Device and method for controlling stable and uniform viscosity of spinning dope of pan-based carbon fiber

Abstract

The application provides a device and method for controlling the viscosity of a PAN-based carbon fiber spinning solution to be stable and uniform. The device for controlling the viscosity of the PAN-based carbon fiber spinning solution to be stable and uniform comprises a concentration kettle, a vacuum condensing system arranged above the concentration kettle, a discharge pump connected to the bottom of the concentration kettle through a pipeline, a stirring tank communicated with the discharge pump through a pipeline, a static mixer and a pressure detection part arranged between the discharge pump of the concentration kettle and the stirring tank, a three-layer paddle stirrer arranged in the stirring tank, a stirring motor arranged on the stirrer, and a current detection part connected with the stirring motor. According to the cooperation of the measurement results, the device for controlling the viscosity of the PAN-based carbon fiber spinning solution to be stable and uniform can adjust the viscosity of the spinning solution in the concentration kettle in real time, and the PAN-based spinning solution is homogenized twice, thereby providing a control device with low cost, simple structure, effective monitoring and adjustment of the viscosity of the spinning solution, and improved uniformity of the spinning solution.

Description

Technical Field

[0001] This invention relates to the technical field of viscosity adjustment for spinning solutions, and particularly to a device for controlling the viscosity of PAN-based carbon fiber spinning solutions to ensure stability and uniformity. Furthermore, this invention also relates to a method of using the device for controlling the viscosity of PAN-based carbon fiber spinning solutions to ensure stability and uniformity. Background Technology

[0002] Currently, the preparation process of PAN-based carbon fibers all employs a batch polymerization reaction followed by continuous spinning. The high-molecular-weight polyacrylonitrile solution obtained after the batch polymerization reaction undergoes ammoniation modification, monomer removal under vacuum conditions, and degassing before entering the spinning solution feed tank. It is then transported to the spinneret by a high-pressure gear pump to form nascent precursor fibers. Due to batch-to-batch variability inherent in batch polymerization and the further increase in conversion rate after polymerization, the viscosity of the resulting high-molecular-weight polyacrylonitrile solution changes, ultimately causing fluctuations in the viscosity of the material in the spinning solution feed tank. Since the viscosity of the polyacrylonitrile-based carbon fiber spinning solution is as high as 500-1000P at operating temperatures, it is difficult to mix spinning solutions of different viscosities uniformly, thus placing high demands on viscosity stability control. Viscosity fluctuations and instability cause changes in the performance parameters of the nascent precursor fibers produced during the spinning process, resulting in higher Cv values ​​and affecting the quality of the final carbon fiber product.

[0003] In the preparation process of high-performance carbon fiber spinning dopes, the viscosity stability control of the dope after degassing and de-sizing is generally achieved using online viscosity measuring tools. The viscosity of the spinning dope is then adjusted based on the measured values ​​and process parameters. However, existing viscosity measuring tools can be broadly categorized into rotary and vibratory types based on their operating principles. Rotary online viscometers, due to limitations in the internal flow channel size, exhibit dead zones and gelation within the instrument system when used for measuring the viscosity of high-viscosity carbon fiber spinning dopes, hindering long-term stable measurements to ensure continuous production. Furthermore, carbon fiber spinning dopes are non-Newtonian fluids, significantly affected by shear rate, material pressure, and temperature changes, requiring sophisticated instrument design, resulting in complex and costly viscosity measuring devices. Vibratory online viscometers, while simpler in structure and easier to clean and maintain, employ electromagnetic resonance principles, involving an electromagnet, vibrator, controllable gain amplifier, and signal processing unit. The algorithm for quality control of the signal and measured viscosity values ​​is complex, and errors are easily overlooked, impacting production stability control. Additionally, their use and maintenance costs are high. Summary of the Invention

[0004] In view of this, the present invention aims to provide a device and method for stable and uniform control of the viscosity of PAN-based carbon fiber spinning solution, so as to provide a low-cost, simple structure, and effective monitoring of the viscosity change trend of spinning solution, thereby improving the uniformity of spinning solution.

[0005] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0006] A device for controlling the viscosity of PAN-based carbon fiber spinning solution to ensure stability and uniformity includes a concentration vessel, a vacuum condensation system mounted on the concentration vessel, a stirring tank connected to the bottom of the concentration vessel via a pipeline, a pressure detection unit located between the concentration vessel and the stirring tank, a stirring motor mounted on the stirring tank, and a current detection unit connected to the stirring motor via a signal.

[0007] When the spinning solution passes through the pipeline, the pressure detection unit displays the pressure reading of the pipeline. When the spinning solution in the mixing tank is stirred at the output end of the stirring motor, the current detection unit displays the current reading of the stirring motor. The vacuum condensation system adjusts the viscosity of the spinning solution in the concentration tank based on the pressure reading and the current reading.

[0008] Furthermore, it also includes a pressure boosting plate with a pressure boosting hole, the pressure boosting hole being located inside the pipeline between the pressure detection unit and the mixing tank, the diameter of the pressure boosting hole being smaller than the diameter of the pipeline.

[0009] Furthermore, the number of pressure boosting holes is multiple.

[0010] Furthermore, a static mixer is connected to the pipeline between the concentration vessel and the pressure detection unit.

[0011] Furthermore, the output end of the stirring motor includes a stirring rod fixedly connected to the rotating shaft of the stirring motor, and a stirring blade assembly disposed on the stirring rod.

[0012] Furthermore, there are multiple stirring blade groups, and the number of stirring blades in the multiple stirring blade groups increases sequentially from top to bottom along the stirring rod.

[0013] Furthermore, a tank wall baffle is provided on the inner wall of the mixing tank, and the tank wall baffle covers the area directly in front of the connection interface between the pipeline and the mixing tank.

[0014] Furthermore, a discharge pump is provided at the connection between the bottom of the concentration vessel and the pipeline, and a feed pump is provided at the bottom of the mixing tank.

[0015] Furthermore, the pressure detection unit is a pressure sensor with a reading display, and the current detection unit is a current sensor with a reading display.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] This invention measures the viscosity of the spinning solution twice, sequentially using a pressure detection unit and a current detection unit. Based on the measurement results, the viscosity of the spinning solution in the concentration vessel can be adjusted in real time using a vacuum condensation system, ensuring that the viscosity of the spinning solution reaches the ideal value. Furthermore, the viscosity measurement using the pressure and current detection units does not involve contact with the spinning solution, thus extending the service life of the pressure and current detection units. The measurement method using pressure and current detection units is simple in structure and low in cost.

[0018] Another object of the present invention is to provide a method for using the apparatus for controlling the viscosity of the PAN-based carbon fiber spinning solution as described above. The method includes the following steps:

[0019] S1: Continuously transport the spinning solution in the concentration vessel to the stirring tank;

[0020] S2: The pressure reading of the pipeline between the concentration vessel and the stirring tank is displayed by the pressure detection unit, and the current reading of the stirring motor is displayed by the current detection unit;

[0021] S3: Based on the combined effect of the pressure reading and the current reading, the viscosity of the spinning solution in the concentration vessel is adjusted to a preset value through the vacuum condensation system.

[0022] Compared with existing technologies, the method of the present invention is easy to operate and can ensure that the viscosity of the spinning solution remains at an ideal value. The PAN-based spinning solution is homogenized and mixed twice by a static mixer and a stirrer with three layers of irregularly shaped stirring blades, thereby providing a low-cost, simple structure, effective method for monitoring and adjusting the viscosity of the spinning solution and improving the uniformity of the spinning solution. Attached Figure Description

[0023] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are for explaining the invention. The directional terms used, such as front / back, up / down, etc., are only used to indicate relative positional relationships and do not constitute an improper limitation of the invention. In the drawings:

[0024] Figure 1 This is a schematic diagram of the device for controlling the viscosity of PAN-based carbon fiber spinning solution according to Embodiment 1 of the present invention.

[0025] Figure 2This is a schematic diagram of the pressure-boosting hole on the pressure plate of the device for controlling the viscosity stability and uniformity of PAN-based carbon fiber spinning solution according to Embodiment 1 of the present invention.

[0026] Explanation of reference numerals in the attached figures:

[0027] 1. Concentrator; 2. Vacuum condensation system; 3. Mixing tank; 4. Pressure detection unit; 5. Stirring motor; 6. Current detection unit; 7. Pressure boosting port; 8. Pressure boosting plate; 9. Static mixer; 10. Stirring rod; 11. Stirring blade assembly; 12. Tank wall baffle; 13. Discharge pump; 14. Feed pump. Detailed Implementation

[0028] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0029] In the description of this invention, it should be noted that if terms such as "upper," "lower," "inner," or "back" appear, indicating orientation or positional relationship, they are based on the orientation or positional relationship shown in the accompanying drawings and are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention. If terms such as "first" or "second" appear, they are also used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0030] Furthermore, in the description of this invention, unless otherwise explicitly defined, the terms "installation," "connection," "joint," and "connector" should be interpreted broadly. For example, a connection can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; or it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention in light of the specific circumstances.

[0031] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. Example

[0032] This embodiment relates to a device for controlling the viscosity stability and uniformity of PAN-based carbon fiber spinning solution. It provides a low-cost, simple-structured control device that effectively monitors the viscosity change trend of the spinning solution and improves the uniformity of the spinning solution. An exemplary structure is shown below. Figure 1 , Figure 2 As shown.

[0033] Overall, the device for controlling the viscosity of the PAN-based carbon fiber spinning solution includes a concentration vessel 1, a vacuum condensation system 2 installed on the concentration vessel 1, a stirring tank 3 connected to the bottom of the concentration vessel 1 via a pipeline, a pressure detection unit 4 installed between the concentration vessel 1 and the stirring tank 3, a stirring motor 5 installed on the stirring tank 3, and a current detection unit 6 connected to the stirring motor 5 via a signal. When the spinning solution passes through the pipeline, the pressure detection unit 4 displays the pressure reading of the pipeline. When the spinning solution in the stirring tank 3 is stirred at the output end of the stirring motor 5, the current detection unit 6 displays the current reading of the stirring motor 5. The vacuum condensation system 2 adjusts the viscosity of the spinning solution in the concentration vessel 1 based on the pressure reading and the current reading. The concentrator 1 has an inlet for the spinning solution, and one end of the pipeline is connected to the bottom of the concentrator 1 and the other end is connected to the top of the mixing tank 3. A discharge pump 13 is installed at the connection between the bottom of the concentrator 1 and the pipeline, and a feed pump 14 is installed at the bottom of the mixing tank 3. By controlling the discharge pump 13, the spinning solution in the concentrator 1 can enter the mixing tank 3 through the pipeline. By controlling the feed pump 14, the spinning solution in the mixing tank 3 can be transported to the next process.

[0034] Furthermore, a pressure boosting plate 8 is installed on the pipeline between the pressure detection unit 4 and the mixing tank 3. The pressure boosting plate 8 has pressure boosting holes 7, which are located inside the pipeline. When spinning solution passes through the pressure boosting holes 7, because the diameter of the holes 7 is smaller than the diameter of the pipeline, some spinning solution accumulates at the holes 7, causing an increase in the pipeline pressure upstream of the holes 7. At this time, the pressure detection unit 4 can more easily detect the pipeline pressure value. In this embodiment, the pressure detection unit 4 is a pressure sensor with a reading display. Of course, there can be multiple pressure boosting holes 7.

[0035] In this embodiment, in order to improve the uniformity of the spinning solution in the concentration vessel 1, a static mixer 9 is connected to the pipeline between the concentration vessel 1 and the pressure detection unit 4. Before entering the stirring tank 3, the spinning solution will first pass through the static mixer 9, and the static mixer 9 will mix the spinning solution to improve the uniformity of the spinning solution.

[0036] In addition, the output end of the stirring motor 5 includes a stirring rod 10 fixedly connected to the rotating shaft of the stirring motor 5, and a stirring blade assembly 11 disposed on the stirring rod 10. After the spinning solution enters the stirring tank 3, the rotation of the output shaft of the stirring motor 5 will drive the stirring blade assembly 11 to rotate, thereby stirring the spinning solution in the stirring tank 3. At the same time, during the stirring process, the current detection unit 6 detects the current of the stirring motor 5 and displays the current value. The viscosity of the spinning solution in the stirring tank 3 is determined by the current value. If it does not meet the standard, the viscosity of the spinning solution in the concentration vessel 1 is increased by the vacuum condensation system 2, so that the concentration of the spinning solution in the stirring tank 3 meets the standard. In this embodiment, the current detection unit 6 is a current sensor with a reading display.

[0037] Based on the above settings, multiple stirring blade groups 11 can be set, and the number of stirring blades in multiple stirring blade groups 11 increases sequentially from top to bottom along the stirring rod 10. In this embodiment, there are at least three stirring blade groups 11, located at the upper, middle, and lower positions of the mixing tank 3. The upper stirring blade group 11 has two stirring blades, which are distributed at 180° around the stirring rod 10. The middle stirring blade group 11 has four stirring blades, which are distributed at 90° around the stirring rod 10. The lower stirring blade group 11 has six stirring blades, which are distributed at 60° around the stirring rod 10. The spinning solution in the spinning solution feed tank undergoes secondary homogenization and mixing through the stirring of the upper, middle, and lower stirring blade groups 11. The stirring blades of the upper stirring blade group 11 scrape away air bubbles on the upper layer and surface of the spinning solution in the spinning solution feed tank. The stirring blades of the middle stirring blade group 11 homogenize and mix the spinning solution, while promoting the movement of a small number of air bubbles in the spinning solution to the upper layer and radially towards the tank wall. The stirring blades of the lower stirring blade group 11 homogenize and mix the spinning solution to the greatest extent possible without introducing air bubbles. Of course, the number of stirring blades in the upper, middle and lower three-layer stirring blade group 11 can also be other numbers.

[0038] In addition, a tank wall baffle 12 is provided on the inner wall of the mixing tank 3, which blocks the spray direction directly in front of the connection interface between the pipeline and the mixing tank 3. When the spinning solution enters the mixing tank 3, the spinning solution will be sprayed onto the tank wall baffle 12 directly in front, and the tank wall baffle 12 blocks the spinning solution, causing the spinning solution to flow downward through the tank wall of the mixing tank 3.

[0039] Based on the above configuration, hot water jackets are fitted onto the outer walls of both the static mixer 9 and the mixing tank 3, with the temperature of the hot water jackets ranging from 30 to 60°C. This is to ensure the temperature requirements are met during the mixing of the spinning solution.

[0040] Additionally, it should be noted that the pressure plate 8 has dimensions of DN200×DN150, the remote pressure gauge on the pipeline before the orifice plate has a range of 0-1MPa, the agitator speed of the spinning solution feed tank is 5-50rpm, and the ammeter range of the feed tank agitator is 0-50A.

[0041] The working process of this embodiment is as follows:

[0042] After injecting the spinning solution into the concentration vessel 1, the discharge pump 13 is turned on, causing the spinning solution to flow into the mixing tank 3 through the pipeline between the concentration vessel 1 and the mixing tank 3. The spinning solution first passes through the static mixer 9, which mixes the spinning solution for the first time to improve its uniformity. Then, after passing through the static mixer 9, the spinning solution is obstructed by the pressure boosting hole 7, which increases the pressure in the pipeline before the pressure boosting hole 7. This allows the pressure detection unit 4 to measure the pressure value at that point. The viscosity of the spinning solution is calculated based on the pressure value. If it does not meet the standard, the viscosity of the spinning solution in the concentration vessel 1 is increased by the vacuum condensation system 2. Then, the spinning solution enters the mixing tank 3 after passing through the pressure boosting hole 7. The tank wall baffle 12 on the tank wall of the mixing tank 3 obstructs the spraying of the spinning solution, causing the spinning solution to flow downward along the tank wall of the mixing tank 3.

[0043] After the spinning solution enters the mixing tank 3, the rotation of the output shaft of the stirring motor 5 drives the stirring blade assembly 11 on the stirring rod 10 to rotate, thus mixing the spinning solution in the mixing tank 3 for the second time and further improving the uniformity of the spinning solution. When the stirring motor 5 is stirring, the current detection unit 6 will detect the current of the stirring motor 5 and display the current reading. The viscosity of the spinning solution in the mixing tank 3 is calculated based on the current reading of the stirring motor 5. If it does not meet the standard, the viscosity of the spinning solution in the concentration kettle 1 is increased again by the vacuum condensation system 2 until the viscosity of the spinning solution in the mixing tank 3 meets the standard. Finally, by controlling the feed pump 14, the qualified spinning solution in the mixing tank 3 can be transported to the next process. Example

[0044] This embodiment relates to a method of using a device for controlling the viscosity of PAN-based carbon fiber spinning solution as provided in Embodiment 1. The method includes the following steps:

[0045] S1: The spinning solution in the concentration tank 1 is continuously transported to the stirring tank 3.

[0046] S2: The pressure reading of the pipeline between the concentration vessel 1 and the stirring tank 3 is displayed by the pressure detection unit 4, and the current reading of the stirring motor 5 is displayed by the current detection unit 6.

[0047] S3: Based on the combined pressure and current readings, adjust the viscosity of the spinning solution in the concentration vessel 1 to the preset value through the vacuum condensation system 2.

[0048] The above operating steps make it easier for workers to operate.

[0049] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A device for controlling the viscosity of PAN-based carbon fiber spinning solution to ensure stability and uniformity, characterized in that: It includes a concentration vessel (1), a vacuum condensation system (2) installed on the concentration vessel (1), a stirring tank (3) connected to the bottom of the concentration vessel (1) via a pipeline, a pressure detection unit (4) installed between the concentration vessel (1) and the stirring tank (3), a stirring motor (5) installed on the stirring tank (3), a current detection unit (6) connected to the stirring motor (5) via a signal, and a pressure boosting plate (8) with a pressure boosting hole (7); When the spinning solution passes through the pipeline, the pressure detection unit (4) is used to display the pressure reading of the pipeline. When the spinning solution in the stirring tank (3) is stirred at the output end of the stirring motor (5), the current detection unit (6) is used to display the current reading of the stirring motor (5). The vacuum condensation system (2) adjusts the viscosity of the spinning solution in the concentration tank (1) according to the pressure reading and the current reading. The pressure boosting hole (7) is located inside the pipeline between the pressure detection unit (4) and the stirring tank (3), and the diameter of the pressure boosting hole (7) is smaller than the diameter of the pipeline; The output end of the stirring motor (5) includes a stirring rod (10) fixedly connected to the rotating shaft of the stirring motor (5), and a stirring blade assembly (11) provided on the stirring rod (10). The stirring blade assembly (11) includes an upper stirring blade assembly, a middle stirring blade assembly, and a lower stirring blade assembly from top to bottom along the stirring rod (10); The upper stirring blade group includes two stirring blades, the middle stirring blade group includes four stirring blades, and the lower stirring blade group includes six stirring blades; and the multiple stirring blades in the same group are distributed at equal intervals around the stirring rod (10) in the circumference.

2. The device for controlling the viscosity of PAN-based carbon fiber spinning solution to ensure stability and uniformity according to claim 1, characterized in that: The number of pressure boosting holes (7) is multiple.

3. The device for controlling the viscosity of PAN-based carbon fiber spinning solution to ensure stability and uniformity according to claim 1, characterized in that: A static mixer (9) is connected to the pipeline between the concentration vessel (1) and the pressure detection unit (4).

4. The device for controlling the viscosity of PAN-based carbon fiber spinning solution to ensure stability and uniformity according to claim 1, characterized in that: The mixing tank (3) is provided with a tank wall partition (12) on its inner wall, which covers the front of the connection interface between the pipeline and the mixing tank (3).

5. The device for controlling the viscosity of PAN-based carbon fiber spinning solution to ensure stability and uniformity according to claim 1, characterized in that: A discharge pump (13) is provided at the bottom of the concentration vessel (1) and the connection point with the pipeline, and a feed pump (14) is provided at the bottom of the mixing tank (3).

6. The device for controlling the viscosity of PAN-based carbon fiber spinning solution to ensure stability and uniformity according to claim 1, characterized in that: The pressure detection unit (4) is a pressure sensor with a reading display, and the current detection unit (6) is a current sensor with a reading display.

7. A method of using the apparatus for controlling the viscosity of PAN-based carbon fiber spinning solution according to any one of claims 1 to 6, characterized in that: The method includes the following steps: S1: The spinning solution in the concentration vessel (1) is continuously transported to the stirring tank (3); S2: The pressure reading of the pipeline between the concentration vessel (1) and the stirring tank (3) is displayed by the pressure detection unit (4), and the current reading of the stirring motor (5) is displayed by the current detection unit (6); S3: Based on the combined effect of the pressure reading and the current reading, adjust the viscosity of the spinning solution in the concentration vessel (1) to a preset value through the vacuum condensation system (2).

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