This article focuses the application of green sand in large scale infrastructure projects.
Excerpt from the December 2011 principle investigation by Craig H. Benson and Sabrina Bradshaw from University of Wisconsin-Madison's Recycled Materials Resource Center.
Foundry sand is high-quality uniform silica sand used to make molds and cores for ferrous and nonferrous metal castings. The metal casting industry annually uses an estimated 100 million tons of foundry sand for production. Over time, foundry sands physically degrade until they are no longer suitable for molds. Consequently, 9 to 10 million tons of sand are discarded each year. However, the discarded foundry sands have remarkably consistent composition and are typically considered a higher quality material than typical bank run or natural sands used in construction. Currently, an estimated 28% of discarded sand is reused in primarily construction related applications, while the remaining sand is discarded in landfills (American Foundry Society 2007). Recycling of foundry sand can:
- save energy
- reduce the need to mine virgin materials
- may reduce costs for both producers and end users
This paper provides a comprehensive overview of the engineering and construction properties of foundry sand for use in Portland cement and concrete, hot mix asphalt, road sub-base layers, embankments, and flowable fill. Recent studies addressing environmental concerns of using foundry sand, an industrial by-product, as a construction material are reviewed. Some case studies are presented to demonstrate successful applications of foundry sand. With the goal of advancing use of foundry sand in construction application, references to resources and tools, such as web-based training and a foundry locator map module, are made available.
General Foundry Sand Properties
Foundry sands consist of green sand and resin sand. Green sands typically comprise of high-quality silica sand, 5-10 percent bentonite clay, 2 to 5 percent water and less than 5 percent sea coal. The green sand process constitutes upwards of 90 percent of the molding materials used. Resin sands are high-quality silica sand usually held together with organic binder in conjunction with catalysts and different hardening/setting procedures. Resin sands are most often used for cores that produce cavities not practical to produce by green sand molding operations, primarily due to strength issues.
Physical properties for foundry sand from green sand systems are listed in Table 1. The grain size distribution of most foundry sand is very uniform, with approximately 85 to 95 percent of the material between 0.6 mm and 0.15 mm (No. 30 and No. 100) sieve sizes. Five to 12 percent of foundry sand can be expected to be smaller than 0.075 mm (No. 200 sieve). The particle shape is typically sub-angular to rounded.
Foundry sand has low absorption, although reported values of absorption were found to vary widely, which can be attributed to the presence of binders and additives (Javed and Lovell 1994ab). The content of organic impurities (particularly from sea coal binder systems) can vary widely (Emery 1993). The specific gravity of foundry sand has been found to vary from 2.39 to 2.70. This variability has been attributed to the amount of fines and additive contents in different samples (Federal Highway Administration 2004, Javed and Lovell 1994ab).
In general, foundry sands are dry, with moisture contents less than 2 percent. Clay lumps and friable particles are sometimes associated with the molded sand and are easily broken up. The variation in hydraulic conductivity (Table 1) is a direct result of the fraction of fines in different foundry sands.
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