Texans examine aluminum.

In 1836, 189 Texans staunchly defended a San Antonio mission known as the Alamo against the raiding Mexican army until the very end. Nearly 160 years later, on April 7-9, 180 foundrymen gathered in San Antonio--just three blocks away from the Alamo--to make sure they will be prepared as changing technology creeps up on them.

Last held in 1991, the AFS Texas Regional reflected a newfound optimism for the Texas foundry industry, said Duane Spaeth, Tyler Pipe Industries. The last four years were difficult for the region's metalcasters, but this determined group, he said, is starting to see the light.

Sixteen speakers detailed induction melting, foundry maintenance, total quality, insulating ladle boards, ferrous charge materials, nobake molding, OSHA issues and how to sell castings. Although Texas is traditionally ferrous foundry land, this year's conference featured several aluminum presentations.

Mechanical Properties

Leslie Armstrong, U.S. Reduction Co., discussed what aluminum casters can expect in terms of mechanical properties. He informed attendees how aluminum is affected by different alloying elements:

Silicon--increases the fluidity of molten aluminum, decreases hot cracking tendency and solidification shrinkage, improves pressure tightness and reduces the coefficient of expansion.

Copper--improves the strength of alloys, reduces internal shrinks, improves machinability and decreases corrosion resistance.

Magnesium--provides improved strength and ductility, improves corrosion resistance and improves machinability.

Noting that castings have much more stringent requirements today, he said the rate of solidification is critical to mechanical properties.

Aluminum Treatment

Mike Webb, Canfield & Joseph, explained what a foundry can do to maximize properties. "With the nature of the foundry, there's something different every day," he said. "If you can't control it externally with chills, then you have to make the metal behave the way you want. Otherwise, your castings will be as random as snowflakes. You can chemically alter the energy required to start solidification by adding a grain refiner."

Added at the point of pouring, titanium boron alters the energy required to start solidification. Many heterogenous nucleation sites cause more grains to start. Therefore, he said, you'll have a more uniform dispersion pattern with more repeatable results--and be in control as to how the grain grows.

Discussing strontium modification, which is added 3-5 minutes before pouring, Webb said silicon generally forms in one direction. If left alone, silicon forms plates that result in a weaker plane. By chemically altering the melt with strontium, a fibrous structure is formed that breaks up sharp corners which are stress points. "It's very valuable because it helps make a pressure-tight casting," he said.

Strontium also finely dispenses hydrogen porosity. Without strontium, if shrinkage occurs, the gas migrates to the heavy section of the casting and forms in the dendritic structure.

Filters/Sleeves

Bob Pischell, Foseco, explained how combining ceramic foam filters and insulated riser sleeves can replace current runner systems.

He noted the importance of getting metal into the cavity in a nonturbulent fashion. Explaining that turbulence causes oxides, he described the beer glass effect. When beer is poured directly into the glass, C[O.sub.2] bubbles will result, or the beer's "head." By altering the flow of the beer into the glass (tilting), Pischell said, you can reduce the foam, or turbulence.

Naturally, ceramic foam filters can remove oxides from entering the casting. When used in the pouring system, they also have a dramatic effect on turbulence--acting as a shock absorber. The more you can do to keep a coherent stream, the better off you are in minimizing oxides and hydrogen.

Pischell also discussed using insulated riser sleeves. Most sand risers are oversized so the metal will keep liquid (thermal sink to maintain temperature). If sleeves are insulated, smaller sleeves can be employed that use less metal, while still providing proper solidification. Removing the runner system and associated risers saves cleaning room time, he said.

He noted combining these two developments are reducing metal consumption in foundries. "Foundries are not in business to make runner systems," he said. "If a mold doesn't make a casting that was shipped, the time and labor to make that mold wasn't profitable."

This method, he said, forces foundrymen to look at the costs. "But the money you save," Pischell said, "becomes profit dollars."