Mining Fleet Achieves 100,000 Hours and Beyond

Mining Fleet Achieves 100,000 Hours and Beyond

Freeport-McMoRan Copper and Gold’s Sierrita open-pit mine is a low-grade copper operation located in southern Arizona, USA, some 48 kilometers (30 miles) north of the Mexican border. While the mine is known for its copper and molybdenum production, the site is currently being recognized for the performance of its fleet of high-hour Caterpillar® 793 trucks—and the people, processes and service excellence that have led to this achievement.

Caterpillar’s first 793A-series truck was put into service at Sierrita in 1991, and is one of five 793s on site that have worked in excess of 100,000 hours. It has undergone more than 200 preventive maintenance services, consumed more than 17 million liters (4.5 million gallons) of fuel, and had 132 tire changes.

“No one really expected this truck to do the hours that it has already achieved,” says mine manager Derek Cooke. “It has already passed even the most optimistic of expectations and is performing well. Indeed, it is Sierrita’s intention that this haul truck will run another 50,000 hours. I think I can safely say there are several more years left in this truck.”

While these factors are significant in themselves, it is the condition of the truck that is most impressive. Despite its age and long hours of service, truck availability remains high at 90.4 percent.

“It’s not the hours run by this machine as well as others in the fleet that is unique, but their condition and the availability that these trucks have enjoyed that is so impressive,” notes Steve Maracigan, account manager at Caterpillar dealer Empire Machinery. “The remarkable availability has been achieved through hard work, pride in workmanship, and an adherence to a structured maintenance process.”

Sierrita’s Connie Puckett, Remote Asset Monitoring Project fleet coordinator, attributes the high hours to the basic maintenance philosophy of her department. “It goes right back to the basics,” she says. “Have a good, thorough Preventive Maintenance (PM) program, do your fluid changes when they need to be done, monitor equipment condition and application, and respond to keep the equipment in the best condition that it can be.”


As mining equipment gets older, its availability tends to decrease. However, this has not been the case for the haul truck fleet operating at Sierrita—due in large part to the fact that the mine has a world-class PM program, with processes and procedures in place to support its equipment fleet.

“The truck fleet was new, the maintenance philosophy was not,” says Puckett. “We were fortunate enough to start with a good piece of equipment, then with Empire and Caterpillar supporting our maintenance philosophy, we’ve kept it that way, and in some cases we’ve actually been able to improve the performance of those trucks.”

One part of Sierrita’s maintenance program is a pre-PM inspection, which involves a thorough inspection of the truck about five days before it is due to arrive at the maintenance shop. This ensures that any replacement parts, specialized equipment and appropriately skilled mechanics are available the minute the truck enters the PM bay.


“The biggest challenge to getting a truck to operate at over 90 percent availability is the sustainability of a robust maintenance program,“ says Larry Kitto, Empire Machinery’s director of mining. “Maintaining this high degree of professionalism does not happen by chance; it is an attitude that starts at the top and filters down—without dilution—to every part of the organization.”

Economic analysis illustrates that it is better to rebuild a well-maintained haul truck that is in good condition, than it is to retire it in order to buy a new one. “Every piece of equipment has a life expectancy,” says Maracigan, “But even after this time, it is still worth maintaining it as replacement costs are so high, and even new trucks still need to be maintained.” Those who set in place a comprehensive program to keep their machines in good condition with high availability are now reaping the rewards which they justly deserve, says Maracigan.


The maintenance team at Sierrita has not changed much over the years, which is unusual for a mining operation, and the pride and diligence they share in maintaining equipment is illustrated by the high availability of the machinery. This team has developed highly consistent processes for maintaining equipment to world-class standards—and has rightly earned the respect of the mine. In fact, an audit of the maintenance program, performed by Empire, Caterpillar and Sierrita, found excellent and effective processes already in place.

Cooke is clear that ensuring that the right things happen comes down to good people. “I would like to say that it’s a complex collection of systems and procedures alone that is the key to our success here at Sierrita, but in the end it is the people who execute it all that make the difference,” he says. “We have excellent people throughout the team. Larry Buhlke, Sierrita’s maintenance superintendent, has high expectations, holds his people accountable and is always looking to correct even the smallest of details. We have a great group of supervisors, and a fantastic work force. They all take pride in their contributions in support of this haul truck fleet—which operates at a level of availability that some mining operations can only dream of.”

The partnership with Empire is key. “Unforeseen breakdowns are a major issue at any mine,” says Tony Sharpe, Empire’s project manager at Sierrita. “Empire and Sierrita’s maintenance and operations staffs work together, doing everything they can to ensure that breakdowns do not occur.” The mechanics have a great relationship with the operational side of the mine, which also contributes to the overall health of the haulage fleet. Each understands the work and responsibilities of the other, says Sharpe, and they all have a mutual respect for each other’s work.

Much of the maintenance work requires a high level of technical expertise and involves many man-hours. Sierrita’s maintenance crews include some of the mine’s most dedicated performers—people who are bright, enthusiastic and experienced. These teams have an emotional buy-in for the machines for which they are responsible, explains Maracigan, as well as an immense sense of pride in keeping them in excellent condition and running at high levels of performance.


One part of the maintenance program is the Component Rebuild program, which involves removing a component that is old, worn out or has reached the end of its useful life, and replacing it with a component that has been rebuilt to meet Cat® standards for durability and reliability. These “old” components are sent to Empire’s component rebuild center, where they are rebuilt and then reinstalled into another Caterpillar machine operating in Empire’s territory.

Sierrita depends on Empire to deliver quality components. “We want to be able to take a component that’s delivered to us and install it on a piece of equipment, maintain it in the way we have been taught is proper and correct, and for that component to run its expected life without any significant issues,” says Puckett, who has been at Sierrita more than 20 years.

The key to successful component management is the development of a detailed Planned Component Replacement (PCR) program, which requires defining a component’s life expectancy, ongoing knowledge of its condition, appropriate response to any reduction in performance and efficiency, and replacement before breakdown, or—at the very extreme—a catastrophic failure. Every major and minor component is set up on a PCR interval.

“A component failure is an indication that your maintenance program has failed,” says Sharpe. “Component rebuild is all about having a process and sticking to it. The dealers know they are investing in the customer’s success through the component rebuild program and that they cannot cut corners, as this will only lead to issues at a later stage.”

Puckett believes part of Sierrita’s success with its high-hour trucks was the ability to build its PCR program from scratch. “We were able to start with a fresh machine and build information as far as our PCR program,” she says. “I’ve been basically watching that truck, keeping track of everything, since it was brand new.”

Sierrita and Empire have moved away from using fixed interval “worked hours” as the sole indicator of when a component should be replaced. “Today we also look at condition-based factors such as cumulative ‘fuel burn’ as a better guide to the total work that an engine has experienced during the course of its life in the application,” explains Kitto. For example, instead of replacing an engine once it has reached its hours-based target life, Empire will now, based on its condition, extend it for another 500 or 1,000 hours—monitoring the filters, oil condition and consumption, and overall operating performance, before making a decision on when to replace the engine.


Another key part of Sierrita’s high-hour success is its condition monitoring program. Condition monitoring describes the collection of routines that facilitate the early detection of changes in equipment health, operation or application severity. These processes support a repair-before-failure approach to equipment management and guide modifications to the maintenance plan, operation or application. In its simplest form, condition monitoring involves studying the state of machine systems and components, as well as external factors, such as application severity, that could —and do—impact equipment health and longevity as a whole.

A successful condition monitoring program can:

  • Reduce the number of failures and unscheduled downtime repair events
  • Favorably impact overall operation and maintenance costs
  • Promote efficient use of labor resources
  • Improve equipment reliability/availability
  • Increase production and reduce cost-per-ton

Sierrita employs a dedicated team that monitors various aspects of equipment operating characteristics including temperatures, pressures and speeds. “Condition monitoring is not an exact science,” says Kitto. “But by monitoring and studying the indicators you gain an improved understanding of the operation of the equipment as well as the operating environment the equipment is working in. Sierrita’s approach to condition monitoring helps support its repair-before-failure strategy, resulting in optimized component costs and equipment availability.”

The aspects of condition monitoring associated with machine components can be sub-divided into three parts:

  • Proactive management of machine systems and components
  • Defect detection
  • Application monitoring and management

The condition monitoring process can be further broken down into sub-processes such as inspections, fluids management, on-board electronic data management, machine systems performance tests, application analysis and learning from failures/failure analysis.

Puckett has described her role as maintenance coordinator as being the “mother” of the truck fleet. “I keep track of the component hours on the trucks, the hours on the trucks themselves, the lubrication changes, making sure everything is done at the correct intervals,” she says. “I also record all of the service that was done to them, all the work orders. It’s my job to see that vital or important information is recorded and kept. I have to schedule it in at the right time. I’m not doing the work to the trucks myself, but I am keeping track of the program so that everybody else knows what they need to do to that truck.”


Paying attention to contamination control has contributed to the high hours achieved by the truck fleet at Sierrita. This reliability and durability initiative helps equipment owners realize superior value through the avoidance of component failures and consequent longer component and product lives, as well as optimized productivity throughout the product’s life cycle.

Contamination control has two parts: Fluid analysis/management and maintenance process/environment cleanliness control.

Fluid analysis/management involves monitoring contaminants and trace elements in lubricating fluids and fuels. Anything that doesn’t belong in a fluid is considered contamination. Particulate contaminants are the most common—and the easiest to control. They include dirt, metals, weld spatter, paint flakes, rag fibers and sealing materials. Heat, water and air also are considered contaminants. They combine to break down the oil’s chemical composition, forming oil oxidation and acids.

“We have found that even a small amount of debris in lubricating fluids can significantly reduce component lives,” explains Kitto. “Lubricants are pumped through an off-board filtration system which removes particles and contaminants to achieve and maintain a higher level of oil cleanliness.”

The second aspect of contamination control monitors the cleanliness of the environment in which the trucks are maintained, as well as the maintenance and repair procedures employed in that environment. To meet the highest standards, maintenance environments must be dust-free, closed from the outside and spotlessly clean.

“Contamination control is something we try to pay a lot of attention to,” says Puckett. “It’s like general good housekeeping. Not only is that a good thing for your equipment as far as keeping contaminants down while you’re working on them, but it’s also a safety factor in our workshops for our employees. It provides a much safer working environment for our folks, so housekeeping is a big deal here.”

Caterpillar has focused a considerable amount of effort on all areas of contamination control for the last five years. The company itself strives to:

  • Build and ship clean components and machines
  • Design machines, engines and components so they are easy to keep clean
  • Provide tools and services to help manage contamination
  • Educate others on the causes and effects of, and solutions for, contamination

Caterpillar dealers play a large role in a successful contamination control program. Empire has an assigned contamination control administrator and follows established procedures within the parts and service departments. Employees receive ongoing training in contamination control and have access to the proper tooling and particle count capability.

Sierrita takes its role in contamination control seriously as well, making sure everyone on the site understands the importance. The shop and parts warehouse operations follow established procedures, and maintenance personnel ensure the equipment meets Cat’s recommended cleanliness targets after self-performed maintenance and repairs. Indeed, the facilities at Sierrita have obtained Caterpillar’s Five Star contamination control rating.


While Sierrita’s high-hour 793 trucks are technically A-series models because of their original frames, they have been extensively upgraded over their years in service and are now more similar to a B-series truck. These upgrades include an electronic injection engine (HD) as well as the addition of the Vital Information Monitoring System (VIMS™) electronic data monitoring system.

As a result of the proactive repair philosophy followed by Sierrita and Empire, overall maintenance costs have been low. Sierrita has taken advantage of every applicable upgrade that Caterpillar has offered as a means of ensuring maximum machine life; as a result, the mine has not had to invest in new replacement equipment. These upgrade programs are just one of the many factors ensuring the truck fleet retains a high level of availability.

“I believe this truck has better performance today than what it had when it was new,” says Buhlke. “It runs a little faster on the ramps and it’s a little more fuel efficient than what it was with the short stroke engine—and the life of the HD engine is considerably more than what we were getting out of the short stroke engine that came with the truck.”

“We’ve done all the frame modifications and any other upgrades that Cat recommended on the truck,” Buhlke continues. “We got that information and we acted upon it to make the truck a better truck.”


Both Sierrita and Empire are actively involved in the training of their maintenance and operations personnel. Training is designed to ensure that both groups of employees work with a high degree of professionalism.

Mining companies know that highly trained and skilled operators will perform safely and efficiently in a variety of weather and road conditions. Sierrita uses PC-based training aids and a haul truck simulator on-site, which allows it to train its operators in the basics of haul truck operation before they are allowed to climb into a full-sized vehicle.

“We never turn a person loose until we feel confident that they can safely handle the truck,” says Cathy Fontes, senior training specialist at Sierrita. “Then we usually give that person another couple of days on day shift driving solo so they really know all the locations and have a full understanding of the truck and then they are assigned to their rotating crew. Once they’re on their crew they do come back and go with another trainer on the night shift, because we feel strongly that night-time driving is a lot different than the initial driving during the day.”

In addition, Sierrita operators are trained to understand how their machines should operate—and the serious situations that could develop if they are not operating properly. This helps Sierrita make any repairs before a serious problem develops.

“I believe that the detailed training we provide does help with machine health,” says Fontes. “We even assign our new drivers back after they’ve been rotating for about a month. They go to the truck shop, shadow a PM mechanic, ask questions. Maybe they don’t understand the mechanical language, but have driven long enough to understand ‘that doesn’t feel right, that doesn’t smell right, that doesn’t sound right.’ It sure helps them understand what makes the truck tick so they can recognize when a problem’s about to happen and I do believe that has helped us obtain longer life on our trucks.”

Empire has a regional training center where it trains its own mechanics as well as those of customers and other dealers. Mechanics’ training courses are similar to an apprentice program. A new employee in the maintenance workshop will work alongside an experienced maintenance technician to learn about both the equipment and its components. In addition, mechanics will attend training classes that are run by the Empire Group at its facilities in Mesa, Ariz.


Following maintenance procedures and programs has a profound effect on the life of Sierrita’s equipment, but mine site operations also play an important role. In particular, Sierrita pays a lot of attention to its haul roads in order to increase the life of its trucks and their components.

“Haul roads are one of the most important things that we have to take care of,” says senior engineer and quality analyst Gary Perry. “We have the ability to capture a lot of data from our Cat trucks. We put people in the trucks and we measured what the responses of the trucks were to the different areas in the pit in each of the haul roads. What we found is that our haul roads, while we thought they were really perfect, were not so perfect.”

Perry explains that the engine was responding differently as they measured the haul roads in 9-meter (30-foot) segments. “We went in and we profiled all of the roads every 9 meters (30 feet) and then we prioritized what areas of the road needed to be fixed,” he says. “We were able to reduce rock spillage, we were able to take the stress off of our equipment, and we were able to take the stress off of our tires from going up and down through ruts. You end up actually taking the stress away from the truck, which saves you money.”

By reducing haul road grade variation, Sierrita was able to increase the speed of the trucks and reduce the number of high-energy transmission shifts. “That reduces the amount of rocks that are being spilled, so it actually is a very good cost savings,” Perry says. “In addition to that there has been a noticeable increase in component lives. Minimizing transmission shifts reduces drive train shock loads and, if you are bouncing up and down with a 236-tonne load (260-short ton load), you’re going to have failures in your struts at some time. You’re also likely to have structural failures that must be repaired. You’re going to have failures in the seats in your truck that can cause employees to get injured. If you fix those haul roads so that you can drive in a pickup at 35 miles an hour (56 kph) comfortably, not bouncing off the roof, you are going to end up having a lot longer component life, a lot less damage throughout the truck, and your drivers are going to have a much better quality of life.”


While Sierrita is happy with the performance of its truck fleet, Perry says that doesn’t mean the site will stop looking for ways to improve. Teams of people will visit other Freeport-McMoRan sites in a constant search for best practices that could improve operations at Sierrita.

“For example, we’ll look at things like water trucks,” says Perry. “How can you use them better? Water trucks are necessary to control the dust, but they can wreck the roads if used incorrectly, so how can we use them differently? What kinds of additives can we use?”

“It’s interesting when you pull in 10 or 15 people from different areas and sit down and try to see what best practices that you can use, whether we’re talking about the trucks, the haul roads, the shovels, or any other areas involved in mining operations,” Perry continues. “One of the things that we’ve done here recently is we’ve put compactors at all of the properties. We’ve got these Cat compactors on our dumps, on our haul roads, on our shovel pits and even out on our drill surfaces where we’re going to be drilling in order to cut down on the stress. That’s the kind of continuous improvement idea that we’re always looking for.”

Perry stresses that open communication is the key to success. “We have constant communications between our operators and our dispatch system,” he says. “If things are going wrong, our operators are actually empowered to directly call the truck shop and talk to the people there in order to communicate information accurately and in a timely manner. Our shovel operators do the same thing. They call back and forth between the operators or to maintenance or to dispatch. There’s a large amount of communications that takes place in order to get things done correctly.”


Freeport-McMoRan Copper and Gold’s Sierrita mine, located 40 kilometers (25 miles) south of Tucson, Ariz. is an open-pit copper/molybdenum operation. The mine’s product feeds a 104,000-tonnes-per-day (115,000-short-tons-per-day) sulphide ore concentrator, a molybdenum plant, two roasters and a rhenium processing facility.

While the Sierrita property was first claimed in the 1890s, the current open pit was begun in 1957. The mine employs approximately 1,000 people. The site produces 73 million kilograms (160 million pounds) of copper and 8 million kilograms (18 million pounds) of molybdenum per year. There are minable reserves of about 1,100 million tonnes (1,200 million short tons). Average ore grade is 0.26 percent Cu, and 0.027 percent Mo.

Sierrita is one of the safest mines in the United States, having earned the federal government's prestigious Sentinels of Safety award as the safest mine in the open-pit hard-rock mine category in 1993, 1997, 1999 and 2001.


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