Research On New Dynamic Secondary Cooling Control And Dynamic Soft Reduction Model Of High Quality Slab

At present,with the vigorous development of my country’s automobile industry,shipbuilding industry,aerospace industry and other manufacturing industries,rapid progress in high-speed rail,bridge construction,etc.,economic development requires higher and higher steel performance.However,the quality problems of continuous casting slabs such as surface cracks,center segregation and center porosity have severely restricted the production of high quality slab continuous casting.Among them,dynamic secondary cooling and soft reduction technology are particularly critical to improve the quality of slabs.But the existing slab continuous casting dynamic secondary cooling and dynamic soft reduction model still have the problems of insufficient control accuracy and insufficient stability,which ultimately leads to insufficient metallurgical effects.In addition,the working status of the secondary cooling nozzle for high quality slab continuous casting has an important impact on the final slab quality.However,most of the current continuous casters still rely on manual inspections,which have many shortcomings such as untimely and insufficiently inspections.Therefore,the research and development of new dynamic secondary cooling control and new dynamic soft reduction model of high quality slab continuous casting,and the development of a real-time diagnostic model for the working status of the secondary cooling nozzle are of great significance for improving the quality of slabs.This paper focuses on a domestic slab continuous caster A that produces high-strength ship plate steel,pressure vessel steel,corrosion-resistant steel and high value-added products as the research object,researches and develops an on-line 3D temperature field simulation model for slab continuous casting,and proposes a new dynamic secondary cooling water control method for slab continuous casting based on the on-line3D temperature field.A real-time diagnosis model for the working status of the secondary cooling nozzle for slab continuous casting is presented.At the same time,based on the three-dimensional solidification morphology characteristics of the casting slab,the new dynamic soft reduction model selects the region that solidifies last in the casting speed direction and has the largest liquid core volume in the transverse direction as the best reduction position for soft reduction,and a method to improve the accuracy and stability of the on-line roll gap control of the slab continuous casting segment is proposed.Finally,these new technologies and new methods obtained and researched were developed and applied to engineering transformation.Through the comparison of the maximum deviation of the target thickness of cold slabs,the deviation of the average thickness of cold slabs,the surface quality of the slabs,the center segregation level of the slabs,and the detection qualification rate after rolling before and after the model application,the industrial application effects of the research and development results are investigated and verified.The main research content and main results of this paper are as follows:(1)Researched and developed an online 3D temperature field simulation model for slab continuous casting.On the basis of the 2D solidification heat transfer model,the"finite thickness slice unit"method is adopted to dynamically and real-time track the temperature information of all slice units on the continuous caster to realize the effect of on-line simulation of the 3D temperature field.The difference between the longitudinal and transverse heat transfer boundary conditions of the casting slab is researched and analyzed,and proposes a method of on-line recognition of the actual water flow density by using the slicing element nodes.By adopting the dual-process architecture method,it eliminates the stuttering phenomenon that occurs during the operation of the monitoring model based on the on-line 3D temperature field simulation calculation due to the order of magnitude increase in the number of computing nodes,and meets the requirements of on-line control of the monitoring and control model.The accuracy and reliability of the on-line 3D temperature field simulation model of slab continuous casting were verified by industry through manual temperature measurement,on-line continuous temperature measurement and nail shooting test.(2)Researched and proposed a new dynamic secondary cooling water control method based on online three-dimensional temperature field for slab continuous casting.A precise secondary cooling water amount control algorithm based on feedforward and feedback control with the heat transfer coefficient as a bridge is proposed.Simulations have verified the adaptability and accuracy of the control method under different process parameters(superheat,casting speed,steel grade),casting speed fluctuations,superheat fluctuations,and on-line nozzle replacement conditions.Developed a new dynamic secondary cooling water amount control model based on an on-line 3D temperature field.This model has been replaced the original traditional dynamic secondary cooling control model on the slab caster B of a domestic steel plant,which based on 2D temperature field and the horizontal cooling difference of the cast slab cannot be considered.Before and after the replacement,the surface and internal quality of the casting slab have improved significantly.(3)Researched and developed a real-time diagnostic model for the working status of the secondary cooling nozzle for slab continuous casting.The diagnosis of the working condition of the secondary cooling nozzle is transformed into the diagnosis of the working condition of the secondary cooling circuit,and on this basis,the working condition diagnosis algorithm of the secondary cooling circuit is researched and proposed.The research puts forward methods to obtain the theoretical flow of the secondary cooling circuit through the nozzle combination method and the BP neural network algorithm in the early and middle stages of model investment respectively.The software design and development of the real-time diagnosis model for the working status of the secondary cooling nozzle is carried out using the Client/Server software architecture,and the industrial application is carried out on a domestic slab caster A.The statistical comparison results show that the accuracy of the model diagnosis has reached 90.2%.(4)The method to improve the accuracy and stability of the online roll gap control of the slab continuous casting sector is studied.A slab continuous casting segment on-line deformation compensation method under the condition of no pressure feedback is proposed.Through on-line calculation of the reaction force of the continuous casting slabs to the segment,the deformation of the segment is obtained,compensating the measurement results of the displacement sensor,and the actual roll gap values are obtained,so as to achieve the purpose of improving the control accuracy of the roll gap of the segment.The force of the segment under different tilt angles is analyzed and researched,and the relationship between the different tilt angles of the segment and the deviation of the inlet and outlet rolLli′g=aps Lii2s+obf t2ai+neδd LLa23s follows:(?)(?)Therefore,the compensation and correction in the control program are carried out,and a method to improve the stability of the reduction metallurgical effect under soft reduction is obtained.A slab target thickness stability control method is proposed to ensure that the target control thickness of the slab is always consistent no matter what working conditions,which based on the total roll gap shrinkage of each steel grade consisting of the basic roll gap shrinkage and the soft reduction shrinkage,and the total roll gap shrinkage is all equal.Finally,it ensures the stability of roll gap control,slab thickness and soft reduction metallurgical effect.(5)Through the design of the four-layer structure software architecture,the researched new dynamic secondary cooling control and new dynamic soft reduction model based on the on-line 3D temperature field have been developed.It is applied to the slab caster A modification project,which is mainly used to produce high-value-added products.The maximum deviation of the cold slab target thickness and the average cold slab thickness deviation have been reduced from 5.5mm to 2.0mm,and from 1.4mm to0.5mm,respectively,which counted starting half a year before and after the application.The precision and stability of roll gap control in the segment have been significantly improved.After the application of the new dynamic secondary cooling control model,compared with the traditional dynamic secondary cooling control model based on the two-dimensional temperature field before the application,the incidence of transverse cracks,longitudinal cracks,and corner cracks on the surface of the cast slab is reduced by 54.02%,56.87%,and 29.38%,respectively,which counted starting half a year before and after the application.The stability of slab surface quality control has been significantly improved.After the application of the new dynamic soft reduction model,compared with the traditional dynamic soft reduction model based on the two-dimensional temperature field before the application,the proportions of slab center segregation grades C0.5 and C1.0 increased by 123.45%and 35.37%,respectively;the proportions of slab center segregation grades C1.5 and C2.0 and above,the ratio decreased by 51.83%and 47.33%respectively,which counted starting half a year before and after the application.So the effect of improving the center segregation of the slab was significant.After the application of the new dynamic soft reduction model,the detection pass rate of all casting slabs feedback from the rolling has increased from 98.1%to 99.5%,which counted starting half a year before and after the application;among this,the detection pass rate of high-strength ship plate steel with strict requirements for center segregation has increased from 73.23%before application to 96.51%,with an increase of23.28%;the detection pass rate of casting slabs has increased significantly,and the fluctuation range has been significantly reduced.