JPH01211887A - Plane heater made of carbon fiber/carbon composite - Google Patents

Abstract

PURPOSE:To reduce the dispersion on the heating surface and obtain a heater with large mechanical strength and good workability by making the alignment pattern of carbon fibers viewed from the vertical direction to the heating surface equal between portions at any portion of the heating surface. CONSTITUTION:A carbonizable material is impregnated in a circular fabric of carbon fibers stacked for artificial isotropy or an unwoven mat of one- direction aligned materials or carbon fibers, and it is baked to form a planar heater 1. When the fabric or the like of carbon fibers corresponding to the shape of the heater 1 is used, carbon fibers have the same alignment at any portion when viewed from the vertical direction to the heater 1, the heat quan tity is made equal. The dispersion of the heating surface is small, the heater with large mechanical strength and various shapes is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a surface heating element made of carbon fiber/carbon composite that generates heat using gel heat.

(Prior art and its problems) In technical fields such as forming various functional thin films on the surface of a substrate, diffusing impurities into the substrate, and heating and melting substances contained in a crucible, it is necessary to An object to be heated, such as a base material, is heated and placed under a predetermined temperature condition. As the heating means in this case, a resistance heating element that generates Joule heat is generally used.

During this heat treatment, the surface temperature distribution of the base material is an important control target, for example, in relation to the characteristics required of the formed thin film, the film formation rate, etc.

For this reason, the heating element is required to have a wide variety of materials and shapes, and the conditions for power supply to the heating element are also appropriately selected.

High-melting point metals such as tungsten and molybdenum and graphite are used as constituent materials for the heating element. Further, the shape of the heating element is designed to be an appropriate shape, such as a plate shape or a cylindrical shape, depending on the required temperature conditions.

However, in the case of a heating element made of a high melting point metal, it is easily deformed by heat and lacks dimensional stability at high temperatures, so its shape changes from its original shape during repeated use.

As a result, the aspect of heating changes, causing the problem that the temperature of the base material, etc. cannot be maintained at a predetermined value.

On the other hand, a graphite (or carbon) heating element has the advantage that it does not undergo thermal deformation as described above and has excellent corrosion resistance, but has the problem of low mechanical strength. Furthermore, since it is brittle, there is a problem in that it is difficult to process it into a desired shape of the heating element during manufacturing.

Generally, a heating element that generates heat by resistance has a small current carrying cross-sectional area, for example, a thin overall shape (in the case of a Fi-shaped heating element).
Alternatively, if the diameter is made smaller (in the case of a rod-shaped heating element), the resistance can be increased and it can be made more compact. However, if a graphite heating element is made thinner or smaller in diameter, the mechanical strength of graphite Since it is small, it may be damaged, for example, during assembly or attachment to a heated object. Therefore, in the case of a graphite heating element, the thickness usually has to be about 10 to 20+ m.

As mentioned above, graphite has excellent heat resistance and corrosion resistance, making it useful as a material for heating elements. The problem is that it cannot be done.

On the other hand, carbon fiber/carbon composites (hereinafter referred to as rC/C composites), which are composites in which the matrix is carbon (or graphite) and the reinforcing material is carbon fibers (or graphite fibers), are known. Since this C/C composite has light weight, high heat resistance, and excellent mechanical strength, attempts have been made to use it as a heating element. discloses that a cured laminated body of a thermosetting resin and a cellulose sheet is graphitized to form a highly anisotropic carbon block, and this is used as a heating element.

Furthermore, in JP-A-58-110411, a mixture of thermosetting resin and carbon fiber is fired in a thin ceramic pipe to form an anisotropic C/C composite, and this is used as a heating element. It was disclosed in Japanese Patent Application Laid-open No. 58
Japanese Patent Application No. 126510 discloses the use of a C/C composite filament as a resistance heating element for use in reinforcing an optical fiber connection. All of the heating elements disclosed herein have greater mechanical strength than those made of graphite, but they are rod-shaped or linear bodies,
It is not formed as a surface or as a whole.

The present invention solves the above problems with conventional heating elements,
It is an object of the present invention to provide a C/C composite surface heating element that has small variations in the amount of heat generated on the heating surface, has high mechanical strength, reduces the risk of breakage, and can be manufactured into precise and complex small shapes. purpose.

(Means for Solving the Problems) In order to achieve the above object, the C/C composite surface heating element of the present invention has a structure that is formed into a surface or a planar shape as a whole, and within the heating surface. No matter which part is taken, the arrangement pattern of carbon fibers seen from a direction perpendicular to the heat generating surface is the same or substantially the same in each part.

The heating element of the present invention is made of a C/C composite.The heating element of the present invention is formed as a plane or as a whole, and the shape of the plane is a plane or a curved surface.

Here, examples of the curved surface include a cylindrical curved surface, a hemispherical curved surface, a parabolic curved surface, a truncated conical curved surface, and the like. The overall shape of the heating element, and hence the shape of the heating surface, is determined depending on the purpose of use of the heating element.

However, in the heating element of the present invention, no matter what shape this heating surface has, no matter which part of the heating surface is taken, when viewed through from a direction perpendicular to the heating surface, the carbon fiber It is necessary that the arrangement pattern of each part be the same or substantially the same.

Note that the site within the heat generating surface as used in the present invention refers to a portion that extends to a certain extent within the heat generating surface and is of a size that is visible in a certain field of view, such as a dot-like portion. I don't mean a tiny part of it. In addition, when a circular fabric or a spiral circular fabric, which will be described later, is used as carbon fiber, the weave density is dense on the inside and coarse on the outside, but this coarse and dense state is not so noticeable. In the present invention, in such a case, the arrangement pattern of the carbon fibers is assumed to be substantially the same.

If this arrangement pattern does not satisfy the above conditions, that is, if the arrangement pattern of carbon fibers differs between each part on the heating surface, the electrical resistance between each part will not be the same, and as a result, the The Joule heat generated also differs. Therefore, if we do not take into account the effects of heat radiation,
Temperature unevenness begins to occur on the heat generating surface.

In order to make the arrangement pattern of the carbon fibers the same or substantially the same between each part in the heat generating surface, the carbon fibers may be arranged in the matrix carbon by the method described below when manufacturing the heat generating element. .

That is, the heating element of the present invention can be manufactured by the following method.

The first method is the prepreg method. In this method, first, a prepreg is used, in which the carbon fiber described later is impregnated with a B-stage thermosetting resin such as phenolic resin or furan resin, or a carbonizable substance such as pitch, and the required number of prepregs are used. It is laminated or wound a necessary number of times to form a desired heating element shape.

Next, the obtained shaped body is fired at a temperature range of 600 to 3000°C in an inert gas atmosphere to thermally decompose the carbonizable substances in the prepreg and carbonize or graphitize it, forming a C/C composite. to obtain a heating element. However, since the obtained heating element is porous and has a low density, it is difficult to impregnate it with the carbonizable substance and sinter it several times to increase the density until it reaches a predetermined density. preferable.

The second method is a resin impregnation method. In this method, raw carbon fibers themselves are laminated or wound and shaped into a heating element shape, and then impregnated with the above-mentioned carbonizable substance and fired. As in the case of the prepreg method, it is preferable to repeat the impregnation and firing process as many times as necessary to increase the density.

The third method is the CVD method. In this method, as in the case of the resin impregnation method, raw carbon fibers are shaped into a heating element shape, and then heat treated in an air stream containing hydrocarbons such as methane and propane at a high temperature of 1000 to 2000°C. This is a method in which a required amount of pyrolytic carbon (or graphite) is deposited on the surface of carbon fibers to form a C/C composite, which is then used as a heating element.

The fourth method is a blending method that can be applied to short fibers having a diameter of about 3 to 15 μm and an aspect ratio of several hundreds. In this method, various molding methods are applied to the mixture of the short fibers and the carbonizable substance,
After molding into the shape of a heating element, this is fired.

In the first to fourth methods described above, the heating element is shaped in advance into the shape of the heating element and then fired, but after firing, machining such as cutting may be performed to form the desired heating element shape.

The carbon fibers used in these methods include the following types.

The first is textiles. The woven fabric may be a plain woven fabric, a m-woven fabric, or a satin woven fabric. Also, JP-A-51-58568
Circular fabrics or spiral circular fabrics disclosed in Japanese Patent Publication No. 59-32291 can be used. The above fabric is shown in the first diagram, which is a plan view of the entire fabric.
As shown in Figure 3, Figures 14 and 15 which are partially enlarged views, and Figure 16 which is a sketch showing the stretched state of the fabric,
Continuous warp and weft yarns made of carbon fibers constitute a plain weave texture or ribbed weave texture, where multiple warp yarns are arranged in the circumferential direction, and the weft yarns are approximately perpendicular to the warp yarns in the portions where they intersect with the warp yarns. intersect with each other, and are generally arranged in the radial direction of the circle drawn by the warp, and the part above the circumference is characterized by the same circles being formed in a continuous layer. be.

The type of structure and shape of the fabric to be used may be determined depending on the shape of the heating element, required characteristics, etc. For example, in the case of a heating element with a relatively complicated shape, it is also preferable to use satin fabric, which has excellent drapability. These woven fabrics may be used alone, or a plurality of woven fabrics may be stacked and used. When used in layers, the direction of the warp or weft between adjacent textiles may be slightly shifted (
For example, by stacking the layers so that they are shifted by 15 degrees or 30 degrees, the anisotropy is improved and the resistance value becomes pseudo-isotropic in the plane. However, the woven fabric can also be used by stacking the warp or weft in the same direction.

The second is a defibrated mat. This is made up of randomly oriented individual short carbon fibers and inherently has pseudo-isotropy.

The third is chopped strand mat. This is a mat made by cutting carbon fiber bundles into predetermined lengths and randomly oriented each cut bundle, and also has pseudo-isotropy.

The fourth is a swirl mat. This is not short fibers, but randomly oriented continuous fibers (or continuous fiber bundles) that may or may not be opened.

The fifth is a tubular braid. It has great elasticity in the radial and longitudinal directions, and can be used either in its cylindrical form or by being crushed flat.

The sixth type is a unidirectionally aligned body of continuous fibers that are aligned parallel to each other in one direction in the form of a tape or sheet.

This is usually impregnated with a B-stage thermosetting resin such as phenolic resin, pitch, etc. to maintain the aligned state.

Separately, it is called unidirectional Bripreg.

The seventh form is short fibers with a small aspect ratio, and is used when producing a heating element by the blending method described above.

The above-mentioned defibrated mat, chopped slant mat, swirl mat, cylindrical braid, and unidirectionally aligned body may be used alone, or may be laminated or wound. When unidirectionally aligned bodies are used by being stacked or wound, it is preferable to make them pseudo-isotropic, as in the case of textiles.

In addition, when using the carbon fibers of the first to sixth embodiments described above in a layered manner, using carbon layer fiber threads and stiffening them together by, for example, single chain stitching, the delamination strength and glabella shear strength of the heating element can be improved. This is preferable because strength, impact strength, etc. are improved.

In the present invention, when carbon fibers are used in a layered or wound manner, the same types and shapes of carbon fibers are used.

The electrical resistance of the heating element of the present invention is determined by the type, form, arrangement, and content of the carbon fibers used, the firing temperature when forming carbon fibers, the type of matrix carbon, the bulk density of the heating element, and the carbon fibers used. /C It changes depending on the firing temperature etc. when making a composite.

(Example) The heating element of the present invention will be described in more detail below based on the attached drawings.

1 to 4 illustrate a heating element that is generally planar. The one in Figure 1 is a non-inductively wound disc-shaped heating element with energizing paths (heating parts) arranged symmetrically on the left and right, and the one in Figure 2 is a disc-shaped heating element with energizing paths (heating parts) arranged in a spiral shape. It is a shaped heating element. Figure 3 shows a rectangular plate-shaped heating element in which the current-carrying path (heating part) is bent in a zigzag manner.
FIG. 4 shows a square plate-shaped heating element in which the area of the energizing path (heating part) is larger than that of the heating elements illustrated in FIGS. 1 to 3.
The surface of the current-carrying path of these heating elements functions as a heating surface. The plate-shaped heating element shown in FIGS. 1 to 4 can be manufactured, for example, as follows. That is,
The four methods described above use carbon fiber fabrics laminated in a pseudo-isotropic manner, unidirectionally aligned bodies, carbon fiber defibrated mats, chopped strand mats, swirl mats, and short carbon fibers. Either of these methods may be used to manufacture a thin C/C composite plate, and then cut it using, for example, a scroll saw to remove portions other than the current-carrying path. for example,
In the case of the heating element 1 shown in Fig. 1, C/C with a predetermined diameter and thickness
Manufacture a composite disk and pass it through the thread trowel
a, terminal lb.

■It is manufactured by removing the other parts, leaving only part b. In the production of the disc-shaped heating element shown in FIGS. 1 and 2, the above-mentioned circular fabric or spiral circular fabric can be used as the carbon fiber.

In addition, in the case of a heating element with a narrow current-carrying bus as shown in Figs. You may.

When these heating elements are viewed from a direction perpendicular to the heating surface, the carbon fibers form the same or substantially the same arrangement pattern in all parts.

Therefore, since the electrical resistance is the same or substantially the same in all parts, the Joule heat generated will be the same or substantially the same in all parts, and as a result, the effect of heat radiation must be taken into account. For example, temperature unevenness within the heat generating surface is eliminated or reduced.

Furthermore, since this heating element is a C/C composite, its mechanical strength is high and it can be processed into thin, narrow, and elongated shapes.

The heating element shown in FIGS. 1 to 4 is, for example, C
It can be used when forming a superconducting thin film on the surface of a substrate by the VD method. That is, when forming thin films of superconducting materials of various compositions on the surface of a substrate by the CVD method, the surface temperature of the substrate is set at about 800 to 1000°C, although it varies depending on the composition of the material to be formed, and An operation is performed to control the in-plane variation in surface temperature to within ±5'C. At this time, in order to set the surface temperature of the base material within the above range, the heating element used must be heated to a maximum temperature of 1200'
This is because it is necessary to generate resistance heat to a temperature of about 300 m², and since it is a CVD method, it is necessary to have resistance to corrosion by the reactive gas used.

FIGS. 5 to 7 illustrate examples of heating elements whose heating surfaces are cylindrical curved surfaces or which are cylindrical curved surfaces as a whole and are effective for use in heating means of tubular furnaces. Fig. 5 shows the cylindrical heating element itself, and Fig. 6 shows a heating element with a separation slit formed in the longitudinal direction of the cylinder and a current-carrying path extending in the longitudinal direction while making a U-turn at the slit position. Further, FIG. 7 shows a helical heating element in which the current-carrying path extends in the longitudinal direction in a spiral manner.

In manufacturing these heating elements, the above-mentioned carbon fiber fabrics, unidirectionally aligned bodies, carbon fiber defibrated mats, chirotube strand mats, swirl mats wound, or carbon fiber braids are used. In the case of the heating elements shown in FIGS. 6 and 7, the C/C composite is cut to form the desired current conduction path. A mixture of carbon fibers and a carbonizable substance may be formed into a cylindrical shape, formed into a C/C composite, and then subjected to cutting. Further, in manufacturing a cylindrical heating element, a filament winding method can be applied when forming the cylindrical heating element. Furthermore, in the case of the spiral heating element shown in FIG. 7, it is also possible to manufacture the spiral body by forming a spiral body using a tape-like unidirectionally aligned body and then firing the spiral body.

In this case, as in the case of the heating element shown in Figures 1 to 4, when viewed through from a direction perpendicular to the heating surface, the carbon fibers have the same or substantially the same arrangement pattern in all parts. is forming. Therefore, since the electrical resistance is the same or substantially the same in all parts, the Joule heat generated will be the same or substantially the same in all parts, and as a result, the effect of heat radiation must be taken into account. For example, temperature unevenness within the heating surface is eliminated,
Or the variation becomes smaller.

FIGS. 8 to 10 illustrate a heating element whose heating surface is a truncated conical curved surface, which is effective for changing the degree of heating of a heated object in the vertical direction. In Figure 8, the entire surface is a heating surface, in Figure 9, slits are formed alternately from the top and bottom ends in the vertical direction, and the current-carrying path is a heating element that bends vertically in a zigzag manner, and in Figure 10, vertical slits are formed. It is a heating element in which slits in the circumferential direction are sandwiched alternately, and the current-carrying path is bent along the side curved surface.

The heating element in Figure 8 is a carbon fiber fabric drawn and shaped, a fabric cut into a shape corresponding to the planar development of the heating element,
Defibrated mat, Chimbudo strand, Swirl mat,
A unidirectionally aligned body, a mixture of short fibers and a carbonizable substance (using a blending method), and a laminate made by suitably combining them can be used to produce τ. As the textile used for drawing and shaping, satin-woven fabrics are preferred because of their good drapability. Furthermore, the aforementioned circular fabric or spiral circular fabric is suitable as the fiber material for this heating element.

The heating elements shown in FIGS. 9 and 10 may be manufactured by cutting the heating element shown in FIG. 8. Alternatively, it can be manufactured by molding a green molded body having a path corresponding to the energization path pattern using a tape-like unidirectional alignment body and firing the green molded body.

FIG. 11 illustrates a half part of a heating element that can be incorporated into a spherical furnace, and its heating surface is a hemispherical curved surface. 1st
FIG. 2 shows an example of a heating element for a calibration furnace during infrared temperature measurement, and its heating surface forms a parabolic curved surface.

These heating elements can also be manufactured in the same manner as the heating elements having truncated conical surfaces shown in FIGS. 8 to 1O.

Note that the present invention is not limited to the above embodiments, and various modifications are possible. In other words, C/C composites can change not only the electrical resistance but also the thermal conductivity by changing the arrangement pattern of carbon fibers.
In the case of the heating element of the present invention, by setting the carbon fibers in a predetermined arrangement pattern, it is possible to adjust the amount of Joule heat generated from the heating element, and it is also possible to adjust the amount of heat conduction of the heating element. Become.

(Effects of the Invention) As is clear from the above explanation, the carbon fiber/carbon composite surface heating element of the present invention has a structure that is formed into a surface or a planar shape as a whole, and which parts of the heating surface are The arrangement pattern of the carbon fibers seen from the direction perpendicular to the heating surface was made to be the same or substantially the same in each part, so the current-carrying bus or 2. The electrical resistance on the heat generating surface is the same or substantially the same at all locations, and the Joule heat generated is also the same or substantially the same at each location.

In addition, C/C composite has high mechanical strength (,
Furthermore, since graphite is not brittle, it is easy to process, and the heating element can be made thin or elongated. In addition, there is less worry about breakage, etc. As a result, the total resistance of the heating element can be increased, so even if the current load is small (even if the heat is generated to the required high temperature), the current load is small. Therefore, not only the heating element itself but also the power supply system,
The electrode system and control system can be made compact.

Furthermore, even if the shape of the object to be heated is complex, the stage before firing,
In other words, the carbon fibers and matrix can be shaped into the shape of the heating element when they are flexible, and C/
Even after it is made into a C composite, its mechanical strength is high and it is not very brittle, so it can be precisely processed without fear of breakage.

Furthermore, since the C/C composite has a higher thermal conductivity than graphite, the heating element of the present invention can start operation at a higher temperature increase rate, that is, at a faster start-up when used.

[Brief explanation of the drawing]

Figures 1 to 4 are all plan views showing the heating element of the present invention, Figures 5 to 12 are perspective views showing still another heating element of the invention, and Figure 13 is a spiral circular woven fabric. The entire plan view, FIGS. 14 and 15 are partially enlarged views, and FIG. 16 is a sketch showing the expanded state. 1... Heating element, 1a... Energized bus, 1b... Terminal. Applicant: Hanawa Thermoelectric Metal Co., Ltd.

Claims (1)

[Claims] Is the arrangement pattern of carbon fibers formed in a plane or in a planar shape as a whole, and the arrangement pattern of carbon fibers when viewed from a direction perpendicular to the heat generation surface, no matter which part of the heat generation surface is taken, the same in each part? , or substantially the same carbon fiber/carbon composite surface heating element.