Foundry Sand

Foundry sand is used to build molds and cores for use in the metalcasting process. The sand is reused and recycled numerous times internally by the foundry before it is rendered unusable. Approximately, 6‒10 million tons of foundry sand is discarded each year. A survey conducted by the American Foundry Society (AFS) revealed that foundries were recycling and reusing 28 percent of discarded sands in non-landfill applications. Proven market applications for metalcasting sand generally break down into three groups:

• Highway and Construction Uses – many types of construction projects require granular materials to level construction sites, create berms or retaining walls, build embankments, or backfill structures. Properly prepared metalcasting sands have been shown to perform well in all of these applications.

• Aggregate Substitutes – in these applications, recycled foundry sands substitute for other fine aggregates in a product that is bound together in some manner. The highest volume uses in manufactured products are: feedstock for Portland Cement kilns, fine aggregate in hot mix asphalt and fine aggregate in flowable fill.

• Manufactured Soils – metalcasting sand is an ideal candidate for soil blending because of its composition, color and consistency. In urban areas, soil scientists in nursery and landscaping companies are manufacturing soils by blending a range of recycled materials with organic matter.

Spent Foundry sand is high quality silica sand that is a by-product from the production of both ferrous and non-ferrous metal castings. Classification of foundry sands depends upon the type of binder systems used in metal casting. Two types of binder systems are generally used, and on the basis of that foundry sands are categorized as: clay-bonded sands (green sand) and chemically-bonded sands.

• Green sand is the most common molding media used by foundries. The sand is not green in color, it is called "green" because it has moisture in it (like green wood) before the sand dries out when molten metal is poured in the mold. Actually, it is black in color due to carbon content. Green sand is composed of naturally occurring materials which are blended together; high quality silica sand (85–95%), bentonite clay (4–10%) as a binder, a carbonaceous additive (2–10%) to improve the casting surface finish and water (2–5%).
• Chemically bonded sands are used both in core making where high strengths are necessary to withstand the heat of molten metal, and in mold making. Chemically bonded sand consists of 93–99% silica and 1–3% chemical binder. There are various types of chemical binder systems used in the foundry industry. The most common chemical binder systems used are phenolic-urethanes, epoxy-resins, furfyl alcohol, and sodium silicates. Chemically bonded sands are generally light in color and in texture than clay bonded sands.

More Resources

US EPA. Provides information on beneficial uses for spent foundry sands, regulatory information and a risk assessment covering manufactured soils, soil-less potting media and roadway subbase.

American Foundry Society (AFS). AFS advocates for the beneficial use of foundry sand.

US Dept. of Transportation - Foundary Sand Facts for Civil Engineers. The purpose of this document is to provide technical information about the potential civil engineering applications of foundry sand. Beneficial use applications covered include: structural fills and embankment, road bases, hot asphalt mix, flowable fills, and portland cement.

American Foundry Society - Industry Practices Regarding the Disposal and Beneficial Reuse of Foundry Sand Results and Analysis. As part of its foundry sand beneficial reuse initiative, the AFS undertook a multi-year data gathering effort to quantify the amount of sand available for reuse, characterize current reuse practices, and identify specific barriers. The results of the survey are summarized in this fact sheet.

American Foundry Society - Foundry Sand Tools & Resources. Links to case studies, tools and resources.

Recycled Materials Resource Center – Foundry Sand. Covers, material properties, management options, market resources, design and environmental considerations.