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  • Writer's pictureHill and Griffith

"A" - Foundry Additives Glossary

A - Foundry Additives Glossary



ACCELERATOR {See: ACID ACCELERATOR - ACTIVATOR­ - ALKYD RESIN - AMMONIUM NITRATE - CATALYST) A chemical substance which hastens a reaction, usually acting as a catalyst - an accelerator is most frequently associated with resins as used in foundry sand mixtures. An example is sodium perborate used with an "air-set" resin binder system, which requires final oven curing for best foundry results. From 10% to 30% by weight of the resinous binder is'·used as the accelerator agent, sometimes referred to in the foundry, as a "catalyst" or "activator." An isocyanate alkyd resin is called an accelerator when used in certain cement-sand mixtures. An accelerated binder is the "Hot Box" type resin. There are three basic foundry types of resin:

  1. Furan type resin-which contains no phenol.

  2. Phenol-Modified-resin-which contains some furfural alcohol.

  3. Phenol wet type resin which contains no furfural alcohol, nor urea formaldehyde. (Also see: AIR-SET PROCESS)

ACID (See: BORIC ACID) An acid is considered a hydrogen compound whose solution has a sour taste, it changes blue litmus paper to red, and dissolves certain metals while liberating hydrogen. Acid reacts with metallic hydroxides. The hydrogen of the acid changes place with the metal of the hydroxide.

ACID ACCELERATOR (See: ACCELERATOR) Is a material that speeds up the natural progression of the acid reaction on another substance.

ACID CURE BINDERS Those binders which function and are activated below a 7.0 pH, or those that cure faster when the total sand mixture is on the acid side. Resins which require phosphoric acid such as the no-bake sand mixtures are examples of acid cured resin binders.

ACID CURING RESINS (See: SELF CURING BINDERS) ACTIVATOR (See: ACCELERATOR and CATALYST) Is a substance that renders another substance curable. An exam­ple would be-Hexa (hexamethylene-tetramine) used in shell molding. The Hexa is used more as a catalyst. The terms "catalyst" and "acti­vator" are often used interchangeably in the foundry - rightly, or wrongly. Another example is sodium perborate, which is called the activator in some cold or air-set binder mixtures. There are other examples.


AGAR-AGAR (See: GUMS) A jelly-like gum which is used in core binders.

AGATE Is a form of silica which is a mixture of both crystalline and col­loidal silica. It consists mainly of the mineral, "chalcedony" which consists of about 98% silica (Si02) and contains metallic oxides and lime. It is not widely used in the foundry industry, but the tailings (fines obtained by screening) are further reduced and then collected for use in certain foundry partings. For example, finely ground agate is used as a non-silica parting compound having less than 1 % free silica (Si02) and is a big advantage when silica is anathema to the health of conscientious foundrymen.

AIR-SET BINDERS (See: AIR-SET PROCESS - NO-BAKE BINDERS - SELF CURING BINDERS) Air-set binders are generally referred to as "no-bake" or "self­cure" binders. The term, "Air-set" does not imply that "air" is an essential part of the curing system for all these binders, but that the binders cure partially, or harden while standing in room air.

AIR-SET PROCESS (See: AIR-SET BINDERS - ALKYD RESIN BINDERS - LINSEED OIL) A core or mold process that contains binders which cure in nor­mal room air by the action of an activator, or catalyst, on the resin binder to induce hardening of the sand mass. (Also see: ACCEL­ERATOR-ACTIVATOR-CATALYST)

ALBANY SAND (See: NATURALLY BONDED SANDS-SAND) A naturally bonded sand used to cast metals where extremely fine casting finish is desired. (Refer to Chapter XX, "Foundry Sands," pages 470-532). ALCOHOL (See: ETHYL ALCOHOLS) Is the common name for ethyl alcohol, but the name applies to a large group of organic substances which have important uses in the foundry industry. Alcohols are principally used in the foundry as solvents and carriers for mold, refractory, or core washes. Alcohol is used as a solvent for specific resins to coat sand used for shell molds, or for cores made by the Cronin (shell) Process. A characteristic of the primary alcohols is that there is always a [CH20H] group in the molecule. The tertiary alcohols are a distinctive [COH] group. Alco­hols are often classified in terms of "saturated" and "unsaturated." Methyl alcohol is like water, amyl alcohol is oily and messyl alcohol is a solid. lsopropyl alcohol is an alcohol used in the foundry with varying percentages of water. It is widely used in commercial light-off mold and core coatings.


ALGINATE (See: SODIUM ALGINATE-THICKENERS) "Sodium Alginate" is derived from a seaweed or kelp. Alginate is a sodium salt of alginic acid used as a thickener in mold and core coatings and washes. It is excellent as a suspending agent when used in minor proportions of a dispersion.

ALKALINE SULPHATES The salts formed from the reaction of sulphuric acid on ammonia, potash, soda, or lithium are known as the alkaline sulphates. Nor­mally, they are soluble in water and sparingly soluble in alcohol. These alkaline sulphates are generally neutral when the salt has been prepared with a strong alkali and a strong acid. Sulphates may be used in certain foundry washes, coatings, and refractory sprays.

ALKYD RESINS (See: LINSEED OIL - RESINS - SELF-CURING BINDERS) A group of thermoplastic synthetic resins known chemically as hydroxycarboxylic resins. Alkyd resins produced from phthalic an­hydride and glycerol are representative types. Some alkyd resins are accelerated by isocyanate to harden into a solid sand mass more quickly, the "Cold Box Process" uses this type. (See: p. 264). Alkyd resins vary greatly with the raw materials used and with varying percentages of composition. They vary from soft rubbery gums to hard brittle solids. The resins are reacted with oils, fatty acids, and other resins such as urea or melamine to make them compatible with drying oils and to impart special characteristics. When mixed with urea-formaldehyde or melamine resin, the alkyd resins give harder and more water resistant coatings. Alkyd resins are finding wider use as binders in coatings for certain cores used in the foundry. They are also used in various foundry core sand mixtures.

ALUMINA (See: ALUMINUM OXIDE - ALUNDUM - BAUXITE­ CORUNDUM) Is an oxide of aluminum, having the chemical symbol, [Al2O3]. It is often called "corundum." Alumina is widely distributed in nature and occurs in the clay-like mineral "bauxite" which has the chemical composition [ Al2O3 • 2H2O], and is a hydrated ore of aluminum. Alumina's melting point is 3670°F. (2021 ° C.) when pure, but since it is generally associated with silica and other minerals, it seldom reaches this higher P.C.E. temperature. Alumina is used in refractory brick, cements, mortars, grog, coatings, refractory chamotte sand and ceramic flours.

ALUMINATE CEMENT (See: BINDERS-CEMENT) This cement is much like Portland Cement (silicate cement), but it contains bauxite as the raw aggregate material. It has high speed or quicky-setting properties. It normally sets as hard in 24 hours as ordinary cement does in 28 days. Aluminate cement is generally com­posed of 38% to 40% alumina (Al2O3); 35% to 38% lime (CaCO3); 15 % to 18 % iron oxide (Fe2O3); and 3 % to 8 % silica (SiO2); plus the combined chemical water. This cement has been used as a binder for cores and molds in the production of larger castings.

ALUMINUM OXIDE (See: ALUMINA-ALUNDUM-CORUNDUM) Is an artificial corundum (Al2O3) produced by fusing bauxite in a special arc type electric furnace in a controlled melting atmosphere. Its specific gravity is 3.75 and its melting point is 3670°F. (2021 °C.) when the aluminum oxide is pure. Aluminum oxide is marketed under one trade name as "Alundum" and is specifically used for refractory and mold coating purposes. "Corundum" or "Alundum" are sub­stituted for silica sand in foundry mixtures for special casting condi­tions. Aluminum oxide is used in the investment casting process and Alundum is added to many refractory coatings used in the foundry.

ALUNDUM (See: ALUMINA-ALUMINUM OXIDE-CORUNDUM A refractory ceramic material used for many foundry purposes.



AMMONIUM DORO-FLUORIDE It is also known as Ammonium Fluoborate [NH.BF 4 J. It is prepared by the reaction of boric acid, hydrofluoric acid, and am­monia, which is similar to that used to prepare sodium and potassium fluoborates. It is used in the foundry as a fluxing agent and as an inhibitor in magnesium foundry sand mixtures.

AMMONIUM CHLORIDE It is also known as Sal Ammoniac. Its chemical composition is [NH4Cl]. It is soluble in water, but sparingly soluble in alcohol. It is used as a fluxing agent in the foundry.

AMMONIUM NITRATE (See: DRIER, CORE) A chemical product which is used as an accelerator, drier, or hastener to furnish more rapid curing of core binders particularly when used with core oils. In a specially prepared form, this crystalline substance having a composition of [NH4N03] is highly explosive in a concentrated form. Its specific gravity is 1.725. It decomposes at about 410°F. (210°C.) and is soluble in water, alcohol and alkalies. It decomposes in contact with core oils at their baking temperatures. Commercially prepared foundry ammonium nitrate is usually adul­terated to make it less explosive when used as a drier or oxidizing agent in foundry core oil mixtures. Less than 0.1 % is used and the amount must be calculated to the percentage of the type of unsaturated binder used in the core oil mixture. If too much ammonium nitrate is used, it usually has the opposite effect on the purpose for its use. The core oil in which an accelerator or drier (dryer) is used must depend upon oxygen to complete the baking (curing). Potassium perman­ganate is also used to accelerate the oxidation and hasten the baking of the cores in the ovens.

AMMONIUM SILICOFLUORIDE It is also known as Ammonium Fluosilicate. It is an odorless crystalline powder. It is about 20% soluble in cold water, and 35% soluble ·in hot water. It is used as an inhibitor in magnesium molding sand mixtures and as a fluxing agent in the foundry for many purposes.


ANAMI GUM (See: GUM) A gum resin extracted by pressing the stem of an African plant and collecting the liquid. It is readily soluble in alcohol. Anami gum has a specific gravity between 1.062 to 1.068 and its melting point is 468°F. (245°C.). It is used in certain core and binder compounds replacing various other gums commonly employed.


ANIMAL Oil (See: Oils)

ANTHRACITE COAL (See: CARBON and COAL) Anthracite is hard coal. It is distinguished by having both a high carbon content and a high specific gravity in contrast to other coals. The specific gravity of clean anthracite is about 1.7. Its carbon content may be as high as 95%, but its fixed carbon content is from 78% to 84%. Anthracite coal yields about 13,200 B.T.U.'s per pound. It burns with very little smoke or odor, and has a great advantage over bituminous coals for heating furnaces even though it is more costly. Anthracite coal replaces graphite in certain less expensive blacking compounds, but not too much anthracite coal is used as "seacoal'' or "coal dust" in foundry facings. Most foundries prefer to use "Bitu­minous Coal" when ground for use as "seacoal" or "coal dust." (Also see: SEACOAL)

ASBESTOS Is a commercial name for a variety of fibrous minerals. Asbestos is a hydrated magnesium silicate. The minerals serpentine and talc are associated with asbestos and are present in most of the commercial grades of foundry asbestos used. Asbestos is used sparingly in the foundry as a replacement for wood flours and other cellulose materials. However, because of the high combined water in asbestos and its high absorption of added temper water, many foundries have turned from its use. It is slightly used in certain molding sands to insulate metals. 1 % to 2 % by weight is used in certain sand mixtures to prevent ex­pansion type defects such as scabs, buckles, or rattails. Keeping molten metal hotter for longer periods is its real value. Asbestos is used more in risering and gating practices than used in foundry sand mixtures.

ASH (See: FLY ASH) A residue from burning, or extraction of the prepared product. Fly ash is at times used in certain core mixtures and as an insulation cover for open risers.

ASPHALT - Natural and Artificial Asphalt (See: COAL TAR - COAL TAR PITCH - GILSONITE - PITCH) It is a black-brownish bituminous substance which may be either semi-solid or solid. It is found in various parts of the world in its natural condition. It is often called, "gilsonite," "oil asphalt," "rock asphalt" or "bituminous rock-impregnated with asphalt." It is a mix­ture of hydrocarbons and is directly related to petroleum. Asphalt usually melts at below 100°F. (38°C.) and is soluble in turpentine, but only partly soluble in alcohol. Artificial asphalt is the heavy residue often called "pitch," when it is obtained from coke or coal by distillation processes. Pitch is jet black in color, very brittle, and has been used by the foundry as both a liquid carbon or a dry ground additive for many years. Pitch is frequently admixed with seacoal in molding sand mixtures. It is used in the foundry for making both skin-dried and dry sand molds. Pitch is used in various core sand mixtures. Up to 5 % by weight is a common percentage for pitch additions in sand-clay mixtures. For use in casting smaller and lighter weight castings, there is the fear of waterproofing the sand grains. For this reason, asphalt type carbons have been sold only in limited tonnages. When used in foundry sand mixtures, pitch gives plastic deformation at higher casting temperatures. It is recommended for use in pellet form for CO2-sodium silicate core and mold mixtures to aid collapsibility.



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

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