A fiber strand drawing method

Abstract

The present invention belongs to the field of spinning technology and equipment and discloses a method for drawing fiber whiskers. The method is to periodically repeat the sequence of "applying force F1 → stopping applying force → applying force F2 → stopping applying force" at a fixed position on the running path of the fiber whiskers during the horizontal movement of the fiber whiskers in the front-to-back direction. The fixed position is located between the front roller and the middle roller of the drawing frame, the pressure of the front roller is 80-250N, and the pressure of the middle roller is 150-300N. The force F1 is the force that causes the fiber whiskers to shift horizontally to the left, and the force F2 is the force that causes the fiber whiskers to shift horizontally to the right. The present invention reduces fiber damage while avoiding accidental drafting and poor drafting, resulting in a better yarn and higher strength.

Description

Technical Field

[0001] The invention belongs to the field of spinning technology equipment and relates to a fiber sliver drawing method. Background Art

[0002] Drawing is a key process in spinning, primarily encompassing drawing and drafting. Drawing involves mixing and feeding multiple fiber strands to improve their uniformity and blending. Drafting involves elongating and thinning the combined fibers, while also increasing their straightness and parallelism, thereby improving the strength of the yarn spun later. Currently, two draw frame methods are used: pinless draw frame and pin-plate draw frame. Pinless draw frame uses rollers or top rollers to hold the fibers in the drafting zone, rather than using needles to control fiber movement. Common methods include roller drafting and apron drafting. Pin-plate draw frame employs rotating upper and lower pin plates in the drafting zone to further improve fiber straightness and parallelism during drafting and improve the internal structure of the yarn. Pinless draw frame is commonly used for cotton and cotton-based synthetic fibers, while pin-plate draw frame is typically used for wool top spinning.

[0003] Industrial polyester staple fibers have high straightness, no curl, and high modulus. During spinning and drawing, the friction and other interactions between fibers are small, resulting in insufficient friction field in the drawing zone of the fiber strands. It is usually necessary to increase the roller pressure to ensure the drawing effect, such as in the literature (Optimization of the first-pass drawing process of phenolic fiber and its influence on yarn quality [J]. Journal of Textile Research, 2016, 37(10): 26-31). However, a large roller pressure will cause severe pressure on the rollers, reducing their service life. In addition, special fibers such as carbon fiber, glass fiber, kiwano fiber, and phenolic fiber have poor shear resistance. When subjected to large pressure from rollers and rollers, the fibers will break and suffer significant fiber damage (compared to the fiber strands before drawing, the fiber damage rate is 20-30%). Therefore, during spinning and drawing, a smaller roller pressure is required to reduce fiber breakage. However, lower roller pressure reduces the strength of the external friction field of the drawing and drafting device, weakening both the drafting force and control force on the fibers during drawing, which is detrimental to the smooth progress of the fiber drafting process. At the same time, specialty fibers such as carbon fibers have a high modulus and high straightness (no curl), resulting in lower fiber-to-fiber interaction forces and a smaller internal friction field within the fiber aggregate within the drafting zone. Furthermore, due to the combined effects of lower roller pressure and a smaller internal friction field, the control effect on the fibers during drafting is very weak, and the fiber speed distribution is very unfocused, which in turn results in worsening rather than improving the uniformity of the fiber strips produced after drawing. Furthermore, the resulting fiber strips are not strong enough, and in subsequent spinning applications, unexpected drafting due to fiber strip breakage or fiber slippage can occur, seriously affecting the quality of the yarn spun in the subsequent process.

[0004] Therefore, a method for drawing fiber strips is needed to solve the above problems, which is of great significance. Summary of the Invention

[0005] The purpose of the present invention is to solve the problems existing in the prior art and provide a method for drawing fiber strands.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A fiber strand drawing method, wherein during the horizontal movement of the fiber strand in the forward and backward directions, the fiber strand is subjected to a periodic repetition of the sequence of "applying force F1 → stopping applying force → applying force F2 → stopping applying force" at a fixed position on the fiber strand's running path;

[0008] The fixed position is between the front roller and the middle roller of the draw frame. The pressure of the front roller is 80-250N, and the pressure of the middle roller is 150-300N. When drawing conventional raw materials, the pressure of the front roller of the draw frame is generally 150-250N, and the pressure of the middle roller is generally 250-300N.

[0009] The force F1 is the force that causes the fiber strands to shift horizontally to the left, and the force F2 is the force that causes the fiber strands to shift horizontally to the right.

[0010] In order to solve the problems in the prior art of industrial polyester staple fibers having high straightness, no curl and high modulus, and small interactions such as friction between fibers during spinning and drawing, which results in insufficient friction field of fiber slivers in the drawing zone, it is usually necessary to increase the roller pressure to ensure its drawing effect. However, a larger roller pressure will cause serious pressure on the rollers, which will reduce their service life, and it is impossible to avoid accidental drawing and poor drawing while reducing fiber damage when spinning and drawing special fibers (such as carbon fiber, glass fiber, and kiwano fiber). On the one hand, the present invention maintains normal roller pressure or controls the roller pressure to be smaller, so as to reduce the damage and breakage of the fibers caused by the roller pressure, and at the same time reduce the fiber damage. The friction of the drafting components, especially the leather rollers, extends the service life of the drafting components; on the other hand, in the process of the fiber strands running in the front-to-back direction, at a fixed position on the running path of the fiber strands, the force F1 and the force F2 are applied alternately to the fiber strands, so that the fibers in different length segments of the fiber strands produce lateral transfers in different directions during drafting, and the fibers are entangled with each other, thereby increasing the internal friction field of the fiber strands during drafting, which can well supplement the problems such as insufficient drafting force caused by the low pressure of the rollers, and increase the total friction boundary strength during drafting, thereby reducing fiber damage while avoiding accidental drafting and poor drafting, so that the yarn is better and stronger.

[0011] As the preferred technical solution:

[0012] In the fiber strand drawing method described above, each application of the force F1 lasts for 0.5-1s, each application of the force F2 lasts for 0.5-1s, and each cessation of the application of the force lasts for 0.1-0.5s.

[0013] In the above-mentioned fiber strand drawing method, the fiber strands are horizontally shifted 2-3 mm to the left from the beginning to the end of each application of the force F1, and the fiber strands are horizontally shifted 2-3 mm to the right from the beginning to the end of each application of the force F2.

[0014] In the method for drawing fiber whiskers as described above, the horizontal distance between the fixed position and the jaws of the middle roller is 3-5 mm smaller than the length L of the fibers in the fiber whiskers. When the fibers are natural fibers, the length L of the fibers in the fiber whiskers is the main length of the fibers in the fiber whiskers. The purpose is to ensure that the fiber whiskers are subjected to force before acceleration. The fiber whiskers are subjected to force before acceleration. First, the head end of the fiber whiskers can complete the transfer of the forward direction before acceleration. When accelerated by the stretching force, the overall transfer amplitude of the fiber whiskers is larger, which is more conducive to the mutual entanglement of the fiber whiskers. Second, the speed of the fiber whiskers is slower before acceleration, which is more conducive to applying force to the fiber whiskers, and the applied force has less effect on the stretching.

[0015] In the method for drawing fiber strands as described above, the distance between the front roller jaws and the middle roller jaws is 8-12 mm larger than the length L of the fibers in the fiber strands. When the fibers are natural fibers, the length L of the fibers in the fiber strands is the main length of the fibers in the fiber strands.

[0016] In the fiber sliver drawing method as described above, the linear speed of the middle roller is 3-6 m / min, and the ratio of the linear speed of the front roller to the linear speed of the middle roller is 3-8.

[0017] In the above-mentioned method for drawing fiber strands, the fibers in the fiber strands are one or more of industrial polyester staple fibers, carbon fibers, phenolic fibers, caltrop fibers and glass fibers.

[0018] A method for drawing fiber strands as described in any of the above items, applying force F1 or force F2 to the fiber strands means simultaneously needling the upper and lower surfaces of the fiber strands, and the needling depth is 1-2 mm. The needling depth should not be too large, otherwise the fibers cannot escape from the needle teeth in time, and the needle teeth will take the fibers away, affecting the stretching. When applying force to the fiber strands by needling, if force is only applied to one side surface of the fiber strand, when the needling depth is small, the force cannot be fully applied to all fibers.

[0019] The present invention also provides a fiber strand drawing device, comprising a front roller and a middle roller arranged at intervals in the front-to-back direction, and an upper flexible needle belt and a lower flexible needle belt located between the front roller and the middle roller;

[0020] The pressure of the front roller is 80-250N, and the pressure of the middle roller is 150-300N;

[0021] The upper flexible needle belt runs in a counterclockwise direction, and the lower flexible needle belt runs in a clockwise direction;

[0022] The upper flexible needle belt is provided with multiple rows of needle teeth I and multiple rows of needle teeth II. The needle teeth I in the same row or the needle teeth II in the same row are arranged at intervals along the width direction of the upper flexible needle belt, and the needle teeth I and needle teeth II in two adjacent rows are arranged alternately at intervals along the length direction of the upper flexible needle belt.

[0023] The lower flexible needle belt is provided with multiple rows of needle teeth III and multiple rows of needle teeth IV. The needle teeth III in the same row or the needle teeth IV in the same row are arranged at intervals along the width direction of the upper flexible needle belt, and the adjacent rows of needle teeth III and needle teeth IV are arranged at intervals along the length direction of the lower flexible needle belt.

[0024] Needle teeth I and III jointly exert a force F1 on the fiber strands, and the force F1 is the force that causes the fiber strands to shift horizontally to the left.

[0025] Needle teeth II and needle teeth IV jointly apply a force F2 to the fiber strands, and the force F2 is a force that causes the fiber strands to shift horizontally to the right.

[0026] As the preferred technical solution:

[0027] According to the fiber strand drawing device described above, when needle tooth I moves to the lowest position, needle tooth I is vertically downward, and the minimum distance between needle tooth I and the edge of the upper flexible needle belt gradually increases along the running direction of the upper flexible needle belt. Needle tooth III simultaneously moves to the highest position, needle tooth III is vertically upward, and the minimum distance between needle tooth III and the edge of the lower flexible needle belt gradually increases along the running direction of the lower flexible needle belt. Needle tooth I and needle tooth III cross each other and are staggered, one on the left and one on the right, imitating the shape of crossed fingers when two hands are clasped together.

[0028] When the needle-free section of the upper flexible needle belt moves to the bottom, the needle-free section of the lower flexible needle belt moves to the top synchronously;

[0029] When needle tooth II runs to the bottom, needle tooth II moves vertically downward, and the minimum distance between needle tooth II and the edge of the upper flexible needle belt gradually decreases along the running direction of the upper flexible needle belt. Needle tooth IV runs to the top synchronously, needle tooth IV moves vertically upward, and the minimum distance between needle tooth IV and the edge of the lower flexible needle belt gradually decreases along the running direction of the lower flexible needle belt. Needle tooth II and needle tooth IV cross each other, and are staggered on the left and right, imitating the shape of crossed fingers when hands are put together.

[0030] As described above, in a fiber strand drawing device, the spacing of the same row of needle teeth I or the same row of needle teeth II along the width direction of the upper flexible needle belt is 0.05-0.1 mm, the spacing of two adjacent rows of needle teeth I and needle teeth II along the length direction of the upper flexible needle belt is 1.1-5.6 mm, the spacing of the same row of needle teeth III or the same row of needle teeth IV along the width direction of the lower flexible needle belt is 0.05-0.1 mm, and the spacing of two adjacent rows of needle teeth III and needle teeth IV along the length direction of the lower flexible needle belt is 1.1-5.6 mm.

[0031] In the fiber strand drawing device as described above, the extension line of the intersection line between needle tooth I and the upper flexible needle belt, as well as the extension line of the intersection line between needle tooth II and the upper flexible needle belt, both form an angle of 15-20° with the edge line of the upper flexible needle belt, and the extension line of the intersection line between needle tooth III and the lower flexible needle belt, as well as the extension line of the intersection line between needle tooth IV and the lower flexible needle belt, both form an angle of 15-20° with the edge line of the lower flexible needle belt.

[0032] As described above, in a fiber strand drawing device, needle teeth I, needle teeth II, needle teeth III and needle teeth IV are all irregular right-angled fan-shaped plates, and the irregular right-angled fan is composed of two line segments and an arc, one end of the two line segments is connected, and the other end is respectively connected to the two ends of an arc, and the two line segments are perpendicular to each other; the length of needle teeth I and needle teeth II along the length direction of the upper flexible needle belt is 5.5-11.2 mm, and the length of needle teeth III and needle teeth IV along the length direction of the lower flexible needle belt is 5.5-11.2 mm; the tooth height of needle teeth I, needle teeth II, needle teeth III and needle teeth IV (i.e., the vertical distance between the bottom end of the needle teeth and the top end of the needle teeth) is 3-5 mm, and the tooth thickness is 0.01-0.02 mm.

[0033] In the fiber strip drawing device as described above, the running speed of the upper flexible needle belt is 3.7-7 m / min, and the running speed of the lower flexible needle belt is the same as that of the upper flexible needle belt.

[0034] The fiber strand drawing device as described above further comprises an upper transmission wheel, an upper tensioning wheel, an upper positioning wheel, a lower transmission wheel, a lower tensioning wheel and a lower positioning wheel located between the front roller and the middle roller;

[0035] The upper transmission wheel and the upper tensioning wheel are arranged at intervals in the front-to-back direction, the upper positioning wheel is located below both the upper transmission wheel and the upper tensioning wheel, and the upper flexible needle belt is simultaneously sleeved on the upper transmission wheel, the upper tensioning wheel and the upper positioning wheel;

[0036] The lower positioning wheel is located below the upper positioning wheel, the lower transmission wheel and the lower tensioning wheel are arranged at intervals in the front-to-back direction, the lower positioning wheel is located above the lower transmission wheel and the lower tensioning wheel at the same time, and the lower flexible needle belt is simultaneously sleeved on the lower positioning wheel, the lower transmission wheel and the lower tensioning wheel.

[0037] The fiber strand drawing device as described above further includes an upper cleaning roller and a lower cleaning roller; the upper cleaning roller is located above the upper transmission wheel and the upper tensioning wheel, and the lower cleaning roller is located below the lower transmission wheel and the lower tensioning wheel.

[0038] The fiber strand drawing device as described above also includes an upper combing needle box with no sealing surface at the bottom and a lower combing needle box with no sealing surface at the top; the upper cleaning roller, upper transmission wheel, upper tensioning wheel and upper positioning wheel are all located in the upper combing needle box; the lower positioning wheel, lower transmission wheel, lower tensioning wheel and lower cleaning roller are all located in the lower combing needle box.

[0039] In the fiber sliver drawing device as described above, the linear speed of the middle roller is 3-6 m / min, and the ratio of the linear speed of the front roller to the linear speed of the middle roller is 3-8 times.

[0040] Beneficial effects:

[0041] (1) The present invention controls the roller pressure to be relatively small, which can reduce the damage and breakage of the fibers caused by the roller pressure, and also reduces the friction of the fibers on the drafting components, especially the top rollers, thereby extending the service life of the drafting components.

[0042] (2) In the process of the fiber whiskers running in the front-back direction, the present invention applies force F1 and force F2 to the fiber whiskers at fixed positions on the running path of the fiber whiskers at intervals, so that the fibers in different length segments of the fiber whiskers produce lateral transfers in different directions during stretching, and the fibers are entangled with each other, thereby increasing the internal friction field of the fiber whiskers (i.e., the interaction between fibers) during stretching. This can well supplement the problem of insufficient stretching force caused by low roller pressure, increase the total friction boundary strength during stretching, thereby reducing fiber damage while avoiding accidental stretching and poor stretching, and making the yarn dryer and stronger.

[0043] (3) The fibers in the special fiber strips made by the present invention have sufficient bonding force, thereby solving the problem of insufficient strength of special fibers such as carbon fiber in forming strips, and can effectively improve the quality of the yarn spun therefrom, such as the evenness, so that it is not easy to break in subsequent applications and produces less accidental stretching. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 Schematic diagram of a fiber strand drawing device according to the present invention;

[0045] Figure 2 Schematic diagram of the needle teeth matching of the upper and lower flexible needle belts of the present invention;

[0046] Figure 3 This is a schematic diagram of the arrangement of the needle teeth of the upper flexible needle belt of the present invention;

[0047] Figure 4 Schematic diagram of needle teeth I and needle teeth II of the flexible needle belt of the present invention;

[0048] Figure 5 Schematic diagram of the arrangement and spacing of needle teeth of the present invention; in the figure, a represents the length of the needle teeth along the forward direction of the flexible needle belt, b represents the spacing between adjacent needle teeth along the forward direction of the flexible needle belt, and c represents the tooth length of the needle teeth;

[0049] Figure 6 Schematic diagram of the principle of the fiber strand drawing method of the present invention;

[0050] In the figure, 1-front roller, 2-middle roller, 3-upper combing needle box, 4-lower combing needle box, 5-upper flexible needle belt, 6-lower flexible needle belt, 7-needle tooth I, 8-needle tooth II, 9-needle tooth III, 10-needle tooth IV, 11-upper transmission wheel, 12-upper tensioning wheel, 13-upper positioning wheel, 14-upper cleaning roller, 15-lower transmission wheel, 16-lower tensioning wheel, 17-lower positioning wheel, 18-lower cleaning roller, 19-fiber strip. DETAILED DESCRIPTION

[0051] Below in conjunction with specific embodiment, further set forth the present invention.Should be understood that these embodiments are only used to illustrate the present invention and are not used in limiting the scope of the present invention.In addition, should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall equally within the scope limited by the appended claims of the application.

[0052] In order to ensure that the properties of the materials used in each embodiment and comparative example are fully disclosed, the manufacturers and brands of the materials are indicated. Products of other manufacturers and brands that meet the requirements of the present invention are also feasible.

[0053] The testing methods for the relevant performance indicators of the following embodiments and comparative examples are as follows:

[0054] Strip unevenness: The fiber strips after leaving the front roller nip in each embodiment are used as samples, and then the samples are measured according to the capacitance method of GB / T3292.1-2008.

[0055] Fiber damage rate: The fiber strips after leaving the front roller nip in each embodiment are used as samples. The length distribution of the fibers in the samples and the fiber strips before drawing is measured using the GB19617-2007 standard. Short fibers are fibers with a length of less than 15 mm. The fiber damage rate is then calculated based on the measurement results. The calculation formula is as follows:

[0056] .

[0057] Example 1

[0058] A fiber strand drawing device, such as Figures 1 to 5 As shown, it includes a front roller 1 and a middle roller 2 arranged in a front-to-back direction at intervals, an upper flexible needle belt 5 and a lower flexible needle belt 6 located between the front roller 1 and the middle roller 2, an upper cleaning roller 14, a lower cleaning roller 18, an upper combing needle box 3 without a sealing surface at the bottom, a lower combing needle box 4 without a sealing surface at the top, an upper transmission wheel 11, an upper tensioning wheel 12, an upper positioning wheel 13, a lower transmission wheel 15, a lower tensioning wheel 16 and a lower positioning wheel 17;

[0059] The pressure of the front roller 1 is 80-250N, and the pressure of the middle roller 2 is 150-300N;

[0060] The linear speed of the middle roller 2 is 3-6 m / min, and the ratio of the linear speed of the front roller 1 to the linear speed of the middle roller 2 is 3-8;

[0061] The upper cleaning roller 14, the upper transmission wheel 11, the upper tensioning wheel 12 and the upper positioning wheel 13 are all located in the upper combing needle box 3; the lower positioning wheel 17, the lower transmission wheel 15, the lower tensioning wheel 16 and the lower cleaning roller 18 are all located in the lower combing needle box 4;

[0062] The upper transmission wheel 11 and the upper tensioning wheel 12 are arranged at intervals in the front-to-back direction, and the upper positioning wheel 13 is located below both the upper transmission wheel 11 and the upper tensioning wheel 12;

[0063] The lower positioning wheel 17 is located below the upper positioning wheel 13, and the lower transmission wheel 15 and the lower tensioning wheel 16 are arranged at intervals in the front-to-back direction. The lower positioning wheel 17 is located above the lower transmission wheel 15 and the lower tensioning wheel 16.

[0064] The upper cleaning roller 14 is located above the upper transmission wheel 11 and the upper tensioning wheel 12, and the lower cleaning roller 18 is located below the lower transmission wheel 15 and the lower tensioning wheel 16.

[0065] like Figures 1 to 3 As shown, the upper flexible needle belt 5 is provided with multiple rows of needle teeth I 7 and multiple rows of needle teeth II 8;

[0066] The needle teeth I 7 in the same row or the needle teeth II 8 in the same row are arranged at intervals along the width direction of the upper flexible needle belt 5. The spacing between the needle teeth I 7 in the same row or the needle teeth II 8 in the same row along the width direction of the upper flexible needle belt 5 is 0.05-0.1 mm.

[0067] Two adjacent rows of needle teeth I 7 and needle teeth II 8 are alternately arranged along the length direction of the upper flexible needle belt 5, and the spacing between the two adjacent rows of needle teeth I 7 and needle teeth II 8 along the length direction of the upper flexible needle belt 5 is 1.1-5.6 mm;

[0068] The extended line of the intersection of the needle tooth I 7 and the upper flexible needle belt 5 and the extended line of the intersection of the needle tooth II 8 and the upper flexible needle belt 5 both form an angle of 15-20 degrees with the edge line of the upper flexible needle belt 5;

[0069] The length of the needle teeth I 7 and the needle teeth II 8 along the length direction of the upper flexible needle belt 5 is 5.5-11.2 mm;

[0070] The upper flexible needle belt 5 is simultaneously sleeved on the upper transmission wheel 11, the upper tensioning wheel 12 and the upper positioning wheel 13; the upper flexible needle belt 5 runs in the counterclockwise direction, and the running speed of the upper flexible needle belt 5 is 3.7-7m / min;

[0071] The lower flexible needle belt 6 is provided with multiple rows of needle teeth III 9 and multiple rows of needle teeth IV 10;

[0072] The needle teeth III 9 in the same row or the needle teeth IV 10 in the same row are spaced apart along the width direction of the upper flexible needle belt 5, and the spacing between the needle teeth III 9 in the same row or the needle teeth IV 10 in the same row along the width direction of the lower flexible needle belt 6 is 0.05-0.1 mm;

[0073] Two adjacent rows of needle teeth III 9 and needle teeth IV 10 are spaced apart along the length direction of the lower flexible needle belt 6, and the spacing between the two adjacent rows of needle teeth III 9 and needle teeth IV 10 along the length direction of the lower flexible needle belt 6 is 1.1-5.6 mm;

[0074] The extended line of the intersection of the needle tooth III 9 and the lower flexible needle belt 6 and the extended line of the intersection of the needle tooth IV 10 and the lower flexible needle belt 6 both form an angle of 15-20 degrees with the edge line of the lower flexible needle belt 6;

[0075] The length of the needle teeth III 9 and the needle teeth IV 10 along the length direction of the lower flexible needle belt 6 is 5.5-11.2 mm;

[0076] The lower flexible needle belt 6 is simultaneously sleeved on the lower positioning wheel 17, the lower transmission wheel 15 and the lower tensioning wheel 16;

[0077] The lower flexible needle belt 6 runs in a clockwise direction, and the running speed of the lower flexible needle belt 6 is the same as the running speed of the upper flexible needle belt 5;

[0078] Needle teeth I 7, needle teeth II 8, needle teeth III 9 and needle teeth IV 10 are all irregular right-angled sector plates. The irregular right-angled sector is composed of two line segments and an arc. One end of the two line segments is connected, and the other end is connected to the two ends of an arc respectively. The two line segments are perpendicular to each other.

[0079] like Figure 2 、 Figure 4 、 Figure 5 As shown, the tooth height of needle teeth I 7, needle teeth II 8, needle teeth III 9 and needle teeth IV 10 is 3-5 mm, and the tooth thickness is 0.01-0.02 mm;

[0080] When the needle tooth I 7 runs to the bottom, the needle tooth I 7 is vertically downward, and the minimum distance between the needle tooth I 7 and the edge of the upper flexible needle belt 5 gradually increases along the running direction of the upper flexible needle belt 5. The needle tooth III 9 runs to the top synchronously, the needle tooth III 9 is vertically upward, and the minimum distance between the needle tooth III 9 and the edge of the lower flexible needle belt 6 gradually increases along the running direction of the lower flexible needle belt 6. The needle tooth I 7 and the needle tooth III 9 cross each other.

[0081] like Figure 1 、 Figure 2 、 Figure 6 As shown, the needle teeth I 7 and the needle teeth III 9 jointly exert a force F1 on the fiber strand 19, and the fiber strand 19 moves horizontally to the left under the action of the force F1;

[0082] When the needle-free section of the upper flexible needle belt 5 moves to the bottom, the needle-free section of the lower flexible needle belt 6 moves to the top synchronously;

[0083] When the needle tooth II 8 runs to the bottom, the needle tooth II 8 is vertically downward, and the minimum distance between the needle tooth II 8 and the edge of the upper flexible needle belt 5 gradually decreases along the running direction of the upper flexible needle belt 5. The needle tooth IV 10 runs to the top synchronously, the needle tooth IV 10 is vertically upward, and the minimum distance between the needle tooth IV 10 and the edge of the lower flexible needle belt 6 gradually decreases along the running direction of the lower flexible needle belt 6. The needle tooth II 8 and the needle tooth IV 10 cross each other.

[0084] The needle teeth II 8 and the needle teeth IV 10 jointly apply a force F2 to the fiber strand 19, and the fiber strand 19 is horizontally transferred to the right under the action of the force F2.

[0085] Comparative Example 1

[0086] A fiber strand drawing device is basically the same as embodiment 1, except that it does not have an upper flexible needle belt and a lower flexible needle belt.

[0087] Comparative Example 2

[0088] A fiber strand drawing device is basically the same as embodiment 1, except that it does not have an upper flexible needle belt.

[0089] Comparative Example 3

[0090] A fiber strand drawing device is basically the same as embodiment 1, except that: there is no needle tooth I in the upper flexible needle belt and no needle tooth III in the lower flexible needle belt.

[0091] Example 2

[0092] A fiber whisker drawing method, wherein, while the fiber whisker (the fibers in the fiber whisker are industrial polyester staple fibers, manufactured by Jiangsu Hengli Chemical Fiber Co., Ltd., with a specification of 1.67 dtex and a length L of 51 mm) is running horizontally in a forward and backward direction, the drawing device of Example 1 is used at a fixed position on the running path of the fiber whisker to perform a periodic and repeated operation of the fiber whisker in the order of "applying force F1→stop applying force→applying force F2→stop applying force"; wherein:

[0093] The number of fibers in the fiber strands is 8, and the weight of a single fiber is 18g / 5m;

[0094] The pressure of the front roller is 250N, the pressure of the middle roller is 300N, the linear speed of the middle roller is 6m / min, the ratio of the linear speed of the front roller to the linear speed of the middle roller is 5, and the running speed of the upper flexible needle belt is 6.7m / min;

[0095] Each time the force F1 is applied, the duration is 0.5s; each time the force F2 is applied, the duration is 0.5s; each time the force is stopped, the duration is 0.1s;

[0096] Each time the force F1 is applied, the fiber strands move 2 mm horizontally to the left; each time the force F2 is applied, the fiber strands move 2 mm horizontally to the right;

[0097] Applying force F1 or force F2 to the fiber strands means simultaneously acupuncturing the upper and lower surfaces of the fiber strands, with a needling depth of 1.6 mm.

[0098] The parameters of the draw frame used are set as follows:

[0099] The distance between the front roller jaws and the middle roller jaws is 9 mm greater than the length L of the fibers in the fiber strands;

[0100] The horizontal distance between the fixed position and the jaws of the middle roller is 4 mm smaller than the length L of the fibers in the fiber sliver;

[0101] The spacing of the needle teeth I in the same row along the width direction of the upper flexible needle belt is 0.05 mm, and the spacing of the needle teeth II in the same row along the width direction of the upper flexible needle belt is 0.05 mm;

[0102] The spacing between two adjacent rows of needle teeth I and needle teeth II along the length direction of the upper flexible needle belt is 1.1 mm;

[0103] The length of needle teeth I and II along the length direction of the upper flexible needle belt is 5.5 mm;

[0104] The extended lines of the intersections of the needle teeth I and the upper flexible needle belt and the extended lines of the intersections of the needle teeth II and the upper flexible needle belt both form an angle of 20° with the edge line of the upper flexible needle belt;

[0105] The spacing between the needle teeth III in the same row along the width direction of the lower flexible needle belt is 0.05 mm, and the spacing between the needle teeth IV in the same row along the width direction of the lower flexible needle belt is 0.05 mm;

[0106] The spacing between two adjacent rows of needle teeth III and needle teeth IV along the length direction of the lower flexible needle belt is 1.1 mm;

[0107] The length of needle teeth III and needle teeth IV along the length direction of the lower flexible needle belt is 5.5 mm;

[0108] The extended lines of the intersection of the needle tooth III and the lower flexible needle belt and the extended lines of the intersection of the needle tooth IV and the lower flexible needle belt both form an angle of 20 degrees with the edge line of the lower flexible needle belt;

[0109] The tooth lengths of needle teeth I, II, III, and IV are all 5.9 mm;

[0110] The tooth height of needle teeth I, II, III and IV is 3 mm, and the tooth thickness is 0.01 mm.

[0111] The mass of the fiber sliver after leaving the front roller nip is 15g / 5m, the sliver unevenness rate is 8%, and the fiber damage rate is 1% compared with the fiber sliver before drawing.

[0112] Example 3

[0113] A fiber whisker drawing method, wherein, while the fiber whisker (the fibers in the fiber whisker are carbon fibers, manufactured by Zhongfu Shenying Carbon Fiber Co., Ltd., with a brand name of SYT45 and a length of 51 mm) is running horizontally in a forward and backward direction, the drawing device of Example 1 is used at a fixed position on the running path of the fiber whisker to periodically repeat the operation of "applying a force F1 → stopping applying the force → applying a force F2 → stopping applying the force" on the fiber whisker; wherein:

[0114] The number of fibers in the fiber strands is 6, and the weight of a single fiber is 16g / 5m;

[0115] The pressure of the front roller is 80N, the pressure of the middle roller is 150N, the linear speed of the middle roller is 3m / min, the ratio of the linear speed of the front roller to the linear speed of the middle roller is 8, and the running speed of the upper flexible needle belt is 3.7m / min;

[0116] Each time the force F1 is applied, the duration is 1 second; each time the force F2 is applied, the duration is 1 second; each time the force is stopped, the duration is 0.5 seconds;

[0117] Each time the force F1 is applied, the fiber strands move horizontally 3 mm to the left; each time the force F2 is applied, the fiber strands move horizontally 3 mm to the right;

[0118] Applying force F1 or force F2 to the fiber strands means simultaneously acupuncturing the upper and lower surfaces of the fiber strands, with a depth of 2 mm.

[0119] The parameters of the draw frame used are set as follows:

[0120] The distance between the front roller jaws and the middle roller jaws is 12 mm greater than the length L of the fibers in the fiber sliver;

[0121] The horizontal distance between the fixed position and the middle roller jaws is 3 mm smaller than the length L of the fibers in the fiber sliver;

[0122] The spacing between the needle teeth I in the same row along the width direction of the upper flexible needle belt is 0.1 mm, and the spacing between the needle teeth II in the same row along the width direction of the upper flexible needle belt is 0.1 mm;

[0123] The spacing between two adjacent rows of needle teeth I and needle teeth II along the length direction of the upper flexible needle belt is 5.6 mm;

[0124] The length of needle teeth I and II along the length direction of the upper flexible needle belt is 11.2 mm;

[0125] The extended lines of the intersection of the needle tooth I and the upper flexible needle belt and the extended lines of the intersection of the needle tooth II and the upper flexible needle belt both form an angle of 15 degrees with the edge line of the upper flexible needle belt;

[0126] The spacing between the needle teeth III in the same row along the width direction of the lower flexible needle belt is 0.1 mm, and the spacing between the needle teeth IV in the same row along the width direction of the lower flexible needle belt is 0.1 mm;

[0127] The spacing between two adjacent rows of needle teeth III and needle teeth IV along the length direction of the lower flexible needle belt is 5.6 mm;

[0128] The length of needle teeth III and IV along the length direction of the lower flexible needle belt is 11.2 mm;

[0129] The extended lines of the intersection of the needle tooth III and the lower flexible needle belt and the extended lines of the intersection of the needle tooth IV and the lower flexible needle belt both form an angle of 15 degrees with the edge line of the lower flexible needle belt;

[0130] The tooth lengths of needle teeth I, II, III, and IV are all 11.6 mm;

[0131] The tooth height of needle teeth I, II, III and IV is 5 mm, and the tooth thickness is 0.02 mm.

[0132] The mass of the fiber sliver after leaving the front roller nip is 13.5g / 5m, the sliver unevenness is 12%, and the fiber damage rate is 10% compared with the fiber sliver before drawing.

[0133] Comparative Example 4

[0134] A fiber strand drawing device is basically the same as that of Example 3, except that the drawing device of Comparative Example 1 is used.

[0135] The unevenness of the fiber sliver after leaving the front roller nip is 21%.

[0136] By comparing Example 3 with Comparative Example 4, it can be seen that the unevenness of the fiber strands after leaving the front roller jaws in Comparative Example 4 is poor. This is because in Example 3, the forces F1 and F2 can be applied alternately to the fiber strands, so that the fibers in different length segments of the fiber strands produce lateral transfers in different directions during stretching, and the fibers are entangled with each other, thereby increasing the internal friction field of the fiber strands during stretching, which can well supplement the problems such as insufficient stretching force caused by the low roller pressure, and increase the total friction boundary strength during stretching, thereby reducing fiber damage while avoiding accidental stretching and poor stretching, making the yarn strands better and improving the unevenness. However, the fibers in Comparative Example 4 cannot be subjected to the effects of the forces F1 and F2 during the drawing process, so that the unevenness of the fiber strands after leaving the front roller jaws is poor.

[0137] Comparative Example 5

[0138] A fiber strand drawing device is basically the same as that of Example 3, except that the drawing device of Comparative Example 2 is used.

[0139] The unevenness of the fiber sliver after leaving the front roller nip is 17%.

[0140] By comparing Example 3 with Comparative Example 5, it can be seen that the unevenness of the fiber strands after leaving the front roller jaws in Comparative Example 5 is poor. This is because the fibers in Comparative Example 5 are only affected by the needle teeth of the lower flexible needle belt during the drawing process, so that the number of fibers affected by the force is small, resulting in insufficient internal friction field of the fiber strands during drawing, and the total friction boundary strength during drawing cannot be increased, resulting in a small degree of improvement in the uneven drawing, which ultimately leads to a decrease in the unevenness of the fiber strands after leaving the front roller jaws.

[0141] Comparative Example 6

[0142] A fiber strand drawing device is basically the same as that in Example 3, except that the fiber strand drawing device of Comparative Example 3 is used.

[0143] The unevenness of the fiber sliver after leaving the front roller nip is 16.5%.

[0144] By comparing Example 3 with Comparative Example 6, it can be seen that the unevenness of the fiber strands after leaving the front roller jaws in Comparative Example 6 is poor. This is because the fibers in Comparative Example 6 are only subjected to forces in one direction during the drawing process, so that the internal friction field of the fibers is not enhanced sufficiently, and the degree of improvement in uneven drafting is small, which ultimately leads to a decrease in the unevenness of the fiber strands after leaving the front roller jaws.

[0145] Example 4

[0146] A fiber whisker drawing method, wherein, while the fiber whisker (the fiber in the fiber whisker is phenolic fiber, manufactured by Gunei Chemical Co., Ltd. of Japan, brand KF0730, and has a length L of 55 mm) is running horizontally in a forward and backward direction, the drawing device of Example 1 is used at a fixed position on the running path of the fiber whisker to perform a periodic and repeated operation of "applying force F1 → stopping applying force → applying force F2 → stopping applying force" on the fiber whisker; wherein:

[0147] The number of fibers in the fiber strands is 6, and the weight of a single fiber is 16.5g / 5m;

[0148] The pressure of the front roller is 150N, the pressure of the middle roller is 200N, the linear speed of the middle roller is 4m / min, the ratio of the linear speed of the front roller to the linear speed of the middle roller is 6, and the running speed of the upper flexible needle belt is 4.65m / min;

[0149] Each time the force F1 is applied, the duration is 0.8s; each time the force F2 is applied, the duration is 0.8s; each time the force is stopped, the duration is 0.4s;

[0150] Each time the force F1 is applied, the fiber strands move horizontally 2.5 mm to the left; each time the force F2 is applied, the fiber strands move horizontally 2.5 mm to the right;

[0151] Applying force F1 or force F2 to the fiber strands means simultaneously acupuncturing the upper and lower surfaces of the fiber strands, with a needling depth of 1.5 mm.

[0152] The parameters of the draw frame used are set as follows:

[0153] The distance between the front roller jaws and the middle roller jaws is 10 mm greater than the length L of the fibers in the fiber sliver;

[0154] The horizontal distance between the fixed position and the middle roller jaws is 5 mm less than the length L of the fibers in the fiber sliver;

[0155] The spacing between the needle teeth I in the same row along the width direction of the upper flexible needle belt is 0.08 mm, and the spacing between the needle teeth II in the same row along the width direction of the upper flexible needle belt is 0.08 mm;

[0156] The spacing between two adjacent rows of needle teeth I and needle teeth II along the length direction of the upper flexible needle belt is 4.4 mm;

[0157] The length of needle teeth I and II along the length direction of the upper flexible needle belt is 8.7 mm;

[0158] The extended lines of the intersections of the needle teeth I and the upper flexible needle belt and the extended lines of the intersections of the needle teeth II and the upper flexible needle belt both form an angle of 16° with the edge line of the upper flexible needle belt;

[0159] The spacing between the needle teeth III in the same row along the width direction of the lower flexible needle belt is 0.08 mm, and the spacing between the needle teeth IV in the same row along the width direction of the lower flexible needle belt is 0.08 mm;

[0160] The spacing between two adjacent rows of needle teeth III and needle teeth IV along the length direction of the lower flexible needle belt is 4.4 mm;

[0161] The length of needle teeth III and IV along the length direction of the lower flexible needle belt is 8.7 mm;

[0162] The extended lines of the intersection of the needle tooth III and the lower flexible needle belt and the extended lines of the intersection of the needle tooth IV and the lower flexible needle belt both form an angle of 16 degrees with the edge line of the lower flexible needle belt;

[0163] The tooth lengths of needle teeth I, II, III, and IV are all 9.1 mm;

[0164] The tooth height of needle teeth I, II, III and IV is 4 mm, and the tooth thickness is 0.02 mm.

[0165] The mass of the fiber sliver after leaving the front roller nip is 14g / 5m, the sliver unevenness is 10%, and the fiber damage rate is 8% compared with the fiber sliver before drawing.

[0166] Example 5

[0167] A fiber strand drawing method, comprising: while the fiber strand (the fibers in the fiber strand are kiwifruit fibers, with a length L of 35 mm) is running horizontally in a front-to-rear direction, the fiber strand is subjected to a periodic, repeated operation of "applying a force F1 → stopping applying the force → applying a force F2 → stopping applying the force" at a fixed position on the running path of the fiber strand using the drawing device of Example 1; wherein:

[0168] The number of fibers in the fiber strands is 6, and the weight of a single fiber is 14g / 5m;

[0169] The pressure of the front roller is 120N, the pressure of the middle roller is 180N, the linear speed of the middle roller is 5m / min, the ratio of the linear speed of the front roller to the linear speed of the middle roller is 3, and the running speed of the upper flexible needle belt is 5.8m / min;

[0170] Each time the force F1 is applied, the duration is 0.6s; each time the force F2 is applied, the duration is 0.6s; each time the force is stopped, the duration is 0.2s;

[0171] Each time the force F1 is applied, the fiber strands move horizontally 2.5 mm to the left; each time the force F2 is applied, the fiber strands move horizontally 2.5 mm to the right;

[0172] Applying force F1 or force F2 to the fiber strands means simultaneously acupuncturing the upper and lower surfaces of the fiber strands, with a depth of 1 mm.

[0173] The parameters of the draw frame used are set as follows:

[0174] The distance between the front roller jaws and the middle roller jaws is 8 mm greater than the length L of the fibers in the fiber sliver;

[0175] The horizontal distance between the fixed position and the middle roller jaws is 3 mm smaller than the length L of the fibers in the fiber sliver;

[0176] The spacing of the needle teeth I in the same row along the width direction of the upper flexible needle belt is 0.06 mm, and the spacing of the needle teeth II in the same row along the width direction of the upper flexible needle belt is 0.06 mm;

[0177] The spacing between two adjacent rows of needle teeth I and II along the length of the upper flexible needle belt is 2.7 mm;

[0178] The length of needle teeth I and II along the length direction of the upper flexible needle belt is 8 mm;

[0179] The extended lines of the intersection of the needle tooth I and the upper flexible needle belt and the extended lines of the intersection of the needle tooth II and the upper flexible needle belt both form an angle of 18 degrees with the edge line of the upper flexible needle belt;

[0180] The spacing between the needle teeth III in the same row along the width direction of the lower flexible needle belt is 0.06 mm, and the spacing between the needle teeth IV in the same row along the width direction of the lower flexible needle belt is 0.06 mm;

[0181] The spacing between two adjacent rows of needle teeth III and IV along the length of the lower flexible needle belt is 2.7 mm;

[0182] The length of needle teeth III and needle teeth IV along the length direction of the lower flexible needle belt is 8 mm;

[0183] The extended lines of the intersection of the needle tooth III and the lower flexible needle belt and the extended lines of the intersection of the needle tooth IV and the lower flexible needle belt both form an angle of 18 degrees with the edge line of the lower flexible needle belt;

[0184] The tooth lengths of needle teeth I, II, III, and IV are all 8.4 mm;

[0185] The tooth height of needle teeth I, II, III and IV is 3.5 mm, and the tooth thickness is 0.01 mm.

[0186] The mass of the fiber sliver after leaving the front roller nip is 10g / 5m, the sliver unevenness rate is 8%, and the fiber damage rate is 8% compared with the fiber sliver before drawing.

[0187] Example 6

[0188] A fiber whisker drawing method, wherein, while the fiber whisker (the fibers in the fiber whisker are glass fibers, manufactured by Chongqing Sanlei Fiberglass Co., Ltd., with a brand name of ECR13-2400 and a length of 51 mm) is running horizontally in a forward and backward direction, the drawing device of Example 1 is used at a fixed position on the running path of the fiber whisker to perform a periodic and repeated operation of the fiber whisker in the order of "applying force F1 → stopping applying force → applying force F2 → stopping applying force"; wherein:

[0189] The number of fibers in the fiber strands is 8, and the weight of a single fiber is 18.5g / 5m;

[0190] The pressure of the front roller is 100N, the pressure of the middle roller is 160N, the linear speed of the middle roller is 6m / min, the ratio of the linear speed of the front roller to the linear speed of the middle roller is 4, and the running speed of the upper flexible needle belt is 7m / min;

[0191] Each time the force F1 is applied, the duration is 0.5s; each time the force F2 is applied, the duration is 0.5s; each time the force is stopped, the duration is 0.1s;

[0192] Each time the force F1 is applied, the fiber strands move horizontally 3 mm to the left; each time the force F2 is applied, the fiber strands move horizontally 3 mm to the right;

[0193] Applying force F1 or force F2 to the fiber strands means simultaneously acupuncturing the upper and lower surfaces of the fiber strands, with a needling depth of 1.8 mm.

[0194] The parameters of the draw frame used are set as follows:

[0195] The distance between the front roller jaws and the middle roller jaws is 11 mm greater than the length L of the fibers in the fiber sliver;

[0196] The horizontal distance between the fixed position and the jaws of the middle roller is 4 mm smaller than the length L of the fibers in the fiber sliver;

[0197] The spacing of the needle teeth I in the same row along the width direction of the upper flexible needle belt is 0.05 mm, and the spacing of the needle teeth II in the same row along the width direction of the upper flexible needle belt is 0.05 mm;

[0198] The spacing between two adjacent rows of needle teeth I and needle teeth II along the length direction of the upper flexible needle belt is 1.7 mm;

[0199] The length of needle teeth I and II along the length direction of the upper flexible needle belt is 8.5 mm;

[0200] The extended lines of the intersections of the needle teeth I and the upper flexible needle belt and the extended lines of the intersections of the needle teeth II and the upper flexible needle belt both form an angle of 20° with the edge line of the upper flexible needle belt;

[0201] The spacing between the needle teeth III in the same row along the width direction of the lower flexible needle belt is 0.05 mm, and the spacing between the needle teeth IV in the same row along the width direction of the lower flexible needle belt is 0.05 mm;

[0202] The spacing between two adjacent rows of needle teeth III and needle teeth IV along the length direction of the lower flexible needle belt is 1.7 mm;

[0203] The length of needle teeth III and needle teeth IV along the length direction of the lower flexible needle belt is 8.5 mm;

[0204] The extended lines of the intersection of the needle tooth III and the lower flexible needle belt and the extended lines of the intersection of the needle tooth IV and the lower flexible needle belt both form an angle of 20 degrees with the edge line of the lower flexible needle belt;

[0205] The tooth lengths of needle teeth I, II, III, and IV are all 8.8 mm;

[0206] The tooth height of needle teeth I, II, III and IV is 3 mm, and the tooth thickness is 0.01 mm.

[0207] The mass of the fiber sliver after leaving the front roller nip is 15g / 5m, the sliver unevenness is 11.5%, and the fiber damage rate is 10% compared with the fiber sliver before drawing.

Claims

1. A fiber strand drawing method, characterized in that: During the horizontal movement of the fiber strands in the forward and backward directions, the fiber strands are periodically and repeatedly operated in the order of "applying force F1 → stopping applying force → applying force F2 → stopping applying force" at a fixed position on the running path of the fiber strands; The fixed position is located between the front roller and the middle roller of the draw frame. The pressure of the front roller is 80-250N, the pressure of the middle roller is 150-300N, and the ratio of the linear speed of the front roller to the linear speed of the middle roller is 3-8; The front roller and the middle roller are arranged at intervals in the front-to-back direction, and an upper flexible needle belt and a lower flexible needle belt are provided between the two; The upper flexible needle belt runs in a counterclockwise direction, and the lower flexible needle belt runs in a clockwise direction; The upper flexible needle belt is provided with multiple rows of needle teeth I and multiple rows of needle teeth II. The needle teeth I in the same row or the needle teeth II in the same row are arranged at intervals along the width direction of the upper flexible needle belt, and the needle teeth I and needle teeth II in two adjacent rows are arranged alternately at intervals along the length direction of the upper flexible needle belt. The lower flexible needle belt is provided with multiple rows of needle teeth III and multiple rows of needle teeth IV. The needle teeth III in the same row or the needle teeth IV in the same row are arranged at intervals along the width direction of the upper flexible needle belt, and the adjacent rows of needle teeth III and needle teeth IV are arranged at intervals along the length direction of the lower flexible needle belt. Needle teeth I and III jointly exert a force F1 on the fiber strands, and the force F1 is the force that causes the fiber strands to shift horizontally to the left. Needle teeth II and IV jointly exert a force F2 on the fiber strands, and the force F2 is the force that causes the fiber strands to shift horizontally to the right. When the needle tooth I moves to the bottom, the needle tooth I is vertically downward, and the minimum distance between the needle tooth I and the edge of the upper flexible needle belt gradually increases along the running direction of the upper flexible needle belt. The needle tooth III moves to the top synchronously, and the needle tooth III is vertically upward. The minimum distance between the needle tooth III and the edge of the lower flexible needle belt gradually increases along the running direction of the lower flexible needle belt. The needle teeth I and the needle teeth III cross each other and are staggered in a left-right arrangement. When the needle-free section of the upper flexible needle belt moves to the bottom, the needle-free section of the lower flexible needle belt moves to the top synchronously; When the needle tooth II moves to the bottom, the needle tooth II moves vertically downward, and the minimum distance between the needle tooth II and the edge of the upper flexible needle belt gradually decreases along the running direction of the upper flexible needle belt. The needle tooth IV moves to the top synchronously, and the needle tooth IV moves vertically upward, and the minimum distance between the needle tooth IV and the edge of the lower flexible needle belt gradually decreases along the running direction of the lower flexible needle belt. The needle teeth II and the needle teeth IV cross each other and are staggered in a left-right arrangement. The spacing of the same row of needle teeth I or the same row of needle teeth II along the width direction of the upper flexible needle belt is 0.05-0.1mm, and the spacing of the two adjacent rows of needle teeth I and needle teeth II along the length direction of the upper flexible needle belt is 1.1-5.6mm. The spacing of the same row of needle teeth III or the same row of needle teeth IV along the width direction of the lower flexible needle belt is 0.05-0.1mm, and the spacing of the two adjacent rows of needle teeth III and needle teeth IV along the length direction of the lower flexible needle belt is 1.1-5.6mm; The extended lines of the intersections of the needle teeth I and the upper flexible needle belt, as well as the extended lines of the intersections of the needle teeth II and the upper flexible needle belt, are both at an angle of 15-20° to the edge of the upper flexible needle belt; the extended lines of the intersections of the needle teeth III and the lower flexible needle belt, as well as the extended lines of the intersections of the needle teeth IV and the lower flexible needle belt, are both at an angle of 15-20° to the edge of the lower flexible needle belt; Needle teeth I, II, III and IV are all irregular right-angled fan-shaped plates. The irregular right-angled fan is composed of two line segments and an arc. One end of the two line segments is connected, and the other end is connected to the two ends of an arc respectively. The two line segments are perpendicular to each other; the length of needle teeth I and needle teeth II along the length direction of the upper flexible needle belt is 5.5-11.2mm, and the length of needle teeth III and needle teeth IV along the length direction of the lower flexible needle belt is 5.5-11.2mm; the tooth height of needle teeth I, II, III and IV is 3-5mm.

2. A fiber strand drawing method according to claim 1, characterized in that: Each time the force F1 is applied, the duration is 0.5-1s; each time the force F2 is applied, the duration is 0.5-1s; and each time the force is stopped, the duration is 0.1-0.5s.

3. A fiber strand drawing method according to claim 1, characterized in that: Each time the force F1 is applied, the fiber strands are horizontally shifted 2-3 mm to the left. Each time the force F2 is applied, the fiber strands are horizontally shifted 2-3 mm to the right.

4. A fiber strand drawing method according to claim 1, characterized in that: The horizontal distance between the fixed position and the middle roller jaws is 3-5 mm smaller than the length L of the fibers in the fiber sliver.

5. A fiber strand drawing method according to claim 1, characterized in that: The distance between the front roller jaws and the middle roller jaws is 8-12 mm greater than the length L of the fibers in the fiber sliver.

6. A fiber strand drawing method according to claim 1, characterized in that: The linear speed of the middle roller is 3-6m / min.

7. A fiber strand drawing method according to claim 1, characterized in that: The fibers in the fiber strands are one or more of industrial polyester staple fibers, carbon fibers, phenolic fibers, caltrop fibers and glass fibers.

8. A fiber strand drawing method according to any one of claims 1 to 7, characterized in that: Applying the force F1 or the force F2 to the fiber strands means simultaneously needling the upper and lower surfaces of the fiber strands, with the needling depth being 1-2 mm.

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