JPS6313314B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates to an electric heating device, and more particularly to an electric heating device in which a coil resistive heating element is embedded within an insulator.

PRIOR ART U.S. Pat. No. 3,500,444 discloses a lightweight ceramic fiber insulator. Because of their energy saving advantages, such ceramic fiber insulation is often used in place of dense refractory bricks as furnace linings. Many of these applications involve oil or gas fired furnaces. However, there is increasing interest in using electrical heating elements in which heating coils are embedded in situ within ceramic fiber insulation, as shown in the above-mentioned US patents. In that patent, a portion of the heating coil is exposed on the surface of the insulator for efficient heat transfer and directionality.

"Problems to be Solved by the Invention" The requirement to expose a part of the coil from the surface of the insulator is extremely difficult in manufacturing. In that patent, the insulation is formed by a vacuum-operated filtration process in which a coil is placed against a screen and the liquid exiting the casting slurry passes through the heating coil and through the screen. removed from the slurry. Ceramic fibers from the slurry are retained by the screen and accumulate around the coil. It is difficult to arrange each individual turn of the coil so that it is partially exposed from the insulating plate.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a highly effective heating device in which the heating coil is embedded in an insulator, and in which each turn of the coil covers the surface of the insulator. are not subject to manufacturing difficulties caused by overexposure.

An advantage of the present invention is that the furnace temperature can be maintained at a significantly lower temperature when the flattened heating coil is embedded within the insulator compared to when the round coil is entirely embedded. This is one of the effects.

"Means and operations for solving the problem" According to one aspect of the present invention, a resistive heating coil included in an electric heating device is embedded in an insulator close to the surface of the insulator and beneath the surface of the insulator. , the coil being longitudinally flattened such that each turn of the coil has a generally linear first portion disposed generally in the plane of the surface of the insulator. There is.

According to another aspect of the invention, the coil is also longitudinally flattened in one plane from the surface of the insulator to the interior, and the coil is embedded in situ within the ceramic fiber. .

According to yet another aspect of the invention, the electric heating device includes:
It is manufactured as follows: making a round heating coil, flattening the heating coil, placing the heating coil on the bottom of a mold, and pouring a slurry containing a suspension of ceramic fibers into the mold. The electrical heating device is manufactured by draining the liquid from the slurry to deposit the ceramic fiber body in a mold, thereby embedding the heating coil within the insulation.

According to yet another aspect of the invention, a method of manufacturing an electric heating device includes flattening each turn of the coil while locating each turn of the coil in a parallel relationship and closely spaced, and then heating the coil after flattening. It includes the step of stretching the coil.

The above-mentioned or other objects of this invention;
Features and advantages will become apparent from the following more detailed description of the preferred embodiments of the invention, as shown in the accompanying drawings, in which the same reference numerals are used for the same parts throughout the different drawings. .

Embodiment An electric heating device 12 implementing the present invention is shown in FIG. This device consists of a large number of flat elliptical heating coils 14, 16, 18, 20, 22, 2 embedded in a ceramic fiber insulator 31.
4, 26, 28, and 30. These heating coils are arranged near a surface 32 of the insulator, which surface 32 becomes the heating surface of the heating device. The back surface 33 of the heating device shown in FIG. 2 is a cooling surface, although its temperature is somewhat higher than the surroundings during operation of the heating device. The insulator is manufactured by U.S. Patent No.
The ceramic disclosed in specification No. 3500444
A fiber type is preferred and may be formed with steps 34 on three sides and a protrusion 36 on the other side. The steps and projections are provided to facilitate the adaptation of a plurality of panel arrangements to each other in the furnace.

The heating coils are electrically coupled in series by a coupling wire 38. These bond wires are welded to each pair of heating coils prior to depositing the insulating material forming the insulator 31. Another method is to eliminate the need for welding between coils.
Connect several coils to one twisted wire
strand). The nine series-wired heating coils are electrically connected to a low voltage, high current power source by terminal pins 40 and 42 that extend through the insulator 31 and project from the cooling surface 33. These terminal pins connect conductors 44,4
6, the coils 14 and 30 are electrically connected to each other. Each conductive wire extends through a hole formed across and through a respective terminal pin and is welded to the terminal pin.

The locking ribbons 48, 50 are also welded to their respective terminal pins. Each of these ribbons is
Preferably, the ribbon surface is approximately 0.060 inches (1.5 mm) thick, 1 inch (25.4 mm) wide, and 2 inches (50.8 mm) long, with the ribbon surface perpendicular to the heating surface 32 of the insulator. It is placed inside the insulator so that Each ribbon is bent at an angle of approximately 90° about a line perpendicular to the heating surface to enhance the ribbon locking effect. Due to this locking ribbon, the terminal pin is rarely pushed through the light insulating material even in the event of a sudden and unintentional axial shock from the cold side of the heating device.

Each coil is longitudinally flattened, and each turn of each coil has a generally linear winding disposed approximately in the surface plane of the insulator, as best seen in FIG. 1 portion 52. Therefore, even though all the coils are fully embedded within the insulating material, a substantial portion of each turn is at the heating surface of the insulator in close proximity to the surrounding air being heated. . Each coil is further flattened longitudinally in a plane from the surface of the insulator to the inside thereof, and each turn of each coil has a substantially linear shape disposed in a plane substantially parallel to the surface of the insulator. The second portion 54 is adapted to have a second portion 54 . Due to this flattening of the coil in the second plane, the internal portion of the embedded coil (as shown in FIG. It will be located closer to the cooling surface 33 and further away from the cooling surface 33.
Therefore, the advantageous effects of each turn of the coil having two flattened sections are: (1) a reduction in the average distance of each turn from the heating surface; (2) a cooling surface; (3) increasing the average distance from the heat source, thereby decreasing the insulation between the heat source and the environment to be heated, and increasing the insulation between the heat source and the surrounding environment; An example of this is that the projected area of the flattening coil, which faces (orients) the interior of the furnace to be processed via an insulating medium, is greatly increased.

In the preferred numerical example of this embodiment, each of the nine coil strips has a diameter of 0.128 inches (3.25 inches).
mm) and 14.44 feet (4.4 m) in length from No. 8 gauge Kanthal A-1 wire. This wire has a circular cross-sectional diameter
It is wrapped in closely spaced turns around a mandrel that is 0.75 inches (19 mm). The coil thus wound is then removed from the mandrel and, while the turns are still closely spaced in parallel relationship, the turns are removed as shown in FIG. , as shown in the end face 56 of the flattened elliptical coil, the maximum outer diameter is
It is flattened into a roughly oval shape with a diameter of 1.244 inches (31.6 mm) and a minimum outer diameter of 0.715 inches (18.2 mm). Six of the flattening coils are then 28
three of the coils are stretched to 33 inches (83.8 cm). These coils are welded to the bonding wire and terminal pins and placed on the bottom of the mold to form the final arrangement shown in FIGS. 1-3 with terminal pins 40 and 42 extending upwardly from the bottom of the mold. placed in
The slurry containing the ceramic fiber suspension is then poured into a mold and the liquid is vacuum pulled from the slurry to deposit the ceramic fiber body and embed the heating coil therein. be done. Note that the long axis of the flattened elliptical coil is parallel to the heating surface of the insulating plate. The result is that the projected area of a resistive heating wire pointing directly into the furnace through the surrounding insulation is larger than that of a round coil. In short, the projected area of the flattened coil 56 shown in FIG.
8, resulting in a ratio of 1.244 to 0.961. This ratio means that the area of the heating wire facing through the insulating medium towards the furnace chamber is increased by approximately 30%.

The features of the structure of the locking ribbon can be understood from the method of manufacturing the electric heating device. Since the ceramic fibers settle to the mold bottom when the liquid is drawn through the mold bottom, it is advantageous for these locking members to be relatively thin in any horizontal plane in order to completely embed them within the insulation. It is. In this preferred embodiment, the locking ribbon is only 0.06 inches (1.5 mm) thick.
This ribbon is thin but 2 inches long (50.8mm)
The terminal pin is bent at an angle of about 90 degrees, which prevents the terminal pin from moving in the axial direction. In this way, the folded locking ribbon is pressed against the inner plane of the insulator 31, so that axial forces are blocked.
The 1 inch (25.4 mm) width of the ribbon provides structural stability for the locking ribbon.

The resistive heating device described above was tested against a panel consisting of round coils. The round comparison coil is also a No. 8 gauge Kansal A-1.
(Kanthal A-1) diameter 0.128 inches (3.3mm)
This coil is made by winding wire of
It is not flattened and has an outer diameter of 0.961 inches (24.4 mm). The flattened coil and the round coil are each completely embedded within separate 5-inch (12.7 cm) thick panels of lightweight ceramic fiber insulation material. The heating device thus formed was used in each experiment.
Separate ovens were operated in two experiments to provide heating surface temperatures of 2000° (1093.3°C) and 2200° (1204.4°C). With the heating surface temperature set in each experiment, the cooling surface temperature was set at 1 inch (25.4 mm) and 2.5 inches (63.5 mm) from the cooling surface.
The temperature at each location at 3 inches (76.2 mm) and the back side of the coil was measured for each test coil. For each heating surface temperature in the experiment, it was confirmed that the back side of the round coil had a higher temperature than the back side of the flattened coil. The results are shown graphically in FIG.

The experimental results for the experiment with a heating surface temperature of 2000°C (1093.3°C) are shown by lines 60 and 62 in FIG. The solid line 60 shows the internal temperature within the insulating panel of the round coil heating device at each selected location, and the dotted line 62 shows the internal temperature of the flattened coil heating device. In this experiment, the back temperature of the round coil 58 was 2295〓 (1257.2°C), but the back temperature of the flattened coil 56 was 2.214〓
(1212.2℃), with a difference of 81〓(27.2℃). In this way, the heating surface temperature is 2000〓 (1093.3℃)
In the experiment, the temperature when the flattened coil was heated was significantly lower than the temperature when the round coil was heated. Similarly, heating surface temperature 2200
In the experiment at 〓 (1204.4℃), the round coil is shown by the solid line 64 and the flattened coil is shown by the dotted line 66, respectively, and the back temperature of the round coil is 2520〓 (1382.2℃), and the flattened coil is shown by the dotted line 66. The back temperature of the coil was 2426〓 (1330.0℃), and the difference was 94〓 (34.4℃).

The increase in temperature difference between the two coils with increasing oven temperature suggests that the benefits of using flattened coils are particularly pronounced at high oven temperatures. 2200〓(1204.4
Research has demonstrated that operating temperatures above 0.4° C.) can be achieved by using flattened, well-embedded heating elements while still retaining a normal lifetime.

The 5 inch (12.7 cm) thick electrical heating panel shown in Figures 1-3 is ideal for use as a new furnace lining. This device has both effective electrical heating and a high degree of thermal insulation from the surroundings. However, embodiments of the invention are not limited to heating devices of the dimensions described above. Not only can the size of the coil be varied, but the depth of the insulation can be easily varied by varying the depth of the ceramic fiber slurry during the casting process. The size of both the coil and insulator will depend on the required capacity, operating temperature,
Directed by physical limitations of the furnace room, etc.

old furnace structures by embedding the flattened coil described above in a thin insulator, e.g. having a thickness less than about twice the depth of the flattened resistive heating coil within the insulator. Provided is a heating device suitable for modifying and remodeling old furnaces or converting old furnaces to electric heating types. As shown in FIG.
includes a top of the insulation 70, a bottom of the insulation 72, and
It has side walls 74, 76 of insulating material. These side walls may have electrical heating elements embedded in them;
Alternatively, the furnace may be simple, burning oil or gas, or the like. If this side wall contains electrical heating elements that have deteriorated over time, these electrical heating elements can be electrically disconnected and left in place. The replacement heating devices 78, 80 are then placed over the old heating elements and secured inside the furnace wall. Since the furnace already has sufficient insulation, each heating device 78,
The insulators 82, 84 of 80 are relatively thin so as not to unnecessarily reduce the volume of the furnace.

As can be easily seen by comparing the depths of the flattened coil 56 and the round coil 58 from the heating surface 32 in FIG. 4, the flattened coil has a thinner insulator than the round coil. Can be completely embedded. This favorable effect goes beyond the advantages of ease of manufacture and high thermal efficiency.

Although this invention has been described with particular reference to preferred embodiments, it will be appreciated that various modifications may be made therein in form and detail without departing from the spirit and scope of the invention as set forth in the claims. This can be understood by those in the business.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of an electric heating panel device in which a flattened coil is embedded in a ceramic fiber insulator according to the present invention, and FIG. 2 is a front end view of the electric heating device of FIG. FIG. 3 is a side end view of FIG. 1, with a portion cut away to show the roughly elliptical shape of the heated coil, and is cut away to show the flattened heating coil and terminal connection pins. 4 is a partially cutaway diagram, and FIG. The figure is a cross-sectional view of a furnace having a modified or replacement electric heating device on its inner wall, which is an embodiment of the present invention. 12... Electric heating device, 14, 16, 18, 20,
22, 24, 26, 28, 30... elliptical coil, 31... insulator, 32... surface of insulator (heating surface), 33... back surface of insulator, 40, 42...
Terminal pin, 44, 46... Conductor, 48, 50...
Locking ribbon, 52... First part, 54... Second part, 56... Flattening coil, 58... Round coil, 78, 80... Replacement heating device, 82, 84
……Insulator.

Claims (1)

[Scope of Claims] 1. A shape-maintaining insulator made of an insulating material and having a heated surface; a plurality of continuous insulators substantially completely embedded in the material of the insulator along the heated surface; a resistive heating coil of wire having turns, each turn of the coil being disposed substantially parallel to and in close proximity to the heating surface of the insulator, and having substantially its entire length exposed to the insulating material; a substantially linear first portion in contact with the first portion; and a second substantially linear portion disposed entirely in the insulator substantially parallel to the first portion and in contact with the insulating material over its entire length. ,
and a heating surface portion proximate to and extending along the first portion of the coil is substantially straight in a direction parallel to the first portion of the coil. the lateral dimension of each turn of the coil in a direction parallel to the first and second portions is greater than the distance that the second portion extends to the first portion; and and means for making an electrical connection to an end of the heating coil. 2. The device according to claim 1, wherein the insulator is made of ceramic fiber. 3. The device of claim 1, wherein each turn of the coil is elliptical. 4. The apparatus of claim 1, wherein the thickness of the insulator is less than or equal to about twice the depth of the resistive heating coil in the insulator. 5. A shape-maintaining insulator of an insulating material having a heated surface and a wire having a plurality of continuous turns substantially completely embedded in the material of the insulator along the heated surface. a resistive heating coil, each turn of the coil having a generally linear first portion disposed substantially on the heating surface of the insulator and in contact with the insulating material over substantially its entire length; a generally linear second portion disposed entirely within the insulator substantially parallel to the portion and in contact with the insulating material over its entire length; the heating surface portion on which the first portion of said coil is disposed is substantially straight in the same direction as the first portion of the coil, and the lateral side of each turn of the coil being in a direction parallel to the first portion and the second portion; An electric heating device, the second portion being dimensioned to be greater than the distance to the first portion; and means extending from the insulator for making an electrical connection to an end of the heating coil.