Optimized Dippers Fine-Tune Shovel Performance

Engineering and Mining Journal, Sep 2005 by Fiscor, Steve

Joint Efforts Between Mine Operators, OEMs, and Researchers Yield Unexpected Benefits

One way to lower the cost per ton for moving overburden, a primary objective for most surface mines, is to increase the shovel's payload per pass. Over the years the mines and original equipment manufacturers (OEMs) developed different dipper designs in a constant pursuit of a few more tons per pass. About five years ago, new shovels were introduced specifically for hardrock mining, oil sands and coal. Now, due to cooperative efforts between the mines, OEMs, and researchers, the dippers for those shovels can be tailored to meet site-specific conditions.

Dipper design plays a crucial role in shovel performance. From an impact, loading, and wear perspective, it's one of the most highly stressed components of the electric mining shovel. The cost for a new dipper can be more than $800,000, so it's important to get it right the first time. When it comes to dipper optimization, designers try to strike a balance between two extremes: a lighter design that's in the shop too frequently for repairs; or a heavier design that's so ironclad that it will never wear out.

Working with CRCMining from Australia, P&H Mining Equipment and a few mine operators have developed a process to optimize the dipper. The results to date have been very promising. A mine with a 4100XPB using a smaller dipper with a non-optimized design would average 110 tons per payload. The new dipper could boost the average to 125 to 130 tons per payload. Because the dipper fills quickly, lower in the bank, and more efficiently, the mines using optimized dippers, according to P&H, are spending less time in stall conditions. The OEM claims that they are also finding that the shovels are cycling at least as well, if not better, even though they are going from 110 to 120 tons per payload.

The process involves rapid prototyping and scale modeling of the dipper and conditions at the mine. Using input from the mines and the OEM, CRCMining uses scale models to determine dipper performance. A new dipper featuring an optimized design went to work on July 1, 2003, at Foundation Coal's Belle Ayr mine in Wyoming, USA. The results from this collaborative design effort, according to P&H, were impressive, prompting the mine to order an identical spare. Currently, a project is under way at a large southwestern U.S. copper mine to similarly optimize dipper performance in hardrock digging conditions.

Dipper Design Without Borders

CRCMining is a non-profit research organization associated with several Australian universities that solves problems for the mining industry and then commercializes that technology. CRCMining is one of approximately 70 cooperative research centers (CRCs) that were established in 1990 by the Australian government. It has introduced innovative mining systems that better manage risk, improve safety, and improve the economic performance of mining operations.

Recently P&H formed a separate Australian company with CRCMining. As part of that relationship, they have been performing scale model dipper testing for several projects. "We are doing a lot of work with CRCMining, not only on dipper design, but also on autonomous technologies for electric mining shovels," said Bill Powers, manager of structure, bucket and dipper engineering for P&H Mining Equipment.

"Three or four years ago we realized that we needed a better set of engineering tools to evaluate the performance of dippers. P&H's engineering department had the ability to design dippers to resist fatigue cracks, but it did not have the tools to design the dipper as it relates to performance and productivity. We decided that we needed something more."

The joint-development effort combines the best of both worlds: CRCMining 's modeling expertise and P&H's structural analysis capabilities. P&H had the tools to evaluate the dipper in terms of its structural performance, specifically finite element analysis and strain gauge testing. But, it didn't have the tools to evaluate how the dipper would perform in the field in terms of productivity and dig time. The scale model testing allows the researchers to evaluate the dipper performance characteristics as it relates to payload, dig energy per ton of payload, and dig time.

CRCMining tests the dippers prior to being built. P&H sends 3-D CAD models for the new shovel/dipper design based on input from the mine. Through a rapid prototyping process, CRCMining casts a 1:25 scale model out of aluminum or stainless steel. These models are an extremely accurate representation of what P&H actually builds at its plant in Milwaukee, Wisconsin, USA.

The process also involves an on-site visit to watch and evaluate a machine working in its current configuration. During the visit, researchers characterize the ore or overburden in terms of fragmentation and bench characteristics. They record operator techniques, such as dig trajectory, and the way each bank feeds the shovel-different at each mine. They measure payload with truck scales and profile the bank with lasers to determine overburden density. While recording this information, they also monitor internal machine functions, such as hoist and crowd forces. Once this on-site testing is complete, materials in the lab are calibrated to reflect what was measured in the field.