This page contains a Flash digital edition of a book.
Fig. 3. Shown is the surface finish of a test casting produced using 100% new domestic olivine sand.


Fig. 4. A blend of 75% new olivine and 25% new silica sand produced a slightly dull surface finish with a few small sand particles adhering to the surface.


Fig. 5. A blend of 50% new olivine and 50% new silica sand produced castings with a smooth surface finish and no pinholes.


Fig. 6. Test castings produced with 100% new silica sand exhibited a clean surface with some adhering sand.


sand is widely and safely used in metalcasting facilities throughout North America, transitioning from olivine to silica does add risk of exposure. “Te hazard in a nonferrous shop is less than it would


be for a ferrous shop,” said Gary Mosher, senior managing scientist for Exponent, Menlo Park, Calif. “But there still can be a hazard there.” Mosher said those facilities shifting from olivine to sil-


ica will have to institute a silica monitoring program along with some added administrative work to keep monitoring records. Some operation procedures and equipment—such as the type of respirators being used—may need to be changed. And switching to silica could change how work- ers’ compensation insurance carriers view the operation. “There’s a lot of nonferrous shops using silica sand.


Switching from olivine can be done,” Mosher said. “But you still have to use caution. It’s not a huge risk, but they will now have a risk where they didn’t before.”


Biasill as Replacement Biasill, which is a slightly finer grade of staurolite sand,


has a low coefficient of thermal expansion and high ther- mal conductivity with an AFS grain fineness number of between 66 and 75 (Fig. 8). “Staurolite is a naturally occurring mineral from Florida,”


LaFay said. “Its unique characteristic is its high density, which gives excellent brass and aluminum casting characteristics.” In a recent test of Biasill, reported in the paper, “Alterna-


tive Molding Material Used in Nonferrous Metalcasting,” by LaFay, Morrison and Charles Rowe, Carpenter Broth-


Fig. 7. A mature 100% silica sand system produced castings with superior surface finish to those produced with 100% new silica sand.


ers Inc., molding properties and resulting castings produced with olivine and Biasill were compared. Casting inspections during the trials showed little to no difference between cast- ings produced with olivine molds vs. Biasill molds. Te round grain shape and higher density of the replacement aggregate appeared to provide comparable surface finish and casting quality to olivine. Molding sand properties between the two sands were


fairly similar with the exception of permeability and density, which did not affect casting quality. However, the higher density of Biasill results in heavier molds. “Biasill is a viable option, but it needs further testing,”


Morrison said. “Most of the metalcasting facilities we have tried so far were squeezer shops, who were worried about the molds being heavier. But we have customers who have found success with it.”


December 2012 MODERN CASTING | 23


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60