Groove structure and application for fiber spinning hot drawing process and hot drawing method and polyacrylonitrile-based carbon fiber precursor

Abstract

The present application relates to polyacrylonitrile fiber manufacturing technology field, disclose a kind of for fiber spinning hot drawing processing recess structure and application and hot drawing method and polyacrylonitrile-based carbon fiber precursor, the recess structure includes: groove wall, around forming recess, the recess is used to hold hot drawing medium, the hot drawing medium is used to provide temperature support for the drawing process of the fiber tow to be stretched;Top has the opening of drawing channel, it is arranged in the recess and extends along the fiber tow drawing direction, for the fiber tow to be stretched in the channel is drawn to provide stable hot drawing medium flow field;Drawing piece, it is arranged in the both ends of drawing channel, for the fiber tow to be stretched provides drawing force.The present application can stabilize the hot water flow field around the fiber tow to be stretched, to improve fiber take-up effect reduce because of hot water fluctuation appears long and short silk, to improve the stability of fiber finished product quality.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of polyacrylonitrile fiber manufacturing, in particular to a groove structure and application for fiber spinning hot drawing treatment and a hot drawing method and polyacrylonitrile-based carbon fiber precursor. BACKGROUND

[0002] Polyacrylonitrile (PAN) fiber has been rapidly developed since its industrial production due to its excellent performance and sufficient raw materials. Currently, carbon fibers are widely used in military industry, rail transportation, wind power generation, and construction due to their excellent mechanical properties, corrosion resistance, and high temperature resistance.

[0003] With the increase of the application field of carbon fibers, the demand for polyacrylonitrile fiber as the main raw material for carbon fiber production is increasing. The spinning methods of polyacrylonitrile fiber mainly include wet spinning, dry-wet spinning, gel spinning, and electrospinning. Among them, wet spinning and dry-wet spinning are important spinning methods for polyacrylonitrile fiber.

[0004] The wet spinning process of polyacrylonitrile fiber is as follows: preparation of spinning solution, swelling and dissolution, filtration, defoaming, spinning and coagulation forming, washing and hot water drawing, oiling, drying and densification, high temperature and high pressure steam drawing, and heat setting. The main purpose of hot drawing is to improve the orientation degree of fiber macromolecules and improve the physical and mechanical properties of the fiber. However, the hot water drawing process of wet spinning is prone to long and short fibers. The presence of long and short fibers affects the uniformity of fiber stress during the pre-oxidation process of polyacrylonitrile fiber, and even causes fiber melting during the pre-oxidation process, thereby affecting the stability of the quality of the subsequent carbonization process and leading to a decrease in the quality of carbon fiber products. SUMMARY

[0005] In the polyacrylonitrile fiber spinning production line, when the fiber is subjected to hot water drawing, the fiber bundle becomes wide due to the fluctuation of hot water, which leads to long and short fibers in the fiber product. The purpose of the present application is to overcome the problem of long and short fibers in the fiber product in the prior art, and to provide a groove structure and application for fiber spinning hot drawing treatment and a hot drawing method and polyacrylonitrile-based carbon fiber precursor, which can stabilize the hot water flow field around the fiber bundle to be drawn, thereby improving the fiber drawing effect and reducing the occurrence of long and short fibers due to the fluctuation of hot water, and further improving the stability of the quality of the fiber product.

[0006] In order to achieve the above-mentioned purpose, the present application provides a groove structure for fiber spinning hot drawing treatment, which comprises:

[0007] A groove wall is formed around a groove for containing a hot drawing medium for providing temperature support for the drawing process of the fiber tow to be drawn;

[0008] A drawing channel with an open top end is arranged in the groove and extends along the fiber tow drawing direction to provide a stable hot drawing medium flow field for the fiber tow to be drawn in the drawing process in the channel;

[0009] A drawing element is arranged at both ends of the drawing channel to provide a drawing force for the fiber tow to be drawn.

[0010] Preferably, a plurality of drawing channels are arranged along the direction perpendicular to the fiber tow drawing direction.

[0011] Preferably, the ports at both ends of the drawing channel are formed as an inlet end and an outlet end.

[0012] Preferably, the inlet end is arranged in a tapered structure that gradually narrows along the fiber tow drawing direction.

[0013] Preferably, the outlet end is arranged in a diverging structure that gradually expands along the fiber tow drawing direction.

[0014] Preferably, a base is detachably arranged in the groove, and the upper surface of the base is provided with at least one sliding groove arranged along the direction perpendicular to the fiber tow drawing direction.

[0015] Preferably, a sliding block is slidably arranged in the sliding groove, and the protruding end of the sliding block is connected to the bottom end of the drawing channel, so that the drawing channel can move along the direction perpendicular to the fiber tow drawing direction.

[0016] Preferably, the drawing element includes a first drawing element arranged at the inlet end of the drawing channel and a second drawing element arranged at the outlet end of the drawing channel.

[0017] The first drawing element is arranged as a spinneret for extruding nascent fibers, and the spinneret includes a plurality of spinneret holes.

[0018] The second drawing element is arranged as a pulley or a guide roller connected to the groove wall.

[0019] The second aspect of the present application provides the application of the groove structure described in the present application in the spinning of polyacrylonitrile fibers, preferably in the production line of polyacrylonitrile fibers with a tow of 3K-50K.

[0020] The third aspect of the present application provides a hot drawing method for polyacrylonitrile fibers, which is carried out in the groove structure described in the present application; including:

[0021] The polyacrylonitrile fiber tow to be drawn is drawn in a stable hot draft medium flow field formed by the drawing channel in the groove under the drawing effect of the draft member.

[0022] Preferably, the temperature of the hot draft medium is (T g +1)~(T g +6)℃, more preferably (T g +3)~(T g +4)℃, wherein T g is the glass transition temperature of the fiber.

[0023] Preferably, the hot draft medium is selected from water or saturated water vapor.

[0024] Preferably, the polyacrylonitrile fiber tow to be drawn is a nascent fiber tow formed by extruding the polyacrylonitrile dope in the spinneret.

[0025] Preferably, the spinning solvent of the polyacrylonitrile dope is selected from at least one of sodium thiocyanate, N,N-dimethylformamide, dimethyl sulfoxide or dimethylacetamide.

[0026] Preferably, the hot draft multiple of the nascent fiber tow is 4~10, more preferably 6~8.

[0027] The fourth aspect of the present application provides a polyacrylonitrile-based carbon fiber precursor prepared by the hot draft method of the present application.

[0028] Through the above technical solution, the groove structure of the present application can stabilize the flow field around the fiber tow to be drawn by arranging the drawing channel in the groove, thereby improving the fiber take-up effect and reducing the occurrence of long and short fibers due to the fluctuation of the hot draft medium, and further improving the stability of the quality of the fiber product. Further, the groove structure of the present application in combination with the process parameters of the hot draft method of the present application can improve the uniformity of the hot water draft of the polyacrylonitrile fiber, improve the take-up effect of the polyacrylonitrile fiber, reduce the occurrence of long and short fibers due to the fluctuation of the liquid, and facilitate the smooth progress of the pre-oxidation and carbonization of the polyacrylonitrile fiber, thereby improving the stability of the quality of the fiber product. Compared with the prior art, the polyacrylonitrile-based carbon fiber precursor prepared by the present application has fewer long and short fibers, thereby having higher physical and mechanical properties and more stable quality. The present application has great significance in solving the problem of fiber long and short fibers caused by the dispersion of the hot draft of the polyacrylonitrile fiber spinning production line, and has great industrial application value. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a top view of the groove structure for fiber spinning hot draft treatment of the embodiment of the present application;

[0030] Figure 2 is Figure 1A sectional view in the E-E direction of the drawing member is added;

[0031] Figure 3 is Figure 1 A sectional view in the F-F direction.

[0032] Reference Signs List

[0033] 1 base; 2 drawing channel; 3 slider; 4 sliding groove; 5 recess; 6 jet; 7 second drawing member. DETAILED DESCRIPTION

[0034] The specific embodiments of the present application will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely intended to illustrate and explain the present application, and are not intended to limit the present application.

[0035] In the present application, the orientation words such as "up, down, left, right" used herein generally refer to the up, down, left, right shown in the drawings, and "inner, outer" refer to the inner and outer relative to the cavity or the axis. In the present application, the long and short filaments refer to the phenomenon that the same bundle of fibers appears long and short due to the widening of the fiber bundle during the production process.

[0036] As Figures 1-3 shown, the first aspect of the present application provides a recess structure for fiber spinning hot drawing treatment, the recess structure comprising:

[0037] a groove wall surrounding the recess 5, the recess 5 being used for containing a hot drawing medium, the hot drawing medium being used to provide temperature support for the drawing treatment of the fiber bundle to be drawn, the groove wall being provided with a hot drawing medium inlet and a hot drawing medium outlet for the circulation of the hot drawing medium;

[0038] a drawing channel 2 with an open top end, disposed in the recess 5 and extending along the fiber bundle drawing direction, for providing a stable hot drawing medium flow field for the fiber bundle to be drawn in the channel 2 for drawing treatment;

[0039] a drawing member, disposed at both ends of the drawing channel 2, for providing a drawing force for the fiber bundle to be drawn.

[0040] It should be noted that when the fiber is stretched by being immersed in the hot drawing medium (such as hot water), the fiber bundle will be widened with the fluctuation of the hot drawing medium, and the over-wide fiber bundle will cause long and short fibers, thereby affecting the uniformity of the fiber stress and the stability of the fiber product quality. In the present application, the stretching channel 2 is arranged in the groove 5, the fiber bundle to be stretched enters one end of the stretching channel 2 and extends out of the other end, the tension provided by the traction member stretches along the axial direction of the stretching channel 2, wherein the stretching channel 2 frames the hot drawing medium around the fiber bundle to be stretched, avoids the fluctuation of the hot drawing medium with the flow (such as the inflow or outflow of the hot drawing medium into or out of the groove 5) of the hot drawing medium outside the stretching channel 2, thereby stabilizing the liquid flow field around the fiber bundle to be stretched, improving the fiber contraction effect, reducing the long and short fibers caused by the fluctuation of the liquid, and further improving the stability of the quality of the fiber product.

[0041] In some embodiments of the present application, a plurality of stretching channels 2 are provided, the plurality of stretching channels 2 are arranged at intervals along the fiber bundle stretching direction, the number of the stretching channels 2 is n+1, wherein n is the number of the fiber bundles; the cross section of each stretching channel 2 can be a half rectangle, a half circle, a half ellipse or a half polygon. In this way, the plurality of stretching channels 2 can increase the processing capacity of the fiber bundle stretching process, thereby improving the stretching efficiency.

[0042] According to a preferred embodiment of the present application, the ports at both ends of the stretching channel 2 are formed as an inlet end and an outlet end; the inlet end is arranged in a tapered structure gradually narrowing along the fiber bundle stretching direction; and the outlet end is arranged in a diverging structure gradually expanding along the fiber bundle stretching direction. This has the advantages of stable flow guiding, reduced fiber damage and reduced broken filaments.

[0043] In some embodiments of the present application, the included angle between the inner wall of the inlet end formed in the tapered structure and the inner wall of the stretching channel 2 between the inlet end and the outlet end is α, 165°≤α≤177°, preferably 170°≤α≤172°. The use of the foregoing parameters can stabilize the flow guiding, reduce the fiber damage caused by the inlet water flow and reduce the broken filaments.

[0044] In some embodiments of the present application, the included angle between the inner wall of the outlet end formed in the diverging structure and the inner wall of the stretching channel 2 between the inlet end and the outlet end is β, 147°≤β≤160°, preferably 153°≤β≤155°. The use of the foregoing parameters can stabilize the flow guiding, reduce the fiber damage caused by the outlet water flow and reduce the broken filaments.

[0045] In some embodiments of the present application, the maximum width dimension of the inner wall of the inlet end formed as a tapered structure and / or the maximum width dimension of the inner wall of the outlet end formed as an expanded structure is B, the width dimension of the stretching channel 2 between the inlet end and the outlet end is A, wherein B = 2*A; further, A is (X+5)~(X+20) mm, preferably (X+10)~(X+14) mm, wherein X is (the number of fibers in the fiber bundle * the fiber diameter when entering the groove 5 / 13) mm. The use of the foregoing parameters can stabilize the water flow and reduce the generation of long and short fibers.

[0046] In some embodiments of the present application, X can range from 2 to 100 mm, preferably from 4 to 60 mm, but X in the present application is not limited to the above numerical range.

[0047] In some embodiments of the present application, the overall length L of the stretching channel 2 is 1-4 m, preferably 2.0-2.5 m.

[0048] In some embodiments of the present application, the height difference between the top end surface of the stretching channel 2 and the stretching surface where the fiber bundle is located is ≥10 mm; the use of the foregoing parameters can enable the fiber to be in a stable flow field and reduce the generation of long and short fibers.

[0049] In some embodiments of the present application, the center distance C of adjacent stretching channels 2 is greater than B.

[0050] In some embodiments of the present application, the draft member includes a first draft member provided on the inlet end side of the stretching channel 2 and a second draft member 7 provided on the outlet end side of the stretching channel 2;

[0051] The first draft member is provided as a spinneret 6 for extruding the nascent fiber, the spinneret 6 adopts the spinneret plate structure with multiple spinneret holes in the prior art, and the number of spinneret holes is preferably 2000-50000; the second draft member 7 is provided as a pulley or guide roller connected to the groove wall;

[0052] The spinneret 6 is connected to the spinning dope feeding pipeline, and the spinneret 6 can be provided through the groove wall or can be provided by extending into the groove 5 through a bent pipeline (so that the position of the spinneret 6 in the groove can be moved according to actual needs); the spinneret 6 is immersed in the hot draft medium, the fiber formed by the spinneret hole is a fiber bundle, the fiber bundle passes through the stretching channel 2, is wound on the pulley or guide roller opposite to the spinneret 6, and is pulled out of the groove 5 upward.

[0053] In some embodiments of the present application, the base 1 is detachably arranged in the recess 5, the base 1 is a circular truncated cone or a truncated prism with a large upper part and a small lower part, facilitating stable placement; the upper surface of the base 1 is provided with at least one sliding groove 4 arranged along the vertical fiber bundle stretching direction; the sliding groove 4 is slidably provided with a sliding block 3, the extending end of the sliding block 3 is connected to the bottom end of the stretching channel 2, so that the stretching channel 2 can move along the vertical fiber bundle stretching direction. In this way, the position of the stretching channel 2 can be moved correspondingly following the movement of the spinneret 6, and at the same time the base 1 is detachable, facilitating the replacement of different sizes of stretching channels according to the spinning requirements, and facilitating the cleaning of the recess structure, ensuring the cleanliness of the spinning environment.

[0054] The second aspect of the present application provides the application of the recess structure of the present application in polyacrylonitrile fiber spinning, preferably in the production line of polyacrylonitrile fiber with a fiber bundle of 3K-50K.

[0055] The third aspect of the present application provides a hot drawing method of polyacrylonitrile fiber, which is carried out in the recess structure of the present application; the hot drawing includes:

[0056] The polyacrylonitrile fiber bundle to be stretched is stretched in the stable hot drawing medium flow field formed by the stretching channel 2 in the recess 5 under the stretching action of the stretching member, so as to improve the hot water drawing uniformity of the polyacrylonitrile fiber, improve the take-up effect of the polyacrylonitrile fiber, reduce the long and short fibers caused by liquid fluctuation, and facilitate the smooth progress of the pre-oxidation and carbonization of the polyacrylonitrile fiber, thereby improving the stability of the quality of the fiber product.

[0057] In the present application, the temperature of the hot drawing medium is (T g +1)~(T g +6)℃, preferably (T g +3)~(T g +4)℃, wherein T g is the glass transition temperature of the fiber, so as to have a suitable drawing temperature and have the advantage of reducing the damage to the fiber caused by inappropriate temperature.

[0058] In the present application, the hot drawing medium is selected from water or saturated water vapor.

[0059] In the present application, the polyacrylonitrile fiber tows to be drawn are nascent fiber tows formed by extruding polyacrylonitrile dope from the spinneret 6; it should be noted that the polyacrylonitrile spinning solution in the present application can be obtained commercially or prepared by conventional methods in the art, for example, using polyacrylonitrile monomers, other comonomers, in the presence of initiators and solvents and other aids to perform polymerization, wherein the specific composition of the polyacrylonitrile spinning solution and the specific types of other comonomers, initiators and solvents and other aids to synthesize the polyacrylonitrile spinning solution have no effect on the technical effects of the present application, and the present application does not make redundant elaboration thereon. In the present application, the spinning solvent of the polyacrylonitrile dope is selected from at least one of sodium thiocyanate, N,N-dimethylformamide, dimethyl sulfoxide or dimethylacetamide.

[0060] In the present application, the heat drawing multiple of the nascent fiber tows is preferably 4-10, preferably 6-8. Thereby, the advantages of reducing excessive drawing and avoiding insufficient drawing, and avoiding the influence of drawing on the mechanical properties of the fibers are achieved.

[0061] The fourth aspect of the present application provides a polyacrylonitrile-based carbon fiber precursor prepared by the heat drawing method of the present application.

[0062] It should be noted that after the polyacrylonitrile fiber is treated by the heat drawing method of the present application, and then subjected to the oiling, drying densification, high temperature and high pressure steam drawing, heat setting treatment in the prior art, the polyacrylonitrile-based carbon fiber precursor is obtained by winding.

[0063] Compared with the prior art, the polyacrylonitrile-based carbon fiber precursor prepared by the present application has fewer long and short fibers, higher physical and mechanical properties and more stable quality.

[0064] The present application will be illustrated by the following examples, but the present application is not limited thereto.

[0065] The following Examples 1-6 are carried out in the groove structure for fiber spinning heat drawing treatment shown in Figures 1-3 including:

[0066] The groove wall forming the groove 5 has an inlet and an outlet for the hot stretching medium to flow hot water. A frustum-shaped base 1 is detachably installed in the groove 5 below the hot water surface. At least two grooves 4 perpendicular to the filament stretching direction are provided on the upper surface of the base. A slider 3 is installed in the groove 4 and can slide along the axis of the groove 4. The protruding end of the slider 4 is connected to the bottom end of the stretching channel 2. The top of the stretching channel 2 has an opening formed into a groove structure with a semi-rectangular cross-section. The inlet and outlet ends at both ends are set as approximately trumpet-shaped. A spinneret 6 with multiple spinnerets is installed on one side of the inlet end of the stretching channel 2. The spinneret 6 is immersed below the hot water surface and connected to the polyacrylonitrile raw material feed pipe. The formed nascent fiber bundles extruded from the spinneret 6 are wound around the guide roller located on the outlet end side of the stretching channel 2 and stretched in the stretching channel 2.

[0067] In Examples 1-6, sodium thiocyanate was used as the spinning solvent, and the solid content of the polyacrylonitrile spinning solution was 12.3%. However, the present invention is not limited to this spinning solvent and this solid content.

[0068] Example 1

[0069] Glass transition temperature T of the fiber g The temperature is 90℃, the hot stretching medium is hot water with a temperature of 94℃, and the hot stretching ratio is 6 times.

[0070] In the groove structure, the angle α between the inner wall of the inlet end and the inner wall of the stretching channel 2 is 170°, the angle β between the inner wall of the outlet end and the inner wall of the stretching channel 2 is 153°, X is 4mm, the width A of the stretching channel 2 located at the outlet end and the inlet end is 14mm, the length L of the stretching channel 2 is 2m, and the number of spinneret holes 6 is 3000.

[0071] The results are shown in Table 1.

[0072] Example 2

[0073] Glass transition temperature T of the fiber g The temperature is 90℃, the hot stretching medium is hot water with a temperature of 93℃, and the hot stretching ratio is 8 times.

[0074] In the groove structure, the angle α between the inner wall of the inlet end and the inner wall of the stretching channel 2 is 172°, the angle β between the inner wall of the outlet end and the inner wall of the stretching channel 2 is 155°, X is 30mm, the width A of the stretching channel 2 located at the outlet end and the inlet end is 44mm, the length L of the stretching channel 2 is 2.5m, and the number of spinneret holes 6 is 24000.

[0075] The results are shown in Table 1.

[0076] Example 3

[0077] The glass transition temperature T of the fiber g was 90°C, the thermal drawing medium was hot water, the hot water temperature was 92°C, and the thermal drawing multiple was 9 times.

[0078] In the groove structure, the included angle α between the inner wall of the inlet end and the inner wall of the stretching channel 2 was 174°, the included angle β between the inner wall of the outlet end and the inner wall of the stretching channel 2 was 157°, X was 8 mm, the width A of the stretching channel 2 located at the outlet end and the inlet end was 25 mm, the length L of the stretching channel 2 was 3 m, and the number of the spinning holes of the spinneret 6 was 6000.

[0079] The results are shown in Table 1.

[0080] Example 4

[0081] The glass transition temperature T of the fiber g was 90°C, the thermal drawing medium was hot water, the hot water temperature was 91°C, and the thermal drawing multiple was 10 times.

[0082] In the groove structure, the included angle α between the inner wall of the inlet end and the inner wall of the stretching channel 2 was 177°, the included angle β between the inner wall of the outlet end and the inner wall of the stretching channel 2 was 160°, X was 15 mm, the width A of the stretching channel 2 located at the outlet end and the inlet end was 35 mm, the length L of the stretching channel 2 was 4.0 m, and the number of the spinning holes of the spinneret 6 was 12000.

[0083] The results are shown in Table 1.

[0084] Example 5

[0085] The glass transition temperature T of the fiber g was 90°C, the thermal drawing medium was hot water, the hot water temperature was 95°C, and the thermal drawing multiple was 5 times.

[0086] In the groove structure, the included angle α between the inner wall of the inlet end and the inner wall of the stretching channel 2 was 168°, the included angle β between the inner wall of the outlet end and the inner wall of the stretching channel 2 was 150°, X was 15 mm, the width A of the stretching channel 2 located at the outlet end and the inlet end was 23 mm, the length L of the stretching channel 2 was 1.5 m, and the number of the spinning holes of the spinneret 6 was 12000.

[0087] The results are shown in Table 1.

[0088] Example 6

[0089] The glass transition temperature T of the fiber g was 90°C, the thermal drawing medium was hot water, the hot water temperature was 96°C, and the thermal drawing multiple was 4 times.

[0090] In the recess structure, the included angle between the inner wall of the inlet end and the inner wall of the stretching channel 2 is 165°, the included angle between the inner wall of the outlet end and the inner wall of the stretching channel 2 is 147°, X is 51 mm, the width A of the stretching channel 2 at the outlet end and the inlet end is 56 mm, the length L of the stretching channel 2 is 4 m, and the number of the spinning holes of the spinneret 6 is 50000.

[0091] The results are shown in Table 1.

[0092] Comparative Example 1

[0093] Different from Example 1, the stretching channel 2 of the application is not used, the hot drawing multiple is 10 times, and the results are shown in Table 1.

[0094] Comparative Example 2

[0095] Different from Example 1, the stretching channel 2 of the application is not used, the hot water temperature is 92℃, the hot drawing multiple is 8 times, the number of the spinning holes of the spinneret 6 is 12000, and the results are shown in Table 1.

[0096] Comparative Example 3

[0097] Different from Example 1, the stretching channel 2 of the application is not used, the hot water temperature is 96℃, the hot drawing multiple is 6 times, the number of the spinning holes of the spinneret 6 is 50000, and the results are shown in Table 1.

[0098] Table 1

[0099]

[0100] Compared with the prior art, the application can improve the hot water drawing uniformity of the polyacrylonitrile fiber, reduce the generation of long and short fibers in the forming process, and the long and short fibers are ≤2 when the fiber length is 10 m.

[0101] The preferred embodiments of the application are described in detail above with reference to the drawings, but the application is not limited thereto. Within the technical concept of the application, various simple modifications can be made to the technical solutions of the application, including the combination of various specific technical features in any suitable manner. In order to avoid unnecessary repetition, the application does not further describe various possible combination manners. However, these simple modifications and combinations should also be regarded as the disclosed content of the application and belong to the protection scope of the application.

Claims

1. A groove structure for fiber spinning hot draft process, characterized by, The groove structure comprises: a groove wall surrounding a groove (5) for containing a hot drawing medium for providing temperature support for the drawing process of the fiber tow to be drawn; a drawing channel (2) with an open top end arranged in the groove (5) and extending in the fiber tow drawing direction for providing a stable hot drawing medium flow field for the fiber tow to be drawn in the drawing channel (2); the two ends of the drawing channel (2) are formed into an inlet end and an outlet end; the inlet end is arranged in a tapered structure gradually narrowing in the fiber tow drawing direction; the outlet end is arranged in a diverging structure gradually expanding in the fiber tow drawing direction; the included angle between the inner wall of the inlet end in the tapered structure and the inner wall of the drawing channel (2) between the inlet end and the outlet end is α, 170°≤α≤172°; the included angle between the inner wall of the outlet end in the diverging structure and the inner wall of the drawing channel (2) between the inlet end and the outlet end is β, 153°≤β≤155°; the maximum width dimension of the inner wall of the inlet end in the tapered structure and the maximum width dimension of the inner wall of the outlet end in the diverging structure are both B, and the width dimension of the drawing channel (2) between the inlet end and the outlet end is A, wherein B=2×A, A is (X+10)~(X+14) mm, wherein X is the number of fiber roots in the tow multiplied by the fiber diameter when entering the groove divided by 13 mm; a drawing element arranged at the two ends of the drawing channel (2) for providing a drawing force for the fiber tow to be drawn.

2. The recess structure according to claim 1, characterized by A plurality of drawing channels (2) are arranged in the groove (5) and are arranged in a staggered manner in the vertical direction of the fiber tow drawing direction.

3. The recess structure of claim 1, wherein A base (1) is detachably arranged in the groove (5), and at least one sliding groove (4) is arranged on the upper surface of the base (1) and arranged in the vertical direction of the fiber tow drawing direction; A sliding block (3) is slidably arranged in the sliding groove (4), and the protruding end of the sliding block (3) is connected to the bottom end of the drawing channel (2), so that the drawing channel (2) can move in the vertical direction of the fiber tow drawing direction.

4. The recess structure of claim 1, wherein The drawing element comprises a first drawing element arranged on the inlet end side of the drawing channel (2) and a second drawing element (7) arranged on the outlet end side of the drawing channel (2); The first drawing element is arranged as a spinneret (6) for extruding nascent fibers, and the spinneret (6) comprises a plurality of spinneret holes; The second drawing element (7) is arranged as a pulley or a guide roller connected to the groove wall.

5. The groove structure according to any one of claims 1-4 is used in the spinning of polyacrylonitrile fibers.

6. The groove structure according to any one of claims 1-4 is used in a polyacrylonitrile fiber production line with a fiber tow of 3K-50K.

7. A heat drawing method of polyacrylonitrile fibers, characterized by, The hot drawing method is carried out in the groove structure according to any one of claims 1-4; comprising: The polyacrylonitrile fiber to-be-stretched filament bundle is stretched in a stable hot draft medium flow field formed by the draft of the draft member in the stretching channel (2) in the groove (5).

8. The hot drawing method according to claim 7, wherein The temperature of the hot drawing medium is (T g +1) to (T g +6) °C, wherein T g is the glass transition temperature of the fiber; and / or The hot draft medium is selected from water or saturated water vapor. and / or The polyacrylonitrile fiber to-be-stretched filament bundle is a nascent fiber filament bundle formed by extrusion of a polyacrylonitrile dope in the spinneret (6).

9. The hot drawing method according to claim 8, wherein The spinning solvent of the polyacrylonitrile dope is selected from at least one of sodium thiocyanate, N,N-dimethylformamide, dimethyl sulfoxide or dimethylacetamide. and / or The hot draft multiple of the nascent fiber filament bundle is 4-10.

10. A polyacrylonitrile-based carbon fiber precursor prepared by the hot draft method according to any one of claims 7-9.

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