Dig it! Bucyrus moves the earth with castings: this surface mining industry OEM uses casting design as a tool to increase the productivity of its shovels and draglines, moving more earth per second than anyone in the world.

Bucyrus International loves castings.

"They are integral to our mining technology." said Ron Maci, manager--value chain management, "Our machines couldn't perform at the necessary production levels without them."

More to the point, Bucyrus loves tough and rugged steer castings.

In the surface mining industry, OEMs understand that their con]portents are going to wear out. Since their systems operate in environments from the Arctic Circle to the deserts of North Africa and constantly slam and drag against iron ore, rocks, sand and coal, the laws of physics deem it so. Therefore, during the design engineering of surface mining systems, steps must be taken to prolong the life of the individual components as long as possible.

For South Milwaukee, Wisconsin-based Bucyrus International, prolonging component life and increasing mining machine productivity often means designing components as castings.

"The geometries and material properties we can achieve with castings improve the functionality of our machines." said Maci. "It is that simple."

As with other industries, surface mining OEMs are being asked by their customers for increased performance at reduced costs and weights. The success of Bucyrus' machinery is based on the amount of material (dirt, sand, rock, etc.) it moves per second. For every pound Bucyrus eliminates from its equipment without a loss in performance, a mining customer can possibly remove one additional pound of material from a mine.

This article examines how Bucyrus is utilizing casting design to increase the productivity of the world's largest surface excavating and mining technology.

Panama to Milwaukee

Throughout its 123-year history, Bucyrus has been involved with such highly-publicized mining operations as the Panama Canal (see "Bucyrus Digs Panama Canal" sidebar) and the 1920 groundreaking for United Artists Studio in Hollywood. In 2000 in Australia, the firm commissioned the largest operating dragline in the world that can move earth the equivalent of two football fields during excavation.

Today, Bucyrus is a global firm with nine international subsidiaries, including offices in China, India, South Africa, Australia and Chile. But each of these offices still defer back to the South Milwaukee headquarters where the firm manufactures the majority of its mining systems. Under its 1 million sq. ft of manufacturing space, Bucyrus manufactures walking draglines, electric mining shovels and/or rotary blast hole drills. (This article focuses (in casting use in the draglines and shovels.)

An electric mining shovel (Fig. 1) picks up the earth material and drops it in a haul track to remove it. An electric walking dragline (Fig. 2) pulls the material from the mining site to a dumpsite, For mining sites, the choice of a shovel or dragline is based as much on the material being mined as amount of material, A shovel typically can handle up to 90 cu yd of material at one time, while a dragline can handle more than double that. Since the equipment is custom for each customer and each mine, the needs of the mine are the foundation for Bucyrus designs.

Milwaukee Manufacturing

During mining system production, Bucyrus encounters an obstacle unique to its industry--the inability to test a hilly assembled mining system before shipping it to the customer location, Due to the size of the machines, operational tests aren't practical at its South Milwaukee manufacturing facility. As a result, the firm only assembles and tests segments of each mining system at its manufacturing facility. Bucyrus actually fully assembles the completed mining systems for the first time at the mine in front of the customer. The firm must rely on the experience of its engineers and component suppliers to ensure that the individual component systems will come together.

From design conception to actual delivery of a dragline mining system, Bucyrus can deliver an operational system in the field in two years. This allows one year for manufacturing and one year for erection in the field (a much shorter timeline exists for shovels). Bucyrus rests on the shoulders of its suppliers to meet the delivery and quality deadlines for this schedule to ensure against assembly issues in the field.

At the heart of Bucyrus suppliers are the foundries. The OEM purchases 4000-5000 tons of castings per year, 90% of which are made in its proprietary low and medium alloy steels. However, Bucyrus is unique in today's OEM market in that is still purchases more than 900 of its castings in North America (even though 75% of its sales are from outside of the U.S.). While the firm says that it has "dabbled" in sourcing to offshore casting suppliers, it believes the continuous face-to-face communication and interaction at both its plant and at the foundry is critical to receiving quality castings.

"We have explored offshore relation ships, but they just don't produce the results we need at this time," said Terry Honeck, purchasing manager. Honeck cited lead-times as a prime concern with foreign suppliers as timeliness is critical to meeting customer needs. But Honeck said the decision relates to quality and reliability as well. "We are not a purchaser of high-production castings, Each of our jobs is more custom and we require constant communication to ensure the casting meets our specifications."

Bucyrus has developed its own vendor appraisal regimen that it fob lows for all casting suppliers. The foundries are rated for performance in areas as diverse as housekeeping, quality systems and accuracy, compatibility with Bucyrus alloys, delivery performance, warranty, reject/scrap rates, value-added capabilities and cost.

"We have learned that we must know our suppliers as well as they know themselves," said Honeck. "Ultimately, Bucyrus is responsible for their parts and the bottom line and we are better managers because of it."

Digging Castings

Maybe the best example of Bucyrus working with its casting supplier to improve' component functionality and cost is with a saddle block component for mining shovels. This component (Fig. 3) was originally designed as a casting and a fabricated plate that were welded together. One day the casting supplier--Buckeye Steel Castings Co., Columbus, Ohio (now Columbus Steel Casting Co.)--took a walk through Bucyrus' manufacturing operation and focused on the labor intensive efforts required to weld the fabricated plate and casting together. This weld experienced quality problems because the sections had to fit perfectly due to the stress the component undergoes in application as the pivot point for the shovel.

"The foundry proposed casting the component as one piece," said Maci. We said they were crazy and they proved us wrong."

The cast component's complex geometry and thick to thin transitions are what posed the difficulties. The 15,660-lb low alloy steel casting is cast in nobake sand molds and has sections its thick as 7 in. and as thin as 1 in. During casting, the foundry has to pay special attention to feeding these thick sections in the middle of the component. The redesign to a one piece casing resulted in a cost savings, as well as the elimination of defects due to welds

Figure 4 is a diagram of an electric mining shovel highlighting certain castings in application.

One supplier Bucyrus interacts with on a daily basis in both its plant and the foundry is Delray Steel Castings. Inc., Melvindale, Michigan. One casting this firm produces lot Bucyrus is a boom point sheave. This casting (Fig. 51, weighing 8000 lb, supports the cables lifting the dipper (which is what is used to pick up the mined material).

The complex geometry of the casting design has tight radii transitions between thick and thin walls. Another critical area of the design is the hub because, in application, it helps support the weight of the cables and the dipper when loaded with material.

The other two areas of the mining systems where castings are integral are the dippers and buckets that actually move the material for the shovels and draglines, respectively.

Dippers

Dippers (Fig. 6) are in essence the "shovel" at the end of the electric mining shovel that picks up the earth material from the mine site. Due to the constant abuse these components receive in application, they must he periodically refurbished on-site and have an expected life of 4-5 years. The focus in designing and casting components for dippers is impact strength, wear resistance and yield strength. More than 600,000 lb of force can be exerted on any single dipper when it lifts the material from a mining site, "anti this can be too much stress if there are too many welded points," said Jim Stanke, technical manager--dipper design.

"From the perspective of dipper engineering, forgings are just slabs of metal that you have to shape when you get them into your own shop." said Stanke. "With castings, we can couple our unique material property requirements co designs with irregular contours and shapes, increasing our products functionality."

The key in dipper (and bucket) design is to enhance material flow into it, ensuring the loading of more material in a shorter amount of time with reduced power. To achieve these characteristics, Bucyrus designs its dippers in a trapezoidal shape using lip angles (the area where the teeth on the front of the dipper are attached) that allow the teeth to efficiently penetrate into the digging face, ensuring free material flow into the dipper body.

While the functionality of the dipper design is critical, weight reduction plays a key role. As mentioned earlier, the less weight that is used to pick up material, the more material that can be picked up. Since the drive in mining is to reduce the cost per ton of material moved and moving more material in a single dipper supports that, Bucyrus pushes its dipper designs toward this end.

Critical to these innovative dipper designs are the castings make up the component's base and sides. While the number of castings per dipper can change based on design, it typically includes several low-alloy steel cast components, which forms the lower half. The upper half of the component is manufactured of plate steel due to the simplicity of the design.

Produced via nobake sand casting by Maynard Steel Casting Co., Milwaukee, the cast components' geometry when assembled has a curvature to it that reproves the breakout force of the dipper in application to increase fill rate. According to Bucyrus, the curved geometry is why the components are cast, as it "wouldn't be economically feasible to do it any other way." In addition, the cast components can achieve the necessary properties at a lower weight than a fabricated assembly.

Buckets

Buckets (Fig. 7) face ninny of the same issues as dippers in terms of the material properties required of the components in application and the weight reduction issues during design. But for the buckets, castings play a role in two areas--a one-piece cast lip at the front of the bucket and right and left clevis plate castings where the chains attach to the bucket.

These components (also produced by Maynard Steel Casting Co.) are expected to achieve critical properties that meet precise minimum requirements. Bucyrus works with the foundry to alter the low-alloy steel for these castings to ensure an increased impact resistance and reduced wear resistance due to the differing environment for buckets in application.

"Because of what we achieve in strength, geometry and shape, castings are the bread and butter of bucket design," said Michael Stolz, project engineer--bucket design. "We are able to put the metal where it is needed." According to Bucyrus, if plate is used for the lips of buckets, it would need to be at least 25% thicker, which would carry a weight and functionality penalty for the dragline mining system.

While geometry and weight reduction are the underlying reasons that the bucket components are cast, Bucyrus also points to how the teeth are assembled to the buckets (or the dippers) as another benefit of a cast lip. Without casting, an adapter would have to be welded to the front of the lip to provide a place to attach the teeth. With a cast lip, this mating point is as-cast.

Digging the Future

The demand for large mining equipment is extremely cyclical but after what has been a prolonged down period for mining machinery in the U.S., a turnaround year is expected this year. As a result, the forecast by Stratecasts, Inc. shows 9% increases in shipments of steel castings to the mining industry for both 2003 and 2004. This will be followed by long-term growth for shipments of carbon and low-alloy, manganese, martensitic-wear resistant and heat-resistant steel castings.

For Bucyrus, this should mean a shift in its sales breakdown. The firm's current sales are approximately 80% for replacement parts and 20% for new machines. In a positive economic cycle, these figures are closer to 50/50.

But this economic outlook has no affect on Bucyrus' outlook toward castings--the firm is in love and will continue to move the earth with them.

RELATED ARTICLE: Bucyrus digs the Panama Canal.

The French first tried to create the Panama Canal in 1879, but failed to accomplish the awesome task. In 1903, following Panama's declaration of independence from Columbia, President Theodore Roosevelt signed a treaty to resurrect the aborted French project to dig a 51-mile canal across the isthmus of Panama, in exchange for rights to the Canal zone.

Leading the way in the creation of the Canal was Bucyrus, who brought in 77 of its shovels and a dredge to help move the 232 million cu. yd of dirt. During creation, President Roosevelt visited the site, becoming the first President to leave the U.S. while serving in office. Reportedly, the President walked through the mud and leaped over ditches into a mammoth Bucyrus shovel to talk to the workers.

On May 20, 1913, two Bucyrus shovels advancing from opposite directions met, completing the Canal cut. The Panama Canal was finally completed the next year and has been hailed since as one of the greatest engineering achievements ever.

For More Information

"Steel Castings Handbook and Handbook Supplements," Steel Founders' Society of America (SFSA), Barrington, Illinois.

"Specifying a Steel Casting," SFSA website at www.sfsa.org