Development of an optimal interval maintenance plan

Abstract

Extraction, haulage and material and processing of ore to get the end products largely depend on the availability, reliability and effective utilization of equipment. Equipment at Namekara mining company takes 45% of the total production costs, so it is important to keep it in normal working conditions and the availability of equipment high. In this study, failure data for the excavator, wheel loader, scrapper, conveyor belt system and haulage trucks were collected and found haulage trucks with the highest failure rate. Haulage equipment was decomposed into individual subsystems and the transmission, hydraulic dumping and the body subsystems were found to be having the highest failure frequencies. Therefore, the reliability study that has been conducted in this research has based mostly on these subsystems of truck N6. Failure and mining data for the three haulage equipment used at the mine was collected from maintenance and mining records and has been analyzed. The data was collected over a seventeen-month period of the mine’s operation. Trend and serial correlation tests to validate the assumption of IID (Independent and Identically Distribution) has been conducted. According to the results, the data collected has been found to be independent and identical meaning the occurrence of the current failures does not depend on the previous failures. Therefore, data can be used to model the sub system’s reliability. FMEA for the three critical subsystems was also carried out followed by fault tree diagrams to analyze the equipment from subsystem level to components level in order to ascertain the root causes of failures and come up with improvements have been made. This was done to improve system performance and also gain a thorough understanding of the infant and direct causes of failures to subsystems and components. FMEA indicated that cylinder seal failure, valve failure, hydraulic pump failure, electrical components failure, clutch failure and failure for the transmission to engage are the most critical failure modes according to their RPN values. The time between failure (TBF) for the three subsystems was analyzed and tested for distribution estimation and the Weibull distribution had a higher correlation coefficient. The reliability study for the subsystems was therefore done using the Weibull distribution. Reliability plots have been obtained for the three subsystems, preventive reliability maintenance intervals for the three subsystems have been obtained. Maintaining reliability and availability of equipment to meet the production requirement is vital for maintenance and production departments of the mine. To achieve these levels, equipment should be maintained at appropriate times to reduce machine/equipment downtimes as well as reducing maintenance costs. KEYWORDS: Reliability centered maintenance (RCM), corrective maintenance (CM), mean time between failures (MTBF), haulage truck, downtime, maintainability.