Statistical Process Control Application in a Rubber Products Factory in Edo State

This research applies Statistical Process Control methods to monitor and improve the production process consistency of a rubber products manufacturing factory in Edo State, South South Nigeria. Rubber product manufacturing involves multiple interdependent process variables including compound mixing ratios, vulcanisation temperature, and moulding pressure, all of which must be maintained within specified limits to ensure consistent product properties. This study selects three critical quality characteristics: tensile strength, hardness (Shore A), and dimensional tolerance, for analysis using X-bar and S control charts constructed from data collected across twenty subgroups of five samples each during a six-week monitoring period. Process capability indices Cp and Cpk are calculated for each characteristic to assess the process's ability to meet specification limits. Results reveal that the tensile strength process is capable but approaching the lower specification limit, suggesting a marginal risk of out-of-specification production. The hardness characteristic shows evidence of assignable cause variation in the form of a systematic upward trend, traced through investigation to gradual thermocouple drift in Vulcaniser Unit 2. Recommendations include recalibrating thermocouple instruments on a bi-monthly schedule, establishing formal operator process capability review meetings, and extending SPC monitoring to a fourth critical characteristic. Keywords: Statistical Process Control, control charts, rubber manufacturing, Edo State, process capability