Like all industries, the mining industry is under increasing pressure to do more with less. Faced with falling profits, J.R. Simplot Co.’s Smoky Canyon Phosphate Mine near Jackson Hole, Wyo., set out to reduce maintenance costs. Like most open pit mines, the mobile equipment was identified as one of the mine’s largest cost centers.
The mine’s reliability team reviewed previous maintenance records and costs and noted that the mine’s mobile equipment consumed 70 percent of the total maintenance budget, with haul trucks making up the largest percentage of these costs. Based on this assessment, the reliability team knew that improvements to haul truck maintenance could result in substantial savings for the company.
In the late 1990s, the mine implemented a condition-based maintenance strategy, which focused on trying to extend the average rebuild interval for the haul truck engines. With an average engine rebuild costing between $130,000 and $160,000, extending engine life was predicted to provide a significant overall cost savings.
By 2001, the average engine rebuild interval was around 18,000 hours, an increase of close to 5,000 hours over the preprogram average of 13,075, and 3,000 hours beyond what the OEM considered normal for this engine model and service. These successes were due largely to switching from a time-based (preventive) maintenance strategy to a condition-based (predictive) approach. The full success story can be found here.1
Buoyed by its success, the mine formed a partnership with Caterpillar’s Contamination Control Product Support Division and Western States Equipment Co. early in 2001.The team planned to study the effects of implementing a contamination control program on the final drives of its Caterpillar 785 haul truck fleet, using periodic offline kidney loop filtration.
The mine’s initial goal was to extend the life of the haul trucks’ final drive groups and differentials, while Caterpillar’s motivation was to provide vital field data on Caterpillar mining equipment to help other customers realize optimum life from their mobile equipment.
The program called for implementation of kidney loop filtration deploying quick connects on the final drives, contamination control training for lube technicians and mechanics, use of high-quality lube oils, regular equipment inspection, improved oil analysis and the integration of magnetic plug inspections and analysis, allowing the mine to transition from a time-based to a condition-based maintenance schedule.
The team met its initial goals on the 785-haul truck fleet, which were to monitor and control contamination levels in the oil systems; extend the oil life; extend the life of differentials and finals; and set up a regular inspection program. At the same time, the team also improved overall fluid cleanliness levels on its Caterpillar 5230 shovels’ hydraulic systems and the hydraulic and transmission systems on its track-type dozers.
Because of the program, the maintenance staff is much more in tune with the mine’s equipment and much better equipped to make fact-based decisions. The contamination control program and the switch to condition-based maintenance allowed the company to defer $280,000 in spending for the first quarter of 2003; proof that the contamination control program is working at Smoky Canyon Mine.
Like many mines, Smoky Canyon Mine is located in a harsh, dirty environment. The mine’s 15 Caterpillar 785 haul trucks operate at the top of a mountain where the temperature often drops to -20°F and the wind keeps the air full of dust, moisture and debris - an environment that makes it extremely hard to keep contaminants out of equipment. Compounding the harsh working environment, the haul trucks transport ore from the shovel across an 8-percent grade.
The program was put into action on February 7, 2001, with Caterpillar supplying a large filter cart for use on the final drive groups and the differentials, a thermal temperature gun to log component temperature, a particle counter to verify pre- and post-filter oil cleanliness and a microscope to measure actual particle size and allow visual wear debris analysis. Caterpillar also sent two consultants to the mine site to train mine personnel on proper use of the equipment.
These consultants set up the filter carts and worked closely with Smoky Canyon personnel, teaching proper installation and removal of filtering equipment, proper methods of sample testing and proper procedures for compiling the documentation that Caterpillar would require. In addition, Simplot personnel attended Noria Corp.’s machinery lubrication course to learn more about the opportunities and strategies that the mine was trying to implement.
The initial program was implemented with four objectives in mind. The first objective was to monitor and control contamination levels in oil systems. The second was to extend the oil life in differentials and final drives from 2,000 hours to 6,000 hours. Next, the team aimed to extend rebuild life in differentials and final drives from 8,000 hours to 16,000 hours. The final objective was to set up a program in which all the mine’s mobile equipment would be inspected every 500 hours. While these goals were certainly ambitious, the team was confident they would meet success based on their earlier success with the haul truck engine program.
Figure 1. Kidney Loop Filter Cart with
10-Micron Filter for Final Drive Filtration
Regular filtration was the team’s main strategy for improving fluid cleanliness levels. To accomplish this, the team added quick-connects to the differentials and final drives on the Caterpillar 785 haul trucks to hook-up a portable filter cart, equipped with a ß10 ³ 75 filter. The filter cart, shown in Figure 1, connected to the truck’s final drive, is capable of pumping 65 gallons of oil per minute and circulates the differential’s 110 gallons for three hours, a total of more than 100 passes. Because the oil is pumped through the system at such a high velocity, the team discovered that the filtration process not only cleans the oil, but dislodges much of the material that normally builds up on component surfaces, keeping the surfaces clean.
The filtering process begins with the truck shutdown; however, the filter cart design and configuration allows the truck to be started during the filtering process. Therefore, the trucks are started and run for about 10 minutes during the process to let the oil circulate; ensuring that the oil in the cylinders and hoses is circulated so that all the oil in the final drive is filtered, not just the oil in the sump.
The haul trucks are filtered in the maintenance shop. To ensure that there is no cross contamination, the team decided to use three separate filter carts for the trucks. One cart filters the final drives and differentials, one filters the transmission and one is used on the hydraulic systems. A ß5 ³ 75 filter is used to filter the haul trucks’ transmission and hydraulic oils (Figure 2). In all cases, an oil sample is taken at the beginning of the filtration process and again three hours later to determine the oil’s cleanliness level.
Figure 2. Transmission and Hydraulic
Carts with 5-Micron Filter
The same program was extended to the mine’s dozers and shovels. Because it is not practical to move the dozers and shovels from the mining site, a filter cart was skid mounted (Figure 3) allowing these machines to be filtered at the work site (Figures 4 and 5).
Figure 3. Skid Mounted Filter Cart
To mitigate cross contamination of the oils, different hoses and filters are used on each system. As with the haul trucks, oil samples are taken at the beginning of the process and three hours later.
Figure 4. Filtering the Transmission and
Hydraulic Systems on a Dozer
Figure 5. Using Filter Cart on
Caterpillar 5230 Shovel Hydraulics
At the onset of the program, the average final drive component life cycle at the mine was 9,116 hours. The average final drive component life cycle bottomed out at 8,769 hours on June 27, 2001, approximately four and a half months after project initiation. This drop was not surprising due to the increased awareness and training of the inspection crew and the addition of component inspection tasks.
Because of this increased emphasis, the inspection crews were able to discover those final drives that were starting to show signs of incipient wear, allowing corrective action to be taken to avoid complete component failure. Consequently, the equipment was repaired at a significant cost savings to the company.
Throughout the two-year program, the average final drive life was 9,448 hours. However, many of the final drives exceeded this average. By the end of 2001, eight final drives had been extended to between 10,000 and 10,500 hours. Today, the average final drive life is up to 12,917 hours with two final drives and one differential having lasted 14,559 hours before rebuild and two other final drives and one differential operated an astonishing 15,997 hours before requiring rebuild.
Mine personnel believe these components could have run longer, but to avoid the risk of a breakdown, the decision was made to rebuild them. There are two additional differentials, however, that have surpassed these figures. One is still running with more than 17,000 hours in operation and the other recently passed 18,000 hours.
By extending the average final drive life, the company has enjoyed substantial savings in rebuild costs. The team estimates that the average final drive rebuild cost through the program was $19,903. With an average drive life of 9,448 hours throughout the program, the final drive rebuild cost averaged $2.11 per hour of operation.
Because the oil in the final drives and differentials is now filtered regularly, every 500 hours, and the components are inspected on the same schedule, the average final rebuild cost has decreased to $17,545.
This rebuild cost reduction along with the increase in final drive life to 12,917 hours has resulted in a 75-cent per hour reduction in the final drive rebuild cost to $1.36 per hour of operation, a cost reduction of more than 35 percent. The maintenance team is not content with these numbers, however, and has increased its goal for the average final drive life to 17,000 hours.
Because many of the current differentials and final drives have been operating under the contamination control program their entire lives, and have therefore been inspected and filtered every 500 hours, the team believes this is an achievable goal. If the goal is met, obviously, the company will enjoy even greater costs savings.
In addition to longer component life, extended oil drains have been possible on the haul trucks resulting in significant cost savings. During the course of the program, the average oil drain interval was extended from 2,000 hours to 6,000 hours for the final drives and differentials, as well as the hydraulics, using a condition-based oil change strategy.
By increasing oil drain intervals, mine personnel estimate the company has saved about $22,443 on oil alone since the program began, without factoring in manpower and other associated costs - costs which often amount to several times the actual oil cost. The savings could become even greater as the oil drain intervals become longer. The finals and differentials on one haul truck recently passed 7,000 hours and oil analysis indicates the oil and the equipment are still in good condition.
Although filtering played the biggest role in lowering the oil contamination levels and increasing component life and oil change intervals, oil analysis was key to the project’s success. At the beginning of the project, the team realized that to meet its goals, it was important to know how the oil was holding up and to determine the amount, size and type of particles suspended in the oil. Therefore, a comprehensive oil analysis program was implemented.
The program included sampling new oil for acid number testing and additive package testing to determine its baseline properties. The same tests are performed at 500-hour intervals for the life of the oil. It is only through this analysis schedule that the team was confident enough to allow the components to operate for such extended periods. In addition, because the original equipment manufacturer’s oil life recommendation is 2,000 hours, careful oil analysis was needed to ensure the oil was holding up at the extended oil drain intervals.
As was mentioned earlier, the final drive and differential oil was sampled as the filtration process began. These samples had an average ISO rating of 21/17/14. The oil was then sampled again after three hours, as the filtration process was completed. The average ISO rating at this point was 17/14/12 - a significant improvement in oil cleanliness (Figure 6).
Figure 6. 785 Hual Truck Differential and Final
Drive ISO Codes Before and After Filtering.
This information is also significant because it is the first trend information the team was able to compile before a final drive failure. Figure 6 shows that even with filtering, the ISO codes did increase slightly before the failure occurred, allowing particle count analysis to function as a predictive warning tool.
Table 1 illustrates the before and after ISO contamination levels not only for the haul trucks, but also for the dozers and shovels. As the table shows, the filtration process resulted in substantial average ISO ratings decreases in all equipment.
In addition to oil analysis and filtration, the team decided to include magnetic plug inspections at the 500-hour interval to supplement the oil analysis data. The drain plugs in the differential and the oil level (fill) plugs in the 785 Caterpillar haul truck final drives are magnetic. As the kidney loop filter cart is hooked to the truck, the magnetic plugs are preserved and the wear debris on these plugs analyzed.
The analysis determines not only the amount or concentration of wear debris, but also the fines, sizes and shapes of the particles. Small changes in this wear debris can be used to forecast the extent and nature of a failure.
In Figure 7, the top two photographs show the condition of a final drive magnetic plug before the filter program began. The plug is covered with fines, flakes and “chunk-like” particles - a commonly observed condition before routine filtration was introduced. The bottom photograph shows a plug after the filtration program was put into place. It is obvious from these photographs that filtering works.
Figure 7. Condition of a Final Drive Magnetic Plug Before and After the Filtering Program
It is only because the oil and components are kept so clean through filtering and contamination control efforts that the magnetic plug inspection is successful. Before the filtration program was introduced, these plugs would have been too dirty to provide any useful indication of component condition.
Now that the oil and plugs are kept clean, the Smoky Canyon Mine team is confident that when abnormal amounts of debris are discovered on the plugs, it is due to a problem with the component and not because of poor maintenance and lube practices. A follow-up article outlining the mine’s magnetic plug inspection program will appear in the September - October issue of Practicing Oil Analysis magazine.
The mine’s program and strategy was simple: Recognize where most maintenance dollars were being spent, determine the dominant root cause of the problems - in this case contamination - and take steps to achieve improved levels of overall fluid cleanliness. Despite its simplicity, the proof is in the data - implementing both predictive oil analysis and visual inspections, and developing a proactive approach to eliminating the causative factors which lead to component wear can have a significant impact on maintenance cost reduction.