Examining Bentonite, Seacoal's Role.

The increased environmental regulations and pressure to reduce costs has forced foundries to revisit their "tried and true" molding practices in hopes of improving the process. For the Molding Methods & Materials Div.'s 18 presentations at this year's Congress, the theme is improvement--in cost, quality and environmental impact.

In their presentation (046), R. Wellbrock, S. Neltner and V.S. LaFay, Hill and Griffith Co., and D.N. Taulbee, Univ. of Kentucky, discussed the application of mass spectrometry as a technique for monitoring the kinetics and extent of decomposition of seacoal and seacoal supplements (anthracite, gilsonite, causticized lignite and ground coke) during metalcasting. In addition, the study reviewed mulling properties of the seacoal supplements and the selection of the materials in a preblend. The testing for this study was performed at the Casting Emissions Reduction Program foundry and the Cast Metals Institute.

According to the presenters, mass spectrometry was an excellent method of simultaneously determining multiple decomposition by-products of seacoal and seacoal supplements. The key, however, is a controlled testing environment to verify the percent reduction of decomposition by-products.

According to the presenters, the study was able to achieve a 50% reduction of decomposition by-products with a blend of anthracite, seacoal and gilsonite. In the future, these materials will become vital ingredients in a preblend. It is critical, said the authors, that when developing preblends for reduced emissions, all of the additives are taken into account. Some additives, although higher in decomposed by-products, are critical to metalcasting. For example, gilsonite, which had the highest amount of decomposition by-product, is critical to enhance the "casting peel" during shakeout.

The last conclusion of the presentation was that the alterations in seacoal and seacoal supplement amounts to reduce emissions will have a minor effect on the mulling/water requirements of prepared molding sand.

In their presentation (060), L. LaForest, Brillion Iron Works, H. Galloway, Unimin Corp., and A.P. Volkmar, consultant, discussed the results of their effort to reduce benzene emissions during 4 years of production at Brillion. This presentation was an update of a 1997 Congress presentation. During the last half of 1997, further study was performed on six different preblends to determine the effect that individual component changes have on benzene emissions. According to the presenters, it was determined that reducing the seacoal addition to molding sand was the easiest way to reduce benzene emissions. The problem was that reducing the seacoal caused problems with the casting peel, resulting in more sand adhering to the castings. This causes a variety of problems throughout shakeout, cleaning and finishing.

According to the presenters, the decision then was to raise the seacoal addition and try incremental drops to determine the effect on both benzene emissions and casting peel. After several trials with preblends that contained seacoal amounts from 0-25%, it was determined that seacoal percentages of 9-15% provide the lowest benzene emissions (0.009-0.01 lb/ton iron) with the best casting peel at the test facility.

In a presentation on the application of the fibrous bonding mechanism to reduce bentonite dosage (122), S.K. Kowatra and S.J. Ripke, Michigan Tech Univ., focused on improving the application of bentonite to reduce the amount required in molding.

The theory behind the study, said the presenters, is that if bentonite dosages to molding sand could be reduced by using it more efficiently, a significant cost savings would result for foundries. Furthering this, if the binding mechanisms of bentonite can be completely understood, then procedures can be developed to use bentonite more efficiently.

According to the presenters, bentonite bonding theory is based on the behavior of bentonite at low percent solids and high mixing shear rates. Under these conditions, bentonite expands, disperses into platelets and dries into a bonding "film" or "gel." However, these are not the conditions that exist during foundry sand preparation, which is carried out at high percent solids and low shear rates.

Using SEM imaging in this study, it was determined that bentonite would form a fibrous network under the proper conditions and that the formation of fibers corresponded with an increase in the bonding of particles by the bentonite. When fibers formed, the specific strength of the bentonite improved. As a result of using compressive shear to develop bentonite fibers, the strength of the bentonite bonding was retained at half of the industry-wide standard dosage.