The key to EPC's future: refining technology.

With a theme of "Managing the Technology," more than 150 foundrymen conferred in Birmingham, Alabama, on September 21-23 to share technological advances and experiences in improving the expendable pattern casting (EPC) process.

Also known as the lost foam process, EPC celebrates a milestone in 1994--the 30-year anniversary of M.C. Flemings' use of unbonded sand with the full mold process.

With a large contingency of foreign delegates, the conference was truly international. Visitors hailed from Australia, Belgium, Canada, Germany, Korea, Mexico, The Netherlands, Turkey and the U.K.

Through 23 speakers and eight exhibits, foundrymen learned of case studies, market assessments, design requirements and defect identifications on the EPC process. They also spent a full day seeing the process in action, at Citation Foam and Vulcan Engineering's Development Center.

"EPC is a value-added process, not a substitute," said conference Chairman Bruce McMellon, Vulcan Engineering. He said if you don't follow the four rules below, "... you'll be one of the well-storied failures you often hear about." The four rules are:

* Design for the process--you can't take an existing part and convert it.

* Do the tooling right--don't shortchange.

* Do equipment right--"We're way beyond the 5-gallon buckets and vibrators," he said. "To do it correctly, you need the right equipment. Don't experiment to see if the process works."

* Control the variables--If you don't, this process will be your worst nightmare.

Defect Identification

In a panel on defects, Raymond Donahue, Mercury Marine, covered three ways defects arise in EPC: lack of permeability control, using hypoeutectic Al-Si alloys when high-cycle fatigue properties are needed, and dimensionally incorrect parts.

The EPC process can engulf and trap foam products of melting and or decomposition, which can create folds. Ironically, he said, the foam problem is also its advantage--allowing the controlled filling of casting with less turbulence.

"System permeability," Donahue said, "is the key to being successful in EPC."

He explained the opportunity for defect-free castings by controlling permeability from the sand side of the metal/coating interface with vacuum assist. He said this advancement allows the highest quality castings to be made at the lowest possible manufacturing costs.

James Flanagan, Babcock and Wilcox Co., noted the challenging job of control in EPC. He pointed out his foundry's problems of foam quality and how its density changed without the firm's knowledge. Because speed (gas evolution) is critical, pouring speeds were tracked. Today, the foundry follows specific recipes for each casting produced, with parameters set for temperature, vacuum, volume of pumps, number of molds and line speed.

Mold Filling

Ron Walling, Cummins Engine Co., and Jonathan Dantzig, University of Illinois, built an experimental flask to directly observe mold filling through a pyrex window.

They discovered pattern elimination occurs by different mechanisms for aluminum and iron. When aluminum is cast, the pattern melts and the cellular structure collapses, and little depolymerization occurs in the mold.

When iron is cast, the pattern still melts and collapses, but the process occurs faster and more depolymerization occurs. More gas is produced by the pattern when iron is used.

Walling and Dantzig also found more heat is required to eliminate the foam pattern at the high temperatures used during the casting of iron than at the lower temperatures of aluminum.

Solving Variability

Terry Cleary, Mercury Marine, discussed a breakthrough his foundry discovered when examining its variability problems with EPC. Perplexed by the variation problems, officials closely studied all aspects of the process.

After reaching no conclusions, the foundry began using chromite sand for casting hypereutectic aluminum alloys and studied its results with silica sands.

"The results were amazingly different," Cleary said. "Quartz silica sand has a rapidly increasing coefficient thermal expansion. It is the most unstable of all media used."

They investigated fused silica, mullite, silicon carbide, carbon sand and chromite sand, and all were improved over the quartz silica. After running two days of production with carbon sand, the results for the material were excellent, he said.