Inclusions and gases in the metal have a significant impact on the strength, fatigue resistance, corrosion resistance, and stress corrosion cracking performance of the material. Effectively controlling the oxidized inclusions in the melt to improve the quality of cast bars and rolled plates has become a common goal pursued by metallurgy, foundry, and material industries in various countries. At present, Aluminum Water Purification Methods are widely used to remove the inclusions in the aluminum alloy melt. AdTech offers CFF filter system for aluminum liquid.
Formation of Inclusions in Aluminum Water
Some of the inclusions in the aluminum alloy come directly from the charge, while most of them are formed during the melting and pouring process, mainly oxide inclusions.
Primary Oxidation Inclusions
All the inclusions before casting are called primary oxidation inclusions, which can be divided into two categories according to size: one is the large inclusions with uneven distribution in the macrostructure, which makes the alloy structure discontinuous and reduces the compactness of the casting. It becomes the root of corrosion and the source of cracks, which obviously reduces the strength and plasticity of the alloy; the other is the fine dispersion inclusions, which cannot be completely removed after refining. It increases the viscosity of the metal melt and reduces the aluminum during solidification The ability of liquid to shrink.
Secondary Oxidation Inclusions
The secondary oxidation inclusions are mainly formed during the casting process. During casting, the aluminum liquid and air contact, and the oxygen and aluminum act to form oxidized inclusions. The aluminum alloy contacts various components in the furnace gas during the smelting process to form compounds such as AL2O3. Al2O3 in the aluminum liquid will increase the hydrogen content of the aluminum residual melt, so the AL2O3 content in the aluminum liquid has a great influence on the formation of pores in aluminum castings.
Aluminum Water Purification Method
Ceramic foam filter technology came out in the 1970s, and it has been widely used in the United States, Canada, Japan, France, Australia, and Switzerland. It is the most effective method to remove the inclusions in the aluminum melt before using the ceramic foam filter plate filter port.
In recent years, some new technologies for purifying aluminum liquid have been studied at home and abroad, such as vacuum dynamic processing, ultrasonic continuous degassing purification, and corundum ceramic filters, which have received very good results. However, these technical methods are relatively complex and costly, and it is difficult to promote them in large quantities in Shangye cattle production. As for the metal filter and fiber cloth filtration, only large inclusions in the aluminum alloy melt can be removed, but the inclusions below the micron level cannot be removed, and the metal filter will also contaminate the aluminum alloy. The use of foam ceramic filter plates can filter out small inclusions and significantly improve the mechanical properties and appearance quality of castings.
Aluminum Water Purification Principle
The ceramic foam filter plate has a multi-layer network and multi-dimensional through holes, and the holes communicate with each other. When filtering, the aluminum liquid carries the inclusions along the tortuous channels and pores, and is directly intercepted, adsorbed, and deposited when it contacts the foamed skeleton of the filter plate. When the melt flows in the hole, the filter plate channel is curved, and the melt flowing through the channel changes the flow direction, and the inclusions collide with the hole wall anvil and firmly adhere to the hole wall.
Use and Selection of Filter Plates
The foam ceramic filter plate is installed in the filter box between the furnace mouth and the diverter plate. The filter box has good thermal insulation performance. The filter boxes and flow channels are as close as possible to the distribution plate. The reason is that it can shorten the flow distance after aluminum water filtration and reduce or avoid the re-oxidation of oxides. The aluminum liquid flows out from the furnace mouth through the filter box, and then flows through the flow channel to the disc.
With the extension of the filtration time, the inclusions on the surface of the filter plate and the wall of the hole increase, the filtration flow rate decreases, and the difference between the front and back increases.
The selection of the ceramic foam filter plate must be based on the flow of aluminum liquid. Second, the cleanliness of the melt, the maximum content of inclusions, and the total throughput of the melt should be considered. The filtering effect of the filter plate is mainly guaranteed by its size and porosity. The larger the porosity of the filter plate, the worse the slag removal effect. For aluminum castings with strict requirements, the foam filter plate with small porosity should be selected.