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The aim of this article is to point out the characteristics of Shewhart and CUSUM charts when applied to electrostatic separation processes and validate their ability to detect special events that may be indicators of out-of-control situations. This article also shows how the effectiveness of statistical process control (SPC) can be improved by using the cumulative sum (CUSUM) chart. Experiments were carried out with a mixture of bronze and aluminum particles (size range: 1-2 mm) by using a plate-type electrostatic separator. The mobile-average Shewhart and CUSUM charts were established based on 20 electrostatic separation tests performed under optimal operating conditions. An out-of-control situation was simulated, and the response of the process was analyzed with both types of charts. The small-shift process response was detected only on the CUSUM chart. See “Nomenclature” for the nomenclature used in this article.
Date of Publication: July-Aug. 2010