Brief Introduction
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Original Title: An Important Link in Ceramic Forming — — Brief Introduction to Degreasing Process Degreasing is a process in which the organic matter in the molding body is removed by heating and other physical methods, resulting in a small amount of sintering. Debinding is the most difficult and important factor in injection molding compared to the processes of batching, forming, sintering, and post-processing of ceramic parts. Incorrect process methods and parameters in the degreasing process can cause inconsistent shrinkage of the product, resulting in distortion, cracking, stress, and inclusions. However, these defects can not be seen after degreasing, and these defects will be exposed only after sintering, but it is too late at this time, because the sintering process is irreversible, and the cracks and deformations generated in the degreasing process can not be compensated by sintering. Therefore, degreasing is also very important for subsequent sintering, especially in mass production, the requirements for degreasing are very high. Degreasing mechanisms generally include a combination of the following processes: (1) evaporation of low molecular weight polymers; (2) oxidative decomposition; and (3) thermal degradation of high molecular weight polymers. It can be seen from this that degreasing is associated with the binder. Generally, the property of the binder determines the degreasing method. In addition to the traditional thermal degreasing and solvent degreasing, the current degreasing process also includes catalytic degreasing and water-based extraction degreasing developed in recent years. Today, let's take a look at several common degreasing processes and their current application status. Introduction of Four Degreasing Processes in Ceramic Forming 1. Thermal degreasing Principle: Thermal degreasing is a commonly used method of degreasing, which is a method of volatilizing or decomposing the binder components from the green body by heating the green body. During thermal debinding, the binder component is softened by heat, and the green body is easy to produce viscous flow deformation under the action of neutral and thermal stress, so the debinding rate is too slow and time-consuming. The control of furnace temperature in thermal degreasing process is also very strict, which should be consistent with the volatilization and pyrolysis of components. At the same time, thermal debinding is limited by size and thickness, and is suitable for relatively small precision ceramic parts. Has that advantage of low price, relatively mature theoretical development and relatively wide application; Disadvantages: low efficiency, long time, and prone to defects, limited to small cross-section products (usually within 5mm) such as ceramic ferrules, bushings and smart wearable consumer electronics products. Expand the full text Figure Thermal degreasing ceramic product Defects such as shrinkage cavity and crack are easy to occur inside the thermal degreasing (the degreasing time is 7-10 days under N2 atmosphere). For example, in the following picture, although the thermal degreasing takes seven to ten days, there are still defects, cracks and cracks inside the product with a thick section. Therefore, thermal degreasing is very harmful to such a large product. 2. Solvent degreasing Principle: Solvent degreasing: firstly, solvent molecules diffuse into the CIM blank,nutsche filter dryer, and then the binder dissolves in the solvent to form a binder-solvent solution. The binder molecules diffuse to the surface of the blank through the binder-solvent solution in the blank, and the binder molecules diffused to the surface of the blank are separated from the blank and enter the solvent solution. Solvent degreasing is composed of two parts. The first part is organic matter (such as paraffin, vegetable oil, etc.), which can be well dissolved in some alkane solvents (such as kerosene, n-heptane, petroleum ether, or solvent oil). The other part is a polymer (polyethylene, polypropylene, etc.) that is insoluble in the solvent and plays a role in supporting the strength of the green body after the soluble components are removed. Residual organic carrier and solvent can eventually be completely removed by rapid heating. The method has that advantage that: 1) the efficiency is high, and the degreasing time is short; 2) the polymer is not dissolve, so that the blank body can be kept from deforming during degreasing; and 3) aft chemical extraction, a continuous channel is formed in the blank body,thin film distillation, so that the subsequent thermal degreasing process can be shortened to several hours. Disadvantages: easy to produce swelling phenomenon, resulting in cracking of the blank; increase the removal process of solvents, and some organic solvents contain toxicity, not environmentally friendly, these solvents must be recycled, increasing part of the cost. Fig. Degreasing and sintering of transparent Al2O3 ceramic cup The degreasing efficiency of organic solvent (oil) is higher than that of thermal degreasing, and it is conducive to the preparation of ceramic products with thicker sections and larger sizes, such as ceramic bezels, gears, ceramic cups, etc. Mobile phones and smart wear products have low feed preparation and degreasing costs and strong practicability. 3. Catalytic degreasing Principle: a catalyst is used to decompose the organic carrier molecules into smaller volatile molecules, which have higher vapor pressure than the organic carrier molecules in other degreasing processes and can quickly diffuse out of the green body. The technology was developed by the German company BASF. Characteristics: The bonding system is generally composed of polyformaldehyde resin and stabilizing additives. Catalytic degreasing is a direct gas-solid reaction. The reaction temperature is generally 110 ~ 150 ℃, which is lower than the melting point of polyformaldehyde resin to prevent the formation of liquid phase. In this way, softening of the green body due to the formation of a liquid phase during thermal debinding, or deformation and defects due to the influence of gravity, internal stress, or viscous flow, are avoided. Therefore, its biggest advantage is that it can control the defects of the green body very well, and it is suitable for making large-size products. The invention has the advantages that the degreasing speed is high, the deformation and the defect of the green body are less, the precision is high, and the invention is more suitable for preparing large-size or thick-section ceramic products, such as ceramic nozzles, bearing balls, automobile decorative parts and the like; Disadvantages: special binder, decarboxylation after extraction ,wiped film evaporator, feed preparation is difficult, liquidity is poor, the cost is high, the current domestic application is less. The left side of the figure below is a schematic diagram of the principle, and the right side is the section of the green body after degreasing. It can be seen that this is very dense and uniform, and the degreasing efficiency is very high. For example, when nitric acid and carboxylic acid are used as catalysts for degreasing, it can reach a depth of 1.5 millimeters per hour, which is faster and safer than our previous degreasing method. 4. Water-based extraction degreasing Water-based extraction degreasing is a new degreasing method developed on the basis of extraction degreasing process. This process has been applied to production (Thermal method) by TPT Company in the United States. The binder system used for water-based extraction degreasing is divided into two parts: one part is water-soluble, such as polyethylene glycol (PEG), polyethylene oxide (PEO), etc., which can be removed by water filtration; The other part is insoluble in water, such as the use of cross-linked polymers such as polyvinyl butyral (PVB) or polymethyl methacrylate (PMMA), which is generally removed by heating. Degreasing is also carried out in two stages: first, the green body is immersed in water, and the water-soluble binder is removed by the leaching of water, and then part of the water-insoluble binder can be removed by heating and other methods. This requires that the water-soluble and insoluble binders be completely miscible in the liquid state, and that the miscibility process be fast, complete within 30 minutes without requiring much energy, and form a homogeneous heterogeneous solution. The green body is degreased in water at 40 ~ 60 ℃. In order to control the leaching speed and the influence of water on the green body, the water should be deionized or added with some special additives, such as anticorrosive, antioxidant, etc. In addition, the water should be stirred continuously. Generally, the water-soluble binder can be removed within 3 hours. At this time, continuous pores have been formed in the green body, which provides a convenient path for the degreasing of the insoluble binder. Generally, the thermal removal time is about 2 hours. Water debinding has the advantages of fast debinding speed, short time, no pollution and relatively less equipment investment for thick section ceramic parts, so it has become an important research direction of debinding. At present, Tsinghua University and German Ceramic Company are developing and testing the technology. Figure Ceramic body after water extraction and degreasing II. Application distribution of degreasing technology 1. Thermal degreasing and organic solvent degreasing processes are mainly used in Japan, China and other Asian countries. For example, Kyocera, Toshiba Ceramics and most domestic ceramic powder injection enterprises. 2. In Germany, France, Britain, the Netherlands and other European countries, the catalytic degreasing process is mostly used. It is mainly fed by BASF, such as German Salentech, British Morgan, French Saint-Gobain, Dutch Formatec, etc. 3. Organic solvent degreasing and thermal degreasing processes are mainly used in the United States. , such as CoorsTec, Ceradyne, etc. Aibang has a mobile phone ceramics supply chain industry cluster, Xiaomi, Huawei, OPPO, vivo and Sanhuan, Lance, Bourne, Gaoge, Dingding, BYD and other enterprises to join, welcome to scan the following QR code: Source of this article: Professor Xie Zhipeng, Tsinghua University Author: Professor Xie Zhipeng Mobile phone shell Dongguan Supai Pneumatic Tools Co., Ltd. 1D04 & 1D05 Dongguan Yize Precision Cutting Tools Co., Ltd. 1D09 Dongguan Anhou Industrial Co., Ltd. 2A03 Dongguan Zhongwang Precision Instrument Co., Ltd. 2C17 & 2C20 Dongguan Gaoquan CNC Machinery Co., Ltd. 1D06, 1D07 & 1D08 Saint-Gobain/Sumitomo Injection Molding Machine 2C03 Jiujiu Seiko 1A 07 Yingtan Longding New Material Technology Co., Ltd. 2A15 Kunshan Shuozhan Electronic Technology Co., Ltd. 2B17 China Steel Research Technology Group Co., Ltd. 2C12 & 2C13 Guangdong Zhenhua Technology Co., Ltd. 1A22 & 1A23 Dongguan Kelong Industrial Co., Ltd. 1A05 Dongguan Shoulei Laser Technology Co., Ltd. 2E08 Shenzhen Bochi Electronics Co., Ltd. 1A20 Dongguan Nazhi Automation Machinery Co., Ltd. 2B04 & 2B06 Dongguan Goode Automation Technology Co., Ltd. 1B11, 1B12 & 1B13 Shenzhen Xintaiming Intelligent Co., Ltd. 2C14 Henan Zhongyue Amorphous New Materials Co., Ltd. 2D13 Dafu Fangyuan 1A28 Onna Technology Kunshan Ximeng Automation Technology Co., Ltd. Oriental Zirconium Industry Shenzhen Star Technology Co., Ltd. Six and electron Dongguan Jiashunda Automation Precision Machinery Co Ltd Shenzhen Yasuda Electronic Technology Co.,molecular distillation systems, Ltd. Yutian Changtong Electronics Co., Ltd. Dongguan Jieyang Electronic Technology Co., Ltd. Dongguan Hongyan Polishing Material Co Ltd Contact number: Return to Sohu to see more Responsible Editor:. toptiontech.com