The filtration purification method is that aluminum melt passes through a filter, so as to separate the solid inclusions suspended in the melt.
According to the filtration properties, the filtering methods of aluminum alloy melt can be divided into surface filtering and deep filtering.
According to the filtering material, it can be divided into mesh material filtering, block material filtering, and liquid layer filtering.
At present, foam ceramic filter molten metal filtration is the widest filtration purification method used in foundry.
Surface filtration refers to the solid impurities mainly deposited on the surface of the filter medium, also known as cake filtration. Net-like material filtration belongs to surface filtration. Deep filtration is also called internal filtration. The solid impurities are mainly deposited inside the pores of the filter medium. As the filtration progresses, the effective filtration section of the pores gradually decreases, the permeability decreases, and the filtration accuracy improves. Bulk material filtration belongs to deep filtration.
The filtering mechanism of the mesh material filter is mainly to mechanically separate the coarse non-metallic inclusions in the melt. It can only trap inclusions in the melt, whose size is larger than the mesh size.
The filtering mechanism of the block material filter made of neutral material is mainly through the deposition, hydrodynamic and direct interception to mechanically separate the solid inclusions in the melt.
The ceramic foam filter has a large specific surface area, and the melt and the filter medium have a sufficient opportunity to contact. When the melt carries the solid impurities and moves along the filter at a variable speed, because the density and speed of the solid inclusions are different from those of the melt, sedimentation occurs under the action of gravity. Due to the non-spherical nature of the solid particles and the uneven shear force field, the solid particles move laterally, thereby being hooked, stuck or adsorbed by the channel walls.
In addition to the above-mentioned filtering mechanism, the block material filter made of active material also produces physical and chemical deep filtration due to the action of surface force and chemical force, so that the melt can be purified more finely. The ceramic foam filter can trap solid inclusions that are much smaller than the diameter of its pores.