JPH0735613B2 - Carbonization treatment method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a carbonization treatment method, and more specifically, to fibers that run inside due to volatile products generated when carbonizing flame-resistant fibers. Is prevented from being adversely affected, there is no fluffing or fiber cutting accident due to volatile products adhering to the inside, and the amount of inert gas used is reduced.
The present invention relates to a carbonization treatment method capable of producing a carbonized fiber having high strength.

[Prior Art and its Problems] Conventionally, a carbonization furnace used for carbonizing flame-resistant fibers has a furnace core tube filled with an inert gas, for example, nitrogen gas, and heated to, for example, a maximum of 2000 ° C. The furnace core tube has a structure in which the flameproof fiber is run.

However, in the conventional carbonization furnace, during the carbonization process,
Volatile products are generated from running fibers. Since the nitrogen gas flow is discharged upward as it is from the upper opening of the lid member provided in the upper opening of the furnace core tube, the high-boiling substance in the generated volatile products is the opening of the lid member. It adheres like a tar to the inside of the cylindrical lid member or to a guide roller or the like arranged above the furnace core tube. When the amount of the tar-like material attached increases, fiber fluff adheres to the tar-like material and closes the upper opening of the furnace core tube and the opening of the lid member. If the openings of the furnace core tube and the lid member are closed, it is necessary to replace the furnace core tube and the lid member or clean the furnace core tube and the lid member, which hinders continuous production of carbon fibers. Even if the upper opening of the furnace core tube and the opening of the lid member are not closed, the running fibers come into contact with the tar-like volatile products,
The fibers are cut or the fibers are fluffed. When fluffing occurs in the fiber, the strength of the carbon fiber decreases.
Further, if the volatile product adheres to the guide roller in a tar shape, smooth running of the fiber is hindered.

In order to solve such a problem, the present inventors have
A side tube is provided in the lid member provided on the upper part of the furnace core tube, and the lid member is heated without being cooled by the heat of the furnace core tube, and the flameproof fiber is used so that air does not enter the furnace core tube. The flow velocity of the inert gas flowing out from the fiber inlet opening at the upper part of the lid member that serves as an inlet for guiding the inside of the furnace core tube to 2 m /
While maintaining for about a second, a large amount of inert gas is discharged from the side tube of this lid member, and most of the volatile products are discharged together with the inert gas from this side tube, and the top opening of the lid member is opened. In addition to preventing the volatile products contained in the nitrogen gas stream flowing from the fiber inlet from adhering to the guide rollers, prevent the volatile products from depositing in tar form near the fiber running path in the carbonization furnace. I tried.

However, when a large amount of inert gas is discharged from the side tube of the lid member, the running fibers fluctuate, and, for example, the guide roller located above the lid member, the upper opening of the lid member and its lower opening, or other parts. Fibers come into contact with
The fibers were fluffed or the fibers were cut. In addition, since a large amount of nitrogen gas is used, there is a problem that the cost of using nitrogen gas increases. Further, if oxygen is mixed in at a high temperature, the strength of the produced carbon fiber is lowered and the yield of the carbon fiber is also lowered. Therefore, it is necessary to increase the amount of the inert gas more than discharging the inert gas from the side pipe.

[Object of the Invention] The present invention has been made based on the above circumstances.

That is, the object of the present invention is that the carbonization treatment can be performed without using a large amount of inert gas, and moreover, volatilization that occurs when the flame-resistant fiber is carbonized fiber and causes tar-like substances. It is to provide a carbonization treatment method in which the carbonization treatment is not hindered by a sexual product.

Another object of the present invention is to first heat-treat a flame-resistant fiber at a low temperature relatively less affected by oxygen to generate a volatile product that causes tar generation from the flame-resistant fiber, The volatile product is discharged from a direction other than the flameproof fiber introduction port to prevent tar-like substances from adhering to rolls and the like, and then to provide a method of carbonizing at high temperature.

Still another object of the present invention is not to use a large amount of inert gas, the fiber running in the carbonization furnace is not hindered by the volatile products generated when carbonizing the flame-resistant fiber, Moreover, it is an object of the present invention to provide a carbonization treatment method using a heating furnace that is easy to perform maintenance work.

[Means for Achieving the Object] An outline of the present invention for achieving the object will be described with reference to the drawings. As shown in FIG. 1, a flameproof fiber 1 obtained by a flameproofing treatment is obtained. Is heated in a preheating furnace 2 to a maximum temperature of 400 to 1000 ° C. under an inert gas atmosphere to preheat most of the inert gas containing volatile products generated from the flame resistant fiber 1. The flame-resistant fiber 1 is heat-treated so as to be discharged from an outlet other than the fiber inlet opening in the furnace core tube in the furnace 2, and the fiber 3 heat-treated in the preheating furnace 2 is carbonized. It is a carbonization treatment method characterized by heating to a maximum temperature of 2000 ° C. in a furnace 4 for carbonization.

Examples of the flame-resistant fibers include phenol-based heat-resistant polymers such as polyacrylonitrile, rayon, polyvinyl alcohol, polyacetylene, lignin, and quinol, polymer systems such as aramid, polyamide, and polyimide, and pitch systems, full-free alcohol systems, etc. It is possible to use those obtained by subjecting the low molecular weight (melting) type compound of (3) as a raw material to the fiber obtained by spinning these raw materials and subjecting the fiber to flame resistance treatment.

However, a preferable flameproof fiber is obtained by spinning a polyacrylonitrile polymer compound and subjecting it to flameproofing.

In the carbonization treatment method according to the present invention, basically, by heating the flame-resistant fiber 1 in the preheating furnace 2 at a relatively low temperature, the fiber 3 that has passed through the preheating furnace 2 is carbonized. In the preheating furnace 2 containing the volatile product, the volatile product was generated to the maximum extent to the extent that the volatile product causing the generation of tar-like substances was no longer produced even when heated at 4. The inert gas is discharged from the outlets other than the fiber inlet opening in the upper part of the furnace core tube in the preheating furnace 2, and then the fibers passing through the preheating furnace 2 are heated in the carbonization furnace 4 to produce carbon fibers. The basic principle is to obtain.

In the preheating furnace 2, if the flameproofing fiber 1 is heated at a low temperature to generate a volatile product from the flameproofing fiber 1, and if the flameproofing treatment in the flameproofing furnace is insufficient, , To complete its insufficient flameproofing treatment. Therefore, in the method of the present invention, the fiber 3 fed into the carbonization furnace 4 has been completely subjected to the flameproofing treatment, and furthermore, the volatile products that cause tar generation have been exhausted. In the carbonization furnace 4, only volatile products such as hydrogen cyanide, nitrogen, carbon monoxide, and hydrogen that do not contain tar are generated, and these volatile products do not cause tar generation. It is possible to carry out a carbonization treatment without any harmful effect.

In this carbonization treatment method, the heating temperature in the preheating furnace 2 is set to a maximum of 400 to 1000 ° C, preferably 400 to 600 ° C, and the heating temperature in the carbonization furnace is set to a maximum of 2000 ° C, preferably 1500 ° C. is important. Here, the maximum temperature of 2000 ° C means that the maximum temperature is equal to or higher than the temperature of the first stage and 2000 ° C.
It means the following.

However, the optimum heating temperature in the preheating furnace 2 varies depending on the type of flameproof fiber and the degree of flameproofing, and even if the flameproofing fiber and the degree of flameproofing are the same, the preheating furnace 2
It also varies depending on the amount of oxygen mixed in the inert gas flowing through. For example, in the case of polyacrylonitrile-based flameproofed fiber which is flameproofed to an oxygen content of about 6%, if the flameproofed fiber passes through the preheating furnace 2 for about 3 minutes, heating The upper limit of temperature is 600 ° C. In any case, the preferable upper limit of the heating temperature in the preheating furnace 2 is within the above temperature range, and the specific optimum maximum temperature of each is determined by the type of flame resistant fiber, the degree of flame resistance, and the preheating. It can be appropriately determined by an experiment depending on the oxygen content in the inert gas flowing in the furnace 2, the time for which the flameproof fiber passes through the preheating furnace 2, and the like.

When heat treatment is carried out in such a maximum temperature range or less, carbonization is not carried out, but, for example, cyclization and condensation reaction in flame-resistant fiber proceed, resulting in volatility causing tar-like substances. A product is produced.

This volatile product is discharged together with the inert gas introduced into the furnace core tube in a direction other than the fiber introduction port of the furnace core tube.

A guide roller is arranged above the furnace core tube to discharge it in a direction other than the fiber introduction port of the furnace core tube, and the inert gas containing the volatile products is discharged upward from the fiber introduction port as it is. Then, the volatile products adhere to the guide roller arranged above the preheating furnace 2 in the form of tar, and the flameproof fiber cannot be smoothly guided. Once tar adheres to the fiber that is being introduced into the furnace, it does not completely evaporate inside the furnace, and some tar condenses and proceeds to the carbonization process while remaining adhered, where the fiber is cut or cut. Even if it does not, the strength of the tar-attached portion of the obtained carbon fiber may be reduced.

Therefore, the preheating furnace used in the method of the present invention is
It has a structure that the heating temperature in the furnace core tube can be up to 400 ~ 1000 ℃ and the inert gas containing volatile products can be discharged in the direction other than the fiber inlet of the furnace core tube. It is important that the preheating furnace has the structure shown in FIG.

As shown in FIG. 2, the preheating furnace 2 mainly includes a furnace core tube 21 and an outer cylindrical body 23 surrounding the furnace core tube 21 and mounting and supporting a heater 22.

The furnace core tube 21 is made of a ceramic containing alumina as a main component and is formed into a cylindrical body having a circular horizontal cross section. A lid member 23A is provided at the fiber inlet and a cooling jacket 2 is provided at the fiber outlet.
Attach 3B respectively. By fixing the cooling jacket 23B portion to the mezzanine floor surface 25 via an appropriate fixing member 24, so that the lower opening of the cooling jacket 23B is located below the lower surface of the mezzanine floor surface 25, This furnace core tube 21 is erected and fixed on the floor surface 25 of the mezzanine floor.

The furnace core tube 21 is erected on the floor surface 25 of the mezzanine floor by placing a water tank (not shown) for cooling and water sealing on the floor surface of the first floor and passing through the furnace core tube 21 to be carbonized. This is because it is necessary to cool the fibers through this water tank.

Further, a gas introduction pipe 26 is provided on the peripheral side surface near the fiber discharge port of the furnace core tube 21, and a gas discharge pipe 27 is provided on the peripheral side surface near the fiber introduction port from the gas introduction pipe 26 to the furnace core tube 21. An inert gas such as nitrogen gas is introduced into the inside of the gas discharge pipe 27
By discharging the nitrogen gas from the furnace, an updraft of nitrogen gas is generated in the furnace core tube 21.

In addition, the inside of the furnace core tube 21 is provided with a narrowed portion 33 at a position slightly lower than the mounting position of the gas discharge pipe 27 to such an extent that the traveling of the flameproof fiber is not impeded.
Even if air flows back into the 23A through its upper opening, the constricted part 3
Since the inert gas is blown up from 3, it is possible to prevent air from being mixed into the furnace core tube 21 and adversely affecting the flameproof fiber. In addition, it is desirable that the narrowed portion 33 can be widened in order to facilitate the passage of the flameproof fiber into the furnace core tube 21 first.

In this way, since it is possible to prevent oxygen from mixing into the furnace core tube 21 from the narrowed portion 33, the inert gas is discharged from the gas discharge tube 27 at a discharge rate such that air flows backward into the lid member 23A. May be discharged. However, if air is mixed into the lid member 23A, the inside of the lid member 23A may be cooled and a tar-like material may adhere, so in order to prevent this, the lid member 23A
A means for heating the inside is provided. This heating also raises the fiber temperature, so that tar vapor can be prevented from aggregating on the fiber surface.

Here, as the material forming the furnace core tube 21, in addition to the alumina, a ceramic material such as silicon nitride, silicon carbide, zirconia, or titanium carbide can be used. Preferred is the above-mentioned alumina.

The inert gas flowing inside the furnace core tube 21 is used in the carbonization furnace 4
It is preferable to effectively utilize the exhausted nitrogen gas. In this preheating furnace 2, since the temperature for heating the flame-resistant fiber 1 is low, if the passage time of the flame-resistant fiber is within about 5 minutes, it is not necessary to remove oxygen as strictly as required in the carbonization furnace 4. This is because the active gas does not have to be an active gas, and if nitrogen gas discharged from the carbonization furnace 4 is used, the nitrogen gas can be saved and the cost can be reduced.

In the cooling jacket 23B located below, the heat of the furnace core tube 21 heated by circulating water causes the heat generated in the furnace core tube 21 to rise to the floor surface 25 of the mezzanine floor.
It has been devised so that it does not conduct to other parts. Then, the nitrogen gas flowing inside the furnace core tube 21 is
Since it is discharged from the furnace core tube 21 from 27, the volatile products generated in the furnace core tube 21 are discharged to the outside of the furnace core tube 21 together with the nitrogen gas stream in a gas state. The lid member
Since 23A is formed in a tubular body having an upper opening and a lower opening, a part of the inert gas flowing through the inside of the furnace core tube 21 passes through the opening of the lid member 23A. Although it may be discharged above the furnace 21, most of the inert gas is discharged from the gas discharge pipe 27, so the volatility of the inert gas discharged above the furnace core tube 21 is high. Product is furnace core tube 21
It does not adhere to the upper guide roller (5A in FIG. 1) in a tar shape.

As shown in FIG. 3, the outer tubular body 23 has a U-shaped horizontal cross section, and has a first member 28 formed of a heat insulating material such as asbestos and a horizontal cross section symmetrical to the first member 28. It is a tubular body having a rectangular shape in horizontal cross section when the second member 29 formed of a heat insulating material such as asbestos is abutted on the abutting surface L. This external cylinder 23
The upper opening and the lower opening are closed by a lid 30 that is divided into two parts. The external cylinder has a vertically split structure and is not particularly limited as long as it can support the heater 22. The external cylinder may be divided into two, such as three. However, the split structure is easier to configure.

Further, the outer cylindrical body 23 includes the first member 28 and the second member 28.
A plurality of heating heaters 22 formed by forming silicon carbide into a round bar shape having a circular vertical cross section and CVD coating the surface of the round bar shaped body with silicon carbide are horizontally mounted between the facing surfaces of the members 29 of FIG. The heating heaters 22 that are handed over and horizontally laid are arranged in parallel in the vertical direction.
The heater 22 is configured to be able to generate heat by electrically connecting 22 and energizing. As a result of this configuration, when the furnace core tube 21 is surrounded by the outer tube body 23, the heater 22 is arranged in the outer tube body 23 so as to sandwich the furnace core tube 21 therein.

Further, the first member 28 and the second member 29 constituting the outer tubular body 23 are provided by a first frame 31 and a second frame 32 which are movable on the mezzanine floor surface 25 by a moving device (not shown) such as casters. , Each supported,
As shown in FIG. 4, when the first frame 31 and the second frame 32 are horizontally moved so as to be separated from each other, the furnace core tube 21 surrounded by the outer cylindrical body 23 is exposed.

In the preheating furnace 2 having the above structure, the furnace heater 21 is heated by energizing the heater 22 to, for example, a maximum temperature of 1000 ° C., and nitrogen gas is supplied from the gas introducing pipe 26 into the furnace furnace pipe 21. Then, by discharging nitrogen gas from the gas discharge pipe 27, a nitrogen rising air stream is revealed in the furnace core tube 21, so that the heat of the heated furnace core tube 21 is not conducted to the mezzanine floor surface 25 and others.
Allow cooling water to flow through the cooling jacket 23B.

Further, a water tank is arranged on the first-floor floor surface immediately below the furnace core tube 21, and the lower cooling jacket 23B is immersed in the cooling water in the water tank. The cooling jacket 23B is soaked in water in order to prevent air from entering the furnace core tube 21 through the opening below the cooling jacket 23B. Further, the cooling jacket 23B is cooled in order to prevent the steam rising from the cooling water in the water tank from being mixed into the furnace core tube 21.

The furnace core tube 21 thus heated to a high temperature in a nitrogen gas atmosphere
When the flame-resistant fiber is circulated from the upper side to the lower side and the flame-resistant fiber is heated, the molecules in the flame-resistant fiber undergo ammonia, carbon monoxide, and dioxide according to complicated reactions such as cyclization reaction and condensation reaction. Volatile products such as carbon, hydrocarbons and water are generated, and these volatile products are discharged from the gas discharge pipe 27 to the outside of the furnace core pipe 21 together with the nitrogen stream. Then, the heat-treated fibers that do not reach carbonization are guided into the water in the water tank from the lower opening of the cooling jacket 23B below the furnace core tube 21, and then to the carbonization furnace 4.

The carbonization furnace 4 may have any structure as long as it can heat the temperature in the furnace core tube 21 to a maximum of about 2000 ° C. in an inert atmosphere, but as a preferable example of the preheating furnace 2, It is preferable to employ the structure shown in FIGS. 2 and 3.

When the method of the present invention is carried out by using the preheating furnace 2 and the carbonization furnace 4 having the structures shown in FIGS. 2 and 3, the flameproof fiber 1 is run through the preheating furnace 2 and the flame resistant fiber 1 is run at the maximum of 400. ~ 1
When heated to 000 ° C, a complicated reaction such as a cyclization reaction proceeds in the flameproof fiber 1 to generate a volatile product, and when the flameproof fiber 1 is insufficiently flameproofed, flameproofing is completed. To do. The generated volatile product is discharged to the outside of the furnace core tube 21 in a gaseous state together with a flow of an inert gas such as nitrogen gas.
The heat-treated fibers 3 which have passed through the preheating furnace 2 are guided to the carbonization furnace 4 and heated to a maximum temperature of 2000 ° C. in the furnace core tube 21 of the carbonization furnace 4 to be completely carbonized.

In this carbonization furnace 4, since the volatile products that cause tar-like deposits have already been generated by the preheating furnace 2 in the fibers 3 that guide the inside of the furnace core tube 21, the maximum temperature is about 2000 ° C. Heating to no longer produces volatile products causing tar deposits, and therefore
Even if the inert gas is discharged further above the fiber introduction port of the furnace core tube 21, the volatile products do not adhere to the guide roller 5B above the furnace core tube 21 in the form of tar. Of course, tar-like substances derived from volatile products do not adhere to any part of the furnace core tube 21 or the lid member 23A of the carbonization furnace 4.

When the preheating furnace 2 and the carbonization furnace 4 having the structures shown in FIG. 2 and FIG. 3 are adopted in the method of the present invention, the heater 22 made of silicon carbide having excellent heat resistance and oxidation resistance is used. Therefore, it is not necessary to introduce nitrogen gas between the furnace core tube 21 and the outer cylindrical body 23. Therefore, it is sufficient to introduce the nitrogen gas only into the furnace core tube 21, so that the consumption amount of the nitrogen gas can be reduced as compared with the conventional device. Further, the exhaust gas of the inert gas used in the carbonization furnace 4 may be introduced into the preheating furnace 2 and used, and the amount of the inert gas used can be saved accordingly.

Since the life of the silicon carbide can be extended under the oxygen atmosphere rather than under the nitrogen atmosphere, the life of the preheating furnace 2 and the carbonization furnace 4 can be extended.

Since the preheating furnace 2 and the carbonization furnace 4 are basically the furnace core tube 21 and the outer cylindrical body 23 that surrounds the furnace core tube 21 and is formed of a heat insulating material, it has a simple structure and can be downsized. To be achieved.

In addition, the oxygen content in the nitrogen gas introduced into the furnace core tube 21
Even if it is adjusted to 1 ppm or less, the furnace core tube 21 may gradually deteriorate due to long-term operation, and it may eventually be necessary to replace it.

In such a case, as shown in FIG. 4, the first frame 31
When the second frame 32 and the second frame 32 are moved away from each other, the outer tubular body 23 has a split structure, so that the first member 28 and the second member 29 supported by these frames are supported.
By moving them away from each other
23 is halved, and the furnace core tube 21 is exposed. Therefore, the exposed furnace core tube 21 is replaced with a new furnace core tube 21. In this way, the replacement work of the furnace core tube 21 is simplified because there is no complicated work such as disassembling the exterior body and the heat insulating material as in the conventional case.

[Effects of the Invention] According to the method of the present invention, (1) the flame-resistant fiber is heated to a maximum of 400 to 1000 ° C. in a preheating furnace to accelerate the cyclization reaction of the flame-resistant fiber and adhere to the tar-like fiber. The volatile products are completely generated, and the fibers that have been heat-treated to such an extent that no volatile products are generated even if they are no longer heated are supplied to the carbonization furnace,
Since this fiber is heated to a maximum temperature of 2000 ° C to carry out the carbonization reaction, in the carbonization furnace, volatile products that become tar-like and adhere are no longer produced, and the furnace core tube and the upper lid of the furnace core tube are no longer produced. The volatile products adhering to the member are prevented from coming into contact with the running fibers to cause fluffing of the fibers and cutting accidents of the fibers, whereby carbonized fibers having high strength can be manufactured. Further, the volatile products generated in the preheating furnace and adhering in a tar shape are mostly discharged to the outside of the furnace core tube in a gaseous state together with the inert gas flow except the upper part of the furnace core tube. It does not adhere to the inner wall of the furnace core tube of the preheating furnace, etc., and in the preheating furnace, there is no adverse effect on the flame-resistant fiber of the tar-like substance due to volatile products.

(2) In a preheating furnace and a carbonization furnace, an external cylinder body surrounding a vertically long furnace core tube in which fibers continuously run has a vertically split structure, and the furnace cylinder tube is sandwiched between the outer cylinder body and the outer cylinder body. By adopting a structure in which the heaters facing and horizontally arranged and supported are made of silicon carbide, the maintenance work can be simplified and the carbonization furnace itself can be downsized, and the consumption can be reduced. It is possible to reduce the amount of inert gas used.

It is possible to provide a carbonization treatment method having excellent advantages such as.

[Examples] Next, the method of the present invention will be specifically described with reference to Examples and Comparative Examples.

Example 1 A preheating furnace and a carbonization furnace having the structures shown in FIGS. 2 and 3 were used. Preheating furnace and carbonization furnace have a diameter of 12
It is a furnace core tube made of alumina and having a length of 200 cm and a length of 200 cm. The heating temperature inside the furnace core tube in the preheating furnace is 500 ° C.
The heating temperature inside the alumina furnace core tube in the carbonization furnace is 1400 ° C. In the furnace core tube of the carbonization furnace, the oxygen gas content was adjusted to 1ppm or less, a nitrogen gas stream was circulated at 2m / sec, and the nitrogen gas discharged from the carbonization furnace was 2m in the furnace core tube of the preheating furnace. It was distributed at an air velocity of / sec.

The flame-resistant fiber was guided at a traveling speed of 0.01 m / sec into the furnace core tube of the preheating furnace, and the fiber exiting the preheating furnace was guided to the furnace core tube of the carbonization furnace to carbonize the flame resistant fiber. .

As a result, there is no fiber cutting accident while traveling 10,000 m,
Moreover, the obtained carbonized fiber has 1 fluff / m,
The strength of the carbonized fiber was 48 kg / mm ² (JIS R7601).

(Comparative Example 1) A carbonization furnace in which a gas exhaust pipe is not provided on the peripheral side surface, and a lid member having a structure in which the gas in the furnace core tube is blown upward as it is from the upper opening portion of the lid member is attached to the upper opening portion of the furnace core tube. The flame-resistant fiber was carbonized under substantially the same heating conditions as in the above example except that the preheating furnace was not used, and a fiber cutting accident occurred after traveling 460 m. Further, the obtained carbonized fiber had a lot of fuzz and its strength was as weak as 350 Kgmm ² .

[Brief description of drawings]

FIG. 1 is an explanatory view showing the method of the present invention, FIG. 2 is a vertical sectional view showing the preheating furnace, FIG. 3 is a partial horizontal sectional view showing the preheating furnace, and FIG. 4 is an external cylindrical body. FIG. 3 is a horizontal cross-sectional view showing a state in which the furnace core tube is exposed by dividing the tube into left and right parts. 1 ... Flame resistant fiber, 2 ... Preheating furnace, 3 ... Fiber after heat treatment, 4 ... Carbonization furnace, 21 ... Furnace core tube, 22 ... Heating heater, 23 ... External cylinder, 33 ... Stenosis

Claims (6)

[Claims] 1. A vertical preheating furnace having a fiber inlet on the upper side and a fiber outlet on the lower side, wherein a gas inlet is provided near the fiber outlet and a gas outlet is provided near the fiber inlet. A flameproof fiber obtained by flameproofing treatment in a preheating furnace having an outlet and having a constriction inside the furnace slightly below the gas discharge port,
By heating to a maximum temperature of 400 to 1000 ° C in the presence of an inert gas flowing from the gas inlet to the gas outlet, most of the inert gas containing a volatile product generated from the flame-resistant fiber. Is heat-treated so that the flame-retardant fiber is discharged from the gas outlet, and the fiber heat-treated in the preheating furnace is heated to a maximum temperature of 2000 ° C. in the carbonization furnace to carbonize the carbon. Processing method. 2. In the preheating furnace and the carbonization furnace, an outer cylinder surrounding a vertically long furnace core tube in which fibers continuously run has a vertically split structure, and the furnace core tube is attached to the outer cylinder. The carbonization treatment method according to claim 1, wherein the heaters which are opposed to each other and are arranged horizontally and supported horizontally are formed of silicon carbide. 3. The carbonization treatment method according to claim 2, wherein the outer cylinder is formed of a heat insulating material and has a vertically divided structure. 4. The carbonization treatment method according to claim 2, wherein the heater is formed by coating silicon carbide on the surface of a rod-shaped body made of silicon carbide by CVD. 5. The carbonization treatment method according to any one of claims 2 to 4, wherein the furnace core tube is made of ceramics. 6. The carbonization treatment method according to any one of claims 2 to 5, wherein the furnace core tube is formed of a ceramic containing alumina as a main component.