Application of PLC in vacuum pressure impregnation equipment control system WANG Jiafu, WANG Xi, LI Yanyan (School of Electrical and Electronic Engineering, Changchun University of Technology, Changchun) Insufficient stability of the graphite electrode production process control, the use of PLC to control the vacuum pressure impregnation system is proposed. The control accuracy has achieved good results in practice.

Fund Project: Jilin Provincial Department of Science and Technology Agency (20050414-2) Wang Jia. Fu, M.A (A66-), t.Master, Fung to engage in automation With the large-scale development of electric furnaces and the development of refining technology outside the furnace, the demand for high-power and ultra-high-power electrodes is increasing, and quality requirements are increasing. The higher. To improve the electrode quality and reduce the electrode consumption index of the ton steel, the key is to increase the bulk density and strength of the electrode, and it is necessary to improve the control accuracy of the control step in the impregnation process.

The vacuum impregnation process of graphite is a key process in the production of graphite electrodes. The control of its process indicators plays a decisive role in the technical indicators such as conductivity, robustness, and lifetime of graphite electrodes.

1 Vacuum Pressure Impregnation Principle Vacuum pressure impregnation is a process in which liquid asphalt is forced into the pores of products under certain temperature and pressure. Under vacuum conditions, negative pressure effects are used to maximize the removal of moisture and gases in the impregnated graphite electrodes. The structure is loosened, and then the purified high-concentration liquid asphalt is added to the impregnation tank, and the large pressure difference and the positive pressure effect are used to accelerate the uniform penetration and diffusion of the impregnation liquid into the impregnated graphite electrode and reduce the product. The pore size increases the density of the product and reduces the porosity and permeability, increases the mechanical strength of the product and improves the electrical and thermal conductivity.

2 Impregnation process and influencing factors The main equipments of the impregnation production system are preheating furnace, impregnated tank, vacuum equipment, pressurizing device and cooling system.

The impregnation process is mainly composed of evacuation, liquid filling (liquid asphalt), impregnation, constant pressure keeping and liquid returning. The immersion process is as shown in Fig. L. Electrode preheating, immersion and vacuuming, M in the main impregnation tank, filling in the impregnation end, and oil return. The pressure process of the constant pressure immersion tank can influence the process factors of the impregnation. The temperature, the degree of vacuum before immersion, and the time of vacuum suction, the preheating temperature of the impregnating agent, the heating temperature of the impregnation tank, the pressure of the impregnation, and the pressure time. Most of the original control systems use relay control. After a person issues a start command, the PLC automatically completes the entire operation process in advance. Pre-operation, after the end of the operation signal, remind management input, early | Where temperature control PLC according to the pre-set process and pressure and temperature, etc.) can be reset, without having to change all forms of bus direct 1 and multiple computers Interesting host, connected to the c-toe program ouPLC system control program flow chart, such as 锾vW.cnki.net workers monitoring the temperature, pressure and time parameters in the production process, manual operation of various devices, due to the presence of human factors, leading to the graphite electrode The control of the production process is not stable enough, which affects the impregnation quality of the graphite electrode, especially the pressure and time control in the constant pressure impregnation stage is inaccurate, so that the impregnated product fails to meet the required technical indicators, resulting in unstable product quality and high reject rate. Use new control systems and controls.

3 Design of vacuum pressure impregnation control system 3.1 System composition The impregnation system consists of air tank, vacuum system, impregnated tank system, liquid level tank and control system. Its structure is shown as follows.

According to the process requirements, the dipping process control of the graphite electrode is performed intermittently. According to the sequence of operations in various steps, the entire control system has more analog values ​​such as temperature and pressure, and the switching of the drive motor and various process valves is also controlled. More.

3.2 Control system composition As shown in the control system, Omron's PLC medium-sized host C200HX controls the entire system, replacing the traditional relay control system and improving the technical level of the control system. Omron's C200HX series PLC is a small and medium-sized programmable controller. The product has features such as strong functions, high speed, flexible expansion, and modular structure. It can be connected to various enterprise management networks through Ethernet proxy servers. Makes a more flexible distributed network. The objects controlled by the immersion control system can be divided into three categories: one is the control of the switch quantity, such as the switch of the can lid, the opening and closing of the valve; the other belongs to the analog output control of the motor speed regulation; the third is Analog detection input, such as liquid level, temperature and pressure in the impregnation tank. Control system components such as the entire system from the host, analog input and output units, digital input and output units, detection components and instruments. According to the composition of the dip control system, the input part is configured with a total of 16 analog input modules (pressure detection 5 points, pressure given 5 points, temperature detection 3 points, temperature given 3 points) and 30 points switch input module; The output section is equipped with 30 switching output modules and 4 analog output modules. The output switch quantity is used for the on-off control of the solenoid valve, the analog quantity is used to control the frequency converter, the speed control of the vacuum pumping and pressure driving motor is realized, and the vacuum and dipping pressure are maintained at the values ​​set by the system.

3.3 Control Methods According to the process requirements of the impregnation process, the operation of the control system is divided into two modes: automatic and manual. The manual method divides the entire operation into several steps according to the process flow, namely the opening and closing of the lid of the impregnation tank, the vacuum of the impregnation tank, the addition of the impregnation liquid, the constant pressure maintenance, the row of the impregnation liquid, and the like. The start and stop buttons are set for each step. The operator performs corresponding operations according to the process requirements. The PLC guarantees the execution order of the operator and the sequence of operation of the equipment to ensure the normal and safe operation of the equipment. The automatic working mode is the operation: the order of the settings and In the conditions, there is no need for the operator to do it: the operator performs the corresponding point:. 4 The main process parameters to be measured in the program design, such as vacuum, pressure, etc., through the PLC built-in PID control algorithm to achieve precise control of the system pressure. The parameters that need to be changed due to process changes (such as the vacuum level, manual operation of the device, and PLC automatic control after the technical change, are greatly improved in terms of graphite impregnation temperature, vacuum degree, weight gain rate and impregnation effect, etc. For details, see Table 2 Table 2 Comparison of major technical indicators Technical transformation of the equipment before the technical transformation of the equipment Equipment after the technical reform of uneven uniform preheating temperature / C vacuum / Pa impregnation pressure / MPa impregnation weight gain rate / impregnation period / h impregnation effect Unstable ability to penetrate the automation level Manual operation PLC automatic control 4 Before and after the transformation of the impregnation system Product performance and comparison of main technical indexes Table 1 shows the comparison of the bending performance, shear performance and pressure resistance performance of the product before and after the impregnation system transformation. 1 It can be seen that the higher the product density, the greater its bending strength, shear strength and compressive strength, and the better its mechanical properties.High pressure impregnation of bitumen as one of the effective ways to increase the densification of graphite electrodes is to improve the mechanical properties of graphite electrodes. The effective process, asphalt carbon residue in the body, it is easy to graphitize, so that the graphite electrode stress is better in the process of stress transmission and distribution, macroscopically embodied as stone Improve the mechanical properties of the electrode, thereby improving the electrical conductivity and the thermal conductivity of the graphite electrode.

Shear Properties Pressure Resistance ~ Project Density Strength Modulus Density Strength Modulus Density Strength Modulus ~~g/on3MPa GPag Before the technical transformation, the entire impregnation control system was a relay 5 Conclusion The vacuum pressure impregnation system based on PLC is a This kind of impregnation method with higher degree of automation has greater improvement than the traditional impregnation method. The impregnation system can be operated in an efficient and stable production condition, ensuring the impregnation quality of the graphite electrode and improving the automation level of the impregnation system.

New technologies and new equipment were used in the dipping process to ensure high vacuum and high pressure impregnation control accuracy and improve product quality. The impregnated product weight gain rate increased from 12% to 13% to 14% compared to the original. Heating and insulation of 15% impregnated tank and impregnant pitch are made of heat-conducting oil as the heat source and are automatically adjusted by PLC. The impregnation temperature is higher and uniform, ensuring the soaking effect.

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