Foam ceramic filters have excellent filtering effects and cause no pollution to alloys. However, if the application method is inappropriate. Not only will the expected results not be achieved, but it will also bring troubles to production and even increase the scrap rate of castings.https://www.rtoceramic.com/products/
I. Materials
The basic materials of foam ceramic filters are silicon carbide, zirconia, and alumina.
- Silicon carbide has excellent strength, high-temperature impact resistance, and chemical corrosion resistance. It can withstand high temperatures of approximately 1560°C. Therefore, foam ceramic filters made of it are also suitable for copper alloys such as copper, bronze, and brass, reducing the turbulence of the copper liquid and rectifying and purifying the molten copper liquid.
- The material of the zirconia foam ceramic filter is zirconia (ZrO₂). The heat resistance temperature is higher than approximately 1760°C. It has extremely high strength and excellent high-temperature impact resistance and is not sensitive to the changes in the pouring temperature of different steel grades. It has a remarkable filtering effect on all steel grades, including carbon steel, stainless steel, cobalt-based and nickel-based superalloys, etc.
- The alumina foam ceramic filter is suitable for a temperature of 1250°C and is suitable for the filtration and purification of aluminum and its alloy solutions. It is also widely used in common sand casting, such as green sand mold casting, and permanent mold casting, such as the casting of automotive aluminum components.
II. Selection of Pore Size
Generally: 10 pores per inch (10ppi) can be used for ductile iron castings, large gray iron castings. And steel castings; 20 pores per inch (20ppi) are used for small gray iron castings, malleable steel castings, and non-ferrous metal castings.
III. Selection of Thickness
The filter must have a certain thickness to prevent it from being burned through. If the filter is burned through, it will artificially cause slag inclusion, leading to the scrapping of the casting. It is recommended that:
- For small lightweight alloy castings such as aluminum alloys, the thickness of 12-15mm is selected; for large non-ferrous alloy castings, 20-25mm is selected.
- For cast iron castings, 10-22mm is selected; for steel castings, ≥20mm is selected.
IV. Placement Position
In the casting production, the foam ceramic filter can be placed horizontally at the bottom of the sprue. Horizontally or vertically in the runner and ingate; when the mold is vertically parted, the filter can be placed on one side of the sprue. To avoid the turbulence of the molten metal. The gating system is generally designed to be semi-closed or open. And due to the flow resistance of the filter. The dimensions of the relevant units of the gating system must be increased accordingly.
Section 4: Straight-hole Ceramic Filters
The filtration and purification of the molten metal can improve the quality of the casting and reduce the loss of scrap castings. The filtration mechanism of the straight-hole ceramic filter is similar to that of the foam ceramic filter, and it has a very good filtering effect. The straight-hole filters are divided into stamping type and extrusion type according to the production method.
The advantages of the stamping type straight-hole filter are:
- High strength: The unique production process ensures that the filter has higher strength than similar filters, eliminating the phenomenon of breakage during the pouring process. And it can be used in the production of larger castings.
- Good filtering effect: It has a good rectifying and filtering composite effect on the molten metal, can effectively remove large inclusions, adsorb fine inclusions in the molten metal. And the passing rate is stable.
- High dimensional accuracy: It ensures the matching accuracy between the filter and the mold; high cost performance: It can further reduce the production cost.