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Table 1. A Comparison of Sand Properties of Silica, Biasill and Green Diamond Aggregates Affecting Metalcasting Operations


used olivine sand first. But choosing which option would work best in an individual metalcasting facility is not as clear cut. Tables 1 and 2 provide side-by-side comparisons of silica, Green Diamond and Biasill. “Te choice is customer specific,”


said Jay Morrison, technical sales rep for Carpenter Brothers Inc., Norton Shores, Mich. “Every customer wants different things, so it comes down to what matches up the closest to what they want.”


Green Diamond as Replacement Metalcasters use olivine sand for a


combination of reasons, including its fine surface finish characteristics, ther- mal expansion properties and elimina- tion of health risks associated with silica sand. When Pride Cast Metals, Cincinnati, found out it would need an alternative to olivine at its aluminum and brass casting facility, it looked for an alternative that would meet certain specifications it had set out to meet two decades ago, when it originally switched to olivine. “We were running olivine for a


purpose,” said Gregg Hamm, vice president of manufacturing for Pride Cast Metals. “First, for health reasons. With olivine you don’t have a concern with silicosis. But we wanted it for its surface finish qualities, too. We do a lot of parts that require a fairly fine finish.” Pride Cast Metals selected Green


Diamond as its replacement aggregate (Fig. 1). Green Diamond is a manufac- tured, silica-free specialty sand out of the U.S. west coast with similar thermal expansion properties to olivine sand. According to LaFay, metalcasters can put Green Diamond into their existing molding sand, slowly replacing olivine until the system is completely based on the new type of aggregate, which was the experience at Pride Cast Metals. “We’ve been using Green Diamond


for a year and a half,” Hamm said. “We have experienced no problems.” But Hamm points out the sand might not be right for other shops, with different requirements from its sand and molds. “It works here, because I like a fine sand for a good surface finish,” he said.


Casting Quality*


Intersection point where alternative sand becomes dominant over olivine


Silica Sand Good


Biasill Good


Bulk Characteristics* (decrease is preferred) Slight increase Slight decrease 25%


50%


Moisture requirement* (decrease is preferred) Aggregate for core sand production *Compared to olivine sand


Decrease Preferred


Decrease Unknown


Green Diamond Good


Similar 35%


Similar Unknown


Table 2. A Comparison of the Green Sand Molding Properties of Silica, Biasill and Green Diamond


Mold density* (lower is preferred)


Moisture requirement for desired compactibility* (lower is preferred)


Green compression strength* (higher is preferred)


Wet tensile strength when using preblend* (higher is preferred)


Permeability* (higher is preferred)


Dry compression strength* (higher is preferred)


*Compared to olivine sand


“But Green Diamond does not have a wide range of sands. You are limited. It matched the type of sand I was using. I also liked that my supplier offered a pre-mull sand, because I’m running a special bond.”


Hamm was using 120 olivine sand


from North Carolina and LA 100 from the west coast. According to Hamm, replacing that with Green Diamond, which he did while also converting to a proprietary organic free preblend, was seamless. During the transition, Pride Cast Metals ran various tests to keep track of how the changes affected mold quality. Te company’s experiences will be pre- sented in a technical paper at the AFS Metalcasting Congress and CastExpo ’13 in April. Hamm noted the only two green sand molding properties that changed when Green Diamond was added to the system were lower permeability and wet tensile strength, but neither change resulted in negative casting-related issues.


Silica as Replacement


In some cases, silica sand makes a suitable alternative to olivine, and several metalcasters have already made the switch, according to LaFay. “Te primary base aggregate substi-


ONLINE RESOURCE


Visit www.moderncasting.com to view research work on the olivine replacement methods discussed in this article.


December 2012 MODERN CASTING | 21


tute is silica sand, which is commonly used in molding operations for green sand,” he said. “Many foundries have successfully gone in that direction and are very close to completing a com- plete conversion from olivine.” Because core processes use silica sand in production, switching to silica sand for molding gives metal- casting facilities the added benefit of using the same aggregate for both core and mold making. According to a 2012 research paper


authored by LaFay, Stephen Neltner, S&B Minerals, Mark Ziegler, Uni- min Corp., and Jerry Tiel, Univ. of Northern Iowa, two silica sands mined and processed in Oregon, Ill., and Roff, Okla., exhibited similar casting characteristics to olivine sand in cast- ing trials (Fig. 2). In the tests, castings produced with 100% new olivine sand exhibited a smooth, clean surface fin- ish with a small proportion of shallow pinhole surface imperfections. Test


Silica Sand Lower


Lower Similar Higher


Higher Lower


Biasill Higher


Lower Similar Higher


Higher Lower


Green Diamond Similar


Similar Similar Higher


Lower Similar


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