from the conferences organized by TANGER Ltd. provisional website
The paper deals with attributes control charts, especially with the control charts for fraction nonconforming, and their use in retrospective analysis of a process. Several forms of these charts are applied in a case study. The study concerns the occurrence of defects, especially the deformations on hot-rolled wire manufactured on the wire rod mill at Arcelor Mittal Ostrava a.s. Number of wire coils with defects is of interest. P charts are used to identify subgroups with an inflated fraction nonconforming that could distort results of evaluating differences in fraction nonconforming between steel grades, hot-rolling temperatures, and wire diameters. In addition, it is shown how to modify the traditional p chart in the case when a substantial part of the points fall outside control limits due to large subgroup sizes.Keywords: Outliers, p chart, Laney’s chart, hot-rolled wire, deformations
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