Abstract: Ceramic materials are widely used in various fields due to their excellent high temperature resistance, high strength, wear resistance, corrosion resistance and other properties. This article introduces the characteristics and progress of several major ceramic forming processing technologies.
1, Introduction
At present, with the continuous expansion of the application fields of new ceramic materials, the requirements for the performance of ceramic materials are becoming more and more stringent. The forming process is one of the important links in the preparation process of ceramic materials. It affects the microstructure of the material to a great extent and determines the performance, application and price of the product. Traditional forming methods such as grouting, plasticity and
dry pressing forming technology and the mature and applied extrusion technology Technologies such as molding, isostatic pressing, and tape casting play an important role in the large-scale production of ceramic materials. However, the above methods can no longer meet the manufacturing requirements of high-precision, complex shapes and multi-layer composite ceramic materials, which greatly limits and hinders the application and development of high-tech ceramic materials.
The development of modern science and technology has brought new vitality to the progress of ceramic material forming technology, especially the development and application of material chemistry and computer technology. The mutual penetration and integration of the three major materials have promoted the development of high-tech ceramic preparation technology. Ceramic forming technology continues to improve and innovate on the basis of traditional methods, and new forming technologies such as centrifugal deposition forming, electrophoretic deposition forming, centrifugal slip molding, injection molding and colloidal forming are constantly emerging. Understand the basic principles, research status and characteristics of these forming technologies, and strengthen application research based on them. For further research and exploration of new forming processes and methods, we must constantly adapt to and meet the needs of high density, complex shapes, precise dimensions and composite functions. The forming needs of ceramic materials play an important role.
2 , Centrifugal deposition forming
Centrifugal deposition forming is a method of preparing plate-like and layered nano-multilayer composite materials. The principle is that different slurries are uniformly deposited layer by layer under the action of centrifugal force to form a whole; particle size or mass can also be used Different layers of materials are deposited with different properties.
The use of centrifugal deposition to form layered materials has the following characteristics:
(1) By depositing different materials, the toughness of the material can be improved;
(2) Each layer deposited can be a combination of electrical, magnetic, and optical properties, and is multi-functional;
(3) New anisotropic materials can be made.
3, Electrophoresis Deposition Forming
Electrophoretic deposition is formed by using a DC electric field to promote the migration of charged particles, and then deposit them on electrodes of opposite polarity to form. During the deposition process, under the action of electrophoretic migration, the particlesAs the distance shortens, Vander Waals attraction plays a major role, the stable dispersion of the slurry begins to be lost, and the powder particles gradually deposit on the electrode. Electrophoretic deposition forming is divided into two consecutive processes: electrophoretic migration of particles and discharge deposition of particles on the electrode. In order for the particles to be deposited on the electrode alone without being affected by other charged particles, the ceramic slurry needs to have good dispersion.
Electrophoretic deposition forming has the following characteristics: simple operation, flexibility and high reliability, so it is suitable for the forming method of multilayer ceramic capacitors, sensors, and gradient functional ceramics, but it is relatively sensitive to changes in process parameters.
4, Centrifugal Grouting
Centrifugal grouting is developed on the basis of traditional grouting. By adjusting process parameters such as pH value, the powder is evenly dispersed in the liquid and deposited and formed under the action of high-speed rotating centrifugal force. Centrifugal grouting combines wet chemical powder preparation with stress-free densification technology. On the one hand, it can prevent powder agglomeration and other defects; on the other hand, it can achieve separate deposition by virtue of the different particle sizes and rotation speeds of the powder. Purpose, it can be used for the preparation of multi-layer and gradient composite functional materials.
Centrifugal grouting has the following characteristics: there are no strict requirements on the solid phase amount of the prepared suspension, and almost no binder is needed, which reduces the adverse effects caused by the degreasing process; the cost is low, easy to control, and is especially suitable for large-scale regular geometric rotating bodies The net size is formed. However, when preparing uniform materials, the particle sizes of the ingredients are too different, and the centrifugal acceleration of the particles is different, which can easily lead to uneven composition and stratification of the green body; centrifugal forming equipment is required.
5 , Injection molding
Ceramic thermoplastic injection molding technology is developed from plastic molding technology. The ceramic powder is heated and mixed with thermoplastic resin, paraffin wax, plasticizer, solvent, etc. (or extruded into slices and granulated) before entering the injection molding machine. After being heated and melted, it acquires plasticity. It is injected into the metal mold cavity from the nozzle at high speed under a certain pressure, and is cooled and solidified in a very short time to form.
Features of injection molding technology: It can form parts with complex shapes, is easy to automate and mass-produce, and has high dimensional accuracy and uniform microstructure. However, the content of organic carriers in injection molding is relatively high, and the green body must be degreased before sintering. Large blanks often lead to the enrichment of organic matter and the rearrangement of particles, making the green body less uniform and prone to cracking. Therefore, this is currently used. Problems that need to be solved urgently in the injection molding process.
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Gel injection molding is a new molding technology developed by the Oak Ridge National Key Laboratory in the 1990s. It organically combines traditional grouting technology with polymer chemistry. The polymer network produces polymerization, causing ceramic particles to gather together to form a ceramic body. Vinyl organic monomers are added to the suspension medium, and with the action of catalysts and initiators, the organic monomers undergo an in-situ polymerization reaction after the ceramic slurry is poured, and polymerize and solidify into a ceramic body. Gel injection molding is a very practical technology with significant advantages:The formed body has good uniformity and high strength, and can be directly machined to obtain the appropriate size; it also shrinks little after firing, making it suitable for precise size forming. Ceramic colloidal injection molding solves two important key technologies: rapid in-situ solidification of ceramic concentrated suspension and controllability of the injection process. Through in-depth research, it was discovered that pressure can quickly induce the in-situ solidification of concentrated ceramic suspensions, thus the pressure-induced ceramic forming technology was invented.
Characteristics of colloidal injection molding technology: a high-density, high-uniformity and high-strength ceramic body can be obtained. This molding technology can eliminate the agglomeration of ceramic powder particles and reduce the deformation and cracking of complex-shaped parts during the sintering process, thus Reduce the amount of machining of final parts and obtain high-reliability ceramic materials and components. This process has no size or thickness restrictions on the molded body, avoids the difficulty in debonding caused by the use of large amounts of organic matter in traditional ceramic injection molding, and realizes the injection process of colloidal molding. It is suitable for large-scale production and is the core technology for the industrialization of high-tech ceramics.
7 Conclusion
At present, new technologies for ceramic forming are constantly emerging, but there are still some shortcomings. When adopting a new forming process, the dispersion of the material, the impact of the slurry ratio on the process, the functionality of the material and the effect of nanomaterials on the process should be taken into consideration, so as to give full play to the advantages of the new forming process and produce High performance ceramic products.
