Sand reclamation issues under study.

Victor LaFay, participant in several molding methods and materials technical presentations at the 1991 Casting Congress, said many steps are involved in the metalcasting process, but sand remains one of the key elements. LaFay, an engineering executive with The Hill & Griffith Co., reported that sand conditioning and reuse are assuming greater foundry operations attention as raw sand costs rise and as costs directly related to sand disposal shoot up. Sand reclamation is an option more and more foundries are taking as a hedge against potentially crippling charges.

The problems of obtaining new sand and disposing of waste sands are not confined to the U.S. German reclamation efforts were discussed in a paper (91-22) prepared by S. Wesp and W. Englehardt, Mercedes-Benz AG. The paper described a core sand reclamation system developed and refined in the last decade.

After three years of reclamation, one influence on costs of the reconditioning system is heat recuperation used to heat the company's buildings. The economics of sand reclamation become evident when one considers a Mercedes comparison: fresh sand (including freight and dumping charges) runs $98/ton; reclaimed sand (including utility costs, plant operating burden) costs just over $43/ton.

A new process was reported in a paper (91-110) prepared by J. Basoms and W. Rossbacher of Acme Resin Corp. The process substantially reduces the binder-induced odor and fume levels produced during mold and coremaking operations. The process uses low-odor, resin-coated sands specially developed for the foundry industry and is particularly suited to shell molding. The sands contain no formaldehyde and only about one-third the hexamethylene of conventional resin-coated sands.

Other reported advantages of the new low-odor sand include: shorter core and mold cycle times, improved peel-back resistance and a reduction in casting defects related to veining and nitrogen.

Modern green sand controls were the subject of a paper (91061) delivered by R. Green of AIMCOR. He discussed green sands characterized on the basis of clay level, green strength efficiency, system processing efficiency and moisture index. Clay levels include clay-poor, clay-rich and the transition between the two.

Green strength efficiency and system processing efficiency classify sands somewhere between moisture-starved and moisture-saturated. The contributions of additives (such as cereal or fireclay) to alter the classification and control were described. When the sand is accurately classified, the paper concluded, the control parameters that cause it to behave consistently then can be specified.

A paper (91-032) delivered by M. B. Krysiak of George Fischer Foundry Systems, Inc. stated that the formulation and process technology for chemically bonded sand systems has advanced dramatically in recent years. Unfortunately, resin-bonded sand testing technology has not kept pace.

While conventional dog bone' tensile testing continues to be the most applied form of resin-coated sand process control, it is a crude means of measuring strength characteristics. This testing method is ineffective in gauging humidity degradation, and lacks the ability to provide reproducible data to correctly monitor critical physical and process parameters.

The focus of Krysiak's presentation was the comparison of European-type disk core abrasion tests with the U.S. "dog bone" standards as a means of comparing resin binders relative to measuring strength, resistance to humidity degradation and to show how refractory coating, when applied to resin-bonded sand, can affect the binder's physical strength.

A technical paper (91-20), written by H. Shriver, K. Barnett and J. Archibald of Ashland Chemical Co., discussed the free radical cure (FRC) mechanism for acrylic epoxy binders and described how virtually all types of cores and molds, previously made in other coldbox or hotbox processes, have used the FRC process successfully. The process has reportedly improved core handling strength, storage properties, erosion resistance, dimensional accuracy and shakeout. It consists of a two-part liquid binder cured with SO[sub.2]

LaFay and Krysiak, in their presentation (91-044) on counteracting the effects of core sand dilution in green sand molding, discussed sand brittleness, friable edges and inclusions as defects that don't always show up in routine sand tests. They recommended friability tests in a squirrel cage to test for surface properties, a cone jolt toughness test to determine the ability to draw a deep pocket, and a sand micrometer test to determine plastic (deformation) characteristics. Proper testing can discover the effects of condensation poisoning by foreign organic compounds.

The effects of rebinding were discussed, including how the graphite coating of sand can interfere with the clay-bonding of core sand. Without a graphite residue, it is possible to reduce the amount of new sand addition. it was recommended that binders that leave a graphite residue be avoided.

In a panel on core handling practices, T. Sandhu, Ford Motor Co., said proper sand mixing can add to core quality. He also reviewed core storage practices and coremaking procedures that aid core support during handling and storage.

L. Simpson of Caterpillar, Inc. discussed and illustrated proper core support and handling, the design of core lift fixtures, ways to effectively apply core wash and methods to extend core shelf life.