CA1213635A - Vacuum-formed electrical heating device and method of production - Google Patents
Vacuum-formed electrical heating device and method of productionInfo
- Publication number
- CA1213635A CA1213635A CA000434781A CA434781A CA1213635A CA 1213635 A CA1213635 A CA 1213635A CA 000434781 A CA000434781 A CA 000434781A CA 434781 A CA434781 A CA 434781A CA 1213635 A CA1213635 A CA 1213635A
- Authority
- CA
- Canada
- Prior art keywords
- heating coil
- tray
- sieve
- vacuum
- heating
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 238000010438 heat treatment Methods 0.000 title claims abstract description 97
- 238000000034 method Methods 0.000 title claims abstract description 21
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 7
- 239000000835 fiber Substances 0.000 claims abstract description 43
- 239000000919 ceramic Substances 0.000 claims abstract description 19
- 238000000465 moulding Methods 0.000 claims abstract description 18
- 239000011230 binding agent Substances 0.000 claims description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 3
- 239000002002 slurry Substances 0.000 claims 2
- 239000000853 adhesive Substances 0.000 claims 1
- 230000001070 adhesive effect Effects 0.000 claims 1
- 239000002657 fibrous material Substances 0.000 claims 1
- 239000000463 material Substances 0.000 abstract description 11
- 238000002425 crystallisation Methods 0.000 abstract description 3
- 230000008025 crystallization Effects 0.000 abstract 1
- 238000004873 anchoring Methods 0.000 description 4
- 239000007788 liquid Substances 0.000 description 3
- 239000005995 Aluminium silicate Substances 0.000 description 2
- 239000002390 adhesive tape Substances 0.000 description 2
- PZZYQPZGQPZBDN-UHFFFAOYSA-N aluminium silicate Chemical compound O=[Al]O[Si](=O)O[Al]=O PZZYQPZGQPZBDN-UHFFFAOYSA-N 0.000 description 2
- 229910000323 aluminium silicate Inorganic materials 0.000 description 2
- 235000012211 aluminium silicate Nutrition 0.000 description 2
- 239000000470 constituent Substances 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 238000013021 overheating Methods 0.000 description 2
- 238000001953 recrystallisation Methods 0.000 description 2
- 239000004411 aluminium Substances 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 239000004033 plastic Substances 0.000 description 1
- 239000002023 wood Substances 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B3/00—Ohmic-resistance heating
- H05B3/20—Heating elements having extended surface area substantially in a two-dimensional plane, e.g. plate-heater
- H05B3/22—Heating elements having extended surface area substantially in a two-dimensional plane, e.g. plate-heater non-flexible
- H05B3/28—Heating elements having extended surface area substantially in a two-dimensional plane, e.g. plate-heater non-flexible heating conductor embedded in insulating material
- H05B3/283—Heating elements having extended surface area substantially in a two-dimensional plane, e.g. plate-heater non-flexible heating conductor embedded in insulating material the insulating material being an inorganic material, e.g. ceramic
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B3/00—Ohmic-resistance heating
- H05B3/20—Heating elements having extended surface area substantially in a two-dimensional plane, e.g. plate-heater
- H05B3/22—Heating elements having extended surface area substantially in a two-dimensional plane, e.g. plate-heater non-flexible
- H05B3/28—Heating elements having extended surface area substantially in a two-dimensional plane, e.g. plate-heater non-flexible heating conductor embedded in insulating material
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B3/00—Ohmic-resistance heating
- H05B3/62—Heating elements specially adapted for furnaces
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T29/00—Metal working
- Y10T29/49—Method of mechanical manufacture
- Y10T29/49002—Electrical device making
- Y10T29/49082—Resistor making
- Y10T29/49083—Heater type
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T29/00—Metal working
- Y10T29/49—Method of mechanical manufacture
- Y10T29/49002—Electrical device making
- Y10T29/49082—Resistor making
- Y10T29/49087—Resistor making with envelope or housing
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Ceramic Engineering (AREA)
- Inorganic Chemistry (AREA)
- Resistance Heating (AREA)
- Blow-Moulding Or Thermoforming Of Plastics Or The Like (AREA)
- Furnace Details (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
In a vacuum-moulding process for manufacturing an electrical heating unit, in which process a resistance heating coil is placed on a sieve-like tray, above a suction box, and a slip is applied thereto, this slip being composed of ceramic fibres, so that a ceramic fibre layer builds up under the action of suction, it is proposed, according to the invention, that portions of the sieve-tray be closed, in regions beneath the resistance heating coil, in particular by means of spacing strips, and that these strips, which cover some of the perforations in the sieve-tray, be placed beneath the resistance-heating coil, but in a manner such that the impervious regions of the sieve-tray are narrower than the width dimensions of the heating coil. These measures lead to the result that the space inside the heating coil remains free of fibre material during the vacuum-moulding operation, so that the temperature difference between the radiating side of the heating coils and their rear side, which lies within the composition forming the fibre block, is smaller than in conventional heating units of this type, in which there is a risk of crystallization of the fibres forming the fibre block. The use of spacing strips produces retaining webs on the radiating side of the fibre block, these webs ensuring that the heating coils are securely anchored.
In a vacuum-moulding process for manufacturing an electrical heating unit, in which process a resistance heating coil is placed on a sieve-like tray, above a suction box, and a slip is applied thereto, this slip being composed of ceramic fibres, so that a ceramic fibre layer builds up under the action of suction, it is proposed, according to the invention, that portions of the sieve-tray be closed, in regions beneath the resistance heating coil, in particular by means of spacing strips, and that these strips, which cover some of the perforations in the sieve-tray, be placed beneath the resistance-heating coil, but in a manner such that the impervious regions of the sieve-tray are narrower than the width dimensions of the heating coil. These measures lead to the result that the space inside the heating coil remains free of fibre material during the vacuum-moulding operation, so that the temperature difference between the radiating side of the heating coils and their rear side, which lies within the composition forming the fibre block, is smaller than in conventional heating units of this type, in which there is a risk of crystallization of the fibres forming the fibre block. The use of spacing strips produces retaining webs on the radiating side of the fibre block, these webs ensuring that the heating coils are securely anchored.
Description
;35 The invention relates to a vacuum-moulded electrical heating unit, in which a resistance heating coil is embedded in an insulating body, in a manner such that a surface zone of the heating coil is exposed at the radiating heating surface, the insulating body being composed of ceramic fibre material. A heating unit of this type is also designated as a heating module. In addition, and primarily, the invention relates to a vacuum-moulding process for manufacturing an electrical heating unit of this type.
The basic technique for vacuum-moulding electrical heating units, which will hencefvrth be termed "heating modules", is described, for example, in U.S. Patent 3,500,444, and in a more modern form in U.S. Patent 4,278,877.
In heating modules which are manufactured according to this vacuum-moulding process, the heating spirals or heating coils are embedded in the ceramic fibre composition, in a manner such that the space inside the heating coils is, under normal circum~tances, filled with fibre material.
The object underlying the invention is to provide heating modules, of the type initially mentioned, together with a vacuum-moulding process for manufacturing them, as a result of which the anchoring of the heating coil, in aluminium ~ilicate fibre compo~ition, is prevented from loosening, or from breaking down, even when the heating coil is heated to an optimum operating temperature, such that, for example, a temperature of 1,150C occurs at the radiating side of the module.
As a result of the invention, the space inside the heating coil remains more or less free of fibre material, so that the temperature difference at the heating coil, between the radiating surface of the heating module and the rear side, i8 considerably reduced, and the heating coil can, in its entirety, be operated at a markedly higher operating temperature, without incurring the danger of gradual loosening from the anchoring inside , -- 1 -- ., ~Z13~35 the fibre block.
Due to the fact that, during the vacuumrmoulding process, spacing elements are placed beneath the heating coils, or the perforation of the sieve-tray is relieved beneath the heating coils, that is to say is absent, the spacing elements or, as the case may be, the impervious regions of the sieve-tray being narrower than the width measurements of the heating coils in a plane parallel with the radiating surface, or are narrower than the diameter of the heating coils, the re~ult is obtained whereby the space inside the heating coils remains substantially free of fibre material, since it is obvious ~hat the openings in the sieve-like tray are partially closed, during the vacuum-moulding operation, over the longitudinal extent of the heating coils, or are absent in these regions.
In a particularly atvantageous embodiment of the invention, strir like elements, hereinafter termed "spacing strips", are positionet beneath the heating coils, during the vacuum-moulding operation, 80 that, although the heating coils are exposed at the radiating surface of the heating module, for reasons which will be further explained below, they are nevertheless displaced, in their entirety, backwart~ into the fibre block by a distsnce corresponding to the thickness of the spacing strips 80 that optimum anchoring is obtained, while at the same time the space indide them remains free of fibre material.
In the text which follow~, the state of the art, the invention and advantageous details, in the form of illustrative embodiments, are explainet in more detail by reference to the drawing, in which:
Figures 1 and 2 show the state of the art;
Figure 3 shows a first illustrative embodiment, in order to explain the vacuum-moulding process according to the invention;
Figure 4 shows, in a diagrammatic representation, the product 1~13~35 resulting from the vacuum-moulding process according to Figure 3;
Figure 5 shows an illustrative embodiment, which is to be preferred, of a vacuumrmoulding process according to the invention, and Figure 6 shows, again in a diagrammatic representation, the product of the vacuum-moulding process according to Figure 5, in order to explain certain advantageous properties.
In all the figures, mutually corresponding parts are identified by the same reference numbers.
In order to explain the starting point for the invention, the conventional vacuum-moulding process is first described by reference to Figure 1.
A heating coil 5 i8 placed on a ~ieve-like tray 1, for example on a perforated plate. A suction box, which is not represented, is located beneath the tray 1, through which box liquid is drawn off, by means of the vacuum which is indicated, generally, by the reference number 2, from a slip 3 which is poured on top, and which is composed of a solution of a binder, in water, containing ceramic fibres. The liquid constituents are drawn off, by suction, through the sieve-like tray 1, and a layer of ceramic fibre~ builds up.
In this conventional process, the space 8 inside the heating coil 5 is, as a rule, also filled with the cersmic fibres, and, moreover, the density in this interior space 8 will correspond to approximately the density of the remainder of the composition forming the ceramic fibre block 4, namely to approximately 200 kg/m .
The technical problems which arise in the course of using heating ~odules of this type are described in the text which follows, by reference to Figure 2.
When the freely radiating surface region of the heating coil 6 i8 brought to an operating temperature of, for example 1,150C, a considerably , ~ - 3 ~Z~35i higher temperature will occur on the opposite side ~the rear side 7) of the heating coil 5, this rear side being completely embedded in the ceramic fibre composition. As a result, it is not possible to heat the heating coil 5, on its side 6 at which its surface radiates freely, to the operating temperature which is, at most, desired, since the rear side 7 would then be overheated. A
problem which is associated therewith is concerned with the maximum possible use temperature or operating temperature of the aluminium silicate fibres which are quite predominantly employed for the fibre composition, these fibres being employed most frequently for economic reasons. More recent experience has shown that the maximum permissible operating temperature for such aluminium silicate fibres is approximately 1,150C. Above this temperature, the fibre~ undergo excessive crystallisation, which leads to the complete loss of their structure and of the properties which are desired. If, now, the heating coil is raised to a temperature of 1,150 C on the side 6 at which the surface radiates freely, the rear side 7 of the heating coil 5 can thus reach a temperature of approximately 1,250 C. This temperature is then approximately 100 C above the maximum permissible operating temperature of the fibres and will lead to exce~sively rapid recrystallisation of the fibre material. As a result, the heating coil 5 loses its grip in the overheated portion of the fibre composition and will detach itself, ~ore or less quickly, from the fibres, above all in the case of roof-elements in~ide a furnace chamber. The heating coil 7 will then initially protrude more and more from the radiating side 9 of the fibre block 4, and will finally fall out.
Figure 3 illustrates a first embodiment of the invention. Strips lO
of adhesive tape are, for example, applied to the sieve-like tray 1 (the perforated plate), these strips covering the perforations over the longitudinal extent of the heating coils 5, that is to say in the direction perpendicular to the plane of the drawing. These strips 10 of adhesive tape --- 121~635 are applied directly beneath the heating coils 5, which are subsequently placed on the perforated plate and lightly fixed. Due to the fact that some of the perforations are closed, the vacuum 2 produce~ no suction effect at these points, so that the space 8 inside the heating coils 5 remains free of ceramic fibre material to the greatest possible extent.
The result of the manufacturing process explained by reference to Figure 3 is shown in Figure 4. Here too, the heating coil 5 lies flush with the ratiating side 9 of the fibre block 4, in a manner similar to the arrangement in the case of the illustrative embodiment shown in Figure 2. The space 8 inside the heating coilq 5 is now empty, that is to say free of fibre material, 80 that the rear side 7 of the heating coils 5 can radiate considerably more freely. By this means, the result is obtained whereby the temperature difference at the heating coil, between the freely radiating side 6 at the radiating surface 9 and the rear side 7, is markedly reduced, thus avoiding undesirable overheating in the region of the rear side 7 of the heating coils 5.
However, this first, basic embodiment of the invention still possesse~ the tisadvantage that the heating coil 5 is now less effectively bonded to the ceramic-fibre block 4, although the above-described recrystallisation effect, due to partial overheating, is no longer observed in the fibres. However, the heating coils 5 are surrounded by fibre material only along their outer periphery and, moreover, they are not held at the freely radiating side 6, a~ is also the case in the state of the art according to Figure 2. Despite the fundamental advantage that the crystallisation of the fibre material no longer occurs, a further difficulty can, however, arise in the ca~e of this design, due to the fact that, as a result of inadequate anchoring, the heating coils fall out of the fibre block, especially when this type of heating module is employed for roof-structures in furnace chambers.
_ 5 _ The idea underlying the considerably improved embodiment of the invention, according to Figures 5 and 6, is to embed the heating coil 5 in ehe composition of the fibre block 4 in a manner such that, on the one hand, the space 8 inside it remains free of ceramic fibres, without, on the other hand, incurring the danger of the heating coils 5 being able to fall out of the fibre block 4, as the result of inadequate adhesion~
The principle underlying the manufacturing process is first explained by reference to the diagrammatic sectional representation shown in Figure 5.
Spacing strips 11 are attached to the sieve-like tray 1, beneath the positions which the heating coils 5 are to occupy. These spacing strips 11 can be composed, for example, of metal, wood or plastic. The width of these spacing strips 11 should, in any case, be somewhat less than the diameter or, as the case may be, the width measurement of the heating coil 5 in a plane parallel with that side 9 of the fibre block 4 which forms the radiating surface, while the thickness of the spacing strips 11 should lie within the range from 0.1 mm, at the minimum, to approximately 30 mm, and preferably within the range from 2 to 10 mm. If now the slip 3 is introduced into the frame, which is not shown in more detail but is equipped with the sieve-like tray 1, and if the liquid constituents are drawn off through the sieve-like tray 1, the fibres accordingly build up in a manner such that the spacing strips 11 are surrounded, while the space for inside the heating coils 5 remains substantially empty, that is to say free of deposits of fibres.
Figure 6 shows the resulting product, in a schematic sectional representation. The freely radiating side 6 of the heating coil 5 no longer lies flush with the radiating side 9 of the fibre block 4, but lies at a position which i9 displaced backwards into the fibre block 4 by a distance corresponding to the thickness of the spacing strips Il. The retaining webs 12, resulting from the presence of the spacing strips 11, partially surround ~2~35 the freely radiating side 6 of the heating coils S, but without the interior space 8 being filled with fibres. As a result, the desired objective was achieved, namely to keep the interior space free of fibres, so that the temperature difference between the radiating side 6 and the rear side 7 of the heating coils 5 is considerably smaller than in the case of the conventional technique, in which the heating coils are completely embedded in the fibre block 4, that is to say with the space 8 inside them filled by fibres.
Moreover, on the other hand, the retaining webs 12 securely hold the heating coils S, so that there is no longer any danger of their falling out, even when this type of heating module is used as a roof-element in a furnace.
As can be seen from the Figures, so-called oval heating coils or heating spirals 5 are provided in those embodiments of the invention which have been described, these coils, or spirals, being of the type which is also described in the abovementioned U.S. Patent 4,278,877, with the advantages mentioned therein. A person skilled in the art can appreciate, without difficulty, that the invention can also be employed, with advantage, for heating coils possessing other cross-sections, for example possessing a round cross-section, or a cross-section which has been deformed into a rectangle.
,~.
.
The basic technique for vacuum-moulding electrical heating units, which will hencefvrth be termed "heating modules", is described, for example, in U.S. Patent 3,500,444, and in a more modern form in U.S. Patent 4,278,877.
In heating modules which are manufactured according to this vacuum-moulding process, the heating spirals or heating coils are embedded in the ceramic fibre composition, in a manner such that the space inside the heating coils is, under normal circum~tances, filled with fibre material.
The object underlying the invention is to provide heating modules, of the type initially mentioned, together with a vacuum-moulding process for manufacturing them, as a result of which the anchoring of the heating coil, in aluminium ~ilicate fibre compo~ition, is prevented from loosening, or from breaking down, even when the heating coil is heated to an optimum operating temperature, such that, for example, a temperature of 1,150C occurs at the radiating side of the module.
As a result of the invention, the space inside the heating coil remains more or less free of fibre material, so that the temperature difference at the heating coil, between the radiating surface of the heating module and the rear side, i8 considerably reduced, and the heating coil can, in its entirety, be operated at a markedly higher operating temperature, without incurring the danger of gradual loosening from the anchoring inside , -- 1 -- ., ~Z13~35 the fibre block.
Due to the fact that, during the vacuumrmoulding process, spacing elements are placed beneath the heating coils, or the perforation of the sieve-tray is relieved beneath the heating coils, that is to say is absent, the spacing elements or, as the case may be, the impervious regions of the sieve-tray being narrower than the width measurements of the heating coils in a plane parallel with the radiating surface, or are narrower than the diameter of the heating coils, the re~ult is obtained whereby the space inside the heating coils remains substantially free of fibre material, since it is obvious ~hat the openings in the sieve-like tray are partially closed, during the vacuum-moulding operation, over the longitudinal extent of the heating coils, or are absent in these regions.
In a particularly atvantageous embodiment of the invention, strir like elements, hereinafter termed "spacing strips", are positionet beneath the heating coils, during the vacuum-moulding operation, 80 that, although the heating coils are exposed at the radiating surface of the heating module, for reasons which will be further explained below, they are nevertheless displaced, in their entirety, backwart~ into the fibre block by a distsnce corresponding to the thickness of the spacing strips 80 that optimum anchoring is obtained, while at the same time the space indide them remains free of fibre material.
In the text which follow~, the state of the art, the invention and advantageous details, in the form of illustrative embodiments, are explainet in more detail by reference to the drawing, in which:
Figures 1 and 2 show the state of the art;
Figure 3 shows a first illustrative embodiment, in order to explain the vacuum-moulding process according to the invention;
Figure 4 shows, in a diagrammatic representation, the product 1~13~35 resulting from the vacuum-moulding process according to Figure 3;
Figure 5 shows an illustrative embodiment, which is to be preferred, of a vacuumrmoulding process according to the invention, and Figure 6 shows, again in a diagrammatic representation, the product of the vacuum-moulding process according to Figure 5, in order to explain certain advantageous properties.
In all the figures, mutually corresponding parts are identified by the same reference numbers.
In order to explain the starting point for the invention, the conventional vacuum-moulding process is first described by reference to Figure 1.
A heating coil 5 i8 placed on a ~ieve-like tray 1, for example on a perforated plate. A suction box, which is not represented, is located beneath the tray 1, through which box liquid is drawn off, by means of the vacuum which is indicated, generally, by the reference number 2, from a slip 3 which is poured on top, and which is composed of a solution of a binder, in water, containing ceramic fibres. The liquid constituents are drawn off, by suction, through the sieve-like tray 1, and a layer of ceramic fibre~ builds up.
In this conventional process, the space 8 inside the heating coil 5 is, as a rule, also filled with the cersmic fibres, and, moreover, the density in this interior space 8 will correspond to approximately the density of the remainder of the composition forming the ceramic fibre block 4, namely to approximately 200 kg/m .
The technical problems which arise in the course of using heating ~odules of this type are described in the text which follows, by reference to Figure 2.
When the freely radiating surface region of the heating coil 6 i8 brought to an operating temperature of, for example 1,150C, a considerably , ~ - 3 ~Z~35i higher temperature will occur on the opposite side ~the rear side 7) of the heating coil 5, this rear side being completely embedded in the ceramic fibre composition. As a result, it is not possible to heat the heating coil 5, on its side 6 at which its surface radiates freely, to the operating temperature which is, at most, desired, since the rear side 7 would then be overheated. A
problem which is associated therewith is concerned with the maximum possible use temperature or operating temperature of the aluminium silicate fibres which are quite predominantly employed for the fibre composition, these fibres being employed most frequently for economic reasons. More recent experience has shown that the maximum permissible operating temperature for such aluminium silicate fibres is approximately 1,150C. Above this temperature, the fibre~ undergo excessive crystallisation, which leads to the complete loss of their structure and of the properties which are desired. If, now, the heating coil is raised to a temperature of 1,150 C on the side 6 at which the surface radiates freely, the rear side 7 of the heating coil 5 can thus reach a temperature of approximately 1,250 C. This temperature is then approximately 100 C above the maximum permissible operating temperature of the fibres and will lead to exce~sively rapid recrystallisation of the fibre material. As a result, the heating coil 5 loses its grip in the overheated portion of the fibre composition and will detach itself, ~ore or less quickly, from the fibres, above all in the case of roof-elements in~ide a furnace chamber. The heating coil 7 will then initially protrude more and more from the radiating side 9 of the fibre block 4, and will finally fall out.
Figure 3 illustrates a first embodiment of the invention. Strips lO
of adhesive tape are, for example, applied to the sieve-like tray 1 (the perforated plate), these strips covering the perforations over the longitudinal extent of the heating coils 5, that is to say in the direction perpendicular to the plane of the drawing. These strips 10 of adhesive tape --- 121~635 are applied directly beneath the heating coils 5, which are subsequently placed on the perforated plate and lightly fixed. Due to the fact that some of the perforations are closed, the vacuum 2 produce~ no suction effect at these points, so that the space 8 inside the heating coils 5 remains free of ceramic fibre material to the greatest possible extent.
The result of the manufacturing process explained by reference to Figure 3 is shown in Figure 4. Here too, the heating coil 5 lies flush with the ratiating side 9 of the fibre block 4, in a manner similar to the arrangement in the case of the illustrative embodiment shown in Figure 2. The space 8 inside the heating coilq 5 is now empty, that is to say free of fibre material, 80 that the rear side 7 of the heating coils 5 can radiate considerably more freely. By this means, the result is obtained whereby the temperature difference at the heating coil, between the freely radiating side 6 at the radiating surface 9 and the rear side 7, is markedly reduced, thus avoiding undesirable overheating in the region of the rear side 7 of the heating coils 5.
However, this first, basic embodiment of the invention still possesse~ the tisadvantage that the heating coil 5 is now less effectively bonded to the ceramic-fibre block 4, although the above-described recrystallisation effect, due to partial overheating, is no longer observed in the fibres. However, the heating coils 5 are surrounded by fibre material only along their outer periphery and, moreover, they are not held at the freely radiating side 6, a~ is also the case in the state of the art according to Figure 2. Despite the fundamental advantage that the crystallisation of the fibre material no longer occurs, a further difficulty can, however, arise in the ca~e of this design, due to the fact that, as a result of inadequate anchoring, the heating coils fall out of the fibre block, especially when this type of heating module is employed for roof-structures in furnace chambers.
_ 5 _ The idea underlying the considerably improved embodiment of the invention, according to Figures 5 and 6, is to embed the heating coil 5 in ehe composition of the fibre block 4 in a manner such that, on the one hand, the space 8 inside it remains free of ceramic fibres, without, on the other hand, incurring the danger of the heating coils 5 being able to fall out of the fibre block 4, as the result of inadequate adhesion~
The principle underlying the manufacturing process is first explained by reference to the diagrammatic sectional representation shown in Figure 5.
Spacing strips 11 are attached to the sieve-like tray 1, beneath the positions which the heating coils 5 are to occupy. These spacing strips 11 can be composed, for example, of metal, wood or plastic. The width of these spacing strips 11 should, in any case, be somewhat less than the diameter or, as the case may be, the width measurement of the heating coil 5 in a plane parallel with that side 9 of the fibre block 4 which forms the radiating surface, while the thickness of the spacing strips 11 should lie within the range from 0.1 mm, at the minimum, to approximately 30 mm, and preferably within the range from 2 to 10 mm. If now the slip 3 is introduced into the frame, which is not shown in more detail but is equipped with the sieve-like tray 1, and if the liquid constituents are drawn off through the sieve-like tray 1, the fibres accordingly build up in a manner such that the spacing strips 11 are surrounded, while the space for inside the heating coils 5 remains substantially empty, that is to say free of deposits of fibres.
Figure 6 shows the resulting product, in a schematic sectional representation. The freely radiating side 6 of the heating coil 5 no longer lies flush with the radiating side 9 of the fibre block 4, but lies at a position which i9 displaced backwards into the fibre block 4 by a distance corresponding to the thickness of the spacing strips Il. The retaining webs 12, resulting from the presence of the spacing strips 11, partially surround ~2~35 the freely radiating side 6 of the heating coils S, but without the interior space 8 being filled with fibres. As a result, the desired objective was achieved, namely to keep the interior space free of fibres, so that the temperature difference between the radiating side 6 and the rear side 7 of the heating coils 5 is considerably smaller than in the case of the conventional technique, in which the heating coils are completely embedded in the fibre block 4, that is to say with the space 8 inside them filled by fibres.
Moreover, on the other hand, the retaining webs 12 securely hold the heating coils S, so that there is no longer any danger of their falling out, even when this type of heating module is used as a roof-element in a furnace.
As can be seen from the Figures, so-called oval heating coils or heating spirals 5 are provided in those embodiments of the invention which have been described, these coils, or spirals, being of the type which is also described in the abovementioned U.S. Patent 4,278,877, with the advantages mentioned therein. A person skilled in the art can appreciate, without difficulty, that the invention can also be employed, with advantage, for heating coils possessing other cross-sections, for example possessing a round cross-section, or a cross-section which has been deformed into a rectangle.
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Claims (8)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A vacuum-moulding process for manufacturing an electrical heating unit, in which process a resistance heating coil is placed on a sieve-like tray, in a frame above a suction box, and a slip is introduced into the frame, this slip being composed of a slurry of ceramic fibers, a binder and water, such that upon the application of suction the ceramic fiber layer builds up under the action of the suction, this layer being cured, and containing the resistance heating coil as an embedded heating element, wherein those portions of the surface of the sieve-like tray which lie beneath the resistance heating coil are designed to be impervious to, and are narrower than, one of the group of maximum diameter and width of the heating coil in a plane parallel with the sieve-like tray.
2. Vacuum-moulding process according to claim 1, characterized in that, in a preliminary operation, strips are placed on the sieve-like tray, at the positions of the heating coil, before the latter is inserted.
3. Vacuum-moulding process according to claim 1, characterized in that, in a preliminary operation, the strips are attached to the heating coil, on the side which is to face the sieve-like tray, their attachment being adhesive and easily releasable.
4. Vacuum-moulding process according to claim 1, 2 or 3, characterized in that the strips are designed as spacing strips possessing a thickness of 0.1 to 30 mm.
5. Vacuum-moulding process according to claim 1, 2 or 3, characterized in that the sieve-like tray is not perforated in those portions of the surface which lie beneath the heating coil.
6. Vacuum-moulding process according to claims 1,2,or 3 characterized in that said strips are designed as spacing strips possessing thickness of 2 to 10 mm.
7. A vacuum-moulded electrical heating unit comprising ceramic fibers which form a ceramic fiber layer (4) and a resistance heating coil (5) directly embedded in and anchored in said ceramic fiber layer, the interior space of said coil being essentially free of ceramic fiber material, the surface region (6) of said coil being exposed at the radiant heating surface; wherein the said surface region of said heating coil exposed at the heating surface is disposed between 1 to 30 mm inward from the outer surface (9) of said ceramic fiber layer, said heating unit being obtained by placing a resistance heating coil on a sieve-like tray, in a frame above suction box, introducing a slip into the frame, said slip being composed of a slurry of ceramic fibers, a binder and water, applying suction by way of said suction box whereby the said layer builds up and is cured, thereby containing the resistance heating coil as an embedded heating element, wherein those portions of the surface of the sieve-like tray which lie beneath the resistance heating coil are designed to be impervious to, and are narrower than, one of the group of maximum diameter and width of the heating coil in a plane parallel with the sieve-like tray.
8. A vacuum-moulded electrical heating unit according to claim 7, wherein the exposed said surface region of said heating coil is disposed at a distance between 2 to 10 mm inward from the outer surface of said ceramic fiber layer.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE3233181A DE3233181C2 (en) | 1982-09-07 | 1982-09-07 | Vacuum-formed, electric, radiant resistance heating device for industrial furnaces and processes for their production, made from ceramic fibers. |
| DEP3233181.9-34 | 1982-09-07 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1213635A true CA1213635A (en) | 1986-11-04 |
Family
ID=6172636
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000434781A Expired CA1213635A (en) | 1982-09-07 | 1983-08-17 | Vacuum-formed electrical heating device and method of production |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US4617450A (en) |
| EP (1) | EP0105175B2 (en) |
| JP (1) | JPS5966094A (en) |
| AT (1) | ATE32157T1 (en) |
| CA (1) | CA1213635A (en) |
| DE (1) | DE3233181C2 (en) |
| MX (1) | MX153420A (en) |
Families Citing this family (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4575619A (en) * | 1984-05-08 | 1986-03-11 | General Signal Corporation | Electrical heating unit with serpentine heating element |
| JPS6116488A (en) * | 1984-06-30 | 1986-01-24 | イビデン株式会社 | Heat insulating heater |
| DE3539881A1 (en) * | 1985-11-11 | 1987-05-14 | Ego Elektro Blanc & Fischer | Electrical radiant heating element for heating heating surfaces, and a method and device for its production |
| US4719336A (en) * | 1986-05-30 | 1988-01-12 | General Signal Corporation | Method of making thermal insulating blocks and electrical heating units and the products thereof |
| US4855576A (en) * | 1986-05-30 | 1989-08-08 | General Signal Corporation | Thermal insulating blocks and utilizing single blocks for electrical heating units |
| GB2192119A (en) * | 1986-06-20 | 1987-12-31 | Kanthal Ltd | Heating devices |
| DE3932854A1 (en) * | 1988-10-05 | 1990-04-12 | Rudolf Wille | Insulated wall panel for heating chamber - has flat heater element covered by perforated internal wall |
| EP0424818B1 (en) * | 1989-10-24 | 1994-12-14 | General Signal Corporation | Furnace and heating unit therefor |
| US5413032A (en) * | 1994-08-18 | 1995-05-09 | The Middleby Corporation | Restaurant type griddle with modular construction and which is load sensitive |
| US5708251A (en) * | 1995-10-30 | 1998-01-13 | Compucraft Ltd. | Method for embedding resistance heating wire in an electrofusion saddle coupler |
| US5847368A (en) * | 1996-06-20 | 1998-12-08 | Koyo Lindberg Limited | Electric heating unit and method of producing same |
| JP5973917B2 (en) * | 2009-11-05 | 2016-08-23 | ウィンストン ウォールボーズ リミテッド | Heating panel and method for the panel |
Family Cites Families (27)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US1317883A (en) * | 1919-10-07 | Method of generating radiant energy and projecting same through free | ||
| US2255518A (en) * | 1938-11-15 | 1941-09-09 | Babcock & Wilcox Co | Electric furnace |
| US2254925A (en) * | 1939-03-30 | 1941-09-02 | Louis E Wirth | Paint disintegrator |
| US2489190A (en) * | 1945-07-13 | 1949-11-22 | Procedes Sauter | Electric heating element |
| US2674775A (en) * | 1946-07-03 | 1954-04-13 | Corwin D Willson | Making molded panels |
| US2744946A (en) * | 1953-11-25 | 1956-05-08 | L & L Mfg Company | Electric furnace and heating unit therefor |
| DE1024181B (en) * | 1955-12-30 | 1958-02-13 | Kanthal Ab | Electric heater |
| US3275497A (en) * | 1962-01-17 | 1966-09-27 | American Thermocatalytic Corp | Method of molding a combustion element of ceramic fibers on a porous support |
| GB1136811A (en) * | 1965-09-14 | 1968-12-18 | Foseco Trading Ag | Production of heat insulating products |
| US3500444A (en) * | 1968-01-16 | 1970-03-10 | Johns Manville | Electrical heating unit with an insulating refractory support |
| US3952408A (en) * | 1970-03-26 | 1976-04-27 | Albert George Docx | Method of assembling a resistance furnace |
| DE2051048C3 (en) * | 1970-10-17 | 1980-10-09 | Glaswerk Schuller Gmbh, 6980 Wertheim | Wire section of a machine for producing a fiber web |
| DE2156361A1 (en) * | 1971-11-12 | 1973-05-17 | Siemens Ag | Ceramic support bodies for coverless resistors - produced by extrusion with intermittent inclusion of foreign substance |
| GB1441577A (en) * | 1972-09-02 | 1976-07-07 | Docx A G | Muffle furnaces |
| US3870861A (en) * | 1974-03-07 | 1975-03-11 | Sola Basic Ind Inc | Electric hot plate heating unit with a ceramic cover |
| US3978183A (en) * | 1974-06-24 | 1976-08-31 | Sybron Corporation | Method of filter molding and electrical heating unit made thereby |
| DE2500586A1 (en) * | 1975-01-09 | 1976-07-15 | Ego Elektro Blanc & Fischer | Boiling plate with a refractory top plate - with plate made of vitrified ceramic material on which pans are placed |
| FR2301148A1 (en) * | 1975-02-11 | 1976-09-10 | Physique Appliquee Ind | Cylindrical electric heating element - is embedded in a refractory pref. a concrete comprising cement and aluminium grains |
| US4272670A (en) * | 1976-05-01 | 1981-06-09 | Docx Albert G | Furnace muffles and furnaces |
| US4091355A (en) * | 1977-01-19 | 1978-05-23 | Btu Engineering Corporation | Anchored coil heater |
| US4278877A (en) * | 1977-12-21 | 1981-07-14 | General Signal Corporation | Electrical heating unit with flattened embedded heating coil |
| CA1115761A (en) * | 1977-12-21 | 1982-01-05 | Ewald R. Werych | Electrical heating unit with flattened embedded heating coil |
| US4247979A (en) * | 1979-03-08 | 1981-02-03 | Eck Richard H | Radiant heater and method of making same |
| DE7930529U1 (en) * | 1979-10-27 | 1980-02-28 | E.G.O. Elektro-Geraete Blanc U. Fischer, 7519 Oberderdingen | HEATING ELEMENT FOR A GLASS CERAMIC COOKING APPLIANCE |
| JPS5678088A (en) * | 1979-11-30 | 1981-06-26 | Riken Kk | Method of manufacturing heater burying refractory formed article |
| DE2950302A1 (en) * | 1979-12-14 | 1981-06-19 | E.G.O. Elektro-Geräte Blanc u. Fischer, 7519 Oberderdingen | ELECTRIC RADIANT RADIATOR, METHOD AND DEVICE FOR PRODUCING IT |
| DE3206508C2 (en) * | 1982-02-24 | 1986-02-27 | KERFA GmbH Industriebeheizungen, 5820 Gevelsberg | Process for the production of an electrical ceramic fiber surface heating element |
-
1982
- 1982-09-07 DE DE3233181A patent/DE3233181C2/en not_active Expired
-
1983
- 1983-03-22 US US06/477,725 patent/US4617450A/en not_active Expired - Fee Related
- 1983-06-30 MX MX197888A patent/MX153420A/en unknown
- 1983-08-17 CA CA000434781A patent/CA1213635A/en not_active Expired
- 1983-08-24 AT AT83108349T patent/ATE32157T1/en not_active IP Right Cessation
- 1983-08-24 EP EP83108349A patent/EP0105175B2/en not_active Expired - Lifetime
- 1983-09-07 JP JP58164897A patent/JPS5966094A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| MX153420A (en) | 1986-10-07 |
| US4617450A (en) | 1986-10-14 |
| EP0105175B1 (en) | 1988-01-20 |
| JPS5966094A (en) | 1984-04-14 |
| ATE32157T1 (en) | 1988-02-15 |
| EP0105175B2 (en) | 1993-06-23 |
| DE3233181A1 (en) | 1984-03-08 |
| EP0105175A1 (en) | 1984-04-11 |
| DE3233181C2 (en) | 1985-08-01 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |