Foam ceramic filtration technology has developed rapidly since the 1970s. After more than 30 years of rapid development, various products such as silicon carbide, zirconium oxide, and alumina have emerged. Silicon carbide foam ceramic filters and lost foam filters are used for filtration in various fields, from molten aluminum to cast iron, cast copper, and cast steel. Silicon carbide foam ceramic filters are mainly used in automotive parts, diesel engine parts, compressors, wind power castings, and high-end machine tool castings, greatly improving the quality and competitiveness of castings while reducing costs.

Filtration Mechanism of Silicon Carbide Foam Ceramic Filters

(1) Rectification. Turbulent liquid metal becomes a stable laminar flow after passing through the filter, avoiding the liquid metal from encapsulating gas, reducing the erosion of the cavity by the liquid metal, fully utilizing the slag-blocking function of the casting system, and avoiding the generation of secondary oxide slag.

(2) Mechanical Screening. Molten metal contains a large number of oxide inclusions, slag, and other large impurities. By selecting a suitable silicon carbide foam ceramic filter, a large number of inclusions can be screened out.

(3) Cake Mechanism. Silicon carbide foam ceramic filters, due to their three-dimensional structure, effectively prevent slag mechanization. Many impurities larger than the filter pore size are trapped at the filter inlet. As the number of trapped impurities increases, a "filter cake" composed of large impurities forms at the filter inlet. The filter cake makes the fluid flow finer, causing impurities smaller than the filter pore size to partially remain on the "filter cake."

(4) Adsorption Mechanism. Silicon carbide foam ceramic filters have a large specific surface area, which is beneficial for adsorbing a large number of fine inclusions.

Performance Requirements of Silicon Carbide Foam Ceramic Filters

(1) The filter should have good environmental temperature resistance and should not slag during transportation and operation.

(2) It should have high-temperature strength, thermal shock resistance, and resistance to corrosion by liquid metals.

(3) It should have good chemical stability and not react with alloy solutions.

(4) It should have suitable pore size, good alloy liquid permeability, strong filtration capacity for non-metallic inclusions, and good appearance quality: no deformation, small dimensional deviation, uniform pore size, and no clogging.

Economic Benefits of Silicon Carbide Foam Ceramic Filter Applications

(1) Using filters can significantly reduce inclusion defects;

(2) Refine grains and improve the mechanical properties of castings;

(3) Improve the machinability of castings;

(4) Improve the internal and external quality of castings;

(5) Simplify the gating system and improve process yield;

(6) Reduce processing allowances and maintenance costs.

Analysis of Silicon Carbide Foam Ceramic Filter Breakage

Currently, the melting point of refractory aggregates used in filter manufacturing is much higher than that of liquid metal. However, due to improper selection and design, filters may be damaged. There are two main reasons:

(1) Due to insufficient refractory resistance, the filter softens under the action of high-temperature liquid metal, and its strength drops sharply. If the impact force exceeds its upper limit, the filter will be partially damaged.

(2) The filter has poor thermal shock resistance, leading to cracking and breakage during quenching and heating. If debris enters the casting, the casting may be scrapped. Therefore, it is crucial to use filters reasonably, safely, and effectively. 

Casting Measures for Silicon Carbide Foam Ceramic Filters

(1) The type and specifications of the filter should be selected according to the specific casting process, and the design size should be as low as possible below the upper limit of the filter. The filters should be distributed in the internal flow channels to ensure that the molten iron passing through each filter does not exceed the standard.

(2) Avoid the molten iron concentration passing through only a portion of the filter, making full use of the entire filter's flow rate; when the filter can only be placed at the lower end of the pouring cup or impeller, the filter can be tilted on the ceramic seat to reduce the impact force of the molten iron.

(3) Use large-pore filter sheets as much as possible to avoid shortening the casting time.

(4) For large castings, especially wind power generation components, when exceeding the limit, the following safety measures can also be taken: The bottom of the silicon carbide foam ceramic filter should be supported by ceramic holes. No more than 3 pieces should be placed continuously if possible. If appropriate, it is recommended to preheat the filter to 100 degrees Celsius.

(5) The initial use of the filter or process changes must be verified through production to confirm that the casting meets the quality requirements and that the filter is not damaged before formal mass production.

As a practitioner of high-quality filtration solutions for the foundry industry, Xinda has been deeply involved in the field of silicon carbide foam ceramic filtration for many years. Leveraging advanced production processes and a rigorous quality control system, Xinda has created a series of silicon carbide foam ceramic filter products that combine excellent filtration performance with a stable service life. These products can be precisely adapted to the casting filtration needs of various fields such as automotive, wind power, and high-end machine tools. Xinda is committed to helping companies improve casting quality and reduce production costs, providing customers with customized product selection and application technology support, and working hand in hand with industry partners to promote the high-quality development of the foundry industry. For more product details and technical solutions, please feel free to contact us.