Method for manufacturing a flame-resistant fiber bundle, a carbon fiber bundle, and a flame-resistant furnace

Abstract

 The present invention addresses the problem of producing high-quality flame resistant fiber bundles and carbon fiber bundles with high efficiency. A method for producing flame resistant fiber bundles by thermally treating aligned acrylic fiber bundles in an oxidizing atmosphere while having the bundles turned around by guide rollers provided at both ends outside the body of a hot-air heating type flame resistant furnace, wherein hot air is supplied, from supply surfaces provided above and / or below the acrylic fiber bundles, in a fiber bundle passage flow path above and / or below a supply nozzle that is for supplying hot air into a thermal treatment chamber and that is provided at one end in a direction in which the acrylic fiber bundles are conveyed, and an air velocity Vf in a direction generally parallel to the direction in which the acrylic fiber bundles are conveyed in the fiber bundle passage flow path, and an air velocity V in a direction generally parallel to the direction in which the acrylic fiber bundles are conveyed in the thermal treatment chamber, satisfy conditions (1) and (2). (1): 1.5 m / s ≤ Vf ≤ 15 m / s, (2): 1.5 m / s ≤ V ≤ 10 m / s

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a flame-resistant fiber bundle and a carbon fiber bundle. More specifically, the present invention relates to a method for manufacturing a flame-resistant fiber bundle and a carbon fiber bundle, and a flame-resistant furnace, which can efficiently produce a high-quality flame-resistant fiber bundle.

Background Art

[0002] Since carbon fibers are excellent in specific strength, specific modulus, heat resistance, and chemical resistance, they are useful as reinforcing materials for various materials and are used in a wide range of fields such as aerospace applications, leisure applications, and general industrial applications.

[0003] Generally, as a method for manufacturing a carbon fiber bundle from an acrylic fiber bundle, an acrylic fiber bundle in which thousands to tens of thousands of single fibers of an acrylic polymer are aligned is fed into a flame-resistant furnace, and is exposed to hot air of an oxidizing gas such as air heated to 200 to 300°C supplied from a heated gas supply nozzle (hereinafter simply referred to as a supply nozzle) installed in the furnace body for heat treatment (flame-resistant treatment). After that, the obtained flame-resistant fiber bundle is fed into a carbonization furnace and heat-treated (pre-carbonization treatment) in an inert gas atmosphere of 300 to 1,000°C, and then further heat-treated (carbonization treatment) in a carbonization furnace filled with an inert gas atmosphere of 1,000°C or higher. In addition, the flame-resistant fiber bundle, which is an intermediate material, is also widely used as a material for flame-retardant woven fabrics by taking advantage of its flame-retardant properties.

[0004] The flame-resistant process has the longest processing time and consumes the most energy during the carbon fiber bundle manufacturing process. Therefore, improving productivity in the flame-resistant process is the most important in the manufacture of carbon fiber bundles.

[0005] In the flame resistance process, in order to enable long-time heat treatment, the apparatus for performing flame resistance (hereinafter referred to as the flame resistance furnace) generally has a structure in which the acrylic fiber is reciprocated horizontally inside the furnace body of the flame resistance furnace multiple times by being rotated by a folding roller disposed outside the furnace body of the flame resistance furnace. In the furnace body of such a flame resistance furnace, a method of supplying hot air in a direction substantially parallel to the traveling direction of the acrylic fiber bundle is called a parallel flow method, and a method of supplying hot air in a direction orthogonal to the traveling direction of the acrylic fiber bundle is generally called an orthogonal flow method. The parallel flow method includes an End To End (hereinafter referred to as ETE) hot air method in which supply nozzles are installed at the ends of the parallel flow furnace and discharge nozzles for the gas inside the furnace body (hereinafter simply referred to as discharge nozzles) are installed at the opposite ends, and a Center To End (hereinafter referred to as CTE) hot air method in which supply nozzles are installed at the center of the parallel flow furnace and discharge nozzles are installed at both ends thereof. Generally, the ETE hot air method has a lower equipment cost than the CTE hot air method.

[0006] Among the methods for improving productivity in the flame resistance process, it is effective to increase the density of the acrylic fiber bundle inside the furnace body of the flame resistance furnace by simultaneously transporting a large number of acrylic fiber bundles. Also, it is effective to increase the traveling speed of the acrylic fiber bundle. However, since the mass per unit volume of the acrylic fiber bundle supplied into the furnace body increases, the amount of heat per unit volume required for heating / heat removal of the acrylic fiber bundle also increases, making temperature control difficult and causing a decrease in the quality of the flame-resistant fiber.

[0007] In addition, when increasing the running speed of the acrylic fiber bundle, in order to obtain the same amount of heat treatment, it is necessary to increase the size of the flame-retardant furnace. Especially when increasing the size in the height direction, it is necessary to divide the building floors into multiple levels or increase the load-bearing capacity per unit floor area, which leads to an increase in equipment costs. Therefore, in order to increase the size of the flame-retardant furnace while suppressing the increase in equipment costs, it is effective to reduce the size in the height direction by increasing the distance per horizontal pass (hereinafter referred to as the flame-retardant furnace length). However, when the flame-retardant furnace length is increased, the heat treatment length becomes longer accordingly, making it difficult to control the temperature of the acrylic fiber bundle. This is particularly more prominent in the case of the ETE hot air method.

[0008] Therefore, when improving productivity in the flame-retardant process of the ETE hot air method, there is a problem that it is necessary to improve the efficiency of the heating performance and heat removal performance of the acrylic fiber bundle running in the furnace body of the flame-retardant furnace.

[0009] In order to solve this problem, Patent Document 1 describes a method of providing the discharge surface of the discharge nozzle separated from the heat treatment chamber and sucking the hot air in the heat treatment chamber to form a flow in the gap between the discharge nozzles, making it easier to heat and remove heat from the acrylic fiber bundle.

[0010] In addition, Patent Document 2 describes a heat treatment method in the CTE hot air method of supplying hot air to the space sandwiched between the supply nozzles arranged in the center of the furnace body to make the temperature of the space between the supply nozzles equal to the temperature of the space inside the furnace body.

[0011] Furthermore, Patent Document 3 describes a method of providing a heating means having a supply surface for blowing out hot air to heat the acrylic fiber bundle in the flow path gap where the acrylic fiber bundle outside the furnace body of the flame-retardant furnace enters the furnace body, although it is a means for improving the sealing performance of the flame-retardant furnace.

Prior Art Documents

Patent Documents

[0012]

Patent Document 1

[0013] However, according to the findings of the present inventors, simply controlling the flow formed in the gap between the exhaust nozzles in Patent Document 1 cannot change the airflow pattern inside the flame-resistant furnace, and there may be cases where the heating and heat removal effects of the acrylic fiber bundle cannot be sufficiently obtained. This is because the airflow pattern (hot air velocity, wind direction) near the acrylic fiber bundle in the flame-resistant furnace is dominant in heat transfer to the acrylic fiber bundle. Therefore, it is considered that simply controlling the airflow at the above-mentioned exhaust nozzles only results in the manifestation of effects between the exhaust nozzles, and sufficient effects may not be obtained.

[0014] Further, in Patent Document 2, by supplying hot air between the supply nozzles, airflow turbulence occurs when the hot air crosses the acrylic fiber bundle. As a result, the yarn sway of the acrylic fiber bundle becomes large even at a low wind speed. Consequently, contact between adjacent acrylic fiber bundles, mixed spinning of acrylic fiber bundles, yarn breakage, etc. may occur. Also, Patent Document 2 only focuses on the temperature uniformity of the airflow between the supply nozzles and the space inside the furnace, and does not disclose controlling the temperature of the acrylic fiber bundle inside the furnace. There are parameters required for controlling the temperature of the acrylic fiber bundle inside the furnace, namely the temperature and velocity of the hot air. Although there is a description regarding the former temperature, there is no detailed description regarding the velocity of the hot air, and there may be cases where the temperature of the acrylic fiber bundle cannot be controlled. Moreover, it is limited to the parallel flow type CTE hot air method, and specific details of the ETE hot air method with lower equipment costs are not described.

[0015] Furthermore, in Patent Document 3, since the hot air supply surface is provided outside the furnace body of the flame-proofing furnace, it may be insufficient to improve the heating and heat removal properties of the acrylic fiber bundle running inside the furnace body of the flame-proofing furnace. Also, since the purpose of Patent Document 3 is to improve the sealing performance of the flame-proofing furnace, the hot air supply direction is outside the furnace body, and the hot air supplied from the supply surface is directly blown out of the furnace body, so an air flow may not be formed between the nozzles through which the acrylic fiber bundle passes.

Means for Solving the Problems

[0016] The method for manufacturing a flame-proofed fiber bundle of the present invention for solving the above problems has the following configuration. That is, it is a method for manufacturing a flame-proofed fiber bundle in which an aligned acrylic fiber bundle is heat-treated in an oxidizing atmosphere while being folded back by guide rollers installed at both ends outside the furnace body of a hot air heating type flame-proofing furnace, and hot air is supplied from a supply surface provided above and / or below the acrylic fiber bundle in the fiber bundle passage flow path above and / or below a supply nozzle for supplying hot air into the heat treatment chamber at one end in the traveling direction of the acrylic fiber bundle, and the wind speed Vf in the direction substantially parallel to the traveling direction of the acrylic fiber bundle in the fiber bundle passage flow path and the wind speed V in the heat treatment chamber in the direction substantially parallel to the traveling direction of the acrylic fiber bundle satisfy conditions (1) and (2). (1) 1.5 m / s ≤ Vf ≤ 15 m / s (2) 1.5 m / s ≤ V ≤ 10 m / s.

[0017] Also, in the method for manufacturing a flame-proofed fiber bundle of the present invention described above, it is desirable to have the following configuration.

[0018] · The wind speed Vf in the direction substantially parallel to the traveling direction of the acrylic fiber bundle in the fiber bundle passage flow path and the wind speed V in the heat treatment chamber in the direction substantially parallel to the traveling direction of the acrylic fiber bundle satisfy conditions (3) and (4). (3) 1.5 m / s ≤ Vf ≤ 10 m / s (4) 1.5 m / s ≤ V ≤ 6 m / s ·On the supply side, the wind speed Vn in the direction orthogonal to the traveling direction of the acrylic fiber bundle satisfies condition (5).

[0019] (5) 0.1 m / s ≤ Vn ≤ 5 m / s ·The temperature of the hot air supplied from the supply surface is 210°C or higher and 295°C or lower.

[0020] ·The single fiber fineness of the acrylic fiber bundle before heat treatment is 0.05 to 0.22 tex.

[0021] Furthermore, the method for producing a carbon fiber bundle of the present invention has the following configuration. That is, The flame-resistant fiber bundle obtained by the above method for producing a flame-resistant fiber bundle is pre-carbonized at a maximum temperature of 300 to 1,000°C in an inert atmosphere to obtain a pre-carbonized fiber bundle, and then the pre-carbonized fiber bundle is carbonized at a maximum temperature of 1,000 to 2,000°C in an inert atmosphere. It is a method for producing a carbon fiber bundle.

[0022] Here, the "substantially parallel direction with respect to the traveling direction of the acrylic fiber bundle" of the present invention is a direction within a range of ±0.7° based on the horizontal line between the vertices of a pair of opposing folding rollers arranged at both ends outside the furnace body.

[0023] Here, the "fiber bundle passage flow path" of the present invention is the space around the acrylic fiber bundle formed along the traveling direction of the acrylic fiber bundle, which refers to the space between adjacent supply nozzles in the vertical direction, or the space between the supply nozzle and the upper surface of the furnace body, or the space between the supply nozzle and the bottom surface of the furnace body.

[0024] Furthermore, the flame-resistant furnace of the present invention has the following configuration. That is, A flame-resistant furnace for heat-treating an acrylic fiber bundle, (i) A furnace body having a slit through which the aligned fiber bundle can enter and exit, (ii) At one end in the traveling direction of the fiber bundle in the heat treatment chamber, a plurality of supply nozzles that are arranged at intervals in the vertical direction and supply hot air into the furnace body, (iii) At the other end of the fiber bundle in the furnace body in the running direction, a plurality of discharge nozzles that are arranged at intervals in the vertical direction and discharge the hot air supplied from the supply nozzle from the heat treatment chamber, and (iv) at least one blower device that circulates the hot air through the supply nozzle and the discharge nozzle, (v) At least one heating device arranged on the flow path of the circulating hot air, (vi) Guide rollers that are arranged at both ends outside the furnace body and cause the fiber bundle to travel back and forth a plurality of times in the heat treatment chamber through between adjacent supply nozzles and between adjacent discharge nozzles, A flame-proofing furnace having, (vii) The supply nozzle has a supply surface for supplying first hot air to the fiber bundle passage flow path above and / or below the supply nozzle and an auxiliary supply surface for supplying second hot air to the side surface inside the heat treatment chamber of the supply nozzle, (viii) A flame-proofing furnace characterized by comprising adjustment means for adjusting the wind speed of the first hot air and the wind speed of the second hot air supplied from the supply nozzle.

Advantages of the Invention

[0025] According to the method for manufacturing a flame-proofed fiber bundle of the present invention, by improving the heating performance and heat removal performance of the acrylic fiber bundle passing through the furnace body of the flame-proofing furnace, high-quality flame-proofed fiber bundles and carbon fiber bundles can be efficiently produced.

Brief Description of the Drawings

[0026]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0027] Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS. 1 to 4. FIG. 1 is a schematic cross-sectional view of a flameproof furnace used in an embodiment of the present invention, and FIG. 2 is a partially enlarged cross-sectional view from around the supply nozzle to around the discharge nozzle therein. Further, FIG. 4 is a partially enlarged cross-sectional view from around the supply nozzle to around the discharge nozzle of a flameproof furnace used in another embodiment of the present invention. Further, FIG. 3 is a schematic diagram showing the airflow pattern from around the supply nozzle to around the discharge nozzle used in the embodiment of the present invention. Note that these drawings are conceptual diagrams for accurately conveying the gist of the present invention, the drawings are simplified, and the flameproof furnace used in the present invention is not particularly limited, and its dimensions and the like can be changed according to the embodiments.

[0028] The present invention relates to a method for producing a flame-retardant fiber bundle by heat-treating an acrylic fiber bundle 2 in an oxidizing atmosphere, which is carried out in a flame-retardant furnace through which an oxidizing gas flows inside. As shown in FIG. 1, the flame-retardant furnace 1 has a heat treatment chamber 3 that blows hot air onto the acrylic fiber bundle 2 that repeatedly travels through multiple running areas in the furnace body 18 by being folded back by guide rollers 4 provided outside the furnace body 18 to perform a flame-retardant treatment. The acrylic fiber bundle 2 is fed into the furnace body 18 through a slit 17 provided in the side wall of the furnace body 18, travels substantially linearly in the heat treatment chamber 3, and is then once sent out of the furnace body 18 through the slit 17 in the facing side wall. Thereafter, it is folded back by guide rollers 4 provided on both sides outside the furnace body 18 and fed into the furnace body 18 again. In this way, the acrylic fiber bundle 2 has its traveling direction folded back multiple times by a plurality of guide rollers 4, repeatedly performing feeding and discharging into the heat treatment chamber 3 multiple times, traveling in multiple stages in the heat treatment chamber 3, and moving downward as a whole from top to bottom in FIG. 1. Note that the moving direction may also be from bottom to top, and the number of times the acrylic fiber bundle 2 is folded back in the heat treatment chamber 3 is not particularly limited and is appropriately designed according to the scale of the flame-retardant furnace 1 and the like. In FIG. 1, the guide rollers 4 are provided outside the furnace body 18, but the guide rollers 4 may also be provided inside the furnace body 18.

[0029] While the acrylic fiber bundle 2 travels in the heat treatment chamber 3 while being folded back, it is heated by hot air flowing from the supply nozzle 5 toward the discharge surface 7 of the discharge nozzle 14, so that the flame-retardant treatment progresses and it becomes a flame-retardant fiber bundle. This flame-retardant furnace 1 is a flame-retardant furnace of the parallel flow type ETE hot air method as described above. Note that the acrylic fiber bundle 2 has a wide sheet-like form in which a plurality of strands are aligned in parallel in a direction perpendicular to the paper surface.

[0030] The oxidizing gas flowing through the heat treatment chamber 3 may be air or the like, and is heated to a desired temperature by a heater 8 before entering the heat treatment chamber 3, and the air volume is controlled by a blower 9, and then blown into the heat treatment chamber 3 from the supply surface 6 and / or the auxiliary supply surface 12 of the supply nozzle 5. Here, the supply surface 6 of the supply nozzle 5 is a supply surface provided to face the supply nozzle 5 adjacent to the upper and lower surfaces of the supply nozzle 5. Here, the auxiliary supply surface 12 of the supply nozzle 5 is a supply surface provided on the side surface facing the discharge nozzle 14 of the supply nozzle 5. Then, the oxidizing gas discharged from the discharge surface 7 of the discharge nozzle 14 to the outside of the heat treatment chamber 3 is discharged into the atmosphere after treating unnecessary substances in an exhaust gas treatment furnace (not shown), but it is not necessarily required that all the oxidizing gas be treated, and a part of the oxidizing gas may be blown into the heat treatment chamber 3 from the supply nozzle 5 again through the circulation path without being treated. Hereinafter, the supply surface 6 of the supply nozzle 5 will be simply abbreviated as the supply surface 6, the auxiliary supply surface 12 of the supply nozzle 5 will be simply abbreviated as the auxiliary supply surface 12, and the discharge surface 7 of the discharge nozzle 14 will be simply abbreviated as the discharge surface 7, respectively.

[0031] The heater 8 used in the flame-proofing furnace 1 is not particularly limited as long as it has a desired heating function, and for example, a known heater such as an electric heater may be used. Regarding the blower 9, it is not particularly limited as long as it has a desired blowing function, and for example, a known blower such as an axial flow fan may be used.

[0032] Further, the guide rollers 4 can control the running speed and tension of the acrylic fiber bundle 2 by changing their respective rotational speeds, which can be determined according to the physical properties of the required flame-proofed fiber bundle and the throughput per unit time.

[0033] Furthermore, by engraving grooves at a predetermined interval and number on the surface layer of the guide roller 4, or arranging a plurality of comb guides (not shown) at a predetermined interval and number in the immediate vicinity of the guide roller 4, the interval and the number of bundles of the acrylic fiber bundles 2 running in parallel can be controlled.

[0034] Conventionally, in order to improve productivity, it has been known that the running speed of the acrylic fiber bundle 2 can be increased, or the number of acrylic fiber bundles per unit distance in the width direction of the flame-resistant furnace 1, that is, the yarn density can be increased. However, when such conditions for improving productivity are applied, the supply amount of the acrylic fiber bundle 2 brought into the furnace body 18 increases with respect to the supply amount of hot air into the furnace body 18 per unit time. As a result, the amount of heat of the hot air that can be used to heat or remove heat from the acrylic fiber bundle 2 relatively decreases. As a result, the temperature controllability of the acrylic fiber bundle 2 deteriorates, and quality deterioration is likely to occur. Therefore, it is conceivable to increase the amount of heat used for heating or removing heat from the acrylic fiber bundle 2 by providing another heating or heat-removing means or increasing the supply amount of hot air. However, there has been a problem that it leads to a significant cost increase such as an increase in equipment cost and an increase in utility cost.

[0035] To address such problems, it is effective to improve the heat transfer efficiency between the acrylic fiber bundle 2 and the hot air. As means, increasing the wind speed of the hot air or approaching a method of making the angle formed by the running direction of the acrylic fiber bundle 2 and the wind direction of the hot air orthogonal can be mentioned. Also, separating the fibers constituting the acrylic fiber bundle 2 to increase the surface area to improve the heat transfer efficiency is also mentioned as a means. However, when the fibers are separated, the adjacent running acrylic fiber bundles 2 are likely to become entangled. Also, as described above, increasing the wind speed of the hot air increases the utility cost and causes an increase in running cost. Also, when changing the wind direction of the hot air to be orthogonal to the acrylic fiber bundle 2, the sway of the acrylic fiber bundle 2 increases, and the adjacent running acrylic fiber bundles 2 are likely to become entangled. Also, when the length of the flame-resistant furnace is increased to enlarge the ETE heat type flame-resistant furnace with low equipment cost, excessive heat generation of the acrylic fiber bundle 2 occurs in the latter half of one pass, making it impossible to control the temperature of the acrylic fiber bundle 2. There were various demerits in improving productivity.

[0036] The method for manufacturing a flame-retardant fiber bundle according to the present invention has been intensively studied to solve the above problems and efficiently produce high-quality flame-retardant fiber bundles. That is, the present inventors have found that while suppressing an increase in equipment costs and running costs and suppressing entanglement between acrylic fiber bundles 2, the heat transfer efficiency between the acrylic fiber bundle 2 and hot air can be improved. Hereinafter, the principle that can improve the heat transfer efficiency between the acrylic fiber bundle 2 traveling in the heat treatment chamber 3 and hot air, which is the most important point of the present invention, will be described in detail.

[0037] First, in order to clarify the difference between the prior art and the present invention, the airflow pattern in the furnace body 18 configured by the prior art will be described with reference to FIG. 5. Note that the length of the arrow of the airflow in FIG. 5 represents the magnitude of the wind speed.

[0038] In FIG. 5, the hot air supplied from the first supply surface 19 of the supply nozzle 5 installed at one end in the furnace body 18 passes through the fiber bundle passage 10 between the supply nozzles 5, and when it reaches the confluence surface 13 where the fiber bundle passage 10 and the heat treatment chamber 3 are in contact, it merges with the hot air supplied from the second supply surface 20 and flows through the heat treatment chamber 3 while gradually relaxing the speed difference between the two. In the prior art, the speed of the airflow in the fiber bundle direction in the fiber bundle passage 10 derived from the hot air supplied from the first supply surface 19 was lower than the speed of the airflow derived from the hot air supplied from the second supply surface 20. For this reason, the wind speed in the vicinity of the acrylic fiber bundle 2 immediately after passing through the confluence surface 13 is maintained in the heat treatment chamber 3 at the wind speed of the airflow flowing in from the fiber bundle passage 10, but is accelerated by the gradual confluence of the airflow derived from the hot air supplied from the second supply surface 20. Then, the confluent airflow reaches the discharge nozzle 14 installed at the other end in the furnace body 18, and most of it is discharged from the discharge surface 7, and a part of it flows out of the furnace body 18 through the space between the discharge nozzles 14.

[0039] Here, in order to improve productivity, when the yarn density of the acrylic fiber bundle 2 is increased (or when the running speed of the acrylic fiber bundle 2 is set to a high condition), the temperature of the acrylic fiber bundle 2 will be described. The acrylic fiber bundle 2 that exits the furnace body 18 is once cooled by the outside air and then enters the fiber bundle passage 10 again and is reheated. However, when the yarn density of the acrylic fiber bundle 2 is increased, the amount of heat required for heat transfer increases, and the acrylic fiber bundle 2 becomes difficult to be heated / heat-removed and cannot be sufficiently heated in the heat treatment chamber 3. In particular, when the wind speed Vf in the fiber bundle passage 10 is small, the acrylic fiber bundle 2 with insufficient temperature rise enters the heat treatment chamber 3 as it is, so the temperature of the heat treatment chamber 3 decreases, and it becomes increasingly difficult to raise the temperature of the acrylic fiber bundle 2. As described above, since the flow velocity of the air current in the vicinity of the acrylic fiber bundle 2 has the greatest influence on heat transfer, the acrylic fiber bundle 2 on the supply nozzle 5 side of the heat treatment chamber 3 is greatly affected by the flow velocity Vf of the hot air passing through the fiber bundle passage 10.

[0040] On the other hand, in the air current form of the embodiment of the present invention, as shown in FIG. 3, hot air is supplied from the supply surface 6 of the supply nozzle 5 provided above and / or below the acrylic fiber bundle 2, and the wind speed Vf in the fiber bundle passage 10 in a direction substantially parallel to the running direction of the acrylic fiber bundle 2 and the wind speed V in the heat treatment chamber 3 in a direction substantially parallel to the running direction of the acrylic fiber bundle 2 are set so as to satisfy the conditions (1) and (2). (1) 1.5 m / s ≤ Vf ≤ 15 m / s (2) 1.5 m / s ≤ V ≤ 10 m / s.

[0041] Here, the wind speed Vf in the fiber bundle passage flow path 10 in a direction substantially parallel to the traveling direction of the acrylic fiber bundle 2 is the average value of the measured values at three points in the width direction including the center in the width direction of the furnace body 3 on the line where the confluence surface 13 and the acrylic fiber bundle 2 intersect. The wind speed V in the heat treatment chamber 3 in a direction substantially parallel to the traveling direction of the acrylic fiber bundle 2 is the average value of the measured values at three points in the width direction including the center in the width direction of the furnace body 3 on the line where the cross section at the center in the traveling direction of the acrylic fiber bundle 2 in the heat treatment chamber 3 and the acrylic fiber bundle 2 intersect. Here, the measured values at each of the three points in the width direction including the center in the width direction of the furnace body 3 are the average values of 30 measured values per second using a thermal anemometer. In the above, the line where the confluence surface 13 and the acrylic fiber bundle 2 intersect means the line where the confluence surface 13 and a virtual surface including a plurality of acrylic fiber bundles 2 traveling in parallel in the machine width direction intersect. The line where the cross section at the center in the traveling direction of the acrylic fiber bundle 2 in the heat treatment chamber 3 and the acrylic fiber bundle 2 intersect means the line where the cross section at the center in the traveling direction of the acrylic fiber bundle 2 in the heat treatment chamber 3 and a virtual surface including a plurality of acrylic fiber bundles 2 traveling in parallel in the machine width direction intersect. Therefore, although the measurement points are included in the virtual surface including a plurality of acrylic fiber bundles 2 traveling in parallel in the machine width direction, since Vf and V are respectively indicators representing the wind speeds in the vicinity of the acrylic fiber bundle 2 in the fiber bundle passage flow path 10 and the heat treatment chamber 3, in FIG. 3 (similarly in FIG. 5), the arrows indicating Vf and V are shown in the vicinity rather than overlapping the acrylic fiber bundle 2.

[0042] When these conditions are met, from the supply surface 6 in contact with the fiber bundle passage channel 10, hot air with a high velocity collides with the acrylic fiber bundle 2, greatly promoting the heat transfer between the acrylic fiber bundle 2 and the hot air. Then, this hot air changes its direction parallel to the traveling direction of the acrylic fiber bundle 2 and flows near the acrylic fiber bundle 2 in the fiber bundle passage channel 10, further promoting heat transfer and causing the acrylic fiber bundle 2 to rapidly increase in temperature. Furthermore, in the heat treatment chamber 3 as well, while maintaining the velocity for the time being, since the hot air flows near the acrylic fiber bundle 2, the heat transfer between the acrylic fiber bundle 2 and the hot air is promoted, and the temperature of the acrylic fiber bundle 2 can be precisely controlled. Therefore, even when the wind speed V passing through the heat treatment chamber 3 is reduced, the temperature of the acrylic fiber bundle 2 can be controlled, making it possible to reduce the volume of the hot air circulated in the flame-retardant furnace 1 itself. Also, by locally supplying the hot air colliding with the acrylic fiber bundle 2 only near the supply nozzle 5 close to the guide roller 4, that is, at a position where the suspension amount of the acrylic fiber bundle 2 is relatively small, heat transfer can be improved without significantly increasing the sway of the acrylic fiber bundle 2.

[0043] Also, when the hot air passing through the fiber bundle passage channel 10 reaches the heat treatment chamber 3, it flows while expanding in the vertical direction. At this time, by supplying some hot air from the auxiliary supply surface 12 as well, the turbulence of the air flow caused by the expansion of the hot air can be suppressed, and ultimately, the mixed fiber formation due to the sway of the acrylic fiber bundle 2 can be suppressed.

[0044] Here, as a method for adjusting the wind speed of the hot air supplied from the supply surface 6 and the auxiliary supply surface 12, adjustment means such as installing a control valve such as a damper in the circulation channel leading to each supply surface, or arranging rectifying members such as perforated plates or honeycombs with different opening ratios on each supply surface may be appropriately provided.

[0045] Thus, in the flame retardant method of the present invention, in the fiber bundle passage 10 which was not considered at all in the prior art, hot air with a high velocity is supplied in a direction orthogonal to the acrylic fiber bundle 2, and in the fiber bundle passage 10, the wind speed Vf in a direction substantially parallel to the traveling direction of the acrylic fiber bundle 2 and the wind speed V in the heat treatment chamber in a direction substantially parallel to the traveling direction of the acrylic fiber bundle 2 satisfy the above conditions (1) and (2), which is extremely important. More preferably, the wind speed Vf in a direction substantially parallel to the traveling direction of the acrylic fiber bundle 2 in the fiber bundle passage 10 and the wind speed V in the heat treatment chamber 3 in a direction substantially parallel to the traveling direction of the acrylic fiber bundle 2 satisfy the conditions (3) and (4), thereby maximizing the effects of the present invention. (3) 1.5m / s ≦ Vf ≦ 10m / s (4) 1.5m / s ≦ V ≦ 6m / s.

[0046] As a case where the conditions (1) and (2) are not satisfied, when the wind speed Vf is less than 1.5 m / s, the acrylic fiber bundle 2 may not be sufficiently heated / degassed. Also, when the wind speed Vf is greater than 15 m / s, the resistance received by the acrylic fiber bundle 2 from the hot air may increase and the yarn vibration may increase.

[0047] Also, when the wind speed V is less than 1.5 m / s, the acrylic fiber bundle 2 may not be sufficiently heated / degassed in the heat treatment chamber 3. Also, when the wind speed V is greater than 10 m / s, the resistance received by the acrylic fiber bundle 2 from the hot air may increase and the yarn vibration may increase. Further, when the wind speed V is greater than 10 m / s, the circulation amount of the hot air in the flame retardant furnace may become excessive and the utility cost may increase.

[0048] Furthermore, with respect to the wind speed Vn in the direction orthogonal to the traveling direction of the acrylic fiber bundle 2 on the supply surface 6, it is more preferable to satisfy condition (5). Thereby, while suppressing the yarn vibration due to the resistance force received by the acrylic fiber bundle 2 from the hot air at a high level, the heat removal and heating of the acrylic fiber bundle 2 can be significantly improved. Here, when the wind speed Vn is less than 0.1 m / s, sufficient heat transfer of the acrylic fiber bundle 2 cannot be obtained, and the temperature may not be increased. When the wind speed Vn exceeds 5 m / s, the yarn vibration may increase. Further, preferably, by setting the wind speed Vn to 3.5 m / s or less, the effects of the present invention can be maximized.

[0049] (5) 0.1 m / s ≤ Vn ≤ 5 m / s. Here, the wind speed Vn in the direction orthogonal to the acrylic fiber bundle 2 on the supply surface 6 is the average value of the measured values at three points in the width direction including the center in the width direction of the furnace body 3 with respect to the direction orthogonal to the fiber bundle traveling direction on the supply surface 6. In the above, the measured values at each of the three points in the width direction including the center in the width direction of the furnace body 3 are the average values of 30 measured values per second.

[0050] Also, with respect to the temperature of the hot air supplied from the supply surface 6, by setting it to 210°C or higher and 295°C or lower, the effect of improving the heat transfer performance becomes more remarkable. In this case, the temperatures of the hot air supplied from the supply surface 6 and the auxiliary supply surface 12 may be different, but from the viewpoints of the temperature controllability of the acrylic fiber bundle 2 and the equipment cost, it is preferable that they are the same.

[0051] Next, another embodiment of the present invention will be described with reference to FIG. 4. The installation position of the supply surface 6 of the supply nozzle 5 is not limited to both sides of the supply nozzle 5, and it may be only the lower surface (not shown) or may be installed only on the upper surface (not shown). By arranging the supply surface 6 only on the upper surface, the acrylic fiber bundle 2 can be suppressed in the gravitational direction, so that an effect of reducing yarn vibration can be expected. Further, by arranging the supply surface 6 on both sides, when the wind speed Vf passing through the fiber bundle passage 10 is constant, the supply wind speed can be halved, so that the turbulence of the air flow around the acrylic fiber bundle 2 can be reduced, and thus the yarn vibration can be further reduced, which is preferable.

[0052] Also, the installation position of the supply surface 6 of the supply nozzle 5 is not limited to the outside of the furnace body (FIG. 2), and it may be closer to the inside of the furnace body, may be arranged separately at a plurality of locations, or may be installed on the entire surface (FIG. 4).

[0053] Furthermore, the auxiliary supply surface 12 of the supply nozzle 5 may not be provided, and hot air may be supplied only from the supply surface 6. In this case, since there is no auxiliary supply surface 12, in order to avoid air flow turbulence caused by the sudden widening of the flow path in the heat treatment chamber 3 from the fiber bundle passage 10, the rectifying plate 16 may be provided to divide the heat treatment chamber 3 only around the traveling position of the acrylic fiber bundle 2 and minimize it (FIG. 4).

[0054] Also, by changing the angle formed by the main flow direction of the hot air supplied from the supply surface 6 and the traveling direction of the acrylic fiber bundle, various effects can be achieved. For example, by making it other than orthogonal, the turbulence of the hot air due to the collision between the acrylic fiber bundle and the supply nozzle 5 can be suppressed. Further, by inclining the main flow direction of the hot air toward the heat treatment chamber 3, a part of the hot air is likely to enter the heat treatment chamber 3, and leakage to the outside of the flameproof furnace 1 can be suppressed. Also, by making the main flow direction of the hot air orthogonal to the traveling direction of the acrylic fiber bundle, the heat transfer efficiency of the acrylic fiber bundle 2 can be improved. Thus, the main flow direction of the hot air may be determined according to the performance required for the acrylic fiber bundle 2 and the flameproof furnace.

[0055] Furthermore, it is preferable that the air volume of the hot air sucked from the discharge surface 7 is larger than the total air volume of the hot air supplied from the supply surface 6 and the auxiliary supply surface 12 of the supply nozzle 5. Thereby, the hot air supplied from the supply surface 6 can easily flow into the heat treatment chamber 3, leakage of the hot air from the heat treatment chamber 3 can be suppressed, and the sealing property can be improved.

[0056] In addition, for the acrylic fiber bundle 2, it is preferable that the throughput per meter of the machine width of the flameproofing furnace is 0.14 to 11 kg / min. The greater this throughput, the more remarkable the effect of improving heat transfer becomes.

[0057] Furthermore, in the method for producing a flameproofed fiber bundle of the present invention, the single fiber fineness of the acrylic fiber bundle 2 is preferably 0.05 to 0.22 tex, more preferably 0.05 to 0.17 tex. By setting it within this preferable range, when adjacent acrylic fiber bundles 2 come into contact, the single fibers are less likely to become entangled, effectively preventing fiber blending between the acrylic fiber bundles. On the other hand, heat can be sufficiently distributed to the inner layer of the single fiber within the furnace body of the flameproofing furnace, making it difficult for the acrylic fiber bundle 2 to have fluffing, and effectively preventing significant fiber blending. Therefore, the quality and operability of the flameproofed fiber bundle become more excellent. Thus, as the single fiber fineness increases, the effect of the present invention with high heat transfer efficiency is manifested, and it becomes possible to sufficiently distribute heat to the inner layer of the single fiber.

[0058] The flameproofed fiber bundle produced by the above method is preferably pre-carbonized at a maximum temperature of 300 to 1,000 °C in an inert atmosphere to produce a pre-carbonized fiber bundle, and carbonized at a maximum temperature of 1,000 to 2,000 °C in an inert atmosphere to produce a carbon fiber bundle.

[0059] The maximum temperature of the inert atmosphere in the pre-carbonization treatment is more preferably 550 to 800 °C. As the inert atmosphere filling the inside of the pre-carbonization furnace, known inert atmospheres such as nitrogen, argon, and helium can be adopted, but nitrogen is preferable from the perspective of economy.

[0060] The pre-carbonized fibers obtained by the pre-carbonization treatment are then fed into a carbonization furnace and carbonized. In order to improve the mechanical properties of the carbon fibers, it is more preferable to perform the carbonization treatment at a maximum temperature of 1,200 to 2,000 °C in an inert atmosphere.

[0061] Regarding the inert atmosphere filling the carbonization furnace, known inert atmospheres such as nitrogen, argon, and helium can be adopted, but nitrogen is preferable from the viewpoint of economy.

[0062] In order to improve the handleability and the affinity with the matrix resin of the carbon fiber bundle thus obtained, a sizing agent may be applied. The type of the sizing agent is not particularly limited as long as the desired properties can be obtained. For example, sizing agents mainly composed of epoxy resin, polyether resin, epoxy-modified polyurethane resin, and polyester resin can be mentioned. The application of the sizing agent can use known methods.

[0063] Furthermore, the carbon fiber bundle may be subjected to electrolytic oxidation treatment or oxidation treatment for the purpose of improving the affinity and adhesiveness with the fiber-reinforced composite material matrix resin, if necessary.

[0064] The acrylic fiber bundle used as the fiber bundle to be heat-treated in the method for producing a flame-resistant fiber bundle of the present invention is preferably composed of acrylic fibers of 100 mol% of acrylonitrile or acrylic copolymer fibers containing 90 mol% or more of acrylonitrile. As the copolymerization components in the acrylic copolymer fibers, acrylic acid, methacrylic acid, itaconic acid, and their alkali metal salts, ammonium metal salts, acrylamide, methyl acrylate, etc. are preferable, but the chemical properties, physical properties, dimensions, etc. of the acrylic fiber bundle are not particularly limited.

Examples

[0065] Hereinafter, the present invention will be described more specifically with reference to the drawings by way of examples, but the present invention is not limited thereto. The wind speed and the amount of yarn vibration measured in each example and comparative example were carried out by the methods described below.

[0066] (1) Measurement method of the fineness of single fibers of an acrylic fiber bundle An acrylic fiber bundle before being fed into the flame-retardant furnace was sampled and measured in accordance with JIS L 1013 (revised version of June 21, 2010).

[0067] (2) Measurement method of wind speed As a thermal anemometer, the average value of 30 measured values of the instantaneous wind speed per second was used, using the Anemomaster High Temperature Anemometer Model 6162 manufactured by Kanomax Japan Co., Ltd. The measurement probe was inserted through the measurement hole (not shown) on the side of the furnace body 18, and on the line where the confluence surface 13 and the acrylic fiber bundle 2 intersect, the average value of the measured values at three points in the width direction including the center in the width direction was defined as Vf. On the line where the central cross-section in the running direction of the acrylic fiber bundle 2 in the heat treatment chamber 3 and the acrylic fiber bundle 2 intersect, the average value of the measured values at three points in the width direction including the center in the width direction was defined as V. On the supply surface 6, with respect to the direction orthogonal to the running direction of the acrylic fiber bundle 2, the average value of the measured values at three points in the width direction including the center in the width direction was measured and defined as Vn.

[0068] (3) Measurement method of the temperature of an acrylic fiber bundle A K-type thermocouple was attached to the running acrylic fiber bundle 2, and the temperature of the acrylic fiber bundle 2 in the heat treatment chamber 3 was measured every second, and the yarn temperature uniformity rate I (%) was calculated. I(n) = (the time from when the temperature of the thermocouple becomes T °C or higher until it becomes T - 5 °C or lower / the passing time of the heat treatment chamber) × 100 (%) Here, T is the temperature T of the hot air supplied from the supply nozzle 5, and I is the arithmetic mean value regarding the values obtained by measuring I(n) five times.

[0069] (4) Operability, quality The judgment criteria were as follows respectively.

[0070] (Operability) It was judged by the frequency of troubles such as fiber blend and fiber bundle breakage per day during 10 consecutive days of operation. Excellent: Average zero times (extremely good level) Good: Approximately 1 to 9 times on average (a level where continuous operation can be maintained sufficiently) Fair: Approximately 10 to 19 times on average (a level where continuous operation can barely be maintained) Poor: More than 20 times on average (a level where continuous operation cannot be maintained).

[0071] (Quality) After the flame-resistant fiber bundle exits the flame-resistant treatment process, it was visually observed at 10 m, and the determination was made based on the number of flyings of 10 mm or more on the flame-resistant fiber bundle that could be confirmed per 1 m. Excellent: 1 or less on average (a level where the fly quality has no impact on the process throughput or the high-order processability of the product) Good: More than 1 and less than 10 on average (a level where the fly quality has little impact on the process throughput or the high-order processability of the product) Fair: 10 or more and less than 20 on average (a level where the fly quality often affects the process throughput or the high-order processability of the product) Poor: 20 or more on average (a level where the fly quality has an adverse impact on the process throughput or the high-order processability of the product).

[0072] [Example 1] The heat treatment furnace of the present invention in FIG. 1 is used as a flame-resistant furnace for carbon fiber production. A plurality of supply nozzles 5 serving as a hot air supply source are installed vertically on both sides of the acrylic fiber bundle 2 traveling in the furnace body 18 at one end inside the furnace body 18. As shown in FIG. 2, supply surfaces 6 are provided on both the upper and lower surfaces of the supply nozzle 5, and auxiliary supply surfaces 12 are provided in the traveling direction of the acrylic fiber bundle 2. Further, perforated plates with an aperture ratio of 30% are provided on the supply surfaces 6 and the auxiliary supply surfaces 12 so that the wind speed in the width direction is uniform, and dampers (not shown) for adjusting the wind speed of the hot air supplied from each supply surface are provided in the circulation flow paths leading to each supply surface.

[0073] Regarding the acrylic fiber bundle 2 running inside the furnace body, 100 acrylic fiber bundles 2 each composed of 20,000 single fibers with a single fiber fineness of 0.11 dtex were aligned, and heat-treated in the flame-retardant furnace 1 to obtain a flame-retardant fiber bundle. Also, the horizontal distance (roll span) L' between the guide rollers 4 at both ends outside the furnace body 18 of the flame-retardant furnace 1 was set to 15 m, the guide rollers 4 were grooved rollers, and the pitch interval (groove pitch) Wp was set to 10 mm. At this time, the temperature of the oxidizing gas in the heat treatment chamber 3 of the flame-retardant furnace 1 was set to 240 - 280 °C. The running speed of the acrylic fiber bundle 2 was adjusted in the range of 1 - 15 m / min according to the length L of the flame-retardant furnace so that sufficient flame-retardant treatment time could be obtained, and the process tension was adjusted in the range of 0.5 - 2.5 g / dtex.

[0074] The obtained flame-retardant fiber bundle was then fired in the pre-carbonization furnace at a maximum temperature of 700 °C, and then fired in the carbonization furnace at a maximum temperature of 1,400 °C. After electrolytic surface treatment, a sizing agent was applied to obtain a carbon fiber bundle.

[0075] The results were as described in Table 1. When the wind speed Vn at the supply surface 6 was 8.5 m / s, the wind speed Vf in the fiber bundle passage 10 was 11.2 m / s, and the average wind speed V in the heat treatment chamber 3 was 7.0 m / s, the yarn temperature uniformity rate was 20%. Under the above conditions, during the flame-retardant treatment of the acrylic fiber bundle 2, there was little fiber mixing due to contact between the acrylic fiber bundles or fiber bundle breakage, etc., and a flame-retardant fiber bundle was obtained with good operability. Also, as a result of visually checking the obtained flame-retardant fiber bundle, it had good quality with few flyings, etc.

[0076] [Example 2] The wind speed Vn at the supply surface was 6.0 m / s, the wind speed Vf in the fiber bundle passage 10 was 3.3 m / s, and the average wind speed V in the heat treatment chamber 3 was 3.0 m / s, and the rest was the same as in Example 1. At this time, the yarn temperature uniformity rate was 17%. Under the above conditions, during the flame-retardant treatment of the acrylic fiber bundle 2, there was no occurrence of fiber mixing due to contact between the acrylic fiber bundles or fiber bundle breakage, etc., and a flame-retardant fiber bundle was obtained with extremely good operability. Also, as a result of visually checking the obtained flame-retardant fiber bundle, it had good quality with few flyings, etc.

[0077] [Example 3] The wind speed Vn on the supply surface was 3.3 m / s, and other conditions were the same as in Example 2. At this time, the yarn temperature uniformity rate was 16%. Under the above conditions, during the flame-retardant treatment of the acrylic fiber bundle 2, no fiber entanglement or fiber bundle breakage due to contact between the acrylic fiber bundles occurred, and a flame-retardant fiber bundle was obtained with extremely good operability. Further, as a result of visually inspecting the obtained flame-retardant fiber bundle, it had extremely good quality with no fluff or the like.

[0078] [Comparative Example 1] As Comparative Example 1, the wind speed Vf in the fiber passage 10 was 1.1 m / s, and the average wind speed V in the heat treatment chamber 3 was 6.0 m / s, and other conditions were the same as in Example 2. At this time, the yarn temperature uniformity rate was 8%. Under the above conditions, during the flame-retardant treatment of the acrylic fiber bundle 2, fiber entanglement due to contact between the acrylic fiber bundles and breakage of single fibers occurred frequently. Further, as a result of visually inspecting the obtained flame-retardant fiber bundle, it had poor quality with a lot of fluff or the like.

[0079]

Table 1

Industrial Applicability

[0080] The present invention relates to a method for manufacturing a flame-retardant fiber bundle and a method for manufacturing a carbon fiber bundle, and can be applied to aircraft applications, industrial applications such as pressure vessels and wind turbines, sports applications such as golf shafts, etc., but the scope of its application is not limited to these.

Explanation of Signs

[0081] 1 Flame-retardant furnace 2 Acrylic fiber bundle 3 Heat treatment chamber 4 Guide roller 5 Supply nozzle 6 Supply surface 7 Discharge surface 8 Heater 9 Blower 10 Fiber bundle passage 12 Auxiliary supply surface 13 Confluence surface 14 Discharge nozzle 16 Flow straightening plate 17 Slit 18 Furnace body 19 First supply surface 20 Second supply surface

Claims

1. A method for producing a flame-retardant fiber bundle, comprising heat-treating an aligned acrylic fiber bundle in an oxidizing atmosphere while folding it with guide rollers installed at both ends outside the furnace body of a hot air heating type flame-retardant furnace, wherein hot air is supplied from a supply surface provided above and / or below the acrylic fiber bundle in the fiber bundle passage above and / or below a supply nozzle for supplying hot air into a heat treatment chamber, which is arranged at one end in the traveling direction of the acrylic fiber bundle, and the wind speed Vf in a direction substantially parallel to the traveling direction of the acrylic fiber bundle in the fiber bundle passage and the wind speed V in a direction substantially parallel to the traveling direction of the acrylic fiber bundle in the heat treatment chamber satisfy conditions (1) and (2). (1) 1.5 m / s ≤ Vf ≤ 15 m / s (2) 1.5 m / s ≤ V ≤ 10 m / s

2. The method for producing a flame-retardant fiber bundle according to claim 1, wherein the wind speed Vf in a direction substantially parallel to the traveling direction of the acrylic fiber bundle in the fiber bundle passage and the wind speed V in a direction substantially parallel to the traveling direction of the acrylic fiber bundle in the heat treatment chamber satisfy conditions (3) and (4). (3) 1.5 m / s ≤ Vf ≤ 10 m / s (4) 1.5 m / s ≤ V ≤ 6 m / s

3. The method for producing a flame-retardant fiber bundle according to claim 1 or 2, wherein the wind speed Vn in a direction orthogonal to the traveling direction of the acrylic fiber bundle on the supply surface satisfies condition (5). (5) 0.1 m / s ≤ Vn ≤ 5 m / s

4. The method for producing a flame-retardant fiber bundle according to any one of claims 1 to 3, wherein the temperature of the hot air supplied from the supply surface is 210°C or higher and 295°C or lower.

5. The method for producing a flame-retardant fiber bundle according to any one of claims 1 to 4, wherein the single fiber fineness of the acrylic fiber bundle before heat treatment is 0.05 to 0.22 tex.

6. A method for producing a carbon fiber bundle, comprising pre-carbonizing a flame-retardant fiber bundle obtained by the method for producing a flame-retardant fiber bundle according to any one of claims 1 to 5 at a maximum temperature of 300 to 1,000°C in an inert atmosphere to obtain a pre-carbonized fiber bundle, and then carbonizing the pre-carbonized fiber bundle at a maximum temperature of 1,000 to 2,000°C in an inert atmosphere.

7. A flame-retardant furnace for heat-treating an acrylic fiber bundle, comprising (i) a furnace body having a slit through which the aligned fiber bundle can enter and exit (ii) A plurality of supply nozzles that are arranged at one end in the traveling direction of the fiber bundle in the heat treatment chamber, spaced apart from each other in the vertical direction, and supply hot air into the furnace body; (iii) A plurality of discharge nozzles that are arranged at the other end in the traveling direction of the fiber bundle in the furnace body, spaced apart from each other in the vertical direction, and discharge the hot air supplied from the supply nozzles from the heat treatment chamber; (iv) At least one blower device that circulates hot air through the supply nozzles and the discharge nozzles; (v) At least one heating device arranged on the flow path of the circulating hot air; (vi) Guide rollers that are arranged at both ends outside the furnace body and cause the fiber bundle to travel back and forth a plurality of times in the heat treatment chamber through between adjacent supply nozzles and between adjacent discharge nozzles, and a flameproofing furnace having the same; (vii) The supply nozzle has a supply surface for supplying first hot air to the fiber bundle passage flow path above and / or below the supply nozzle on the upper surface and / or the lower surface, and an auxiliary supply surface for supplying second hot air to the side surface inside the heat treatment chamber of the supply nozzle; (viii) A flameproofing furnace characterized by comprising adjustment means for adjusting the wind speed of the first hot air and the wind speed of the second hot air supplied from the supply nozzle.

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