The basic principle of using displacement sensors in the material flow valve measurement at Lenggang Steel is as follows: When the material flow valve opens to unload material, when the actual opening degree of the material flow valve (detected by a magnetostrictive displacement sensor) reaches the angle set by Lenggang Steel, both the material flow valve opening solenoid valve and the material flow control valve solenoid valve are de-energized, and the hydraulic cylinder stops at the set angle position. After the furnace charge is unloaded, both the material flow valve opening solenoid valve and the material flow control valve solenoid valve are energized again, and the material flow valve is fully opened. When the time is up, the material flow valve is closed. The biggest advantage of this method is that the control is simpler than the original control method.
Lenggang employs a PLC control system responsible for acquiring the actual opening value of the furnace top material flow valve (detected and converted into actual angle by a magnetostrictive displacement sensor ) and receiving opening magnitude and action commands from the furnace top control system. After analysis and processing, the opening command is converted into a 4-20 mA electrical signal and sent to the integrated amplifier of the proportional valve to control its opening. When the PLC outputs 12 mA, the material flow valve is stopped; when the PLC outputs 16 mA, the material flow valve is open; and when the PLC outputs 8 mA, the material flow valve is closed. This control method achieves an accuracy of approximately 0.8 degrees.
The basic principle is as follows: When the blast furnace receives the charging command, the PLC outputs a 16mA current, which is also applied to the proportional valve coil. This opens the material flow valve cylinder to discharge the material. When the actual opening degree of the material flow valve (detected by a magnetostrictive displacement sensor ) reaches the set angle, the PLC outputs a 12mA current, which is also applied to the proportional valve coil. The material flow valve immediately stops, and simultaneously, the solenoid valve (hydraulic lock) of the material flow control valve is de-energized, and the cylinder stops at the set angle position. After the furnace charge is discharged, the proportional valve coil is energized again with a 16mA current. Simultaneously, the solenoid valve (hydraulic lock) of the material flow control valve is energized, and the material flow valve cylinder fully opens. When fully open, the proportional valve coil receives a 12mA current, and the solenoid valve (hydraulic lock) of the material flow control valve is de-energized, and the material flow valve stops. When the fully open time is up, the proportional valve coil is energized again with an 8mA current. Simultaneously, the solenoid valve (hydraulic lock) of the material flow control valve is energized, and the material flow valve cylinder closes. Because we corrected the angle between the actual opening value of the material flow valve and the set opening value of the material flow valve, the error cannot be greater than ±0.8 degrees. This control method can basically meet the material feeding requirements of the cold steel blast furnace, but the control accuracy is not high enough. Since closed-loop control has not yet been realized, the continuous adjustment and control of the speed and thrust of the oil cylinder has not yet been realized, and there are still some defects.
Future improvement directions and strategies for Lenggang's material flow valve control. To achieve both high thrust and speed while maintaining ideal accuracy, Lenggang aims to combine open-loop and closed-loop control methods for the material flow valve, enabling continuous adjustment and control of the cylinder's speed and thrust. It is important to note that due to the high amplification factor of the hydraulic servo proportional system, coupled with the inherent frequency of the mechanical system, improper adjustment of PID parameters (such as proportional, derivative, and integral coefficients, delay time, and offset) can easily lead to system oscillations. Therefore, the setting of various PID parameters requires repeated experimentation to achieve the best results.
