How to select the corresponding foam ceramic products for different casting processes?

As the equipment manufacturing industry transitions towards high-quality development, casting, as the core fundamental process of equipment manufacturing, directly impacts the quality and performance of end products through its technological level. Foam ceramics, as an advanced inorganic non-metallic material with excellent characteristics such as high porosity, high temperature resistance, and corrosion resistance, have become a key auxiliary material for optimizing casting processes and enhancing casting quality. However, there are numerous types of casting processes, and significant differences exist in temperature, pressure, and casting precision requirements among different processes. How to scientifically select corresponding foam ceramic products has become an important issue for many casting enterprises to improve production efficiency and reduce costs.

According to statistics from the China Foundry Association, the domestic usage of foam ceramic filters for casting exceeded 210 million pieces in 2023, marking a 42% increase compared to 2020. Among these, silicon carbide-based products accounted for 68%, reflecting the continuous rising demand for high-performance foam ceramic materials in the casting industry. Industry experts indicate that the selection of foam ceramics must closely align with the core characteristics of casting processes, taking into account factors such as filtration efficiency, thermal stability, and cost control. Only in this way can their role in purifying metal liquids and enhancing casting quality be fully realized, avoiding issues such as casting defects and material waste caused by improper selection.

Sand casting, as the most widely used and longest-established casting process, utilizes natural quartz sand as the mold material. It features low cost, flexible mold making, and adaptability to large, irregular-shaped castings, and is widely applied in the production of large mechanical bases, heavy-duty machine tool housings, and other products. For sand casting processes, the industry generally recommends the use of silicon carbide or alumina foam ceramic filters. These foam ceramics have a moderate porosity, typically ranging from 60% to 80%, and the pore size can be selected from 15PPI to 30PPI according to the casting size. They can effectively filter non-metallic impurities from the molten metal and adapt to the temperature fluctuations inherent in sand casting conditions. At the same time, their cost is relatively reasonable, meeting the production needs of sand casting for large-scale, low-cost manufacturing. The head of a foundry enterprise in Foshan explained that after using the appropriate foam ceramic filters, the impurity removal rate of sand casting castings has significantly improved, and the yield of good castings has increased by more than 8% compared to before.

Metal mold casting utilizes high-temperature resistant metal materials such as steel and copper alloys to create permanent molds that can be reused. It offers advantages such as high production efficiency, good consistency of castings, and excellent surface quality. It is primarily used for the production of small and medium-sized high-precision castings such as automotive parts and hardware tools. Due to the good thermal conductivity of metal mold casting molds and the rapid cooling rate of the molten metal, there is a high demand for the thermal shock stability of foam ceramics. Therefore, mullite-based or cordierite-based foam ceramic products with excellent thermal shock stability should be selected. These products show no significant cracking after rapid thermal cycling from 1000°C to room temperature, adapting well to the frequent temperature changes in metal mold casting. Additionally, their high dimensional accuracy prevents casting defects such as slag inclusion caused by ceramic damage.

High-pressure casting involves injecting molten metal into metal molds under high pressure and high speed, resulting in castings with high compactness, stable mechanical properties, and fast production pace. It is the mainstream production process for high-precision castings such as automotive engine housings and aluminum alloy wheels. This process has more stringent requirements for the strength and impact resistance of foam ceramics, necessitating the use of high-strength silicon carbide foam ceramics. These ceramics can withstand a maximum operating temperature of 1500℃ and have a compressive strength of over 10MPa, capable of withstanding the impact of high-pressure molten metal. Additionally, their three-dimensional mesh structure effectively rectifies the flow of molten metal, ensuring uniform microstructure distribution in the casting and reducing defects such as porosity and looseness. The silicon carbide foam ceramic filter developed by a material enterprise in Suzhou has been widely applied in high-pressure casting production lines, significantly enhancing the machining performance and overall mechanical properties of castings for the enterprise.

High-end precision casting processes such as vacuum casting and investment casting are primarily used for the production of high-end castings in aerospace, military, medical equipment, and other fields. These processes demand extremely high purity and dimensional accuracy of the castings, and require the entire process to be conducted in an oxygen-free or high-precision controlled environment. For such processes, zirconia-based or special alumina foam ceramic products with high purity, uniform pore size, and high filtration accuracy should be selected. Foshan Feite New Material Co., Ltd. has independently developed a special zirconia foam filter with a unique high-temperature phase structure, which can effectively remove tiny impurities from the molten metal with an impurity removal rate of over 98%. This filter meets the production requirements of high-end precision castings and has been applied in the manufacturing of high-end castings in the aerospace field.

As an environmentally friendly casting process, lost foam casting utilizes combustible foam plastic to create molds. During pouring, the high-temperature molten metal vaporizes and disappears the mold, featuring no parting surface, high casting precision, and outstanding environmental friendliness. It is suitable for the production of complex box-type and shell-type castings. In this process, foam ceramics must possess excellent high-temperature resistance and chemical stability to prevent reaction with vaporized plastic residues. Additionally, they must be compatible with the pouring characteristics of lost foam casting, selecting foam ceramic filters with moderate pore size to ensure smooth filling of the mold cavity by the molten metal and reduce casting defects.

Industry experts remind that when selecting foam ceramic products, foundry enterprises should not only consider the characteristics of the casting process, but also comprehensively consider factors such as the material of the molten metal, pouring temperature, and casting size. For example, nodular iron castings generally use 10PPI and 15PPI foam ceramic products, while gray iron and cast copper castings are suitable for 15PPI and 20PPI products. For aluminum alloy castings, 20PPI and 30PPI products are recommended. When the casting weight is large, thicker foam ceramics should be selected to ensure filtration efficiency and structural stability. At the same time, enterprises should choose suppliers with technical strength and quality assurance, and seek professional technical guidance when necessary to achieve precise adaptation of foam ceramic products to the casting process.

With the application of technologies such as 3D printing and nano-modification in the field of foam ceramics, the structural designability and performance of foam ceramics have been further enhanced, enabling them to better meet the needs of various new casting processes. In the future, as the casting industry transitions towards green, precision, and intelligent development, foam ceramics, as key auxiliary materials, will play a crucial role in supporting enterprises in enhancing their core competitiveness through scientific and precise selection. This will facilitate the casting industry to achieve quality improvement, efficiency enhancement, and green development.