Device and method for concentrating sunlight to pre-oxidize carbon fiber

Abstract

The present invention discloses a device and method for pre-oxidizing carbon fiber by concentrating sunlight. The device mainly includes a wire-releasing device, a quartz tube, a catalyst micro-injection pump, a hot air device, a sunlight concentrating device and a wire-collecting device. The wire-releasing device is located at the front end of the system, the quartz tube is installed on the right side of the wire-releasing device, the catalyst micro-injection pump and the hot air device are respectively located on the upper and lower sides of the quartz tube, the right side of the catalyst micro-injection pump and the hot air device and the two sides of the quartz tube are respectively installed with sunlight concentrating devices, and the rightmost end of the quartz tube is installed with a wire-collecting device. In the method of the present invention, concentrated sunlight or a xenon lamp is used to directly heat the carbon fiber, the temperature response is fast, and a large number of heating and heat preservation devices are omitted; a catalyst solution is injected by a micro-injection pump, the concentration and dosage of the catalyst can be quantitatively controlled, the pre-oxidation rate is accelerated, the skin-core structure is reduced, and the temperature of the carbon fiber surface is controllable by adjusting the distance from the Fresnel lens to the carbon fiber surface.

Description

Technical Field

[0001] The invention relates to the field of carbon fiber pre-oxidation processing and manufacturing, and in particular to a device and method for concentrating sunlight to pre-oxidize carbon fiber. Background Art

[0002] Pre-oxidation is an important process in the production of PAN-based carbon fibers. In this process, the linear molecular chains of PAN precursors are transformed into pre-oxidized fibers with a heat-resistant trapezoidal structure, laying the foundation for subsequent carbonization and graphitization. If the solid oxygen rate is too fast during the pre-oxidation process, the outer layer of the carbon fiber will first undergo cyclization to form a dense cortex, which will prevent oxygen from continuing to diffuse into the core and eventually form a skin-core structure, causing the pre-oxidation process to take too long and significantly increasing production costs. There are currently two types of pre-oxidation devices:

[0003] (1) Direct heating pre-oxidation equipment

[0004] The direct heating pre-oxidation equipment electrically heats the furnace, and its heat passes through the air from the furnace wall and finally acts on the surface of the carbon fiber. In this process, since the thermal conductivity of the air in the furnace is very low, more time and energy consumption are required to reach the pre-oxidation temperature before pre-oxidation. The uniformity and stability of the carbon fiber pre-oxidation temperature directly depend on the working conditions of the furnace body: when the outside temperature is low (such as in winter), an insulation layer is required to ensure that the temperature of the furnace body does not drop; when the outside temperature is high (such as in summer), the reaction heat of the carbon fiber is easy to accumulate inside the fiber and cause overheating. At this time, a temperature monitor needs to be installed in the furnace and the fire extinguishing system needs to be ready to start at any time.

[0005] This equipment has a simple structure, low cost and is equipped with a heat exchanger, thermal insulation layer, etc. However, its disadvantages are that the furnace is large and consumes a lot of energy. The existing process and equipment can account for 8%-12% of the carbon fiber production cost. For carbon fiber production lines, there is still a lot of room for energy saving and consumption reduction.

[0006] (2) Microwave heating pre-oxidation equipment (Chinese patents CN208362540U, CN207891472U)

[0007] Microwave heating pre-oxidation is a new method that has been mentioned more frequently in recent years. Its advantages are:

[0008] ① Uniform heating. During microwave heating, microwaves penetrate the carbon fiber and directly act on the inside of the fiber. Heat is generated from the inside and the heat is uniform.

[0009] ② Fast heating rate. This is determined by the principle of microwave heating: during microwave heating of carbon fiber, the polar molecules inside the carbon fiber vibrate strongly and convert kinetic energy into thermal energy, thus avoiding heat loss through other channels.

[0010] However, microwave heating of carbon fiber has not been widely used in the pre-oxidation process of carbon fiber for the following reasons:

[0011] ① Although the microwave power covers a wide range, the pre-oxidation temperature is around 240°C, and the power window adjusted to 240°C is narrow, making the operation difficult.

[0012] ② Microwave ovens require a metal shell as a shielding shell, and the aperture of the holes on its surface can only be around 1 / 5 of the microwave wavelength, making it difficult to place a temperature measuring device through the holes to measure the temperature of the fiber surface in real time. At this time, the microwave oven is equivalent to a "dark box", and it is not easy to observe the fiber changes with the naked eye, which can easily cause fires. Summary of the invention

[0013] In order to reduce the energy consumption of direct pre-oxidation equipment and avoid the problem of difficult temperature measurement in microwave pre-oxidation, the patent of this invention proposes a device and method for pre-oxidizing carbon fiber by concentrating sunlight, changing the heating method of the pre-oxidized fiber, greatly reducing energy consumption, and controlling the temperature of the carbon fiber by controlling the displacement of the Fresnel lens, thereby achieving gradient heating.

[0014] The technical solution to achieve the above-mentioned purpose is: a device for concentrating sunlight to pre-oxidize carbon fiber, mainly comprising a wire-releasing device, a quartz tube, a catalyst micro-injection pump, a hot air device, a solar light concentrating device and a wire-collecting device, the wire-releasing device is located at the front end of the system, the quartz tube is installed on the right side of the wire-releasing device, the catalyst micro-injection pump and the hot air device are respectively located on the upper and lower sides of the quartz tube, the solar light concentrating devices are respectively installed on the right side of the catalyst micro-injection pump and the hot air device and on both sides of the quartz tube, and the wire-collecting device is installed at the rightmost end of the quartz tube.

[0015] When the equipment is working, the wire-releasing device and the wire-collecting device at both ends of the quartz tube apply a drawing force to the carbon fiber precursor by drawing. Under the action of the traction force, the carbon fiber precursor slowly passes through the quartz tube. During the carbon fiber traction process, the micro-injection pump quantitatively injects the catalyst solution, and disperses and precipitates it on the surface of the carbon fiber with the circulating hot air, which is conducive to the diffusion of oxygen into the fiber, thereby delaying the formation of a dense trapezoidal barrier layer on the surface. The hot air device consists of a blower, a molten salt graphite container, a Fresnel reflector, and a U-shaped heat exchanger: the molten salt graphite container contains a low-melting-point molten salt, which has a large heat capacity and heat conductivity value. The Fresnel reflector concentrates sunlight on the wall of the molten salt graphite container. The wall is heated and conducts heat to the inside of the molten salt. The molten salt melts and releases heat. The air containing 8%-10% oxygen is heated by the heat exchanger, and is blown into the quartz tube from the lower inlet of the quartz tube by the blower and discharged from the end outlet of the quartz tube. The hot air provided by the hot air device can provide oxygen for the pre-oxidation of carbon fiber on the one hand, and can take away the heat generated by pre-oxidation on the other hand. The solar light focusing device consists of a stepper motor, a ball screw, a linear guide, a slider, a workbench, a Fresnel lens group, a xenon lamp, an infrared thermometer and a displacement feedback adjustment module. The stepper motor drives the ball screw and the linear guide to move linearly, and the workbench is fixed on the slider. The Fresnel lens focuses the simulated sunlight emitted by the xenon lamp on the surface of the carbon fiber. The different distances between the Fresnel lens and the surface of the carbon fiber will cause different temperatures on the surface, and the distance is controlled by the stepper motor and the ball screw. The carbon fiber irradiated by the concentrated sunlight slowly moves forward in the quartz tube and is finally collected into a roll by the collection device.

[0016] The present invention provides a device for pre-oxidizing carbon fiber by concentrating sunlight. Since the spectrum of xenon lamp irradiation is basically the same as the solar spectrum, the sunlight of the device can be the sunlight irradiated by the sun or the simulated sunlight emitted by the xenon lamp. The power of the xenon lamp is selected according to the temperature (200-300°C) projected onto the surface of the carbon fiber precursor.

[0017] The present invention provides a device for collecting sunlight to pre-oxidize carbon fiber. The temperature of the surface of the carbon fiber precursor can be automatically adjusted by the sunlight collecting device: when the infrared thermometer measures that the surface temperature of the fiber precursor is higher than the set value, the displacement feedback regulating module adjusts the rotation of the ball screw so that the workbench is away from the carbon fiber surface by a certain distance; when the infrared thermometer measures that the surface temperature of the fiber is lower than the set value, the displacement feedback regulating module adjusts the rotation of the ball screw so that the workbench is close to the carbon fiber surface by a certain distance. The displacement feedback regulating module can control the temperature of the carbon fiber surface to be maintained near the set temperature.

[0018] The present invention provides a device for concentrating sunlight to pre-oxidize carbon fiber. The catalyst solution in the micro-injection pump can be boric acid, metaboric acid, tetraboric acid, boric anhydride or boric ester, etc. The introduction of boron element can greatly improve the tensile strength of carbon fiber precursor and can inhibit the "skin-core" structure formed during the heating process.

[0019] The present invention discloses a device for pre-oxidizing carbon fiber by concentrating sunlight. The molten salt in the hot air device adopts Hitec molten salt, and the melting point data window thereof is relatively wide: between 142-435°C. The required molten salt is obtained by adjusting the molten salt ratio according to the pre-oxidation temperature of 200-300°C. The molten salt container in the hot air device adopts a graphite container, and the heating device can adopt a Fresnel reflector or a rotating parabolic concentrator or a parabolic cylindrical concentrator. The gas flow rate blown out by the blower should match the carbon fiber wire feeding speed, and the gas contains 8%-10% oxygen. The heat exchanger in the device can adopt a U-tube heat exchanger.

[0020] The present invention discloses a device for pre-oxidizing carbon fiber by concentrating sunlight, wherein the quartz tube can be linear or spiral. The length of the linear quartz tube is designed according to the wire-feeding speed and the pre-oxidation time: the length of the quartz tube = the wire-feeding speed * the pre-oxidation time. The maximum radius of the spiral quartz tube = the wire-feeding speed * the pre-oxidation time / 2π. When the quartz tube is relatively long, a micro-groove pulley can be cast inside the quartz tube to support the carbon fiber.

[0021] The present invention provides a device for pre-oxidizing carbon fiber by concentrating sunlight. A plurality of Fresnel transmission mirrors can be arranged in parallel in the solar energy focusing device. The distance between each lens and the surface of the carbon fiber is different. The carbon fiber will experience different heating temperatures during the wire feeding process, thereby realizing gradient heating pre-oxidation of the device.

[0022] The invention discloses a method for pre-oxidizing carbon fiber by using a device for pre-oxidizing carbon fiber by concentrating sunlight: first, a fiber discharge device discharges carbon fiber precursor, and two sides of a quartz tube are provided with a micro-injection pump and a hot air device respectively; the angle of a Fresnel reflector in the hot air device is adjusted to collect sunlight onto the surface of a graphite container, the collected sunlight heats the graphite container to melt the molten salt in the container, and then a blower is turned on, the blower heats air containing 8%-10% oxygen through a U-tube heat exchanger outside the graphite container, and the heated hot air is discharged into the quartz tube from the bottom inlet of the quartz tube and discharged from the discharge port; when the hot air is stably discharged, a catalyst solution (such as a boric acid solution) is quantitatively injected by a micro-injection pump, the solution enters the quartz tube and is dispersed and deposited on the surface of the carbon fiber precursor along with the hot air; then the speed of a stepper motor is adjusted, and then a ball screw is spirally advanced to drive a slider to move on a linear guide rail; a workbench is connected to the slider, and the movement of the slider drives the workbench to move linearly; when the distance from the Fresnel transmission mirror on the workbench to the carbon fiber precursor reaches a set value, the stepper motor stops working. At the set distance, the carbon fiber precursor can reach the set temperature required for pre-oxidation. The infrared thermometer can display the surface temperature of the carbon fiber precursor in real time. When the surface temperature is higher or lower than the set value, the infrared thermometer transmits the temperature signal to the displacement feedback module. The displacement feedback module automatically adjusts the speed of the stepper motor to control the up and down movement of the Fresnel lens, and finally achieves the effect of quantitatively controlling the surface temperature of the carbon fiber. To achieve gradient heating, multiple groups of Fresnel lenses need to be added in parallel, and the distance from each group of lenses to the carbon fiber precursor is set according to the required temperature. Finally, the pre-oxidized carbon fiber passes through the quartz tube and is reeled by the wire collection device.

[0023] Compared with the existing technology, the present invention has the following beneficial effects:

[0024] (1) The present invention uses concentrated sunlight or xenon lamps to directly heat the carbon fiber, which has a faster temperature response than the traditional pre-oxidation furnace air heating. At the same pre-oxidation temperature, a large number of heating and heat preservation devices are eliminated, which fundamentally reduces energy consumption and costs.

[0025] (2) The present invention adopts a micro-injection pump to inject the catalyst solution, which can quantitatively control the concentration and dosage of the catalyst, accelerate the pre-oxidation rate, and reduce the skin-core structure.

[0026] (3) The present invention uses a quartz tube as the pre-oxidation furnace body, which has two beneficial effects: First, if the temperature is too high, the carbon fiber may catch fire. The use of a transparent quartz tube can directly observe the wire movement of the carbon fiber during the pre-oxidation process, and timely handle it to avoid fire damage caused by personal injury and property loss. Second, microwave pre-oxidation devices mostly use metal shells and the size of the surface openings is limited. Therefore, it is not easy for the temperature measuring device to directly detect the temperature of the carbon fiber surface, which increases the cost and technical difficulty of coupling the microwave pre-oxidation device with the temperature measuring device. The present invention uses a quartz tube to adjust the surface temperature measuring device in time according to the progress of the carbon fiber.

[0027] (4) The present invention can achieve controllable carbon fiber surface temperature by adjusting the distance between the Fresnel lens and the carbon fiber surface, and achieve gradient heating of the carbon fiber by adding multiple sets of parallel Fresnel lenses. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of a concentrated sunlight pre-oxidation device according to the present invention.

[0029] Figure 2 The schematic diagram of the Fresnel transmission mirror in the solar light pre-oxidation equipment of the present invention is to concentrate the sunlight to heat the carbon fiber.

[0030] In the figure: 1-wire unwinding device, 2-carbon fiber precursor, 3-micro injection pump, 4-xenon lamp, 5-Fresnel transmission mirror group, 6-stepping motor, 7-infrared thermometer, 8-displacement feedback adjustment module, 9-quartz tube, 10-exhaust port, 11-wire collecting device, 12-linear guide rail, 13-slider, 14-ball screw, 15-workbench, 16-U-type heat exchanger, 17-Fresnel reflector group, 18-blower, 19-graphite container. DETAILED DESCRIPTION

[0031] The present invention relates to a device for concentrating sunlight to pre-oxidize carbon fibers. Figure 1 and Figure 2 As shown, it mainly includes a wire-releasing device 1, a quartz tube 9, a catalyst micro-injection pump 3, a hot air device, a solar light focusing device and a wire-collecting device 11. The wire-releasing device 1 is located at the front end of the system, the quartz tube 9 is installed on the right side of the wire-releasing device, the catalyst micro-injection pump 3 and the hot air device are respectively located on the upper and lower sides of the quartz tube 9, the solar light focusing devices are respectively installed on the right side of the catalyst micro-injection pump 3 and the hot air device and on both sides of the quartz tube 9, and the wire-collecting device 11 is installed at the rightmost end of the quartz tube 9.

[0032] The hot air device is composed of a blower 18, a molten salt graphite container 19, a Fresnel reflector group 17 and a U-shaped heat exchanger 16: the molten salt graphite container 19 contains a low melting point molten salt, which has a large heat capacity and heat conductivity value. The Fresnel reflector group 17 concentrates sunlight on the wall of the molten salt graphite container 19, and the wall is heated to transfer the heat to the inside of the molten salt, and the molten salt melts and releases heat. The air containing 8%-10% oxygen is heated by the heat exchanger 16, and is blown into the quartz tube from the lower side inlet of the quartz tube 9 by the blower 18, and discharged from the end outlet of the quartz tube 9. The hot air provided by the hot air device provides oxygen for the pre-oxidation of carbon fiber on the one hand, and can take away the heat generated by the pre-oxidation on the other hand. The sunlight collection device is composed of a stepper motor 6, a ball screw 14, a linear guide 12, a slider 13, a workbench 15, a Fresnel lens group 5, a xenon lamp 4, an infrared thermometer 7 and a displacement feedback adjustment module 8. The stepper motor 6 drives the ball screw 14 and the linear guide 12 to move linearly, and the workbench 15 is fixed on the slider 13. The Fresnel lens 5 focuses the simulated sunlight emitted by the xenon lamp 4 on the surface of the carbon fiber precursor 2. Different distances between the Fresnel lens 5 and the carbon fiber surface will cause different surface temperatures, and the distance is controlled by the stepper motor 6 and the ball screw 14. The carbon fiber irradiated by the concentrated sunlight moves slowly in the quartz tube and is finally collected into a roll by the wire collection device 11.

[0033] The present invention relates to a method for pre-oxidizing carbon fiber by gathering sunlight. First, a fiber discharge device 1 discharges carbon fiber precursor 2, and a micro-injection pump 3 and a hot air device are respectively provided on both sides of a quartz tube 9. The angle of a Fresnel reflector 17 in the hot air device is adjusted to collect sunlight onto the surface of a graphite container 19. The collected sunlight heats the graphite container 19 to melt the molten salt in the container. At this time, a blower 18 is turned on. The blower 18 heats the air containing 8%-10% oxygen through a U-tube heat exchanger 16 outside the graphite container 19. The heated hot air is discharged into the quartz tube 9 from the bottom inlet of the quartz tube 9 and discharged from an exhaust port 10. When the hot air is stably discharged, a catalyst solution (such as a boric acid solution) is quantitatively injected by a micro-injection pump 3. The solution enters the quartz tube 9 and is dispersed and deposited on the surface of the carbon fiber precursor 2 along with the hot air. Then, the speed of the stepper motor 6 is adjusted, and then the ball screw 14 spirally advances, driving the slider 13 to move on the linear guide rail 12. The workbench 15 is connected to the slider 13, and the movement of the slider 13 drives the workbench 15 to move linearly. When the distance from the Fresnel transmission mirror 5 on the workbench 15 to the carbon fiber precursor 2 reaches the set value, the stepper motor 6 stops working. At the set distance, the carbon fiber precursor 2 can reach the set temperature required for pre-oxidation. The infrared thermometer 7 can display the surface temperature of the carbon fiber precursor 2 in real time. When the surface temperature is higher or lower than the set value, the infrared thermometer 7 transmits the temperature signal to the displacement feedback module 8, and the displacement feedback module 8 automatically adjusts the speed of the stepper motor 6 to control the up and down movement of the Fresnel lens 5, and finally achieves the effect of quantitatively controlling the surface temperature of the carbon fiber. If gradient heating is to be achieved, multiple groups of Fresnel lens groups 5 need to be added in parallel, and the distance from each group of lenses 5 to the carbon fiber precursor 2 is set according to the required temperature. Finally, the pre-oxidized carbon fiber 2 passes through the quartz tube 9 and is wound up by the wire collection device 11.

Claims

1. A device for concentrating sunlight to pre-oxidize carbon fibers, characterized in that: It mainly includes a wire-releasing device, a quartz tube, a catalyst micro-injection pump, a hot air device, a solar light concentrating device and a wire-collecting device. The wire-releasing device is located at the front end of the system, the quartz tube is installed on the right side of the wire-releasing device, the catalyst micro-injection pump and the hot air device are respectively located on the upper and lower sides of the quartz tube, and solar light concentrating devices are respectively installed on the right side of the catalyst micro-injection pump and the hot air device and on both sides of the quartz tube, and a wire-collecting device is installed at the rightmost end of the quartz tube; the hot air device consists of a blower, a molten salt graphite container, a Fresnel reflector and a U-shaped heat exchanger: the molten salt graphite container contains a low-melting-point molten salt with a large heat capacity and heat conductivity. The Fresnel reflector concentrates sunlight on the wall of the molten salt graphite container, and the wall is heated to conduct heat to the inside of the molten salt, and the molten salt melts and releases heat; it contains 8%-10% The oxygen-rich air is heated by a heat exchanger and blown into the quartz tube from the lower inlet of the quartz tube by a blower and discharged from the end outlet of the quartz tube; the solar light focusing device is composed of a stepper motor, a ball screw, a linear guide, a slider, a workbench, a Fresnel lens group, a xenon lamp, an infrared thermometer and a displacement feedback adjustment module. The stepper motor drives the ball screw and the linear guide to move linearly, and the workbench is fixed on the slider; the Fresnel lens focuses the simulated sunlight emitted by the xenon lamp on the surface of the carbon fiber. Different distances between the Fresnel lens and the surface of the carbon fiber will cause different temperatures on the surface, and the distance is controlled by the stepper motor and the ball screw; the carbon fiber irradiated by the concentrated sunlight slowly moves forward in the quartz tube and is finally collected into a roll by the wire collection device; the quartz tube is linear or spiral, and a micro groove pulley is cast inside the quartz tube.

2. The device for concentrating sunlight to pre-oxidize carbon fibers according to claim 1, characterized in that: The catalyst solution in the microinjection pump is boric acid, metaboric acid, tetraboric acid, boric anhydride or boric ester.

3. The device for concentrating sunlight to pre-oxidize carbon fibers according to claim 1, characterized in that: The molten salt in the hot air device uses Hitec molten salt, which has a wide melting point data window: between 142-435°C; the molten salt ratio is adjusted according to the pre-oxidation temperature of 200-300°C to obtain the required molten salt.

4. The device for concentrating sunlight to pre-oxidize carbon fibers according to claim 1, characterized in that: Multiple Fresnel mirrors are arranged in parallel in the solar focusing device. The distance between each lens and the surface of the carbon fiber is different. The carbon fiber will experience different heating temperatures during the wire feeding process, thereby realizing gradient heating pre-oxidation of the device.

5. A method for pre-oxidizing carbon fibers by concentrating sunlight, characterized in that: The device for pre-oxidizing carbon fiber by concentrating sunlight as described in claim 1 is used, firstly, the fiber unwinding device unwinds the carbon fiber precursor, and a micro-injection pump and a hot air device are respectively provided on both sides of the quartz tube; Adjust the angle of the Fresnel reflector in the hot air device to focus sunlight on the surface of the graphite container. The focused sunlight heats the graphite container to melt the molten salt in the container. At this time, turn on the blower, which heats the air containing 8%-10% oxygen through the U-tube heat exchanger outside the graphite container. The heated hot air is discharged into the quartz tube from the bottom inlet and discharged from the outlet. When the hot air is discharged stably, the micro-injection pump quantitatively injects the catalyst solution, and the solution enters the quartz tube and is dispersed and deposited on the surface of the carbon fiber precursor along with the hot air; then the speed of the stepper motor is adjusted, and the ball screw spirally moves forward, driving the slider to move on the linear guide; the workbench is connected to the slider, and the movement of the slider drives the workbench to move linearly; when the distance from the Fresnel transmission mirror on the workbench to the carbon fiber precursor reaches the set value, the stepper motor stops working; at the set distance, the carbon fiber precursor can reach the set temperature required for pre-oxidation, and the infrared thermometer displays the surface temperature of the carbon fiber precursor in real time. When the surface temperature is higher or lower than the set value, the infrared thermometer transmits the temperature signal to the displacement feedback module, and the displacement feedback module automatically adjusts the speed of the stepper motor to control the up and down movement of the Fresnel lens, and finally achieves the effect of quantitatively controlling the surface temperature of the carbon fiber; finally, the pre-oxidized carbon fiber passes through the quartz tube and is wound up by the wire collection device.

6. The method for pre-oxidizing carbon fibers by concentrating sunlight according to claim 5, characterized in that: It is necessary to add multiple groups of Fresnel lenses in parallel, and the distance from each group of lenses to the carbon fiber raw filaments is set according to the required temperature to achieve gradient heating.

7. The method for pre-oxidizing carbon fibers by concentrating sunlight according to claim 5, characterized in that: Sunlight is sunlight or simulated sunlight emitted by a xenon lamp.

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