Design And Application Of Laminar Cooling Control System For Hot Strip Mill

Laminar cooling is one of the main production processes of hot strip.It controls the number of valves to reduce temperature to the specified coiling temperature,improving the microstructure and mechanical properties of the strip.The coiling temperature is a key parameter that decides the quality and the shape of the strip.However,the cooling process is affected by the strip's conditions(material,thickness,speed,etc.),heat transfer methods(heat conduction,convection,radiation,etc.)and operating conditions(equipment,water quality,ambient temperature,etc.).Therefore,it is very important to build an accurate and stable laminar cooling process control system to ensure product quality.Under the background of the renewal of the laminar cooling system of the Pan Steel1450 mm hot rolling mill,this dissertation analyzes the reasons of the poor control accuracy of the laminar cooling process.This dissertation improves and designs the heat transfer mechanism models and control function in the laminar cooling control system which applied in practical production.The main works of the dissertation are summarized as follows.(1)The temperature calculation models of temperature gradient in the strip and the heat release from phase changing were proposed.The thickness of the strip was divided into some temperature layers,within which the heat transfer processes was calculated with finite difference.The enthalpy,the latent heat of phase transformation and the corresponding specific heat were calculated based on the fraction of austenite and ferrite,and the incremental temperature due to phase transformation was calculated.(2)A laminar cooling control system was designed consisting of four parts: the setup for calculating the opening number of valves,the feedforward of the valves adjustment,the feedback in the vernier quench zone and the adaption function.The setup was used to decide the status of valves and predict the coiling temperature with the finite difference.The setup calculation would be recalculated to get the more accurate predicting coiling temperature when the coiling temperature was measured.Then the deviation between the recalculated value and the measured coiling temperature was considered as reference value of controllable sample section to calculate the feedback compensation.Separate regression calculations are done for the first half and second half of the coil temperature to modify the adaption parameters and adjust the cooling water.(3)Based on the proposed control method of the laminar cooling,the model software was developed and applied to the field debugging in double production and practical production in the Pan Steel 1450 mm hot rolling mill.Contrasting with the old control system,the control problem of coiling temperature for thicker strips and low coiling temperature strips was solved effectively.The hit rate increased to 94% where the coiling temperature errors are controlled in the range of ±15?.