PC3000 Excavator

CAN YOU DIG IT?

One of the largest excavators operating in Alabama helps MS&R handle tough layers of overburden, lower operating costs.

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The way Randy and Kenny Robison tell the story, they’ve visited every coal mine that would let them in the door to survey the best mining practices. They’ve spent nearly their entire lives working in coal operations – starting out on lube and grease trucks and working their way up to respected industry leaders in Alabama, USA. As owners of MS&R since 1989, the two brothers have created a niche for themselves in providing coal for Alabama’s metallurgical coal market.

A great deal of the knowledge the Robisons have amassed over the years has come from observing – taking note of what works and what does not. In early Spring 2004, they blazed a trail of their own in Alabama coal mining history when they commissioned a PC3000 Super Shovel from Komatsu America. Outfitted with a backhoe attachment and a 21 yd³ bucket, MS&R’s PC3000 is currently one of the largest mining excavators working in the state of Alabama.

“We decided about four or five years ago to use larger mining equipment,” says Randy Robison. “The costs of labor, blasting, fuel and materials were going up. Improvements in production came as we started running larger, more efficient machines. They generated more yardage and production per hour, significantly reducing costs. Each time we’ve increased equipment size, it reduced our mining costs. We are producing more coal because of the changes.”

Alabama Coal Market Drives Changes

Kenny Robison is responsible for operations at MS&R’s Merritt Rogers mine while Randy Robison runs the company’s newer Sloan Mountain pit. Merritt Rogers churns out 200,000 tons of coal per year while Sloan Mountain is projected to produce 250,000 tons of coal annually.

The different equipment at each pit is a perfect example of the changing Alabama coal market. Just a few years ago, Alabama’s coal miners were running 85-ton haul trucks – models now upgraded to 100-ton capacities, with progressive miners like the Robisons moving to 150-ton trucks. The Merritt Rogers mine still runs 100-ton trucks loaded by a 15 yd3 excavator. The brothers knew, however, that a larger machine loading larger trucks would provide them the most efficient package for the new Sloan Mountain site. Kenny is quick to add that Sloan Mountain will always out-produce his Merritt Rogers mine due to the larger machine:

“The 50,000 ton difference in production between our two sites can be attributed to the implementation of the larger, 21 yd3 excavator over the smaller 15 yd3 model we use now at Merit Rogers.”

“We set these mines up,” explains Randy Robison, “around the cost of the equipment, paying for the mine infrastructure in five years. Many times that dictates the size of the digging tool. This particular mine was set up to work in a five-year plan. It’ll run seven to eight years on the downside, it could run 10-12 depending on what the markets do. The market changes – it’s like a roller coaster – it always changes.”

Within that time frame, the Robisons are banking on 50,000 hours from the Komatsu PC3000. This 557,900 lb backhoe features a breakout force of 191,000 lb., crowd force of 179,800 lb and a bucket capacity of 21 yd3. When comparing the PC3000 to similar sized excavators, the need for a reliable, cost-effective digging tool drove the purchasing decision for Sloan Mountain.

“This particular machine (Komatsu PC3000) has been around for a number of years,” says Randy Robison. “It has a good service record, and we knew that the pump system would have a great service life. The weight of the machine was a big issue due to the fact that it improved digging performance. There were other issues that went into our decision to purchase this machine. What it boiled down to was Tractor & Equipment Co. Inc.’s (Komatsu’s Alabama equipment dealer) ability to ensure that the machine would stay in production. Tractor and Equipment has another PC3000 running in their territory, therefore, we knew they would have the ability to service this size excavator. Tractor and Equipment services the excavator promptly and to our satisfaction.”

Uncovering More Coal Faster With A Larger Excavator

Even in a fluctuating market, MS&R has created a solid niche for itself. Its major market is the metallurgical coal market where end users produce coke from coal with consistently low ash counts. With ash counts in the 2 to 2.5 percent range and a sulfur content running 0.6 percent, the company’s mines produce some of the best metallurgical mine run coal in the state of Alabama and, some have said, in the world.

The quality of coal is a constant in the Robison’s grand experiment – the method of retrieving the coal is the variable. Both pits feature four seams of coal (Lick Creek (not mined), Upper Jefferson, Lower Jefferson and Black Creek) separated by varying depths of overburden and interburden, comprising extremely hard sandstones, siltstones and clays. The layers of overburden and interburden above the Lick Creek, Upper Jefferson and Lower Jefferson seams are blasted and removed with the Komatsu PC3000. The machine is an excellent match with the three 150-ton Komatsu 510E trucks, placing capacity loads in four to five passes. But the biggest difference found with the larger PC3000 is it’s brute digging force, reducing the time needed to dig through the blasted rock, which often includes unexpectedly large boulders and rock sheaths.

“The PC3000 is the best balanced machine we’ve had so far for digging overburden,” says Randy Robison. “We don’t have the bounce, wobble and wiggle we had with some of the other machines.”

The progression to larger loading equipment has been consistent. In the past, MS&R ran a 13.5 yd3 wheel loader that was effective as long as the rock was very well blasted. But they were plagued with many tire failures due to the hard sandstone, and poor traction when operating below water table in wet conditions. The company then switched to a 260,000 lb excavator and later to a 400,000 lb excavator, but never found the productivity they were looking for until the 557,900 lb PC3000 was brought into operation.

“We had one boulder,” recalls Randy Robison, “where we put two D10 dozers behind it and could not budge it. We took the PC3000 and easily dragged it out of our way. It is a much more powerful machine than anything we have had in the past. We are seeing the biggest improvement with this machine in our mining operation when we encounter poorly fractured overburden. We sometimes have a blast that doesn’t fracture the rock like it should, leaving us with oversized rock to move. This machine can dig through this material more efficiently than other machines we have operated. This keeps our production on schedule in spite of the oversized or poorly blasted overburden.”

The Komatsu PC3000’s cycle and swing times are roughly the same as the 400,000 lb excavator being used across the river at the Merritt Rogers pit, but operators have reported the PC3000 has more responsive controls when digging and swinging, which can lead to a more comfortable and productive operator. One simple premise, however, makes the PC3000 more efficient: it’s a larger machine with a larger bucket feeding larger trucks. Randy Robison states MS&R typically moves 12,000- to 15,000-bank yd3 of overburden per shift with two 10-hour shifts, and 26 full production days per month.

A River Runs Through It… And Wreaks Havoc on Tires

The Black Warrior River separates the Merritt Rogers and Sloan Mountain mines, a picturesque amenity for a coal mine, but also a cause for many of the equipment headaches suffered by Randy and Kenny Robison. Each site excavates as low as 30-45 feet below the river’s water level to reach the lowest Black Creek seam, creating wet, low-traction conditions throughout the year. When wet wheel loader and truck tires slip and spin on a hard, abrasive material like sandstone, frequent tire failures are inevitable and result in costly downtime.

The above problems led MS&R to do away with the large wheel loader as its main loading implement and seek alternative loading methods for its operations. Many coal mines position large backhoe-type excavators above the trucks they are loading, meaning that the trucks are spotted on the next bench down. This allows the backhoe operator to have a true unobstructed view of the truck bed to achieve a more balanced, even load into the truck, reducing wear and tear on truck suspensions and tires. This method also allows a much shorter average swing angle, reducing cycle time and increasing production rates. This method is employed by MS&R on the upper benches, away from the wet areas below river level.

In MS&R’s case, when loading directly above the lowest Black Creek coal seam, the wet, abrasive sandstone floor can seriously advance the wear of truck tires. In these cases, MS&R loads its trucks in a side-by-side formation with the truck and PC3000 on the same level. While this eliminates some of the visibility advantage of loading from above, it ensures the trucks are always operating on relatively dry surfaces. The Komatsu PC3000 features a well-elevated cab, which allows the operator to see well into the truck bed, even with the same level loading conditions.

The water infiltration is also a big reason why MS&R purchased the PC3000 with the backhoe configuration versus shovel version.

“A shovel might be a more efficient machine for us,” says Randy Robison, “but it would not work well for us in our present mining condition due to the fact that we are mining below the river level. This creates a lot of water seepage into the pit area. With the excavator, we dig an area down to the water level. We then move back in this area and chop a hole in the pit floors to dewater so that our hauling equipment does not have to operate in the wet conditions.”

“The larger equipment is cheaper to run,” says Randy Robison. “Every time we’ve gone up in size, it’s reduced our mining costs. In years past, we’ve mined some of our shallower overburden with some of the smaller equipment. If we had this larger equipment back then, it would have improved our situation. Our bottom line would have been improved.”

Assessing Needs and Making Equipment Purchases Accordingly

The Robisons are currently happy with the size of the fleet operating at Sloan Mountain and don’t see a need, based on the size of their operations, to go with anything larger – but don’t hold them to it.