Pier Foundry converted a complex 34-piece weldment to a single ductile iron casting that saved its mining customer time and money.

Nicholas Leider, Associate Editor

(Click here to see the story as it appears in the July/August issue of Metal Casting Design & Purchasing.)

In early 2013, a manufacturer of industrial mining fans in the Western U.S. explored the possibility of converting a hub in a ventilation fan from a weldment to a casting. Originally a 34-piece steel fabrication, the component faced a demanding environment in a mining operation where it rotates as fast as 3,600 RPM.

The customer’s engineers identified the component as a potential conversion because each fabrication required 11 hours of in-house labor for machining and welding. The customer, however, was relatively unfamiliar with the variety and demands of casting processes. It uses a few cast components, primarily the aluminum blades that attach to the hub. But those designs have remained relatively unchanged for decades, limiting the customer’s current engineering team’s experience with castings.

The fan manufacturer partnered with Pier Foundry & Pattern Shop, St. Paul, Minn., to supply what would become a one-piece ductile iron casting. After a six-month collaborative effort that included a number of design iterations and simulations, the metalcaster delivered sound castings via its green sand molding line that led to significant benefits for the customer. The casting conversion reduced costs by more than 30%, saving the customer a projected $41,000 in the first full year of production.

Additionally, the fan supplier has increased shop capacity because the castings are delivered ready for assembly, allowing sawing, machining and welding resources to be used for other assemblies. Since the successful collaboration on this first mining hub, Pier and its customer have begun exploring conversion possibilities in other size ventilation units, and the two expect to increase collaboration in the future.

Casting Crash Course

Although the fan manufacturer’s engineers knew the complex weldment was a good candidate to be converted to a casting, Pier Foundry faced a challenge in educating them about design considerations unique to metal castings.

“They are not buying a stock item off a shelf,” said said Duane Rice, sales specialist, Pier Foundry. “There is a well-defined process from design through production and delivery. We need to understand their design intent and what’s critical to them, so we can provide the best product at the lowest price. When converting to a casting, you are starting with a clean slate. You don’t necessarily want to recreate the weldment.”

To ease collaboration between the two design teams, Pier Foundry started off with a “Casting 101” course for the customer’s mechanical engineer.

“The company was relatively new to castings,” said John Dulaney, sales and engineering manager, Pier Foundry. “They virtually had no experience with what it takes to make a good casting: fillets, feed paths, draft—all of those considerations. Once they got through a bit of initial instruction, their designer provided the first version of what they would need to meet fit, form and function.”

Though relatively new to metal castings, the customer’s design team used the crash course in metalcasting to ease its transition to the new process.  

“Pier helped us develop a greater understanding of designing for metal castings,” said the buyer’s mechanical engineer. “They were easy to work with.”

The casting design featured a number of isolated sections, including the 10 spokes emanating from the central hub. The varying thick and thin sections required a number of iterations from the Pier team to ensure proper feeding and maximize casting yield.

While aiding in design to improve castability, Pier Foundry deferred to the customer for finite element analysis to ensure the design would hold up to the rigors of the mining application. The customer, meanwhile, allowed Pier Foundry to concentrate on casting-specific design considerations.

“For the most part, I designed the product to do what we needed and to hold up to the constraints we put on it,” said the casting buyer’s mechanical engineer. “They then let me know what was possible and if you could pour metal into something of that shape. I wanted Pier to add draft angle and handle the other requirements for castings.”

Pier Foundry relied on its simulation software to provide verification that the casting’s gating and riser design would lead to sound castings. Pier then produced the necessary tooling for the coreless green sand mold. After passing Pier Foundry’s internal testing for soundness, the castings were shipped to a local contractor for machining and painting before the customer received hubs that were ready to be assembled, balanced and installed in the ventilation system.

Realizing the Benefits

The casting conversion reduced overall manufacturing costs 30% by simplifying the component from 34 pieces of steel that required sawing, rolling, machining, fit-up and welding to a single casting. Such a savings is significant, but the benefits extended beyond the bottom line.

“It’s not just about saving money, it’s also about freeing up time to do more value-added things, like adding assembly capacity and selling the product,” Dulaney said.

The casting also performed above expectation when the customer’s engineers put the component through an intense series of tests.   

“It’s supposed to last forever and that’s what our customers expect,” said the customer’s engineer. “I did a lot of destructive testing when we received the castings. We built the hub into an impeller and fired steel rods at it. We couldn’t break the thing. We haven’t had them in the field for 10 years yet, but from our testing we believe they are plenty capable.”

The casting conversion also improved performance related to the adjustable blades on the outside of the hub. The original weldment had a flat outer edge, which created a gap between the blade base and hub when the blades were rotated. With the casting’s spherical outer surface, now the blades can rotate while remaining tight to the hub.

“In the weldment, where the hub was cylindrical, you had a big gap when the blades are at a low angle,” the customer’s mechanical engineer explained. “Now we can curve the blades’ tails to match the outside of the hub, which helps with the performance of the fan.”

Because the manufacturer produces ventilation systems in a wide range of sizes, the two firms have started to explore changing more hubs from weldments to castings. In addition to the lessons learned in this case, Pier’s time spent instructing the customer on the casting process continues to pay off.

“Now that they’ve been through this first casting design, it will open a lot of doors for them,” Rice said. “They are looking at upcoming projects to see if there are casting opportunities right off the bat. It has opened their minds to a completely new process for their product.”