Anti-deformation efficient degreasing technology for large-size silicon nitride ceramic

Abstract

The invention discloses an anti-deformation efficient degreasing technology for large-size silicon nitride ceramic, and belongs to the technical field of ceramic products. According to the method, industrial honeycomb-shaped activated carbon is adopted to be processed, so that a blank subjected to thermal desorption is completely matched in the honeycomb-shaped activated carbon, the blank is completely fixed in the activated carbon, and a molten binder is sucked out of the blank under the action of capillary force, so that efficient degreasing is realized, and after the binder in the blank is softened at a high temperature, the binder in the blank is subjected to thermal desorption; according to the technology, the defect that the periphery of the blank is not uniform due to removal of the binder can be overcome, and the blank is embedded in the honeycomb-shaped activated carbon, so that the honeycomb-shaped activated carbon plays a certain role in supporting the blank.

Description

Technical Field

[0001] This invention relates to the field of ceramic products technology, and in particular to a high-efficiency degreasing technology for preventing deformation of large-size silicon nitride ceramics. Background Technology

[0002] Silicon nitride ceramics, due to their high hardness, excellent thermal shock resistance, and high-temperature resistance, are widely used in high-precision fields such as aerospace turbine blades, bearings, and cutting tools. Ceramic injection molding (CIM) is the core process for fabricating complex-shaped silicon nitride ceramic parts. The process mainly includes steps such as mixing, granulation, injection, debinding, and sintering. The core challenge lies in the debinding stage—removing organic binders from the ceramic preform using physical or chemical methods while avoiding defects such as cracking and deformation during debinding. This step directly affects the quality and performance of the final product. During thermal debinding, the injection-molded preform shrinks due to the removal of binders, plasticizers, and other organic additives. Uneven localized shrinkage can cause cracking. The removal of plasticizers can lead to insufficient strength, resulting in deformation and collapse. Furthermore, failure to promptly remove organic additives from the preform during thermal debinding can cause internal defects such as pores. Summary of the Invention

[0003] This invention uses solvent degreasing for large-sized ceramic parts to remove some of the organic binders inside the blank. The solvent-degreased blank is then embedded inside honeycomb activated carbon and subjected to thermal degreasing and siphon degreasing under nitrogen protection. This effectively prevents defects such as cracks and deformation from occurring in the blank during the degreasing process and significantly improves the degreasing efficiency.

[0004] A high-efficiency degreasing technology for large-size silicon nitride ceramics to prevent deformation, characterized by the following steps: S1. Internal mixing and granulation: Silicon nitride powder and sintering aid are first put into an internal mixer and mixed. During the mixing process, organic additives are gradually added in proportion, and the mixture is granulated.

[0005] S2. Injection Molding: Add the granulated granules into the injection molding machine, adjust the temperature and pressure to 75MPa-95MPa, injection temperature: 155℃-175℃, holding pressure: 70-85MPa.

[0006] S3. Degreasing and loading fixture processing: The industrial honeycomb activated carbon is surface-processed on a precision machine tool according to the shape of the injection part. The honeycomb activated carbon used in this invention has a pore size of 1.5mm. The thickness of the activated carbon is generally determined according to the size of the injection blank, which is generally 5-10 times the size of the blank.

[0007] S4. Solvent degreasing: After injection molding, the blank is placed in kerosene and heated for solvent degreasing, and then dried. The drying temperature is controlled at 70-80℃ and the drying time is 8-12 hours.

[0008] S5. Hot degreasing: Place the dried sample into the prepared activated carbon carrier fixture, and place the activated carbon fixture with the embedded blank into the degreasing furnace for high-temperature hot degreasing.

[0009] Furthermore, the degreasing environment in steps S1-S5 is a nitrogen atmosphere.

[0010] Furthermore, in step S4, the degreasing temperature is between 400-800℃.

[0011] Furthermore, in step S4, the degreasing atmosphere can be air, nitrogen, argon, or vacuum.

[0012] This invention describes a process that gradually removes the binder while preserving the green body structure through physical or chemical methods. The core of this invention is to achieve a dynamic balance between gas removal and green body strength through the rational design of the binder composition and debinding process, providing a defect-free green body for subsequent sintering. Traditional thermal debinding processes involve heating the formed green body, causing the binder to evaporate or thermally decompose into small gas molecules. These gases are then transported from the inside to the outside into the air through diffusion / permeation, thus removing the binder. The atmospheric environment significantly affects debinding efficiency: in an oxidizing atmosphere, the binder reacts with oxygen to accelerate gas generation, but if the gas evaporates too quickly and cannot be discharged from the green body in time, it will accumulate inside, forming defects such as pores, bubbles, or cracks. This risk is particularly prominent in large-sized or complex-shaped parts. To prevent defects caused by uneven dimensional shrinkage or delayed gas discharge due to organic binder decomposition during subsequent thermal debinding processes, this invention is designed to address these issues.

[0013] Therefore, a combination of solvent degreasing and thermal degreasing is employed. Solvent degreasing is primarily used for molded preforms with binders such as grease or polymers, where grease and polymers are immiscible. During degreasing, the preform is immersed in a solvent, and solvent molecules diffuse into the preform, while the grease dissolves in the solvent molecules and diffuses to the preform surface before detaching. In the subsequent thermal degreasing process, to prevent uneven shrinkage of the preform, industrial honeycomb activated carbon is used to process it, ensuring the preform is completely fitted into the honeycomb activated carbon and firmly fixed inside. The preform, fixed by the activated carbon, undergoes nitrogen-protected heat treatment for further degreasing. Because honeycomb activated carbon is prone to oxidation in an aerobic environment, and the organic binders inside the preform react with oxygen, decomposing rapidly, defects such as collapse or cracking may occur in the degreased preform. Using a nitrogen atmosphere for degreasing can prevent the honeycomb activated carbon from oxidizing and effectively prevent defects such as collapse caused by low strength due to the removal of internal plasticizers; since activated carbon is a type of degreasing adsorbent.

[0014] The core principle of siphon degreasing is to draw molten binder out of the green body through capillary action, thereby achieving efficient degreasing. The binder in the green body softens at high temperature and is then drawn out by porous activated carbon through capillary action. In the initial stage, the heating rate can be appropriately increased, and a suitable holding temperature of around 130℃ can be maintained, as the siphon efficiency is highest at this temperature. This allows the binder to flow inside the green body, ensuring uniform distribution and preventing uneven defects around the green body caused by binder removal. Since the green body is embedded within the honeycomb activated carbon, it provides a certain degree of support. Detailed Implementation Example

[0015] High-purity α-Si3N4 powder (D50=0.8 μm, purity ≥99.9%) was used as the matrix material and mixed with a sintering aid system (4 wt% Al2O3-Y2O3 composite additive, molar ratio 1:1) at a mass fraction of 96%. Multiphase dispersion was achieved by wet ball milling. The ball milling media consisted of anhydrous ethanol and silicon nitride balls at a ball-to-material ratio of 5:1. The multi-component binder system and granulation were as follows: PW: 6wt%, LDPE: 3wt%, EVA: 3wt%, DBP: 2wt%, SA: 1wt%. The mixing parameters were: temperature: 120℃, speed: 65rpm. The granulation process was twin-screw extrusion granulation (L / D=40) to obtain homogeneous feed particles with a particle size of 1-2mm.

[0016] Injection molding: Injection temperature 165℃, injection pressure: 80MPa (filling), holding pressure: 75MPa (lasting 15s); mold temperature: 50℃, cooling: 10s; injection molded part size: 100*100*5mm.

[0017] Degreasing and loading fixture processing: Industrial honeycomb activated carbon is surface-processed on a precision machine tool according to the shape of the injection part. The honeycomb activated carbon used in this invention has a pore size of 1.5mm and a thickness of 60mm (30mm at the top and 30mm at the bottom). The fixture is processed according to the blank size.

[0018] Solvent degreasing: Solvent system: kerosene; process parameters: soak at 60℃ for 8 hours, then remove the blank and dry it.

[0019] Hot degreasing: The dried blank is embedded in an activated carbon fixture and placed in a degreasing furnace. Hot degreasing is carried out under nitrogen protection. The degreasing process is as follows: Serial Number Temperature (°C) Time (min) Serial Number Temperature (°C) Time (min) room temperature 0 Phase 11 325 50 Phase 1 100 20 Phase 12 325 60 Phase 2 100 30 Phase 13 375 50 Phase 3 150 50 Phase 14 375 30 Phase 4 150 30 Phase 15 450 75 Phase 5 225 75 Phase 16 450 30 Phase 6 225 30 Phase 17 500 50 Phase 7 275 100 Phase 18 500 30 Phase 8 275 60 Phase 19 600 100 Phase 9 300 50 Phase 20 600 0 Phase 10 300 60 Example

[0020] High-purity α-Si3N4 powder (D50=0.8 μm, purity ≥99.9%) was used as the matrix material and mixed with a sintering aid system (4 wt% Al2O3-Y2O3 composite additive, molar ratio 1:1) at a mass fraction of 96%. Multiphase dispersion was achieved by wet ball milling. The ball milling media consisted of anhydrous ethanol and silicon nitride balls at a ball-to-material ratio of 5:1. The multi-component binder system and granulation were as follows: PW: 6wt%, LDPE: 3wt%, EVA: 3wt%, DBP: 2wt%, SA: 1wt%. The mixing parameters were: temperature: 120℃, speed: 65rpm. The granulation process was twin-screw extrusion granulation (L / D=40) to obtain homogeneous feed particles with a particle size of 1-2mm.

[0021] Injection molding: Injection temperature 165℃, injection pressure: 80MPa (filling), holding pressure: 75MPa (lasting 15s); mold temperature: 50℃, cooling: 10s; injection molded part size: 100*100*5mm.

[0022] Solvent degreasing: Solvent system: kerosene; process parameters: soak at 60℃ for 8 hours, then remove the blank and dry it.

[0023] Hot degreasing: The dried blank is placed in a mold and embedded with activated carbon powder. It is then placed in a degreasing furnace and hot degreasing is carried out under nitrogen protection. The degreasing process is the same as in Example 1. Comparative Example 1 High-purity α-Si3N4 powder (D50=0.8 μm, purity ≥99.9%) was used as the matrix material and mixed with a sintering aid system (4 wt% Al2O3-Y2O3 composite additive, molar ratio 1:1) at a mass fraction of 96%. Multiphase dispersion was achieved by wet ball milling. The ball milling media consisted of anhydrous ethanol and silicon nitride balls at a ball-to-material ratio of 5:1. The multi-component binder system and granulation were as follows: PW: 6wt%, LDPE: 3wt%, EVA: 3wt%, DBP: 2wt%, SA: 1wt%. The mixing parameters were: temperature: 120℃, speed: 65rpm. The granulation process was twin-screw extrusion granulation (L / D=40) to obtain homogeneous feed particles with a particle size of 1-2mm.

[0024] Injection molding: Injection temperature 165℃, injection pressure: 80MPa (filling), holding pressure: 75MPa (lasting 15s); mold temperature: 50℃, cooling: 10s; injection molded part size: 100*100*5mm.

[0025] Solvent degreasing: Solvent system: kerosene; process parameters: soak at 60℃ for 8 hours, then remove the blank and dry it.

[0026] Hot degreasing: The dried blanks are placed in a degreasing furnace and hot degreasing is performed using an air atmosphere. The degreasing process is as follows: Serial Number Temperature (°C) Time (min) Serial Number Temperature (°C) Time (min) room temperature 0 Phase 11 325 50 Phase 1 100 20 Phase 12 325 60 Phase 2 100 30 Phase 13 375 50 Phase 3 150 50 Phase 14 375 30 Phase 4 150 30 Phase 15 450 75 Phase 5 225 75 Phase 16 450 30 Phase 6 225 30 Phase 17 500 50 Phase 7 275 100 Phase 18 500 30 Phase 8 275 60 Phase 19 600 100 Phase 9 300 50 Phase 20 600 0 Phase 10 300 60 Comparative Example 2 High-purity α-Si3N4 powder (D50=0.8 μm, purity ≥99.9%) was used as the matrix material and mixed with a sintering aid system (4 wt% Al2O3-Y2O3 composite additive, molar ratio 1:1) at a mass fraction of 96%. Multiphase dispersion was achieved by wet ball milling. The ball milling media consisted of anhydrous ethanol and silicon nitride balls at a ball-to-material ratio of 5:1. The multi-component binder system and granulation were as follows: PW: 6wt%, LDPE: 3wt%, EVA: 3wt%, DBP: 2wt%, SA: 1wt%. The mixing parameters were: temperature: 120℃, speed: 65rpm. The granulation process was twin-screw extrusion granulation (L / D=40) to obtain homogeneous feed particles with a particle size of 1-2mm.

[0027] Injection molding: Injection temperature 165℃, injection pressure: 80MPa (filling), holding pressure: 75MPa (lasting 15s); mold temperature: 50℃, cooling: 10s; injection molded part size: 100*100*5mm.

[0028] Solvent degreasing: Solvent system: kerosene; process parameters: soak at 60℃ for 8 hours, then remove the blank and dry it.

[0029] Hot degreasing: The dried blanks are placed in a degreasing furnace and hot degreasing is performed using an air atmosphere. The degreasing process is the same as that in Comparative Example 1. project Blank dimensions (mm) Degreasing rate (%) Surface condition Defects such as cracks and bubbles Example 1 100 99.1% uniform shrinkage of blank No bubbles, no cracks Example 2 100 97.9% A small amount of adhesive powder No obvious cracks Comparative Example 1 100 92.2% Micro-folds Obvious edge defects Comparative Example 2 100 93.1% Micro-folds Cracks appeared at the edges Examples 1 and 2 show that degreasing under a nitrogen atmosphere effectively reduces the defect rate. This indicates that different forms of activated carbon exert a capillary effect during the thermal degreasing process, preventing blistering and cracking of the billet due to the volatilization of internal organic matter after solvent degreasing followed by thermal degreasing. Furthermore, the honeycomb activated carbon fixture provides support and a capillary effect, resulting in uniform dimensional shrinkage of the billet after degreasing. Comparing Examples 1 and 1, it is found that while degreasing under an air atmosphere and the heat treatment process are the same, the organic additives inside the billet undergo severe oxidation and volatilization in an aerobic environment. The delayed gas removal causes surface defects, and the volatilization of the binder inside the billet in an aerobic environment leads to uneven shrinkage and noticeable cracks at the edges. Comparative Examples 1 and 2 show that obvious defects and cracks appear in the billet before and after degreasing in an aerobic environment. This indicates that the degreasing atmosphere has a significant impact on degreasing efficiency. By introducing honeycomb activated carbon, deformation of the blanks before and after degreasing can be effectively prevented, greatly improving degreasing efficiency.

Claims

1. A high-efficiency degreasing technology for large-size silicon nitride ceramics to prevent deformation, characterized in that: its steps include: S1. Internal mixing and granulation: Silicon nitride powder and sintering aid are first put into an internal mixer and mixed. During the internal mixing process, organic additives are gradually added in proportion, and the mixture is granulated. S2. Injection molding: Add the granulated granules into the injection molding machine, adjust the temperature and pressure to 75MPa-95MPa, injection temperature: 155℃-175℃, holding pressure: 70-85MPa; S3. Degreasing and loading fixture processing: The industrial honeycomb activated carbon is surface-processed on a precision machine tool according to the shape of the injection part. The honeycomb activated carbon used in this invention has a pore size of 1.5mm. The thickness of the activated carbon is generally determined according to the size of the injection blank, which is generally 5-10 times the size of the blank. S4. Solvent degreasing: After injection molding, the blank is placed in kerosene and heated for solvent degreasing and then dried. The drying temperature is controlled at 70-80℃ and the drying time is 8-12 hours. S5. Hot degreasing: Place the dried sample into the prepared activated carbon carrier fixture, and place the activated carbon fixture with the embedded blank into the degreasing furnace for high-temperature hot degreasing.

2. The large-size silicon nitride ceramic anti-deformation and efficient degreasing technology according to claim 1, characterized in that: The degreasing environment in steps S1-S5 is a nitrogen atmosphere.

3. The large-size silicon nitride ceramic anti-deformation and high-efficiency degreasing technology according to claim 1, characterized in that: In step S4, the degreasing temperature is between 400-800℃.

4. The large-size silicon nitride ceramic anti-deformation and high-efficiency degreasing technology according to claim 1, characterized in that: In step S4, the degreasing atmosphere can be air, nitrogen, argon, or vacuum.