Considering process solutions or beneficial reuse options to resolve where all the spent foundry sand will go.
Article excerpt from the Foundry Management & Technology February 2020 issue by Rob Steele.
For years, foundries have been asking, “Where will all the sand go?” They have looked for ideas or innovations to deal with over 10 million tons of spent green sand from molding and core making operations annually — and particularly for sustainable treatment processes. Specifically, they have been looking for process solutions or options for beneficial reuse of all that sand.
Let’s focus on the green-sand dust collector fines, usually rich in active clay and carbon. The ideal treatment technique would:
1) reclaim active clay and lustrous carbon from the dust collector material
2) use a water-based reclamation process to separate sand, clay, and carbon
3) implement no chemicals or unusual by-products
4) result in a clay slurry that has excellent performance characteristics
The cost of disposal has been the driver for analyzing the savings potential of treatment/recovery processes, but the real spur to finding a new approach may be in the rapidly increasing logistics cost for inbound clay and carbon, and the safety restrictions that impose delays and surcharges on rail and trucking services. You may add to these factors the further difficulties resulting from weather patterns and the impact on infrastructure.
A realistic economic look at 20% clay and carbon reduction in consumption will save the average foundry at least $350 per ton, based on the amounts of clay and carbon consumed.
The proven technologies available today — which can be sized according to the foundry binder in use and can be fixed or mobile — offer a viable solution.
The advantage of hydrated clay / bond is that it has shown immediate improvements in molding-sand system performance, along with an added benefit from reduced benzene, toluene, and xylene (BTX) emissions.
The slurry is easily mulled or mixed-in during green sand preparation, and the improved green sand properties that result include:
• Increased green strength at equivalent MB clay levels;
• Reduced friability
• Improved flowability and toughness
• Increased wet-tensile strength
• Increased green compressive and shear strengths
Any such change in a foundry’s technologies and operating practices, as this will be, requires a commitment by the production team to work on application optimization, and to engineer the steps for integrating it into a green-sand system.
For foundries considering the potential for green-sand dust processing, the following is an example of a supplier-recommended analysis that would inform that consideration:
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