In foundry production, casting waste caused by casting defects such as non-metallic inclusions generally accounts for 50% to 60% of the total number of rejects. The use of metal liquid filter technology can effectively reduce or eliminate all kinds of non-metallic inclusions, purification Liquid casting alloy. The ceramic foam filter (CFF, Ceramic Foam Filter) uses polyurethane foam as the carrier, after being hydrolyzed, immerses him in a coating made of ceramic powder, binder, sintering aid, suspending agent, etc., and then squeezes out excess coating. The ceramic coating is evenly applied to the carrier skeleton to form a green body, which is then dried and fired at a high temperature. 1 Filtration Mechanism The foam ceramic filter separates the inclusions in the liquid casting alloy by three physical and chemical actions on the molten metal to achieve the effect of purifying the molten metal [45]. 1) Filter cake mechanism: A complex foam ceramic structure can be used. High-efficiency mechanical dross, when the molten metal passes through a complicated ceramic foam filter, through the mechanical separation of the filter media, the inclusions larger than the filter surface pores are filtered out, and precipitated in the filter liquid metal flows into End, become an integral part of the filter. As the accumulation of inclusions on the surface of the filter increases, a layer of “filter cake†is gradually formed, which further reduces the thickness of the molten metal flow path. As a result, the surface of the newly added filter media can filter out finer inclusions. At the same time, the media also has a filtering effect. Among the numerous small holes penetrating the ceramic body, some show tiny slits, and some have dead angles. These different areas of change are possible locations for trapped inclusions, inside the filter. There is also a "filter cake" effect. 2) Surface effect: When the molten metal flows through the ceramic body with complex structure, it is divided into many small streams, which increases the contact area and contact probability of inclusions in the molten metal and the filter medium, because the surface of the filter is pole. Micro concave and convex surface, concave size is about 1 ~ 10μm, electrostatic adsorption and adhesion of the inclusion of closure effect. 3) Rectification effect: When the metal liquid flows through the ceramic foam filter, it is divided into many small units of the stream, its diameter is smaller, so that the Reynolds number (Re = vd / r) becomes smaller, so that the flow tends to layer Flow movement. When the molten metal is in the laminar flow state, since the density of the molten metal liquid is much greater than the density of the inclusions, the inclusions are allowed to float for a sufficient time to remove, that is, the ceramic foam filter can assist the runner to block the dross. After the filter is placed in the gating system, the assisted flow of the molten metal increases, and the molten metal flowing in the runner is likely to form a full movement and reduce the flow velocity, which is favorable for the inclusions to float and stay on the top surface of the runner. 2 Application of Foam Ceramics 2.1 Aluminum Alloy Casting Filtering Aluminum alloys can easily absorb gas and mix in non-metallic impurities during the melting and forming of castings, thereby reducing the serviceability and processing performance of castings. At present, the successfully developed ceramic foam filter provides a new type of high efficiency filter for the production of aluminum alloy castings. Different from the usual single-layer drilling sieves and glass fiber screens, it has a multi-layered network and curved through-holes, which can effectively filter out small non-metallic inclusions in the aluminum alloy melt, thus improving the casting's quality. The foam ceramic filter is used for the filtration of aluminum alloy melts, usually cordierite is used, and the mesh size is 0.8-1.0mm. Xi'an Aircraft Manufacturing Company uses (90mm×80mm×20mm) foam ceramic filter to make the oil pump bend head, The passing rate of castings such as clutch housings and converter housings has increased by 40% to 70%. This alone results in an annual production value of 2 million yuan for the company and a profit of 300,000 yuan. 2.2 Copper Alloy Casting Filtration Non-ferrous metal melts (brass, bronze, zinc, tin) also generate oxidized and non-metallic impurities during the casting process, resulting in a large amount of waste products. If the use of ceramic foam filters can greatly reduce scrap rate. Filtration of copper alloy melt is usually selected cordierite, mesh size 1.0 ~ 1.2mm.2.3 Steel casting filter ceramic foam is also suitable for ball-milled cast iron, alloy steel, stainless steel and other high-temperature alloy casting filter. Steel alloys have a large specific gravity and a high melting point. They require high-temperature strength, softening temperature, and thermal shock resistance of foam ceramics to be higher than aluminum and copper. Usually selected alumina and silicon carbide foam ceramic filter, filter mesh size of 2 ~ 3mm. 2.4 Automotive exhaust gas purification processor catalyst carrier With the continuous development of the automotive industry in China, automobile exhaust emissions have become the main environmental pollution source. Due to its high specific surface area, good thermal stability, wear resistance, low toxicity, and low density, foam ceramics have been widely used as carriers for automotive exhaust catalytic converters. The installation of ceramic foam automobile exhaust gas catalytic converter in the exhaust pipe of gasoline vehicles can convert the harmful gases of CO, HC and NOx emitted by gasoline vehicles into CO2, H2O, and N2, and the conversion rate can reach over 90%; it is used in diesel vehicles. On the carbon purification rate of 50%. When the foamed ceramic filter element is filled with carbon particles, catalytic oxidation or electronically controlled combustion can be used to regenerate the carbon particles, and the long-term use can be achieved. 2.5 Other applications In high temperature conditions, foam ceramics have excellent heat radiation characteristics, are used to enhance heat transfer and porous medium combustion technology, the effect is significant. Foam ceramics can also be made into photocatalyst carriers. Nano titanium dioxide is coated on the foam ceramic carrier and is excited by ultraviolet rays. It has strong photocatalytic oxidation degradation characteristics and can catalyze the degradation of organic matter and microorganisms, thereby purifying the air. Foam ceramic can also be made into chemical tower packing, gas material, gas stove energy-saving burning board and so on. In summary, the application of foam ceramics will bring great economic and social benefits to modern industry and modern life. Since the ceramic foam is easy to use, inexpensive, and simple in manufacturing process, it can be made into foam ceramic products suitable for different purposes through the choice of materials and process control. Foam ceramics with excellent characteristics have been recognized by more and more people, he will be widely used in metallurgy, chemical industry, environmental protection, energy conservation, medicine, electronics and other fields, the prospects are very broad. 3 Test results In the area of ​​foam ceramic materials, some research processes have also been carried out in this laboratory. Mainly through experiments to verify the impact of various process parameters on the performance of ceramic foam filters, to find out more reasonable and perfect process parameters, in order to improve the performance of the filter and produce a higher filtering temperature of the molten steel and superalloy Zirconia-based ceramic foam filter. The test results show that: 1) ZrO2-based ceramic foam filter should be prepared using 80% aqueous solution of aluminum dihydrogen phosphate as binder; 2) The best ratio of ceramic powder of ZrO2-based ceramic foam filter (sintering agent is Al2O3). For: w (ZrO2) = 80%, w (Al2O3) = 20%; 3) The compressive strength of foam ceramics increases with the increase of Al2O3 content, but when the Al2O3 content reaches 10%, the compressive strength increases slowly; 4 ) The bending strength of foam ceramics increases with the increase of Al2O3 content, but the peak strength of Al2O3 peaks when Al2O3 content reaches 20%, and then decreases with the increase of Al2O3 content; 5) The temperature raising system during sintering is the key Should adopt a slow heating system. Sintering rate is as follows: below 500°C 1～2°C/min; Above 500°C is 3°C/min.4 Development trend of ceramic foam filter As mentioned above, in the past 20 years, after the efforts of foundry workers, foam ceramic filter The device and its application in the field of liquid casting alloy filtration have made great progress. According to incomplete statistics, nearly 10 domestic ceramic foam filter production lines have been put into production so far, and the total annual production volume has reached millions. However, according to estimates, the potential annual demand for the foundry industry in China is about 100 million pieces. Therefore, in the new century, research, production, application and promotion of ceramic foam filters need to continue to be strengthened, and the focus of work should be on the following aspects: 1) Development and production of new types of low cost with low sintering temperature and short sintering time Foam ceramic filter; 2) Development and production of new foam ceramic filters suitable for various active alloys and high temperature physical and chemical properties; 3) Development and production of special-shaped foam ceramic filters suitable for investment casting, metal casting and other special casting processes (4) In-depth study of the filtration and purification mechanism of foam ceramic filters and the mechanism of their influence on the metal solidification process; 5) Systematic research on the application technology of foam ceramic filters, including the choice of aperture and thickness, the placement method, and the design of the casting system, Casting temperature and speed and control of metal hydraulic heads; 6) Carry out serialization and standardization of ceramic foam filters. 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