A laser heating carbon fiber graphitization device and a clean maintenance method for the inner wall of the heating cavity thereof

Abstract

This invention discloses a laser-heated carbon fiber graphitization device and a method for maintaining the cleanliness of the inner wall of its heating cavity, belonging to the field of carbon fiber graphitization technology. The device discloses that, by uniformly introducing inert gas along the circumferential direction of the inner wall of the reflective cavity through the tangential airflow outlet of a spiral guide device, and in conjunction with a concentric guide structure with an annular gap arranged concentrically with the outlet end and the inner wall, the wall-adhering airflow maintains a complete annular flow path from the inlet to the outlet without dissipation. Simultaneously, the two work together to form a continuous and stable wall-adhering airflow barrier on the inner wall surface of the cavity, and a central airflow zone with a velocity lower than the wall-adhering airflow in the area where the central carbon fiber is located. This creates a differentiated airflow field where high speed on the wall surface and low speed in the center coexist, effectively solving the core problems in existing technologies where the lack of a dedicated wall protection structure leads to the free diffusion and long-term accumulation of carbon vapor on the high-reflectivity inner wall, causing continuous attenuation of reflectivity and unstable processing temperature.

Description

Technical Field

[0001] This invention belongs to the field of carbon fiber graphitization technology, specifically relating to a laser-heated carbon fiber graphitization device and a method for maintaining the cleanliness of the inner wall of the heating chamber. Background Technology

[0002] High-temperature graphitization of carbon fibers is a key process for improving their modulus, purity, and mechanical properties. The high-temperature environment can transform the disordered carbon structure inside the carbon fiber into a regular graphite crystal structure. In the current mainstream laser graphitization process, the laser reflection and heat-gathering effect of the high-reflectivity cavity inner wall can achieve an ultra-high temperature processing environment of over 2800℃ under low laser power input conditions, effectively reducing equipment energy consumption and laser device losses.

[0003] However, the existing process has significant technical flaws: when laser irradiates carbon fiber to a temperature exceeding 2800℃, carbon sublimation occurs on the surface of the carbon fiber, generating a large amount of fine carbon vapor. This carbon vapor, suspended inside the cavity, easily diffuses with the airflow and adheres to the surface of the high-reflectivity inner wall of the cavity. After long-term processing, a dense layer of carbon vapor forms on the inner wall. This layer significantly reduces the laser reflectivity of the inner wall, leading to a decrease in the laser reflection and heat concentration effect inside the cavity. With a constant laser output power, the actual processing temperature inside the cavity continuously decreases, causing instability in the carbon fiber graphitization temperature, ultimately resulting in uneven graphitization, large differences in mechanical properties, and low product yield.

[0004] Currently, there is no specific internal wall anti-contamination and cleaning solution in the industry. Carbon vapor can only be removed by manually wiping and cleaning the cavity during regular shutdowns. This not only interrupts the production process and reduces production efficiency, but manual cleaning may also damage the highly reflective inner wall surface, causing irreversible loss of reflectivity, increasing equipment maintenance costs and production losses. It cannot meet the needs of continuous and stable high-end carbon fiber graphitization processing and production.

[0005] Chinese patent application CN104760953A discloses a laser tunnel total internal reflection axial focusing graphitization furnace and a controllable laser ultra-high temperature graphitization device. It uses laser heating to achieve carbon fiber graphitization and is equipped with an inert gas sealing protection structure, solving the problems of high energy consumption and uneven temperature in traditional graphitization. However, it only uses a conventional cavity inert gas sealing structure, with the core purpose of preventing oxidation and maintaining high temperature. It does not design a dedicated protective structure for the carbon sublimation and carbon deposition problem of carbon fibers above 2800℃, lacks a wall-mounted airflow barrier design, a combination structure of spiral flow guide and concentric gap flow guide, and a differentiated airflow field parameter control scheme. Therefore, it cannot solve the core problems of carbon vapor adhesion and reflectivity attenuation on the inner wall of the high-reflectivity cavity. Summary of the Invention

[0006] The purpose of this invention is to provide a laser-heated carbon fiber graphitization device and a method for maintaining the cleanliness of the inner wall of the heating cavity, in order to solve the technical problems of carbon vapor adhesion and reflectivity attenuation on the inner wall of a high-reflectivity cavity that cannot be solved by existing methods.

[0007] To achieve the above objectives, the present invention employs the following technical solution: This invention discloses a laser-heated carbon fiber graphitization device, comprising a reflective cavity, the inner wall of which is made of a high reflectivity material; an inert gas inlet is provided at the fiber inlet end of the reflective cavity, and a spiral guiding device is provided inside the inlet end; the spiral guiding device is used to guide the inert gas put into the inert gas inlet tangentially into the interior of the reflective cavity, and to make the inert gas diffuse uniformly along the circumferential direction of the inner wall of the reflective cavity. The fiber outlet end of the reflective cavity is provided with a concentric flow guiding structure. The concentric flow guiding structure is arranged concentrically with the inner wall of the reflective cavity, and there is an annular gap between the concentric flow guiding structure and the inner wall of the reflective cavity. The annular gap constitutes a gas outlet for exporting gas from inside the reflective cavity. The reflective cavity is used for carbon fibers to pass through along their axial direction. The carbon fibers are located in the central region of the reflective cavity, and a laser light source is provided on the outside. The spiral flow guiding device works in conjunction with the concentric flow guiding structure to form a wall-mounted airflow barrier on the inner wall surface of the reflective cavity, and to form a central airflow zone in the central region of the reflective cavity with a velocity lower than that of the wall-mounted airflow barrier, thus creating a differentiated airflow field with a velocity difference between the inner wall surface and the central region.

[0008] Furthermore, the spiral guide device is an integrated spiral blade structure; the surface of the spiral guide device has a spiral with a spiral angle of 10°~45°; The width of the annular gap between the concentric flow guiding structure and the inner wall of the reflective cavity is 3mm to 5mm.

[0009] Furthermore, the airflow velocity in the wall-mounted airflow barrier region is 2m / s to 5m / s.

[0010] Furthermore, the airflow velocity in the central airflow zone is less than 2 m / s.

[0011] Furthermore, the high reflectivity material is a high-temperature resistant, high-reflectivity metallic material or a high-temperature resistant, high-reflectivity ceramic material; The spiral blades fit seamlessly into the inner wall of the reflective cavity.

[0012] Furthermore, the laser emission direction of the laser source is directed toward the interior of the reflective cavity, for emitting laser light into the interior of the reflective cavity to heat the carbon fiber.

[0013] This invention also discloses a method for keeping the inner wall of a laser heating cavity clean using a wall-attached airflow, applied in the laser-heated carbon fiber graphitization process. The graphitization process uses a high-reflectivity material to prepare the inner wall of the reflective cavity, and includes the following steps: S1: An inert gas inlet and an inlet spiral guide device are installed at the fiber inlet end of the reflective cavity. The inert gas inlet is connected to an external inert gas source, and the spiral guide device is located downstream of the inert gas inlet. A concentric guide structure is installed at the fiber outlet end of the reflective cavity. The concentric guide structure is concentrically arranged with the inner wall of the reflective cavity and forms an annular gap between them. The annular gap constitutes the gas outlet. S2: Inert gas is introduced into the spiral guide device through the inert gas inlet, and is introduced into the interior of the reflective cavity in a tangential manner through the spiral guide device. After being rectified by the spiral guide device, it diffuses evenly along the circumferential direction of the inner wall of the reflective cavity. S3: By controlling the intake flow rate of inert gas, an annular wall-mounted airflow barrier is formed on the inner wall surface of the reflective cavity. At the same time, the airflow velocity around the carbon fiber in the central region of the reflective cavity is lower than the airflow velocity of the wall-mounted airflow barrier, forming a differentiated airflow field with velocity difference between the wall surface and the central region. S4: During the high-temperature graphitization heating of carbon fiber by the laser source, the carbon vapor generated by the high-temperature sublimation of carbon fiber is blocked by the wall airflow barrier, preventing the carbon vapor from contacting and adhering to the inner wall of the reflective cavity, thus continuously maintaining the cleanliness of the inner wall of the reflective cavity. After being dynamically blocked by the wall airflow barrier, the carbon vapor is discharged from the reflective cavity through the gas outlet with the airflow.

[0014] Furthermore, the inert gas is argon or nitrogen.

[0015] Furthermore, the temperature of the laser-heated carbon fiber graphitization treatment is higher than 2800°C.

[0016] Furthermore, by matching the inlet pressure and flow rate of the inert gas, the airflow velocity of the wall-mounted airflow barrier is stabilized at 2m / s to 5m / s.

[0017] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a laser-heated carbon fiber graphitization device. Inert gas is uniformly introduced along the circumferential direction of the inner wall of a reflective cavity through the tangential airflow outlet of a spiral guide device. Combined with a concentric guide structure with an annular gap and concentrically arranged outlet end with the inner wall, the adhering airflow maintains a complete annular flow path from inlet to outlet without dissipation. Simultaneously, the two elements work together to form a continuous and stable adhering airflow barrier on the inner wall surface of the cavity, and a central airflow zone with a velocity lower than the adhering airflow velocity is formed in the area where the central carbon fiber is located. This creates a differentiated airflow field where high-speed airflow on the wall surface coexists with low-speed airflow at the center, enabling the carbon fiber to be graphitized at high temperatures above 2800℃. During the heating process, the carbon vapor generated by sublimation cannot penetrate the inner wall due to the momentum and velocity barrier of the airflow on the wall. At the same time, the low-speed airflow in the center confines the carbon vapor in the central region of the cavity and directs it to be discharged axially from the gas outlet. The velocity difference between the wall and the center forms a shear layer that further inhibits the radial diffusion of carbon vapor. The airflow on the wall also has a dynamic purging function, continuously carrying away the trace amounts of carbon vapor that tend to the wall. This effectively solves the core problems in the existing technology where the lack of a dedicated protective structure on the wall leads to the free diffusion of carbon vapor and its long-term accumulation on the high-reflectivity inner wall, resulting in continuous attenuation of reflectivity and unstable processing temperature.

[0018] This invention also discloses a method for maintaining the cleanliness of the inner wall of a laser heating cavity using wall-mounted airflow. Through differentiated airflow field design, the method blocks the adhesion of high-temperature sublimated carbon vapor to the inner wall of the cavity from the source, completely solving the problem of decreased inner wall reflectivity caused by carbon vapor contamination in traditional processes. It can maintain the cleanliness of the inner wall of the cavity and the constant laser reflectivity for a long time. Under the premise of constant laser power, it can stably ensure the ultra-high temperature processing environment inside the cavity and significantly improve the temperature stability of carbon fiber graphitization processing.

[0019] Furthermore, by strictly controlling the airflow velocity around the carbon fiber in the center of the cavity to be below 2m / s, the high-speed airflow is avoided from disturbing the carbon fiber bundle, effectively preventing problems such as carbon fiber displacement, shaking, and deformation, ensuring the stability of the carbon fiber processing shape, and guaranteeing the consistency of product processing accuracy and mechanical properties.

[0020] Furthermore, this invention eliminates the need for manual cleaning of the cavity during machine downtime, completely avoiding the drawbacks of frequent downtime maintenance in traditional processes. It significantly improves the continuous operation capability of the production line, reduces manual maintenance costs, equipment wear and tear, and production downtime losses, resulting in a significant increase in production efficiency. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the overall structure of the laser-heated carbon fiber graphitization device of the present invention. Figure 2 Three-view diagram of the spiral guide device; Where: a - front view; b - left view; c - sectional view; Figure 3 This is a schematic diagram of the airflow field distribution inside the cavity of the present invention; The components include: 1. Carbon fiber; 2. Inert gas inlet; 3. Laser source; 4. Outlet concentric flow guide device; 5. Gas outlet; 6. Spiral flow guide device; 7. Reflecting cavity. Detailed Implementation

[0022] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0023] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0024] The purpose of this invention is to solve the problem in the existing laser-heated carbon fiber graphitization process where carbon vapor generated by high-temperature carbon sublimation adheres to the inner wall of the cavity, reduces the reflectivity of the inner wall, and leads to unstable processing temperature. The invention provides a method to keep the inner wall of the laser heating cavity clean by using wall-mounted airflow, thereby achieving dynamic anti-contamination inside the cavity, continuously maintaining the cleanliness and constant reflectivity of the inner wall, ensuring stable graphitization processing temperature, and improving product processing quality and production efficiency.

[0025] Based on the above objectives, this invention proposes a laser-heated carbon fiber graphitization device, such as... Figure 1As shown, the device includes a reflective cavity 7, the inner wall of which is made of a high-reflectivity material. The reflective cavity 7 has a fiber inlet end and a fiber outlet end. The fiber inlet end of the reflective cavity 7 is provided with an inert gas inlet 2, which is used to connect to an external inert gas source. Downstream of the inert gas inlet 2 is an inlet spiral guide device 6, which has a tangential airflow outlet. The tangential airflow outlet communicates with the interior of the reflective cavity 7. The spiral guide device 6 is used to guide the inert gas introduced through the inert gas inlet 2 tangentially into the interior of the reflective cavity 7, and to uniformly diffuse the inert gas along the circumferential direction of the inner wall of the reflective cavity 7. The fiber outlet end of the reflective cavity 7 is provided with a concentric guide structure 4, which is arranged concentrically with the inner wall of the reflective cavity 7, and an annular gap exists between the concentric guide structure 4 and the inner wall of the reflective cavity 7. This annular gap constitutes a gas outlet 5, which is used to... The gas inside the reflective cavity 7 is discharged; the reflective cavity 7 is used for the carbon fiber 1 to pass through along its axial direction, and the carbon fiber 1 is located in the central region of the reflective cavity 7; a laser source 3 is provided outside the reflective cavity 7, and the laser emission direction of the laser source 3 is towards the inside of the reflective cavity 7. The laser source 3 is used to emit laser into the reflective cavity 7 to heat the carbon fiber 1; the inlet spiral guide device 6 cooperates with the concentric guide structure 4 to form an annular wall-mounted airflow barrier on the inner wall surface of the reflective cavity 7, and to form a central airflow zone in the central region of the reflective cavity 7 with a velocity lower than that of the wall-mounted airflow barrier. There is a velocity difference between the airflow velocity of the wall-mounted airflow barrier and the airflow velocity of the central airflow zone, forming a differentiated airflow field with a velocity difference between the wall surface and the central region, so as to block the carbon vapor generated by the high-temperature sublimation of the carbon fiber 1 during the high-temperature graphitization heating of the carbon fiber by the laser source 3.

[0026] Preferably, such as Figure 2 As shown, the spiral guide device 6 is an integrated spiral blade structure; the spiral guide device 6 has more than 10 spiral blades, with a thickness of 1mm-2mm, mainly to ensure strength, and the pitch is adjusted according to the tooling size (3-5 times the diameter of the reflective cavity, ultimately requiring a spiral angle of 10-45°).

[0027] Preferably, the width of the annular gap between the concentric flow guiding structure 4 and the inner wall of the reflective cavity 7 is 3mm to 5mm. The concentric flow guiding structure 4 is an annular tube structure with a hollow middle (through which carbon fiber 1 passes), and the outlet is processed into a flange structure to be fixed to the outer shell of the cavity. The material is high temperature resistant (generally graphite).

[0028] Preferably, the high reflectivity material is a high-temperature resistant, high-reflectivity metal material or a high-temperature resistant, high-reflectivity ceramic material; specifically, it is a polished metal (copper, tungsten, molybdenum, etc.) and then gold / silver plating on the surface of the polished metal; it can also be a polished alumina ceramic or other materials.

[0029] Preferably, the airflow velocity in the wall-mounted airflow barrier region is 2 m / s to 5 m / s; The airflow velocity in the central airflow zone is less than 2 m / s.

[0030] This invention also discloses a method for maintaining the cleanliness of the inner wall of a laser heating cavity using wall-mounted airflow, applied in the laser-heated carbon fiber graphitization process. The graphitization cavity uses a high-reflectivity material to prepare the inner wall. The core improvement lies in the formation of a zoned differentiated airflow field through the flow guiding structure at both ends of the cavity combined with the tangential inlet of inert gas, thereby achieving contamination-proof and clean protection of the inner wall. The specific operation steps include the following: 1. Cavity structure modification: A spiral guide device 6 is fixedly installed at the fiber inlet end of the reflective cavity 7. The spiral angle of the spiral guide device 6 is strictly controlled to be 10-45° to ensure the rectification effect of tangential airflow introduction. A concentric guide structure 4 is set at the fiber outlet end of the cavity. This structure is completely concentric with the inner wall of the reflective cavity 7, and the gap between it and the inner wall of the reflective cavity 7 is precisely controlled to be 3-5mm to form an annular air outlet channel. 2. Inert gas guide air intake: High-purity dry inert gas is selected as the protective and blocking airflow. The inert gas is introduced into the interior of the reflective cavity 7 from the tangential channel of the spiral guide device 6 at the inlet end. Through the guiding effect of the spiral blades of the spiral guide device 6, the gas is uniformly diffused along the circumferential direction of the inner wall of the reflective cavity 7. 3. Airflow field parameter control: By precisely adjusting the inlet pressure and flow rate of the inert gas, a continuous, stable, and annular wall-attached airflow barrier is formed on the inner wall surface of the reflective cavity 7, and the wall-attached airflow velocity is strictly controlled at 2-5 m / s; at the same time, relying on the flow guide structure design at both ends of the cavity, the airflow velocity in the carbon fiber processing area in the center of the cavity is controlled below 2 m / s, forming a differentiated airflow field of high-speed wall-attached airflow and low-speed stable airflow in the center; the precise adjustment of the inlet pressure and flow rate of the inert gas is first determined by fluid simulation, as well as the airflow velocity in the cavity. In actual use (cold state), the wind speed in different areas of the cavity can be tested by an anemometer.

[0031] 4. Dynamic Clean Protection: During the laser high-temperature graphitization process, the carbon vapor generated by the sublimation of carbon fiber 1 is constrained by the low-speed airflow in the center and concentrated in the central area of ​​the reflective cavity 7, preventing it from diffusing to the inner wall of the cavity. At the same time, the high-speed airflow adhering to the wall forms a physical barrier, completely preventing carbon vapor from adsorbing and adhering to the inner wall of the cavity. In addition, the airflow adhering to the wall can carry a small amount of suspended carbon vapor out of the cavity from the annular gap at the outlet end, continuously maintaining the cleanliness of the inner wall of the cavity.

[0032] Specifically, the method includes the following steps: S1. An inert gas inlet 2 and a spiral guide device 6 are installed at the fiber inlet end of the reflective cavity 7. The inert gas inlet 2 is connected to an external inert gas source, and the spiral guide device 6 is located downstream of the inert gas inlet 2. A concentric guide structure 4 is installed at the fiber outlet end of the reflective cavity 7. The concentric guide structure 4 is concentrically arranged with the inner wall of the reflective cavity 7 and forms an annular gap between them. The annular gap constitutes a gas outlet 5. The carbon fiber 1 is inserted along the axial direction of the reflective cavity 7 into the central region of the reflective cavity 7, and the laser source 3 is placed outside the reflective cavity 7 with the emission direction of the laser source 3 facing the interior of the reflective cavity 7. S2. Inert gas is introduced into the spiral guide device 6 through the inert gas inlet 2, and is tangentially introduced into the interior of the reflective cavity 7 through the spiral guide device 6. After being rectified by the spiral guide device 6, it diffuses evenly along the circumferential direction of the inner wall of the reflective cavity 7. S3. By controlling the inlet flow rate of the inert gas, an annular wall-attached airflow barrier is formed on the inner wall surface of the reflective cavity 7. At the same time, the airflow velocity around the carbon fiber 1 in the central region of the reflective cavity 7 is lower than the airflow velocity of the wall-attached airflow barrier, forming a differentiated airflow field with velocity difference between the wall surface and the central region. S4. The laser source 3 is activated to heat the carbon fiber 1 at high temperature for graphitization. During the heating process, the wall-mounted airflow barrier is used to block the carbon vapor generated by the high-temperature sublimation of the carbon fiber 1, preventing the carbon vapor from contacting and adhering to the inner wall of the reflective cavity 7, and continuously maintaining the cleanliness of the inner wall of the reflective cavity 7. After being dynamically blocked by the wall-mounted airflow barrier, the carbon vapor is discharged from the reflective cavity 7 through the gas outlet 5 with the airflow.

[0033] Example 1 A method for keeping the inner wall of a laser heating cavity clean using wall-attached airflow includes the following steps: Step 1: Install an inert gas inlet 2 and a spiral guide device 6 at the fiber inlet end of the reflective cavity 7 (copper tube surface plated with silver). The inert gas inlet 2 is connected to an external inert gas source. The spiral guide device 6 is located downstream of the inert gas inlet 2. The spiral angle of the spiral guide device 6 is 25°, and the spiral blades are seamlessly attached to the inner wall of the reflective cavity 7. Install a concentric guide structure 4 at the fiber outlet end of the reflective cavity 7. The concentric guide structure 4 is concentrically arranged with the inner wall of the reflective cavity 7 and forms an annular gap between them. The width of the annular gap is 4mm, and the annular gap constitutes the gas outlet 5. Insert the carbon fiber 1 along the axial direction of the reflective cavity 7 into the central area of ​​the reflective cavity 7, and place the laser source 3 outside the reflective cavity 7 with the emission direction of the laser source 3 facing the inside of the reflective cavity 7. Step 2: Select high-purity argon as the inert protective gas. Introduce the argon gas into the inlet spiral guide device 6 through the inert gas inlet 2. The argon gas is then introduced into the interior of the reflective cavity 7 in a tangential manner through the spiral guide device 6. After being rectified by the inlet spiral guide device 6, the argon gas diffuses evenly along the circumferential direction of the inner wall of the reflective cavity 7. Step 3: Adjust the argon gas inlet flow rate and pressure to form an annular wall-mounted airflow barrier on the inner wall surface of the reflective cavity 7. The airflow velocity of the wall-mounted airflow barrier is stably maintained at 3.5 m / s, while the airflow velocity around the carbon fiber 1 in the central region of the reflective cavity 7 is controlled at 1.2 m / s, forming a differentiated airflow field with velocity differences between the wall surface and the central region. Step 4: Start the laser source 3 to heat the carbon fiber 1 at high temperature for graphitization. Set the heating temperature to 2900℃. During the heating process, use the wall-mounted airflow barrier to block the carbon vapor generated by the high-temperature sublimation of the carbon fiber 1, preventing the carbon vapor from contacting and adhering to the inner wall of the reflective cavity 7. The carbon vapor is constrained by the central low-speed airflow in the central area of ​​the reflective cavity 7. After being dynamically blocked by the wall-mounted airflow barrier, it is discharged from the reflective cavity 7 with the airflow through the gas outlet 5.

[0034] After 24 hours of continuous processing, the inner wall of the reflective cavity 7 was inspected. There was no obvious carbon vapor adhering, the reflectivity of the inner wall was consistent with that before processing, the temperature fluctuation inside the cavity was less than ±5℃, and the uniformity of carbon fiber graphitization met the standard.

[0035] Example 2 A method for keeping the inner wall of a laser heating cavity clean using wall-attached airflow includes the following steps: Step 1: Install an inert gas inlet 2 and a spiral guide device 6 at the fiber inlet end of the reflective cavity 7 (copper tube surface plated with silver). The inert gas inlet 2 is connected to an external inert gas source. The spiral guide device 6 is located downstream of the inert gas inlet 2. The spiral angle of the spiral guide device 6 is 10°, and the spiral blades are seamlessly attached to the inner wall of the reflective cavity 7. Install a concentric guide structure 4 at the fiber outlet end of the reflective cavity 7. The concentric guide structure 4 is concentrically arranged with the inner wall of the reflective cavity 7 and forms an annular gap between them. The width of the annular gap is 3mm, and the annular gap constitutes the gas outlet 5. Insert the carbon fiber 1 along the axial direction of the reflective cavity 7 into the central area of ​​the reflective cavity 7, and place the laser source 3 outside the reflective cavity 7 with the emission direction of the laser source 3 facing the inside of the reflective cavity 7. Step 2: Select high-purity argon as the inert protective gas. Introduce the argon gas into the inlet spiral guide device 6 through the inert gas inlet 2. The argon gas is then introduced into the interior of the reflective cavity 7 in a tangential manner through the spiral guide device 6. After being rectified by the inlet spiral guide device 6, the argon gas diffuses evenly along the circumferential direction of the inner wall of the reflective cavity 7. Step 3: Adjust the argon gas inlet flow rate and pressure to form an annular wall-mounted airflow barrier on the inner wall surface of the reflective cavity 7. The airflow velocity of the wall-mounted airflow barrier is stably maintained at 2m / s, while the airflow velocity around the carbon fiber 1 in the central region of the reflective cavity 7 is controlled at 1.0m / s, forming a differentiated airflow field with velocity differences between the wall surface and the central region. Step 4: Start the laser source 3 to heat the carbon fiber 1 at high temperature for graphitization. Set the heating temperature to 2900℃. During the heating process, use the wall-mounted airflow barrier to block the carbon vapor generated by the high-temperature sublimation of the carbon fiber 1, preventing the carbon vapor from contacting and adhering to the inner wall of the reflective cavity 7. The carbon vapor is constrained by the central low-speed airflow in the central area of ​​the reflective cavity 7. After being dynamically blocked by the wall-mounted airflow barrier, it is discharged from the reflective cavity 7 with the airflow through the gas outlet 5.

[0036] After 24 hours of continuous processing, the inner wall of the reflective cavity 7 was found to be free of carbon vapor buildup, the reflectivity showed no attenuation, and the processing temperature remained stable.

[0037] Example 3 A method for keeping the inner wall of a laser heating cavity clean using wall-attached airflow includes the following steps: Step 1: Install an inert gas inlet 2 and a spiral guide device 6 at the fiber inlet end of the reflective cavity 7 (copper tube surface plated with silver). The inert gas inlet 2 is connected to an external inert gas source. The spiral guide device 6 is located downstream of the inert gas inlet 2. The spiral angle of the spiral guide device 6 is 45°, and the spiral blades are seamlessly attached to the inner wall of the reflective cavity 7. Install a concentric guide structure 4 at the fiber outlet end of the reflective cavity 7. The concentric guide structure 4 is concentrically arranged with the inner wall of the reflective cavity 7 and forms an annular gap between them. The width of the annular gap is 5mm, and the annular gap constitutes the gas outlet 5. Insert the carbon fiber 1 along the axial direction of the reflective cavity 7 into the central area of ​​the reflective cavity 7, and place the laser source 3 outside the reflective cavity 7 with the emission direction of the laser source 3 facing the inside of the reflective cavity 7. Step 2: Select high-purity argon as the inert protective gas. Introduce the argon gas into the inlet spiral guide device 6 through the inert gas inlet 2. The argon gas is then introduced into the interior of the reflective cavity 7 in a tangential manner through the spiral guide device 6. After being rectified by the inlet spiral guide device 6, the argon gas diffuses evenly along the circumferential direction of the inner wall of the reflective cavity 7. Step 3: Adjust the argon gas inlet flow rate and pressure to form an annular wall-mounted airflow barrier on the inner wall surface of the reflective cavity 7. The airflow velocity of the wall-mounted airflow barrier is stably maintained at 5 m / s, while the airflow velocity around the carbon fiber 1 in the central region of the reflective cavity 7 is controlled at 1.8 m / s, forming a differentiated airflow field with velocity differences between the wall surface and the central region. Step 4: Start the laser source 3 to heat the carbon fiber 1 at high temperature for graphitization. Set the heating temperature to 2950℃. During the heating process, use the wall-mounted airflow barrier to block the carbon vapor generated by the high-temperature sublimation of the carbon fiber 1, preventing the carbon vapor from contacting and adhering to the inner wall of the reflective cavity 7. The carbon vapor is constrained by the central low-speed airflow in the central area of ​​the reflective cavity 7. After being dynamically blocked by the wall-mounted airflow barrier, it is discharged from the reflective cavity 7 through the gas outlet 5 with the airflow.

[0038] After 24 hours of continuous processing, the airflow barrier effect along the wall is excellent, with no carbon vapor adhering to the inner wall, and the heat retention performance of the cavity is stable with no temperature decay.

[0039] Comparative Example The traditional non-wall-adhering airflow protection process is adopted, meaning that the inlet spiral guide device 6 is not installed at the fiber inlet end of the reflective cavity 7, nor is the concentric guide structure 4 installed at the fiber outlet end; only inert gas is introduced for conventional atmosphere protection. Under the same processing conditions of 2900℃, after continuous processing for 30 minutes, obvious carbon vapor adhesion appears on the inner wall of the reflective cavity 7, the reflectivity of the inner wall decreases by more than 22%, the fiber temperature in the cavity drops by more than 200℃, the degree of graphitization of the product is uneven, the pass rate drops significantly, and the fiber thermal conductivity decreases by 80~100W / mk.

[0040] Figure 3The simulation results of this invention were analyzed using Flow Simulation. The simulation analysis shows that when the airflow is taken at three cross-sections along the length of the reflective cavity 7, the airflow velocity distribution values ​​in the central region and near the wall region of the corresponding cross-sections are as follows: the airflow velocity near the wall region is about 3.0 m / s, and the velocity in the central region is about 0.4 m / s. The airflow velocity shows a clear annular distribution, with a low airflow velocity in the central region and a high airflow velocity in the outer ring region, which is completely consistent with the function described in this invention.

[0041] In summary, this invention, through the tangential flow guidance of the spiral flow guiding device 6 and the outlet constraint of the concentric flow guiding structure 4, combined with precise airflow parameter control, can stably achieve clean protection of the inner wall of the reflective cavity 7, completely solving the technical drawbacks of carbon vapor adhesion leading to the attenuation of inner wall reflectivity and unstable processing temperature in traditional processes. It balances processing stability, product quality and production efficiency, and has extremely high industrial application value.

[0042] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A laser-heated carbon fiber graphitization device, characterized in that, The system includes a reflective cavity (7), the inner wall of which is made of a high reflectivity material; the fiber inlet end of the reflective cavity (7) is provided with an inert gas inlet (2), and a spiral guide device (6) is provided inside the inlet end; the spiral guide device (6) is used to guide the inert gas put into the inert gas inlet (2) into the interior of the reflective cavity (7) in a tangential manner, and to make the inert gas diffuse evenly along the circumferential direction of the inner wall of the reflective cavity (7); The fiber outlet end of the reflective cavity (7) is provided with a concentric flow guide structure (4). The concentric flow guide structure (4) is arranged concentrically with the inner wall of the reflective cavity (7), and there is an annular gap between the concentric flow guide structure (4) and the inner wall of the reflective cavity (7). The annular gap constitutes a gas outlet (5) for exporting the gas inside the reflective cavity (7). The reflective cavity (7) is used for the carbon fiber (1) to pass through along its axial direction. The carbon fiber (1) is located in the central region of the reflective cavity (7), and a laser source (3) is provided outside. The spiral guide device (6) and the concentric guide structure (4) work together to form a wall-mounted airflow barrier on the inner wall surface of the reflective cavity (7) and to form a central airflow zone with a velocity lower than that of the wall-mounted airflow barrier in the central region of the reflective cavity (7), thus forming a differentiated airflow field with a velocity difference between the inner wall surface and the central region.

2. The laser-heated carbon fiber graphitization device according to claim 1, characterized in that, The spiral guide device (6) is an integral spiral blade structure; the surface of the spiral guide device (6) has a spiral with a spiral angle of 10°~45°; The width of the annular gap between the concentric flow guiding structure (4) and the inner wall of the reflective cavity (7) is 3mm to 5mm.

3. The laser-heated carbon fiber graphitization device according to claim 1, characterized in that, The airflow velocity in the wall-mounted airflow barrier area is 2m / s to 5m / s.

4. The laser-heated carbon fiber graphitization device according to claim 1, characterized in that, The airflow velocity in the central airflow zone is less than 2 m / s.

5. The laser-heated carbon fiber graphitization device according to claim 1, characterized in that, The high-reflectivity material is a high-temperature resistant, high-reflectivity metallic material or a high-temperature resistant, high-reflectivity ceramic material. The spiral blades fit seamlessly with the inner wall of the reflective cavity (7).

6. The laser-heated carbon fiber graphitization device according to claim 1, characterized in that, The laser emission direction of the laser source (3) is toward the interior of the reflective cavity (7), and is used to emit laser into the interior of the reflective cavity (7) to heat the carbon fiber (1).

7. A method for maintaining the cleanliness of the inner wall of a laser heating cavity using a wall-attached airflow, characterized in that, In the laser-heated carbon fiber graphitization process, the graphitization process uses a high-reflectivity material to prepare the inner wall of the reflective cavity (7), and includes the following steps: S1: An inert gas inlet (2) and an inlet spiral guide device (6) are installed at the fiber inlet end of the reflective cavity (7). The inert gas inlet (2) is connected to an external inert gas source, and the spiral guide device (6) is located downstream of the inert gas inlet (2). A concentric guide structure (4) is installed at the fiber outlet end of the reflective cavity (7). The concentric guide structure (4) is concentrically arranged with the inner wall of the reflective cavity (7) and an annular gap is formed between them. The annular gap constitutes the gas outlet (5). S2: Inert gas is introduced into the spiral guide device (6) through the inert gas inlet (2), and is introduced into the interior of the reflective cavity (7) in a tangential manner through the spiral guide device (6). After being rectified by the spiral guide device (6), it diffuses evenly along the circumferential direction of the inner wall of the reflective cavity (7). S3: By controlling the inlet flow rate of inert gas, an annular wall-attached airflow barrier is formed on the inner wall surface of the reflective cavity (7), while the airflow velocity around the carbon fiber (1) in the central region of the reflective cavity (7) is lower than the airflow velocity of the wall-attached airflow barrier, thus forming a differentiated airflow field with velocity difference between the wall surface and the central region. S4: During the process of high-temperature graphitization heating of carbon fiber (1) by laser light source (3), carbon vapor generated by high-temperature sublimation of carbon fiber (1) is blocked by wall airflow barrier, preventing carbon vapor from contacting and adhering to the inner wall of reflective cavity (7), and continuously maintaining the cleanliness of the inner wall of reflective cavity (7). After being dynamically blocked by the wall airflow barrier, carbon vapor is discharged from reflective cavity (7) through gas outlet (5) with airflow.

8. A method for maintaining the cleanliness of the inner wall of a laser heating cavity using wall-attached airflow according to claim 7, characterized in that, The inert gas is argon or nitrogen.

9. A method for maintaining the cleanliness of the inner wall of a laser heating cavity using wall-attached airflow according to claim 7, characterized in that, The laser-heated carbon fiber graphitization process is performed at a temperature higher than 2800℃.

10. A method for maintaining the cleanliness of the inner wall of a laser heating cavity using wall-attached airflow according to claim 7, characterized in that, By matching the inlet pressure and flow rate of the inert gas, the airflow velocity of the wall-mounted airflow barrier is stabilized at 2m / s to 5m / s.

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