SEMI-MARKOV COMPARISON OF CORRECTIVE AND PREVENTIVE MAINTENANCE IN CEMENT GRINDING: A SIMULATION-BASED RELIABILITY AND PROFIT STUDY

Cement grinding relies on interacting electrical and mechanical equipment, for which an apparently minor fault can reduce throughput or progress to a complete interruption. This study compares two maintenance policies within a common seven-state stochastic reliability model. Model I permits a developing or neglected fault to progress to serious failure, Model II replaces that route with successful preventive intervention. The models retain identical category-specific fault occurrence intensities and use semi-Markov transition distributions, regenerative first-passage equations, and renewal-reward measures. Numerical inputs originate from a observed 24-month cement-grinding dataset containing 214 fault events over 16,259.13 operating hours, unobserved escalation and restoration behaviour is specified as hypothetical. Under the exponential particular case, operating-time mean time to system failure increases from 164.10 h (corrective policy) to 207.17 h (preventive policy), a 26.24% increase. Long-run binary availability increases from 97.88% to 98.32%, while modelled profit rises from approximately ₹89,647 to ₹90,430 per hour under the stated throughput and cost assumptions. Reliability functions and a break-even policy-cost calculation provide additional insight into this trade-off. These are conditional simulation-based findings, not measured improvements at an industrial installation. The results illustrate a transparent framework for evaluating when early intervention in developing faults justifies its maintenance burden.