Giving New Life to Old Shovels
A Wyoming, USA-based company finds ways to chop, cut and rebuild aging rope shovels for additional years of service
By Russell A. Carter, Managing Editor
Like death or taxes, decisions on whether to repair or replace crucial production equipment are inevitable in almost any mining operation. The questions that must be answered before that decision can be made range from the macro level (Will current market prices and future prospects justify a purchase?) to the micro (If we tear this machine apart and find hidden problems, where does that leave us?)
Depending on an operation's location, workforce experience and capabilities, capital equipment and maintenance budgets, and a host of other factors, the risk/reward pendulum may swing clearly toward one alternative or the other. Generally, it's not that easy. Sometimes the answer lies buried in the metal: If the equipment is so old that spare parts, documentation—or technicians/engineers familiar with the equipment—are no longer available, is it worthwhile to 'reinvent the wheel' and attempt a rebuild?
For mines struggling to keep production at peak levels, time may be more important than money—but the money still must be spent wisely. Is it smarter to bite the bullet and spend millions on a new, state-of-the-art shovel—and then wait for a year or two before it can be delivered, for instance; or spend much less time and money by having an older shovel rebuilt, but run the risk of finding unfixable problems that leave the mine without a shovel, and three to six months further into the replace/repair dilemma?
L&H Industrial, a heavy equipment engineering, fabrication and service company based in Gillette, Wyoming, USA, is intent upon expanding the comfort zone for its mining customers contemplating large-scale rebuilds. Founded in the mid-1960s, L&H initially focused on design and fabrication services for the oil and gas industry but later expanded in the 1980s to include the rapidly growing coal mining operations in northeastern Wyoming's Powder River Basin. Along with routine field-and shop-based welding and machining services, L&H offered large-scale machine boring capabilities that were previously unavailable in the area.
Over the years, mining customers asked the company to find ways to replace broken or worn-out components on a variety of shovels and draglines, and L&H used those opportunities to design and fabricate its own versions of the failed parts, eventually building a heavy-metal catalog of L&H-branded components that currently includes replacement parts ranging from complete swing systems and components for Bucyrus, Marion and P&H shovels, down to dipper pins and bushings, even crawler shoes. Machine services include hoist drum and point sheave rebuilding, among others.
In addition to its parts and fabrication businesses, L&H has joined the uncrowded ranks of qualified shovel rebuilders. After acquiring a set of shovel jacks in 2005, L&H performed its first rebuild—on an Idaho-based machine—in 2006, and has since grown its expertise in rebuild planning, engineering and execution to the point where Jason Percifield, L&H's field service manager, said, "I don't think there is anything on a shovel—milling, —that we can't do."
Over the past year, L&H has completed two major shovel rebuilds, both for PRB coal producers. The first of these, described by Editor Steve Fiscor in the March 2011 issue of our sister publication Coal Age (see "Electric Shovel Rebuilds," pp. 31–33), was an ambitious, fast-track project to rebuild the failing carbody of an aging P&H 2800 shovel that had racked up more than 100,000 hours of service.
After removal of the 2-in.-thick bottom plate from the revolving frame (left), the surrounding metal was prepped to accept a new, 4-in.-thick plate (shown at right).
As explained in that article, L&H personnel had worked on the shovel previously and had a good grasp of the machine's main problems—but even so, once work began and the shovel was undecked, unanticipated additional repairs were required.
The original plan for the rebuild, according to Percifield, was to simply buy a used carbody, rebuild it and install it in place of the failing unit. However, L&H subsequently developed a plan to rebuild the original unit by cutting out the entire center section of the carbody and replacing it with fresh metal.
"We specified and purchased all of the materials," Percifield said. "The original carbodies used a cast gudgeon to hold the center pin. We decided to upgrade to a high-end forging for the gudgeon and prefabbed the entire structure in our shop so we could cut the old section out and drop the new piece into place.
"However, shortly after we started this project, we discovered a number of problems," Percifield said. "We ended up working on it for several extra days because of the extent of the repairs. Basically we replaced every bulkhead in the revolving frame as it was undecked. We remachined everything on the car-body and the revolving frame—every gear case and transmission. We remilled every surface. We had 8,000 hours of welding on the revolving frame—about four times what you would see on a normal job."
Despite the need to quickly find a qualified forge that could produce the gudgeon casting in time to meet the rebuild's compressed schedule, and the amount of welding required to complete the rebuild, the project was completed in November 2010, and at last report the shovel was operating satisfactorily. Both the mine and L&H consider it a success. "The big story is that no one had ever done this before and it took a ton of engineering to make it happen," Percifield said.
Expanding the Scope
L&H's most recent shovel rebuild was commissioned by another PRB coal company, this time involving one of the only three Marion 301-Ms now operating in the U.S.—all in service at PRB mines— and encompassing an even larger scope of work that called for undecking, replacement of the carbody, replacement of the original gudgeon with a forged unit and extensive reinforcement of the shovel's revolving frame.
Facing another tight schedule, L&H personnel were able to employ another of the company's inventions to expedite the early stages of this project that involved lifting the shovel body to remove the carbody, in this case, using a set of lifting jacks developed in-house—with third-party assistance— and manufactured just in time to be put to work on the Marion rebuild. According to Percifield, the jack set resembles existing units in use throughout the industry but incorporates specific features and design improvements that make the equipment easier to use and more efficient. Another benefit of the L&H design is that it requires only six semi-truckloads to transport the jack set from site to site.
L&H had worked on the failing shovel since 2007, fixing cracks found in the revolving frame structure and then being called back within six months to find an identical problem. "The metal was fatigued and couldn't stand up to the stress of operation anymore," said Percifield. The mine wanted to get several more years of production out of the machine, but the only obvious repair approach seemed to call for a complete rebuild of the revolving frame—a process that would involve not just welding and machining but replacement of electrical and other systems, and would take much longer than the mine could afford to have the shovel out of service.
Exploratory meetings between the customer and L&H began roughly a year before the project actually got under way, in an attempt to devise a repair that would get the shovel back in operation within the mine's schedule while giving it the sturdiness to provide more years of round-the-clock service. The two parties settled on a novel approach—another case of "not having heard of anyone else trying such a thing," according to Percifield—that involved not only replacing the carbody and installing a new swing system on the new unit, but also cutting out barn-door-sized sections of heavy metal floorplate from the center section of the revolving frame's top and bottom decks and replacing them with plates that were twice as thick. Along the way, L&H also would install a forged center-pin gudgeon to replace the original cast piece, and reinforce the bulkheads between the top and bottom decks.
Although it was sailing in mostly uncharted waters on this repair, the company had some basis for confidence in the outcome: it had polished its large-rebuild skills on the earlier project, it was familiar with the repair history and current condition of the shovel in question—and it also had one of Marion's original shovel engineers on the staff. Still, "no one wanted to get into this [rebuild] and find out we couldn't actually make it work," said Percifield. "It was a calculated risk on the customer's part as well as ours, but we'd worked with the mine people often in the past and felt it could be done." And, at about a fifth of the cost of a new shovel purchase.
Once the project was given the green light by the owner, L&H held planning meetings with mine personnel on a weekly basis for two months. L&H's engineers conducted finite element analysis studies to determine where the actual stress points were on the structures marked for refurbishment, and how best to design the repairs and replacements needed to extend the shovel's service life. Actual work at the shovel disassembly area at the mine began April 25, 2011.
After the shovel's upper housing was lifted off the carbody and all of the hoist machinery unbolted from the top deck of the revolving frame, L&H used a laser scanner to survey and record the exact dimensions and profile of the existing top and bottom decks. Then, welders cut out a rectangular section from the center of the revolving frame's bottom deck, beveled the edges of the side plates around the cutout, and welded into place a 4-in.-thick replacement plate.
They followed the same procedure for the top deck after reinforcing the web of supporting bulkheads inside the frame's internal space. Once the new 4-in.-thick top plate, which weighed 43,000 lb—about 13,000 lb more than the 2-in. plate it replaced—was welded into place, the next step was to install the new forged gudgeon for the shovel's center pin.
At the time of E&MJ's visit in mid-June, all of that activity had been accomplished, almost all welding had been completed on the revolving frame repair, and workers were ready to begin machining the top surface of the upper plate before reinstalling the hoist machinery. Work was also progressing on installing the new swing system on the replacement carbody. L&H finished its portion of the shovel rebuild in mid-July.
Percifield said the job took roughly 10 weeks. "We felt it was was a successful project. We were able to conduct the job from start to finish, including the engineering of the mod, provision of all parts including a brand new carbody swing system, using our jacking system to separate the revolving frame from the carbody, and all field and shop labor. L&H put about 17,500 man-hours into this project without a lost-time accident. We burned approximately 6,500 lb of 1/16-in. welding wire and countless numbers of air arc carbons, but only had 40 in. of rejectable weld—or about 5 lb of wire."