Production process of ultra-large silicon carbide thin-wall diffusion tube

Abstract

The invention discloses a production process of an ultra-large silicon carbide thin-wall diffusion tube, which belongs to the technical field of silicon carbide, and comprises the following steps: raw material mixing, granulation, volatile matter detection, die filling, segmented isostatic pressing forming, demolding, drying and shaping, sintering, bonding forming and the like. The ultra-long diffusion pipe can be machined in the mode of split machining in the die filling process and bonding after sintering, the thin-walled pipe can be machined through the isostatic pressing forming technology, the rubber cylinder is adopted for assisting the steel inner die to be separated in the die releasing process, the rubber cylinder tightly wraps the green body branch pipe body, all the positions of the green body branch pipe body are stressed in a balanced mode, and the service life of the green body branch pipe body is prolonged. The strength of the green body branch pipe body can be enhanced, the green body branch pipe body is prevented from being damaged in the separation process of the steel inner mold, the green body branch pipe body is prevented from being damaged in the carrying process, large-diameter diffusion pipes can be machined, and the machining efficiency of large-diameter, ultra-long and thin-wall pipe bodies is effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field of silicon carbide, and in particular to a production process for an ultra-large silicon carbide thin-wall diffusion tube. Background Art

[0002] The diffusion tube is a special device for solar silicon wafers to absorb boron ions. The silicon wafer is placed in the diffusion tube and heated in an electric heating furnace. The thermal conductivity of the diffusion tube is utilized. As the temperature in the furnace rises, the temperature inside the diffusion tube gradually rises. When the temperature reaches 900°C, boron chloride gas is blown into the diffusion tube. The boron chloride is decomposed by heat, and the boron ions are adsorbed on the silicon wafer. After cooling, a layer of boron film is attached to the silicon wafer. The diffusion tube is an important production tool in the processing of solar silicon wafers. In order to improve the efficiency and quality of boron film attachment of single-furnace solar silicon wafers, the market has increasingly stringent requirements on diameter, length and wall thickness. Therefore, the market prospects for large-diameter, ultra-long and thin-walled diffusion tubes are broad. The existing silicon carbide tube forming methods include casting, extrusion and isostatic pressing. However, the above methods have the following disadvantages when processing large-diameter, ultra-long and thin-walled tubes: 1. Casting molding requires a mold that is too large, which makes demoulding difficult. The strength of the green body after molding is low, and it is difficult to transfer, which makes it difficult to dry and sinter in the next step. In addition, the tube body after demoulding is very easy to deform and damage, and the yield rate is very low; 2. Extrusion molding: the tube body must be extruded together with the inner mold during extrusion, otherwise the tube body is easy to deform. At the same time, because the tube body is extruded together with the inner mold, the tube body and the inner mold fit closely, demoulding is difficult, it is easy to be damaged, and the yield rate is low; 3. Isostatic pressing: Thin-walled silicon carbide tubes with a diameter of less than 300 mm and a length of less than 1000 mm have been widely processed by isostatic pressing, especially in the refractory industry. However, when isostatic pressing is used for ultra-long and large-diameter thin-walled tubes with further increased diameter and length, it is inevitable that demolding is difficult and easy to damage. Summary of the invention

[0003] In order to solve the problems existing in the prior art, the present invention provides a production process for super-large-sized silicon carbide thin-walled diffusion tubes. The method of split processing and bonding after sintering can be used to realize the processing of super-length diffusion tubes, and the isostatic pressing process can be used to realize the processing of thin-walled tubes. During demolding, a rubber tube is used to assist the separation of the steel inner mold. The rubber tube tightly covers the green split tube body, so that the force at each position of the green split tube body is balanced, which can enhance the strength of the green split tube body, avoid damage to the green split tube body during the separation process of the steel inner mold, and avoid damage to the green split tube body during transportation. The processing of large-diameter diffusion tubes can be completed, and the processing efficiency of large-diameter, super-length and thin-walled tubes can be effectively improved.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is as follows: A production process for an ultra-large silicon carbide thin-wall diffusion tube comprises the following steps: 1) Raw material mixing: Mix the following raw materials in parts by weight: 100 parts of silicon carbide powder, 13 parts of high-quality high-purity graphite powder and an appropriate amount of binder and mix them evenly; 2) Granulation: the uniformly mixed raw materials are passed through a granulator to obtain particles with a diameter of no more than 80 microns and then the materials are awakened; 3) Volatile content test: perform weight test on the pellets after the material is awakened to determine the amount of volatile content; 4) Mold loading: The diffusion tube is processed in sections using a tubular split mold, and a steel inner mold with a base at one end is installed in an outer mold. A steel tray abutting against the base is mounted on the steel inner membrane in the outer mold, and the base is sealed and fitted with one end of the outer mold. Then, the weighed particles are filled from the other end of the outer mold into the gap between the steel inner mold and the outer mold, and then the sealing cover mounted on the steel inner mold is used to seal the other end of the outer mold to complete the mold loading; 5) Isostatic pressing: put the completed tubular split mold into the isostatic pressing equipment, adjust the pressure between 90±20MPa according to the size of the volatile matter, maintain the pressure for 5-15 minutes and then slowly release the pressure; 6) Demolding, taking the green body with the steel inner mold out of the isostatic pressing device, and then separating the steel inner mold with the green body from the outer mold with the cooperation of the base, and then vertically placing the end of the steel inner mold with the base downward, and then wrapping the outer side of the green body with a rubber tube in close contact, and lifting the steel tray upward under the support of the rubber tube, separating the green body with the rubber tube from the steel inner mold, and then separating the rubber tube from the green body, and completing demoulding; 7) Drying and shaping: the demoulding green pipe body is placed in a drying oven at 200°C for 2 hours, and after drying, the green pipe body is shaped and shaped to obtain the green pipe body; 8) Sintering: the dried blank pipe body is loaded into a sintering furnace for sintering. The sintering temperature is controlled at above 1700°C to obtain the diffusion tube pipe body; 9) Bonding: bonding the sub-tubes of the diffuser tubes in sequence to install the finished diffuser tube in the length direction, and the length of the obtained finished diffuser tube is not less than 4200 mm.

[0005] Preferably, 1) during the raw material mixing process, the silicon carbide powder is composed of 50% of silicon carbide powder with a particle size of F400 and 50% of silicon carbide powder with a particle size of F1200.

[0006] Preferably, 6) during the demoulding process, the rubber tube is provided with a through opening along the axial direction, and the rubber tube is wrapped and fixed with an adhesive tape when it is wrapped around the outside of the green blank branch pipe body.

[0007] Preferably, 6) during the demoulding process, the inner diameter of the rubber tube is 2 mm smaller than the outer diameter of the green body.

[0008] Preferably, 4) during the molding process, a soft rubber sleeve is provided at one end of the steel tray away from the base, and a plurality of grooves are provided on the side wall of the steel tray.

[0009] Preferably, 4) during the molding process, the outer mold and the sealing cover are both made of rubber material.

[0010] Preferably, the diameter of the steel tray is not greater than the diameter of the base.

[0011] Preferably, 4) during the molding process, the distance between the inner steel mold and the inner wall of the outer mold is set to 4-8 mm, and the inner diameter of the outer mold is not less than 400 mm.

[0012] Preferably, 4) during the isostatic pressing process, both the inner wall of the outer mold and the surface of the steel inner mold are sprayed with a release agent.

[0013] The beneficial effects of the present invention are as follows: 1. The present invention adopts isostatic pressing of dry powder to produce a green body with high strength and thin wall thickness. A rubber tube is used to assist the steel inner mold to be separated during demoulding. The rubber tube tightly covers the green body branch pipe, so that the force at each position of the green body branch pipe is balanced, which can enhance the strength of the green body branch pipe, avoid the green body branch pipe from being damaged during the steel inner mold separation process, and avoid the green body branch pipe from being damaged during the transportation process, which can further reduce the processing requirements of the pipe wall thickness; 2. The present invention adopts a process of segmented pressing and bonding after sintering, which can meet the processing requirements of ultra-long tubes. The segmented processing and sintering process can effectively reduce the processing difficulty of ultra-long tubes and reduce the volume of the sintering furnace, which is conducive to reducing the cost investment; 3. In the present invention, the steel tray cooperates with the steel inner mold, and the steel inner mold can be separated from the green billet pipe body by lifting the steel tray, which can effectively reduce the demoulding difficulty. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a schematic diagram of the mold structure in a production process of an ultra-large silicon carbide thin-wall diffusion tube of the present invention; Figure 2 This is a schematic diagram of a demoulding structure in a production process of an ultra-large silicon carbide thin-wall diffusion tube of the present invention; Figure 3 The present invention is a schematic diagram of the structure of a rubber tube in a production process of an ultra-large silicon carbide thin-wall diffusion tube.

[0015] In the figure: 1-base, 2-steel inner mold, 3-steel tray, 4-outer mold, 5-sealing cover, 6-rubber tube, 7-green tube body. DETAILED DESCRIPTION

[0016] In order to facilitate understanding by those skilled in the art, the present invention is further described below with reference to the accompanying drawings.

[0017] A production process for an ultra-large silicon carbide thin-wall diffusion tube comprises the following steps: 1) Raw materials are mixed in the following weight proportions: 100 parts of mixed silicon carbide powder with a particle size of 50% F400 and 50% F1200, 13 parts of high-quality high-purity graphite powder and an appropriate amount of binder are mixed evenly; 2) Granulation: the uniformly mixed raw materials are passed through a granulator to obtain particles with a diameter of no more than 80 microns and then the materials are awakened; 3) Volatile matter detection: perform weight detection on the pellets after the material is awakened to determine the amount of volatile matter; 4) Moulding, such as Figure 1 As shown, a tubular split mold is used to process the diffusion tube in sections, and a steel inner mold 2 with a base 1 at one end is installed in an outer mold 4, the base 1 is sealed and fitted with one end of the outer mold 4, and the steel inner mold 2 is fixedly installed on the base 1. A freely movable steel tray 3 is mounted on the steel inner film, and the steel tray 3 is in contact with the base 1. A soft rubber sleeve is provided at one end of the steel tray 3 away from the base 1, and a plurality of grooves are provided on the side wall of the steel tray 3. Then, the weighed particles are filled from the other end of the outer mold 4 into the gap between the steel inner mold 2 and the outer mold 4, and the particles are in contact with the soft rubber sleeve on the steel tray 3. Then, a sealing cover 5 mounted on the steel inner mold 2 is used to seal the other end of the outer mold 4, and the mold is completed. 5) Isostatic pressing: put the completed tubular split mold into the isostatic pressing equipment, adjust the pressure between 90±20MPa according to the volatile content, maintain the pressure for 5-15 minutes and then slowly release the pressure. The greater the volatile content in the particles, the lower the pressure in the isostatic pressing equipment, so as to ensure that the green split tube body has sufficient strength after forming; 6) Demolding: Take the green body 7 with the steel inner mold 2 out of the isostatic pressing device, and then push the base 1 to separate the steel inner mold 2 with the green body 7 from the outer mold 4 with the cooperation of the base 1. Figure 2-3As shown in the figure, after the green body 7 with the steel inner mold 2 is taken out, the base 1 is placed vertically downward on a plane, and then the rubber tube 6 with an opening through it in the axial direction is separated along the opening and covered on the outside of the green body 7, and then the rubber tube 6 is wrapped and fixed with an adhesive tape to make the rubber tube 6 and the green body 7 fit tightly, and the steel tray 3 is lifted up through the groove under the support of the rubber tube 6, and the green body 7 with the rubber tube 6 is separated from the steel inner mold 2 under the support of the steel tray 3, and then the adhesive tape is cut, and the rubber tube 6 is pulled open from the opening position to separate the rubber tube 6 and the green body 7, and the demoulding is completed; 7) Drying and shaping: placing the demoulded green pipe body 7 in a drying oven at 200° C. for 2 hours, and shaping the green pipe body after drying; 8) Sintering: the dried blank pipe body is loaded into a sintering furnace for sintering. The sintering temperature is controlled at above 1700°C to obtain the diffusion tube pipe body; 9) Bonding: bonding the sub-tubes of the diffuser tubes in sequence to install the finished diffuser tube in the length direction, and the length of the obtained finished diffuser tube is not less than 4200 mm.

[0018] 6) During the demolding process, the inner diameter of the rubber tube 6 is 2 mm smaller than the outer diameter of the green body 7. By utilizing the elasticity of the rubber itself, it can be ensured that the rubber tube 6 completely covers the green body 7 and that the inner wall of the rubber sleeve is fully fitted with the steel tray 3, so that each part of the green body 7 is evenly stressed, which is beneficial to improving the structural strength of the green body 7. Therefore, during the molding process, the distance between the inner wall of the steel inner mold 2 and the outer mold 4 is maintained at 4-8 mm, and the inner diameter of the outer mold 4 is not less than 400 mm.

[0019] The diameter of the steel tray 3 is not greater than the diameter of the base 1 .

[0020] The above contents are merely examples and explanations of the structure of the present invention. The technicians in this technical field may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the structure of the invention or exceed the scope defined by the claims, they should all fall within the protection scope of the present invention.

Claims

1. A production process for ultra-large silicon carbide thin-wall diffusion tubes, characterized in that: The steps include: 1) Raw material mixing: Mix the following raw materials in parts by weight: 100 parts of silicon carbide powder, 13 parts of high-quality high-purity graphite powder and an appropriate amount of binder and mix them evenly; 2) Granulation: the uniformly mixed raw materials are passed through a granulator to obtain particles with a diameter of no more than 80 microns and then the materials are awakened; 3) Volatile content test: perform weight test on the pellets after the material is awakened to determine the amount of volatile content; 4) Mold loading: The diffuser tube is processed in sections using a tubular split mold. A steel inner mold with a base at one end is installed in an outer mold. The base is sealed and fitted with one end of the outer mold. The weighed particles are then filled into the gap between the steel inner mold and the outer mold from the other end of the outer mold. The sealing cover 5 mounted on the steel inner mold is then used to seal the other end of the outer mold to complete the mold loading. 5) Isostatic pressing: put the completed tubular split mold into the isostatic pressing equipment, adjust the pressure between 90±20MPa according to the size of the volatile matter, maintain the pressure for 5-15 minutes and then slowly release the pressure; 6) Demolding, taking the green body with the steel inner mold out of the isostatic pressing device, and then separating the steel inner mold with the green body from the outer mold with the cooperation of the base, and then vertically placing the end of the steel inner mold with the base downward, and then wrapping the outer side of the green body with a rubber tube in close contact, and lifting the steel tray upward under the support of the rubber tube, separating the green body with the rubber tube from the steel inner mold, and then separating the rubber tube from the green body, and completing demoulding; 7) Drying and shaping: the demoulding green pipe body is placed in a drying oven at 200°C for 2 hours, and after drying, the green pipe body is shaped and shaped to obtain the green pipe body; 8) Sintering: the dried blank pipe body is loaded into a sintering furnace for sintering. The sintering temperature is controlled at above 1700°C to obtain the diffusion tube pipe body; 9) Bonding: bonding the sub-tubes of the diffuser tubes in sequence to install the finished diffuser tube in the length direction, and the length of the obtained finished diffuser tube is not less than 4200 mm.

2. The process for producing an ultra-large silicon carbide thin-wall diffusion tube according to claim 1 is characterized in that: 1) During the raw material mixing process, the silicon carbide powder is composed of 50% silicon carbide powder with a particle size of F400 and 50% silicon carbide powder with a particle size of F1200.

3. The process for producing an ultra-large silicon carbide thin-wall diffusion tube according to claim 1 is characterized in that: 6) During the demoulding process, the rubber tube is provided with a through opening along the axial direction, and the rubber tube is wrapped and fixed with an adhesive tape when it is wrapped around the outside of the green tube body.

4. The process for producing an ultra-large silicon carbide thin-wall diffusion tube according to claim 3 is characterized in that: 6) During the demoulding process, the inner diameter of the rubber tube is 2 mm smaller than the outer diameter of the green pipe body.

5. The process for producing an ultra-large silicon carbide thin-wall diffusion tube according to claim 1 is characterized in that: 4) During the molding process, a soft rubber sleeve is provided at one end of the steel tray away from the base, and a plurality of grooves are provided on the side wall of the steel tray.

6. The process for producing an ultra-large silicon carbide thin-wall diffusion tube according to claim 5, characterized in that: 4) During the molding process, the outer mold and the sealing cover are made of rubber material.

7. The process for producing an ultra-large silicon carbide thin-wall diffusion tube according to claim 5 is characterized in that: The diameter of the steel tray is no greater than the diameter of the base.

8. The process for producing an ultra-large silicon carbide thin-wall diffusion tube according to claim 6 is characterized in that: 4) During the mold installation process, the distance between the inner wall of the steel inner mold and the outer mold is set to 4-8 mm, and the inner diameter of the outer mold is not less than 400 mm.

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