1.Mechanical stirring method
The mechanical stirring method is the oldest and simple stirring method. It is different from the electromagnetic stirring method in that the stirring function is realized by the rotation of the blade or the stirring rod. The principle of forming the non-dendritic crystal is similar to the electromagnetic stirring method.
The control of the solid phase ratio of the alloy needs to be achieved by changing the ambient temperature around the alloy. The amount of shear speed depends on the speed of rotation of the agitating tool.
The advantage of the mechanical agitation method is that the device required for agitation is relatively simple, low in cost, operability and easy to control. The same shortcomings are also obvious. The limited stirring speed leads to low production efficiency, the stirring environment is difficult to seal, and impurities and gases are easily mixed.
2. Electromagnetic stirring method
The electromagnetic stirring method utilizes the phenomenon of electromagnetic induction. A rotating magnetic field is added to the outside of the metal solution to cause the molten metal to undergo a cutting magnetic line motion to generate an induced current, and the current magnetic effect causes the molten metal to stir vigorously to promote the formation of non-dendrites.
The stirring speed of the liquid can be controlled by the magnetic field strength of the applied magnetic field and the rotational speed of the magnetic field. There are two methods for generating a rotating magnetic field: alternating current is applied to both ends of the induction coil and permanent magnets are rotated by the motor.
The advantage of electromagnetic stirring is that the mixing process does not require the use of a stirring tool (blade or rod) to increase the purity of the alloy metal. In addition, the treated metal can be carried out in a closed container, which avoids the incorporation of gas, reduces the generation of pores during the molding process, and reduces the defects of the blank. At the same time, the operability is strong and controllable, and the stirring speed can be controlled by the magnetic field strength and the rotation speed, and the control is precise and the range is wide. However, the disadvantage is that the energy consumption is large, and the manufactured billet is expensive, which is not conducive to the production of large-sized components.