Although most of the slag inclusions are removed from the aluminum melt during refining, some fine slag particles, especially slag particles below a few microns, are difficult to remove by furnace refining and online refining methods, and they are still suspended in the aluminum melt. Strict filtration treatment of molten aluminum is required before casting and rolling. That is, let the aluminum melt pass through a certain filter medium, so that the impurity particles in the melt are intercepted by the surface of the filter medium or captured by the inside of the filter medium, so as to achieve the purpose of purifying the aluminum melt.
There are many ways for filtration treatment of molten aluminum, mainly include corundum tube filter, deep bed filter, foam ceramic filter, and so on.
The deep bed filter is made up of layers of alumina balls and alumina grit of appropriate size. The size and stacking method of alumina balls and gravel are determined according to the quality requirements of the final product.
The filter bed is a porous medium. The bed body is designed and calculated according to the requirements to ensure that the aluminum liquid achieves laminar flow, prevents secondary pollution from destroying the alumina layer, and makes the path of the aluminum liquid flow through the tortuous filter layer under gravity as long as possible, so that the impurity particles are intercepted Or deposited on the filter bed. It is suitable for high-demand, large-volume, semi-continuous casting production needs, and a single casting-rolling production line with small output.
In the current application, the deep bed filter must be completely immersed in the molten aluminum liquid, otherwise the temperature of some parts will be too low, causing the aluminum liquid to solidify, reducing the flow area, shortening the flow path, and affecting the effect and use of the filter bed. life. Therefore, before the bed is filtered, on the one hand, it must be fully preheated and keep the bed heated evenly. On the other hand, it is necessary to fill the filter bed with a proper temperature of molten aluminum and a proper flow rate. The filling procedure is: inject liquid aluminum from the outlet of the filter bed, make the aluminum liquid rise from the bottom of the filter bed, and slowly spread over the top of the filter bed to ensure that the filter bed is 100% immersed in the liquid aluminum.
Foam ceramic filter is characterized by easy use, low initial pressure, better filtering effect, and relatively cheap price, so it has been widely used. In casting and rolling production, most manufacturers use this filtering method.