Research On Quality Evaluation Method Of Steel Strip And Sensitivity Analysis

Steel strip is one of the important products in the steel industry and one of the important raw materials which concerns national economy and people’s livehood, whose surface quality and comprehensive quality directly affect the final product quality and performance. With the increasingly fierce market competition, product quality has increasingly become a core factor for enterprises to improve their market share. Steel strip quality is directly related to economic benefit, survival and development of iron and steel enterprises. However, low evaluation will reduce enterprise’s deserved income, and high evaluation can cause commute even claim risk, will also bring economic loss to enterprise. So the scientific and accurate evaluation of surface quality and comprehensive quality is particular important for enterprises and consumers.Though online surface inspection systems for steel strip have been widely applied, analysis datas of inspection results can’t be used for surface quality evaluation. The traditional surface quality evaluation report is only based on experiences of inspection personnels and surface defects’ description of the related standard, can’t reflect consumer demand and doesn’t comply with definition of quality in ISO9000:2000series standard. By comparing each index value of steel strip and the related index regulation numerical of the national standard or the enterprise standard to judge the steel strip is qualified or not, the traditional comprehensive quality evaluation result is just "qualified product" or "non-confirming product" and can’t realize rank appraisal. In addition, the traditional quality evaluation method gives just the evaluation result and not scientific analysis of evaluation result, so enterprises can’t realize continuous improvement of product quality and targeted process control through the traditional quality evaluation method.Main works and achievements of the thesis are as follows:(1)In order to make surface quality evaluation result not only reflecting the degree of conformity, but also reflecting the degree of satisfying consumer demand, the surface quality will be evaluated from two aspects. On the one hand, evaluated from enterprise’s perspective on the basis of the integration of surface defects’analysis datas such as categories, quantities and severities to achieve surface quality evaluation result which conforms to standard; on the other hand, according to different demands of consumer, evaluated from consumer’s perspective on the basis of surface defects’analysis datas such as distributions and locations to achieve surface quality evaluation result which satisfies consumer.(2)Surface quality evaluation model based on production enterprise is established. The model is divided into two steps:the first step is to determine the severity evaluation value whose basic datas are defect area, defect length, defect perimeter, defect slenderness ratio and defect shape factor of each surface defect, the second step is to divide a great variety of surface defects into several major categories based on the analysis of "The definition and description of product defects" to simplify categories of defects, then by combining with major category defect severity evaluation values which are calculated from severity evaluation values of all single defect and different influence degrees of major category defects, the result is used for evaluating the surface quality. Finally surface quality evaluation based on production enterprise is realized.(3)Surface quality evaluation model based on consumer demand is established. In accordance with whether surface defects have influence on using steel strip or not, surface defects are reclassified from consumer’s perspective. Aiming at different layout features of strip and plate steel, one dimensional layout algorithm for strip and two dimensional layout algorithm for plate steel are proposed respectively. The utilization of defect free steel strip and the utilization of defective steel strip which is based on surface defects’analysis datas such as distributions and locations are obtained, the utilization of defect free steel strip is the evaluation reference value, and the ratio of two utilizations can be used as defective steel strip surface quality evaluation value which satisfies consumer.(4)In order to achieve multi level evaluation of steel strip comprehensive quality, the classification result will be designed to five levels. The concept of the standard boundary of steel strip is proposed based on necessary modifications to the existing national standards. The evaluation matrix is constituted by index values of steel strip which will be evaluated and the standard boundary of steel strip, then normalized index values are aggregated by using AWA operator. Comprehensive quality decision rules are put forward for evaluating the level of steel strip which will be evaluated and distinguishing the difference between the same level steel strips. Finally multi level evaluation is realized.(5)The comprehensive quality of subsequent product will be improved by avoiding quality shortcomings which have not been appeared previously and controlling quality shortcomings which have been appeared. An attribute value sensitivity analysis method by comparing a furnace number (or batch) steel strip and its corresponding standard boundary of steel strip is proposed for obtaining quality shortcomings and steel strip index which makes comprehensive quality level upgrading easily, then scientific guidance for how to improve product comprehensive quality and how to avoid product comprehensive quality degradation is provided.(6)The stability of evaluation result directly influences the credibility of evaluation. The larger the stable intervals of index weights are, the more stable the evaluation result is, otherwise, the more unstable the evaluation result is. In the light of how to solve the stable intervals, by comparing multiple furnace numbers (or batches) steel strip and their respective corresponding standard boundary of steel strip, an attribute weight sensitivity analysis method is proposed for determining the stable intervals of index weights which ensure that each steel strip comprehensive quality will not be changed.