The study on filtration mechanism is the basis for the development and application of any kind of filtration technology. The surface interface interaction between inclusions and filtration in the high-temperature melt is very complicated, and the flow process of the melt in the filter is difficult to observe, although filter cakes have been proposed. Relevant theories such as effect, mechanical interception, deep bed adsorption, and rectifying scum, but so far have not yet formed a unified understanding. Aluminum melt filtration is not a single physical screening process, but under certain conditions, particles and filters pass between Collision, interception, deposition, diffusion, flow fluctuations, chemical reactions, etc., form the result of a multi-factor coupling based on a certain mechanism. These factors include: filter parameters (pore size and distribution, filter order (ppi), Filter media size, shape, porosity, channel tortuosity, material) impurity parameters (inclusion size, quantity, concentration, nature), melt parameters (temperature, time, flow rate, viscosity, specific gravity, filtration volume, pressure head, alloy type) , Use of refiner, filtration rate, upstream treatment, etc.).
The study on filtration mechanism mainly investigates the influence of various parameters on the behavior of melt filtration and trapping from the perspectives of thermodynamics, kinetics and fluid mechanics. The flow field mass transfer model of the melt filter medium inclusions predicts and optimizes the actual filtration process and t filtration efficiency. In this regard, researchers from various countries have carried out multi-angle research through the establishment of models and industrial tests for different filtering methods, and have achieved many beneficial results.
In the early 1980s, two types of filtration mechanisms were summarized: deep bed filtration and filter cake filtration. The mathematical model system is used to describe the short-term filtration mechanism and filtration efficiency of various filtration parameters for TiB2 particles in the aluminum melt. The relationship between the kinetic parameter filter medium size, inclusion size, and melt flow rate is given, and the experimental simulation verification.
In addition to the physical filtration mechanism, the chemical adsorption between the filter and the inclusions is also one of the filter surface trapping mechanisms. The filter channels are relatively small, and the melt has a sufficient contact area with the inner wall of the filter. The inclusions are close to the wall surface driven by the liquid flow, and usually there is no infiltration between the inclusions and the molten metal, especially the smaller the size of the inclusions, the worse the wettability, once the inclusions are in contact with the surface of the filter medium with better relative wettability, It is easy to break away from the molten metal and be adsorbed by this surface.
The rectification effect is also one of the physical mechanisms of filtration. The rectification ability of the filter (net) makes the turbulent metal liquid flow through the filter (net) into a laminar flow state. After the melt flows through the filter, it needs to go through a longer transition zone to restore the turbulent state, which reduces the secondary oxidation of the molten metal and the erosion of the mold, and plays an obvious role of scum.