The sedimentation operation often takes a long time, and the suspended solid particles in the liquid cannot be completely separated. The filtration is not only a fast separation speed, but also less impurities after separation. So molten metal filtering is a common and effective method for separating suspensions.
Molten Metal Filtering is an operation in which a certain porous substance is used as a medium to treat the suspension. Under the action of external force, the liquid in the suspension passes through the pores of the medium, while the solid particles are intercepted, thereby realizing the separation of liquid and solid. The suspension processed by the filtration operation is called mud, the porous material is called the filter medium, the liquid passing through the medium pores is called the filtrate, and the retained material is called the filter cake or filter residue.
There are two main ways to filter molten metal
Deep filtration mechanism: The solid particles in the suspension are smaller than the pores of the filter medium. Therefore, these particles can enter the long and curved pores, and are collected in the pores under the action of gravity, diffusion and inertial forces, and are affected by molecular forces. It adheres to the inside of the filter medium under the action of static electricity. This filtration is carried out inside the medium, such as a deep bed filter.
Filter cake filtration (or surface filtration): Particles larger than the pores and the same as the pores accumulate on the surface of the medium to form a filter cake. At the beginning of filtration, very small particles also enter or pass through the pores of the medium, so the filtrate may be turbid. After the filter cake is formed, the filter cake acts as a filter medium (equivalent to a depth filter medium) in the subsequent filtration of the suspension, which can separate the smaller particles in the feed suspension. Surface filtration generally treats high-concentration suspensions.
The ceramic foam filter has two functions of cake filtration and deep filtration, and is the most widely used filter medium in molten metal filtering.