Improving Sand Performance.

This year's Molding Methods & Materials Div. provided 16 presentations. Covering a broad range of topics, improving sand and nobake system performance was on the minds of all.

In a presentation by D.A. Neill, F.S. Cannon and R.C. Voigt, Pennsylvania State Univ., J. Furness, Furness-Newburge, and R. Bigge, Wheland Foundry(01-077), case histories of foundries using advanced oxidation (AO) techniques were explored. AO systems have been installed on green sand systems at five U.S. foundries since 1996. According to these foundries, they have experienced a decrease in the amount of clay, seacoal and new sand additions to their sand systems while decreasing or maintaining unchanged levels of scrap since installing an AO system. In addition, their sand systems have seen an increase in green compressive strength and muller efficiencies above the necessary levels, presenting an opportunity to diminish the premix feed rate into the system.

AO clarifier black water systems allow foundries to segregate active clays and seacoal from undesirable silica fines so that these active clays and seacoal can return to the sand system while the sand fines and dead clays are disposed. The system uses an AO process that generates reactive radicals and highly oxidized species such as ozone, which, when combined with the blackwater system, can degrade, breakdown and or mineralize organics at low temperatures. In essence, it cleans recycled foundry sand to allow mold additives to better adhere to the sand grains. These systems also have facilitated more effective extraction of active clay from the dust of wet collectors or baghouse collectors. The clay is returned to the green sand system via the black water, diminishing the makeup levels of both new sand and premix (clay, seacoal and additives).

Presenters highlighted one high-production foundry that installed an AO system and saw its premix addition drop from 140-150 lb/ton of metal poured to 110-120 lb/ton, while total new sand consumption dropped from 520 lb/ton of metal pour to 325 lb/ton. Concurrently, average green compressive strength rose from 24-29 psi to 30-32 psi, muller efficiency rose from 57-63% to 65-68%, total scrap rate dropped up to 34% and sand-related scrap dropped up to 19%.

A presentation by J.M. Werling and S.G. Baker, Indianapolis Casting Corp., titled "The Effects of Humidity on a Phenolic Urethane Cold Box System (01-033)," detailed conclusions based on work performed at their foundry to eliminate a humidity problem.

"High humidity on a phenolic urethane coldbox resin system has a detrimental effect on a foundry core system," they said. "The cores begin to degrade as moisture accumulates on or is absorbed into the core or core wash coating."

Beyond the effects of humidity, the foundry also evaluated the cores and the individual constituents that make them up to determine if they absorb or resist moisture.

The results established by the presenters detailed a direct relationship between humidity and core tensile strength with the resin, anti-veining agent and corewash used by the foundry. This results whether or not the core is coated with wash. When measuring the individual constituents of the core, each constituent's ability to absorb humidity, when added together, exceeds what the core can absorb. This is due to the density and lack of surface area of the core produced by the foundry.

According to the presenters, the study confirmed the theory that moisture degrades the sand's binder to binder and sand to binder bond. The moisture attacks these bonds and weakens and softens them depending upon the duration they are exposed to the moisture. Once the moisture has had an effect, the core only can regain a portion of its original strength even if the moisture is expelled because the bonds already have been damaged. The cores are damaged because the moisture reacts with the part II of the bond, causing the bond to become a gelatin.

V.S. LaFay, S.T. Neltner, R.J. Wellbrock and D.E. Arrowood, Hill and Griffith Co., discussed a recent investigation to determine the significant differences between the various sources of cellulose consumed in the foundry industry (01-001).

The goal of many investigations is to differentiate one material from another to determine which is better for use. In the case of this investigation, the researchers were surprised to find that all the cellulose materials tested--ground oat hulls, peanut shells, com cobs and wood flour--can be added at the same level in either preblend or individually and produce a quality mold. The gas evolution studies verified that each of the materials will contribute the same gas levels. In addition, each of the materials will not contribute to the nitrogen "fissure effect" as long as the wood flour is from a hard wood source.

In other presentations, topics covered included core venting, mold dimensional changes, investment casting modeling and mold by-product decomposition.