The steel strips produced in steel-making plants, are used as raw material in many other industries, so quality control is an essential aspect. One factor that indicates the quality of a steel strip is the number of defects, such as holes or scratches, on its surface. This paper describes a technique to detect an especially harmful type of surface defect called periodical defect. These defects are a periodic pattern on the surface of the strip. Using a backtracking algorithm all the individual defects contained in the strip are examined to determine which defects compose a set which constitutes a periodical defect. An implementation of this clustering technique was tested using a set of real steel strips, whose characteristics were previously stored in a database. A test environment to quantify the goodness of the results and to determine the best values to parameterize the clustering algorithm has also been developed. During the rolling of steel strips, periodically repeated defects can occur. Such defects are particularly detrimental to the quality of a steel strip, because they do not consist of a single mark on the surface of the strip, but of many marks along the length of the strip, creating a periodic pattern. These defects are characterized as being a series of marks in the same transversal coordinate, being equally spaced at a constant distance in the longitudinal coordinate, and having the same shape. A set of these defects is called a periodical defect. It is important to detect the existence of these defects as soon as possible to prevent their occurrence in the next steel strips to be rolled. If these defects are not detected, the steel strips may be unsuitable for marketing. Having effective software to perform this task will not only improve steel strip quality, but will also avoid the financial loss caused by having to discard defective steel strips.
['Francisco Bulnes', 'Daniel F. García', 'Julio Molleda']
A Technique for Clustering Individual Defects from Images of Steel Strips with Periodical Defects