WO2012075548A2

WO2012075548A2 - Heating element

Info

Publication number: WO2012075548A2
Application number: PCT/BE2011/000069
Authority: WO
Inventors: Leo Albert Julia Gypen; Gunter Knevels; Edward Strzebonski
Original assignee: Polyvision, Naamloze Vennootschap
Priority date: 2010-12-10
Filing date: 2011-12-07
Publication date: 2012-06-14
Also published as: BE1019697A3; WO2012075548A3

Abstract

Electrical heating element (11) consisting of a steel plate (13), with dielectrically insulating or otherwise enamel undercoats on the back (15) and on the front (14), provided or otherwise with an electrically insulating enamel topcoat (16) on the undercoat, if present, on the back, to which electrical resistors (17) for heating are affixed, covered or otherwise with an overlay, characterised in that the heating element (11) has an enamel topcoat (14a) on the undercoat on the front (14), on which a picture or pattern (14b) is annealed for communicative messages and/or publicity purposes and/or decorative purposes, whereby all coats have an annealing temperature above 600 °C.

Description

Heating element

The present invention relates to a heating element for warming people in their everyday surrounds or objects in their everyday surrounds.

More specifically the heating element is intended for electrical heating by means of an enamelled steel plate.

It is known that in electrical heating the heat emitted by radiation is more efficient than by convection.

The radiation increases with the fourth power of the absolute temperature (T⁴ in degrees Kelvin) . Enamelled steel has a high emission coefficient for heat radiation, i.e. 0.9.

Instead of heating the surrounding air as convection heating does, the radiant heat is absorbed directly by people and objects. This ensures more efficient energy consumption.

Moreover, enamelled steel offers benefits such as resistance to high temperatures, scratch resistance, resistance to acids, and it is colourfast and practically indestructible .

Enamelled steel can withstand high temperatures because it can absorb thermal expansion on account of the inherent built-in tensile stresses in the steel core and the compressive stresses in the enamel layers.

Electrical heating panels are already known in which an enamelled steel plate has heating resistors on the back, embedded in an electrical insulating layer, that is laminated on a fireproof plate such as calcium silicate, which itself is covered with a plate of galvanised steel. Such a heating panel can for example be mounted in the ceiling with the galvanised steel against the ceiling and the heated enamelled steel turned to the underlying room.

Such plates (for example, Alliance Vitratherm) can reach temperatures of up to 80°C.

Similar plates for vertical installation in heating elements against the walls of rooms were also put on the market by Alliance (today called PolyVision) , in which the temperature reached by the heating element can rise to 240°C, with a maximum of 275°C.

A disadvantage of such heating panels of enamelled steel is that temperatures above 300 °C cannot be achieved, while the radiation increases with the fourth power of the temperature in degrees Kelvin, and the radiation in Watts/m² at 450°C for example is more than five times as high than at 220°C. Another disadvantage of such heating elements is that the enamelled surface of the heating element, which is turned towards the room, has no decoration and is a monochrome colour .

In order to respond to this, there are electrical heating panels that have an additional decorative panel to better integrate the heating element into a room (www. redwell . com) . Enamelled decorative panels are used for this that are secured in front of the heating element by a holder, and which do not form part of the heating element itself. The heating resistors are affixed in the heating element and do not have any direct contact with the enamelled decorative plate.

A disadvantage of such heating elements with a decorative panel is that when heating up and cooling down, annoying tapping noises can occur as a result of the expansion or contraction of components .

Another disadvantage of such a heating panel is that the decorative plate itself is not heated by the heating resistors, but indirectly heated by the heating element resulting in heat losses and a lower temperature of the heating panel and thus a lower fraction of radiant heat. The lower the fraction of radiant heat, the higher the temperature of the heated room has to be to give the same feeling of warmth, and thus the greater the C0₂ emissions for the same heating. A further disadvantage of such a heating panel is that the cost is higher to give the same feeling of warmth.. The purpose of the present invention is to provide a solution to the aforementioned disadvantages and other disadvantages by providing an electrical heating element consisting of a steel plate, with enamel undercoats, electrically insulating or otherwise, on the back and on the front; equipped or otherwise with an electrically insulating enamel topcoat over the undercoat, if present, on the back, to which electrical resistors, covered or otherwise with an overlay, for heating are affixed, whereby the heating element has an enamel topcoat on the undercoat, if present, on the front, on which a picture or pattern is annealed for communicative messages and/or decorative and/or publicity purposes, and whereby all coats have an annealing temperature above 600 °C.

An advantage of a heating element according to the invention is that the heating element itself already has a decorative picture, such that the mounting of an additional decorative panel becomes superfluous.

Another advantage of this heating element is that it only consists of one part, such that disturbing noises caused by the expansion and contraction of components under the influence of the temperature are prevented.

An advantage is also that the enamel layer with the decorative or communicative or publicity pattern is heated directly by the heating resistors such that there are no heat losses and the temperature of the heating plate can be higher and it can emit a higher fraction of radiant heat and whereby less C02 is emitted into the environment. The cost (kWh) for the consumer is also lower to provide the same feeling of warmth.

Another advantage attached to such a heating element is that a second panel is no longer required for a communicative message, which leads to cost savings and space savings.

Preferably the annealed colour picture is formed by means of screen printing, digital inkjet printing, toner jet printing, stamp printing or by the transfer (produced by screen printing, inkjet or toner jet) of a suitable enamel (paste, ink or powder) followed by annealing at a high temperature .

This technique presents the advantage that any coloured pattern, such as a painting for example, can be annealed in the enamel at high temperature, such as 800°C, so that the pattern is colourfast, heat resistant, scratch resistant and resistant to graffiti, and requires no further maintenance .

Preferably the enamelled steel of the heating element according to the invention consists of stainless steel. Stainless steel ensures that the iron diffuses into the enamel layers less, such that the reliability at high temperatures is greater than with conventional types of enamelable steel. In addition, the insulating layer can consist of an enamel undercoat and topcoat or a dielectric placed locally or otherwise or over the entire surface. An advantage of using stainless steel in combination with suitable dielectric insulating enamels in the heating element is that this material is resistant to temperatures of up to 500°C, such that the fraction of the emitted heat, emitted as radiant heat, increases substantially, which has a favourable effect on the temperature required in the heated room and ensures less CO₂ production for the same heating effect. The cost (kWh) for the consumer is also lower .

A heating element at a higher temperature also offers the advantage that a smaller area of heating element is needed to achieve the same heating capacity. The frame for the heating element is also smaller and the cost will thus fall.

Preferably the enamelled steel in the heating element consists of decarbonised steel or enamelable low-carbon steel .

An advantage of using such carbon-free or low carbon steel is that it enables better adhesion of the enamel layer on the steel. As an option the steel plate or the heating element used, in addition to being of a flat form, can also be of a curved form, both a convex or concave form.

An advantage of such a curved form is that the heating element can thus be built into objects or walls that are not flat, which enables new architectural applications. The invention also relates to a method for manufacturing a heating element consisting of applying, or otherwise, electrically insulating or non-electrically insulating enamel undercoats to the front and back of a steel plate; the application of an enamel topcoat on the undercoat, if present, on the front, , on which a picture or pattern is annealed for communicative messages, and/or publicity purposes and/or decorative purposes; the optional application of a coat of electrically insulating enamel topcoat above the undercoat, if present, on the back; the affixing of electrical resistors to the back that are covered or otherwise with an overlay; the annealing of all layers above 600°C.

Preferably in this method for manufacturing a heating element, a stainless steel plate is used that is roughened by means of sandblasting or pearl blasting or by scouring before the plate is given enamel layers. This steel plate can also be decarbonised steel or enamelable low-carbon steel .

Preferably the two sides of the heating element are coated with enamel layers by roller coating in a continuous enamelling line or by screen printing.

Preferably an enamel undercoat is applied to the front and back of a steel plate by coating both sides with an enamel undercoat, and the enamel undercoat is annealed at a temperature between 700°C and 1000°C, better even between 830°C and 920°c, and best at 850°C. Preferably the application of an enamel topcoat to the front of a steel plate, and the application or otherwise of an electrically insulating enamel topcoat on the back is done by coating both sides with an enamel topcoat, and the enamel topcoat is annealed between 650 °C and 950 °C, better even between 800°C and 890°C, and best at 820°C.

Preferably an electrically insulating enamel layer is applied to the back of a stainless steel plate by partially coating the back by screen printing with an electrically insulating enamel layer, on which an electrically conductive silver paste is screen printed, and above which a topcoat is screen printed, while the front is coated asymmetrically over the entire surface with an enamel layer on which a coloured picture or pattern is annealed.

Preferably in the method to manufacture a heating element, the steel plate is coated on the back and front with an electrically insulating enamel layer.

Preferably, in the method the picture or pattern on the enamel topcoat is applied to the front by means of screen printing, digital inkjet printing, toner jet printing, stamp printing or via a transfer (produced by screen printing, inkjet or toner jet) before the picture or pattern is annealed on the enamel topcoat, whereby the communicative and/or publicity and/or decorative enamel layer is annealed at a temperature between 600 °C and 1000°C, better even between 650°C and 850°C. Preferably the electrical resistors for heating and the electrically insulating enamel layer are applied to the back by means of screen printing or another printing or transfer technique for silver paste, whereby a circuit is formed.

Preferably an overlying pattern of glass is applied onto the circuit of silver paste by means of screen printing before it is all annealed at a temperature of 600°C to 950°C, better even from 620°C to 680°C, and best at 650°C, whereby this overlying glass pattern is either annealed together with the silver paste circuit (2 coat/1 fire) or separately (2 coat/2fire) . Preferably conductive terminals are attached to the circuit by means of electrically conductive epoxy glue, or by means of welding, brazing, welding or mechanical fasteners.

If legally required, an earth pin is affixed by means of spot welding at a place where the enamel layer has been sanded away.

In a preferred method, the back of the heating element is glued against the front of a fire retardant chipboard, which itself has its back glued to a galvanised plate.

With the intention of better showing the characteristics of the invention, a preferred embodiment is described hereinafter by way of an example, without any limiting nature, of a heating element according to the invention, with reference to the accompanying drawings, wherein: figure 1 schematically shows a cross-section of an electrical heating element according to the state-of- the-art .

figure 2 shows a detail F2 of figure 1 on a larger scale .

figure 3 schematically shows a cross-section of a heating element according to the invention,

figure 4 shows a communicative message applied to the heating element according to the invention.

figure 5 shows a first step of the method for manufacturing a heating element according to the invention .

figures 6, 7, 8 and 9 show subsequent steps of the method of figure 5.

figure 10 shows an optional additional step of the method.

figure 11 schematically shows a cross-section of an alternative embodiment of a heating element according to the invention.

Figure 1 schematically presents a cross-section of an electrical heating element 1 according to the state-of-the- art, consisting of a fireproof core material 2 on the back screened by galvanised steel 3, and on the front with a decorative panel 4 of enamelled steel and recesses 5 in the core material in which there are heating resistors 6.

Figure 2 shows a cross-section of a heating resistor 6 on a larger scale, in which the resistance wire 7 of the heating resistor is illustrated, surrounded by electrical insulation 8 and by a heat-resistant and electrically insulating sheath 9. This heating resistor is embedded in grooves of the core material 2 by means of a glue 10. The operation of the heating element 1 according to the state-of-the-art is simple and as follows. The electrical heating resistors 6 are heated by an electric current and emit their heat to the layer of glue surrounding it. The enamelled plate in itself does not have electrical heating resistors and is heated through the glue layer 10 and through the core material 2 that surrounds the resistors.

The heat generated in the electrical resistor 6 first has to go through the heat-resistant and electrically insulating sheath and then through the glue, such that energy loss occurs twice here, and a large percentage of the heat is dissipated sideways into the core material 2 and is not directly emitted to the enamelled steel panel 4. The embodiment shown is that of a heating element 1 that is secured against the wall or ceiling, and has an enamelled steel monochrome panel 4 on the front. The heating element reaches a temperature of 80 °C and the core material 2 together with the top plate 3, of galvanised steel, protect the wall or ceiling against too high a temperature.

Figure 3 shows a heating element 11 according to the invention, consisting of an enamelled steel plate 12 formed by a steel support 13, with an enamel undercoat 14 on the front and also with an enamel undercoat 15 on the back, to which a ceramic insulating layer 16 is applied to the back to which heating resistors 17 are affixed, which themselves are covered by a protective and covering glass layer 18. On the enamel undercoat 14 on the front, a second enamel coat 14a is applied on which a ceramic colour picture 14b or pattern is annealed. This pattern can be a communicative message and/or publicity message and/or have a more decorative purpose. For example, on the front there can be an indication of an emergency exit as shown in figure 4, or another communicative message can be portrayed without a separate panel having to be manufactured or installed for this indication 14b. The invention enables such a message to be applied in a durable way during the manufacture of the heating element, which saves costs and materials. The operation of the heating element 11 is very simple and as follows. The electricity supply to the heating element 11 is as a rule controlled by a thermostat, which ensures that a certain ambient temperature is reached. The electricity supply through the heating resistors 17 heats them up, such that the heat is transferred directly to the enamelled steel plate 12. The hot steel plate primarily emits its heat as radiant heat, which gives a subjectively warmer feeling for people than with convection heat. The heating element 11 can for example take on the form of a painting hanging on the wall, and is thus no longer visible as an inconvenient heater in the room.

The decoration on the heating element 11 is moreover colourfast, scratch resistant, heat resistant, acid resistant and graffiti resistant and requires no maintenance .

Figure 5 shows a first step of the method for manufacturing a heating element 11 according to the invention that can be heated to 350-500°C.

In this first step ferritic stainless steel 19 of 0.7mm thick, for example, with a chrome content of 16% to 18% (AISI 430), or 17% to 20% chrome (AISI 444) for example, is first sandblasted or pearl blasted or scoured or roughened to obtain good adhesion of the enamel and is then coated with an enamel undercoat 20 on the top 14 and bottom 15 and then dried and annealed in an oven at 850°C. Then the back 16 is coated with insulating enamel 21 and the front 14 with coloured enamel 22. These topcoats are dried and annealed in an oven at 850°C. The resulting enamelled steel is stored on a roll or plate by plate. The advantage of continuous enamelling in an enamelling line is the low cost per m² due to the high automation and reduced enamel losses.

Figure 6 shows a second step of the production process in which the enamel decoration 14b on the enamel topcoat 14a is applied to the front of the enamelled steel plate by means of screen printing, digital inkjet printing, toner jet printing, stamp printing or by transfer (produced by screen printing, inkjet or toner jet) of a suitable enamel (paste, ink or powder) . Then the plate is annealed in an oven at 800°C.

Figure 7 shows a third step of the production process in which the heating resistors are screen printed on the back 16 of the plate as a circuit 17 of silver paste, consisting of insulating enamel 16 and enamel undercoat 15 after which the circuit is dried.

As shown in figure 8, an overlay of glass 18 is then screen printed over the circuit 17 and everything is annealed vertically at temperatures between 500°C and 900°C, for example at 650 °C.

An advantage of such covered heating resistors 17 is that they are thus corrosion resistant.

Figure 9 shows a fourth step of the production process in which conductive terminals 23 are attached to the circuits of heating resistors 17 by means of an electrically conductive epoxy glue 24.

An advantage of such terminals 23 is that their adhesion to the heating element 11 is very robust. If legally required an earth pin can be affixed (not shown in the drawings) by means of spot welding at a place where the enamel coat has been sanded away, and this to prevent charge accumulation. In a fifth step of the method the circuit of electrical resistors 17 is electrically tested at voltages up to 350V and the heat emission is measured as a control. In figure 10 a sixth and optional production step is shown in which the heating element 11 is glued by its back 15 to the front of a fire retardant chipboard 24, which itself is glued by its back to a 0.40mm thick galvanised plate 25. An advantage of this construction is that the wall or ceiling is protected by the fire retardant chipboard 24 and the structurally strengthening galvanised plate 25 against the high temperature of the heating element. Figure 11 shows an alternative embodiment in which the heating element 11 consists of a stainless steel plate 13, which is partially coated on the back with an electrically insulating enamel layer 16 by means of screen printing, on which an electrically conductive silver paste 17 is screen printed, and above which a topcoat 18 is screen printed, while the front is asymmetrically coated over the entire surface with an enamel layer 14a on which a coloured picture or pattern 14b is annealed. An advantage of this construction is that the stainless steel does not have to be coated over the entire surface of the back, which leads to material savings.

The present invention is by no means limited to the embodiment described as an example and shown in the drawings, but a heating element 11 according to the invention can be realised in all kinds of variants, without departing from the scope of the invention.

For example, alternative methods for manufacturing such heating elements are possible in which the enamel undercoat is applied, which is then dried and an enamel topcoat coat applied, which is then also dried, after which the two layers together are annealed in one passage in an oven at around 850°C.

Another alternative method consists of applying the enamel topcoat in one coat directly to the steel, which may be nickel-plated steel or otherwise.

Claims

Claims .

1.- Electrical heating element (11) consisting of a steel plate (13), with electrically insulating or otherwise enamel undercoats on the back (15) and on the front (14); provided or otherwise with an electrically insulating enamel porcelain (vitreous) topcoat (16) on the undercoat, if present, on the back, to which electrical resistors (17) for heating are affixed, covered with an overlay or otherwise, characterised in that the heating element (11) has aenamel porcelain (vitreous) topcoat (14a) on the undercoat, if present, on the front (14), on which a picture or pattern (14b) is annealed for communicative messages and/or publicity purposes and/or decorative purposes, and whereby all coats have an annealing temperature above 600 °C.

2.- Electrical heating element (11) according to claim 1, characterised in that the steel (13) of the heating element consists of stainless steel.

3.- Electrical heating element (11) according to claim 1, characterised in that the steel (13) of the heating element consists of decarbonised stee or enamelable low-carbon steel .

4.- Electrical heating element (11) according to claim 1, characterised in that the steel plate or the heating element presents a flat or curved surface, both in the convex or concave form.

5. - Electrical heating element (11) according to claim 2, characterised in that the stainless steel (12) is roughened by means of sandblasting or pearl blasting or scouring, for example, before the enamel coats are applied.

6. - Method for manufacturing a heating element (11) consisting of applying or otherwise electrically insulating or non-electrically insulating enamel undercoats to the front (14) and back (15) of a steel plate (13); applying an enamel topcoat (14a) to the undercoat, if present, on the front (14), on which a picture or pattern (14b) is annealed for communicative messages and/or publicity purposes and/or decorative purposes; as an option applying an electrically insulating enamel topcoat (16) above the undercoat, if present, on the back (15); affixing electrical resistors (17) to the back (15) that are covered or otherwise with an overlay; the annealing of all coats above 600°C.

7. - Method for manufacturing a heating element (11) according to claim 6, characterised in that the steel plate (13) consists of stainless steel.

8. - Method for manufacturing a heating element (11) according to claim 6, characterised in that the steel plate (13) consists of decarbonised steel or enamelable low- carbon steel.

9. - Method for manufacturing a heating element (11) according to claim 7, characterised in that the stainless steel is roughened by means of sandblasting or pearl blasting or scouring, before being provided with enamel coats.

10. - Method for manufacturing a heating element (11) according to claim 6, characterised in that the coating of both sides with enamel layers is done by roller coating in a continuous enamelling line or by screen printing.

11. - Method for manufacturing a heating element (11) according to claim 6, characterised in that the application of an enamel undercoat to the front (14) of a steel plate (13) and to the back (15) of it is done by coating both sides with an enamel undercoat and annealing the enamel undercoat at a temperature between 700°C and 1000°C, better even between 830°C and 920°C, and preferably at 850°C.

12.- Method for manufacturing a heating element (11) according to claim 6, characterised in that the application of an enamel topcoat to the front (14) of a steel plate (13) and the application or otherwise of an electrically insulating enamel topcoat to the back (15) by coating both sides with an enamel topcoat and the annealing of the enamel topcoats between 650 °C and 950 °C, better even between 800°C and 890°C, and preferably at 820°C.

13. Method for manufacturing a heating element (11) according to claim 6, characterised in that the heating element (11) consists of a stainless steel plate (13) that is partially coated on the back with an electrically insulating enamel layer (16) by means of screen printing, on which an electrically conductive silver paste (17) is screen printed, and above which a topcoat (18) is screen printed, while on the front the entire surface is asymmetrically coated with an enamel layer (14a) on which a colour picture or pattern (14b) is annealed.

14. Method for manufacturing a heating element (11) according to claim 6, characterised in that the heating element 11 consists of a steel plate (13) that is coated on the back and front with an electrically insulating enamel layer (16) .

15.- Method for manufacturing a heating element (11) according to claim 6, characterised in that the colour picture or pattern (14b) is applied to the enamel topcoat (14a) on the front by means of screen printing, digital inkjet printing, toner jet printing, stamp printing or via a transfer (produced via screen printing, inkjet, or toner jet) before being annealed onto the enamel topcoat (14a).

16.- Method for manufacturing a heating element (11) according to claim 12, characterised in that the application of a communicative and/or publicity and/or decorative enamel coat to the front (14) is done at a temperature between 600 °C and 1000 °C, better even between 650°C and 850°C.

17.- Method for manufacturing a heating element (11) according to claim 6, characterised in that the application of the electrical resistors (17) for heating the electrically insulating enamel layer (16) on the back is done by screen printing or another printing or transfer technique for silver paste, whereby a circuit is formed.

18. - Method for manufacturing a heating element (11) according to claim 13, characterised in that an overlying pattern of glass (18) is applied onto the silver paste circuit by screen printing before it is all annealed at a temperature of 600°C to 950°C, or even better at 620°C to 680°C, and preferably at 650°C, whereby this overlying glass pattern is either annealed together with the silver paste circuit (2 coat/1 fire) or separately (2 coat/2 fire) .

19. - Method for manufacturing a heating element (11) according to claim 14, characterised in that conductive terminals (23) are affixed to the circuit of heating resistors (17) by means of electrically conductive epoxy glue (24), or by means of welding, brazing, soldering or by means of mechanical fasteners.

20. - Method for manufacturing a heating element (11) according to claim 14, characterised in that an earth pin is affixed by spot welding at a place where the enamel layer has been sanded away, if this is a legal requirement.

21. - Method for manufacturing a heating element (11) according to claim 6 characterised in that the heating element (11) obtained has its back (15) glued to the front of a fire retardant chipboard (24), which itself is glued by its back to a galvanised plate (25) .