Ceramic Foam Filtration is widely used for molten aluminum filtering. Molten aluminum filtering is an important step in the aluminum casting process.
After the aluminum melt is refined in the smelting furnace, refining in the static furnace and online refining, the gas content has been greatly reduced, and it is basically in the critical minimum state. Larger particles of inclusions in the melt are basically carried by the refining agent, but there are still a certain number of small particle inclusions in the melt, which will have a certain impact on the mechanical properties and physical and chemical properties of the material. Therefore, it must be filtered by Ceramic Foam Filtration before casting.
At present, the main filtration methods commonly used at home and abroad are ceramic foam filter filtration, corundum tube filtration, and deep bed filter filtration. The factors that affect the filtering effect are the properties of the alloy melt, the initial concentration of inclusions in the melt, the porosity of the filter, the thickness of the filter, the filtering speed of the melt, and the filtering time.
When the alloy is determined, the properties of the molten metal are determined. After the melt passes through the smelting furnace, static furnace, and online refining, the particle size of its inclusions no longer changes. Once the filter is selected, its porosity is a fixed number.
The filtration efficiency is only related to the thickness of the filter and the speed at which the melt passes through the filter. The greater the thickness of the ceramic foam filter, the better the filtering effect. The faster the melt passes through the filter, the worse the filtering effect. Cast-rolling production, the amount of melt filtration per unit time is small, the flow rate is slow, and the casting-rolling is mostly pure aluminum and soft alloys. There are few inclusion particles and the inclusions are easily absorbed by the filter, and the filtration efficiency is high. Relatively speaking, the melt is easier to purify. Generally, 50PPI and 30PPI two-stage ceramic foam filters are used for filtration. The thickness and area of the filter sheets are determined by the specific overflow calculation to meet the requirements.
Compared with casting and rolling, the production situation of casting is more complicated. As mentioned above, the flow rate is large, and the flow rate of the filter is 2.5-3.5 times higher than that of the cast-rolling, which reduces the filtering effect. Therefore, in order to ensure the same filtration efficiency, the flow area of the filter must be increased so that the flow rate per unit area of the filter is equal to it. Secondly, the chance of duralumin and super-hard aluminum alloy melts containing tiny slag particles is much higher than that of pure aluminum and soft alloys. For this reason, the efficiency of filtration cannot be reduced, but must be greatly improved to achieve high purity of the melt. To ensure the quality of the final product. Therefore, it is best to use corundum tube filter, which not only increases the surface area of the filter in contact with the melt, but also reduces the flow rate per unit area of the melt, and ensures the filtration efficiency and total flow rate to meet production needs. It also reduces the pore size of the filter and increases the porosity to improve filtration accuracy and reduce the number of residual fine particles in the melt.
A corundum tube with a length of 0.889m and an outer diameter of 0.102m is equivalent to a ceramic filter plate of 0.258m^2, which can greatly improve the quality of cast products and meet the needs of high-end products. However, it should be pointed out that this increases the initial pressure of the filtered melt, which will increase the difficulty of the operation and increase the cost of filtration.