Foundry sands

Foundry sand (FS) consists primarily of clean, uniformly sized, high-quality silica sand or lake sand that is bonded to form molds for ferrous (iron and steel) and nonferrous (copper, aluminum, brass) metal castings [81-87]. Ferrous (iron and steel) industries account for approximately 95% of foundry sand used for castings. The automotive industry and its parts suppliers are the major generators of foundry sand. 

In addition to green sand molds, chemically bonded sand cast systems are also used. These systems involve the use of one or more organic binders in conjunction with catalysts and different hardening/setting procedures. Foimdry sand makes up about 97% of this mixture. Chemically bonded systems are most often used for cores (used to produce cavities that are not practical to produce by normal molding operations) and for molds for nonferrous castings. 

The annual generation of foundry waste (including dnst and spent foundry sand) in the United States ranges from 9-13.6 million metric tons (10-15 million tons) [83-85]. 

---

Resins. As mentioned above, both furfural and furfuryl alcohol are widely used in resin apphcations. Another resin former, 2,5-furandimethanol [1883-75-6] (BHME), is prepared from furfuryl alcohol by reaction with formaldehyde. It is usually not isolated because oligomerization occurs simultaneously with formation (competing reaction). Both the monomer and oligomers are very reactive owing to difuntionahty, and are used primarily as binders for foundry sand (72) and fiberglass insulation (147,148). 

Iron oxide is also used for nonpigmentary applications, eg, ferrites (qv) and foundry sands making total world demand for iron oxide close to 1 X 10 t. The principal worldwide producers of iron oxide pigments are Bayer AG (ca 300,000 t/yr worldwide), and Harcros Pigments Inc., a subsidiary of Harrisons Crosfield PLC. In the United States, Bayer produces the Bayferrox line of iron oxide pigments in New Martinsville (see Iron compounds). 

Carbon dioxide is widely used in the hardening of sand cores and molds in foundries. Sand is mixed with a sodium siHcate binder to form the core or mold after which it is contacted with gaseous carbon dioxide. Carbon dioxide reacts with the sodium siHcate to produce sodium carbonate and bicarbonate, plus siHcic acid, resulting in hardening of the core or mold without baking. 

Material dried Ammonium sulfate Foundry sand Metallurgical coke... 

Siilfuric acid from iron pyrites Paint pigments roasting of metallic oxides Refractory clays calcination of refractory clay to reduce shrinkage Foundry sand removal of carbon from used foundry sand Fullers earth calcination of fuller s-earth material... 

Processes have been commerciahzed for the direct reduction of ematite to high-iron, low-oxide produces. Foundry sand is also calcined to remove organic binders and release fines. 

Outside the field of biomaterials it has been patented for use as a cement for underwater pipelines, as a foundry sand and as a substitute for plaster... 

Foundries purchase new, virgin sand to make casting molds, and the sand is reused numerous times within the foundry. However, heat and mechanical abrasion eventually render the sand unsuitable for use in casting molds, and a portion of the sand is continuously removed and replaced with virgin sand. The removed sand becomes spent foundry sand, which is discarded from the foundry facility. 

Spent foundry sand can be divided, based upon bonding processes, into two categories—spent green sand and spent chemically bonded sand. Spent green sand is black in color due to its carbon content, and has clay contents that result in a fraction of the material passing a No. 200 sieve (0.075 mm). Chemically bonded sands are generally yellowish in color and coarser in texture than clay bonded sands. 

Physical properties involve tests of the physical index parameters of the materials. For spent foundry sand, these parameters include particle gradation, unit weight, specific density, moisture content, adsorption, hydraulic conductivity, clay content, plastic limit, and plastic index. These parameters determine the suitability of spent foundry sand for uses in potential applications. Typical physical properties of spent green foundry sand are listed in Table 4.5. 

The grain size distribution of spent foundry sand is very uniform, with approximately 85 to 95% of the material between 0.6mm and 0.15mm (No. 30 and No. 100) sieve sizes. Five to twelve percent of foundry sand can be expected to be smaller than 0.075 mm (No. 200 sieve). The particle shape is typically subangular to round. Spent foundry sand gradations are too fine to satisfy the fine aggregate standard specified in specification ASTM C33 Standard Specification for Concrete Aggregates. 

Spent foundry sand has low absorption and is nonplastic. Reported values of absorption were found to vary widely (0 to 5%), which can also be attributed to the presence of binders and... 

Typical Physical Properties of Spent Green Foundry Sand... 

Source From AFS, Alternative Utilization of Foundry Waste Sand, final report (Phase I) for Illinois Department of Commerce and Community Affairs, American Foundrymen s Society, Des Plaines, IL, July 1991. Javed, S. and Lovell, C.W., Use of Foundry Sand in Highway Construction, Joint Highway Research Project No. C-36-50 N, Purdue University, West Lafayette, IN, July 1994. Javed, S., Lovell, C. W., and Wood, L.E., Waste Foundry Sand in Asphalt Concrete, in Transportation Research Record, No 1437, Transportation Research Board, Washington, DC, 1994. 

The chemical compositions of materials are usually expressed in terms of simple oxides calculated from elemental analysis determined by x-ray fluorescence. For spent foundry sand, the chemical parameters include bulk oxides mass composition, loss on ignition, and total oxygen demand. Table 4.6 lists the general chemical properties of spend foundry sand. It is shown that spent foundry sand consists primarily of silica dioxide. 

Depending on the binder and type of metal cast, the pH of spent foundry sand12 can vary from approximately 4 to 8. As such, it has been reported that some spent foundry sands can be corrosive to metals.14 Spent foundry sand must be monitored to assess the need to establish controls for potential phenol discharges.91516... 

Foundry Sand Sample Chemical Oxide Composition... 

Few studies have been conducted to determine organic residues in spent foundry sand and leachates from disposal sites. It is reported that several organic compounds are present in the spent foundry sand but have concentrations below the regulated toxicity characteristic limits. Organic compounds of concern include benzoic acid, naphthalene, methylnaphthalenes, phenol, methylenebisphenol, diethylphenol, and 3-methylbutanoic acids.12 These compounds are thought to be derived from the decomposition of organic binders such as phenolic urethane, furan, and alkyd isocyanate. 

Typical mechanical properties of spent foundry sand are listed in Table 4.7. Spent foundry sand has good durability characteristics as measured by low microdeval abrasion and magnesium sulfate... 

In-plant reclamation refers to the sand reclamation process in a foundry facility, which directly minimizes the generation of spent foundry sand. Sand reclamation includes physical, chemical, or thermal treatment of foundry sands so they may be safely substituted for new sand in molding and core-making mixes. 

The beneficial reuse of foundry solid waste has long been carried out informally, particularly in the U.S. Foundry solid waste has always been used as fills around the foundry or nearby neighborhood. With the promulgation of strict environmental protection laws, foundry solid waste is now required to be landfilled. Later, spent foundry sand was selected as a daily cover for landfills that are cover short. However, many recyclers believe that foundry solid waste should not necessarily be disposed of in landfills where other hazardous industrial waste belongs, simply because the main fraction of foundry solid waste is nonhazardous and has value in fully or partially substituting for currently in-use materials, for example, construction aggregates, soils, and minerals. Thus, reuse of foundry solid waste is marketable. 

Spent foundry sand is thought of as a beneficial substitute for fine sand for use in portland cement concrete. Prior to acceptance of inclusion, test standards applied on conventional fine sand shall be referred to as the standards for spent foundry sand to compare the physical properties of conventional sand and spent foundry sand. The most important parameters are particle size distribution, fineness modulus, dust content, density, organics content, deleterious materials content, and grain shape. Although no spent foundry sand satisfies all of the specifications, foundry sand can be blended with conventional sand to be incorporated into the concrete matrix. The replacing ratio normally starts at one-third. 

---