With the development of science and technology and industrial production requirements, people increasingly stringent requirements on the quality of castings, some castings not only requires a qualified chemical composition, microstructure, mechanical properties, but also requires excellent inherent quality and external quality. However, the traditional casting process and technology often can not meet these requirements, the main reason is that a large number of non-metallic inclusions in the alloy lead to a variety of casting defects. Casting production, due to non-metallic inclusions such as casting defects caused by casting reject rate is generally up to 50% of the total number of scrap -60%. Non-metallic and debris from more sources. For example, when the charge is not clean, it will contain a large number of inclusions, the burden of moisture in the smelting process to form inclusions; casting system design, casting system and mold strength is inadequate, casting process caused by sand, sand core In the birth, desulfurization, spheroidization, alloying treatment, if the process will cause inclusions into the mold; metal liquid contact with the air to form oxidized inclusions. Therefore, in order to reduce the non-metallic inclusions, people should not only strictly control the preparation of raw materials, alloy, colleagues must also take effective measures in the casting process to clean the metal liquid. Filter purification technology is developed in this case.
Filtration technology has been used for decades in the history of foundry production, but initially it was only the use of steel mesh, perforated steel, porous core and other simple filter into the gating system to filter out large non-metallic inclusions. From the early 1960s, aluminum silicate fiber, glass fiber, high silica glass fiber and other two-dimensional structure of the filter, and in production have been applied, and achieved certain results. However, these filters can only filter through the mechanical screening effect of large metal inclusions in the liquid and a small number of small inclusions. Aluminum silicate fiber filter due to the low degree of refractoriness and strength, can only be used for non-ferrous alloys and small castings filter, it is difficult for a long time to withstand the impact of high temperature metal liquid; filter cast steel and other high temperature alloy molybdenum silk can be used And boron nitride fiber filter, but because of its high cost, application is limited, and now the application is more high-silica glass fiber filter. The early 20th century, the early 70s, the United States the first successful development of sintered porous ceramic filter to solve the problem of refractory particles filter leakage and easy to use the inconvenience of the problem, but the early 1980s and the United States the first successful development of straight hole honeycomb Ceramic filters, porosity is still small, generally less than 50%, metal liquid flow rate is relatively low since 1978, aluminum foam ceramic filter for the first time since the success of the ceramic foam filtration technology has been rapid development. Foam ceramic filter with a unique three-dimensional connectivity curved mesh reticular framework so that it has up to 80% -85% of the open porosity, filtration efficiency of up to 95%, thereby significantly reducing casting rejection and welding rate. In addition, it can simplify the casting system, improve the microstructure, thereby improving the casting process yield and productivity, improve the casting internal quality, mechanical properties and mechanical processing performance. Therefore, the foam ceramic filter has a good application prospects.
Since the 21st century, the development of science and technology and high-quality castings to filter purification technology requirements to further promote the development of refractory fiber filter, porous ceramic filter, foam ceramic filter, honeycomb ceramic filter. At the same time, in order to meet a variety of metal filtration and purification technology requirements, has developed a zirconium, carbon, MgO quality, high quality silica gel and other filters. In addition, also developed a combination of the trial of the filter, such as filters and riser sets of combinations, filters and molds within the combination of ball and inoculation, not a combination of aperture filters, straight hole and foam ceramic filter Combinations and so on.
In developed countries, a variety of materials, a variety of processes, all sizes of castings have been widely used filter, greatly improving the casting quality and process yield. With the continuous improvement of the casting technology and the quality of the casting, people have become more and more aware of the filtration technology. At present, China's ceramic foam from research to production has been basically formed system, begun to take shape, and in the magnesium alloy, aluminum alloy, copper alloy and cast iron and other fields to obtain large-scale applications, and achieved great economic benefits.
With the further application of filtering technology to promote the application of the filter more refined, flexible, convenient, scientific, accurate, multi-layer filtering technology and the combination of filtering applications will continue to improve and expand. |
