Roll surface monitoring in the hot strip mill

One of the main concerns of today's hot strip mills is to ensure the strip surface quality requirements due to the still rising customer demands. In spite of the progress made in process technology, the occurrence of surface defects on the final product can still not be completely precluded. The cause of these surface defects can be found at different levels of the production process but one of the most important origins of the surface defects is related to the work roll surface degradation. The aim of this Pilot and Demonstration project was to develop an on-line inspection system for the observation of the complete work roll width. The system is based on the prototype CCD camera inspection system that has been developed within the frame of the ECSC research program 72010-GB/206 (92 - E1.03). To assist the mill operators in controlling the surface state of the work rolls during rolling and to decide intermediate roll changes, an integrated image analysing system has been added. In this way strip surface defects caused by work roll surface degradation can be anticipated. The work program consisted of three major parts: - the development of an inspection system for automatic full width work roll observation, based on the prototype CCD camera inspection system (combined CCD inspection system and translation system), - the development of an on-line analysing system to interpret the images, recognise the work roll surface defects and the gravity of it and the presentation of this information for the mill operators, and - the set-up of a computer tracking system which integrates all information related to the work roll degradation (e.g. rolling parameters, friction evolution, parametric analysis of the images, calculated work roll temperature evolution,...). The main parts of the new developed inspection system are: - an improved inspection head with an integrated cooling circuit - a translation/rotation system to observe the complete work roll width and to assure the perpendicular position of the inspection head - two intermediate cabinets containing controllers for basic functions - a data processing cabinet with two industrial PC's The full-width work roll surface inspection system has successfully been developed and installed in stand F2 at the hot strip mill of Sidmar. The results of full-width inspection show clearly the necessity to observe the work roll at several places as the deterioration of the surface can be different over the work roll width. The aptitude and the functionality of the system have been proven. The only shortcoming of the system has been the occurrence of blurred images during a few periods. It is expected that by an intensive use of the system the origin will be detected and a permanent solution can be found. An image-processing algorithm has been developed defining discriminating parameters in clear relation to the work roll surface degradation. The algorithm is implemented in both offline and online software allowing a laboratory tuning and an everyday use in the mill. The complete system has been implemented in the Hot Strip Mill with a LAN access. Hereby all information can be remotely accessed for statistical analysis. A specific operator interface has been created to enable on-line observation and off-line evaluation off the work roll surface. By this, objective intermediate roll changes can be performed to anticipate product surface defects.