A polyacrylonitrile-based carbon fiber precursor filament original station filament exchange method

Abstract

This invention relates to a method for changing polyacrylonitrile (PAC)-based carbon fiber precursor yarn at a specific workstation. When the PAC-based carbon fiber precursor yarn sequentially passes through a pre-oxidation furnace, a low-temperature carbonization furnace, and a high-temperature carbonization furnace for pre-oxidation, low-temperature carbonization, and high-temperature carbonization treatments: When changing yarn at the Nth workstation, the tail end of the first PAC-based carbon fiber precursor yarn bundle running at the Nth workstation is connected to the head end of the second PAC-based carbon fiber precursor yarn bundle to be replaced; the connection point is a joint. After the yarn change at the Nth workstation, after the joint on the yarn bundle running at the Nth workstation passes through the last pre-oxidation furnace and before entering the low-temperature carbonization furnace inlet, the joint is connected to the yarn bundle running at the Mth workstation, so that the joint can smoothly pass through the carbonization furnace with the help of the yarn bundle running at the Mth workstation. This invention increases the probability of the yarn bundle joint passing through the low-temperature and high-temperature carbonization furnaces, reduces yarn breakage and roller entanglement accidents, and improves production efficiency.

Description

Technical Field

[0001] This invention relates to the field of polyacrylonitrile-based carbon fiber technology, and in particular to a method for changing polyacrylonitrile-based carbon fiber precursor yarn at the original work site. Background Technology

[0002] In the production process of polyacrylonitrile-based carbon fiber, a certain weight of polyacrylonitrile-based carbon fiber precursor spools need to be placed on a yarn unwinding frame. The unwinding filament bundles undergo pre-oxidation, low-temperature carbonization, high-temperature carbonization, surface treatment, sizing, and winding processes to finally obtain a spooled carbon fiber product. Once the filament bundle is used up or the filament bundle has quality abnormalities, it needs to be connected with a new filament bundle (the connection between the old filament bundle and the new filament bundle is called a joint) so that production can continue.

[0003] Following the pre-oxidation process is the low-temperature carbonization stage, where the reaction is more vigorous. The pre-oxidized fiber transforms from a trapezoidal structure to a disordered graphite structure, resulting in significant changes in its microstructure and weight, making the splice extremely prone to breakage. If the splice breaks during subsequent carbonization, the fiber tension suddenly decreases, easily causing roller entanglement accidents in the oxidation section. Furthermore, personnel must open the furnace bars to re-splicing and separating the fibers, increasing their workload. In addition, opening the furnace bars can easily introduce air into the low-temperature carbonization furnace, disrupting the process atmosphere and leading to a decline in product quality. If the fiber splice remains unbroken and does not melt during subsequent carbonization, the continuity and stability of production can be guaranteed.

[0004] In addition, for large filament bundles, the pre-oxidation process involves greater tensile stress, resulting in a more intense pre-oxidation reaction and easier breakage of the joints. When running in the low-carbon furnace, the joints almost completely break, requiring continuous feeding and splitting of the filaments, which results in significant waste.

[0005] In summary, there is an urgent need for a method for in-situ yarn replacement of polyacrylonitrile-based carbon fiber precursors to increase the probability of the yarn bundle joints passing through the carbonization furnace (low-temperature carbonization furnace, high-temperature carbonization furnace), reduce yarn breakage and roller entanglement accidents, and improve production efficiency. Summary of the Invention

[0006] In view of this, the present invention provides a method for changing the yarn in the original position of polyacrylonitrile-based carbon fiber precursor, the main purpose of which is to increase the probability of the yarn bundle joint passing through the carbonization furnace (low temperature carbonization furnace, high temperature carbonization furnace), reduce yarn breakage and roller entanglement accidents, and improve production efficiency.

[0007] To achieve the above objectives, the present invention mainly provides the following technical solutions:

[0008] On one hand, embodiments of the present invention provide a method for changing polyacrylonitrile-based carbon fiber precursor yarn at the original work site, wherein, when the polyacrylonitrile-based carbon fiber precursor yarn is sequentially passed through a pre-oxidation furnace, a low-temperature carbonization furnace, and a high-temperature carbonization furnace for pre-oxidation treatment, low-temperature carbonization treatment, and high-temperature carbonization treatment:

[0009] When changing the yarn at the Nth station, the tail end of the first polyacrylonitrile-based carbon fiber precursor yarn bundle currently running at the Nth station is connected to the head end of the second polyacrylonitrile-based carbon fiber precursor yarn bundle to be replaced; wherein, the connection part is a joint.

[0010] After the wire is changed at the Nth station, when the connector on the wire bundle running at the Nth station passes through the last pre-oxidation furnace and before entering the inlet of the low-temperature carbonization furnace, the connector on the wire bundle running at the Nth station is connected to the wire bundle running at the Mth station, so that the connector can pass smoothly through the low-temperature carbonization furnace and the high-temperature carbonization furnace with the help of the wire bundle running at the Mth station.

[0011] It should be noted that "low-temperature carbonization treatment," "high-temperature carbonization treatment," "low-temperature carbonization furnace," and "high-temperature carbonization furnace" are well-known terms in this technical field. The conventional production process for polyacrylonitrile-based carbon fiber is as follows: the polyacrylonitrile-based carbon fiber precursor is passed sequentially through a pre-oxidation furnace, a low-temperature carbonization furnace, and a high-temperature carbonization furnace to undergo pre-oxidation treatment, low-temperature carbonization treatment, and high-temperature carbonization treatment.

[0012] Preferably, the Mth station is the station where the yarn needs to be changed; or the Mth station is the station where yarn winding begins and the finished yarn has not reached the set length.

[0013] Preferably, the interval between the Mth station and the Nth station must be such that the joint on the filament bundle running at the Nth station can be opened by the tension of the filament bundle itself; preferably, the Mth station is the station farthest from the Nth station that needs to change filaments; or the Mth station is the station farthest from the Nth station that has started to take in filaments and the finished filament has not yet reached the set length.

[0014] Preferably, if the fiber is 1K specification, the interval between the Mth and Nth workstations must ensure that the tension on the joint of the filament bundle running at the Nth workstation is 150-1000 CN; if the fiber is 3K specification, the interval between the Mth and Nth workstations must ensure that the tension on the joint of the filament bundle running at the Nth workstation is 300-1000 CN; if the fiber is 6K specification, the interval between the Mth and Nth workstations must ensure that the tension on the joint of the filament bundle running at the Nth workstation is 500-2000 CN; if the fiber... For a 12K fiber specification, the interval between the Mth and Nth workstations must ensure that the tension on the joint of the filament bundle running at the Nth workstation is 1000-5000 CN; for a 24K fiber specification, the interval between the Mth and Nth workstations must ensure that the tension on the joint of the filament bundle running at the Nth workstation is 2000-10000 CN; for a 48K fiber specification, the interval between the Mth and Nth workstations must ensure that the tension on the joint of the filament bundle running at the Nth workstation is 3000-20000 CN.

[0015] Preferably, if the distance between the Mth station and the Nth station is insufficient for the joints on the yarn bundle running at the Nth station to open due to the tension of the yarn bundle itself, then weft threads need to be added to prevent misalignment.

[0016] Preferably, the method for connecting the tail end of the first polyacrylonitrile-based carbon fiber precursor bundle currently operating at the Nth workstation to the head end of the second polyacrylonitrile-based carbon fiber precursor bundle to be replaced includes:

[0017] The tail end of the first polyacrylonitrile-based carbon fiber precursor bundle is braided into the second polyacrylonitrile-based carbon fiber precursor bundle to form the first braided section.

[0018] The head end of the second polyacrylonitrile-based carbon fiber precursor bundle is braided into the first polyacrylonitrile-based carbon fiber precursor bundle to form the second braided section.

[0019] There is a set length of unbraided portion between the first braided section and the second braided section.

[0020] Preferably, the connector includes a first braided portion and a second braided portion; and an unbraided portion between the first braided portion and the second braided portion;

[0021] Specifically, the unbraided portion of the connector located between the first braided section and the second braided section is braided onto the yarn bundle operating at the Mth workstation. Preferably, the yarn bundle operating at the Mth workstation is divided into two strands and braided with the two strands of yarn bundle on the unbraided portion.

[0022] Preferably, the length of the unbraided portion is 10-20cm.

[0023] Preferably, the first braiding section includes multiple sub-braiding sections, and the second braiding section includes multiple sub-braiding sections; preferably, the first braiding section includes 3-5 sub-braiding sections, and the second braiding section includes 3-5 sub-braiding sections; preferably, the length of the sub-braiding section is 3-5 cm.

[0024] Preferably, the spacing between the multiple sub-braided sections in the first braided section is 3-5 cm; and / or the spacing between the multiple sub-braided sections in the second braided section is 3-5 cm;

[0025] Preferably, when polyacrylonitrile-based carbon fiber precursors experience fiber breakage after pre-oxidation treatment, the broken fiber is woven into a fiber bundle at another workstation before entering the low-temperature carbonization furnace, so that the broken fiber can pass smoothly through the low-temperature carbonization furnace and the high-temperature carbonization furnace with the help of the fiber bundles running at other workstations.

[0026] Compared with the prior art, the in-situ yarn replacement method for polyacrylonitrile-based carbon fiber precursor of the present invention has at least the following beneficial effects:

[0027] This invention provides a method for changing polyacrylonitrile-based carbon fiber precursor at the same workstation. When the polyacrylonitrile-based carbon fiber precursor is sequentially passed through a pre-oxidation furnace, a low-temperature carbonization furnace, and a high-temperature carbonization furnace for pre-oxidation, low-temperature carbonization, and high-temperature carbonization treatments: When changing the precursor at the Nth workstation, the tail end of the first polyacrylonitrile-based carbon fiber precursor bundle currently running at the Nth workstation is connected to the head end of the second polyacrylonitrile-based carbon fiber precursor bundle to be replaced; wherein the connection point is a connector; after changing the precursor at the Nth workstation, when the connector on the precursor bundle running at the Nth workstation passes through the last pre-oxidation furnace and enters the low-temperature carbonization furnace inlet, the connector on the precursor bundle running at the Nth workstation is connected to the precursor bundle running at the Mth workstation, so that the connector can smoothly pass through the carbonization furnace with the help of the precursor bundle running at the Mth workstation. Here, by using the above method, the splice is attached to another station (the station furthest away) before entering the low-temperature carbonization furnace. This operation is called "double insurance." If the splice accidentally breaks in the low-temperature carbonization furnace, it can still pass smoothly through other stations, thus avoiding the sudden weakening of fiber tension and roll entanglement accidents caused by broken fibers. Broken fiber accidents require opening the furnace bars, re-splitting and separating the fibers, increasing the labor intensity of personnel. In addition, opening the furnace bars can easily introduce air into the low-temperature carbonization furnace, disrupting the process atmosphere and leading to a decline in product quality. The method of the present invention avoids these problems.

[0028] Furthermore, this embodiment of the invention provides a method for replacing polyacrylonitrile-based carbon fiber precursor at the same workstation. The method involves connecting the tail end of the first polyacrylonitrile-based carbon fiber precursor bundle currently operating at the Nth workstation to the head end of the second polyacrylonitrile-based carbon fiber precursor bundle to be replaced, as follows: The tail end of the first polyacrylonitrile-based carbon fiber precursor bundle is braided into the second polyacrylonitrile-based carbon fiber precursor bundle to form a first braided section; the head end of the second polyacrylonitrile-based carbon fiber precursor bundle is braided into the first polyacrylonitrile-based carbon fiber precursor bundle to form a second braided section; wherein a predetermined length of unbraided portion is left between the first braided section and the second braided section. Here, the joint includes the first braided section, the second braided section, and the unbraided portion located between the first braided section and the second braided section; here, the unbraided portion is used to braid the joint onto the precursor bundle at the Mth workstation. In addition, both the first braided section and the second braided section include multiple sub-braided sections, which makes the connection between the first polyacrylonitrile-based carbon fiber precursor bundle and the second polyacrylonitrile-based carbon fiber precursor bundle more robust due to the multiple stress points.

[0029] In addition, it should be noted that since the replacement of fibers at the original work station is an occasional event, if adhesive is applied to the fiber bundle joint, although the joint can pass through the carbonization furnace smoothly, due to the close spacing between fiber work stations, it is unavoidable that the adhesive will be contaminated on the fibers at adjacent work stations, interfering with the furnace atmosphere and the normal operation of the fibers.

[0030] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the tail end of the first polyacrylonitrile-based carbon fiber precursor bundle (old filament bundle) and the head end of the second polyacrylonitrile-based carbon fiber precursor bundle (i.e., new filament bundle, the bundle to be replaced) in an embodiment of the present invention; wherein, the circles in the figure are the parts that need to be braided, and the part between the two circles is the unbraided part.

[0032] Figure 2 This is a schematic diagram of the braiding of the tail end of the first polyacrylonitrile-based carbon fiber precursor bundle (old filament bundle) and the second polyacrylonitrile-based carbon fiber precursor bundle (i.e., new filament bundle, the bundle to be replaced) in an embodiment of the present invention.

[0033] Figure 3 This is a schematic diagram showing how, when changing the yarn at the Nth workstation, the tail end of the first polyacrylonitrile-based carbon fiber precursor yarn bundle currently running at the Nth workstation is connected (braided) to the head end of the second polyacrylonitrile-based carbon fiber precursor yarn bundle to be replaced.

[0034] Figure 4 This is a schematic diagram showing the splice on the filament bundle running at the Mth station after the filament bundle has been changed at the Nth station and before it enters the inlet of the low-temperature carbonization furnace after the filament bundle passes through the last pre-oxidation furnace. Detailed Implementation

[0035] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the specific embodiments, structures, features, and effects according to the present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments. In the following description, different "an embodiment" or "an embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0036] This invention primarily provides a method for in-situ yarn changing of polyacrylonitrile-based carbon fiber precursor, applicable to yarn changing of polyacrylonitrile-based carbon fiber precursor with two or more shafts. This method does not affect other normally operating yarn bundles, and the joint is loose, preventing overheating. Before the joint reaches the inlet of the low-temperature carbonization furnace, it is woven into another shaft at the in-situ yarn changing station, increasing the probability of the joint passing through the low-temperature and high-temperature carbonization furnaces. Practical experience has shown that this yarn changing method achieves a 95% success rate for the joint to pass through the low-temperature and high-temperature carbonization furnaces, reducing yarn breakage and roller entanglement accidents and improving production efficiency.

[0037] The main solutions of this invention are as follows:

[0038] This invention provides a method for in-situ fiber replacement of polyacrylonitrile-based carbon fiber precursor. Specifically, when the polyacrylonitrile-based carbon fiber precursor is sequentially passed through a pre-oxidation furnace, a low-temperature carbonization furnace, and a high-temperature carbonization furnace for pre-oxidation, low-temperature carbonization, and high-temperature carbonization treatments:

[0039] First, when changing the yarn at the Nth station, connect the tail end of the first polyacrylonitrile-based carbon fiber precursor yarn bundle currently running at the Nth station to the head end of the second polyacrylonitrile-based carbon fiber precursor yarn bundle to be replaced; the connection point is a joint.

[0040] It should be noted that any one of the workstations that performs wire changing is defined as the Nth workstation.

[0041] Better, such as Figures 1-3As shown, the connection method is as follows: First, the tail end of the old raw yarn bundle (first polyacrylonitrile-based carbon fiber raw yarn bundle 1) is woven into the new raw yarn bundle (second polyacrylonitrile-based carbon fiber raw yarn bundle 2) on the other side to form the first braided section; after an interval of 10-20cm, the head end of the new raw yarn bundle (second polyacrylonitrile-based carbon fiber raw yarn bundle 2) is woven into the old raw yarn bundle (first polyacrylonitrile-based carbon fiber raw yarn bundle 1) on the other side to form the second braided section; each braided section consists of 3-5 small sub-braided sections, the length of the sub-braided sections is between 3-5cm, and the interval between the sub-braided sections is 3-5cm, requiring the braid to be soft and loose.

[0042] Second, after the wire is changed at the Nth station, when the connector on the wire bundle running at the Nth station passes through the last pre-oxidation furnace and before entering the inlet of the low-temperature carbonization furnace: (e.g.) Figure 4 As shown, the connector 3 on the wire bundle running at the Nth station is connected to the wire bundle 4 running at the Mth station, so that the connector can pass smoothly through the low-temperature carbonization furnace and the high-temperature carbonization furnace with the help of the wire bundle running at the Mth station.

[0043] Preferably, the Mth station is the station where the yarn needs to be changed (because if the yarn needs to be changed, the original yarn on that shaft is usually almost finished or of poor quality and will eventually need to be cut; using that shaft will not affect the finished yarn being collected). Alternatively, the Mth station is the station where yarn collection has just begun (i.e., the station where yarn collection has started and the collected finished yarn has not yet reached the set length; the set length is less than 500 meters).

[0044] Preferably, the Mth workstation needs to meet the following condition: the distance between the Mth workstation and the Nth workstation must ensure that the joint can be unfolded by the tension of the yarn bundle itself. Otherwise, the joint is easily twisted and misaligned, affecting the yarn bundles of other workstations. Of course, if the Mth workstation and the Nth workstation are adjacent, the joint will not be easy to open due to the close distance. In this case, weft threads can be added to avoid misalignment, but the operation is inconvenient. The weft thread is added as follows: When adding the weft thread, first pass one end of the weft thread through the yarn bundle of the alternate workstation in sequence, and then pass the other end of the weft thread through the yarn bundle of the alternate workstation (one workstation away from the first added weft thread) in sequence. After the weft thread is added, slightly lift the weft thread to confirm whether each yarn bundle is inside the weft thread. If all yarn bundles are at the same horizontal position, it means that all yarn bundles are inside the weft thread. Tie the two ends of the weft thread together.

[0045] Therefore, the Mth station is preferably the station that needs to change wires that is furthest from the Nth station.

[0046] In summary, the method of the present invention is as follows: Assuming that multiple workstations (at least two workstations) need to change the wire at the original workstation, when changing the wire at a certain workstation first (the workstation where the wire change is performed is defined as the Nth workstation), the old and new wire bundles are first braided to form a joint; before the joint reaches the inlet of the low-temperature carbonization furnace, the unbraided portion of the joint located between the first braiding section and the second braiding section (the unbraided portion, see...) is... Figure 3 The portion circled in the diagram is braided onto the Mth station, which is the furthest from the original station and also requires a yarn change (it should be braided onto the furthest station possible, as the spacing between stations allows for self-separation by the tension of the yarn bundle itself without the need for weft yarns; if it is adjacent to the original station requiring yarn change, weft yarns are needed to prevent misalignment; additionally, during braiding, the portion of the yarn bundle to be braided on the Mth station is divided into two strands, and the unbraided portion on the joint is divided into new and old strands, resulting in four-strand braiding). This method is called "double insurance," which ensures that if the joint breaks accidentally in the low-temperature carbonization furnace, it can still pass smoothly through other stations. Since the carbon fibers prepared at the above stations also need to be removed and replaced, there is no issue of damaging the normally functioning yarn bundle. After the joint exits the high-temperature carbonization furnace, a yarn change is performed at the Mth station, at which point the Mth station is redefined as the Nth station, and the yarn change and braiding steps are repeated.

[0047] In addition, the above-mentioned method of the present invention can also be extended to the operation of breaking pre-oxidized wires to increase the probability of the broken pre-oxidized wire joints passing through low-temperature carbonization furnaces and high-temperature carbonization furnaces.

[0048] The present invention will be further illustrated below with specific embodiments and comparative examples:

[0049] In the following embodiments, the first polyacrylonitrile-based carbon fiber precursor bundle is referred to as the old filament bundle; and the second polyacrylonitrile-based carbon fiber precursor bundle is referred to as the new filament bundle.

[0050] Example 1

[0051] The entire production line operates on 1K polyacrylonitrile-based carbon fiber precursor, which sequentially passes through a pre-oxidation furnace, a low-temperature carbonization furnace, and a high-temperature carbonization furnace for pre-oxidation, low-temperature carbonization, and high-temperature carbonization treatments. The stations requiring fiber replacement are: #1, #2, #3, and #4. The fiber replacement and conveyor steps are as follows:

[0052] 1) Each shift consists of 4 people divided into 2 groups to carry out the work. Two people, A and B, are responsible for cutting the yarn bundle that needs to be replaced, wrapping the yarn tail around the swing arm of the yarn unwinding frame, and then turning the control switch of the yarn unwinding device at this station to the "OFF" state.

[0053] 2) Two people, C and D, loosen the nut of the spindle to be replaced (if the nut is tight, a large wrench can be used to loosen it), remove the paper tube of the wire bundle and set it aside, confirm the direction of the wire bundle exit (the wire exits from above the wire spool), and then put the new wire onto the corresponding spindle at the work station and tighten the fixing bolt.

[0054] 3) Two people, A and B, bind the old and new raw yarn ends at station #1 (at this time, station #1 is changing yarn, defined as the Nth station), and then turn the switch on the small control box of the yarn spindle to the "ON" position (at this time, the yarn bundle is under tension and easy to braid). Figure 1 and 2 As shown, the tail end of the old raw silk bundle at station #1 is woven into the new raw silk bundle on the other side to form the first braided section; at intervals of 10-20cm, the head end of the new raw silk bundle is woven into the old raw silk bundle on the other side to form the second braided section; each braided section consists of 3-5 small sub-braided sections, the length of the sub-braided sections is between 3-5cm, and the interval between the sub-braided sections is 3-5cm, requiring the braid to be soft and loose.

[0055] 4) After the joint of station 1 passes through the last pre-oxidation furnace and before it reaches the inlet of the low-temperature carbonization furnace, the fibers with a spacing of 10-20cm between the first braided part and the second braided part on the joint (i.e., the unbraided part on the joint) are braided onto station 4, which is the furthest away from it (at this time, station 4 is defined as the Mth station).

[0056] 5) After the joints from stations #1 and #4 exit the high-temperature carbonization furnace, change the yarn at station #2 (at this point, station #2 is defined as the Nth station). Repeat steps 1), 2), and 3) above for station #2. After the joint from station #2 passes through the last pre-oxidation furnace and reaches the inlet of the low-temperature carbonization furnace, braid the fibers (i.e., the unbraided portion of the joint) with a 10-20cm interval between the first and second braided portions on the joint from station #2 onto station #4, which is the furthest away (at this point, station #4 is defined as the Mth station).

[0057] 6) After the joints from stations #2 and #4 exit the high-temperature carbonization furnace, change the yarn at station #3 (at this time, station #3 is defined as the Nth station). Repeat steps 1), 2), and 3) above for station #3. After the joint from station #3 passes through the pre-oxidation furnace and reaches the inlet of the low-temperature carbonization furnace, braid the fibers (i.e., the unbraided part on the joint) that are 10-20cm apart between the first and second braided parts of the joint from station #3 onto station #1, which is the furthest away from it (at this time, station #1 is defined as the Mth station; at this time, station #1 has just finished taking in the yarn, and the finished yarn is far from reaching the specified length, so braiding it onto station #1 is the least loss-making approach).

[0058] 7) After the joints from stations #1 and #3 exit the high-temperature carbonization furnace, perform a fiber replacement at station #4 (station #4 is now defined as the Nth station). Repeat steps 1), 2), and 3) above for station #4. After the joint from station #4 passes through the last pre-oxidation furnace and reaches the inlet of the low-temperature carbonization furnace, braid the fibers (i.e., the unbraided portion of the joint) that are 10-20cm apart from the first and second braided portions of the joint from station #4 onto station #1, which is furthest away (station #1 is now defined as the Mth station).

[0059] 8) Once all the splices of the raw yarn from the four stations have been moved to the winding machine, cut off the splice parts and rewind them.

[0060] In addition, in the above steps, when the joint of the Nth station is braided onto the filament bundle of the Mth station, the joint opens under its own tension (150-1000CN).

[0061] In Example 1, the above steps ensured that all the raw yarns at the four workstations were successfully loaded onto the racks without any yarn breakage incidents.

[0062] Example 2

[0063] The entire production line operates on 3K polyacrylonitrile-based carbon fiber precursor, which sequentially passes through a pre-oxidation furnace and a carbonization furnace (low-temperature carbonization furnace and high-temperature carbonization furnace) for pre-oxidation and carbonization treatments (low-temperature carbonization and high-temperature carbonization). The stations requiring fiber replacement are: 1#, 10#, 11#, 12#, and 13#. The fiber replacement and conveyor steps are as follows:

[0064] 1) Each shift consists of 4 people divided into 2 groups to carry out the work. Two people, A and B, are responsible for cutting the yarn bundle that needs to be replaced, wrapping the yarn tail around the swing arm of the yarn unwinding frame, and then turning the control switch of the yarn unwinding device at this station to the "OFF" state.

[0065] 3) Two people, C and D, loosen the nut of the spindle to be replaced (if the nut is tight, a large wrench can be used to loosen it), remove the paper tube of the wire bundle and set it aside, confirm the direction of the wire bundle exit (the wire exits from above the wire spool), and then put the new wire onto the corresponding spindle at the work station and tighten the fixing bolt.

[0066] 3) Two people, A and B, bind the new and old raw silk ends at station #1 (at this time, station #1 is defined as the Nth station), and then turn the switch on the small control box of the silk spindle to the "ON" position (at this time, the silk bundle is under tension and easy to braid). Figure 2As shown, the tail end of the old raw silk bundle #1 is woven into the new raw silk bundle on the other side to form the first braided section; at intervals of 10-20cm, the head end of the new raw silk bundle is woven into the old raw silk bundle on the other side to form the second braided section; each braided section consists of 3-5 small sub-braided sections, the length of the sub-braided sections is between 3-5cm, and the interval between the sub-braided sections is 3-5cm, requiring the braid to be soft and loose.

[0067] 4) After the joint of station 1 passes through the last pre-oxidation furnace and reaches the inlet of the low-temperature carbonization furnace, the fibers with a spacing of 10-20cm between the first braided part and the second braided part on the joint of station 1 (i.e., the unbraided part on the joint) are braided onto station 13, which is the furthest away from it (at this time, station 13 is defined as the Mth station).

[0068] 5) After the joints at stations #1 and #13 exit the high-temperature carbonization furnace, change the yarn at station #10 (at this time, station #10 is defined as the Nth station). For station #10, repeat steps similar to 1), 2), and 3). After the joint at station #10 passes through the last pre-oxidation furnace and reaches the inlet of the low-temperature carbonization furnace, braid the fibers (i.e., the unbraided portion of the joint) with a 10-20cm interval between the first and second braided portions on the joint at station #10 onto the station farthest away, station #1 (at this time, station #1 is defined as the Mth station; because station #1 has just finished taking in yarn, the finished yarn is far from reaching the specified length, so braiding it onto station #1 is the least loss-inducing approach).

[0069] 6) After the connectors at stations #1 and #10 exit the high-temperature carbonization furnace, change the yarn at station #11 (at this time, station #11 is defined as the Nth station). Repeat steps similar to 1), 2), and 3) above for station #11. When the connector at station #11 reaches the inlet of the low-temperature carbonization furnace, braid the fibers (i.e., the unbraided portion of the connector) that are 10-20cm apart from the first and second braided portions on the connector at station #11 onto the station #1, which is furthest away from it. At this time, station #1 is defined as the Mth station.

[0070] 7) After the joints at stations #1 and #11 exit the high-temperature carbonization furnace, perform a yarn change at station #12 (at this time, station #12 is defined as the Nth station). For station #12, repeat steps similar to steps 1), 2), and 3) above. When the joint at station #12 reaches the inlet of the low-temperature carbonization furnace, braid the fibers (i.e., the unbraided portion of the joint) that are 10-20cm apart between the first and second braided sections of the joint at station #12 onto the station farthest away, station #1.

[0071] 8) After the joints at stations #1 and #12 exit the high-temperature carbonization furnace, perform a fiber replacement at station #13 (at this time, station #13 is defined as the Nth station). For station #13, repeat steps similar to 1), 2), and 3) above. When the joint at station #13 reaches the inlet of the low-temperature carbonization furnace, braid the fibers (i.e., the unbraided portion of the joint) that are 10-20cm apart from the first and second braided portions on the joint at station #13 onto the station farthest away.

[0072] 9) Once all the splices of the raw yarn from the above 5 stations have been run to the winding machine, cut off the splice parts and rewind them.

[0073] In addition, in the above steps, when the joint of the Nth station is braided onto the filament bundle of the Mth station, the joint opens under its own tension (300-1000CN).

[0074] After adopting the above steps in Example 2, all the raw yarns at the 5 workstations were successfully put on the rack, and no yarn breakage accidents occurred during the process.

[0075] Example 3

[0076] The entire production line operates on 6K polyacrylonitrile-based carbon fiber precursor, which sequentially passes through a pre-oxidation furnace and a carbonization furnace (low-temperature carbonization furnace and high-temperature carbonization furnace) for pre-oxidation and carbonization treatments (low-temperature carbonization and high-temperature carbonization). The stations requiring fiber replacement are: 1#, 2#, 3#, 4#, and 5#. The fiber replacement and conveyor steps are as follows:

[0077] 1) Each shift consists of 4 people divided into 2 groups to carry out the work. Two people, A and B, are responsible for cutting the yarn bundle that needs to be replaced, wrapping the yarn tail around the swing arm of the yarn unwinding frame, and then turning the control switch of the yarn unwinding device at this station to the "OFF" state.

[0078] 2) Two people, C and D, loosen the nut of the spindle to be replaced (if the nut is tight, a large wrench can be used to loosen it), remove the paper tube of the wire bundle and set it aside, confirm the direction of the wire bundle exit (the wire exits from above the wire spool), and then put the new wire onto the corresponding spindle at the work station and tighten the fixing bolt.

[0079] 3) Two people, A and B, bind the old and new raw silk ends at station #1 (at this time, station #1 is defined as the Nth station). Then, turn the switch on the small control box of the silk spindle to the "ON" position (at this time, the silk bundle is under tension and easy to braid). The tail end of the old raw silk bundle at station #1 is braided into the new raw silk bundle on the other side, forming the first braided section; at intervals of 10-20cm, the head end of the new raw silk bundle is braided into the old raw silk bundle on the other side, forming the second braided section; each braided section consists of 3-5 small sub-braided sections, each sub-braided section being 3-5cm long and spaced 3-5cm apart, requiring a soft and loose braid. Figure 2 As shown.

[0080] 4) After the No. 1 station joint passes through the last pre-oxidation furnace and reaches the inlet of the low-temperature carbonization furnace, the fibers with a spacing of 10-20cm between the first and second braided parts on the No. 1 station joint (i.e., the unbraided part on the joint) are braided onto the No. 5 station, which is the furthest away from it (at this time, the No. 5 station is defined as the Mth station).

[0081] 5) After the joints at stations #1 and #5 exit the high-temperature carbonization furnace, perform a fiber replacement at station #2 (station #2 is defined as the Nth station). For station #2, repeat steps similar to steps 1), 2), and 3) above. After the joint at station #2 passes through the last pre-oxidation furnace and reaches the inlet of the low-temperature carbonization furnace, braid the fibers (i.e., the unbraided portion of the joint) that are 10-20cm apart from the first and second braided portions of the joint at station #2 onto station #5, which is the furthest away (at this time, station #5 is defined as the Mth station).

[0082] 6) After the joints at stations #2 and #5 exit the high-temperature carbonization furnace, perform a wire replacement at station #3 (at this time, station #3 is defined as the Nth station). For station #3, repeat steps similar to 1), 2), and 3) above. After the joint passes through the last pre-oxidation furnace and reaches the inlet of the low-temperature carbonization furnace, braid the fibers (the unbraided portion of the joint) between the first and second braided sections of the joint at station #3, spaced 10-20cm apart, onto station #5, which is the furthest away from it.

[0083] 7) After the joints from stations #3 and #5 exit the high-temperature carbonization furnace, perform a fiber replacement at station #4 (at this time, station #3 is defined as the Nth station). For station #4, repeat steps 1), 2), and 3) similar to those above. When the joint reaches the inlet of the low-temperature carbonization furnace, braid the fibers (i.e., the unbraided portion of the joint) that are 10-20cm apart between the first and second braided sections of the joint from station #4 onto station #1, which is furthest away from it.

[0084] 8) After the joints at stations 1# and 4# exit the high-temperature carbonization furnace, change the yarn at station 5# (at this time, station 5# is defined as the Nth station). For station 5#, repeat steps 1), 2), and 3) above. After the joint passes through the last pre-oxidation furnace and reaches the inlet of the low-temperature carbonization furnace, braid the fibers (i.e., the unbraided part of the joint) between the first and second braided parts of the joint at station 5# onto the station 1#, which is furthest away from it.

[0085] 9) Once all the splices of the raw yarn from the 5 stations have been moved to the winding machine, cut off the splice parts and rewind them.

[0086] In addition, in the above steps, when the joint of the Nth station is braided onto the filament bundle of the Mth station, the joint opens under its own tension (500-2000CN).

[0087] In this embodiment, all five workstations successfully had their raw yarns loaded onto the racks without any yarn breakage incidents.

[0088] Example 4

[0089] The entire production line operates on 12K polyacrylonitrile-based carbon fiber precursor, which sequentially passes through a pre-oxidation furnace and a carbonization furnace (low-temperature carbonization furnace and high-temperature carbonization furnace) for pre-oxidation and carbonization treatments (low-temperature carbonization treatment and high-temperature carbonization treatment). The stations requiring fiber replacement are: #1 and #2. The fiber replacement and conveyor steps are as follows:

[0090] 1) Each shift consists of 4 people divided into 2 groups to carry out the work. Two people, A and B, are responsible for cutting the yarn bundle that needs to be replaced, wrapping the yarn tail around the swing arm of the yarn unwinding frame, and then turning the control switch of the yarn unwinding device at this station to the "OFF" state.

[0091] 2) Two people, C and D, loosen the nut of the spindle to be replaced (if the nut is tight, a large wrench can be used to loosen it), remove the paper tube of the wire bundle and set it aside, confirm the direction of the wire bundle exit (the wire exits from above the wire spool), and then put the new wire onto the corresponding spindle at the work station and tighten the fixing bolt.

[0092] 3) Two people, A and B, bind the old and new raw silk ends at station #1 (at this time, station #1 is defined as the Nth station). Then, turn the switch on the small control box of the silk spindle to the "ON" position (at this time, the silk bundle is under tension and easy to braid). The tail end of the old raw silk bundle at station #1 is braided into the new raw silk bundle on the other side, forming the first braided section; at intervals of 10-20cm, the head end of the new raw silk bundle is braided into the old raw silk bundle on the other side, forming the second braided section; each braided section consists of 3-5 small sub-braided sections, each sub-braided section being 3-5cm long and spaced 3-5cm apart, requiring a soft and loose braid. Figure 2 As shown.

[0093] 4) After the No. 1 station joint passes through the last pre-oxidation furnace and reaches the inlet of the low-temperature carbonization furnace, braid the fibers between the first and second braided parts of the No. 1 station joint at a interval of 10-20cm (i.e., the unbraided part on the joint) on the adjacent No. 2 station (since there are no other stations further away, it can only be braided on the adjacent station), and at the same time braid the weft threads of 10 stations to prevent the two from getting tangled together.

[0094] 5) After the joints at stations #1 and #2 exit the high-temperature carbonization furnace, change the yarn at station #2 (at this time, station #2 is defined as the Nth station), repeating steps similar to 1), 2), and 3) above. After the joint at station #2 passes through the last pre-oxidation furnace and reaches the inlet of the low-temperature carbonization furnace, weave the fibers (i.e., the unbraided portion on the joint) between the first and second braided sections of station #2, spaced 10-20cm apart, onto the adjacent station #1, while simultaneously weaving 10 weft threads to prevent them from tangling together.

[0095] 6) Once all the splices of the raw yarn at both workstations have been moved to the winding machine, cut off the splice parts and rewind.

[0096] In this embodiment, the raw yarns at both workstations were successfully loaded onto the racks without any yarn breakage incidents.

[0097] Comparative Example 1

[0098] The entire production line operates on 1K polyacrylonitrile-based carbon fiber precursor, which sequentially passes through a pre-oxidation furnace, a low-temperature carbonization furnace, and a high-temperature carbonization furnace for pre-oxidation, low-temperature carbonization, and high-temperature carbonization treatments. The stations requiring fiber replacement are: #1, #2, #3, and #4. The fiber replacement and conveyor steps are as follows:

[0099] 1) Each shift consists of 4 people divided into 2 groups to carry out the work. Two people, A and B, are responsible for cutting the yarn bundle that needs to be replaced, wrapping the yarn tail around the swing arm of the yarn unwinding frame, and then turning the control switch of the yarn unwinding device at this station to the "OFF" state.

[0100] 2) Two people, C and D, loosen the nut of the spindle to be replaced (if the nut is tight, a large wrench can be used to loosen it), remove the paper tube of the wire bundle and set it aside, confirm the direction of the wire bundle exit (the wire exits from above the wire spool), and then put the new wire onto the corresponding spindle at the work station and tighten the fixing bolt.

[0101] 3) Two people, A and B, bind the new and old raw silk threads at workstations #1, #2, #3, and #4, and then turn the switch on the small control box of the silk spindle to the "ON" position (at this time, the silk bundle is under tension, which facilitates weaving). Figure 1 and 2 As shown, the ends of the old raw silk bundles at stations 1#, 2#, 3#, and 4# are woven into the new raw silk bundles on the other side to form the first woven section; at intervals of 10-20cm, the ends of the new raw silk bundles are woven into the old raw silk bundles on the other side to form the second woven section; each woven section consists of 3-5 small sub-woven sections, the length of which is between 3-5cm, and the interval between the sub-woven sections is 3-5cm, requiring the woven section to be soft and loose.

[0102] 4) The connector enters the production unit and is then taken up by the winding machine. The connector part is cut off and the wire is rewound.

[0103] Table 1 shows the sequential passage of continuous polyacrylonitrile-based pre-oxidized fibers through a low-temperature carbonization furnace after the connection of Example 1 and Comparative Example 1.

[0104] Table 1

[0105] Equipment Name Example 1 Comparative Example 1 Low-temperature carbonization furnace All 4 passed Only 2 passed

[0106] Comparative Example 2

[0107] The entire production line operates on 3K polyacrylonitrile-based carbon fiber precursor, which sequentially passes through a pre-oxidation furnace, a low-temperature carbonization furnace, and a high-temperature carbonization furnace for pre-oxidation, low-temperature carbonization, and high-temperature carbonization treatments. The stations requiring fiber replacement are: 1#, 10#, 11#, 12#, and 13#. The fiber replacement and conveyor steps are as follows:

[0108] 1) Each shift consists of 4 people divided into 2 groups to carry out the work. Two people, A and B, are responsible for cutting the yarn bundle that needs to be replaced, wrapping the yarn tail around the swing arm of the yarn unwinding frame, and then turning the control switch of the yarn unwinding device at this station to the "OFF" state.

[0109] 2) Two people, C and D, loosen the nut of the spindle to be replaced (if the nut is tight, a large wrench can be used to loosen it), remove the paper tube of the wire bundle and set it aside, confirm the direction of the wire bundle exit (the wire exits from above the wire spool), and then put the new wire onto the corresponding spindle at the work station and tighten the fixing bolt.

[0110] 3) Two people, A and B, bind the new and old raw silk ends at workstations #1, #10, #11, #12, and #13, and then turn the switch on the small control box of the silk spindle to the "ON" position (at this time, the silk bundle is under tension and easy to braid). Figure 1 and 2 As shown, the tail ends of the old raw silk bundles at stations 1#, 10#, 11#, 12#, and 13# are respectively woven into the new raw silk bundles on the other side to form the first woven section; at intervals of 10-20cm, the head ends of the new raw silk bundles are woven into the old raw silk bundles on the other side to form the second woven section; each woven section consists of 3-5 small sub-woven sections, the length of the sub-woven sections is between 3-5cm, and the interval between the sub-woven sections is 3-5cm, requiring the weave to be soft and loose.

[0111] 4) The connector enters the production unit and is then taken up by the winding machine. The connector part is cut off and the wire is rewound.

[0112] Table 2 shows the sequential passage of continuous polyacrylonitrile-based pre-oxidized fibers through a low-temperature carbonization furnace after the connection of Example 2 and Comparative Example 2.

[0113] Table 2

[0114] Equipment Name Example 2 Comparative Example 2 Low-temperature carbonization furnace All 5 passed Only 3 passed

[0115] Comparative Example 3

[0116] The entire production line operates on 6K polyacrylonitrile-based carbon fiber precursor, which sequentially passes through a pre-oxidation furnace, a low-temperature carbonization furnace, and a high-temperature carbonization furnace for pre-oxidation, low-temperature carbonization, and high-temperature carbonization treatments. The stations requiring fiber replacement are: 1#, 2#, 3#, 4#, and 5#. The fiber replacement and conveyor steps are as follows:

[0117] 1) Each shift consists of 4 people divided into 2 groups to carry out the work. Two people, A and B, are responsible for cutting the yarn bundle that needs to be replaced, wrapping the yarn tail around the swing arm of the yarn unwinding frame, and then turning the control switch of the yarn unwinding device at this station to the "OFF" state.

[0118] 2) Two people, C and D, loosen the nut of the spindle to be replaced (if the nut is tight, a large wrench can be used to loosen it), remove the paper tube of the wire bundle and set it aside, confirm the direction of the wire bundle exit (the wire exits from above the wire spool), and then put the new wire onto the corresponding spindle at the work station and tighten the fixing bolt.

[0119] 3) Two people, A and B, bind the new and old raw silk threads at stations 1#, 2#, 3#, 4#, and 5#, and then turn the switch on the small control box of the silk spindle to the "ON" position (at this time, the silk bundle is under tension and easy to braid). Figure 1 and 2 As shown, the ends of the old raw silk bundles at stations 1#, 2#, 3#, 4#, and 5# are respectively woven into the new raw silk bundles on the other side to form the first woven section; at intervals of 10-20cm, the ends of the new raw silk bundles are woven into the old raw silk bundles on the other side to form the second woven section; each woven section consists of 3-5 small sub-woven sections, the length of the sub-woven sections is between 3-5cm, and the interval between the sub-woven sections is 3-5cm, requiring the weave to be soft and loose.

[0120] 4) The connector enters the production unit and is then taken up by the winding machine. The connector part is cut off and the wire is rewound.

[0121] Table 3 shows the sequential passage of continuous polyacrylonitrile-based pre-oxidized fibers through a low-temperature carbonization furnace after the connection of Example 3 and Comparative Example 3.

[0122] Table 3

[0123] Equipment Name Example 3 Comparative Example 3 Low-temperature carbonization furnace All 5 passed Only 2 passed

[0124] Comparative Example 4

[0125] The entire line operates on 12K polyacrylonitrile-based carbon fiber precursor, which sequentially passes through a pre-oxidation furnace, a low-temperature carbonization furnace, and a high-temperature carbonization furnace for pre-oxidation, low-temperature carbonization, and high-temperature carbonization treatments.

[0126] The stations requiring wire replacement are #1 and #2. The wire replacement and conveyor procedures are as follows:

[0127] 1) Each shift consists of 4 people divided into 2 groups to carry out the work. Two people, A and B, are responsible for cutting the yarn bundle that needs to be replaced, wrapping the yarn tail around the swing arm of the yarn unwinding frame, and then turning the control switch of the yarn unwinding device at this station to the "OFF" state.

[0128] 2) Two people, C and D, loosen the nut of the spindle to be replaced (if the nut is tight, a large wrench can be used to loosen it), remove the paper tube of the wire bundle and set it aside, confirm the direction of the wire bundle exit (the wire exits from above the wire spool), and then put the new wire onto the corresponding spindle at the work station and tighten the fixing bolt.

[0129] 3) Two people, A and B, bind the new and old raw silk threads at workstations #1 and #2, and then turn the switch on the small control box of the silk spindle to the "ON" position (at this time, the silk bundle is under tension, which facilitates weaving). Figure 1 and 2 As shown, the tail ends of the old raw silk bundles at stations 1 and 2 are respectively woven into the new raw silk bundles on the other side to form the first woven section; at intervals of 10-20cm, the head ends of the new raw silk bundles are woven into the old raw silk bundles on the other side to form the second woven section; each woven section consists of 3-5 small sub-woven sections, the length of the sub-woven sections is between 3-5cm, and the interval between the sub-woven sections is 3-5cm, requiring the woven section to be soft and loose.

[0130] 4) The connector enters the production unit and is then taken up by the winding machine. The connector part is cut off and the wire is rewound.

[0131] Table 4 shows the sequential passage of the continuous polyacrylonitrile-based pre-oxidized fibers after the connection of Example 4 and Comparative Example 4 through the low-temperature carbonization furnace.

[0132] Table 4

[0133] Equipment Name Example 4 Comparative Example 4 Low-temperature carbonization furnace Both rods passed. 0 roots passed

[0134] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A method for in-situ re-fiber replacement of polyacrylonitrile-based carbon fiber precursor, characterized in that, When polyacrylonitrile-based carbon fiber precursors are sequentially passed through a pre-oxidation furnace, a low-temperature carbonization furnace, and a high-temperature carbonization furnace for pre-oxidation, low-temperature carbonization, and high-temperature carbonization treatments: When changing the yarn at the Nth station, the tail end of the first polyacrylonitrile-based carbon fiber precursor yarn bundle currently running at the Nth station is connected to the head end of the second polyacrylonitrile-based carbon fiber precursor yarn bundle to be replaced; wherein, the connection part is a joint. After the wire is changed at the Nth station, when the connector on the wire bundle running at the Nth station passes through the last pre-oxidation furnace and before entering the inlet of the low-temperature carbonization furnace, the connector on the wire bundle running at the Nth station is connected to the wire bundle running at the Mth station, so that the connector can pass smoothly through the low-temperature carbonization furnace and the high-temperature carbonization furnace with the help of the wire bundle running at the Mth station. The method for connecting the tail end of the first polyacrylonitrile-based carbon fiber precursor bundle currently operating at the Nth workstation to the head end of the second polyacrylonitrile-based carbon fiber precursor bundle to be replaced includes: The tail end of the first polyacrylonitrile-based carbon fiber precursor bundle is braided into the second polyacrylonitrile-based carbon fiber precursor bundle to form the first braided section. The head end of the second polyacrylonitrile-based carbon fiber precursor bundle is braided into the first polyacrylonitrile-based carbon fiber precursor bundle to form the second braided section. There is a set length of unbraided portion between the first braided portion and the second braided portion; The connector includes a first braided section and a second braided section; and an unbraided section between the first braided section and the second braided section; Specifically, the unbraided portion of the connector located between the first braided portion and the second braided portion is braided onto the filament bundle operating at the Mth workstation.

2. The method for changing polyacrylonitrile-based carbon fiber precursor fibers at the original work site according to claim 1, characterized in that, The Mth station is the station where the yarn needs to be changed; or the Mth station is the station where the yarn winding has started and the finished yarn has not reached the set length.

3. The method for changing polyacrylonitrile-based carbon fiber precursor fibers at the original work site according to claim 1, characterized in that, The distance between the Mth station and the Nth station must be such that the joint on the filament bundle running at the Nth station can be opened by the tension of the filament bundle itself.

4. The method for changing polyacrylonitrile-based carbon fiber precursor fibers at the original work site according to claim 3, characterized in that, The Mth station is the station furthest from the Nth station that needs to change the yarn; or the Mth station is the station furthest from the Nth station that has started taking in the yarn and the finished yarn has not yet reached the set length.

5. The method for changing polyacrylonitrile-based carbon fiber precursor fibers at the original work site according to claim 3, characterized in that, If the fiber is of specification 1K, the interval between the Mth station and the Nth station must ensure that the tension received by the joint on the filament bundle running at the Nth station is 150-1000CN. If the fiber is of specification 3K, the interval between the Mth station and the Nth station must ensure that the tension on the joint of the filament bundle running at the Nth station is 300-1000CN. If the fiber is of 6K specification, the interval between the Mth station and the Nth station must ensure that the tension on the joint of the filament bundle running at the Nth station is 500-2000 CN. If the fiber is of 12K specification, the interval between the Mth station and the Nth station must ensure that the tension on the joint of the filament bundle running at the Nth station is 1000-5000 CN. If the fiber is 24K specification, the interval between the Mth station and the Nth station must ensure that the tension on the joint of the filament bundle running at the Nth station is 2000-10000CN. If the fiber is 48K, the interval between the Mth station and the Nth station must ensure that the tension on the joint of the filament bundle running at the Nth station is 3000-20000 CN.

6. The method for changing polyacrylonitrile-based carbon fiber precursor fibers at the original work site according to claim 1, characterized in that, If the distance between the Mth workstation and the Nth workstation is insufficient for the joints on the yarn bundle running at the Nth workstation to open due to the tension of the yarn bundle itself, then weft threads need to be added to prevent misalignment.

7. The method for changing polyacrylonitrile-based carbon fiber precursor fibers at the original work site according to claim 1, characterized in that, The filament bundle running at the Mth station is divided into two strands, which are then braided with the two strands on the unbraided portion.

8. The method for changing polyacrylonitrile-based carbon fiber precursor fibers at the original work site according to claim 1, characterized in that, The length of the unbraided portion is 10-20cm.

9. The method for changing polyacrylonitrile-based carbon fiber precursor fibers at the original work site according to claim 1, characterized in that, The first braiding section includes multiple sub-braiding sections, and the second braiding section includes multiple sub-braiding sections.

10. The method for changing polyacrylonitrile-based carbon fiber precursor fibers at the original site according to claim 9, characterized in that, The first braiding section includes 3-5 sub-braiding sections, and the second braiding section includes 3-5 sub-braiding sections.

11. The method for changing polyacrylonitrile-based carbon fiber precursor fibers at the original work site according to claim 9, characterized in that, The length of the sub-braided section is 3-5cm.

12. The method for changing polyacrylonitrile-based carbon fiber precursor fibers at the original site according to claim 9, characterized in that, The spacing between the multiple sub-braid sections in the first braided section is 3-5cm.

13. The method for changing polyacrylonitrile-based carbon fiber precursor fibers at the original work site according to claim 9, characterized in that, The spacing between the multiple sub-braid sections in the second braided section is 3-5cm.

14. The method for changing polyacrylonitrile-based carbon fiber precursor yarn at the original work site according to any one of claims 1-13, characterized in that, When polyacrylonitrile-based carbon fiber precursors experience fiber breakage during pre-oxidation treatment, the broken fiber is woven onto a bundle of fibers at another workstation before entering the low-temperature carbonization furnace. This allows the broken fiber to pass smoothly through the low-temperature and high-temperature carbonization furnaces using the fibers from the other workstations.

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