Heavy equipment repair specialists complete a different type of project with tight timeline
By Steve Fiscor, Editor-in-Chief
Repairing draglines, electric shovels and mills, L&H Industrial has refurbished many pieces of large mining machinery. A little less than two years ago, the BNSF Railway, a customer familiar with L&H’s experience with heavy maintenance projects, approached them with a novel piece of equipment, a bucket-wheel reclaimer. The engineers at L&H enjoy a challenge, but they had never worked on this type of machinery before and they didn’t want to disappoint. This machine had a 14-ft-diameter bucket wheel, and two 40- to 45-ft discharge booms. BNSF needed this unit back in production before Lake Superior thawed so it could start loading taconite mined in Minnesota on ships that move the iron ore to steel mills along the Great Lakes.
BNSF invited L&H to inspect the bucket wheel and give them an estimate for the repair, explained Jerrod Driskill, project manager, L&H Industrial. “The machine was 50 years old and BNSF could no longer get parts for it,” Driskill said. “They weren’t sure what to do. Anticipating a dramatic increase in ore handling at the Superior, Wisconsin, facility, there was considerable timeline pressure. They basically had a year to resurrect this machine and get it running.”
After a preliminary inspection, Driskill and his team determined that the machine was unrepairable, as far as resurrecting the existing structures. Originally, the shiploading facility was equipped with three bucket wheels. More recently, two machines were handling all of the iron ore with the third unit sitting idle. They discussed options with BNSF and told them that they thought they could provide a machine that was 80% new, using some remaining parts of the structure.
Contract negotiations took nearly six months. Working with BNSF, L&H wrote the initial Scope of Work (SoW) contract. L&H wanted to help them get the unit back into production, but they also needed to set some realistic goals as far as expectations and the timeline. “They thought they could get through one more loading season with two, but starting in April, they would need all three machines operating,” Driskill said. L&H commissioned the third machine in January and it was operational on February 1. When the locks re-opened in April, BNSF would be ready to load taconite at full capacity.
In the original SoW for BNSF, L&H detailed what they thought they could do. They admitted up front they had limited knowledge about bucket wheels. Knowing how many bucket wheels are operating in the mining business though, they were eager to accept the project. So L&H took the unusual step of asking the customer to write an SoW so that they could see what BNSF was expecting from the project. BNSF responded with a 40-page document.
A 40-page SoW is fairly extensive, Driskill explained. “We had never seen anything like that,” Driskill said. “One of the reasons the document was so lengthy is that they detailed a set of legal specifications for every item on the machine. For them, much of the criteria were beyond what the OEM had specified.”
Driskill knew L&H could handle the structure, they were somewhat unsure of the smaller components. Working with L&H engineers and the company’s electrical partners, Driskill rewrote that report, quoted a price for machine repair and gave them a timeline for delivery; BNSF accepted it.
THE PROJECT BEGINS
During the second week of January 2014, L&H began tearing the machine down. They transported it to the company’s main shop in Gillette, Wyoming, which took another two weeks. While L&H is renowned for its field work, they needed to get the data off the structures. “Few prints existed and they were not usable,” Driskill said. “We did not have time to completely re-design every piece and run the load calculations. So we broke the machine down and brought it back to Gillette. Our engineering department used laser trackers and Faro arms to measure and model the machine. We could construct a model from finite element analysis and understand the dynamic loads on the structure.” The engineers reviewed the entire machine and determined where they could eliminate failure points.
The object of this exercise was to build a better machine. For years, L&H has taken great pride in discovering why a machine or a part failed and then rebuilding it to better handle those conditions.
The most significant improvement for the project was upgrading the materials. “The grades of steels have improved so much since this machine was originally built,” Driskill said. “We changed the weldments fit-up and designs on all of the structures to eliminate high-stress joints.”
The bucket wheel is hooked to a ladder boom. It scoops up iron ore and dumps it onto one of two booms (an inclined discharge boom and an outer discharge boom) that discharge the ore off the back of the machine. That whole structure sits on top of the main revolving frame, which had to be rebuilt. The main revolving frame sits atop a car body with side frames that propel the unit.
One of the biggest design changes was with the rear revolving frame, Driskill said. “The rear revolving frame and engine house serves as the counterweight to balance the machine when it’s digging,” he said. “We built a completely enclosed, pressurized engine house. We put everything inside, including the lube systems, the PLCs, and the MMC room, which serves as the brains for the machine.” Previously, all of these components were exposed to the elements, where temperatures can dip to -40°F. Everything is now housed in a heated room.
Looking back at the project, the swing system sort of surprised the L&H engineers. It was configured differently from what’s typically found on a mining shovel. A shovel or a dragline would have one swing rack and this machine had one swing rack with two ring gears—one on the outside and one on the inside. “Everything works concentrically,” Driskill explained. “Two swing systems were running on the same ring gear. We had never seen that before. It’s usually one way or the other. This was a double-sided ring gear with one set of swingers on the inside and one set of swingers on the outside.”
The complication for L&H was the machining and getting all of the gearing to set in place concentrically. If one or the other was off, the machine would not swing, Driskill said. “With the constraints on the mainframe, we had very little room to move anything or options for any changes,” Driskill said. “It took some time to get everything clocked and timed right.”
A BETTER MACHINE ENTERS THE YARD
Since it was commissioned, BNSF has been moving stockpiles and testing it. This new machine has a greater capacity and it has PLCs installed to control that capacity. The conveyor system on to which the bucket wheel discharges has a capacity of 3,500 to 4,000 tons per hour. “This machine is set to run at that level. Our goal was to reduce the downtime,” Driskill said. “We wanted to run 90% to 95% efficient and that’s where the electrical upgrades play a significant role. With the new electrical package, we placed limits on this machine. Previously, they had no limits and they could tear the machine up. With the PLC and upgrades to the structure, the operators are limited as far as the damage they can inflict on the machine.”
L&H invested 26,000 man-hours in this project with no incidents in the shop or the field. “At times, this unit looked like an ant pile,” Driskill said. “We were driven to get this done for this customer. We set goals and we do our best to achieve them. We run 24/7, so the only solution is to just put more guys on the project than we normally would.”
There were times when L&H had to pull men from other projects. “None of our other jobs suffered, but company-wide, everyone knew time was of the essence,” Driskill said. “Even the engineers that designed this machine put on their hard hats, grabbed some wrenches and helped assemble it. You don’t normally see that.”
L&H is now hoping it will work with BNSF on replacing the other two units. “We have had a conversation about it,” Driskill said. “Our feeling is that we would go 100% new on another machine for them. We would commission a new one and decommission an old one. We would stamp our footprint on this one 100%. Knowing what we know, we know we can make some more upgrades beyond this project.”
As seen in Engineering and Mining Journal.