Underground » Maintenance
This report addresses the problems of low utilization of the face equipment in Australia longwall mines by analyzing the failure data collected in Moranbah North longwall face equipment. The primary source for determining the production delays has been the ASI databases provided by Moranbah North. The historical data covers the period from 2-May-2000 until 11-February-2002.
The following is a summary list of the conclusions and recommendations based on the findings presented in the first five chapters of this report; data from other sites analysed by the project team in parallel; and discussions with the OEMs and industry engineers.
Low Utilisation: The typical utilisation of a longwall face is less than 50% across the industry. Half of this can be attributed to delays associated with face equipment failures. This needs to be improved if longwall is to have a long-term future in the Australian mining industry. Significant improvements can be obtained through design/engineering changes, reliability-centred maintenance (RCM), operator aids, on-line fault detection and condition monitoring, and increasing automation.
Maturity of Technology:AbstractText
Accuracy of Data: Longwall technology does not have the same maturity as equipment in other parts of the mining industry, eg surface mining or preparation plants. This is the primary cause of the low utilisation rates mentioned above. The mining industry and the OEMs need to address this together with the third-party research and consulting service providers through reliability-centred equipment design, better tools to select equipment that provides the best fit to the site conditions and the production requirements; and continuous improvements in site production and maintenance practices.
The detail accuracy of the downtime data captured from deputies' reports is questionable. This is unfortunate because accurate detail data is essential to identify the critical deficiencies in equipment design and operating practices. Better downtime recording tools need to be implemented. This can be done in a cost-effective manner.
The role for the OEMs:The mining industry should explore frameworks in which to actively involve the OEMs in addressing the reliability shortcomings identified through an ongoing process of detailed data collection and accompanying root cause failure analysis.
Accountability: It is strongly recommended to stop the practice of assigning the responsibility for each downtime event to different engineering sections. Appropriate data recording and reporting structures should be put in place to make the minimisation of downtime the equal responsibility of all site production and maintenance staff. In the current practice, the responsibility of every downtime delay is assigned to either Production (Mining), or Mechanical or Electrical Engineering sections. This has the potential to cause unnecessary and inconsequential disputes while obstructing the effort to identify the real root cause of the problem and to create options for its correction.
Scheduled Maintenance: The present implementation of the scheduled maintenance function needs to be reviewed. This is best done on a site by site basis using rigorous methodologies such as Reliability-Centred Maintenance(RCM). We believe that regular weekly planned maintenance shifts and the way they are organised today are not helping reduce the frequencies of the top ten failure categories. This observation is based on analysis of failure data which indicates that most failures occur randomly following an exponential failure probability distribution. Periodic replacement strategies are of limited use against such failure patterns.
Equipment Availability: This is related to the preceding two recommendations. The equipment availability targets should be based on the total calendar time. For example, for a 7/24 operation, this would be 24 x 365 hours for the year. High equipment utilisation is a target across the year not only during the planned production shifts.
On-line Condition Monitoring: Technologies should be developed to continuously monitor the conditions of critical components such as the shearer, the down drives, the AFC system, and the roof supports against developing faults. In many instances, such faults are detectable by monitoring the process data collected through a Citect or a similar system. The development of some failure modes, however, can only be detected from data collected at high sample rates. Both approaches should be rigorously pursued.
Operator Feedback:Technologies should be developed to provide the operating crew with feedback on both immediate and long-term consequences of their operating practice in terms of machine availability and productivity. The experience of the project team on other types of mining machinery, eg draglines, shovels, and hydraulic excavators, indicates that the operators are capable of taking corrective action and self-training when they are made aware of practices that have undesirable productivity and reliability consequences.
Automation: As acknowledged in the preceding recommendation, the operator behaviour has a significant impact on the condition of the machine. Face automation, when fully implemented and after the initial teething problems are overcome, is expected to drive the machine according to the best operating practice, with a subsequent increase in equipment availability. In the meantime, partial automation using VS drives for the AFC and the shearer systems along with an adaptive speed control mechanism may help to realise the optimum combination of cutting, haulage and AFC speeds under different conditions. Investigation of these options was outside the scope of this project and more research is needed in this area.