Intermediate frequency induction type carbon fiber self-heating graphitization furnace

Abstract

The present application relates to a kind of intermediate frequency induction type carbon fiber self-heating graphitization furnace, and specifically relates to a kind of equipment for carbon fiber continuous graphitization production, belongs to carbon fiber production technical field.The device mainly has graphite guide wheel, metal box, hearth graphite pipe, insulation layer, argon pipeline, temperature measuring instrument, intermediate frequency transformer, intermediate frequency power supply, brush, grounding cable and speed measuring mechanism composition.The present application is based on the induced current generated by carbon fiber passing through intermediate frequency transformer to make itself heat generation high temperature a kind of technology, working principle is that system is through acquisition carbon fiber running speed automatically controls the output power of intermediate frequency power supply, so that carbon fiber temperature in hearth is controlled in 2500~3200 ℃ range, compared with existing indirect heating graphitization furnace, this graphitization furnace has the advantages of fast heating speed, long hearth life, temperature field control accurate, graphitization yield is high, energy saving is remarkable, easy to operate and the like.

Description

I. Technical Field

[0001] This invention belongs to the field of carbon fiber material production, specifically relating to a carbon fiber graphitization heating device based on the self-heating of carbon fiber. II. Background Technology

[0002] Carbon fiber is a fibrous carbon material, which is made of organic fibers such as sheet-like graphite microcrystals stacked along the fiber axis and obtained by carbonization and graphitization. It has the advantages of high temperature resistance, ablation resistance, creep resistance, electrical conductivity, thermal conductivity, low density and small coefficient of thermal expansion. It is an important reinforcing material in advanced structural composite materials and has a wide range of applications in national defense and civilian fields.

[0003] The graphitization heating process of carbon fiber is a key step in the production of high tensile strength and high modulus carbon fiber. The specific process involves heating carbon fiber in an environment of 2500-3200℃ under the protection of inert gas. During the graphitization process, carbon fiber can further remove about 5% of non-carbon elements, while carbon atoms are arranged in a graphite structure, transforming from a two-dimensional disordered graphite structure to a three-dimensional ordered structure at the microscopic level. The crystal size increases and the degree of orientation increases, thereby improving the modulus of carbon fiber.

[0004] 1. Current Status of Research on Carbon Fiber Graphitization Methods and Equipment at Home and Abroad

[0005] Currently, there are six main types of carbon fiber graphitization methods and equipment under research both domestically and internationally: (1) Microwave plasma heating method and device. This method is a technology invented by Felix LP et al. in the United States that uses microwave plasma technology and electromagnetic radiation to graphitize carbon fibers. Its advantage is that it uses low-pressure and low-temperature plasma technology for graphitization, but its disadvantage is that it cannot be continuously produced. It is still under research. (2) High-frequency plasma heating technology: This technology is invented by Murai of Japan and uses high-temperature plasma to continuously graphitize carbon fibers. The device uses a high-frequency oscillator to discharge under a high-frequency electric field. The temperature suitable for carbon fiber graphitization is obtained by adjusting the current. The advantages are low energy consumption and fast heating speed. The disadvantages are unstable temperature control, inconvenient operation in a vacuum environment, and difficulty in industrialization. (3) DC arc plasma heating device: This device is invented by the Shanxi Coal Chemistry Institute of the Chinese Academy of Sciences and uses DC arc plasma to graphitize carbon fibers. The device uses argon gas as the working medium and applies an 80A DC current to two electrodes at a pressure of 0.3-0.5MPa. It generates continuous high-temperature arc plasma through discharge and graphitizes carbon fibers by passing them through a local area of ​​plasma at 2500-3500℃. The advantages of this technology are simple process and low production cost. The disadvantages are difficulty in temperature distribution and temperature field control, and little hope of industrialization. (4) Solar furnace: Hideo Kurioka of Japan invented a device that uses sunlight as a heat source to graphitize carbon fibers. The device uses a plane mirror and a sun-tracking device to track sunlight and sends the sunlight to a concave mirror for focusing, with a focusing temperature of 1500-3500℃.The advantage of solar furnaces is that they provide a new way to use solar energy without electricity. The disadvantage is that the temperature field is completely dependent on meteorological conditions, and the temperature and temperature distribution are difficult to control, making industrialization unrealistic. (5) Direct current heating method: George E and Julius S Shinko of Union Carbide Corporation in the United States invented a device that allows direct current to pass through carbon fibers, using their own resistance to heat them to high temperatures for continuous graphitization. Theoretically, direct current heating can greatly reduce energy loss. However, due to the high resistivity of carbon fibers, the required heating voltage is much greater than the 36V safety voltage, making it unsafe to operate. This method has not yet been industrialized. (6) Medium frequency induction eddy current heating furnace: The Shanxi Coal Chemistry Institute of the Chinese Academy of Sciences applied for an invention patent (application number is 2024111). Patent 51662.9 (publication date: November 12, 2024) proposes a device for graphitizing carbon fibers using a medium-frequency induction eddy current heating method. The device uses graphite material to make a flat furnace chamber, and a rectangular solenoid-shaped induction coil is sleeved on the outside of the flat furnace chamber. The alternating magnetic field generated in the induction coil passes through the graphite furnace chamber wall and generates eddy currents in the graphite furnace chamber wall. The eddy currents cause the graphite furnace chamber wall to generate high temperature for graphitization. Since the graphite material is not magnetic, the efficiency of converting electromagnetic field energy into eddy currents is low, the energy consumption is large, and the heating speed is not fast enough.

[0006] 2. Carbon fiber graphitization furnaces currently in use in industrial production both domestically and internationally.

[0007] Although there are many methods and technologies under research both domestically and internationally, so far, only two types of carbon fiber graphitization furnaces are actually used in industrial production: resistance heating furnaces and induction eddy current heating furnaces. Both of these belong to indirect heating furnaces, and the following will explain each of these two types of heating furnaces one by one.

[0008] (1) Resistance heating graphitization furnace: This furnace utilizes the electrical conductivity of graphite. A voltage is applied across the graphite tube, and when current flows through the tube, the heating element acts as a resistor and is heated, creating a uniform high-temperature zone inside the tube. Carbon fibers, protected by an inert gas, pass through the tube and are heated. The advantages of this furnace are its relatively uniform temperature distribution in the high-temperature zone and its easily controllable temperature field, meeting the heating requirements of 1500–2800℃. However, if the furnace temperature is raised to 3000–3200℃, the furnace lifespan will not exceed 15 days. Therefore, the operating temperature of the resistance heating furnace cannot exceed 2800℃. Currently, resistance heating furnaces are commonly used in the 1500–2800℃ heating range. Its disadvantages include high energy consumption, slow temperature rise, and short lifespan of the heating element.

[0009] (2) Induction eddy current heating graphitization furnace

[0010] An induction eddy current heating graphitization furnace is a device that uses a medium-frequency electromagnetic field to generate eddy currents inside a graphite tube, thus producing heat. Carbon fibers pass through the graphite tube under the protection of an inert gas atmosphere for graphitization heating. The working principle involves applying a medium-frequency voltage to both ends of a hollow solenoid coil wound with copper tubing. A graphite tube is suspended inside the solenoid. When the solenoid is energized, the medium-frequency electromagnetic field generated by the solenoid induces eddy currents in the graphite tube wall, heating the tube. The graphite tube has an inlet and an outlet for the carbon fibers. The carbon fibers pass through the graphite tube under the protection of the inert gas atmosphere, thus being heated. By adjusting the output power of the medium-frequency power supply, a suitable temperature and temperature distribution can be obtained inside the graphite tube. Advantages: Temperature and temperature distribution are relatively easy to control, enabling industrial-scale production. Disadvantages: Carbon fiber is non-magnetic, resulting in low eddy current heating efficiency and high energy consumption. If the furnace temperature is 3000-3200℃, actual production shows that the furnace life is generally no more than 15 days. Replacing the furnace is costly and time-consuming, thus leading to high production costs.

[0011] In view of the problems of short furnace life and high energy consumption in carbon fiber industrial production, after long-term research, a medium-frequency induction self-heating graphitization furnace for carbon fiber has been invented. This invention utilizes the induced current (non-eddy current) generated by the carbon fiber to generate its own heat to 3000-3200℃, while the furnace temperature is below 2500℃. The furnace only provides a passage for the carbon fiber to run, and only plays a role in heat preservation and anti-oxidation. Therefore, energy consumption is significantly reduced and the furnace life is greatly extended. Actual production shows that the furnace life exceeds one year. III. Summary of the Invention

[0012] This invention discloses a medium-frequency induction carbon fiber self-heating graphitization furnace.

[0013] Appendix Figure 1 The diagram is for the present invention and is also an abstract drawing. The system mainly consists of three units: (1) Carbon fiber filament transmission path unit: including graphite guide wheels 3, 4, 5, 9, 10, 11, and metal housings 2 and 12; (2) Heat preservation and anti-oxidation unit: including furnace graphite tube 13, heat preservation layer 14, temperature measuring instrument 15, and argon gas supply pipe 16; (3) Induction heating unit: including Hall speed probe 19, medium frequency power supply 18, medium frequency toroidal transformer 17, brushes 6 and 8, and grounding cable 7.

[0014] This invention is a technology based on the induced current generated when carbon fibers pass through an intermediate frequency transformer, causing them to heat up and produce high temperatures. Utilizing the self-heating of carbon fibers for graphitization is a direct heating method. (See attached...) Figure 1It can be seen that when carbon fiber 1 passes through graphite guide wheels 3, 4, 5, 9, 10, and 11 at a certain speed, since the carbon fiber passes through the middle of the intermediate frequency transformer 17, the carbon fiber between graphite guide wheels 5 and 9, together with the grounding cable 7, brushes 6 and 8, and guide wheels 5 and 9, constitutes the secondary circuit of the intermediate frequency transformer 17. When the intermediate frequency voltage generated by the intermediate frequency power supply 18 is input to the primary coil of the intermediate frequency transformer 17, an induced current flows through the carbon fiber between graphite guide wheels 5 and 9. The induced current heats up the carbon fiber through its own resistance. Based on the speed of the carbon fiber, the rotational speed of guide wheel 4 is measured by Hall effect speed probe 19. The speed signal is fed back to the intermediate frequency power supply 18. The intermediate frequency power supply 18 automatically adjusts the output power according to the speed feedback signal to heat the carbon fiber to 2500℃~3200℃, thereby realizing the continuous graphitization production of carbon fiber. In order to avoid the carbon fiber from oxidizing at high temperature, the metal boxes 2 and 12 are respectively sealed and connected to both ends of the graphite tube 13 in the furnace to form a communicating vessel. Argon gas enters the heating zone from the gas inlet pipe 16 and fills the graphite tube 13 and the metal boxes 2 and 12 with argon gas. The carbon fiber will not oxidize when heated in the argon gas environment. 15 is a radiation temperature measuring instrument to measure the heating temperature in real time. 14 is a heat insulation layer to prevent heat loss.

[0015] This invention pertains to direct-heating graphitization furnaces, which, compared with existing indirect-heating graphitization furnaces (such as resistance heating furnaces and induction eddy current heating furnaces), have advantages such as fast heating speed, long furnace life, precise temperature field control, high graphitization output, significant energy saving, simple and convenient operation, and low production cost. IV. Description of the attached drawings

[0016] Figure 1 This is a schematic diagram of the present invention, and also serves as an abstract drawing.

[0017] Combination Figure 1 Describe the names and functions of each component. 1 is carbon fiber; 2 is a metal enclosure with a door and sealing function, in which graphite guide wheels 3, 4, and 5 are installed. Graphite guide wheel 5 slides in contact with brush 6. 12 is also a metal cavity with a door, in which graphite guide wheels 9, 10, and 11 are installed. Graphite guide wheel 9 slides in contact with brush 8. Brushes 6 and 8 are reliably grounded through cable 7, ensuring the carbon fiber outside the furnace is not electrified and guaranteeing operator safety. 13 is the furnace graphite tube; 14 is the insulation layer; 15 is a radiant temperature measuring instrument; 16 is an argon gas supply pipe; 17 is a medium-frequency toroidal transformer; 18 is a medium-frequency power supply. The furnace graphite tube 13 and the insulation layer 14 both pass through the center of the medium-frequency toroidal transformer 17. 19 is a Hall effect speed probe used to measure the rotational speed of guide wheel 4. Argon gas enters the graphite tube 13 from 16, filling the furnace with argon gas to prevent high-temperature oxidation of the carbon fiber.

[0018] Figure 2This is a schematic diagram of a medium-frequency induction power supply unit system.

[0019] Figure 2 In the diagram, 17 is a medium-frequency transformer and 18 is a medium-frequency power supply. V. Detailed Implementation Methods

[0020] Figure 1 This is a schematic diagram of the present invention. As can be seen from the diagram, the system mainly consists of three units:

[0021] (1) Carbon fiber filament drive path unit: including graphite guide wheels 3, 4, 5, 9, 10, 11, and metal housings 2 and 12.

[0022] (2) Heat preservation and anti-oxidation unit: including furnace graphite tube 13, heat preservation layer 14, temperature measuring instrument 15, and argon gas supply pipe 16.

[0023] (3) Induction heating unit: including Hall speed probe 19, medium frequency power supply 18, medium frequency toroidal transformer 17, brushes 6 and 8 and grounding cable 7.

[0024] Specific implementation: Metal housings 2 and 12 are welded from stainless steel plates. The front of the housing has a door with sealing rings around its perimeter. Guide wheels 3, 4, 5, 9, 10, and 11 are made of graphite material. Depending on the number of fibers passing through them, the guide wheels can be designed as single-groove or multi-groove. The preferred guide wheel diameter is 80–120 mm. The guide wheel shaft is machined from stainless steel. The main parameters of the intermediate frequency power supply 18 are: operating frequency 1kHz–20kHz, maximum output power 50kW, and intermediate frequency transformer power not less than 60KVA. To ensure the uniformity of carbon fiber heating, the heating power must satisfy P = kND. 2 V represents the tracking relationship, where N is the number of carbon fibers, D is the diameter of each fiber, V is the running speed of the carbon fibers in the furnace, and k is a coefficient determined by the specific heat capacity ratio, resistivity, linear expansion coefficient, and maximum heating temperature of the carbon fibers. This intermediate frequency power supply can be purchased from the market as required. The intermediate frequency transformer 17 is a toroidal transformer, and its structure is shown in the attached figure. Figure 2 As shown, the components can be custom-made by the intermediate frequency transformer manufacturer. Brushes 6 and 8 are standard parts and can be purchased directly from the market. Graphite tube 13 can be custom-made from a carbon fiber manufacturer. Graphite tube 13 is connected to the stainless steel housings 2 and 12 using flanges to ensure a tight seal. The insulation layer 14 uses multiple layers of graphite cotton to ensure the temperature on the outside of the insulation layer meets safety requirements. The temperature measuring instrument 15 is a radiation temperature measuring system, requiring a measurement range of 1500–3500℃. This instrument can be purchased from the market. The argon gas inlet pipe 16 is made of graphite material. The Hall effect speed probe 19 is an NPN normally open model with a detection distance of not less than 10mm. For safety and aesthetics, the entire system is installed in a cabinet welded from steel plates, channel steel, and angle iron.

Claims

1. An intermediate frequency induction type carbon fiber self-heating graphitization furnace, characterized by It consists of six graphite guide wheels, two metal sealed cavities, a graphite tube with insulation, a medium-frequency power supply, a medium-frequency transformer, a radiation thermometer, a speed probe, two brushes, a grounding wire, and an argon gas supply pipe. Its structure and connection are as follows: the six graphite guide wheels are installed inside the two metal enclosures; the graphite tube with insulation passes through the middle of the toroidal medium-frequency transformer, with both ends of the graphite tube sealed to the two metal enclosures; the medium-frequency power supply outputs medium-frequency voltage to the primary winding of the medium-frequency transformer; the two brushes are slidably connected to the two graphite guide wheels; the grounding cable connects the two brushes to the ground; the argon gas pipe, graphite tube, and two metal enclosures form a communicating vessel; the temperature measuring instrument measures the furnace temperature through the insulation layer; the speed probe measures the rotational speed of the guide wheels; and carbon fiber passes through the guide wheels and within the graphite tube.

2. The intermediate frequency induction type carbon fiber self-heating graphitization furnace according to claim 1, characterized by, The six graphite guide wheels and the graphite tube with the insulation layer form a wire feeding channel.

3. The intermediate frequency induction type carbon fiber self-heating graphitization furnace according to claim 1, characterized by, The graphite tube with the wound insulation layer passes through the middle of the toroidal intermediate frequency transformer.

4. The intermediate frequency induction type carbon fiber self-heating graphitization furnace according to claim 1, characterized by, The two ends of the graphite tube are respectively sealed and connected to two metal boxes.

5. The intermediate frequency induction type carbon fiber self-heating graphitization furnace according to claim 1, characterized by, The intermediate frequency power supply operates at a frequency of 1kHz to 20kHz, with a maximum output power of 50kW, and the intermediate frequency transformer has a power of not less than 60KVA.

6. The intermediate frequency induction carbon fiber self-heating graphitization furnace according to claim 1, characterized in that, The two brushes are slidably connected to the corresponding two graphite guide wheels, and both brushes are grounded through wires.

7. The MF induction carbon fiber self-heating graphitization furnace according to claim 1, characterized in that, The insulation material wrapped around the graphite tube is graphite wool, and an argon gas input pipe and a radiation temperature measuring instrument are installed through the insulation layer.

8. The intermediate frequency induction carbon fiber self-heating graphitization furnace according to claim 1, characterized in that, The two metal boxes have doors on the front, and the doors are fitted with sealing rings around their perimeter.

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