Mold Level Control System

MLC-V235 Continuous Casting Mold Level Automatic Measurement System


Overview

The automatic control for the molten steel level of the mold is one of the key technologies of continuous casting production. It is very important to reduce the labor intensity of workers, improve production efficiency, improve the quality and output of casting billet, reduce overflow and breakout of steel and improve the management level of steelmaking and continuous casting.

The molten steel is poured into the mold. In order to prevent overflow, the molten steel level must be kept stable. Otherwise, during the casting process, if the level will fluctuate too much, and slag will be involved, forming surface slag inclusion on the surface of the casting billet, affecting the quality of the billet. The test points out that the relationship between the level fluctuation and the depth of casting billet surface slag inclusion is as follows:

The experience has shown that surface slag inclusions can be eliminated when the level fluctuation is within ±10mm. At the same time, if the level fluctuation is more than 10mm, the rate of longitudinal cracks on the casting billet surface is 30%. It means that the level fluctuation directly affects the surface quality of the casting billet.

The principle is shown in the figure

A high-frequency exciting winding is installed above the molten steel surface of the mold. The magnetic field produced by exciting winding make induced eddy current appear. The magnetic field generated by the induced eddy current is in the opposite direction to the magnetic field generated by the high-frequency exciting winding, which changes the impedance of the high-frequency exciting winding. Under the condition that the winding material and structure, steel grade, temperature remain unchanged, the coil impedance change only has a single-value function relationship with the height of the molten steel level. As long as the impedance change of the high-frequency winding is detected, the change of the molten steel level in the mold can be converted.



The components of the system

Continuous casting mold level automatic control system is composed of eddy current tyoe molten steel level gauge, controller and digital actuator for adjusting the opening of tundish stopper.

The detection end of the mold level automatic control system is ① eddy current displacement sensor, which uses the eddy current mutual inductance effect between the energized coil and the metal conductor to detect the distance. The effective signal of the eddy current sensor is amplified and linearized by the circuit of ② mold level gauge, which converts the 0-150mm change in the molten steel level of the mold into a standard signal of 4-20mA.DC, and then transmits it to the ③ control computer to complete data processing and system control functions. We can also control the actuator manually and automatically through the ④on-site operation display control panel, and the opening of the stopper is controlled by the ⑤ actuator to realize the automatic control of the molten steel level.

1 Eddy current sensor;

2 mold level gauge;

3 control computer;

4 On-site operation display control panel;

5 digital actuator;



The function and software implementation

In order to overcome these disturbances, the mold level control strategy adopts PID control. And on the basis of PID control, self-adaptive correction and feedforward control are introduced to form an advanced control system. The level control is the main loop, and there is a proportional gain of the main loop controller. According to the self-adaptive correction of the mold width change and feedforward compensation of casting speed, so as to further reduce and eliminate liquid level fluctuations caused by mold width adjustment and casting speed changes.

In order to reduce the frequent action of the stopper, the system adopts the intergarting time change of the controller, and automatically selects a longer intergarting time when the molten steel level fluctuates lightly. And the system will choose a shorter intergrating time when molten steel level fluctuates greatly. Thereby, the fluctuation of the controlled object caused by the frequent action of the stopper rod is suppressed.

In the signal processing of molten steel level gauge, an appropriate filtering link is added and the vibration frequency synchronous filter is used for filtering processing, which can overcome the interference of mold vibration frequency and amplitude variation.


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