124, wherein the electrical connections 122, 124 are insulated from the pipe 111 by means of seals 132, 134 and the pipe is sealed to the outside.

From the WO 01/94861 A For example, a tubular heating element with printed electrical resistors is known, which are encased by one or more layers of dielectric material and arranged on a tubular base body and electrically connected to each other. The printed resistor is enveloped by the layer or layers of dielectric material. For certain applications, an outermost layer is configured as an outer abrasion resistant sheath, e.g. B. in the form of a protective sheath of a metallic, tubular sacrificial or protective element.

A disadvantage of tubular heating elements of the prior art is that very many production steps are required during their production. Also, the arrangement of the heating conductor, the filler with which the heating element is isolated from the (protective) tube and secured, thermally not optimal, since relatively large thermal masses are to be heated; This is especially evident in the thermal reaction time of such tubular heating elements. Also, it is not possible in the pipe heating elements described above to integrate a temperature sensor for detecting the temperature of the medium to be heated in the pipe heater. Finally, due to the construction of the known heating module, much volume of the medium to be heated is displaced.

The invention has for its object to provide a heater that allows a fast heat transfer to the medium to be heated with a high efficiency, the heater with the same heating capacity as less volume of the medium to be heated to displace as a conventional pipe heater.

The above object is achieved by a heating device with the features of claim 1. In the subsequent claims 2 to 11 are advantageous embodiments of this.

It is another object of the invention to provide a manufacturing method for a to propose heating device according to the invention, which allows a simple and shorter production of the heating device according to the invention.

The above object is achieved in terms of manufacturing by a manufacturing method according to claim 12. In the subsequent claims 13 to 15 are advantageous embodiments of this.

The electric heating device for heating a liquid medium has a main body or base carrier, also called a substrate. As a basic body are in principle all conceivable geometric shapes, depending on application requirements conceivable. At least on one surface of the base body, at least one heating conductor in the form of a structured resistance heating conductor layer is arranged in a heating region of the heater, which serves to convert electrical energy into heat and has at least two electrical connections which are made and contactable in a connection region of the heating device. Between the base body and the Heizleiterschicht a dielectric layer is arranged. At least one cover layer electrically insulates the heater trace from the medium, wherein the heater is coated at least in the heating region such that pores in the heat conductor layer and in the dielectric layer are openly sealed to the media, i. penetration or diffusion of the liquid medium into the dielectric layer or heat conductor layer is prevented. Further, the surface of the heater has at least in the heating area against the medium non-stick or anti-soiling properties.

In one embodiment of the electrical heating device, the base body is a tube closed at least in the area of a first pipe end, that is to say a tubular base body. In this case, this tubular base body has a heating area which can be brought into contact with the medium to be heated and which is provided with a multiplicity of flow openings in a further development. On an inner surface or an outer surface of the tubular base body then the functional layers, namely the dielectric layer, the at least one Heizleiterbahn in the form of the patterned resistance Heizleiterschicht and the cover layer are provided.

The embodiment of the heating device according to the invention with an open tube end on the part of the body with the heating area offers, for example, the possibility to connect a pump with which the circulation of the medium to be heated along the inner surface can be additionally increased by supply or by suction. This is not possible with the tubular heaters described above. In this context, it should be noted that it is also possible to close the tubular body at both ends of the pipe.

In principle, flow openings in the base body can have all possible shapes, but they are preferably designed as round holes or elongated holes. In the embodiment with the tubular base body, the flow openings are particularly preferably distributed at regular intervals over the entire heating area. Due to these flow openings, the heater is then in the heating area when used according to the invention - except for the connection area - completely with the entire surface, d. H. the inner surface and the outer surface of the tubular body, with the liquid medium to be heated in direct contact, i. the heating area is submerged or immersed in the medium; this is the case in the connection area only for the inner surface. As a result, a faster heat transfer to the medium is achieved, and the efficiency of the heater over the conventional tubular heaters is further improved. In particular, material stresses due to the thermal expansion of the individual materials are significantly reduced or avoided by the good heat dissipation over the entire heating area in the heating device.

By the embodiment of the heating device according to the invention without a homogeneous closed jacket as in the conventional tubular heating element described above, the production is simplified considerably. Further advantages include the material savings by, for example, the elimination of the filler and the associated weight reduction, but also the significantly faster thermal reaction time due to the significantly reduced thermal masses. In addition, a "dry" connection area can be ensured without much effort during operation.

With regard to the heat conductor layer, it should be noted that good results have been achieved with metal, metal alloy, eg Kanthal or Nikrothal, but also with ceramic-metal composites, so-called composites. Particularly suitable for this purpose are thermally sprayed or cold-gas-sprayed metals or metal alloys.

Alternatively, application of the heat conductor layer in the sol-gel layer method has proved to be suitable. In this case, a sol is a colloidal solution with very small, finely divided, freely mobile particles, e.g. Graphite, nickel, silver. By evaporation of the solvent, the sol gels to sol-gel, the particles approach each other and form a three-dimensional network. Further heating enhances cross-linking. After cooling, the network is permanent.

It should also be noted that in the embodiment with a tubular basic body (abbreviated to the tube design) resistance heating elements can be provided both on the inside and on the outside of the main body of the heating device according to the invention.

Another advantage of the construction of the heating device according to the invention is that very simply one or more electrical sensor elements of various functions can be provided in addition. Such a sensor element can be arranged in isolation on a surface of the base body, wherein its electrical connections are preferably also arranged in the connection area and can be contacted. In principle, the sensor element can be a very wide variety of sensor types which can be used to monitor the heating device or the heating process or the medium to be heated.

Thus, a temperature sensor can serve for the control and / or thermal monitoring and protection of the resistance heating element. Basically, however, it is also possible to perform the function of monitoring the medium to be heated and the thermal monitoring and protection of the resistance heating element by two or more different sensor elements. It should be noted in particular that the position of a corresponding temperature sensor is crucial, in particular for the precise and reliable control or regulation of a heating element.

Accordingly, a sensor element may be a temperature sensor which is located directly next to or on the at least one heating conductor track and from this and optionally is arranged electrically isolated and sealed against the medium. Thus, it is possible in the heating device according to the invention, almost ideal to realize a thermal monitoring of the heating element and / or detection of the medium temperature. Thus, the corresponding temperature sensor can be arranged almost directly at the respectively relevant measuring location, ie directly on or next to the heating conductor or in direct or indirect thermal contact with the medium. This can advantageously be almost excluded thermal overloading of the heating element. The provision of the temperature sensor required for this purpose is much easier to implement than would be possible with a conventional tubular heater. Preferably, the temperature sensor is arranged on the base body in the heating region, it being possible for the temperature sensor to be arranged either on the inner surface or on the outer surface in the case of the tube version. This is particularly contrary to the desire to be able to capture the temperature of the medium to be heated as directly as possible. In the above-described conventional tubular heater this is not possible.

Furthermore, one or another sensor element can be a securing element for securing the heating device. Such a fuse element, for example, interrupt the heating element in a fault or fault, such as a dry run of the heater, interrupt. For this purpose, it is particularly easy in the heating device according to the invention - preferably in the connection area - to integrate such a fuse element in the heating element. The hedge may consist in a thermal protection but also in an electrical fuse of the heating element. In the first variant, the temperature of the heating element is monitored by means of a corresponding temperature sensor and the heating current is interrupted or regulated accordingly. In the case of electrical protection, the heating current is monitored and interrupted, limited or regulated when a certain value is exceeded. However, it is also possible to provide a control circuit externally or in the connection region of the heating device, which monitors the heating current and controls it accordingly.

Particularly advantageous has been found that the structure of the heater the use of sensor elements in the form of an SMD component (SMD, surface mounted device) allows. These can be arranged almost at any desired location on the heating device, ie both in the heating area, which is in "wet" area with the medium to be heated in contact and in the connection area, as a "dry" area in the built-in heater in a tub outside, that is shielded from the medium to be heated.

Especially the closed end of a tubular base body also allows a reliable detection of the medium temperature even directly in the connection region arranged there, since the inner surface of the base body is in contact here with the medium. In addition, it is advantageous that a sensor element arranged there does not have to be sealed off or insulated from the medium. In this case, there is an advantageous embodiment of the heating device according to the invention with a temperature sensor for monitoring or recording the medium temperature in the way to arrange a commercial NTC or PTC element with a sleeve, such as a metal sleeve made of chrome-nickel steel, in the closed end of the tubular body , Thus, this pipe end can be particularly easily closed by the sleeve of the temperature sensor is used as a lid, which, for example, when the tubular body and the sleeve are made of metal, can be materially connected by welding with the base body made of metal. Also, the temperature sensor is particularly advantageous with the medium to be heated in direct contact.

It should also be noted that, depending on requirements, sensors for other physical measured variables can also be used as sensor elements at the above positions, such as, for example, a pressure sensor or a sensor for detecting the pH, etc.

Basically, any material with good thermal conductivity and at the same time sufficiently high melting point or a small coefficient of thermal expansion is suitable for the main body. An austenitic or a ferritic or duplex stainless steel is preferred for the main body, but also Non-ferrous metals such as aluminum, aluminum alloys, copper, copper alloys are suitable. For cost considerations, it is particularly preferable to use carbon steel as base body material, for example cold rolled steel. It should be noted, however, that the base body can also be made of a ceramic, glass or a metal-ceramic composite, such as a metal matrix composite or cermet.

In particular, if the material of the base body itself is electrically conductive, a dielectric layer as a first covering layer with a thermal spraying method is for electrical insulation directly on the base body. Ceramic layers, preferably of aluminum oxide, zirconium oxide, titanium oxide, chromium oxide, glass frit such as borosilicate or a mixture thereof, have proven to be suitable for this purpose. Likewise, an enamel layer or glass layer is suitable as the first cover layer. The dielectric layer can also be applied by means of the abovementioned sol-gel method, silicon oxide, titanium oxide, zirconium oxide and aluminum oxide sol gels having proven particularly suitable.

In the past, it has proven to be particularly problematical that cracks may occur in a thermally stressed brittle layer, especially if several layers have different elasticity properties (or with different thermal expansion behavior), especially in the case of ceramic or glass layers. This is disadvantageous in a heating device which has an electrical current-carrying heating conductor in operation and is immersed in a mostly electrically conductive medium to be heated, since shorts can occur due to cracks. In this context, it has proved to be advantageous to provide expansion joints in the dielectric layer between the heating conductor tracks of the resistance heating conductor layer. As a result of this measure, cracking in the functional layers, ie the dielectric layer, the resistance heating conductor layer and the cover layer mentioned below, is reduced by the thermal loads occurring during operation, in particular the good heat dissipation due to the complete contact of the base body the liquid medium ensures that the dielectric layer and the cover layer in the inventive Operational use can not replace or be blown off.

It has been found that the dielectric layer and the resistance-Heizleiterschicht when generated by a thermal spraying method such as atmospheric plasma spraying (APS), high velocity flame spraying (HVOF), powder flame spraying, arc and cold gas spraying or by means of a sol-gel process particularly good mechanical properties exhibit. This is mainly due to the porous layer structure of the layers produced by the above-mentioned methods, since in this case a compensation of the different elasticity properties or the different thermal expansion behavior is advantageously achieved.

It has also been found that in the case of the abovementioned porous layers in immersed operation, water molecules penetrate into the pores or accumulate there. As a result, conductive paths are formed in this layer, which primarily serves for electrical insulation, which can lead to short circuits or higher leakage currents. Therefore, it has been found to be particularly advantageous to provide the pores of the dielectric layer, especially at the optionally provided expansion joints, the optionally provided flow openings and at least at the end faces of the layer at the edge of the body, with the cover layer, d. H. to seal. A sealing of the resistance-Heizleiterschicht has been shown to be beneficial to avoid corrosion. Overall, an infiltration of these layers or a frontal penetration of liquids into the porous layers is advantageously prevented.

To protect the heater during operation against external influences and for sealing or sealing and isolation from the medium, the heater is therefore at least in the heating area, d. H. in the wet area, provided with an applied medium-tight and electrically insulating cover layer. This layer should have a thermal conductivity in the range of 1 to 50 W / mK.

It should be noted that this covering layer can of course also be composed of several layers, one of which is required in each case Functions "electrically isolating", "against the medium to be heated caulking or sealing" and has an "anti-Soiling property".

Particularly suitable for sealing the pores have been: nanocomposite coatings, such as organic paints or coatings with inorganic-organic polymer matrix with incorporated inorganic particles, siloxanes and silicone oils. These materials penetrate into the pores of the porous layers and seal them against the penetration of the liquid to be heated medium, such as water.

As a finishing top coat or last covering layer, the outer surface is equipped with the non-stick or anti-soiling properties. The topcoat is designed so that neither lime nor other organic substances can deposit on the heater in the heating area. This ensures a constant and uniform heat transfer from the heating to the medium via the heating area.

Preferably, the sealing or pore-sealing cover layer itself already has anti-soiling properties. In this case, the covering layer can be, for example, a nanostructured protective layer, for which nanostructured materials or material combinations are preferably used. For a single layer embodiment of the cover layer, i. Pore sealing, electrical insulation and anti-soiling property, for example, a hybrid polymer, which is applied as a sol-gel coating, for example, with a hybrid polymer with an inorganic-organic polymer matrix, is suitable. Namely, the hybrid polymer is thin enough to penetrate into the open pores of the porous layers and additionally forms a dense film on the surface by crosslinking. The hydrophobic sol-gel surfaces are not only dirt repellent, they also increase the corrosion resistance of the coated resistive heat conductor layer.

In the case of a cover layer in multilayer design, silicones or modified silicones, polyimides, polyamideimide, polyesterimides or modified polyesterimides have proven suitable for the topcoat. But also glass or ceramic layers by means of screen printing or spraying followed by Drying and baking are applied. An important feature of the topcoat here is still to prevent outgassing of the covering layer which seals the pores in the dielectric layer and the resistance heating conductor layer.

In one embodiment of the heating device according to the invention, both the dielectric layer and the cover layer of enamel or glass, since both requirements are met by these substances in terms of the necessary electrical insulation and the seal against the medium to be heated.

In this context, it should be emphasized that the coating of the entire heater at least in the heating area, which is in submerged operation in contact with the medium to be heated, with the cover particularly advantageous the use of base metals, for. As unalloyed steels allowed for the body. Thus, the base body can be made from inexpensive cold rolled steel as the starting material.

An additional advantageous development of the heating device according to the invention is directed to the problem of so-called "hotspots". Hotspots to be considered in this context during operation sites are considered in a heater where sometimes significant excess temperatures occur. Such hotspots can occur due to local external contamination, but also due to the design caused at certain points of the heating element. For example, in the connection region of the heating device, it is not desirable for the heating conductor to convert electrical energy into heat there. But even at so-called reversal points of the heating element, which are necessary at least once at the open end of the pipe, the occurrence of such local overheating was found. Therefore, the Heizleiterbahn (s) are set at reversal points and in the connection area with respect to the remaining Heizleiterbahn that they have a lower resistivity at such locations. This can be achieved in principle by increasing the effective heating conductor cross section at reversal points or in the connection region, for example by providing more heating conductor material. Particularly preferred However, if the Heizleiterbahn at the reversal points or in the connection area of a resistive material having a higher conductivity than the remaining Heizleiterbahn or provided there on the Heizleiterbahn an additional Heizleitermaterial with a lower electrical resistance or is applied. In the invention, preference is given to using thermally sprayed or cold-gas sprayed metals or metal alloys, but also thick-film pastes, such as silver / palladium pastes, or electrically conductive polymers, such as silver-filled epoxide.

With regard to the connection region, it should be noted that if the connections and optionally the part of the heating conductors have a lower electrical resistance from the connection region to the heating region of the at least one heating element than the remaining part of the resistance heating element, the connection region of the heating device according to the invention thereby forms a "cold zone". represents, d. H. a zone in which almost no heat is dissipated by the heating element. This additionally ensures that when the medium temperature in the connection area is detected, it can be measured correctly and is not falsified by heat from the heating conductor.

With regard to the insulation and sealing of the electrical resistance heating conductor layer with respect to the medium as well as with respect to the base body, it should be noted that of the materials used for the respective covering layers a high-voltage resistance of at least 1250VAC, preferably 3750VAC, a maximum leakage current of 0.75mA, preferably 0 , 25mA, a chemical stability to the medium in a PH range of 5 to 10, preferably 7 to 10 and a thermal conductivity of at least 1 W / mK, preferably from 10 to 50W / mK can be achieved.

A development of the heating device according to the invention consists in the integration of a heating device according to the invention or several heating devices according to the invention in a heating module, wherein substantially between the connection area and the heating area on the one or more heating devices arranged in parallel to a running around the body seal to seal a mounting hole For the heating module is arranged. Such a seal can be embodied, for example, as a conical seal, which is injection-molded directly onto the heating device, for example with a material suitable for a seal, with simultaneous corresponding shaping. This ensures a seal between the heating area and the connection area at the same time.

A refinement of the heating module consisting of providing a flange assembly with standard dimensions instead of the above-mentioned seal. Such a flange assembly then essentially comprises at least one flange, a clamping piece and a seal arranged between flange and clamping piece, wherein the at least one heating devices are fixed to the flange or the clamping piece and the seal is arranged between the connection region and the heating region.

Further, in the heating module for the electrical contacting of the at least one heating device and optionally one or more sensor elements, a connection plug part, which for example offers a standardized plug connection, can be provided.

The method for producing a heating device of the invention basically consists of the following steps: producing a basic body; Applying a first electrically insulating dielectric layer to the base body using one of the above-mentioned thermal spraying methods; Applying at least one structured heating conductor layer to the dielectric layer by one of the above-mentioned thermal spraying methods; and applying an electrically insulating, medium-tight and non-stick properties covering layer on the heater at least in the heating region, wherein pores in the dielectric layer and the Heizleiterschicht are sealed medium-tight.

In addition, as an additional intermediate step, the application of an adhesive layer with one of the abovementioned thermal spraying methods onto the base body between the base body and the dielectric layer can be provided.

The step of applying an electrically insulating, medium-tight and non-stick properties having cover layer can be performed in addition to a single-layer embodiment of the following intermediate steps as a two-layer design with the following steps: applying at least in the heating of a first the pores in the dielectric layer and the heat conductor layer medium-tight sealing sealant layer; and applying at least in the heating region a second nanostructured anti-soiling layer over the cover layer. The nanostructured anti-soiling layer has to electrically isolate the properties from the medium.

Finally, as a further intermediate step after the application of the dielectric layer, a step may additionally be provided for producing expansion joints in the dielectric layer next to and / or between heating conductor tracks in the structured heating conductor layer.

It has also proved to be favorable to roughen the main body before applying the first covering layer by means of blasting, etching or grinding. Subsequently, the dielectric layer is applied by means of one of the abovementioned methods, preferably by means of thermal spraying or cold gas spraying.

The heating conductor layer is applied by means of one of the abovementioned methods, preferably by means of a thermal or a cold spraying method. It is possible by laser structuring, water jet cutting, laser micro jet method, sandblasting, etching, milling or grinding of the entire surface applied Heizleiterschicht to give the desired Heizleiterstruktur, whereby different temperature ranges can be created, but also the electrical heating of the heater can be set at a given supply voltage can.

It is also possible to produce the heating conductor structure by a stencil technique. In this case, a template made of a non-stick material on the dielectric layer is applied (laminated or screen printed) and then applied the Heizleiterschicht. After applying the heat conductor layer, the template is then removed again. However, heating conductor structures have become also successfully produced by direct structured coating with a fine coating jet.

Fig. 1

eine Draufsicht auf ein Rohrheizelement des Standes der Technik;

Fig. 2a

eine Seitenansicht, einer ersten Ausführungsform der erfindungsgemäßen Dickschicht-Rohr-Heizung mit SMD-Temperaturerfassungselement;

Fig. 2b

eine Schnittansicht der Dickschicht-Rohr-Heizung der Fig. 2a;

Fig. 3a

eine Seitenansicht, einer zweiten Ausführungsform der erfindungsgemäßen Dickschicht-Rohr-Heizung, wobei ein Temperaturerfassungselement in dem verschlossenen Rohrende des Grundkörpers angeordnet ist;

Fig. 3b

eine Schnittansicht der Dickschicht-Rohr-Heizung der Fig. 3a;

Fig. 4

eine Draufsicht auf ein Heizmodul mit zwei erfindungsgemäßen Dickschicht-Rohr-Heizungen;

Fig. 5a

eine Seitenansicht eines Heizmoduls mit einer Flanschbaugruppe;

Fig. 5b

eine Schnittansicht des Heizmoduls der Fig. 5a;

Fig. 6

eine Detailansicht eines Heizleiterumkehrpunktes auf einer erfindungsgemäßen Dickschicht-Rohr-Heizung;

Fig. 7a-7d

jeweils eine Querschnittsansicht der Anordnung der Funktionsschich- ten in verschiedenen Ausführungen;

Fig. 7e

eine Querschnittdarstellung der Funktionsschichten gemäß einer weiteren Ausführung; und

Fig. 8

eine perspektivische Darstellung eines Ausführungsbeispiels einer Heizvorrichtung der Erfindung.

Further advantages of the invention will be explained in connection with the explanations of embodiments of the present invention together with the drawing figures. The terms "left", "right", "bottom" and "top" used herein refer to the drawing figures with normally legible figure names. Furthermore, it should be pointed out that in the individual drawing figures with the same leading digit (for example, key figure 2: Fig. 2a, 2b ) like parts are identified by like reference numerals. It shows:

Fig. 1

a plan view of a tube heater of the prior art;

Fig. 2a

a side view, a first embodiment of the thick film tube heater according to the invention with SMD temperature sensing element;

Fig. 2b

a sectional view of the thick-film tube heater of Fig. 2a ;

Fig. 3a

a side view, a second embodiment of the thick-film tube heater according to the invention, wherein a temperature detecting element is arranged in the closed tube end of the base body;

Fig. 3b

a sectional view of the thick-film tube heater of Fig. 3a ;

Fig. 4

a plan view of a heating module with two thick-film tube heaters according to the invention;

Fig. 5a

a side view of a heating module with a flange assembly;

Fig. 5b

a sectional view of the heating module of Fig. 5a ;

Fig. 6

a detailed view of a Heizleiterumkehrpunktes on a thick film tube heater according to the invention;

Fig. 7a-7d

each a cross-sectional view of the arrangement of the functional in various designs;

Fig. 7e

a cross-sectional view of the functional layers according to another embodiment; and

Fig. 8

a perspective view of an embodiment of a heating device of the invention.

Fig. 2a shows a plan view of an embodiment of a thick-film heater according to the invention, which is designed as a thick-film pipe heater 200. Clearly visible is a tubular body 201 with an open tube end 202 and a closed tube end 204 which is closed by a cover 206.

In the Fig. 1 For example, the thick-film pipe heater 200 is shown schematically in a mounting position in a tub wall 210. For attachment in and simultaneous sealing of the installation opening of the tub wall 210, a seal 220 in the form of a conical seal is sprayed onto the thick-layer tube heater 200. The connection area thus lies on the dry side of the tub and extends from the closed tube end 204 to the tub wall 210 defined plane. Thus, the heating area of the thick-film pipe heater 200 lies on the right-hand side of the tub wall 210 in the so-called wet area, ie is in direct contact with the medium to be heated during operation. The heating area extends approximately from the tub wall 210 to the open tube end 202.

Clearly visible are flow openings 230, which are arranged regularly spaced from each other over the entire heating area. The flow openings 230 here have the shape of oblong holes, which are formed obliquely to a vertical pipe cross-section with an angle α in the base body 201 of the thick-film pipe heater 200.

Next, the heating element 240 is applied to the base body 201, which extends bifilar guided over the entire heating area. In this case, each run a conductor 242 as a forward conductor and a conductor 244 as a return conductor parallel to each other with a slope substantially the angle α of Flow openings 230 corresponds.

In the connection area, electrical connections 252 and 254 for the heating conductor 240 are arranged. It should be noted that, as mentioned above, the electrical connections 252, 254 are made by using a material with a lower electrical resistance or by applying additional interconnect material compared to the remaining heating conductor 240 as so-called cold connections. Furthermore, a temperature sensor 260 for detecting the temperature of the medium to be heated is provided in the connection region. It should be noted that the electrical connections of the temperature sensor 260 in the Fig. 2a can not be seen, but these are basically designed similar to the electrical connections or interconnects of the heat conductor 240th

Fig. 2b shows a sectional view of the thick film tube heater 200 of the Fig. 2a , It should be noted that hereinafter only additional recognizable features over the Fig. 2a be explained. Good to see in Fig. 2b one of the fundamental advantages of the thick-film tube heater 200 according to the invention, which is that in the heating region both the outer surface 212 and the inner surface 214 of the tubular base 201 are in contact with the medium to be heated. Thereby, together with the regularly spaced flow openings 230, an optimal circulation of the medium to be heated on or along the surface of the thick-film pipe heater 200 and thus a faster removal of heat is ensured.

Another advantage is that the medium to be heated is also in the connection area on the inner surface 214 with the main body 201 of the thick-film tube heater 200 in contact and thus detected in the connection area by means of the temperature sensor 260 very accurately and unadulterated by the heating effect of the heating can be.

Clearly visible in the Fig. 2b is also the embodiment of the conical seal 220, which can be formed, for example, at the end of the production of the thick-film tube heater 200 according to the invention between the connection area and heating area outside by means of a spraying process. On the one hand This embodiment ensures a simple sealing of the connection area with the medium at the transition between the outer surface 212 and the seal 220, and secondly, the thick-layer tube heater 200, together with the seal 220, forms a heating module which is at the place of intended use Use very easy to install.

The Fig. 3a shows a side view of a second embodiment of the invention. The main difference in the Fig. 3a illustrated thick-film pipe heater 300 opposite to in the Fig. 2a and 2b illustrated thick-film tube heater 200 consists in the integration of a temperature sensor 360 ( Fig. 3b ) at the closed tube end 304 of the tubular Grundko body 301. Instead of the cover 206 in the Fig. 2a and 2b is in the embodiment of the thick film tube heater 300 in the Fig. 3a closed the tube end 304 by integration of the temperature sensor 360 in this pipe end 304. In this case, for example, a commercially available NTC / PTC element in a metal sleeve, for. As a chromium-nickel steel sleeve, are used, wherein the steel sleeve also acts as a housing for the sensor as well as a lid for the tubular body 301 at the closed end of the pipe 304.

It should be mentioned as particularly advantageous at this point that a commercially available temperature sensor with a plug connection 362, for example in the form of a so-called RAST housing, can be used here. In the Fig. 3b is the section marked with the dotted circle D of Fig. 3a shown as a detail section. Particularly well, the integration of the temperature sensor 360 can be seen with a sleeve in the tubular body 301. The sleeve of the temperature sensor 360 can, for example, be connected in a form-fitting manner to the tubular base body 301 by welding at the pipe edge 308. In this embodiment, the thick-film tube heater 300 according to the invention thus a very accurate temperature monitoring of the medium to be heated can be guaranteed because, as in the detail section D of Fig. 3b clearly visible, the sleeve of the temperature sensor 360 with the medium to be heated facing the outside 364 is almost completely in contact.

In the Fig. 4 a plan view of a heating module with two thick-film tube heaters 401 and 402 according to the invention is shown, the structure of which substantially the thick-film tube heater 200 of the Fig. 2a and 2b respectively. That in the Fig. 4 Heating module 400 shown is an example of how several of the thick-film pipe heaters according to the invention can be integrated particularly simple and advantageous parallel to each other in a heating module. The individual thick-film pipe heaters 401, 402 can be connected both electrically in parallel and in series, depending on the requirements of the respective field of use.

The heating module 400 has a seal 420 for installation in a tub wall 410, which in turn is arranged between the connection area and the heating area of the respective thick-film tube heaters 401, 402. The seal 420 is essentially again a conical seal, which allows a particularly simple installation in the tub wall 410. In order to enable a simple electrical connection of the existing safety devices or the connections of the heating conductors, a so-called RAST housing 430 with two plug connections 432, 434 between the two thick-film tube heaters 401, 402 is provided in this embodiment.

Since in the field of heating elements for washing machines, dishwashers, etc. certain dimensions have become established as a quasi-standard with respect to the installation opening in the respective tubs, the thick-film tube heaters according to the invention can of course also be integrated with a corresponding flange assembly into a heating module , wherein the outer dimensions of the flange assembly are then adapted to this quasi-standard of the household appliance industry. This has the advantage that manufacturers of the household appliance industry, who want to use these new heating elements, do not adapt the installation openings on their devices or have to change. Thus, the old technology of tubular heating elements can be replaced without problems and without any time or development effort against the new technology according to the present invention.

An example of a heating module 500 with standard flange assembly is shown in FIGS Fig. 5a and 5b shown. In Fig. 5a 2 shows a side view of the heating module 500 with a flange assembly 510, which consists essentially of a flange 512, a seal 514 and a clamping piece 516. To the left of the flange assembly 510 is the mating portion of one of the two thick film tube heaters (FIG. Fig. 5b : 501, 502) of the heating module 500. In the connection area, there are the two electrical connections 522, 524 and also the corresponding connections for a temperature sensor 530 provided in SMD design. Furthermore, a connection lug 518 for connecting a protective conductor to the flange 512 can be seen.

More precisely, the integration of the two thick-film tube heaters 501 and 502 in the heating module 500 in the Fig. 5b shown a plan view of a cross section of the heating module 500 of Fig. 5a shows. It can easily be seen that the two thick-film tube heaters 501, 502 are each mechanically fixed in or on the flange 512, wherein the seal 514 is arranged between the flange 512 and the clamping piece 516. Centrally in the flange assembly 510, a through hole is provided which extends through both the clamping piece 516, the seal 514 and the flange 512, through which through-hole a screw 542 is guided, which is pressed with a screw 543 in the clamping piece 516 and thereby against a rotation relative to the clamping piece 516 is secured. The screw end 544 opposite the screw end 543 protrudes from the flange and is provided there with a nut 545. When the nut 545 is tightened, the collet 516 presses the seal 514 against the flange 512 fixed to the thick film tube heaters 501, 502. As a result, the seal 514 swells at the periphery and seals against the mounting opening of the container (not shown). from. It should be noted that the flange assembly 510 is also designed this way may be that the clamping piece 516 is fixed to the thick-film tube heaters 501, 502 and the flange 512 remains movable.

In the following, a few more comments are to be made concerning the production of the thick-film pipe heater according to the invention. As a carrier for the functional layers of the thick-film pipe heater according to the invention, a stainless steel pipe, in particular of an austinitic or ferritic stainless steel, is particularly suitable because of its corrosion resistance. As Grundköper but basically any metal pipe can be used, in which optionally an additional corrosion protection is applied; Preferably, the tubular base body, or any other geometric base body is made of a cold strip steel section.

Since manufacturing technology attaching the flow openings, for example in the form of holes or slots in a tube designed as time-consuming and labor-intensive, has proven in the production of the basic body in tubular form for the thick-film pipe heating advantageous, a tubular Grundköper from a flat strip of material, in which the flow openings are punched or are to produce, by winding and then form-fitting connection of the abutting edges. This Grundköper is then closed at the pipe end to which the connection area is to be provided with a lid or, if provided in the pipe end, the installation of a temperature sensor with corresponding sleeve-shaped housing, left open. But it can also be attached at this point a corresponding sleeve, preferably made of the same material as the body, instead of the lid.

Before the functional layers of the thick-film tube heater are applied to the tubular base body, an additional preparatory method step may be inserted, which consists of suitably roughening the surface of the tubular base body by a radiating, etching or grinding process.

Since the preferred material for the base body is a metal which is inherently electrically conductive, the base body must be electrically insulated from the heat conductor to be applied. For this purpose, in the next step, a first electrically insulating dielectric layer is applied to the base body substantially over the entire surface of the base body. Finally, a multi-layer or multi-layer structure is conceivable, for example, to improve the thermal expansion behavior. Preferably, the dielectric layer is applied by means of one of the aforementioned methods. As the first electrically insulating dielectric layer and simultaneous corrosion protection, an enamel or glass layer is also suitable.

In order to further reduce the problem of crack formation in thick-film heating in the functional layers discussed above, expansion joints may be provided in the first cover layer at this point in the production process. Preferably, these expansion joints are arranged such that they are between and / or adjacent to those to be applied later Heizleiterbahnen lie. The expansion joints may be produced by means of a water jet cutting process, laser ablation processes or other suitable mechanical processes such as grinding, milling, blasting (in stencil technology or directly applied). But also chemical processes, such as etching, can be used.

At this point, it should again be pointed out that, since the dielectric layer is a porous layer, in particular a layer with open pores, in order to ensure a sufficient sealing, in particular of the end faces of the dielectric layer in relation to the medium to be heated in later use, Also, the area around the edges of the flow openings and at the pipe ends or the edges of the body should not be covered by the dielectric layer. This can be achieved by masking the slots or tube ends before applying the dielectric layer. But it is also possible to apply the first covering layer over the entire surface and then selectively remove it by means of a suitable abrasive method (abrasive process); here are for example water jet cutting and laser ablation, but also any other suitable mechanical method, such as grinding, milling or abrasive blasting using stencil technology or in direct application, can be used. Even chemical ablation processes, such as etching, are possible.

After producing the first covering layer and, if necessary, the expansion joints, the heating conductor layer is applied to the tubular base body. In principle, metals, metal alloys, ceramic-metal composites (so-called metal matrix composites or cermets) which are applied to the dielectric layer by means of one of the methods mentioned at the outset are suitable for the heating conductor layer. Successful trials have also been undertaken by means of screen-printed and subsequently fired resistor pastes.

Since the electrical connections of the heating conductors are preferably provided contactable on a pipe end of the tubular body, the heating element is preferably performed bifilar over the surface of the body and therefore a reversal point must be provided at the open end of the pipe. At this point it should be noted that when applying the Heizleiterschicht the possibility of forming different temperature zones by varying the Heizleiterdicke, Heizleiterbreite or by varying the distance between the Heizleiterbahnen is possible.

This aspect is in the Fig. 6 in a detailed view of a Heizleiterumkehrpunktes 630 on a thick-film tube heater 600 according to the invention. The detailed drawing shows the open tube end 602 of the tubular base body 601 with the Heizleiterbahnen 610 and a flow opening 620. At the Heizleiterumkehrpunkt 630 occurs in the Heizleiterführung inevitably on a very small space a 180 ° turn on the two Heizleiterbahnen 611, 612 of the bifilar heating 610 meet each other. At such Heizleiterumkehrpunkten 630 has been shown that there occur significantly higher electrical current densities, creating a hot spot. This problem is caused by additional application of conductor material 632 at such Heizleiterumkehrpunkten 630 (the same is in principle also at the contacting points in the connection area possible) counteracted. By this measure, a significant reduction in the resistivity of the conductor 610 at such locations and thus a significant reduction in temperature can be ensured. As an additional conductor (web) material 632 are particularly suitable materials such as a silver / palladium paste, which is applied after application of the heat conductor layer at the contacting points or the reversal points, but also electrically conductive polymers such. As silver-filled epoxy, or metals or metal alloys that can be thermally sprayed or cold sprayed.

After application of the heat conductor layer and appropriate treatment of the Kontaktierungsbereiche or reversal points, the pores of the porous dielectric layer and the porous resistance Heizleiterschicht are sealed by means of a single or multi-layer system and electrically isolated from the medium in operation during operation. For this purpose, as described above, a sealing layer and the topcoat are applied in a two-layer process or a single layer which has all the required properties in a one-layer process.

In the following, a two-layer process is described by way of example: First, a covering layer is applied, for which in principle the materials described below or the respective application methods are suitable. In principle, inorganic lacquers and lacquers with an organic-inorganic polymer matrix with embedded particles, such as nanocomposite lacquers, can be used here. Silicones and silicone oils are also suitable for sealing the pores in the porous layers.

Finally, the heater is still provided with a topcoat, such as a nanostructured anti-soiling layer. The particularly advantageous effect of such a layer lies in the reduction of cooking noise or the prevention of limescale, ie lime deposits. Furthermore, these layers are particularly mechanically resistant.

As already discussed in detail elsewhere, an important aspect for the practicality of the heating device of the invention on the one hand in the frontal covering and sealing of the pores of a possibly porous dielectric layer or the pores in a resistance heating conductor layer. Furthermore, for reasons of corrosion protection, it may be necessary to hermetically seal the main body at least in relation to the medium to be heated, or preferably completely. To show the Fig. 7a to Fig. 7d schematic detail views in each case of a section through the tube jacket 701 of the tubular base body and the functional layers, wherein in particular the open tube end 702 of the thick-film tube heater and the nearest flow opening 730 are shown.

The respectively in the Fig. 7a or 7b illustrated layer construction relates to the embodiment of a heating device of the invention, in which a corrosion-resistant material was used for the base body, such as an alloyed steel or a ceramic. Here, the basic body does not necessarily have to be completely sealed against the medium.

In the Fig. 7a is the material, eg. As glass or enamel, for the dielectric layer 710 for insulating the heating element 720 relative to the tube jacket 701 itself tightly against the medium to be heated. For this reason, the sealing of the end faces 712 at the pipe end 702 or at the flow openings 730 with respect to the medium can be dispensed with here. Finally, the heating element 720 is electrically insulated from the medium to be heated by means of a cover layer 750 and sealed.

In the execution, in Fig. 7b is shown, a cover of the end faces 712 of the dielectric layer 710 was additionally provided, because this here from a porous, ie not dense to the medium to be heated layer, as they arise just in thermally sprayed materials exists. To ensure this complete coverage of the respective end faces 712 of the dielectric layer 710 at the open tube end 702, at the flow openings 730, as well as at the expansion joints 740, it may be ensured before applying the cover layer 750 by means of an abrasive process be removed that the dielectric layer 710 to the pipe jacket 701. This is possible, for example, by laser ablation, water jet cutting, etching, milling or abrasive blasting (with stencils or in direct method). This can be done simultaneously with the manufacture of expansion joints 740.

The respectively in the Fig. 7c or 7d shown layer structure relates to the execution of a heater of the invention, in which a corrosion-prone material was used for the body, such. As a carbon steel. Therefore, in these embodiments, the main body has been completely sealed off from the medium by the cover layer 750.

In another embodiment, both the dielectric layer 710 and the second cap layer 750 are comprised of an enamel or a glass layer (not shown). In the Fig. 7c and 7d It can also be clearly seen that the covering layer 750 completely seals the main body 701, the dielectric layer 710 and the resistance heating conductor layer 720 to the outside and electrically isolates them.

In the Fig. 7e a further embodiment for the layer structure of the thick film heater according to the invention is shown. In this case, an adhesive layer 705 is provided between the surface of the main body 701 and the dielectric layer 710, which ensures improved adhesion of the functional layers on the main body 701. On the adhesive layer, the dielectric layer 710 is arranged, on which the heating conductors of the patterned resistance heating conductor layer 720 are located. The layers 705, 710 and 720 were applied by a method in which the generated layers have a porous structure; which is desirable as explained above. In particular, the open pores of these layers are closed by means of a seal 751, ie sealed against the liquid medium to be heated. This seal 751 is in the Fig. 7e indicated by the dots in the layers 705, 710 and 720. Finally, the entire layer structure of the layers 705, 710 and 720, including the seal, is finally finished with a so-called topcoat or surface anti-soiling layer 752 grafted, which in particular has such non-stick properties that no substances such as lime or washing substances can accumulate on the heater during operation of the heater in the heating area.

Finally, in the Fig. 7a to 7d also the cross section of Heizleiterumkehrpunktes 724 layer structure to recognize (in the Fig. 7a and 7d provided with reference numerals). In this case, the two heating conductors 721, 722 leading to the heating conductor inversion point 724 can be seen, which are both connected to one another by interconnect material 727 (approximately the same layer thickness as the resistance heating conductor layer 720) and coated with an additional layer of conductor material 728. By this measure, the electrical resistance of Heizleiterumkehrpunkts 724 is set much lower than at the remaining locations of the heating element 720. Thus, no hotspot can occur at this point in operation. As additional interconnect material 728, for example, a silver / palladium paste can be used in the production.

Another advantageous aspect of the thick-film heater according to the invention consists in the possibility of the electrical heat output during manufacture individually, d. H. z. B. according to the respective intended application or installation position in the application to be able to adapt. In this case, two different approaches are available in the thick-film heater of the invention. Once it is possible to apply the resistive heat conductor layer on the dielectric layer over the entire surface without structuring and then to structure by an erosive method, the resistance heating conductor layer according to the requirements. This structuring can be carried out by abrasive techniques, for example by laser structuring, water jet cutting, abrasive blasting, etching, milling and grinding.

A second possibility to adjust the electric power of the heating conductor is to apply the resistance heating conductor layer with the desired structure directly. Template techniques are suitable for this purpose, in which, for example, a mask is applied to the first cover layer by applying an anti-sticking material by means of screen printing, in which case subsequently on the unmasked areas the Heizleitermaterial is applied. However, it is also possible to apply the resistive heat conductor layer by a direct patterning coating without a template, for example with a fine coating jet or automated handling systems. In this case, the application width can be controlled, for example, via the variation of the distance of the jet nozzle from the first covering layer.

It should also be noted that in addition to the embodiment mainly described here with a single bifilar Heizleiterbahn and multitracking can be used, for example, four electrically parallel individual Heizleiterbahnen be performed instead of a single trace over the Grundköper. The advantage here is that it has been found that this can further avoid the occurrence of hotspots by deposits of foreign substances during operation of the heater. In addition, in case of failure of a single heating conductor, the operation of the thick-film pipe heater continues - with correspondingly lower heat output - possible. Furthermore, it is also possible to provide a plurality of heating conductors, which can be contacted individually in the connection area, on the base body.

Finally, the electric power of the heater can also be adjusted by resistance trimming. In this case, the electrical resistance and thus implemented in the Heizleiterbahn heat output is made by adjusting the Heizleiterbahnbreite or Heizleiterbahndichte. Thus, the resistance trimming over the web width of the heat conductor can be performed as follows: First, the Heizleiterbahn is structured with a sufficient width and thickness on the prepared body, then the electrical resistance of the heating element is measured, from this, the current quotient of the resistivity of the heating element and the cross section and thus the currently required conductor track width are calculated. This calculated width is finally adjusted by appropriate removal of Heizleiterbahnmaterial. As an alternative approach, the resistance trimming on the Heizleiterbahndicke is possible: Here, first, the Heizleiterbahn with a sufficient thickness and width on the structured basic body, then the electrical resistance of the heating element is measured and by so-called "micro forging" the Heizleiteroberfläche without abrasive (abrasive) effect with simultaneous measurement of the current resistance, the desired electrical resistance is set.

With regard to the temperature monitoring in the thick-film pipe heater according to the invention, it should be noted that here two aspects are of interest. On the one hand, the heating power should be able to be regulated in operation as a function of the desired temperature of the medium to be heated. But on the other hand, a monitoring of the Heizleitertemperatur should be done in order to detect abnormal operation and possibly interrupt the supply of electrical energy to the heating element. For temperature control, a temperature sensor in SMD design at any desired location, d. H. in the dry or wet area, be provided. At this point it should be pointed out again that this is conceivable both on the outer surface and the inner surface of the tubular body. Likewise, fuse elements can be provided to protect the heat conductor against overheating immediately next to or on an active Heizleiterbahn. Here, too, sensor components in SMD design are fundamentally suitable. But thick-film fuses can also be integrated at the respective desired location on the surface of the thick-film pipe heater in the above-described production process by means of screen printing or plasma spraying.

For contacting the electrical connections of the heating conductor or the electrical connections of the sensor elements integrated in the thick-film pipe heater, the connection plug parts described above can be pushed onto the connection region of the pipe with correspondingly suitable contacting. In this case, the temperature control or temperature monitoring and the line part can be performed separately or integrated in a male part. Suitable methods for connecting the connections to the connection points on the thick-film tube heating are soldering, friction welding, Ultrasonic welding or laser welding. But a contact via suitable spring contacts is possible.

Finally, again with reference to a perspective view of a heating module 800 with a thick film tube heater according to the invention in the Fig. 8 the main advantages resulting from the structure of the invention summarized. Shown is a heating module 800 with the tubular base body 801, which is divided functionally into the heating area 810 and the connection area 820. This results in the possibility of a simple installation of the heating module 800 by means of a seal 870 between the heating area 810 and the connection area 820. It has been shown that other standardized installation measures can be provided instead of the (cone) seal. At the right end of the heating area 810, in which the heating conductor 840 extends bifilarly over the tubular base body 801, there is the open tube end 802, in which the flow openings 830 can be seen. The tubular design of the heating with the open tube end 802 and the flow openings 830 represents a significant advantage, since this type compared to the conventional tubular heaters, a reduction of the displaced volume of the medium to be heated of about 25% is achieved. In addition, a particularly effective heat transfer to the medium to be heated and thus a faster heating than conventional tubular heaters is achieved. Next, the tubular structure of the thick-film tube heater according to the invention is ideal for the direct integration of temperature sensor elements 862, 864 but also other sensors (pressure sensors, pollution sensors, etc.) in SMD design both within, ie in the heating area 810, as well as outside It is also advantageous that in the connection area at the closed pipe end 804 a connection housing 850 with RAST plugs 852, 854 can be provided in a particularly simple manner, which provides a simple and safe Connection of the heating conductor 840 and also the temperature sensor elements 862, 864, for temperature monitoring of the medium to be heated and for thermal protection or monitoring of the heating element Serve 640, allow. Due to the significant reduction in the components of the thick-film pipe heater compared to a conventional pipe heater - for example, shown in the Fig. 1 - A significant shorter production time is achieved. This leads to not inconsiderable cost savings on the part of the manufacturer and thus represents a significant competitive advantage. Ultimately, the thick-film pipe heater according to the invention has a particularly effective protection against calcification and caking of organic substances due to the provided second and third cover layer, resulting in the reliability and Longevity of a thick-film pipe heater according to the invention significantly increased compared to the known tubular heaters.

With the present invention, a heating device for heating a liquid medium and a method for producing such a heating device have been proposed. The electric heating device has a main body, which may be provided in a heating area with a plurality of flow openings and in a development is a closed at least in the region of a first end tube. At least on one surface of the base body, the functional layers of the heating device are arranged, wherein at least one heating conductor is provided in the form of a structured thermally sprayed resistance Heizleiterschicht for converting electrical energy into heat with at least two electrical terminals that are designed and contacted in a terminal area, and there is a thermally sprayed dielectric layer between the heat conductor layer and the base body. In this case, at least in the heating region, pores of the resistance heating conductor layer and the dielectric layer are sealed against the medium and the resistance heating conductor layer is electrically insulated from the medium, in particular the surface in contact with the liquid medium to be heated during operation has non-stick properties.

Claims (15)

1. An electrical heating apparatus for the heating of a liquid medium, comprising:

   - a base body (201; 301; 601; 701;) having at least one heat conductive path (610) for transforming electric energy into heat, arranged in form of a structured resistor heat conductive layer (720) on a surface of the base body in a heating area (810) with at least two electrical terminals (252, 254; 522, 524) which are formed in a terminal area (820) and are contactable,

   - a dielectric layer (710) arranged between the base body (201; 301; 601; 701;) and the heat conductive layer (720), and

   - at least one covering layer (750) which insulates electrically the heat conductive path (610) and the dielectric layer (710) against the medium,

   characterized in that the heating apparatus is coated at least in the heating area (810) such that open pores in the heat conductive layer (720) and the dielectric layer (710) are sealed against the medium, and the surface of the heating apparatus shows anti-sticking characteristics against the medium at least in the heating area (810).
2. The heating apparatus as claimed in claim 1,
   wherein expansion joints are provided in the dielectric layer (710) beside and/or between adjacent heat conductive paths (610) formed in the resistor heat conductive layer (720).
3. The heating apparatus as claimed in any one of the above claims,
   wherein the base body (201; 301; 601; 701;) selectively consists of stainless steel, non-ferrous metal, ceramics, glass or a composite thereof.
4. The heating apparatus as claimed in any one of the above claims,
   wherein the dielectric layer (710) is thermally injection moulded and consists of aluminium oxide (AlO₃), zirconium oxide (ZrO₂), titanium oxide (TiO₂), silicon oxide (SiO₂), chromium oxide (Cr_2O3), borosilicate or a mixture thereof.
5. The heating apparatus as claimed in any one of the claims 1 to 3,
   wherein the dielectric layer (710) is a sol-gel-layer based on aluminium oxide (AlO₃), zirconium oxide (ZrO₂), titanium oxide (TiO₂) or silicon oxide (SiO₂).
6. The heating apparatus as claimed in any one of the above claims,
   wherein the covering layer (750) is a nanocomposite-varnish, a siloxane or a silicone-oil.
7. The heating apparatus as claimed in any one of the above claims,
   wherein the anti-adhesive-layer is a glass or ceramics layer, or a sol-gel-layer, or is a layer formed by silicone, a modified silicone, a polyimide, a polyamide-imide, a modified polyester-imide.
8. The heating apparatus as claimed in any one of the above claims,
   wherein the heat conductive layer (720) is thermally injection moulded and consists of a metal, a metal alloy or a ceramics-metal-composite.
9. The heating apparatus as claimed in any one of the above claims,
   wherein a thermally injection moulded sticking layer consisting of metal or a metal alloy, is additionally provided between the dielectric layer (710) and the base body (201; 301; 601; 701).
10. The heating apparatus as claimed in any one of the above claims,
    wherein the base body (201; 301; 601; 701) is further a tube being closed in the region of a first tube end.
11. The heating apparatus as claimed in any one of the above claims,
    wherein the base body (201; 301; 601; 701) has a plurality of flow openings (230; 620; 730; 830) in the heating area (810).
12. A method for manufacturing a heating apparatus as claimed in claims 1 to 11, comprising the steps of:

    - producing a base body (201; 301; 601; 701);

    - applying a first electrically insulating dielectric layer (710) onto the base body (201; 301; 601; 701) by a thermally injection moulding process;

    - applying at least one structured heat conductive layer (720) onto the dielectric layer (710) by a thermally injection moulding process, wherein the method is characterized by the step:

    - applying an electrically insulating covering layer (750), which is medium-tight and shows anti-sticking characteristics, onto the heating apparatus at least in the heating area, wherein pores in the dielectric layer (710) and the heat conductive layer (720) are sealed medium-tight.
13. The method for manufacturing a heating apparatus as claimed in claim 12, further with applying a sticking layer onto the base body (201; 301; 601; 701).
14. The method for manufacturing a heating apparatus as claimed in claims 12 or 13,
    wherein the step of applying an electrically insulating covering layer (750) which is medium-tight and shows anti-sticking characteristics, consists of the following intermediate steps:

    - applying a first sealing layer sealing the pores in the dielectric layer (710) and the heat conductive layer (720) medium-tight at least in the heating area; and

    - applying a second nano-structured anti-soiling-layer over the covering layer (750) at least in the heating area.
15. The method for manufacturing a heating apparatus as claimed in any one of the claims 12 to 14,
    further with producing of expansion joints in the dielectric layer (710) beside and/or between the heat conductive path (610) in the structured heat conductive layer (720).

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