Performance analysis of the temporary stockpile reclaimer system in the mining industry using the Overall Throughput Effectiveness (OTE) method

. The increasing target of coal mining production every year needs to be supported by a reliable performance of the temporary stockpile reclaimer system, in order to ensure a smooth transfer of coal from the temporary stockpile to the main stockpile and achieve the production target. Based on the Overall Equipment Effectiveness calculation, it has been found that the performance of the reclaimer and conveyor system is still below the standard, at 31.04% and 40.26% respectively. Damage to one of the tools in the reclaimer system can cause production to stop and result in wastage and losses. By using the FMEA method and the Six Big Losses, two major potential losses have been identified as the causes of the decline in the reclaimer system performance, namely idling and minor stoppage losses, and equipment failure losses. Efforts to improve the system's performance include making changes in the height and width of the temporary stockpile to minimize obstacles such as coal material overflow, and regular maintenance should be conducted to ensure optimal system performance.


Introduction
The achievement of coal production targets can be realized when the smooth operation of coal production is supported by equipment that can work effectively.In the production process, the reclaimer plays a role in transferring coal from the temporary stockpile to the main stockpile, so the reclaimer needs to work optimally during the designated period without experiencing disruptions, and its productivity should be maintained.However, in this case, a machine or equipment that experiences downtime, speed losses, or produces defective products indicates that the machine is not working effectively [1].
The readiness of equipment is crucial for production activities.With good equipment performance, the resulting products will meet the quality standards and set targets.However, there is often negligence in equipment maintenance, where corrective action is only taken when damage occurs.This disruption in the production process leads to wastage and losses.The reclaimer system utilizes the continuous mining method, which means that if there is a problem with one of the equipment, the entire production process will be disrupted and result in the failure to achieve production targets.
In order to understand the impact of the effective performance of the reclaimer system on the smooth operational production of coal in the mining unit, a study was conducted to identify the causes of high downtime by measuring the performance of the reclaimer equipment using the Overall Throughput Effectiveness (OTE) analysis method.The measurement of OTE value for this equipment is crucial to determine whether its performance aligns with the defined standard [2].If not, efforts should be made to improve the performance of the production machine so that it can operate optimally.With the support of the Six Big Losses method, the root causes of issues that affect equipment performance can be identified, and by utilizing the Failure Mode and Effect Analysis (FMEA) method, continuous improvement efforts can be implemented [3].

Methods
This research is based on observations of individual [3,4]activities or other investigated objects, and the data source used in the research was obtained directly through observations and recordings conducted on-site.The data used in this research is based on primary data obtained directly through observations, operational reports, and direct interviews with key informants at the site related to the reclaimer system.Data collection involves field research and direct observation of the research object.The data is then processed following the following steps: measuring the value of Overall Equipment Effectiveness (OEE) [5], Overall Throughput Effectiveness (OTE), calculating the value of losses, creating a fishbone diagram, and conducting Failure Mode Effect Analysis (FMEA), followed by the analysis and conclusion phase.

Measurement of Overall Equipment Effectiveness (OEE)
The process of transferring coal from the temporary stockpile to the main stockpile utilizes a reclaimer equipment consisting of a Bucket Wheel Excavator (BWE), Belt Wagon (BW), Cable Rail Car (CRC), and Conveyor (CS).These components need to be constantly operational simultaneously, as any damage to one of the equipment can result in a halt to the production process [6].Based on the data in Figure 2, the average OEE value of the reclaimer is 31.04%.This value is far below the standard OEE value based which is a reference OEE value for heavy equipment such as excavators working in mines, set at 77% [7].The low OEE value is attributed to the low availability rate of the reclaimer equipment, mainly due to a significant amount of time wasted due to idling time or waiting time when the stockpile location is not ready for the transfer of coal from the temporary stockpile to the main stockpile.
In Figure 3, the OEE value of the conveyor system shows an average availability rate of 40.26%.This value is below the world-class standard OEE of 85% according to the Japan Institute of Plant Maintenance (JIPM) [8].This value can still be further improved through improvement efforts to achieve the world-class standard OEE value.

Measurement of Overall Throughput Effectiveness (OTE)
This measurement aims to determine the overall performance and effectiveness of the system within a single line (sub-system).The data used in this calculation are the average OEE values of the reclaimer and conveyor system over six periods.To calculate the Overall Throughput Effectiveness, the formula is used, as shown in the following equation: Based on Figure 4, the average OTE value is 12.98%, which is below the standard percentage of effective OTE, set at 65.45%.This value is obtained by calculating the OTE using the formula for the series subsystem, with the standard OEE value for Excavators according to the Japan Institute of Plant Maintenance (JIPM).The low OTE value is attributed to the significant amount of time spent on obstacles and standby time caused by waiting to resume operations after encountering overflow material obstacles.

Measurement of Losses Value
The calculation is useful for identifying losses such as equipment breakdown losses, setup and adjustment losses, and breakdown losses in Table 1 and Table 2.
The main factor identified for Idling and Minor Stoppages losses is the presence of obstacles due to the unavailability of the location for coal material discharge, resulting in a significant waste of potential coal transfer time.Temporary stoppages occur due to minor disruptions, one of which is the overflow of excavation material during the transfer between conveyor chutes.This requires approximately 5-10 minutes for the equipment to resume normal operation.On the other hand, Equipment Failure Losses occur due to delayed maintenance schedules, leading to equipment or component damage in the reclaimer, rendering it unable to operate and perform production activities.

Cause and Effect Diagram Analysis
The root cause factors analyzed using the fishbone diagram consist of human, machine, method, material, and work environment.Figure 5 represents the cause and effect diagram of the factors contributing to the low OEE value.Consequently, the consequences of failures occurring in the reclaimer equipment are described in the calculation of the Risk Priority Number (RPN) in Table 3 and Table 4.The highest RPN values indicate the severity of the issues that need to be prioritized in order to find solutions for further improvement [9].Apart from natural factors, the highest RPN value is attributed to the overflow of excavation material, with an RPN value of 360.This is caused by the height of the stockpile exceeding the operational standard.This obstacle can be minimized by maintaining the stockpile height according to the existing standard, which is 12 meters.In actuality, the stockpile height exceeds the boundary marker, as evidenced by the piles exceeding the height of the boundary markers at the stockpile location.To reduce the potential obstacle of material overflow, operators can be trained to enhance their skills in operating the equipment when faced with coal material overflow, ensuring that the coal transfer production remains in line with the work plan.The component instability with an RPN value of 320 is due to the machine operating almost non-stop for 24 hours and the equipment components being located in an open area.Therefore, regular maintenance and checks are necessary to ensure the stability of the equipment.By following the Standard Operating Procedures, such as cleaning the machine at the beginning of each shift, conducting a 15-minute equipment check at the start of the shift, and ensuring proper functionality of the machine when initially operated, operators or workers involved will have a sense of ownership and increase their knowledge of the equipment they are using.This will enable the equipment or components to operate optimally.The jammed roll conveyor with an RPN value of 315 is caused by a build-up of dirt on the conveyor's bearing and a large pile of coal material beneath the roll conveyor due to material overflow.Therefore, it is necessary to maintain consistency in cleaning the conveyor line and conducting regular checks on the roll conveyor to prevent damage to other components such as torn or thin conveyor belts.The component age with an RPN value of 320 is due to the condition of the components being old and located in an open area.Therefore, regular scheduling of component replacements is necessary to prevent more severe damage that could cause production to halt.
The constraint of specific coal demand with an RPN value 162 is due to the limited demand for such specific coal specifications.In the six periods, this resulted in the unavailability of a designated location for storing the coal material from the reclaimer.Therefore, effective coordination within the team is necessary to ensure the readiness of the location.Operator reliability with an RPN value of 126 is influenced by the expectation that operators consistently pay attention to the excavation indicators of the reclaimer, thereby avoiding motor protection issues caused by excessive material load on the conveyor.Insufficient knowledge of the equipment they operate can result in damage, decreased productivity, and financial losses for the company.Therefore, it is necessary to provide operator refreshment training to ensure operator reliability and their attentiveness in handling coal excavation overflow obstacles in accordance with the applicable procedures.Inclined belt conveyor with an RPN value of 112 is caused by roll conveyors not functioning properly, such as jamming or accumulation of dirt beneath the belt conveyor.Therefore, regular inspection and thorough cleaning along the conveyor line are necessary to address this issue.Insufficient equipment inspection method with an RPN value of 105.Component inspection is crucial to maintain the performance and productivity of the reclaimer equipment for achieving coal transfer production.Consistency in recording inspection data is necessary to track the historical condition of the equipment during the operating period, as it serves as a reference for conducting improvement analysis.Damage to equipment components with an RPN value of 60 is due to the delay in implementing maintenance and insufficient supervision and care for the reclaimer equipment components.There is a need for supervision and reporting to reduce the potential for more severe component damage that could lead to production disruptions.The attached maintenance schedule shows that maintenance is primarily focused on replacing already damaged components or conducting major repairs.However, minor repairs such as stuck rolls and unstable equipment component/electric motor conditions have not been adequately addressed.Strengthening the Planned Maintenance pillar needs to be emphasized because with effective planned maintenance, we can reduce sudden equipment failures and better control the level of component damage [4].Therefore, to improve the quality of equipment or component repairs during planned maintenance by the maintenance unit, the mining unit should support better maintenance practices by implementing scheduled cleaning routines.

Conclusion
From the OTE calculation results, with an average value of 12.9%, it is caused by the low availability value of the reclaimer and conveyor system from the OEE calculation, with an average of 39.43%.Using the Six Big Losses method, two major losses were identified as the causes of the low performance of the reclaimer system, namely idling and minor stoppage losses, as well as minor stoppage losses with values of 40.49% and 16.12%.To improve the availability value of the reclaimer system, it is necessary to adjust the height and width of the temporary stockpile according to the maximum height of the reclaimer system, which is 12 meters, with a width of 90 meters.The size of the coal material should be 20 x 20 cm to minimize the obstruction of coal overflow.The company needs to adhere to the scheduled maintenance time for planned maintenance in order to achieve optimal equipment performance.Regular component inspections should also be conducted to ensure that the equipment can detect and prevent errors during production.
Based on the conducted research, a suggestion that can be given to the company is to provide operators with an understanding of the importance of reporting damages and performing regular equipment cleaning.The company should enhance the operators' sense of responsibility in maintaining and caring for the equipment they use on a daily basis by emphasizing the importance of collaboration between the operator team and the maintenance department.This will lead to improved reliability of the reclaimer equipment and the achievement of production targets.

Table 1 .
Value of Six Big Losses (Setup and Adjusment Losses, Reduced Speed Losses, Idling and Minor Stopages Losses) for the Reclaimer System

Table 2 .
Value of Six Big Losses (Defect Losses,Reduced Yield Losses, Equpment Failure Losses) for the Reclaimer System

Table 3 .
FMEA for Equipment Failure Losses

Table 4 .
FMEA for Idling and Minor Stopages Losses