WO2001035700A1

WO2001035700A1 - Safety panel for high-efficiency heating by electricity

Info

Publication number: WO2001035700A1
Application number: PCT/IT1999/000414
Authority: WO
Inventors: Bruno Ceraso; Aldo Stabile
Original assignee: Cedal Srl; Cadif Srl
Priority date: 1999-11-09
Filing date: 1999-12-20
Publication date: 2001-05-17
Also published as: DE69917685D1; DE69917685T2; KR100637066B1; IL149305A0; CN1378765A; TW474111B; JP2003514359A; CA2390030A1; US6654551B1; EP1228669A1; JP3682651B2; ITMI992336A1; KR20020059672A; EP1228669B1; AU2000700A; IT1319291B1; ATE268100T1

Abstract

Panel (10) for heating by an electric resistance obtained from a serpentine (55) of highly conductive material formed of a thin continuous strip of constant width, having a high ratio between width and thickness, that generates radiant heat by means of electromagnetic waves, placed inside a flat metal chamber (96) given a hermetic seal by continuous welds (90-95) along all its joins, obtained from a basic rectangular tray-shaped structure (11) and from similarly tray-shaped closing structures (80, 81) placed side by side in the basic structure (11).

Description

Safety panel for high-efficiency heating by electricity

The invention concerns electric generators of heat. There are countless processes and types of apparatus for generating heat all based essentially on the combustion of gas, fuel oil and coal, and on electric resistances.

The thermal chain so set up conditions the thermal efficiency of these heating systems

Heat may be produced in a boiler or oven and is transferred from there, by means of a diathermic liquid such as water or oil, to a central heating plant that supplies warmth to indoor areas or rooms, or to the bodies to be heated by conduction or convention In the first case the heater must be placed in contact with the body to be heated. In the second case heat from the hotter body is passed into the environment or to the body to be heated by some fluid, such as air for example.

The heating device must have a large surface area to enable great quantities of heat to be emitted at a low thermal head in order to avoid overheating the walls of the device which would damage the fluid circulating inside.

The diathermic liquids must posses certain characteristics, above all that of maintaining stability at a high temperature. For temperatures up to 310-350°C mineral oils are often used today in the form of high-boiling fractions of oil refined to remove unsat- urated substances that might become polymerized, while special additives are put in to improve thermal stability so interrupting chain reactions and cracking.

The mode of radiancy transfers heat from the hot body to the colder body by means of electromagnetic waves. This mode is usually realized by electric heating elements that transform electric energy into thermal energy.

To assist radiancy metal reflectors are used to diffuse heat rays but efficiency is generally lower than diffusion by other methods as the electric elements reach very high temperatures and heat the air closest to them so setting up a convective movement. With the methods described it will be clear that there is considerable loss of heat along the thermal chain, especially on account of the great differences in temperature between the flame or electric heating elements and that of the body to be heated, the actual quantity of energy used, compared with that available, therefore being very low.

Generation of heat by radiancy through emission of electromagnetic waves creates a risk of deflagration especially in installations where inflammable substances in the gaseous or aeriform state are present. From the foregoing it will be seen that present methods of creating radiancy are expensive, low in efficiency and possibly dangerous. The above invention permits heat to be generated by emission of electromagnetic waves, achieving a much higher level of efficiency than that possible with other methods, eliminating all danger and offering other considerable advantages as will be explained below. Subject of the invention is a panel for heating by means of an electric element placed in a flat metal chamber hermetically sealed by continuous welding along all the joins among the various components of the chamber.

The electric heating element consists of a serpentine of highly conductive material, formed of a thin continuous strip of constant width presenting a high ratio between width and thickness, laid in lengths placed side by side, at a reciprocal distance for electrical insulation, terminating in two contacts that can be con-nected to a source of electric current, generating radiant heat by means of electromagnetic waves.

The two contacts are connected to two opposing terminals in each of which is a screw to fix the two electric feed wires that pass through hermetically sealed bushes placed on a rectangular plate situated at one end of the panel. The serpentine is placed in the hermetic metal chamber over a sheet of mica laid on the bottom, is covered with a second sheet of mica and is formed of a series of U-shaped bends crossed through by a series of parallel strips of mica laid transversally. At one side of the serpentine the first strip passes below the first part of a bend, above the second part of said bend, below the first part of the next bend, over the second part of said bend, below the first part of a successive bend, and so on till it reaches the opposite side of the serpentine. The second strip, begun at a short distance from the first, passes over the first side of a bend in the serpentine, below the seond part p. of said bend, over the first part of the next bend, below the second part of said bend, over the first part of a successive bend, and so on till it reaches the opposite side of said serpentine. The third strip is laid so as to follow a route similar to that of the first strip, while the fourth strip follows a route similar to that of the second strip, and so on right to the end of the serpentine. The chamber is substantially box-shaped and is formed of a basic rectangular tray-shaped structure, of a sheet of metal bent at 90° to make the four sides, continuously welded at the corners, and of one or more tray-shaped closing structures laid side by side inside the basic structure, also consisting of a metal sheet bent at 90° to make the four sides with continuous welds at the corners. The external length of said closing structures corresponds to the internal length of the basic structure less the width of the rectangular plate that carries the electric wiring. Overall external width of said closing structures corresponds to the internal width of the basic structure.

The external height of said closing structures corresponds to the internal height of the basic structure less the sum of the thickness of the serpentine, of the sheets of mica placed under and over it, and of the interposed strips of mica.

The edges of the basic structure, of the closing structures and of the upper surface of the rectangular plate inserted at one end of the basic structure between the closing structures and the edge of said basic structure, are therefore tangential to one and the same geo- metrical plane.

The edges of said closing structures lie side by side with the edges of the basic structure and with the edge of the inner side of the rectangular plate. The edges of the other three sides of this plate match with the edges of the sides of the basic structure.

A continuous weld is made along all the matching edges of the basic and closing structures.

The height of the chamber so formed substantially corresponds to the thickness of the serpentine, plus the thickness of the two sheets of mica and plus the thickness of the interposed strips of mica, the effect of all this being to ensure a hermetic seal to the chamber thus removing any risk of infiltration of inflammable gaseous substances, both on account of the hermetic seal and due also to lack of sufficient free volume inside the chamber to receive enough air and cause a deflagration. According to the type of execution the serpentine may be made of copper, brass or some other material.

In one type of execution the strip of the serpentine is about 0.5 mm thick and about 7 mm wide.

In one type of execution the panel is applied in one or more units to the walls of the chambers of a continuous oven.

The various units of the panel are aligned and opposite each other.

The oven may be placed vertically or horizontally as required.

In one type of execution, an impregnated band is passed into the chambers of the continuous oven, for drying and polymerizing, said band unwinding from a coil at the entrance and winding onto another coil on leaving the chambers after polymerization produced by the effect of radiancy.

In another type of execution, a bend in a continuous conveyor belt is passed into the chamber of the continuous oven, said belt being supported at entry to and exit from the chamber by two rollers, one of which is motor-driven so that sheets treated with paints, inks and other materials can be laid one after another on said belt for polymerization.

In another type of execution, at both longitudinal ends of the oven there is a continuous chain fitted with automatic pincers, which chain,^' forming a pair with the opposite one, picks up, one after another, with its automatic means, sheets of copper or other material treated with paints, inks or some other substance, from a flat surface at the starting end of the chamber of the oven, and carries them inside said chamber.

In one type of execution one or more of the panel units are placed around closed spaces so forming static ovens to produce physical and chemical changes in materials.

In another type of execution one or more of the panel units are placed at the inner walls, which may also include the bottom, of baths, tanks and the like, into which fluid materials are poured for physical or chemical transformation.

In another type of execution one or more of the panel units are placed on the flat areas of an apparatus, of devices in general, whose purpose is to radiate heat, such as hotplates and the like. In another type of execution, one or more units of the panel, are placed inside buildings to provide needed warmth. In another type of execution one or more units of the panel, are placed inside buildings where heat is required for certain kinds of production. The invention offers evident advantages.

By placing the serpentine, that transforms electrical energy into thermal energy, inside a hermetically sealed metal chamber, of a size substantially the same as that of said serpentine with its sheets of mica, and creating said hermetic seal by continuous welds along all the matching edges of the parts forming said chamber, the described panels can also be used in installations and in places where the risk of deflagration exists due to the presence of inflammable gaseous substances. Heat is generated by electric current already diffused and therefore at the temperature required for carrying out the processes without any need for diffusers, providing a much higher level of efficiency compared with that obtainable with materials well known to be classified as resistive. In this latter type of material the electrones strongly resist separa- tion from the core this being the effect of passage of electric current. In highly conductive materials such as copper, brass and the like used in this present patent application, the electrones offer far less resistance to separation from the core such as is caused by passage of electric current. As emission of heat is linked to the path taken by the electrones, it follows that transformation of electric energy into thermal energy using highly conductive materials of suitable dimensions, takes place at a considerably higher level of efficiency than that achievable with ordinary resistive materials. From the above it will be seen that subject panels present two basic characteristics:

- a degree of efficiency much greater than that of ordinary generators of heat for transformation of electric energy;

- complete safety from deflagration making them usable in practi- cally ahy installation and in any environment.

The fact of obtaining a method of high-efficiency heating by electricity, one that is free from risk, even in places where deflagration may occur, means that the invention here described can be used with all the advantages pertaining to electric heating, namely maximum possibility of adjustment, easy installation, very low bulk and weight compared with other forms of heating. The above also shows that these panels provide an interesting application in impregnating systems, in ovens for drying and for polymerizing paints and inks as well as in a wide range of instalia- tions and equipment.

Particularly in the fields of impregnating means for polymerization of bands for printed circuits, great importance is attached to the drastic reduction in waste, as seen in Figures 5 and 6 respectively relating to radiographic pictures of bands made either with the usual method of heating or with heating by the panels subject of the invention. Characteristics and purposes of the disclosure will be made still clearer by the following examples of its execution illustrated by diagrammatically drawn figures.

Fig. 1 The panel with electric serpentine in a sealed chamber, with detail, in perspective.

Fig. 2 An exploded perspective of the panel, with cut-away detail. Fig. 3 The serpentine, with detail, in perspective. Fig. 4 Vertical oven for polymerizing a fiberglas band, made using a set of the described panels, front view with perspective detail of one panel.

Fig. 5 Radiographic picture of a piece of impregnated band after polymerization by a traditional means of heating. Fig. 6 Radiographic picture of a piece of impregnated band after polymerization using a set of panels subject of the invention. Fig. 7 Front view of a horizontal oven for polymerizing an impregnated band, made with a set of the described panels, and detail of one panel in perspective.

Fig. 8 Front view of a horizontal oven for polymerizing sheets of copper and the like treated with paints, inks and other substances, showing chain and pincers, made with the described panels, and detail of one panel in perspective. Fig. 9 Detail of the oen in Figure 8, side view. Fig.10 Front view of a horizontal oven for polymerizing sheets of copper and the like treated with paints, inks and other substances, showing the conveyor belt, made with the described panels, and detail^" of one panel in perspective.

The panel 10 comprises a basic metal structure 11 in a single tray- shaped rectangular piece, with a bottom 12 and sides 13, formed by bending at 90° the metal sheet from which said base is formed, and with welds 15 at the corners 14.

The insulating sheet 20 of mica is laid on said bottom 12. Over said sheet 20 the electrical complex 30 is laid, this comprising the serpentine 55 with contacts 50 and 51 fixed to the opposing oblong terminals 31 , 32 connected by the insulating bridge 34 and pins 35. On top of the terminals are screws 36 to hold the ends of the electric wires 40 which connect to the main electric feed passing through the bushings 42, sealed against deflagration, inserted into holes made for them in a crosswise rectangular plate 43 whose internal length corresponds to the internal width of the basic structure 11.

A set of parallel strips 60, 61 of mica and others laid crosswise are inserted into said serpentine 55.

As seen in the detail in Figure 3, the first strip 60 passes under the first part of a bend 70 in the serpentine, over the second part of said bend 70, under the first part of the next bend 71 , over the second part of said bend 71 , under the first part of a successive bend 72 and so on as far as the opposite side of the serpentine. At a short distance from the first strip, a second strip 61 passes over the first part of the bend 70 in the serpentine, under the second part of said bend, over the first part of the next bend 71 , under the second part of said bend 71 , over the first part of a bend 72 and so on to reach the opposite side of the serpentine. The third strip follows the same route as the first one, while the fourth strip follows that of the second strip, and so on to the end of the set of parallel strips.

A second sheet 21 of mica is laid over the described serpentine. Over said second sheet of mica, the two closing tray-shaped structures 80 and 81 are laid, placed side by side lengthwise. The sum of the widths of said two structures 80, 81 corresponds to the internal widith of the structure 11 , while the length of said structures 80, 81 corresponds to the internal length of said basic structure 11 , less the width of the rectangular plate 43. Each of the structures 80, 81 is obtained from a metal sheet that forms the bottom 85 bent to 90° at the sides, to form the sides 86 closed by welds 88 at the corners 87 where they join. The external height of the sides of said structures 80,81 corresponds to the depth of the basic structure 11 less the sum of the thickness of the sheets of mica 20 and 21 and of the serpentine 55 with its strips like strips 60, 61. On completion of assembly the panel 10 appears as shown in Fig.1. The upper edge of the basic structure 11 , of the closing structures 80, 81 and the upper face of the plate 43 lie substantially on the same geometrical plane and all their edges, like 90-95, are welded. These welds ensure a total hermetic seal for the chamber 96 (detail in Figure 1), so created between the basic structure 11 and the closing structures 80, 81.

As the height of chamber 96 corresponds to the sum of those of the sheets of mica 20 and 21 , of the serpentine 56 and of the crosswise strips like 60, 61 , the free volume in said chamber is so very small that, even in the event of infiltration of explosive gases during a heating process, the quantity of said gases would be insignificant and an explosion would be impossible.

The serpentine 55 is made of highly conductive material such as copper, brass and the like. Resistance to passage of the current needed to transform electric energy into thermal energy and its diffusion, is determined by the dimensions of said serpentine, namely by its very slight thickness, about 5 mm, by its great width and by its length. Figure 4 shows an example of application of the panels 10 in an oven for polymerization 100. Said oven presents the structure 101 that supports the pulley 102 around which the fiberglas band 105 unwinds, said band being impregnated with resin so that it will receive sufficient heat for polymerization when passing through the chambers 106, 107. Heat is transmitted by electromagnetic waves from the panels 10. Transformation of the solvent in gaseous substances, possessing characteristics which may even be explosive, need give no cause for concern as the panels provide safety against deflagration. These panels not only increase efficiency and avoid danger, but also permit greater radiancy by means of electromagnetic waves that first act substantially in the central part of the body to be polymerized and then on its surface.

Many of the presently used heating systems act in the opposite way, first on the surface of the body and then inside it; this leads to drawbacks because the polymerized surface material hinders penetration of heat inside the body creating bubbles and other irregularities. Especially in parts for printed circuits, these bubbles cause much damage preventing the parts from operating properly. Figure 5 shows a radiography of a piece of band 120 polymerized by ordinary convection systems, the bubbles 122 being clearly visible especially among the fiberglass fibres 121. Figure 6 shows a radiography of a band 125 polymerized by the panels subject of the invention where no bubbles or other imperfections can be found among the fiberglas fibres 126. Figure 7 illustrates a polymerization oven 130 substantially similar to that seen in Figure 4, but operating horizontally. The chamber 132 in the oven 130 is formed of two sets 133, 134 of panels 10 like those already described, aligned on two opposite geometrical planes, and is supported by uprights 135 fixed below to the base 136 and, at the top, to the head 137. The supports 140 and 141 at entry and exit to the chamber 132, carry the pairs of rollers, respectively to guide 142 and pull 143 the band 148 to be polymerized. Figure 8, front view, with side view detail Figure 9, illustrates a horizontal polymerization oven 150 for sheets of copper or other material treated with paints, inks and the like. The chamber 152 in the oven 150 is formed of two sets 153 and 154 of panels 10, like those described, aligned above and below, and is supported by the uprights 155 fixed to the base 156. and above, to the head 157.

The painted copper sheets, like 160, placed on the bed with the roller surface 165, are drawn along by a set of pincers 161 support- ed by two continuous chains, like 162, placed parallel between them, at the two longitudinal ends of the oven 150, and operated by electric ratiomotors 163 through gear wheels 164. The painted sheets 160 are picked up by the pincers 161 and carried along by the continuous parallel chains 162 to the exit from the chamber 152, and there laid on the bed with roller surface 166. Figure 10 illustrates a polymerization oven 170 substantially similar to the oven 150 already described, in which is a chamber 172 formed of two aligned and opposing sets 153, 154 of panels 10, like those described, supported by a structure 171 similar to the structure 151 described earlier.

Said structure 171 carries a conveyor belt 175 supported at its two ends by rollers 176 and 177 situated at the beginning and end of said structure 171. The beds 178 and 179, with roller surfaces, respectively support the painted sheets to be polymerized, like sheet 180, and those already polymerized, like sheet 181.

Sheets 180 to be polymerized are laid one after another on the conveyor belt 175 that draws them inside the chamber 172 and, after polymerization, carries them to the exit onto the bed 179.

Claims

1. Panel (10) for heating by an electric resistance (55), characterized in that the electric resistance (55) is put in a flat metal chamber (96) hermetically sealed by continuous welding (90-95) along all the joints among the components of the chamber (96).

2. Panel (10) for heating by an electric resistance as in claim 1 , characterized in that the electric resistance (55) is formed of a serpentine of highly conductive material consisting of a thin continuous strip of constant width, having a high ratio between width and thickness, laid in lengths side by side reciprocally at a distance for electrical insulation, terminating at two contacts (50, 51 ) connect- able to a source of electric current generating radiant heat by means of electromagnetic waves.

3. Panel (10) for heating by an electric resistance as in claim 2, characterized in that the two contacts (50, 51) are connected to two opposing terminals (31 , 32) each comprising a screw (36) to fix the two electric feed wires (40) passed through the hermtically sealed bushings (42) placed on a rectangular plate (43) situated at one end of the panel (10).

4. Panel (10) for heating by an electric resistance as in claims 1 and 2, characterized in that the serpentine (55) is placed in the hermetically sealed metal chamber (96) over a sheet of mica (20) laid on the bottom (12), is covered with a second sheet (21) of mica and is formed of a series of U-shaped bends (70-72) crossed through by a series^ of transversal parallel strips (60, 61) of mica, the first strip (60) at the start of the serpentine (55), passing under the first part of the bend (70), over the second part of said bend (70), under the first part of the next bend (71 ), over the second part of said bend (71), under the first part of a successive bend, and so on as far as the opposite side of said serpentine (55), the second strip (61) at a short distance from the first one (60), passing over the first part of the bend (70) of the serpentine (55), under the second part of said bend (70), over the first part of the next bend (71), under the second part of said bend (71), over the first part of a successive bend, and so on as far as the opposite side of said serpentine (55), the third strip being laid so as to follow a path similar to that of the first strip (60), while the fourth strip resumes a path similar to that of the second strip (61), and so on to reach the end of the serpentine (55).

5. Panel (10) for heating by an electric resistance as in claims 1-3, characterized in that the chamber (96) is substantially box-shaped and is formed of a rectangular tray-shaped basic structure (11), consisting of a metal sheet bent at 90° at its four sides, having continuous welds (15) at the corners (14), and of one or more tray- shaped closing structures (80, 81) inserted side by side into the basic structure (11 ), similarly formed of a metal sheet bent at 90° at its four sides, with continuous welds (88) at the corners (87), the external length of said closing structures (80, 81) corresponding to the internal length of the basic structure (11) less the width of the rectangular plate (43) that supports the electric wires (40), the total external width of said closing structures (80, 81), placed side by side, corresponding to the internal width of the basic structure (11), the external height of said closing structures (80, 81) corresponding to the internal height of the basic structure (11) less the sum of the thickness of the serpentine (55), of the sheets of mica (20, 21) placed over and under it and of the interposing strips (60, 61) of mica, so that the edges of the basic structure (11), of the closing structures (80, 81) and the upper surface of the rectangular plate (43) placed at one end of the basic structure (11) between the closing structures (80, 81) and the edge of said basic structure (11), are substantially tangential to one and the same geometrical plane, the edges of said closing structurres (80, 81) lying side by side at the edges of the basic structure (11) and at the edge of the inner side of the rectangular plate (43), the edges of the other three sides of this latter matching with the edges of the sides of the basic structure (11), a continuous weld (90-95) being made along all the matching edges of the basic structure (11) and of the closing structures (80, 81), the height of said chamber (96) substantially corresponding to the thickness of the serpentine (55), plus the thickness of the two sheets (20, 21) of mica and plus the thickness of the interposed strips (60, 61) of mica, the effect of all this being to ensure a hermetic seal to the chamber (96) so removing any risk of infiltration of inflammable gaseous substances both on account of the presence of said hermetic seal and because of there being insufficient free volume inside the hermetic chamber (96) to receive a quantity of air that could give rise to a deflagration.

6. Panel (10) for heating by an electric resistance, as in claim 2, characterized in that the serpentine (55) is made of copper.

7. Panel (10) for heating by an electric resistance, as in claim 2, characterized in that the serpentine (55) is made of brass.

8. Panel (10) for heating by an electric resistance, as in claim 2, characterized in that thickness of the serpentine (55) is approximately 0.5 mm.

9. Panel (10) for heating by an electric resistance, as in claim 2, characterized in that the width of the strip that forms the serpentine (55) is approximately 7 mm.

10. Panel (10) for heating by an electric resistance, as in claims 1 -5, characterized in that it is applied, in one or more units, to the walls of the chambers (106, 107, 132, 152) of a continuous oven (100, 130, 150).

11. Panel (10) for heating by an electric resistnce as in claim 10, characterized in that its various units are aligned and opposite.

12. Panel (10) for heating by an electric resistance as in claim 10, characterized in that the oven (100) is placed vertically.

13. Panel (10) for heating by an electric resistance as in claim 10, characterized in that the oven (130) is placed horizontally.

14. Panel (10) for heating by an electric resistance as in claim 10, characterized in that an impregnated band (105, 148) to be dried and polymerized is passed into the chambers (106, 107, 132) of the continuous oven (100, 130), said band unwinding from a coil at the entrance and winding onto a coil at the exit from the oven (100, 130) after polymerization produced by the effect of radiancy.

15. Panel (10) for heating by an electric resistance as in claim 10, characterized in that a bend in a continuous conveyor belt (175) passes inside the chamber (172) of the continuous oven (170), said belt being supported at its two ends, at entry to and exit from the oven (170), by two rollers (176, 177) one of which is motor-driven to allow sheets (180, 181) for polymerization, treated with paints, inks and other substances, to be laid one after another on said belt (175).

16. Panel (10) for heating by an electric resistance, as in claim 10, characterized in that at each longitudinal end of the oven (150) is a continuous chain (162) fitted with automatic pincers (161), which chain, operating as a pair with the opposite continuous chain, picks up with its automatic means sheets (160) of copper or other material to be polymerized, treated with paints, inks and other substances, one after another from a bed (165) at the beginning of the oven (150), and carries them inside the chamber (152) of the oven (150).

17. Panel (10) for heating by an electric resistance, as in claims 1-5, characterized in that, one or more units (10) of it are placed around closed spaces to create static ovens in which to produce physical and chemical changes to materials.

18. Panel (10) for heating by an electric resistance as in claims 1-5, characterized in that one or more units (10) of it are placed at the intermal walls, and even on the bottom, of baths, tanks and the like, into which fluid materials are poured for producing physical or chemical changes.

19. Panel (10) for heating by an electric resistance as in claims 1-5, characterized in that one or more units (10) of it are placed on the flat areas of pieces of apparatus, devices in general, to be used for radiating heat such as hotplates and the like.

20. Panel (10) for heating by an electric resistance as in claims 1 -5, characterized in that one or more units (10) of it are placed inside buildings where environmental warmth is required.

21. Panel (10) for heating by an electric resistance as in claims 1 -5, characterized in that one or more units (10) of it are placed inside buildings where heat is required for certain types of production.