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Reclamation & feeding explored.

As in all casting methods, researchers are looking for ways to improve reclamation and feeding systems in investment casting.

Presenting a paper on the possibilities of investment shell materials reclamation for this year's Casting Congress was T.M. Peters, University of Missouri-Rolla. Typically, ceramic components of investment casting shells are used for only one cycle of shell production and then discarded. He found that of the three main investment shell compositions, two can be recovered and reused.

Peters discovered that aluminosilicate stucco reclamation, a major component of many investment shells, can be recovered in a form suitable for reuse as backup stucco.

Zircon can be concentrated in an impure form, and subsequent caustic liberation treatments can remove the intermixed silica phases. Size and quantities, however, are disadvantages in processing. Reuse of such zircon in investment casting is possible but requires careful qualification testing, he said.

Fused silica, the most widely used shell material, isn't reusable because thermal cycles during investment casting cause significant fractions of the amorphous material to crystallize. Crystalline silica also isn't reusable for investment casting.

Mineral processing methods are capable of producing concentrates of various shell components. Recommended processes of reclamation are roll crushing, screening, gravity settling or heavy medium separation.

Covering the problems associated with investment casting feeding, T.V. Rama Prasad, PCC Airfoils, Inc., Cleveland, and V.Kondic, University of Birmingham, Birmingham, England, conducted a landmark study for providing a general solution of feeding system design in casting processes.

The root of feeding problems begins at pouring, when alloys begin to shrink in volume as they cool. Feeders freeze slower than the casting, thus allowing some of the liquid in the feeders to flow into the casting toward the area where shrinkage is taking place. By identifying and correlating the processing factors that control the feeding processes for various alloys, shapes and molds, feeding problems can be controlled, the authors said.

The solution for a complete feeding system design must focus on dimensions, shape, location, method of attachment of feeders to the casting and selection of materials used for feeder walls, Rama Prasad and Kondic stated.

They believe a feeding system for combined cooling of the casting and feeder can be designed to eliminate shrinkage or control the shrinkage volume cavities left in the solid casting. Rama Prasad and Kondic included an outline for designing feeding systems and calculating feeder dimensions.
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Title Annotation:96th AFS Casting Congress Milwaukee; core materials in metal casting
Publication:Modern Casting
Date:Jun 1, 1992
Words:396
Previous Article:Material changes emerging.
Next Article:Sand reuse heads discussion.
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