Preparation method of thermoplastic extrusion molding ceramic tube

Abstract

The invention belongs to the technical field of ceramic tube preparation, and particularly relates to a preparation method of a thermoplastic extrusion molding ceramic tube. A preparation method of a thermoplastic extrusion-molded ceramic tube comprises the following specific steps: (1) mixing silicon carbide powder, boron carbide and carbon black by a wet process, and carrying out spray granulation to prepare granules; (2) sequentially adding the granules, an adhesive, a plasticizer and a lubricant into an internal mixer for mixing, extruding and cutting to prepare thermoplastic mixed granules; (3) putting the mixed granules into a spiral reamer extruder, heating and melting, and extruding and molding to obtain a ceramic tube green body; (4) performing vacuum-pumping cracking on the ceramic tube green body; and (5) performing high-temperature sintering in a high-temperature sintering furnace to obtain the ceramic tube. According to the invention, the basic material is prepared into granules in advance, and the plasticity, strength and extrusion conditions of the biscuit are adjusted by changing different binders, plasticizers and lubricants according to different sizes of produced products, so that the flexibility and diversity of production are improved.

Description

Technical Field

[0001] The invention relates to a method for preparing a thermoplastic extrusion-molded ceramic tube. Background Art

[0002] If radioactive materials leak from the heat exchange tubes of nuclear heat exchangers during operation, it will cause radioactive hazards to surrounding workers, residents and the environment. Ceramic tubes are resistant to high temperatures, corrosion and radiation and can work for a long time at high temperatures in oxidizing, corrosive atmospheres and radiation environments. Therefore, they are often used in heat exchange tubes of nuclear heat exchangers, certain types of electrolytic cells and other applications.

[0003] At present, the preparation method of ceramic tubes is mainly extrusion molding. For extrusion molding, the mixture needs a certain degree of plasticity. Patent CN102515768A introduces a method for preparing silicon carbide ceramic tubes. The mixture adds deionized water accounting for 25wt% of the base material as a solvent, which belongs to a water-based silicon carbide plastic mixture. The prepared ceramic tube blank has a high moisture content, poor roundness retention, and is prone to deformation and cracking during the subsequent drying process. Using organic polymer materials as plasticizers can greatly improve the plasticity of barren materials, so organic materials have begun to be frequently used in the extrusion molding process to form plastic flow. This is not only because plasticity is crucial for ceramic blank extrusion molding, but also by adding appropriate organic matter in the ceramic extruded blank or in the mixed raw materials, the mechanical strength of the blank can be improved, which is convenient for the transportation and subsequent machining of the blank.

[0004] In principle, three different types of organic system materials can be used for ceramic material extrusion molding, namely solvent-based systems, thermoplastic systems and thermosetting systems. Among them, the main advantage of thermoplastic system adhesive material extrusion molding is that the corrosiveness of the raw materials is lower than that of other system adhesives, and the contour of the extruded blank is more accurate, making the manufacture of microstructures easier. For microstructures with very small cross-sectional areas, the extrusion pressure can be as high as 70~80Mpa. Under such high pressure, the phase separation effect is usually not observed when using thermoplastic system adhesives.

[0005] Among the existing methods for preparing ceramic tubes formed by extrusion of thermoplastic system bonding materials, the technical path that is particularly close to the innovative solution of the present invention is the use of specific thermoplastic resins as plasticizers. This technology significantly enhances the extrusion performance of ceramic mixtures by utilizing the high plasticity of thermoplastic resins, thereby ensuring the excellent performance of ceramic tubes in shape maintenance and dimensional accuracy. However, this technology still faces several shortcomings: first, the high cost of specific thermoplastic resins directly pushes up the overall production costs; second, the harmful substances that may be released during processing and use threaten both environmental safety and the health of workers; third, the close combination of ceramics and thermoplastic resins makes the recycling and reuse of discarded ceramic tubes extremely difficult, which is not conducive to the recycling of resources; finally, although the thermoplastic system shows obvious advantages in extrusion molding, phase separation or body deformation may still occur under extremely high pressure (such as 70~80Mpa), which undoubtedly limits its application potential in the field of microstructure manufacturing. Therefore, the present invention is committed to overcoming the limitations of the prior art by optimizing the selection and ratio of plasticizers and improving the extrusion molding process, aiming to improve the preparation efficiency and quality of ceramic tubes while reducing costs and reducing the impact on the environment. Summary of the invention

[0006] In view of the above problems, the purpose of the present invention is to provide a method for preparing a thermoplastic extrusion-molded ceramic tube. In this method, the base material is pre-prepared into a granular material, and the plasticity, strength and extrusion conditions of the blank are adjusted by changing different binders, plasticizers and lubricants according to the different sizes of the products produced, thereby improving the flexibility and diversity of product production.

[0007] The technical solution of the present invention is: a method for preparing a thermoplastic extrusion-molded ceramic tube, comprising the following steps: S1: Wet-mixing silicon carbide powder and a sintering aid to form a base material, and preparing a granular material by spray granulation; the silicon carbide powder accounts for 90-98wt% of the base material, and the sintering aid accounts for 2-10wt% of the base material; S2: adding the pellets obtained in step S1, a binder, a plasticizer, and a lubricant to an internal mixer in sequence for mixing, extrusion, and cutting to form a thermoplastic mixed pellet; the binder accounts for 2-5wt% of the total mass of the base material, the plasticizer accounts for 0.5-15wt% of the total mass of the base material, and the lubricant accounts for 1-15wt% of the total mass of the base material; the mixing temperature is 95-105°C; S3: putting the mixed granular material into a spiral cutter extruder, heating and melting it, and then extruding it into a ceramic tube green body; S4: The ceramic tube green body enters a high-temperature sintering furnace for vacuum cracking, the vacuum degree is 100-200Pa, and the low temperature is set at 200℃~800℃, so that the binder, plasticizer and lubricant in the ceramic tube green body are vacuum cracked, and low-temperature debinding is performed, and the time used is 8~10 hours; S5: Under the protection of inert gas, the green blank after low-temperature debinding is heated to 1900~2300℃ in a high-temperature sintering furnace for sintering at a heating rate of 0.5~10℃ / min and a sintering time of 24~26 hours to finally obtain a ceramic tube.

[0008] The particle size of the silicon carbide powder in step S1 is 0.5-0.6 μm.

[0009] During the wet mixing in step S1, deionized water as a solvent and a dispersant are added, and the mixture is stirred and mixed at a speed of 20-30 r / min for 7-9 hours; the mass ratio of deionized water to base material is 1:1, and the amount of dispersant is 0.1-2wt% of the base material; after spray drying in a spray granulation tower, the deionized water is removed.

[0010] The dispersant is tetramethylammonium hydroxide or ammonia water, and the mass concentration of the ammonia water is 15-25%.

[0011] In step S2: the binder is one or a mixture of polyethylene, polypropylene, polybutylene, ethylene glycol acetate, polyoxymethylene, polymethyl methacrylate; the plasticizer is one or a mixture of methyl polyethylene glycol, polyethylene wax, ether methyl cellulose, methyl polysiloxane, dimethyl diethoxy silane, paraffin; the lubricant is one or a mixture of stearic acid or glyceryl stearate, polyethylene wax, paraffin.

[0012] In the step S2, a porous die and a spiral auger are sequentially arranged at the outlet end of the internal mixer, and the mixture obtained after mixing in the internal mixer is extruded by the porous die and cut by the spiral auger to obtain thermoplastic mixed granular material.

[0013] The ceramic tube green body extruded by the extruder in step S3 needs to be cooled and hardened before being subjected to vacuum cracking in step S4. The cooling and hardening time is at least 1 hour at room temperature.

[0014] The technical effects of the present invention are as follows: 1. The present invention prepares the base material into granular material in advance, and adjusts the plasticity, strength and extrusion conditions of the blank by changing different binders, plasticizers and lubricants according to the different sizes of the products produced, thereby improving the flexibility and diversity of product production. 2. The present invention uses a thermoplastic extrusion molding process, which makes the extruded blank have higher mechanical strength and more accurate contours during the high-temperature molding process, and can keep the roundness of the microstructure to a greater extent during the extrusion production process, so it is particularly suitable for preparing microstructures with very small cross-sectional areas. DETAILED DESCRIPTION

[0015] Example 1 A method for preparing a thermoplastic extrusion-molded ceramic tube comprises the following steps: S1: Wet-mixing silicon carbide powder and a sintering aid to form a base material, and preparing a granular material by spray granulation; the silicon carbide powder accounts for 90-98wt% of the base material, and the sintering aid accounts for 2-10wt% of the base material; S2: adding the pellets obtained in step S1, a binder, a plasticizer, and a lubricant to an internal mixer in sequence for mixing, extrusion, and cutting to form a thermoplastic mixed pellet; the binder accounts for 2-5wt% of the total mass of the base material, the plasticizer accounts for 0.5-15wt% of the total mass of the base material, and the lubricant accounts for 1-15wt% of the total mass of the base material; the mixing temperature is 95-105°C; S3: putting the mixed granular material into a spiral cutter extruder, heating and melting it, and then extruding it into a ceramic tube green body; S4: The ceramic tube green body enters a high-temperature sintering furnace for vacuum cracking, the vacuum degree is 100-200Pa, and the low temperature is set at 200℃~800℃, so that the binder, plasticizer and lubricant in the ceramic tube green body are vacuum cracked, and low-temperature debinding is performed, and the time used is 8~10 hours; S5: Under the protection of inert gas, the green blank after low-temperature debinding is heated to 1900~2300℃ in a high-temperature sintering furnace for sintering at a heating rate of 0.5~10℃ / min and a sintering time of 24~26 hours to finally obtain a ceramic tube.

[0016] The particle size of the silicon carbide powder in step S1 is 0.5-0.6 μm.

[0017] During the wet mixing in step S1, deionized water as a solvent and a dispersant are added, and the mixture is stirred and mixed at a speed of 20-30 r / min for 7-9 hours; the mass ratio of deionized water to base material is 1:1, and the amount of dispersant is 0.1-2wt% of the base material; after spray drying in a spray granulation tower, the deionized water is removed.

[0018] The dispersant is tetramethylammonium hydroxide or ammonia water, and the mass concentration of the ammonia water is 15-25%.

[0019] In step S2: the binder is one or a mixture of polyethylene, polypropylene, polybutylene, ethylene glycol acetate, polyoxymethylene, polymethyl methacrylate; the plasticizer is one or a mixture of methyl polyethylene glycol, polyethylene wax, ether methyl cellulose, methyl polysiloxane, dimethyl diethoxy silane, paraffin; the lubricant is one or a mixture of stearic acid or glyceryl stearate, polyethylene wax, paraffin.

[0020] In the step S2, a porous die and a spiral auger are sequentially arranged at the outlet end of the internal mixer, and the mixture obtained after mixing in the internal mixer is extruded by the porous die and cut by the spiral auger to obtain thermoplastic mixed granular material.

[0021] The ceramic tube green body extruded by the extruder in step S3 needs to be cooled and hardened before being subjected to vacuum cracking in step S4. The cooling and hardening time is at least 1 hour at room temperature.

[0022] Example 2 The ceramic tube is prepared by using a method for preparing a thermoplastic extrusion-molded ceramic tube as described in Example 1, comprising the following steps: S1: Wet-mix a base material consisting of 96wt% silicon carbide powder, 1wt% boron carbide and 3.0wt% carbon black; the wet-mixing process is as follows: deionized water as a solvent and tetramethylammonium hydroxide as a dispersant are added to the base material, and stirred and mixed for 7-9 hours at a speed of 20-30 r / min; the mass ratio of deionized water to the base material is 1:1, and the amount of the dispersant is 0.5wt% of the base material; then the wet-mixed product is spray-dried by a spray granulation tower, and the inlet temperature of the spray drying tower is set to 220°C, the outlet temperature is set to 110°C, and the rotation speed of the physicochemical disk is set to 7500-8500 r / min, so that the deionized water is removed to obtain a granular material with a water content of ≤0.5%; S2: adding the pellets obtained in step S1 to an internal mixer, adding a binder consisting of polyethylene powder and commercial wax accounting for 2wt% of the total mass of the base material, stirring, adding methyl polyethylene glycol accounting for 12wt% of the total mass of the base material as a plasticizer, stirring and mixing, and finally adding 15wt% of polyethylene wax accounting for 15wt% of the total mass of the base material as a lubricant, stirring and mixing, the temperature of the mixture is 100°C, the speed is 35HZ, and the time is 30-40 minutes to prepare a mixed mud; the weight ratio of polyethylene powder to commercial wax is 5:1; the mixed mud is extruded at 95-105°C and a pressure of 8-10MPa, and then cut to prepare a thermoplastic mixed granular material, the granules are solid cylinders of Ø8*10; S3: The mixed granular material prepared in the previous step is put into a spiral auger extruder. The die of the spiral auger extruder is a die that can prepare a cylindrical hollow ceramic tube. The mixed granular material is heated and melted at a temperature of 95° C. and extruded through the die. The die is cooled by water to obtain a silicon carbide ceramic tube green body.

[0023] S4: In the low temperature stage of the high temperature sintering furnace, when the temperature gradually rises to 700℃, the binder, plasticizer and lubricant polymer in the green body are vacuum cracked to split these components into monomers, water, carbon dioxide, small molecule alkanes and alkenes, and evaporate them. This process is called the debinding stage. This stage needs to be heated to 120℃, 460℃ and 700℃ for 30 minutes each, and the heating rate is 1.5~2℃ / min. This stage takes a total of 9 hours. The low-temperature debinding of pressureless sintered silicon carbide ceramic materials is to remove impurities and volatiles in the pretreatment stage before sintering, improve the purity and density of the material, optimize its mechanical properties, etc., to prepare for the subsequent high temperature sintering process and ensure that the final product has excellent performance; S5: Continue to increase the temperature of the high-temperature sintering furnace, and continue to sinter the ceramic tube after low-temperature pre-sintering in a high-temperature argon protection environment. When the sintering temperature is between 700 and 2000°C, the heating rate is 2°C / min, and the temperature gradient nodes of 1400°C, 1600°C, 1800°C and 2000°C are kept warm for 30 minutes. When the sintering temperature is in the range of 2000 to 2200°C, the heating rate is reduced to 0.5°C / min, and the temperature nodes of 2100°C and 2200°C are kept warm for 20 minutes respectively. Finally, a sintered ceramic tube is obtained, and its density is 3.12g / cm3.

[0024] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for preparing a thermoplastic extrusion-molded ceramic tube, characterized in that: The following steps are involved: S1: Wet-mixing silicon carbide powder and a sintering aid to form a base material, and preparing a granular material by spray granulation; the silicon carbide powder accounts for 90-98wt% of the base material, and the sintering aid accounts for 2-10wt% of the base material; S2: adding the pellets obtained in step S1, a binder, a plasticizer, and a lubricant to an internal mixer in sequence for mixing, extrusion, and cutting to form a thermoplastic mixed pellet; the binder accounts for 2-5wt% of the total mass of the base material, the plasticizer accounts for 0.5-15wt% of the total mass of the base material, and the lubricant accounts for 1-15wt% of the total mass of the base material; the mixing temperature is 95-105°C; S3: putting the mixed granular material into a spiral cutter extruder, heating and melting it, and then extruding it into a ceramic tube green body; S4: The ceramic tube green body enters a high-temperature sintering furnace for vacuum cracking, the vacuum degree is 100-200Pa, and the low temperature is set at 200℃~800℃, so that the binder, plasticizer and lubricant in the ceramic tube green body are vacuum cracked, and low-temperature debinding is performed, and the time used is 8~10 hours; S5: Under the protection of inert gas, the green blank after low-temperature debinding is heated to 1900~2300℃ in a high-temperature sintering furnace for sintering, the heating rate is 0.5~10℃ / min, the sintering time is 24~26 hours, and finally a ceramic tube is obtained;.

2. The method for preparing a thermoplastic extrusion-molded ceramic tube according to claim 1, characterized in that: The particle size of the silicon carbide powder in step S1 is 0.5-0.6 μm.

3. The method for preparing a thermoplastic extrusion-molded ceramic tube according to claim 1, characterized in that: During the wet mixing in step S1, deionized water as a solvent and a dispersant are added, and the mixture is stirred and mixed at a speed of 20-30 r / min for 7-9 hours; the mass ratio of deionized water to base material is 1:1, and the amount of dispersant is 0.1-2wt% of the base material; after spray drying in a spray granulation tower, the deionized water is removed.

4. The method for preparing a thermoplastic extrusion-molded ceramic tube according to claim 2, characterized in that: The dispersant is tetramethylammonium hydroxide or ammonia water, and the mass concentration of the ammonia water is 15-25%.

5. The method for preparing a thermoplastic extrusion-molded ceramic tube according to claim 1, characterized in that: In step S2: the binder is one or a mixture of polyethylene, polypropylene, polybutylene, ethylene glycol acetate, polyoxymethylene, polymethyl methacrylate; the plasticizer is one or a mixture of methyl polyethylene glycol, polyethylene wax, ether methyl cellulose, methyl polysiloxane, dimethyl diethoxy silane, paraffin; the lubricant is one or a mixture of stearic acid or glyceryl stearate, polyethylene wax, paraffin.

6. The method for preparing a thermoplastic extrusion-molded ceramic tube according to claim 1, characterized in that: In the step S2, a porous die and a spiral auger are sequentially arranged at the outlet end of the internal mixer, and the mixture obtained after mixing in the internal mixer is extruded by the porous die and cut by the spiral auger to obtain thermoplastic mixed granular material.

7. The method for preparing a thermoplastic extrusion-molded ceramic tube according to claim 1, characterized in that: The ceramic tube green body extruded by the extruder in step S3 needs to be cooled and hardened before being subjected to vacuum cracking in step S4. The cooling and hardening time is at least 1 hour at room temperature.