“Te foundry is nothing more than a logistics movement,” said vice presi- dent Tom Brown. When Benton Foundry brought in
a new 10-ton Inductotherm furnace in the 1990s, the casting facility opted to remove its existing cupola furnace to make room. “Logistically and long-term, it made the most sense,” Brown said.
“We didn’t want to build around it and fight it for the next 25 years.” Along those lines, Benton
Foundry engineered its molding operations in such a way that the line requiring the most metal was placed nearest to the furnace. “You want to keep your metal as
close to the largest use in the facility as possible,” Brown said. “We have a
IMPROVING ALUMINUM MELT QUALITY
If your metalcasting facility isn’t in line for a complete overhaul, improve- ments in melt treatment and mainte- nance procedures can be made with little capital investment and without major changes to the shop floor. In aluminum casting facilities, the presence of gas in the melt must be properly measured and controlled. In a 2005 study, Geoffrey Sigworth, Foseco, revealed improved melt treatment practices in U.S. metalcasting facilities had a considerable impact on aluminum tensile properties. Filtered and degassed castings showed a significant improve- ment over untreated castings. The use of a rotary impeller degasser for a longer degassing treatment further improved tensile properties (Fig. 1).
“The [test bars in the study] were of the same alloy, mold and heat treatment,” Sigworth said. “The only thing different is melt treatment. An eight-10-minute treat- ment can remove 80% of the porosity.” Sigworth recommends aluminum metalcasters invest in a good rotary impeller head that will produce small bubbles. Square, blocky heads do not work as well, he said.
In addition to degassing, flux or chlorine treatments can be used to reduce gas in your aluminum melt. When the bubbles from a small amount of purge gas come into contact with the metal, it forms a liquid salt. If the bubble bumps into an oxide, the oxide will stick to a salt layer and be removed with the bubble. Sigworth said some systems are designed for injection but perform degas- sing well, so it’s important for metalcast- ing facilities to make sure they have the best equipment for both functions. Metalcasters can control their melt treatment and quality with gas testing,
20 | MODERN CASTING April 2012
28 x 32-in. line that makes 1,000-lb. blocks of sand and takes up to 400 lbs. of metal per mold sitting right next to the furnace. We moved the 20 x 24-in. machines further down, and the manual machines are at the tail end because they represent 2.5% of the business and use the least amount of sand and iron.” Benton Foundry applied logistics
Furnaces should be well sealed with a tight-fitting cover to keep out air, which can cause oxidation in the melt and lead to slag.
according to Dan Groteke, Q.C. Designs, St. Joseph, Mich. “The higher the service of the application, the higher the risk and more testing that is required,” Groteke said. Along with chemistry analysis reports, stress and strength tests, reduced pressure testing can be used as a means of metal control.
“Most operations run reduced pres- sure testing, but not as a control,” Groteke said. “Foundries use it as a visual test, which is subject to error, and then don’t do much with the information.” Metalcasting facilities can use reduced pressure testing to hold density, which is a reflection of gas content and metal quality, within a certain range, Groteke said.
Proper furnace maintenance also is critical to efficient melting.
“Good furnace practices, such as maintenance, repair and probably some- thing in the way of dross recovery are important,” Groteke said.
According to Sigworth, casting facilities should adhere to a regular furnace cleaning schedule that is set according to type of furnace, volume of metal and alloy.
“Aluminum is very reactive, and the oxides in aluminum are heavier and denser than the metal, especially in magnesium-containing alloys,” Sigworth said. “If you don’t do a good job cleaning, it will collect in the bottom and end up in your castings.”
Furnaces with hydraulic lifts for tilting allow for easy cleaning, Sigworth said. “Those furnaces are more expensive, but worth the money, in my opinion.”
Fig. 1. Advanced metal treatment significantly improves aluminum material properties.
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