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Green Sand Metalcasting Foundry News

"W, X, Y, Z" - Glossary of Foundry Additives (Including core oils)

Posted by Hill and Griffith Company on Sep 4, 2018 9:24:48 PM

W, X, Y, Z - Foundry Additives Glossary


"Sodium silicate," "soluble glass," and "silicate of soda" are all called "water glass." Water glass is a composition of various ratios of Na, O to SiO, in dry crystalline or hydrated form. It is used as a binder in mold and core sand mixtures. The Carbon Dioxide (C02)-Sodium Silicate Process is used by the foundry industry. When 2% to 4% sodium silicate (Water Glass) is added to a clean silica sand or a refractory sand and carbon dioxide gas is passed through this formed mold or core, it hardens into a refractory mass, making excellent cores and molds for certain castings. Sodium silicate dissolves in hot water. Sodium silicate (water glass) is made by melting sodium carbonate with silica or by applying heat and melting sodium carbonate together with sand, charcoal and soda. This product, fused sodium silicate, is then ground and dissolved in boiling water for use as a foundry binder. Sodium and potassium carbonate can also be made into a double soluble water glass. 

Neo-Bond is a waterless binder which is very popular in the foundries where waterless binders are required. No temper water is necessary. Five percent (5%) by weight Neo-Bond, plus less than 2% of a high viscous coastal oil is all that is required when mulled together to form a waterless molding sand mixture. Waterless binder mixtures have produced, and are producing castings, with better detail than more expensive processes such as shell molding. Such waterless mixtures are molded "green" and are generally a low cost repetitive operation. Waterless binders, such as Neo-Bond, are used with fine silica sands, olivine, zircon, or Hevi-Sand mixtures.


Most organic binders are soluble to some extent in water. For example, cereals, corn flour, dextrin, lignins, proteins, starch and others are core or mold binders soluble, or partly so, in water. Those having this ability are called, "water soluble binders." Sodium silicate is such a binder, but is most often termed a, "chemical binder."

Is the name given to a variety of substances which may be of an extract of vegetable or animal origin. Waxes consist of esters, free fatty acids, free alcohols and hydrocarbons. They differ from fats in that glycerin is not separated upon saponification. Wax is usually harder than a fat. The most familiar wax to foundrymen is "beeswax" obtained from deposits of the honey bee. Beeswax is widely used in the pattern shop and is dispersed in certain liquid parting compounds as one of the ingredients. Other waxes used in the foundry are the vegetable waxes, such as candelilla wax and Japan wax. The most popular mineral wax is paraffin wax obtained from petroleum. Some ceresin wax is used in the foundry as a substitute for beeswax and other waxes. Waxes have a low melting point and are soluble in mineral spirits, particularly alcohol. Waxes are insoluble in water. Wax is soluble in ether and miscible in all proportions with oils and fats. The principal uses of wax in the foundry are in pattern shops, as ingredients of liquid partings, as patterns for the Jost wax process, fillets on patterns, and as a substance for certain foundry compounds. Mixtures of wax are formed into rods and sheets for use as foundry wax vents in cores and molds.

It is used for coating patterns and as an ingredient in liquid partings.


WETTING AGENTS Are chemicals used in making solutions, slurries, emulsions, or compounds to reduce the surface tension and give greater penetration, ease of mixing and stability of a liquid. Wetting agents are chemicals having a large hydrophobic group associated with a smaller hydrophilic group. They are used in molding sands, washes, and coatings. They are added in minor amounts with water. Non-ionic wetting agents appear to work best with bentonites and clay mixtures.

An oil that was used in most core oils in early foundry practice. There are different grades of whale oil. Whale oil contains oleic, stearic, palmitic, and other acids. The specific gravity is about 0.92 for a No. 5 grade. Whale oil is used in numerous industries, but in the foundry it has usually centered around core oil formulations.

The edible seed grains of wheat are ground and reduced to a flour. The hard wheats usually have smaller grains, but are richer in proteins. Wheat, oat, corn and other grain flours are used in the core room in 0.25% to 2% additions. They are used in mixtures of core or mold pastes. Their largest use is as an additive to core mixtures but other applications have limitations. 




Foundry wood flour is not finely ground sawdust but is a wood fiber product that has been completely disintegrated and sized to an optimum fineness for foundry use. Wood flour is recommended as an additive to sand mixtures in all types of foundries for improving molding and core sand practice­ particularly in steel foundries for partial replacement of the cereal, if used. It is one of the best known materials used for reducing volume changes in sand mixtures at elevated temperatures. It also improves collapsibility and tends to eliminate certain casting surface defects which may be caused by excessive sand expansion. From 0.5% to 2 % by weight in most cases is a sufficient wood flour addition. About 0.5% wood flour works well with 4% C or D grade seacoal. 1% works well with a 4% pitch addition in foundry sand mixtures.

All cellulose additives do not produce the same desired molding results. Some are strongly acid. A few have been colored by metallic oxides. Some contain very high percentages of moisture as received while others are dried below 5% moisture. Some are coarse, others are ground very fine and are much lighter in bulk volume. Investigations show that several are more water repellent than others. Since wood flour does not possess the gumminess or stickiness of cereal, it imparts better flowability to the sand mixture, giving a harder rammed mold. Wood flour sands do not dry out as rapidly as cereal bonded sands, but on the other hand, cereal bonded sands give a better mold skin hardness. Using a combination of wood flour and cereal, it provides the advantages of each. The rapid reducing atmosphere which wood flour offers when metal is poured into the molds aids in the peeling of the casting and fewer oxidizing defects occur in the mold cavity. Investigations have shown that a reducing rather than an oxidizing atmosphere in the mold cavity is advantageous. The metal lies more quietly in the mold which means less action at the mold-metal interface. Wood flour, by furnishing a reducing atmosphere, helps produce a smoother casting surface, which consequently reduces cleaning costs. The low ignition point of finely ground wood flour tends to absorb considerable mold oxygen by combustion in the mold cavity when the metal enters the mold. This is particularly true in casting gray iron, ductile (nodular) iron or malleable iron. Best casting results are obtained if wood flour is added to room temperature sand mixtures. To obtain the best results, wood flour should contain little ash and have a low ignition point. Wood flour, whether soft or hard wood, has approximately equal burn-out properties (which govern expansion properties), if ground to the same sieve analysis. Some investigators report that a coarser wood flour overcomes more sand expansion than a finer wood flour. A fine wood flour tends to absorb more water which in turn may defeat the purpose for its use. For best results, no more than 5% to 10% wood flour should be retained on a No. 50 U.S. Standard Sieve when making a fineness test. This offers security from high expansion characteristics of a molding sand, but yet does not alter casting finish. Coarser wood flours contribute to rougher casting finishes. Five Star wood flour is a specially designed foundry wood flour.


Zirconium silicate (ZrSiO4) is a foundry zircon sand and is used in the foundry as a molding sand, core sand or asa refractory. Zirconium oxide as well as zircon sand are the refractories that fall under this description. It is obtained from a natural sand deposit, but zirconium silicate, garnet, ilmenite, and rutile comprise only 2% of the total of heavy grades in the beach sand deposits. Zircon sand replaces silica sand in the foundries where greater heat resistant qualities are desired. The melting point of pure zirconium silicate is about 3614° F. (1990°C.). To increase refractoriness and to give a more stable core or mold, zircon sand is accepted in many foundry practices. The Australian material, when calcined, has been found to be a superior grade for foundry use.

Zircon sand is a zirconium silicate and is a very refractory foundry sand or flour. It has low thermal expansion and high thermal conductivity. Both the sand and flour are added to silica sand mixtures to resist metal penetration. It is also used for refractory purposes, such as ladle linings.

Review of "Glossary of Foundry Additives" by Clyde A. Sanders, American Colloid Company

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