Behemoth: Upgrading a 25-year-old dragline

Vulcan Materials Co. upgrades the Bucyrus-Erie King Midas dragline – a 25-year-old marvel.

There’s nothing mythical or fictitious about King Midas, the 25-cu.yd. modular Bucyrus-Erie 680-W walking dragline that was first purchased in 1989 by Ohio’s R&F Coal Co. In addition to bringing faster cycling times and AC electrics to coal pits, the more than 2-million-lb. dragline’s 225-ft. boom at 40 degrees, powered by a Siemens AC drive, proved to be the fastest cycling large dragline of its day.

When Vulcan Materials Co. purchased the colossal machine to help its Sanger Sand & Gravel plant in Sanger, Calif., achieve expansion goals, transporting and upgrading the machine caused a new kind of stir.

“We purchased the dragline in 2007,” says Max Pfaff, Vulcan’s area operations manager. “It was delivered to the Sanger plant site in 70 truck loads. For the next 10 months, we rebuilt, upgraded and modernized the entire machine, including the electrical system, which was our main concern.”

In order to successfully convert the King Midas AC system to modern electrical elements, Vulcan brought in Aaron Lunberg, then employee of Drives and Control Services, now owner of Wyoming’s Electrical Technical Services and Repair. Lunberg’s engineering expertise and military training in electronics quickly allowed him to evaluate the state of the aging behemoth.

“From today’s perspective, the old AC system was a monster,” Lunberg says. “It was very intricate and over-engineered. It was very complex, with over 50 circuit cards and thousands of wires. Over time, those tiny wires become brittle and break, making the machine very difficult to maintain.”

Electrical upgrade
Just prior to evaluating King Midas, Lunberg upgraded a similar machine, Ursula, a Bucyrus-Erie 2570WF. He partnered with the team at Current Power Solutions in Houston, John Franks and Nate Norris, to develop an upgrade plan.

“I had the benefit of seeing Crystal River Quarry’s swing drive run for two or three months after her upgrade without any AC incidents. That confirmed for me that the upgrade was the best option,” Lunberg says. “When I discussed the benefits of our upgrade plan to Max, along with the fact that maintenance would be so much easier and the machine would be so much more effective, there was no question about proceeding.”

Bringing King Midas up to speed required the dedicated labor of a team of people that included Lunberg and several Vulcan electricians.

“Vulcan’s electricians, Aaron Altaffer and Nathan Roberts, played a large role in the success of this upgrade,” Lunberg says. “We had to take every bit of the old wiring system off in order to begin setting up the new system. It took about four months worth of 12-hour days to complete the transition. Since it’s been done, we’ve been able to maintain a nearly 99 percent availability rating on King Midas. If the dragline was running with 50 percent availability using that old AC system, I would be surprised.”

Bringing King Midas to the Vulcan plant was no snap decision. The company did plenty of homework before settling on an expansion plan.

“We mine to a depth of 100 ft. in an area with significant agricultural production and a very high water table,” Pfaff says. “As part of our expansion plan, we looked at changing our mobile pit fleet by reducing our ground water pumping, as well as diesel usage and emissions. We knew it would be beneficial to reduce our overall environmental footprint as part of our expansion.”

Sanger expansion
For more than 50 years, the Vulcan Materials Sanger Sand & Gravel plant has supplied construction aggregates, asphalt materials and concrete as part of Vulcan’s group of West Region facilities. Sanger Sand & Gravel occupies 880 acres in Fresno County, Calif.

The plant operates along the Kings River and scenic Kings Canyon Highway and is surrounded by agricultural production activities. Kings River follows the eastern edge of the site and Collins Creek and China Creek flow through the northwestern part of the property. Employees actively manage 32 acres of the property for wildlife, as well as 150 acres of the adjacent China Creek County Park.

It was in 2005 that Vulcan recognized the need to expand the Sanger facility. The site’s mining equipment slated for replacement included pit dewatering pumps, an excavator and three haul trucks.

“Essentially we wanted to go from dry mining to a wet mining process and eliminate any possible fluctuations in the surrounding water table,” Pfaff says. “We felt it was the right thing to do for the environment, the local community and our operations.”

In assessing their options, Vulcan explored use of either a dredge or an electric dragline.

“We settled on the dragline because of our cobble size and the clay content of our reserve deposit,” Pfaff says. “With these conditions, we felt that pit material wouldn’t flow underwater to a dredge bucket, which would result in a ‘post hole’ scenario. We also had safety concerns related to personnel and equipment about using a dredge on the water. Since the dragline excavates from the pit bank, we felt that would reduce safety risks.”

Hoist interlock
King Midas has always earned the respect of its operators. In a 1989 mining newsletter – The Surface Miner – an R&F operations engineer reported that the machine’s cycle time had exceeded the company’s expectations. A dragline operator cited “the special hoist interlock and the quick swing as the main reasons for the outstanding cycle time.”

The King Midas hoist interlock ties the hoist and drag drum together mechanically in the hoist mode using the momentum of the paying out drag drum to increase hoist speed. This is accomplished through use of a special gearing arrangement and increases hoist speed as much as 20 percent. Joystick controls help reduce operator fatigue and improve cycle times.

“By far, the biggest improvement in our mining process for the Sanger crew was the King Midas modernized electrical system,” Pfaff says. “The machine now boasts a fully upgraded AC electrical system to drive all motors. With few exceptions, the system has proved to be very reliable.”

King Midas electrical equipment includes a 1,750-hp hoist motor, 1,750-hp drag motor, two 330-hp swing motors, two 390-hp walking motors and a main transformer (1,800 KWA).

The dragline deck includes an electrical control room, main power transformer, and drag and hoist motor. The main electrical systems feature a controlled-frequency drive, static AC control, three-phase, 60 Hz, 4160 7200 V power.

To replace the trucks used in their prior mining activities, Sanger constructed 4,000 ft. of overland conveyor, which fed directly to the plant surge pile.

King Midas is responsible for digging 75 to 100 ft. in depth to stockpile sand and gravel. A Caterpillar 990 loader feeds the pit line conveyor to deliver material to the plant for processing.

Learning curve
“Mechanically, our crew went through a long learning curve in order to understand how to efficiently use this new dragline,” Pfaff says. “Hands-on training for operators has been and continues to be supplied through Caterpillar (which purchased Bucyrus-Erie). Operators are now comfortable with operating and maintaining the machine. We’ve had a lot of help and advice from others running draglines across the country.

Since it was first permitted and walked off the construction pad at the mining site, King Midas has garnered attention for Vulcan’s Fresno operations.

“It’s a real draw with the local community and mining site tour groups,” Pfaff says. “It’s a unique piece of equipment in this area. Just the sheer size of the machine draws excitement when people watch it dig or walk. Usually the first question we hear is ‘How does it move?’ We’ve experienced a lot of positive press and recognition from this upgrade.

“Financially, we’re operating at about the same cost as we did when we used a dry mining operation,” Pfaff adds. “The market downturn late in 2008 had the most impact on this, but with recovery taking hold we’ll see lower costs from our efforts going forward. Vulcan Materials made this upgrade possible, but the real heroes of this story are the Sanger employees who make it all work every day.”

King Midas Specifications

Base
Outside diameter – 39 ft.

Bearing area – 1,195 ft.

Rollers – 56 with average diameter of 8 ft.

Swing rack pitch diameter – 17 ft.

Revolving frame
Machinery frame width – 44 ft., 6 in.

Machinery frame length – 50 ft., 4 in.

Girder depth – 48 in.

Electrical Motors
According to manufacturers of IGBT (insulated gate bipolar transistors) and FRED (fast recovery epitaxial diodes), development of IGBTs has increased the efficiency of AC electrical motors in recent years, promising 70 percent faster turn-off times than previous generation devices. Speed range is increased by reducing inverter dead time and proportionally expanding the PWM duty cycle and modulated frequency range. Also, the new devices’ gate characteristics have three times greater noise immunity, and dv/dt induced turn-on current is reduced by a factor of two compared to similar devices.

Loretta Sorensen is a freelance writer in Yankton, S.D. She produces material on a variety of topics, serves as a ghostwriter, and has authored her own books.