Tons of reasons for a new welding positioner

Figure 1The electric shovels P&H Mining manufactures, such as this one loading copper-bearing ore into a material hauler, can weigh up to 1,200 tons. The dippers on the largest trucks can gather up to 100 tons of material in one swoop. Photos courtesy of P&H Mining Equipment, Milwaukee.

Fabricating an electric shovel with a working weight of 1,200 tons is no small feat. For P&H Mining Equipment, however, it's no big deal. The Milwaukee company has been making metal components and assemblies since 1884, when Alonzo Pawling and Henry Harnischfeger first opened their machine shop. In 1930 it was one of the first companies to move away from heavily riveted cranes and excavator products in favor of an all-welded approach. That reduced the weight of the equipment and delivered stronger machines, which in turn helped construction and mining companies reduce their cost-per-ton performance.

Almost 80 years later those types of companies still are looking to reduce operational costs. The only difference is the stakes are a lot larger.

That's led to the development of P&H's large electric shovels (see Figure 1), the largest of which is equipped with a dipper that can gather up to 100 tons of material and release it into the bed of a heavy-duty hauler every 30 seconds. P&H also manufactures "walking draglines," which have a working weight of nearly 6,000 tons and use giant buckets to move as much as 135 tons of material per dig cycle in coal mining operations. In short, manufacturing mining equipment is a big business. (See "Just How Big?" sidebar to learn more.)

It also requires big manufacturing tools, and relying on 1960s-era equipment to manufacture these modern metal mining monsters proved to be a problem at P&H.

Setting the Table

P&H considers welding to be one of its core competencies, according to Mark Dietz, P&H's manager of public relations. It regularly uses submerged arc welding, flux-cored arc welding, and gas metal arc welding to fabricate its mining equipment. All welders are certified with AWS D1.1, D14.1, D14.3, B2.1, and MIL Spec 248D.

In Building 171 on the company's Milwaukee manufacturing campus, an old positioning table didn't provide much assistance to the welders. As the equipment components had grown larger over the years, the table did not have the capacity to handle the "car bodies" that were the base for the P&H electric mining shovel (see Figure 2a). The car bodies support the shovel crawler frame and the belt assemblies (see Figure 2b) and act as the platform for the shovel's revolving frame and body. Without the car bodies, the electric shovels couldn't operate (see Figure 3).

The table had to remain in a fixed position—it could not rotate or tilt when a component was attached. This could prove troublesome for welders who didn't have the luxury of moving the extra-large components to a position most beneficial for manual welding processes (see Figure 4).

In late 2008 P&H decided it didn't want to be stuck with its positioning problem anymore. It had been in communication with Koike Aronson Inc./Ransome, Arcade, N.Y., sporadically over the previous few years about perhaps replacing the table and finally made the decision to purchase a new one.

Building the Table

Koike is no stranger to building welding positioning tables. It routinely builds several each year—from 100 pounds up to 1,200 tons. This job was challenging in the sense that P&H had included height restrictions in its specs for the positioning table.

"Normally it would have been higher, but because of the crane height, we could only stay around a 10-foot height," said Koike's Don Burgart, welding product manager.

Figure 2(a) and (b) These illustrations show the car body weldment, which is the heart of the electric shovel's lower structure, and how it is the means of support for the shovel's frame and belt assemblies.

The table had to have a rated capacity of 244,000 lbs., enough to accommodate P&H's 4100BOSS car body, and would be about 20 ft. wide and 10 ft. deep. Burgart said it was a traditional positioner design—with the large table, trunnion, and base frame—just on a much larger scale.

"At Koike, we manufacture our own gearboxes. They were 5 ft. tall for this project," Burgart said of the four boxes fabricated for the table.

Thanks to recent investments in large machining centers, Koike was able to handle about 95 percent of manufacturing for the table in-house, according to Burgart. That control over the manufacturing process helped the company deliver the positioner within its stated 24-week lead-time, which took into account time needed to receive large bearings from an outside supplier.

At P&H welding team leaders were preparing the foundation for the new positioning table. The positioner foundation is 10 ft. wide by 18 ft. long by 12 ft. deep, and the turning pit is 13 ft. wide by 33 ft. long by 10 ft. deep. About 280 yards of concrete was poured to construct the foundation and the pit.

Putting the Table to Use

The positioning table was delivered to P&H in late summer (see Figure 5). Like P&H's electric shovels which are shipped as components, the positioning table arrived in Milwaukee in two sections. Installers had to bolt the base to the ground, finish the electrical work, and bolt the table and tilting axis to the base.

Dietz reported that P&H's manufacturing team is in a better position to handle the large car bodies now (see Figure 6) and push them through the welding operation at a much faster rate. Not only is the new table able to move in ways that the old table could no longer, the positioner also has a cordless remote that has proven useful for welders looking to make a quick adjustment to the table.

P&H estimates that its equipment products are used in nine out of 10 surface mining operations in the world, and this one table will enable the company to keep up with that robust customer demand.

Figure 3The electric shovels are so large that they are shipped as components and assembled at the work site.