Deposits in the form of seams are most often exploited by means of mechanised longwall systems. Hard coal seams of various thicknesses are mined by plowing and shearer complexes. Both solutions are commonly used in Polish and global mining. Mechanised longwall systems consist of many machines, the most important of which are the mining machine, powered support, armoured face conveyor and beam stage loader. The article is concerned with the failure frequency of longwalls equipped with plow and shearer longwall systems in one of the Polish hard coal mines. The analysis covers a period of 13 months of the mine’s operation, during which 2,589 failures were recorded. It was carried out for all longwalls exploited in that period, i.e. five plow and five shearer ones, operating in six different sections. In the analysed period, these longwalls worked for an average of 150 days, and a total of 1,484 days. The analysis takes into account the basic division of failures used in the mining branch, i.e. mining, electrical and mechanical failures. The plow and shearer complexes were analysed separately, taking into account the failure category for all devices. A comprehensive analysis of the failure rates has revealed that the failure rate of longwalls equipped with plow complexes is noticeably higher than that of shearer ones. Moreover, it has been demonstrated that mining failures are prevalent in the analysis of both the number of failures and the average duration of failures.

To increase their competitive advantage in turbulent marketplaces, contemporary manufacturers must show determination in seeking ways to: fulfill buyer orders with quality merchandise; meet deadlines; handle unexpected production disruptions; and lower the total relevant expense. To tackle the abovementioned challenges, this study explores an economic manufacturing quantity (EMQ) model with machine failure, overtime, and rework/disposal of nonconforming items; the goal is to find the best fabrication uptime that minimizes total relevant expenses. Specifically, we consider a production unit with overtime capacity as an operational feature that is linked to higher unit and setup costs. Further, its EMQ-based process is subject to random nonconforming items and failure rates. Extra screening separates the reworkable nonconforming items from scrap, and the rework is executed at the end of each cycle of regular fabrication. The failures follow a Poisson distribution, and a machine repair task starts as soon as a failure occurs; the fabrication of the lot that was interrupted resumes after the repair has been carried out. A decision model is built to capture the characteristics of the problem. Mathematical and optimization processes help in determining the optimal fabrication uptime. A numerical example not only illustrates the applicability of the research outcomes, but also reveals a diverse set of information about the individual or joint influences of deviations in mean-time-to-failure, overtime factors, and rework/disposal ratios linked to nonconforming rates related to the optimal replenishment uptime, total operating expenses, and various cost contributors; this facilitates better decision making.