In the foundry industry, the purity of molten iron directly affects the mechanical properties, surface quality and product qualification rate of castings. Traditional filtering methods (such as honeycomb ceramic filters and refractory fiber meshes) are often difficult to remove tiny inclusions efficiently, while silicon carbide (SiC) ceramic foam filters have become a key material for improving the purity of molten iron due to their unique three-dimensional mesh structure and excellent physical and chemical properties. This article will explore its working principle, performance advantages and practical application effects in depth.
Sources and hazards of impurities in molten iron
Molten iron is easily mixed with a variety of impurities during smelting, transportation and pouring, mainly including:
Non-metallic inclusions: oxides such as SiO₂ and Al₂O₃, which come from furnace charge, slag or refractory erosion.
Slag: slag phase produced during desulfurization and dephosphorization.
Gas: dissolved gases such as H₂ and N₂, which form pores after cooling.
These impurities can cause:
✔ Casting defects (pores, slag inclusions, shrinkage)
✔ Decreased mechanical properties (reduced fatigue strength and toughness)
✔ Increased processing difficulty (tool wear, rough surface)
SiC Ceramic Foam Filter for Molten iron filtration
Silicon carbide ceramic foam filters are the most commonly used in the production of molten iron. The excellent performance of silicon carbide ceramic foam filters stems from its unique material properties and exquisite structural design. Silicon carbide material itself has an extremely high melting point (about 2700℃) and excellent high-temperature stability, which can easily cope with the high-temperature impact of molten iron. It has a low thermal expansion coefficient and excellent thermal shock resistance, and can maintain structural integrity in a rapid cooling and heating working environment. These characteristics make silicon carbide ceramic foam filters an ideal choice for molten iron filtration.
Silicon carbide ceramic foam filters purify molten iron through the triple mechanisms of mechanical interception, adsorption capture and turbulence regulation:
Mechanical interception – physical barrier of three-dimensional mesh structure
From the microscopic structure, silicon carbide ceramic foam filters present a three-dimensional interconnected mesh structure with a high porosity of 70%-90%, and the pore size range is usually 0.5-10mm (corresponding to 10-30PPI). When molten iron flows through the filter, this unique structure enables inclusions larger than the pore size (such as slag, sand particles) to be directly intercepted on the filter surface.
Adsorption capture – surface chemical action
Silicon carbide (SiC) reacts weakly with oxides (such as FeO and MnO) in molten iron at high temperatures to form low-melting-point compounds that adsorb tiny particles (<50μm).
The adsorption efficiency can be further improved by optimizing the filter surface coating (such as Al₂O₃ reinforcement layer).
Turbulence control – stable pouring flow
The porous structure of the filter can break up the turbulence of the molten iron, reduce air entrainment, transform the turbulent molten iron flow into a smooth laminar flow, make the molten metal fill the mold smoothly, and significantly reduce the secondary oxidation and air entrainment during the pouring process.
Practical application cases and data verification
In practical applications, the performance of silicon carbide ceramic foam filters is impressive. Take a certain automotive parts foundry as an example. When using traditional filtering methods, the porosity defect rate of castings is as high as 8%, which seriously affects product quality and production efficiency. After installing a 20PPI silicon carbide filter in the pouring system, the porosity of the castings dropped to below 1.2%, and the product qualification rate was significantly improved. What is even more surprising is that due to the improvement of the purity of the molten iron, the mechanical properties of the castings have also been significantly improved, the tensile strength has increased by 12%, and the tool life of subsequent machining has been extended by 30%.
Behind this performance improvement is a rigorous scientific principle. Silicon carbide materials react slightly with certain oxides in molten iron at high temperatures to form low-melting-point compounds. This property enhances the filter’s ability to capture tiny inclusions.
How to maximize the filtering effect?
Model matching: Select the appropriate pore size according to the temperature and flow rate of molten iron (e.g. 10-15PPI is commonly used for gray cast iron, and higher strength is required for ductile iron).
Correct installation:
Preheat the filter to 200-300℃ to avoid thermal shock.
Ensure that the filter completely covers the casting section to avoid molten iron bypass.
Process synergy: Combined with slag remover, inert gas protection, etc., to achieve all-round purification.
Conclusion
Silicon carbide ceramic foam filters significantly improve the purity of molten iron through their unique porous structure and material properties, and have become an indispensable part of modern casting processes. As the casting industry continues to increase its requirements for casting quality, leading companies such as SEFU will continue to optimize filter technology to provide customers with more efficient and durable solutions.
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