Development of crystallizer vibration law

- Nov 16, 2019-

The crystallizer changed from static to vibration, which caused widespread concern and interest of continuous casting workers. People have carried out experimental research work, studied the mechanism of cohesive steel leakage, and developed various crystallizer vibration laws.

 

The earliest appearance is the rectangular velocity vibration law, based on the theory of “pull-welding”, which is characterized in that the crystallizer moves synchronously with the casting blank when it descends, and then rises at a casting speed of 3 times, so-called 3: Type 1 vibration mode. This vibration mode is effective for demolding the cast slab and has been applied in the early stage. However, its main disadvantage is that the machining is difficult, and there is a strict electrical interlock between the vibration mechanism and the drawing mechanism. The speed changes greatly at the turning point of the ascending and descending, and the equipment impact is large, which is not conducive to the use of high-frequency vibration. However, the use of this waveform causes the fixed crystallizer to become a vibrating crystallizer, giving the crystallizer technology a leap.

 

With the advent of the negative sliding theory, the rectangular velocity law is replaced by the trapezoidal velocity law, which is characterized by a longer period of time during which the crystallizer moves downwards, and its velocity is slightly larger than the casting speed, that is, “negative slipping motion”, so that the billet The compressive stress is generated in the shell, which can press the shell of the cracked shell to force the shell of the bonded shell to be demoulded. The speed of the crystallizer changes gently at the rising and falling turning points, which improves the stability of the equipment and the appearance of trapezoidal waves. The production of continuous casting is smoother. This speed waveform has been used for many years, and the theory of negative sliding has been used ever since.

 

With the continuous development and improvement of the negative sliding theory, the sinusoidal velocity law appears, and the sinusoidal vibration velocity law is realized by the eccentric wheel. This vibration law breaks the limitation of the speed relationship between the crystallizer and the slab, and focuses on its demolding effect. The eccentric wheel is used instead of the cam. The sinusoidal vibration still has a small negative sliding stage, which is beneficial to demoulding and The welding of the cracked shell is gentle, the speed and acceleration change are gentle, the eccentric wheel equipment is simple, easy to manufacture, install and maintain, the motion precision is high, the equipment movement is stable, the impact is small, and it is easy to adopt higher frequency vibration. Sinusoidal vibration is still widely used.

 

The characteristic of the non-sinusoidal vibration velocity waveform is that the time for the crystallizer to move up to the maximum displacement is delayed by a period of time compared with the sinusoidal vibration, the speed of the upward movement of the crystallizer is small, and the speed of the downward movement is large. The negative sliding time is short, which is beneficial to reduce the depth of the surface of the casting blank, and the long sliding time can increase the consumption of the protective slag, enhance the lubrication between the mold wall and the shell, and the difference in the positive sliding speed can reduce the friction. The force reduces the tensile stress in the shell and reduces the tensile crack; the negative sliding amount is large, that is, the displacement of the crystallizer relative to the downward movement of the slab is large, which is favorable for the forced demolding of the slab. Because non-sinusoidal vibration can obtain reasonable process parameters, adapt to high pulling speed, and obtain good surface quality, it has received people's attention and has been recognized by many continuous casting workers as one of the key technologies for developing efficient continuous casting.


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