Zincing thickness control system and method

Abstract

The invention discloses a zincing thickness control system and method. Based on a feedforward plus feedback control structure, a neural network model is adopted to overcome the defect of low modeling accuracy in a traditional method, an integration-based varying lag time computing method and a time displacement offset correction technology are adopted to realize effective feedback of time varying large-lag measured information, and the difficulty of model mismatch caused by nonmeasurable external disturbance and operating point drift is overcome. The zincing thickness control system and method can be used for effectively overcoming the problems of large lag, nonlinearity and strong interference in a zincing production process and realizing automatic closed-loop control on plating thickness, thus achieving the effects of remarkably improving the product quality, reducing excessive zinc consumption, reducing switching time between products with different specifications, and the like.

Description

technical field [0001] The invention relates to the technical field of galvanizing process control, in particular to a galvanizing thickness control system and method. Background technique [0002] Galvanizing: here refers to hot-dip galvanizing, also called hot-dip galvanizing and hot-dip galvanizing, which is an effective metal anti-corrosion method and is mainly used in metal structure facilities in various industries. Hot-dip galvanizing is to immerse the rust-removed steel parts in the molten zinc solution, so that the surface of the steel components is attached with a zinc layer, so as to achieve the purpose of anti-corrosion. [0003] Galvanized products are widely used in construction, home appliances, automobiles and other industries due to their good corrosion resistance. The important technical indicators to measure the quality of galvanized products include the thickness and uniformity of the coating, that is, the thickness of the coating of galvanized products m...

AI Technical Summary

Problems solved by technology

[0004] 1. The on-line measurement of coating thickness needs to use a thickness gauge. Due to the process requirements of galvanizing production, the installation position of the thickness gauge is often far away from the air knife, resulting in a large measurement lag in the system. At the same time, in the actual plating In zinc production, affected by upstream and downstream production capacity, the speed of the galvanizing line changes at any time, so the measurement lag time of the system is not a fixed value, but time-varying (generally 70 seconds to 120 seconds), subject to Due to the influence of external disturbances, the thickness of the coating has been in a fluctuating state. Directly using the information of the thickness gauge for closed-loop control of coating thickness feedback will result in a large overshoot and a long adjustment time, which further increases the difficulty of thickness control in galvanized production. , leading to large fluctuations in coating thickness and difficult to control product quality;

[0005] 2. The production process of galvanizing is affected by many complex physical factors such as aerodynamic force and boundary flow layer. The final thickness of the zinc layer is the result of the joint action of variables such as air knife pressure, air knife distance, and production line speed. These variables The principle of influence on the thickness of the coating is relatively complex and there are many disturbance factors, which have strong nonlinearity. It is difficult to establish an accurate system model by using the traditional mechanism modeling method;

[0006] 3. There are various external random disturbances in the actual industrial site, such as: changes in the composition and temperature of the zinc liquid, changes in plate shape, fluctuations in air knife pressure, etc. These external disturbances will affect the thickness of the coating and cause a large quality fluctuations

Due to the lack of effective control technology to overcome the above difficulties, coating thickness control has always been a difficult problem in galvanizing production. At present, most galvanizing lines in domestic iron and steel enterprises adopt manual control based on feedback information from thickness gauges. This method is restricted. Due to the operator's experience and sense of responsibility, the control accuracy is low, the anti-disturbance is poor, the transition time is long when the product specification changes, and the quality fluctuates greatly. It is often impossible to obtain the expected product quality, and even irregular operations that violate the process requirements

Uneven coating and large fluctuations in thickness force manufacturers to artificially increase the setting value of coating thickness to ensure that product quality still meets the requirements of thickness control indicators when the working conditions fluctuate greatly. high cost

In order to solve the above problems, there are related domestic patents and literatures that propose a model-based feedforward / feedback control system, such as the patent "An Automatic Control System for Hot-dip Galvanizing Line Coating Thickness" with the publication number CN102912275A, whose model is based on the mechanism , based on the production history data, the least square method and other methods are used to establish piecewise linear fitting parameters. Due to the use of the feedforward + feedback design method, the method proposed in this invention has the advantages of overcoming the fluctuation of coating quality caused by measurable and uncontrollable disturbances. However, for the highly nonlinear production process of galvanizing, it is difficult for the linear segment model to accurately and comprehensively reflect the nonlinear characteristics of the system in the galvanizing process, and the prediction accuracy of the model is not high, which restricts the quality of system control At the same time, the feedback controller proposed in this patent directly uses the information of the thickness gauge for feedback control. As mentioned above, in the production process of galvanizing, the installation position of the thickness gauge is subject to the requirements of the process and the actual production line layout It is often installed at a position far behind the actuator (air knife). In addition, affected by the upstream and downstream production capacity, the speed of the galvanizing production line changes at any time, resulting in a large time-varying measurement lag. The above method ignores the influence of time-varying coating thickness measurement and large pure lag factors, which will easily lead to the occurrence of system fluctuations, overshoot and longer transition time; , Sichuan Metallurgy, 2006: 28 (6)), introduced the coating thickness control system provided by VAI company. The feedforward controller of this system mainly compensates for the change of line speed by adjusting the air pressure of the air knife, while the feedback controller takes priority Use air knife pressure adjustment, when it is saturated, use air knife distance to adjust

The calculation of feedforward and feedback control quantities mentioned in this document is based on sensitivity calculation, and the relationship between coating thickness and speed, air knife pressure, and air knife spacing is linearized near the current working point, and there is also a control The accuracy is low, the model cannot be corrected online, and the time-varying and large lag problem of feedback cannot be effectively solved.

Therefore, although the current automatic control system for coating thickness in China adopts a feedforward + feedback architecture, the control effect is not ideal due to factors such as the large lag in measurement and the limitations of the prediction model itself.

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