Study Of Analysis Model Of The Internal Quality Defect For The Continuous Casting Billet Based On Standard Analysis

Billet is one important product in the metallurgical process, and high quality billet is the common goal of all the metallurgical enterprises. The quality defect would appear in the product, due to the improper implementation of production process parameters. Since the difference of field situations, there is no uniform standard in the implementation of production process parameters. And quality defect is usually caused by the processing parameters which are inconsistent with the field situation. The process standard, best adapting to the actual site of production, is needed to direct the production to reduce the probability of quality defect. And the product quality analysis should be based on the process standard analysis. Aiming at the problems above, the internal quality analysis model based on the standard analysis is proposed. The continuous casting process parameters were analyzed and adjusted by the standard analysis model, and the internal quality defect of billet was analyzed based on the standard analysis.The main works are as follows:(1) The causes of internal quality defect of the billet have been analyzed, and the internal quality analysis model of the billet has been established. From the two sides of composition of molten steel and continuous casting process, the fault tree of internal cracks during the stage from steelmaking to continuous casting was established. The fault tree was based on the theory of critical strain. The fault tree during the stage from steelmaking to continuous casting was analyzed by the software of FTA. The 26 minimal cut sets of the internal cracks have been found by the qualitative analysis model.(2) The continuous casting process parameters have been analyzed and adjusted by the standard analysis model in the theory of statistical process control. Almost 30000 samples of the continuous casting process parameters during July 2006 in a metallurgical factory have been analyzed by the standard analysis model. The standard limits of seven continuous casting process parameters have been established by the Xbar-R chart in statistical process control. The execution curve of each continuous casting process parameter was drawn and the failure data of each parameter was recorded in order to calculate the failure rate of the continuous casting process parameters. Based on the standard limits, the continuous casting process parameters on the furnace number of 267 in July have been adjusted by the standard. After six adjustments most of the continuous casting process parameters have been adjusted below the standard limits.(3) The weight relations among the continuous casting process parameters have been analyzed. The internal quality defects of the products in the factory were analyzed based on the standard analysis. The weight relations among the continuous casting process parameters were analyzed by three kinds of objective weighting methods. According to the results of quantitative analysis, the multiple correlation coefficient weight method was set to be the default weight analysis method of the continuous casting process parameters. After the quantitative analysis of the billet internal quality analysis model, the probability of internal cracks was 22.57%. The result was based on the weights of parameters and the failure rate of the parameters. The actual macroscopic result on site was 20.62%. The deviation between the results was 1.95%. It indicated that the internal quality analysis model was correct. The result of the quantitative analysis without continuous casting process standard analysis was 23.45%. The comparison shows that the internal quality defect analysis model based on continuous casting process standard analysis model was more accurate then the one before.