CN1329567C - Continuous carbon fibre graphitizing method and apparatus - Google Patents

Abstract

The present invention relates to a method and a device of continuous graphitization for a carbon fiber, and the present invention uses a plasma torch heating technique. The carbon fiber is partially heated with a high temperature of 2000 to 3000 DEG C to generate graphitization by using the plasma heating technology; the temperature and the temperature distribution of the plasma torch are controlled by output power of a control power source and load air volume. The temperature is measured by infrared, and the drafting uses a differential retracting wire device. The present invention has the advantages of novel method, simple operation and low energy consumption, and is an operable method of the continuous graphitization for the carbon fiber.

Description

A method and device for continuous graphitization of carbon fibers

technical field

The invention belongs to a method and a device for continuous graphitization of carbon fibers, in particular to a process and a device for continuous graphitization of carbon fibers by using a plasma torch.

technical background

Carbon fiber and graphite fiber are mainly used as the most important reinforcement materials of advanced structural composite materials, and are widely used in spacecraft, aerospace vehicles, satellites, military industry and high-end sporting goods.

Graphite fiber is made by graphitizing carbon fiber at 2000°C-3000°C under the protection of inert gas. The tensile modulus of carbon fiber can be greatly improved through graphitization. At present, the industrialized production of high-performance graphite fibers and the formation of series products are Japan and the United States. my country's graphite fiber is still in the development stage, and the level is far behind that of foreign countries.

The key factors affecting the graphitization of carbon fiber are high-temperature equipment and high-temperature heat treatment technology. Among them, the high-temperature equipment graphitization furnace is particularly critical. Ultra-high temperature and stable temperature distribution are the basis for preparing high-performance graphite fibers.

Carbon fiber graphitization using plasma technology is a new research field. Plasma is a non-condensed system composed of a large number of charged particles, which is produced by ionization of gas under heating or strong electromagnetic field. , Molecules, active free radicals and rays.

At present, it has been reported that the use of plasma technology for graphitization research is a device for continuous graphitization heat treatment of carbon fibers using high-temperature thermal plasma invented by Japanese Murai (Patent Gazette: Zhao 59-38323). Discharge under a high-frequency electric field, in the presence of inert gases helium and nitrogen, generate a high-frequency heating plasma source, by adjusting the current and the flow rate of the mixed gas to obtain the temperature and temperature distribution suitable for carbon fiber graphitization, the entire graphitization device is set In a closed vacuum container, vacuum replacement is carried out by a vacuum pump, exhaust gas is continuously removed and inert gas helium and nitrogen are injected, and the carbon fibers in the closed container are continuously graphitized at a high temperature of about 3000°C to form graphite fibers.

Continuous graphitization of carbon fibers can also be carried out by using DC arc plasma (CN1399017A, CN1399016A). The device uses the inert gas argon as the working medium, and applies a 30-200A direct current between the two electrodes under a pressure of 0.3-0.5Mpa to generate a continuous high-temperature arc plasma through discharge, and passes the carbon fiber through the plasma at 2500°C- Graphitization is carried out in the local high temperature region of 3500°C.

The technology of carbonization and graphitization of carbon fiber using microwave plasma technology and electromagnetic radiation (US6372192B1) uses a microwave generator with a frequency of 2.45GHz and a power of 6KW to generate plasma by microwave discharge. The plasma is in a non-equilibrium state and gaseous atoms At room temperature, electrons have a very high temperature and have enough energy to graphitize the fiber. In this device, carbon fiber is placed in a vacuum quartz tube and placed in a plasma and electromagnetic radiation field. Through the coupling of plasma and electromagnetic radiation, the electromagnetic energy is utilized by the fiber, resulting in a large amount of energy acting on the fiber and causing the carbon fiber to generate graphite. and then increase the degree of carbonization and graphitization of carbon fibers by gradually increasing the electric power.

Comparing the reported devices for carbon fiber graphitization using plasma technology, it can be found that the thermal plasma graphitization device invented by Murai in Japan has high requirements for vacuum, and the entire graphitization process, including fiber feeding and receiving devices, is in the same In the vacuum chamber, this brings inconvenience to the operation and control; the DC arc plasma graphitization device uses the plasma arc to heat the fiber, but because the fiber passes through the arc horizontally, the fiber is heated unevenly, which affects the graphitized fiber. Stability; the carbonization and graphitization of carbon fiber using microwave plasma technology and electromagnetic radiation is difficult to be used in industrial production due to the intermittent graphitization and the vacuum.

Contents of the invention

The object of the present invention is to provide a method and device for continuous graphitization of carbon fibers with simple equipment and low energy consumption using a plasma torch.

The method for continuous graphitization using carbon fiber as a raw material in the present invention comprises the following steps: the carbon fiber is first desized in an acetone solution and the residence time is 1-10 minutes; The residence time of the fiber in the plasma torch is 5-120 seconds, and the draft ratio is kept at -5-5%, and the plasma gas is argon; the concentration of the fiber after graphitization is 0.5-2.5% by mass The epoxy resin acetone solution is used for sizing, and the residence time is 10-180 seconds; the sized fibers are dried at 150-350°C for 1-5 minutes, and finally graphite fibers are obtained.

In order to realize the method of the present invention, a device for continuous graphitization of carbon fibers with a plasma torch has been designed. The device adopts high-frequency induction technology, and specifically includes a high-frequency generator, an induction coil and a plasma torch, and is characterized in that the plasma torch has two internal and external Layer concentric quartz glass tube, the outer quartz glass tube is 1-2 times longer than the inner quartz glass tube, the inner quartz glass tube is cylindrical at one end and tapered at the other end, with carbon fiber at the tapered end of the inner quartz glass tube Wire inlet and plasma gas inlet, there is a cooling gas inlet on the outer quartz glass tube at the same tapered end as the inner quartz glass tube, the induction coil is located on the outer quartz glass tube, and the high frequency generator is connected to the induction coil .

The above-mentioned high-frequency generator adopts self-excited inductive coupling, the frequency is 27-50MHz, and the power is 2-10KW.

The above-mentioned induction coil is a copper tube with 2-4 turns.

As mentioned above, the connection between the cooling air inlet and the outer quartz glass tube is connected in a tangential direction.

The above-mentioned inert gas argon should be purified, and the oxygen content in the argon should be controlled below 2ppm, and the dew point of water should be below -64°C.

The induction coil is set on the plasma torch, and the other end is connected to the high-frequency generator. When the high-frequency current passes through the induction coil, a strong oscillating magnetic field is generated in the torch with gas; the plasma torch is composed of two layers of concentric quartz glass tubes composition. Among them, the inner tube is fed with argon gas to ignite the plasma, and the outer tube is fed with argon gas as a cooling gas, which is introduced along the tangential direction and spirally rises. Its function is to blow the plasma away from the inner wall of the outer quartz tube, which can Protect the quartz tube from being burned, and part of the argon flow also participates in the discharge process. The outer tube is more than twice as long as the inner tube to ensure that a plasma torch is formed inside the quartz glass tube to prevent the carbon fiber from being oxidized during the graphitization process. During use, first use the igniter to ionize the argon gas in the inner tube, then the electrons and ions are accelerated under the high-frequency magnetic field to produce impact ionization, the electrons and ions increase sharply, and eddy currents are induced in the gas at this time. The high-frequency induction current generates a large amount of heat energy and promotes the ionization of the gas to maintain the high temperature of the gas, thereby generating a plasma torch.

Both the plasma gas and the cooling gas entering from the air inlet adopt a tangential entry method, so the high-temperature gas forms a rotating circulation, and at the same time, due to the skin effect of high-frequency induction, the flow moves on the outer circumference of the circular circuit, so the plasma torch has Ring structure, and the higher the frequency, the more obvious this phenomenon. The plasma torch has a flame core area, an inner flame area, and a tail flame area. The temperature in the flame core area is as high as several thousand or even 10,000 degrees, while the temperature in the central channel area of the annular plasma torch is lower. By adjusting the output of the high-frequency generator Plasma torches with different temperature distributions can be obtained by power and gas flow. The carbon fiber passes through the center of the annular plasma torch, and high-temperature graphitization can be performed by using the local high temperature of the plasma torch. In addition, the argon gas entering from the air inlet also acts as a protective gas, and the carbon fiber needs to be protected by an inert gas during the graphitization process to prevent it from being oxidized at high temperature.

Compared with the existing related technologies, the present invention has the advantages of novel process, simple equipment, low energy consumption, and fast heating rate. Compared with other plasma graphitization devices, it avoids the disadvantages of vacuum system and poor heating stability, and can be implemented Continuous operation, in addition, the equipment is small in size, light in weight, and easy to operate, suitable for the production and development of high-performance graphite fibers, and has potential industrial application prospects.

Description of drawings

Fig. 1 is the structural representation of the plasma carbon fiber continuous graphitization device of the present invention

As shown in the figure, 1 is the carbon fiber, 2 is the plasma air inlet, 3 is the cooling air inlet, 4 is the outer tube, 5 is the inner tube, 6 is the induction coil, 7 is the high frequency generator, 8 is the inlet Silk mouth.

The plasma torch is two layers of concentric quartz glass tubes inside and outside. The outer layer of quartz glass tube 4 is 1-2 times longer than the inner layer of quartz glass tube 5. The inner layer of quartz glass tube 5 is cylindrical at one end and tapered at the other end. The tapered end of the quartz glass tube 5 has a carbon fiber inlet 8 and a plasma gas inlet 2, and the outer quartz glass tube 4 at the same end as the inner quartz glass tube 5 has a cooling gas inlet 3 and an induction coil 6 Located on the outer quartz glass tube 4, the high frequency generator 7 is connected with the induction coil 6.

Detailed ways

Example 1

Using 3K carbon fiber as raw material, the fiber stays in the acetone solution for 3 minutes, and after being dried at 200°C for 3 minutes, it enters the plasma graphitization device 6, the frequency of the high-frequency generator is 27MHz, and the draft ratio of the fiber is -1 %, the flow of argon plasma gas 2 is 2L/min, the flow of cooling gas 3 is 15L/min, the residence time of fiber in the plasma torch is 15 seconds, the output frequency of adjusting high-frequency generator 3 is 2KW, the sizing agent The concentration is 2%, the residence time is 20 seconds, and finally dried at 200° C. for 3 minutes to obtain graphite fibers. The properties are shown in Table 1.

Example 2

Using 3K carbon fiber as raw material, the fiber stays in the acetone solution for 5 minutes, and after being dried at 300°C for 1 minute, it enters the plasma graphitization device 6, the frequency of the high-frequency generator is 27MHz, and the flow rate of the argon plasma gas 2 is 2L /min, the flow rate of cooling air 3 is 15L/min, the residence time of fiber in plasma torch is 15 seconds, the draft ratio of fiber is 1%, the output frequency of adjusting high-frequency generator 3 is 2.5KW, the sizing agent The concentration is 5%, the residence time is 20 seconds, and finally dried at 200° C. for 3 minutes to obtain graphite fibers. The properties are shown in Table 1.

Example 3

Using 3K carbon fiber as raw material, the fiber stays in the acetone solution for 10 minutes, and after being dried at 300°C for 1 minute, it enters the plasma graphitization device 6. The frequency of the high-frequency generator is 27MHz, and the draft ratio of the fiber is 2%. , the flow rate of the argon plasma gas 2 is 2L/min, the flow rate of the cooling gas 3 is 15L/min, the residence time of the fiber in the plasma torch is 15 seconds, the output frequency of the high-frequency generator 3 is adjusted to be 3KW, and then the sizing is carried out. The concentration of the sizing agent is 2%, the residence time is 120 seconds, and finally dried at 300° C. for 1 minute to obtain graphite fibers. The properties are shown in Table 1.

Example 4

Using 3K carbon fiber as raw material, the fiber stays in the acetone solution for 5 minutes, and after being dried at 150°C for 5 minutes, it enters the plasma graphitization device 6. The frequency of the high-frequency generator is 27MHz, and the power is 5KW. By adjusting the draft device, the draft ratio of the fiber is 2%, the flow rate of the argon plasma gas 2 is 1L/min, the flow rate of the cooling gas 3 is 15L/min, the residence time of the fiber in the plasma torch is 15 seconds, adjust the high frequency generator 3 The output frequency is 3KW, and then sizing is carried out, the concentration of the sizing agent is 2%, the residence time is 120 seconds, and finally the graphite fiber is obtained by drying at 300°C for 1 minute. The properties are shown in Table 1.

Example 5

Using 3K carbon fiber as raw material, the fiber stays in the acetone solution for 8 minutes, and after being dried at 250°C for 3 minutes, it enters the plasma graphitization device 6, the frequency of the high-frequency generator is 27MHz, and the draft ratio of the fiber is 4%. , the flow rate of the argon plasma gas 2 is 3L/min, the flow rate of the cooling gas 3 is 15L/min, the residence time of the fiber in the plasma torch is 15 seconds, the output frequency of the high-frequency generator 3 is adjusted to be 3KW, and then the sizing is carried out. The concentration of the sizing agent is 2%, the residence time is 120 seconds, and finally dried at 250° C. for 3 minutes to obtain graphite fibers. The properties are shown in Table 1.

The performance of graphite fiber under the different embodiments of table 1

Power (KW) Tensile strength (Gpa) Tensile modulus (Gpa) elongation(%) Example 1 3.01 350 0.9 Example 2 2.85 365 0.8 Example 3 2.69 398 0.7 Example 4 3.23 362 0.8 Example 5 2.31 455 0.5

The invention adopts the plasma torch to carry out the continuous graphitization of carbon fiber, which can effectively use energy, reduce production cost, and has simple equipment, fast heating rate, and avoids vacuum system. It is a new method and equipment for continuous graphite of carbon fiber, and has potential industrialization Take advantage of prospects.

Claims (4)

1, a kind of device that is used for the carbon fiber continuous graphitization comprises radio-frequency generator (7), induction coil (6) and plasmatorch pipe, it is characterized in that the plasmatorch pipe is inside and outside two-layer concentric quartz glass tube, outer quartz glass tube (4) than the long 1-2 of internal layer quartz glass tube (5) doubly, internal layer quartz glass tube (5) is that an end is a cylindricality, the other end is taper, at internal layer quartz glass tube (5) taper one end carbon fiber wire inlet (8) and plasma (orifice) gas air inlet (2) are arranged, with the outer quartz glass tube (4) of the same end of internal layer quartz glass tube (5) taper on cold gas import (3) is arranged, induction coil (6) is positioned on the outer quartz glass tube (4), and radio-frequency generator (7) links to each other with induction coil (6).

2, a kind of device that is used for the carbon fiber continuous graphitization as claimed in claim 1 is characterized in that described radio-frequency generator (7) adopts the coupling of auto-excitation type inductance, and frequency is 27-50MHz, and power is 2-10KW.

3, a kind of device that is used for the carbon fiber continuous graphitization as claimed in claim 1 is characterized in that described induction coil is a copper pipe, and the number of turns is the 2-4 circle.

4, a kind of device that is used for the carbon fiber continuous graphitization as claimed in claim 1 is characterized in that described cold gas import (3) and being connected of outer quartz glass tube (4) are that tangential direction connects.