The automatic argon blowing system for ladle introduced in this paper takes the mass flow controller as the core, matches the corresponding hardware detection, software programming and so on. The pipeline and hardware modification, the signal connection between mass flow controller and computer are briefly introduced. It has been successfully applied to ladle bottom blowing system in steelmaking and achieved good results. The basic principle of argon blowing in ladle: argon is used as an inert gas and passes through the special permeable bricks at the bottom of the ladle to pass into the steel water. Harmful gases such as H2, N2 and O2 in molten steel form a large number of small bubbles in the molten steel to reduce their content in molten steel. Argon can also make the molten steel surge in the ladle, the molten steel is fully stirred, the alloy, Deoxidizer and desulfurizer added into the molten steel are melted rapidly, and the composition and temperature of the molten steel are uniform. At the same time, gas nucleation and inclusion particles collide with each other, and non-metallic inclusions in molten steel float into slag. Argon bottom blowing plays an important role in purifying molten steel and improving steel quality. For LF ladle refining furnace and VD vacuum degassing refining furnace, in order to ensure the quality of molten steel, the whole process of argon blowing must be carried out. Initially, the most basic control mode is manual mode.
By observing the molten steel rolling situation and the pressure gauge on the spot before the ladle by the operator, the argon pressure is controlled by manually pulling the ball valve. The gas source is supplied by argon in the pipeline or bottled argon. This method can only control the pressure of argon, but the actual bottom blowing flow rate can not be accurately controlled, the use effect is very poor. With the improvement of knowledge, argon blowing control consisting of pressure relief valve, solenoid valve, pneumatic film regulating valve and other control elements has gradually emerged. Operators are required to set the corresponding argon pressure and flow parameters on the industrial computer in the control room by observing the steel boiling situation on the spot and telling the control room. This method is better than manual method, but the control curve of pneumatic control valve is soft and the reaction time is slow, which can not meet the requirements of field control. Another way is to control the flow through the flow valve group. Flow valves are designed for several valve groups with fixed flow rate, such as 5 L/m, 10 L/m and 20 L/m, which can be used to control seven different flow rates. This method can control the reaction time quickly, but the disadvantage is that it can not set any flow parameters within the flow range. The automatic argon blowing system for ladle introduced in this paper takes the mass flow controller as the core, carries on the corresponding transformation to the pipeline, and the mass flow controller connects with the computer or the PLC signal through the standard signal, so as to meet the requirement of precise measurement and precise control of the gas flow. Mass Flow Controller mainly measures the gas flow accurately and controls the set flow accurately. The main functional components are mass flow detection part, shunt channel, flow control valve, signal processing circuit and pipe shell, etc. The principle of capillary heat transfer temperature difference method is used to detect the mass flow rate of the gas. The working principle diagram is shown in Figure 1. The sensor of this kind of detection mode is little affected by temperature and pressure, so there is no need for extra temperature and pressure compensation. The flow signal measured by the mass flow detection component through the sensor heating bridge is converted by a special amplifier and compared with the set voltage corresponding to the set flow. The difference signal obtained by comparison is amplified to control the control valve, so that the detected signal is consistent with the set signal. The function of the shunt is to expand the flow through the flow controller.
From the flow direction, the laminar flow is generated between the main channel and the capillary. The input and output flow of the mass flow controller are in the form of standard voltage or current. Mass flow controller can be connected with computer, PLC or corresponding flow indicator to realize display control.
A dedicated a / D, thermostatic element D / a conversion template is required for the direct connection of the mass flow controller with the computer. When the mass flow controller is in the process of long-term use or installation and debugging, the zero point may be offset, and the zero offset need to be proofread. The Mass Flow Controller directly communicates with the computer in signal docking as shown in Figure 2. Generally, there are two branches of ladle to control two air permeable bricks. Each ventilation line is equipped with independent flow regulation control, which makes the heat exchange in ladle go smoothly. Each branch of the ladle automatic argon blowing system uses a mass flow controller as the control core, and a solenoid valve is set up in the front and back pipes for the input and removal of the controller.
A side blowing pipe is set beside the automatic control circuit for molten steel crust breaking, and the pipeline can be purged to ensure the safety of the automatic control circuit. A branch diagram of the ladle automatic argon blowing system is shown in Fig. 3. The ladle automatic argon blowing system has been reformed by mass flow control, and it runs steadily.
Some conclusions can be drawn from the application of the system. Mass flow controller is used for precise measurement and control of gas mass flow. It has the advantages of high precision, good repeatability, fast response, stability and reliability, and wide working pressure range. Mass flow controller is easy to operate. Good openness can be used not only with the flow indicator, but also directly with the computer to achieve automatic control of the system. Installation and use can take a variety of ways.
The control mode of ladle automatic argon blowing system using MFC control mode is advanced. The gas control in smelting process has the following advantages: accurate control, accurate measurement, flow stability, maintenance-free, high reliability, strong anti-interference ability, fast response and high automation. Mass flow controller can be widely used in electronic process equipment, vacuum coating, petrochemical industry, metallurgy, pharmaceuticals, optical fiber fusion, analysis and measurement instruments, gas distribution and other industries. The author is brief: 1979-, male, man, University, assistant engineer, research direction: Measurement and control instrument direction.