Mathematical Models And Quality Control Of Billet Continuous Casting

Based on the cooperative project of Shougang group and Northeastern University,"Key technology and equipment research for automatic high performance billet continuous casting machine", the main control modules are researched and developed for the process control system in billet continuous casting machine. The main works are shown as following:(1) Based on the Shougang billet caster, the hardware and software constitution of computer control system are designed. Three databases, namely, the history database, real-time database, management database, are developed. There are57tables and more than1000data items in it. Human-machine interface are finished. Adequate data have been provided to process control modules in billet continuous casting.(2) The PID control method is studied and used in mould level control system of Shougang billet caster. Experiments show that the model is reliable. The Automatic stopper open system of the arc of billet continuous casting machine is introduced in this paper. Artificial casting process is imitated and the actions are executed during auto casting. These parameters are optimized in process of pilot production.(3) Temperature field software algorithm research and development work are carried out in continuous casting billet. And the accuracy of the model applied in the caster is verified. By consideration of Longitudinal and transverse airspace in the mould, heat transfer is non-homogeneous. So heat exchange model related to airspace is introduced. At the same time The model can be used to calculate the target water quantity for every cooling loop and predict the optimum process parameters in continuous casting. It could as a base of the development of on-line control models (such as on-line water quantity control model, on-line quality prediction model). It shows that the calculation results match well with actual data. It was shown that the model can meet the requirement.(4) Aimed at the shougang billet caster, water quantity control methods are researched for every cooling loop in the secondary cooling zone of billet caster and program are developed. Based on the requirements of different production conditions, experience model method the water dynamic adjustment method and intelligent secondary water quantity control method based case reasoning technology have been given. Examples of calculation show that control effect of the water dynamic adjustment method is better than the experience model method because of less surface temperature fluctuations.(5) Some disadvantages can be overcome using the method based case filling, that is, time varying dynamics and nonlinearity, moreover, the temperature of the billet cannot be measured continuously in the cooling solidification process. And temperature data of the case library come from heat transfer model through offline computing. If a valid reference case does not be retrieved, the experience model is used to calculate the second water quantity on-line and heat transfer model is used to amend it off-line. And then the new cases are recorded in the case database. Water quantity in secondary zone can controlled on-line through using the offline model. The simulation results show that control effect of the case filling method is better than the experience model method which certifies the effectiveness of the case-based reasoning model.(6) Aimed at the inner crack defects in billet, the causes of defects and the effects on continuous-casting billet quality are analyzed. And then the function of billet inner crack quality judging is defined. The dynamic distribution plan about the reference weights is confirmed. Production rules are established according to different requirement on billet quality defects of different steel categories. Some process parameters are collected in billet production and the judging results of inner crack are verified off-line. It was shown that the judging results can meet the calculating results of heat transfer model. Inner crack defects of billet have been forecasted using the expert system in the plant and judging values can meet actual values with good prediction accuracy rate of83.3%.The research mentioned above is valuable in theory and application for the improvement of present billet continuous casters and design of new caster in process control system.