JPH06280117A - Heating furnace for graphite fiber production - Google Patents

Abstract

PURPOSE:To prolong the life of the resistance heater element by covering the cylindrical heating resistor made of graphite with a high-melting material on its surface. CONSTITUTION:The heating resistor 1 of graphite cylinder for heating yarn Y is covered with a high-melting material 2 melting over 2800 deg.C and having a coefficient of thermal expansion from equal to till less than 2.0 times that of the heater material such as W, Ta, HfC, TaC, NbC, VC, SiC, HfN, TaN, ZrN, HfB2, TaB2, NbB2, WB, TiB2). The outside surface of the covering layer is protected with a carbon yarn layer 3 to inhibit or prevent the covering layer 2 from being deteriorated or peeled. The covering layer is formed by plasma- spraying or vacuum-spraying.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating furnace for producing graphite fiber. More specifically, the present invention relates to a heating furnace for producing graphite fibers, which is for producing graphite fibers having high physical properties continuously and efficiently.

[0002]

2. Description of the Related Art Conventionally, a large number of heating furnaces such as resistance furnaces, induction furnaces, arc furnaces and plasma furnaces have been used as high temperature heating furnaces for firing carbon materials such as carbon fibers and various industrial materials such as ceramic materials. In particular, a heating furnace of the Tammann furnace type (hereinafter referred to as a “Tanman heating furnace”), which is a resistance furnace using graphite as a resistance heating element, has a relatively simple heating means. Widely used for heat treatment of materials.

In order to perform high temperature heating of at least 2000 ° C. or higher using this Tammann type heating furnace, an electric current is passed through a cylindrical resistance heating element made of graphite, and Joule heat is generated to allow the resistance heating element to stand still or inside. The article to be heat-treated which continuously passes is heated and calcined. This heat treatment is usually carried out in an inert gas such as nitrogen or argon or under reduced pressure vacuum.

The resistance heating element made of this graphite melts even in a high temperature range of 2000 to 3000 ° C., which cannot be practically used in the resistance heating element made of a metal material or a ceramic material.
Since it does not cause decomposition, it functions sufficiently as a resistance heating element, and it is a relatively inexpensive material, but if it is used for a long time at the above-mentioned high temperature, it gradually wears out and deteriorates, making continuous use difficult. There was a flaw. Particularly, in order to produce a high-performance graphite fiber, it is necessary to heat it at a high temperature of 2500 ° C. or higher, and the wear deterioration of the resistance heating element becomes more remarkable in this temperature range.

That is, if the thickness of the resistance heating element becomes thin due to wear and deterioration, the electrical resistance at that portion locally increases, and wear is accelerated at an accelerated rate. Since the temperature distribution changes, it becomes an impediment factor to the quality stability of the baked product. Therefore, it is necessary to replace the resistance heating element with a new one over time. For safety reasons, it is necessary to replace the resistance heating element after cooling the furnace, but especially in a large heating furnace, a series of operations such as cooling, dismantling, assembly, and reheating require a lot of time and labor. , The shorter the replacement cycle of the resistance heating element,
Not only the material cost of the resistance heating element but also the productivity is significantly impaired, and the firing cost is increased.

As a method for solving such a problem, a method of suppressing the evaporation and oxidation of the carbon of the heating element by winding and laminating a carbon fiber yarn on the outer peripheral surface of the cylindrical graphite resistance heating element (Japanese Patent Publication No. 59-59-
No. 25936) or a resistance heating element made of graphite is coated with paste zirconia (ZrO ₂ ) on the outer peripheral surface thereof, and the heat generation is caused by moisture in the air adsorbed on the carbon material for heat retention around the heating element. A method for reducing body wastage (JP-A-63-62182) and a method for forming a gas-impermeable film on the inner surface of the furnace core tube of a heating furnace for producing a glass preform for optical fibers (JP-A-4-50129). Gazette) has been proposed. Further, although there is no description of an application example as a heating furnace, a method of coating the surface of a carbon-based base material with a metal material and a ceramic material in order to improve the oxidation resistance of the carbon-based material (JP-A-4-59978). For the purpose of improving the oxidation resistance and high temperature strength of the carbon fiber composite material, the surface layer of the carbon fiber composite material is made of Si or Hf carbide, nitride or carbonitride and the outer layer thereof is made of Ti or B carbide, nitride or A coated carbon fiber reinforced composite material coated with carbonitride (JP-A-3-290375) has been proposed.

[0007]

However, even in the case of the resistance heating element proposed in the above Japanese Patent Publication No. 59-25936, the surface of the heating element can be obtained only by winding and laminating the carbon fiber yarn at a high temperature of 2500 ° C. or higher. There is a problem that it is not possible to sufficiently prevent the evaporation of carbon from the inside and prevent the permeation of oxidizing gas.

Further, in the resistance heating element for producing tungsten carbide (WC) powder proposed in the above-mentioned JP-A-63-62182, since the zirconia coated on the surface of the resistance heating element is in a paste form, 2500 When applied to a heating furnace at a temperature of not lower than 0 ° C., zirconia is melted, the coating layer is broken, and the outer peripheral surface of the resistance heating element is exposed, so that there is a drawback that evaporation of carbon from the surface of the heating element cannot be suppressed.

Further, in the heating furnace for producing a glass preform for optical fibers proposed in Japanese Patent Laid-Open No. 4-50129,
Since the gas impermeable film is formed only on the inner surface of the furnace core tube, carbon evaporation mainly occurs on the outer surface of the furnace core tube in the high temperature range of 2500 ° C or higher, and the evaporation of carbon occurs only by coating the inner surface. There is almost no suppression effect.

Further, in the oxidation-resistant coating method of carbonaceous material proposed in Japanese Patent Application Laid-Open No. 4-59978, the platinum sintered layer which prevents the permeation of oxidizing gas is melted at 2000 ° C. or higher and the coating layer is formed. Is destroyed, the surface of the carbon-based base material is exposed, and evaporation of carbon cannot be suppressed. Further, the coated carbon fiber reinforced composite material proposed in JP-A-3-290375 for the purpose of improving oxidation resistance and high temperature strength is a base material although it has an effect of gas impermeability of the coating layer. Since the carbon fiber reinforced composite material has electrical anisotropy and the structure is non-uniform, it cannot be applied as a heating furnace for producing graphite fiber which is an application of the present invention.

The present invention has been made in view of the above circumstances. At the same time, the evaporation of carbon from the surface of the resistance heating element is blocked or remarkably suppressed, and at the same time, the permeation of an oxidizing gas is prevented, so that the high temperature of 2500 ° C. or higher is achieved. It is an object of the present invention to provide a heating furnace provided with a resistance heating element that can significantly extend the life.

[0012]

The present invention has the following constitution in order to solve the above problems. That is, in a heating furnace having a cylindrical resistance heating element made of a graphite material, a high melting point of 2800 ° C. or higher and a coefficient of thermal expansion equal to or higher than the resistance heating material of 2.0 times or less are provided on the outer surface of the heating element. A heating furnace for producing graphite fibers, characterized in that a coating layer made of a melting point material is formed.

In the present invention, the coating layer formed on the outer surface of the resistance heating element must be made of a material that does not melt even at 2800 ° C., and the vapor pressure at a high temperature of 2000 ° C. or higher is higher than that of carbon. It is significantly lower and requires almost no sublimation. This is because in a heating furnace for producing graphite fibers, it is necessary to perform heat treatment at a temperature of 2000 ° C. or higher in order to obtain graphite fibers, but in order to obtain graphite fibers having a higher elastic modulus, for example, high temperature treatment of 2500 ° C. or higher is required. It is necessary, and when coating a substance that melts or sublimes below 2800 ° C, the coating layer melts and sublimes during temperature rise, destroying the morphology, and evaporating or oxidizing the heating element carbon from that part. Not only is it not possible to extend the life of the resistance heating element, but also the electrical resistance changes at the part where the coating layer is broken, and the temperature distribution becomes uneven, so that the desired quality of graphite fiber cannot be obtained. is there.

In the heating furnace for producing graphite fiber of the present invention, the thermal expansion coefficient of the compound forming the coating layer is made equal to or more than 2.0 times the thermal expansion coefficient of the resistance heating element in the temperature range used. Is. When the thermal expansion coefficient of the compound forming the coating layer is less than or equal to the thermal expansion coefficient of the resistance heating element or exceeds 2.0 times, the coating layer peels from the resistance heating element during heating or the coating layer This may cause cracks and deterioration of the resistance heating element.

The thermal expansion coefficient is defined by the following equation. That is, when the size of the test body from a certain reference temperature t ₀ to a certain temperature t changes from L ₀ to L, L = L ₀ {1 + α (t
Let α represented by −t ₀ )} be a coefficient of thermal expansion.

From the point of view of practicality, W, Ta, HfC, TaC,
NbC, ZrC, TiC, VC, SiC, HfN, Ta
N, ZrN, TiN, BN, HfB ₂ , TaB ₂ , Nb
At least one selected from B ₂ , WB, TiB ₂ and ZrB ₂ is preferable.

In the coating layer made of the high melting point material, the carbon element ratio is high on the outer surface of the resistance heating element, and the gradient of the high melting point metal and the high melting point compound increases continuously in the surface direction of the coating layer. It is more preferable to use a tissue. The term "gradient structure" as used herein means to continuously or stepwise from one composition (in the case of the present invention, carbon of the heating element) to another composition (in the case of the present invention, one or more compositions of the above-mentioned refractory metal or compound). Means a changing set of organizations. In this case, the composition of the graded structure in the thickness direction is such that, when one kind of high melting point substance is coated, the concentration of the high melting point substance is in the range of 20 to 80% at a half thickness position of the coating layer. Is preferred.

From the viewpoint of complete prevention of peeling and cracking of the coating layer, it is preferable that the coating layer has a graded structure. When the coating layer has a graded structure, the difference in thermal expansion is relaxed because the composition gradually changes, and the phenomenon that the coating layer peels from the resistance heating element or cracks occur in the coating layer is suppressed. be able to. Further, a carbon fiber yarn coated with carbon fibers or a carbide, nitride or boron compound similar to the compound applied as the coating layer of the resistance heating element is wound around the outer peripheral surface of the resistance heating element having the coating layer. By laminating the layers, the thermal expansion of the coating layer can be absorbed and relaxed, and the resistance heating element and the coating layer can be firmly bonded.

The heating furnace of the present invention will be specifically described below with reference to the drawings.

FIG. 1 is a schematic vertical sectional view showing an embodiment of the heating furnace for producing graphite fiber of the present invention. In FIG. 1, 1
Is a cylindrical resistance heating element made of graphite for heating the yarn Y continuously passing through the inside, and 2 is a resistance heating element having a melting point of 2800 ° C. or more and an expansion coefficient of 2800 ° C. or more on the outer surface of the resistance heating element 1. The coating layer is made of one or more metals or compounds that are equal to or less than 2.0 times the resistance heating material. Reference numeral 3 denotes a carbon fiber yarn layer formed by winding a plurality of carbon fiber yarns on the outer peripheral surface of the resistance heating element having the coating layer. Reference numeral 4 denotes an outer cylinder made of graphite with the heating element 1 as a concentric core, and is provided to reflect radiant heat to the inside and lengthen the soaking zone. Reference numeral 5 is a felt-like heat insulating material made of carbon or graphite for holding the outer cylinder 4 and keeping the furnace warm. The outside of the heat insulating material 5 is further covered and protected by a furnace shell 6 made of a thin steel plate.

Further, terminal portions 1a and 1b having a larger cross-sectional area than the central portion of the resistance heating element are formed at both ends of the resistance heating element 1, and a current is supplied to the resistance heating element 1 at each terminal portion. An electrode 7 (not shown) for is fixed. The electrode 7 is connected to a low-voltage, large-current power supply unit, and the resistance heating element generates Joule heat when energized by the power supply unit. Reference numerals 8a and 8b respectively denote an inlet and an outlet of the yarn Y, and the ring-shaped member 9 having the inlet and outlet is fixed to the openings of the terminal portions 1a and 1b, so that the heat supplied to the inside of the resistance heating element can be prevented. It also serves as a seal part for preventing active gas from leaking to the outside. As described above, in order to prevent the yarn Y and each member in the furnace from deteriorating due to oxidation, the inside of the resistance heating element 1 and the inside of the furnace shell 6 are usually filled with an inert gas such as nitrogen or argon. .

The coating layer 2 removes foreign matters and the like on the outer surface of the resistance heating element 1 in advance, and at the same time, roughens the surface of the material to give an anchor effect to the coating material. Therefore, the coating layer is formed after sandblasting. Preferably. The surface roughness is such that the center line average roughness (Ra) specified by JIS B 0601 is 3 to 10 μm and the maximum height (Rmax) is 50.
A range of μm or less is preferable.

The coating can be formed, for example, by plasma spraying in an air atmosphere or an inert gas atmosphere such as nitrogen or argon, or by vacuum spraying under a reduced pressure of 30 to 300 Torr (inert gas atmosphere). it can. From the viewpoint of preventing peeling and cracks from occurring, the base material of the base material is less likely to appear, and the gas is less likely to pass through to improve the evaporation suppressing effect of the resistance heating element carbon.
The thickness is preferably 1000 μm, more preferably 50 to 500 μm. Further, it is also preferable to employ the CVD method under a reduced pressure of 30 to 300 Torr in order to form a denser film. When the coating is formed by the CVD method, the thickness of the coating is smaller than that of the thermal spraying method.

The particle size of the high melting point metal powder or the high melting point compound powder used for thermal spraying is not particularly limited, but 1
Any material having a thickness of 00 μm or less and usually used for thermal spraying may be used.

At this time, if a means for winding and laminating the carbon fiber yarn on the outer peripheral surface of the resistance heating element is adopted, the carbon vapor which passes through the defective portion of the coating layer and is gradually evaporated is completely blocked or remarkably suppressed. Not only that, the thermal expansion of the coating layer is absorbed and relaxed by the thermal contraction of the carbon fiber situation, effectively preventing the coating layer from peeling or cracking from the resistance heating element, and firmly bonding the resistance heating element and the coating layer. It is possible to do so, which is preferable.

The carbon fiber thread layer 3 is formed by firing a general carbon fiber thread obtained by firing organic fibers such as pitch-based, cellulose-based, and acrylic-based fibers in an inert gas at 800 ° C. or higher as a resistance heating element. It is wound multiple times on the outside of the, and its laminated thickness cannot be determined unconditionally depending on the wall thickness of the heating element, but if the wall thickness of the heating element is about 10 mm, it will be 5 to 20 mm.
A degree is preferable. Incidentally, usually commercially available carbon fiber threads are often provided with a sizing agent such as an epoxy type,
Since these sizing agents are decomposed and gasified when heated and pollute the atmosphere in the furnace, it is preferable to remove the sizing agent before winding and laminating on the outside of the resistance heating element. More preferably, fiber yarn is used. The total fineness of the carbon fiber yarns is not particularly limited, but usually 1000 to 20000 denier is used. In addition, since this wound layer is located outside the resistance heating element 1 and is heated for a long time to be graphitized,
Either carbonized yarn or graphitized yarn can be used.

Furthermore, since the carbon fibers to be wound and laminated are located near the outer peripheral side of the resistance heating element, they are exposed to high temperatures and, by themselves, tend to evaporate and wear to some extent. In order to effectively prevent this, a high melting point compound having a melting point of 2800 ° C. or higher on the carbon fiber surface, for example, a carbide such as TiC, NbC, TaC, and SiC, or BN, TaN, HfN.
CV which is usually carried out with a refractory compound such as a nitride such as NbB ₂ , TaB ₂ , ZrB ₂ or the like.
It is preferable to use a carbon fiber yarn formed by the method D. In this case, the carbon fiber surface matrix is prevented from appearing and the carbon evaporation suppression effect is reduced, while the fiber itself is too thick and the resistance heating element becomes difficult to wind around the outer peripheral surface of the resistance heating element. It is preferable that the thickness of the high melting point compound film is 0.05 to 2 μm from the viewpoint of preventing the carbon fiber from easily breaking and reducing the effect of suppressing the evaporation loss of the carbon fiber.

When the carbon fiber yarns are wound and laminated, it is preferable that the carbon fiber yarns are closely adhered to the outside of the resistance heating element and closely wound so that there is no space between the yarns. For example, a winding machine or a lathe is used. While rotating the heating element, 10 carbon fibers
It is more preferable to wind and laminate at a constant tension of about 0 to 1000 g substantially perpendicular to the axial direction of the heating element.

Further, in order to suppress evaporation of carbon from the resistance heating element and the carbon fiber wound and laminated on the outer peripheral surface of the resistance heating element and further enhance the heat insulating effect, a flexible material is formed on the outside of the carbon fiber yarn winding layer. The sheet-shaped graphite may be wound and laminated.

[0030]

EXAMPLES Next, the embodiments of the present invention will be specifically described with reference to Examples and Comparative Examples.

<Example 1> Inner diameter 30 mm, outer diameter 50 mm
Niobium carbide (NbC) having an average particle diameter of 40 μm is formed on the outer surface of the central portion (length 600 mm) of a graphite resistance heating element made of graphite (thickness of central portion 10 mm) and length 1250 mm.
Was plasma sprayed in the atmosphere to form a coating layer having a thickness of 200 μm. Next, this NbC-coated resistance heating element was set in the heating furnace shown in FIG.
The temperature was raised to 000 ° C and continuous operation was performed. For temperature control at 3000 ° C, power control is performed by measuring the surface temperature of a small graphite block set at the center of the heating element pipe with a radiation thermometer installed at one end of the heating element in the axial direction (outside the heating furnace). did.

After the start of the operation, it took 17 days for the heating element to wear out and break and could not be operated, and the life of the heating element of the present invention was significantly extended as compared with Comparative Example 1 below, and the effect was recognized. The results are shown in Table 1.

[0033]

[Table 1] <Embodiment 2> With respect to the resistance heating element in which the same NbC as that used in Embodiment 1 is plasma-sprayed, 120 is formed on the outer peripheral surface thereof.
A carbon fiber yarn having no sizing agent of 00 filaments was tightly wound with a winding tension of about 250 g so as to be orthogonal to the cylindrical axis to form a carbon fiber yarn layer having a thickness of 5 mm.

Next, NbC wound with this carbon fiber yarn is wound.
The coating resistance heating element was set in the heating furnace shown in FIG. 1 and, in the same manner as in Example 1, 3000 ° C. in an argon gas atmosphere under normal pressure.
The temperature was raised to 0 and continuous operation was performed.

On the 20th day from the start of operation, the primary current reached near the upper limit value, the secondary current began to largely fluctuate, and the operation became impossible. Therefore, the operation was stopped and the heating element was taken out after cooling and observed. There is no abnormality in the coated heating element,
It was found that the NbC coating effect was great. However, the carbon fiber yarn layer wound and laminated on the outer peripheral surface of the heating element was damaged and deteriorated in the central portion, and was in contact with the inner surface of the outer cylinder 4 shown in FIG. The results are also shown in Table 1.

<Embodiment 3> In Embodiment 2, except that the carbon fiber coated with NbC on the surface of the single yarn by the CVD method is used instead of the carbon fiber wound around the outer peripheral surface of the NbC thermal spray resistance heating element. The heating furnace was operated in exactly the same manner. The NbC coating on the carbon fiber is 500
NbCl ₅ was reduced in a N ₂ atmosphere with H ₂ at ˜600 ° C., followed by continuous carbonization in a reaction gas of CH ₄ at 1100 ° C. in a two-step process. As a result, a coated carbon fiber having a coating thickness of 1 μm was obtained. The carbon fiber used as the base material was 12000 filaments without sizing.

On the 27th day from the start of the operation, the operation became impossible due to the current fluctuation, but there was almost no wear of the heating element,
Furthermore, the damage suppressing effect of the NbC coating of carbon fiber was recognized. The results are also shown in Table 1.

<Embodiment 4> Inner diameter 30 mm, outer diameter 50 mm
(The thickness of the central portion is 10 mm) and the length is 1250 mm. The central portion (length 6) of the cylindrical resistance heating element made of high density isotropic graphite.
00 mm) on the outer surface by low pressure CVD method 1300
The NbC was coated at 100 ° C. at 100 ° C. for about 3 hours. NbCl ₅ , CH _{4, and H 2} were used as source gases, and NbCl ₅
The flow rate was constant at 0.3 l / min. The thickness of the obtained coating layer was 100 μm.

The NbC-coated heating element was set in the heating furnace shown in FIG. 1 and, similarly to Example 1, the temperature was raised to 3000 ° C. in an argon gas atmosphere to continuously operate. It took 20 hours for the cylindrical heating element to wear out and break, and to be unable to operate, and the life of the heating element was significantly improved as compared with Comparative Example 1 shown below. The results are also shown in Table 1.

<Embodiment 5> A cylindrical resistance heating element made of graphite similar to that used in Embodiment 4 has a central portion (length 600 m).
m) on the outer surface by a low pressure CVD method at 1300 ° C., 10
NbC was coated at 0 Torr for about 3 hours. NbCl ₅ , CH ₄ , and H ₂ were used as the source gas, and the flow rate of NbCl ₅ was increased from 0 liter / minute to 0.6 liter / minute at a rate of 0.2 liter / hour, so that NbC was removed from the surface of the heating element.
A 100 μm thick coating layer having a gradually increasing gradient was formed. FIG. 2 shows a result of analyzing the obtained coating layer by EPMA. It is shown that the Nb concentration has a graded structure in which the concentration of Nb continuously increases from the outer surface of the heating element carbon to the surface of the coating layer. Recognize.

This NbC-coated heating element was set in the heating furnace shown in FIG. 1 and, similarly to Example 1, the temperature was raised to 3000 ° C. in an argon gas atmosphere to continuously operate. It took 23 hours for the cylindrical heating element to wear out and break, and to become inoperable, and the life of the heating element was significantly improved as compared with Comparative Example 1 shown below. The results are also shown in Table 1.

<Comparative Example 1> Inner diameter 30 mm, outer diameter 50 mm
A single piece of a cylindrical resistance heating element made of graphite (thickness of the central portion: 10 mm) and having a length of 1250 mm was set in the heating furnace shown in FIG. 1, and continuously operated at 3000 ° C. as in Example 1. After 36 hours, the heating element was depleted due to wear and became inoperable. The results are also shown in Table 1.

<Comparative Example 2> In Example 2, as a result of continuous operation under exactly the same conditions as in Example 2, except that the outer surface of the resistance heating element was not coated with NbC by spraying, the heating element was heated for 6 days. Became depleted due to wear and tear and became inoperable. The results are also shown in Table 1.

<Comparative Example 3> In Example 1, as a result of continuous operation under exactly the same conditions as in Example 1 except that the film thickness of the NbC coating layer of the resistance heating element was changed to 10 μm, the heating element was found to disappear in 2.5 days. It broke down due to wear and tear and could not be operated. The results are also shown in Table 1.

[0045]

According to the heating furnace of the present invention, the coating layer made of a metal having a high melting point and a compound having a high melting point blocks or significantly suppresses the evaporation of carbon from the outer surface of the resistance heating element, and the resistance due to the evaporation of carbon is reduced. It is possible to prevent or reduce the wear and deterioration of the heating element as much as possible. Further, by making the composition of the coating layer a gradient structure, it is possible to reduce the difference in thermal expansion between the resistance heating element and the coating layer, and to suppress the peeling or cracking of the coating layer from the heating element. Further, by winding and laminating a carbon fiber thread on the outer peripheral surface of the resistance heating element, not only the evaporation of carbon from the surface of the resistance heating element is suppressed, but also the thermal contraction of the carbon fiber itself causes the resistance heating element and the coating layer to be separated. It is possible to absorb and relax the difference in thermal expansion, and prevent the coating layer from peeling or cracking from the heating element. Furthermore, by winding and laminating the carbon fiber yarn coated with the high melting point compound on the outer peripheral surface of the resistance heating element, it is possible to prevent deterioration of the carbon fiber itself due to wear.

Therefore, the heating furnace of the present invention can continuously produce the graphite fiber even at a high temperature of 2500 ° C. or higher, with the life of the resistance heating element being greatly extended.

According to the present invention, it is possible to provide a heating furnace for graphite fiber production having a cylindrical resistance heating element made of graphite, which has a long life by suppressing evaporation and oxidation of the resistance heating element carbon.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view of an embodiment of a heating furnace for producing graphite fibers of the present invention.

FIG. 2 shows a coating layer of NbC gradient structure by EPMA,
The graph which analyzed in the cross section direction of a cylindrical heating element.

[Explanation of symbols]

 1: Cylindrical resistance heating element 1a, 1b: Heating element terminal part 2: Cylindrical resistance heating element coating layer 3: Carbon fiber yarn layer 4: Graphite outer cylinder 5: Felt-like heat insulating material 6: Furnace shell 7: Electrode 8a: Inlet 8b: Outlet 9: Ring-shaped member Y: Thread

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Internal reference number FI Technical indication location H05B 3/62 7913-3K (72) Inventor Tomihiro Ishida 1515 Tsutsui, Matsuemae, Iyo-gun, Ehime Toray Co., Ltd. Ceremony Company Ehime Plant (72) Inventor Toshihide Sekido 1-1-1, Sonoyama, Otsu City, Shiga Prefecture Toray Co., Ltd. Shiga Business Site (72) Inventor Hideo Saruyama 1515 Tsutsui, Matsumae-cho, Iyo-gun, Ehime Prefecture Toray Co., Ltd. Ehime Plant (72) Inventor Takaki Masaki 1-1-1, Sonoyama, Otsu City, Shiga Prefecture Toray Co., Ltd. Shiga Plant

Claims (5)

[Claims] 1. A heating furnace having a cylindrical resistance heating element made of a graphite material, having a melting point of 280 on the outer surface of the heating element.
A heating furnace for producing graphite fibers, characterized in that a coating layer made of a high melting point material having a coefficient of thermal expansion of 0 ° C. or higher and a resistance heating element material which is equal to or more than 2.0 times is formed. 2. The coating layer on the outer surface of the heating element is W, Ta, Hf.
C, TaC, NbC, ZrC, TiC, VC, SiC,
HfN, TaN, ZrN, TiN, BN, HfB ₂ , T
The heating furnace for producing graphite fibers according to claim 1, wherein the heating furnace is formed of at least one selected from aB ₂ , NbB ₂ , WB, TiB ₂ , and ZrB ₂ . 3. The heating furnace for producing graphite fibers according to claim 1, wherein the coating layer has a gradient structure that continuously changes from the outer surface of the heating element to the outer surface of the coating layer. 4. The heating furnace for producing graphite fiber according to claim 1, wherein a carbon fiber yarn is wound and laminated on an outer peripheral surface of a heating element having a coating layer. 5. A melting point of 280 on the surface of a single fiber of carbon fiber yarn.
The heating furnace for producing graphite fiber according to claim 4, wherein carbon fiber yarns coated with a high melting point compound of 0 ° C. or higher are wound and laminated.