Molten Aluminum Filtration is to pass the aluminum melt through a filter to separate the solid inclusions suspended in the melt. There are many molten aluminum filters used in foundry. The following is the classification according to the molten aluminum filtration methods.
Classification of Molten Aluminum Filtration Method
According to the filtering properties, the filtering method of aluminum alloy melt can be divided into two types: surface filtering and deep filtering. According to the filtering material, it can be divided into mesh material filtering (such as glass cloth, metal mesh), bulk material filtering (such as deep bed filter, ceramic foam filter) and liquid layer filtration (such as flux layer filtration, electric flux refining) three categories.
Surface filtration refers to the filtration of solid impurities mainly deposited on the surface of the filter medium, also called filter 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 macroscopic and coarse non-metallic inclusions in the melt through the action of the fence. It can only trap inclusions in the melt whose size is larger than the mesh size (assuming that the inclusions cannot be deformed). The filtration mechanism of the block material filter made of neutral materials is mainly to separate the solid inclusions in the melt mechanically through deposition, hydrodynamics, and direct interception.
The bulk material filter has a large specific surface, and the melt and the filter medium have a sufficient opportunity to contact. When the melt carries solid impurities along the slender channels of the filter with variable cross-sections for variable speed movement, due to solid inclusions The density and speed of the melt are different, so it is possible to deposit under the action of gravity. Also, 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. The above phenomenon is strengthened by the formation of a low-pressure vortex area where the cross-section of the pore channel changes suddenly. 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 effect of surface force and chemical force, so that the melt can be purified more finely.
The bulk material filter can trap solid inclusions that are much smaller than the diameter of its pores. Liquid layer filter is to wash liquid metal with liquid flux. Its filtering mechanism is based on the physical and chemical reaction between flux and non-metallic inclusions and the wetting, adsorption and dissolution of inclusions by flux.