C - Foundry Additives Glossary
CALCINED CERAMIC GROG (See: BRICK, CRUSHED-CHAMOTTE-GROG) Many finely ground, calcined, ceramic, grog materials are used in compounds serving the foundry. A few are ground firebrick, kyanite, magnesite, mullite, sillimanite, quartz, ganister, flint, fireclay, chromite, olivine and many other refractory products. They are graded and used in numerous core compounds, mold compounds, sand mixtures, and for special refractory purposes throughout the foundry.
CALCITE (See: LIME-LIMESTONE) Calcite is a calcium carbonate, or limestone ( CaC03 ). Its specific gravity is 2.72 and it has a Mob's Hardness of three (3). Limestone is not usually added to foundry sands, as it is considered a contaminant in foundry sand mixtures. Calcite is usually deposited from the residue of marine shell fragments. It is added to certain refractories and a few coatings to encourage fusion. Calcite is not generally considered a foundry sand additive, but ground limestone which has been saturated with stearic acid or a wax is used as a dry parting compound. Also it is used with saturated stearate and hexa in shell molding.
CALCIUM ALGINATE (See: ALGAE) Calcium alginate (a hydrophyllic colloid from treatment of marine algae) holds some unusual benefits for foundry sand. It improves fluidity and flowability, carbonizes leaving practically no ash, prevents loss of moisture during storage and minimizes dust. About 2 % alginate, 4% bentonite, 2 % temper water, in an AFS Gr. Fn. 65 silica sand mixture increases permeability from 80 to 108 and boosts shear strength. It also benefits core sand mixtures in amounts up to 0.05% for oil sand cores, 0.3 to 0.8% for CO2-sodium silicate core mixtures and 1 % in a facing sand mixture.
CALCIUM LIGNIN (See: LIGNIN-LIGNIN SULFONATE) It was used more widely in the foundry in the early 1900's. It was called "lignin sulphate," "paper mill sulphate," "paper mill resin" or "paper mill liquid." It was boiled down into a sulphide liquid containing about 60% solids. It is. and was, used as a mold and core sand binder.
CALCIUM SULPHATE (See: GYPSUM [CaSO4]) Is a hydrated mineral having the composition of [CaSO4 • 2H2O]. It is used in some foundry investments. The mineral "gypsum" is a calcium sulphate [CaSO4J, but calcium sulphate is a hydrous calcium sulphate. It is soft, having a Mob's Hardness of only 1.5 to 2. Its specific gravity is 2.31 to 2.33. Consequently, this material has been referred to as "Plaster of Paris," because of the vast deposits of gypsum found in the quarries of the Montmartre district of Paris. This gypsum is burnt and prepared for many purposes. Gypsum, Plaster of Paris and hydrous calcium sulphate are referred to as being one, and are used in many nonferrous investment foundry practices. It is also used in making certain patterns for the foundry. It has extensive use in nonferrous foundries more so than ferrous foundries. It is used as insulating sleeves for heads and risers in certain foundry practices.
CARBON (See: ANTHRACITE COAL-ASPHALT-BITUMINOUS COAL-CHARCOAL-COAL-COAL DUST-COAL TAR PITCH-COKE-FACINGS-GILSONITE-LIGNITE-PEAT-PITCH-SEACOAL-TAR) Carbon is second only to silicon as the chemical element most commonly used in the foundry. Carbon occurs in many combinations and in many different forms. It may be colorless and transparent as with the diamond, or it may be opaque and black as in pitch. It may be porous as in charcoal, or solid as in graphite. It may be in a liquid state ::\S in natural asphaltums, or dry as in lamp black. It is ever present in gases, minerals, organic materials, but specifically in coal. Carbon's chemical symbol is [C]. Its specific gravity varies from 1.9 to 3.52. Carbon has the property of dissolving in most molten ferrous metals, principally gray (cast) iron. Carbon has a great influence on most all ferrous metals. Gray (cast) iron, nodular iron, malleable iron and steel. contain carbon as either in graphitic flakes, in the combined state, or what is known as "spheroidal" (Nodular Graphite). The carbon atom has the peculiar property of forming "ring compounds." There are as many compounds of carbon, as all the known compounds of the other elements. The foundry sand technologist uses carbon in the form of graphite, plumbago, carbon black, lamp black, coke, petroleum pitch, petroleum coke, gilsonite, charcoal, carbonized wood flour, acetylene black, ground coal, Green Shell Carb and many others: Acetylene gas, a source of colloidal carbon, is easily generated by the action of water on calcium carbide. When acetylene gas is ignited, it leaves a sooty deposit on the mold or sand surface, which acts as a refractory barrier to the hot metal. Many blacking compounds are used by the foundryman which contain a variety of carbons or assorted carbon minerals. Many different types of carbon blackings are used for certain foundry purposes. Carbon in most forms does not allow the ferrous metals to wet the mold's or core's sand surfaces when it is present. The foundryman thinks of carbon more as "seacoal," "pit.ch," "gilsonite" or "carbonized wood flour," than as simply "carbon." Refer to these products. CARBON BLACK (See: LAMP BLACK) l;his is the carbon deposited on a surface from the incomplete combustion of a burning gas. Usually the carbon black is deposited by contact of a flame on a cold metallic surface, but it is also manufactured by the incomplete combustion of a natural gas in a closed chamber. The carbon black deposited by the first method is called "channel black" taking its name from the metallic channel iron first used as the depositing metal surface. It is called by other names such as "soft black" and "lamp black." The fine solid carbon particles are collected and packaged for the foundry market. Carbon black is used in many compounds associated with the foundry. It is also used as a pigment in certain proprietary foundry products so as to reduce their recognition when one or more items are blended for resale.
CARBON CELLULOSE (See: CARBONIZED WOOD FLOUR GREEN SHELL CARB)
Mixtures of carbon and cellulose such as "Carbonized Wood Flour" and "Green Shell Carb" are classified under this terminology.
CARBON DIOXIDE (CO2) A commercial gas with the chemical symbol of the compound [CO2]. It is used to harden the sodium silicate binder used in the "CO2 Process." It is used to harden silicate binders in refractories, cores, molds, ladles and other needs in the foundry.
CARBONITE (See: CELLULOSE) This was first a name given to a natural coke found in England. Later, the name applied to a natural coke found in Virginia. Carbonite referred to a coke0like mineral formed by the baking action of igneous rocks on seams of bituminous coal. It was formerly used as a coke. It was also a name given for activated charcoal made from a mixture containing finely ground anthracite coal, pitch and sulphur. The trade name "Carbonite" is claimed to be held by the General Abrasive Company, Inc., first used as a silicon carbide abrasive. However, the foundry industry also recognizes a commercial trade name "Carbonite" as a mixture of a cellulose, coal, pitch, or perhaps other additives. Since it contains different products and different percentages, check with a producer, e.g., The Hill & Griffith Company for recommended use and application data for their foundry additive.
CARBONIZED WOOD FLOUR (See: CELLULOSE-FIVE STAR WOOD FLOUR-GREEN SHELL CARB-WOOD FLOUR) Description Carbonized Wood Flour is another type of wood flour used by many foundrymen. It is a one unit package combination, combining the effectiveness of both wood flour and seacoal. Carbonized wood flour is prepared for the foundry by specification. It is a mixture of wood flour with a controlled carbon additive that contains a certain percentage of volatile and fixed carbon. The ratio of carbon to wood flour varies by the specifications of the foundry. Normally, carbonized wood flour contains at least 60%cellulose material, unless the foundry requests a change. Recommended Use Carbonized wood flour should be added as a replacement for wood flour, corn cob flour, or other cellulose additives and a portion of the carbon. Normal additions to gray iron, ductile and malleable foundry sand mixtures are between 1 % to 3 % by weight. Some foundries have used up to 4% by weight, but the cellulose part of the carbonized wood flour was in a reduced percentage. Molding mixtures containing seacoal or pitch may be sharply reduced when carbonized wood flour is used. A good mixture for a green sand addition is one part by volume seacoal and three parts by volume carbonized wood flour.
Advantages 1) Carbonized wood flour acts like wood flour, yet it does not absorb as much water as cellulose or corncob flours. It tends to lubricate sand grains when rammed. It works well with finer sands, creating a better mold surface. 2) Carbonized wood flour mulls more rapidly into a sand mixture with less balling-up than other cellulose materials. 3) Better flowability is offered sand mixtures when carbonized wood flour is used. 4.) Castings peel better from carbonized wood flour sand mixtures than when straight cellulose is added. 5) Less burn-out and more durability is found with carbonized wood flour than other cellulose materials. Less ash is noted. 6) Seacoal and pitch are more compatible with carbonized wood flour than straight cellulose additives. 7) Sand mixtures have less tendency to dry-out than where straight cellulose materials are used. Thus, molding sand mixtures containing carbonized wood flour are less brittle than other mixtures containing only cellulose additives.
CARNAUBA WAX (See: WAX) It is derived from exudations on the leaves of the palm tree. It melts at 185° F. (85°C.) and has a specific gravity of 0.995. It is soluble in alcohol and alkalies. It is used principally as the wax for making patterns which are used in the "Lost Wax Process."
CASEIN PLASTIC (See: CORE BINDERS-PROTEINS)
CATALYST (See: ACCELERATOR-ACTIVATOR-FURAN-HEXAMINE) Is a substance which permits or promotes a reaction without entering into the reaction itself. An improper foundry example, which uses the term "catalyst," is phosphoric acid used in conjunction with the furan no-bake resin binder systems. Catalysts are added to thermoplastic compounds to cause the resins to thermo-set. Catalysts are usually strong oxidizing agents. A catalyst for the cold-box process is triethylamine. The hexamine resin for pre-coating sand used for shell molding is incorrectly referred to as a catalyst in the foundry, as it participates in the reaction. Certain of them would be better referred to as "activators." NOTE: Air-cooling must also be differentiated from air-setting, as air-cooling does not require external baking heat, the curing action is exothermic. CELLFLO (See: CELLULOSE- GRAIN CELLULOSE- WOOD FLOUR) The best ground, grain product, cellulose offered to the foundry industry is Cellflo. It is a ground, screened, oat hull product tailored to foundry molding or core sand requirements.
Fineness Less than 5% is retained on the U.S. Standard No. 50 sieve of an undried sample. 15% is retained on a U.S. Standard No. 50 sieve of a dried sample at 240° F. (l16°C.).
Recommended Use Approximately 0.25% to 2% by weight Cellflo is used in a foundry mold or core sand mixture. Cellflo is added in the same manner as wood flour or corn flour and may directly replace any of the cellulose additives used by direct weight addition.
There have been many pros and cons regarding the best measuring, whether by volume or by weight. Cellflo is so unique a cellulose product that it furnishes some green compression strength and increases deformation in most molding sand mixtures. A comparison of its behavior characteristics depends upon the type of cellulose it replaces. Cellulose materials that are lighter in density may be directly replaced by Cellflo.
Replacing Seacoal There are several foundries now using only 3 % additions of Cellflo, having replaced all the seacoal in the molding sand. This is not always recommended, but it is being done. Foundries claim they obtain better flowability, better pattern draws, a more uniform sand mixture and a molding sand that is less prone to expansion defects, such as scabs, buckles, or rat-tails. Where hard ramming is encountered, the use of Cellflo is a suggested solution to the many problems associated with high density molding. It is suggested that 3 to 4 parts seacoal and 1 part Cellflo are quite compatible, and it is recommended that they be used in combination for high pressure molding. Most other cellulose additives decrease green compression strength so sharply that an additional amount of clay bond is usually made which'-increases the cost of the molding mixture. Some acid type cellulose additives have a low pH value which is quite noticeable on the clay bond. Acid cellulose additives kill the strength of western (sodium) bentonite when used as the bond in the molding mixture. This is not true when Cellflo is used in the sand mixture replacing acid cellulose additives.
Overcomes Expansion Defects Like most cellulose additives, Cellflo possesses the same quality as other fibrous products which overcome sand expansion defects, particularly those defects occurring on flat casting surfaces. Where improper and irregular ramming exists, 1 % to 1.5 % Cellflo generally cures this difficulty. Cellflo separates the sand grains without absorbing a large amount of temper water in sand mixtures which is common with other cellulose additives.
Deformation Cellflo increases deformation slightly which is uncommon with competitive products. Many foundries have found that higher priced cereal additions can be eliminated in green molding sand mixtures by substituting Cellflo on a weight basis. Cellflo additions in these molding sand mixtures do not subtract from the flowability, as it does not absorb excessive water. The more temper water required in a sand mixture, the less flowability of the mixture. Other cellulose products tend to absorb more water than Cellflo.
Brittle Molding Sand Some complain that where cellulose products are added to mold or core sand mixtures, the mixtures tend to dry out faster and become brittle. One particular cellulose product is ground so coarse that when added to a foundry sand mixture the mold's edges can actually be blown off with little effort after the molds stand for a short time. It is important that the fineness of grind be controlled rather closely. Any coarsely ground cellulose material should be avoided, particularly if finer base sands are used. Cellflo sand mixtures have lesser tendency to dry-out than certain cellulose products which accept water rapidly but release water rapidly. Some say that Cellflo in its natural form does not require as much water as other cellulose products, hence less drying-out occurs. It is further claimed that because Cellflo imparts deformation to the molding mixture, mold edges are less brittle. An impact tester measures this property and where molds tend to crack while moving on conveyors, the impact test should be of value in controlling both toughness and slump of the molding sand being used. Dry Compression Strength Lumpy molding sand and hard baked molds or cores are not found where Cellflo is added. Shake-out is greatly improved with Cellflo present. It is similar to the reaction of Five Star Wood Flour, but it is superior to other cellulose products which claim equal results.
CELLULOSE (See: CARBONIZED WOOD FLOOR-CELLFLO-CEREAL-FIVE STAR WOOD FLOUR-WOOD FLOUR) Description Many forms of cellulose additives are used by the foundry industry. These include wood flour and cereals such as: rye flour, wheat flour, and corn flour. There are also various cellulose materials such as ground residue by-products such as oat hulls, rice hulls, alfalfa fines, grain chaff, flax seed pressings, corn cob flour, and numerous others. Some are developed from residues of chemical by-products.
Ash Content Foundrymen should test all cellulose materials to determine their ash content before using them in core or molding sand mixtures. The foundryman should subject cellulose products to intense heat to see whether they turn into a slag mass, an asphalt-like residue, lacquer, or a soft white ash which they should. There are some cellulose products that turn to hard, black lumps, and build-up in the molding sand after constant use. If the cellulose is first heated by the sand laboratory, the selection will generally be determined bv thf• lack of residue which each cellulose leaves.
pH Value The foundryman should avoid any cellulose product that changes the pH abruptly in the system sand. Some cellulose products are found to be highly acid and have the capability of actually corroding a steel metal bin when stored for a reasonable length of time. This corrosion test can be determined in the laboratory by placing an ordinary steel sample into the cellulose which has been wetted slightly. If corrosion shows on the metal container or plate, foundrymen should not use such cellulose products in their molding sand systems. This corrosion may be harmful to bins, hoppers, elevators and other steel parts where molding sand may cling or cake for a few days. The foundry may have . expensive maintenance problems and the direct cause may be unknown to them. Likewise, any fine corrosive cellulose product with a very low pH value (acid) indicates a high acid content. This acid cellulose should not be sucked into high priced dust exhaust or reclamation systems. When the collected cellulose fines come in contact with water, the dust reclamation system may corrode and be so badly damaged that it may have to eventually be replaced.
Fumes-Smoke The foundryman should always check fumes or smoke generated by cellulose products when they are added to the molding sand. Excessive smoke is a hazard that foundry workers dislike and pollution occurs. Laws are being regulated against smoke pollution. Any cellulose product that liberates an unusual amount of fumes (usually generated from the sulphur present in the product) should be investigated further, as normally cellulose materials do not contain high percentages of sulphur. The fumes may be created by a treatment to which the cellulose by-product has been subjected, prior to its manufacture for foundry use. Cellflo is recommended because it is not highly acid, has low impurities, low ash, less smoke, low fumes, low sulphur, and usually delivers to the foundry for the lowest costs. Although the most popular cellulose additive is wood flour, many others have been advocated for foundry use. Corncob flour is one such additive. Many available materials can be classified as cellulose. The list is rather lengthy but includes such materials as alfalfa fines, rice hulls finely ground, chaff from other grains, pulverized nut hulls such as pecan or peanut, ground cotton-seed pulp after the extraction of the oil, milled tung-oil pulp, ground flaxseed pressings, furfural residue and others too numerous to list. Cellflo has been foundry tested and approved.
CEMENT (See: ALUMINATE CEMENT-GLYCERIN-HI-EARLY PORTLAND CEMENT-LUMNITE CEMENT-PORTLAND CEMENT) There are many different names and definitions for "cement" used in the foundry. Cement is a binder. It is an adhesive for many products and has many different analyses. However, foundry cement is a natural cement produced by the crushing of a sandy limestone, heating or burning it, then grinding it into the final product for proper commercial size. Cements occur in so many different categories and nanres that it would be too difficult to cover all of them in this limited space. Portland Cement is generally used in the foundry where cement is used as the binding ingredient for molds and cores. It is also dusted on the surface of certain molds to obtain better surface strength. Certain cement sand mixtures are accelerated by small additions of an alkyd resin with an isocyanated process. Other cement mixtures add finely ground ferro-silicon to develop an exothermic reaction, the amount is dependent on the ambient temperature present when used. During the winter season the setting rate of cement sand mixtures are slowed down considerably. A third fluid cement type mixture contains approximately 8%by weight cement in the sand mixture, to which is added a 4% molasses accelerator. This hastens the setting time considerably. Foundrymen sometimes refer to glues and gums as binders or "cements." Bonds are sometimes called "cements" in the foundry.
CEREAL (See: CORN FLOUR-RYE FLOUR-WHEAT FLOUR)
CEREAL BINDERS (See: CORN FLOUR-DEXTRIN-GELATINIZED STARCH-STARCH)
History As most early foundry materials first came to the U.S.A. from England, so originated the practice of using cereal binders (starch) in molding sand mixtures.
Classes Presently, foundry cereal binders fall into three classes, namely:
Gelatinized starches made from the wet milling of corn starch.
Gelatinized corn flour made from the dry milling of hominy grits, or meal.
Dextrine ( dextrin) made from corn starch.
Processes The corn milling processed cereal is widely used in foundry practice. As explained by millers, the kernel of the corn consists of the hull, germ, soft stock, hard stock, and grit. The hull and germ are removed as much as possible from the grit and soft stock. The hard part of the kernel flows toward the hominy and grits processing, and the soft stock with the hard stock composes the meal. The grits or meal are moistened with water, then heated, and are finally run on to hot rolls which gelatinize and flake the grits. The resulting flakes are then ground, screened and prepared for shipment to the foundry. Some foundries use the more expensive dextrin as a replacement for the less expensive corn flour cereal binders and claim good results by obtaining highet dry strength where needed in sand mixtures. Many different types of dextrin are used in mold and core sand mixtures, but the foundry prefers "Canary Dextrin." Dextrin is water soluble which easily migrates to the surface of the cores or molds. It provides less "buffing" action on sand expansion than do cereals in sand mixtures. ( Refer to Dextrin)
Use of Cereal To review or attempt to establish a substantial foundation as to the effective utilization of cereal would be a great task. Those using cereal binders praise its effectiveness, but the foundry's use of cereal is not indispensable. Since cereals, such as: corn, wheat, or rye flour have many interesting properties, features that appeal to one foundryman may be considered a disadvantage by another. It is possible that one of the advantages of cereal binders, under certain working conditions, may be the difference between saleable and nonsaleable castings, or castings that require considerable rework, depending upon how the cereal is employed. Corn flour cereal is used more widely in the foundry than other cereals. A choice of foundry corn flour grades may be: the heavy weight flour, the intermediate weight, or the light weight grades.
Use in Steel Sand Mixtures Cereal is used by all types of metal foundries to some extent, but it is most widely used in the casting of steel. Ordinarily, steel sand mixtures contain a certain percentage of cereal, usually in the amounts of 0.5% to 2% by weight. The early synthetic (compounded) molding sands were very angular and the grains possessed an uneven distribution. Cereals were used with these base sands to overcome the many disadvantages which accompanied their base properties. Therefore, cereal became a prominent foundry raw material and has remained as such.
Mold Atmosphere Cereal binders seem to alter the texture and behavior of the sand mixture while the metal is being poured. This may be due to the cereal furnishing a reducing atmosphere in the mold cavity, the same as seacoal or wood flour offers to gray iron, ductile, or malleable foundry sand mixtures. Being a volatile cellulose substance, it tends to use some of the oxygen in the mold cavity when the metal ignites it upon entering the mold. A carbon film is partially deposited on the sand grains which allows the metal to flow more evenly without attacking the sand's surface.
Synthetic (Compounded) Sand Mixtures Users of synthetic (compounded) sands bonded with 4% to 5% bentonite or 10% to 12% fireclay have found it advantageous to use approximately 0.5% to 2.5% cereal additions. Temper water requirements increase with additions of cereal. The best working quantity of cereal in molding sands is in additions of 1 % to 2 % by weight. Cereal binder and sodium bentonite bond seem to possess the same optimum moisture content, and these two substances are very compatible. Cereal and sodium bentonite bonded sand mixtures furnish the highest green compression strength at slightly under 2 % moisture content, although 3.0% to 3.5% water is most normally used in practice. Steel foundries have recognized this, which is also the reason why the bentonite bonds are popular.
Molding Properties Cereal increases the dry compression strength of molding sand, but shows a decrease of these values when excessive additions are made. There may be many answers to this condition, but it seems the cereal binder absorbs more of the water in the mixture, leaving a smaller amount of water available for the clay bond. Fireclay, for example, is worked at moistures of 5% to 6% by weight, therefore, the moisture range is higher. 1 % loss of water at a 6% temper water range is not as critical as when working at lower water levels of say, 2% to 3.5% by weight.
Flowability of Sand Mixtures Cereal gives a tougher mold skin hardness to molding sand mixtures with greater resilience, and consequently, flowability of the sand mixture is decreased. Heavy additions of cereal to molding sands are frowned upon because of the increased ramming demands which develop at the bench or the molding machine.
Brittle Molding Sands Molding sands which are brittle; i.e., having edges that are friable may be easily corrected, if cereal is added. This may only be a temporary cure, as the real answer may be poor distribution of the base sand grains, low bentonite content, and/or low temper water. Sands which have a too uniform grain distribution with too narrow a spread of grain sizes are. generally more brittle than other base sands.
Effect of Permeability Additions of cereal to molding sands decrease the permeability of most rammed sand mixtures, but the hot permeability seems to be increased because the burning-out of the cereal by the hot, liquid metal opens the sand grain voids which the cereal occupied.
Moisture Pick-up Foundries adding cereal to molding sands in excessive amounts find the molding sand tends to "ball-up" into small pellets. Because of cereal's great affinity for water, this phenomenon can happen. For this very reason, cereal incorporated in molding sand lengthens the moisture range which allows the molding sand to become more workable. Whether it is an advantage, or disadvantage, is completely up to the foundryman, but without proper mulling, excessive cereal additions are not advisable.
Mold Surface Properties Many foundrymen use cereal in sand mixtures because collapsibility is increased in the system sand after the metal has been cast. Molds made of sand mixtures containing cereal are distinctly less friable on the surface when air dried, as is common in many steel practices. When using cereal, the grains of sand at the mold surface do not rub off as easily as when only bentonite or fireclay bonds are used in the molding mixture. Friability is increased with the use of coarser base sands. Many foundries producing heavy castings are sometimes encouraged to use cereal because it broadens the temper water range of the sand mixture. Also, the soluble substance in the cereal tends to migrate to the surface of the mold or core and a film deposit is formed. Spraying the surface of the mold with a diluted mixture of dextrin, glutrin (lignin) or molasses water tends to offer similar film surface effects.
Weak Molding Sands Foundries having weak molding sands are sometimes encouraged to use cereal, particularly where large copes are concerned. If the foundry is in the habit of using gaggers, rods, or bars to hold mold sections, cereal may be added to increase the sand toughness, to give better sand support, and to aid cope lifting.
Expansion Difficulties High expansion of molding sands having too narrow a grain distribution; i.e., those sands having an accumulation of sizes on two or three adjacent screens, sometimes benefit from cereal additions. Cereal impairs flowability, thus it hinders sand expansion caused from hard, or excessively dense rammed molds. Cereal fills the sand voids and furnishes a "cushion" between the sand grains.
Southern Bentonite Replaces Cereal A recent trend working successfully in some foundries is to substitute southern bentonite for the more costly cereal in backing sands in order to obtain greater flowability. The elimination of the cereal in backing sands is recommended. It is more economical to use a good flowable bonding clay which is also less expensive. Southern bentonite furnishes even greater bonding power than cereal in backing sands. The effect obtained by the use of bentonite for cereal is higher green strength combined with easier shake-out. This reduces unnecessary labor costs by eliminating the excessive ramming of the molds when a tough sand mixture is used. The use of southern bentonite lowers material costs and decreases sand reclamation costs.
Wood Flour Replaces Cereal Wood flour or Cellflo are used as partial replacements for cereal in molding sands, which has proven quite satisfactory, even in the casting of steel. Wood flour or Cellflo additions to a sand mixture guard against over-ramming. The particles of cellulose act as a cushion and resist the close packing effect of the sand grains caused by unusually hard ramming of the mixture. Because cellulose increases flowability, wood flour insures an even ramming and avoids "spotty" high density areas of the mold. In the early days, sawdust containing rosin was used as an ingredient for molding sand mixtures. Years ago, foundrymen claimed that the rosin had a strengthening effect on the mold when the metal was cast, as the rosin was reduced to a molten form. The rosin actually had a weakening effect when it cooled into a solid form. Since then, finely ground wood flour has become favored over coarse sawdust to avoid ruining casting finish. It is worthwhile to investigate a wood flour as a partial replacement for the cereal bond because cellulose distinctly acts as a buffer against sand expansion and furnishes a good mold atmosphere which allows the metal to lie more quietly after it enters the mold. Scabbing action is less likely to occur at elevated temperatures where wood flour, Cellflo or cereal are used in molding sand mixtures.
Cereal Bond Affects Sand Mixtures as Follows: Green Compression Strength-Increases (however, increased amounts of temper water decreases green compression strength, even with larger amounts of cereal bond added to the mixture) . Dry Compression Strength-Increases, as moisture is increased. Hot Compression Strength-Decreases. Green Permeability-Decreases. Baked Permeability-Increases slightly. Flowability-Decreases rapidly, as moisture is increased. Shatter Index-Increases. Temper Water-Increases (control is essential). Mulling Time--Increases. Moisture Pick-Up--Increases. Mold Hardness-Decreases (if ramming is held constant). Deformation-Increases, as moisture is increased. Sand Expansion--Cereal decreases scabs, buckles, and rat-tails by lowering the mass expansion of the rammed sand mold. (One of the quickest ways to eliminate expansion defects is to add approximately 0.5% to 1.5% of cereal to molding sand mixtures.)
CERESIN (See: WAX) A wax used for patterns in the "Lost Wax Process." Ceresin is melted and cast into dies to form the wax pattern.
CHALK (Asbestine)-(See: LIMESTONE) Is another type of limestone, which consists mostly of microscopic shells and plant remains which were usually deposited by water action. The White Cliffs of Dover are striking beds of chalk formed in this manner. It is porous and soft. It is used as the base of certain commercial dry parting compounds.
CHAMOTIE (See: BRICK, CRUSHED-CALCINED CERAMIC GROG-COMPO GROG) A refractory molding media, consisting of ground calcined refractories, ground firebrick or fired clays which are bonded with plastic refractory clays and the mixture is called "Chamotte." It is tempered and then pugged to a proper mulled consistency. It is used more widely in Europe than in the U.S.A. in a molding mixture.
CHARCOAL (See: CARBON--COKE) Charcoal is an amorphous form of carbon which is made by enclosing wooden billets in a retort furnace, then exposing them to a red heat for several hours. Charcoal is also made in nature by covering large heaps of cut wood logs with earth and permitting the wood to burn slowly for about a month. Charcoal's specific gravity is 1.5 to 2.0, and it is insoluble in water. Charcoal is used in pulverized form singly, or in blends, as a foundry dry blacking ingredient. When charcoal is suspended with clay, bentonite or other ingredients, it is used to dust molds where extremely fine casting finish is desired in both ferrous and nonferrous foundries. A print-back of the pattern after charcoal dusting gives excellent detail to the surface of the casting. Two (2) percent additions are used in some nonferrous molding mixtures. Charcoal had wider use in past foundry history. It has generally been replaced with other more economical grades of carbon, and equal results have been obtained. Green Shell Carb, a commercial carbon additive, has replaced charcoal in most foundry sand mixtures. Charcoal briquettes are also used as fuel to dry molds, when required, in larger casting production.
CHEMICAL AGENTS Any organic or inorganic element, or compound, which is involved by intent, or by accident, or by natural reaction in the founding process is called a chemical agent. Many chemical agents are used in the foundry for molding, coring, spraying, or for other foundry needs.
CHEMICAL RESIN BINDERS (See: COLD CURED RESINS-RESINS) The principal foundry types are: 1) Alkyd resins. 2) High furfuryl alcohol fur an resins. 3) Natural resins.
CHEMICAL SETTING BINDERS (See: ALKYD RESIN BINDERS-BINDERS-BONDS-CORE BINDERS-LINSEED OILOILS)
CHILE SALTPETER (See: SODIUM NITRATE)
CHINA CLAY (See: CLAYS-KAOLIN) Is a commercial, ceramic, kaolinite clay of higher purity than kaolin. China clay is concentrated by a washing process which is then used in many foundry washes, coatings or compounds. China clay is more widely used in the ceramic industry than in the foundry. More kaolins are used in the foundry than the cleaner and usually more expensive China clays.
CHINA WOOD OIL (See: CORE BINDERS-CORE OIL-OILS TUNG OIL)
CHROMITE OR CHROMITE-SPINEL (See: HEVI-SAND) A mineral having as its essential constituent, the chrome bearing spine!, has the chemical formula [(Fe, Mg)O• (Cr, Al, Fe)2O3]. It is concentrated, heated, screened, sized, and made available as a foundry sand aggregate. Chromite is an ore of chromium, commonly called chrome ore when used as a refractory. The concentrated chromite ore which is known as "Hevi-Sand" is actually a chromite-spine!. The mineral composition of chromite-spine! is [FeO • MgO • Cr2O3 • Al2O3]. Chromite in its natural form is massively granular. Commercial grades vary from 35% to 60% chromic oxide (Cr2O3 ). Its Moh's hardness is 5.5 and its specific gravity is approximately 4.6. Chromite has an extremely high melting point of about 3.900° F. (2150° C.) and most of the commercial chromite ore is mined outside of the United States. The most popular concentrated chromite is "Hevi-Sand." Finer chromite, Hevi-Sand Flour, is also available as a sand additive.
CINDERS A residual, granular product obtained as near-ash by the forced firing of coal. Cinders may also be the slag from a blast furnace practice. Cinders are sometimes employed as non-active fillers for large cores or molds to facilitate venting and to encourage proper collapsibility.
CLAYS (See: BENTONITE-BONDING CLAY-CHINA CLAYCOAL MEASURE CLAY-FIRECLAY-KAOLIN-KAOLINITE-SHALE-SOUTHERN BENTONITE-VOLCLAY - WESTERN BENTONITE) Clays are hydrous aluminum silicates. They are mingled with mineral impurities and are colored by the action and reaction of water contining metallic oxides and organic matter. The general term, "Clay" describes all earths that form a plastic mass when wetted with water and which may be formed into a shape and then harden to retain its shape when dried, heated, or fired. The principal clays used in the foundry industry by mineral names, are: ( 1) kaolinite (fireclay), (2) montmorillonite (bentonite), (3) illite (shale-like) and some local mixtures of clays oft-times referred to as "fireclays," are actually contaminated "kaolinites.:' Fine quartz (SiO2) sand, mica and feldspar are found in most fireclays, and in some of the lesser refractory clays. Kaolins and commercial fireclays are generally the most used refractory for foundry use and contain only small amounts of alkali which allows them to withstand higher temperatures. Calcareous clays are known as "Marls," but are not widely used in the foundry industry. Many fireclays contain pyrite ( iron sulphide) in excessive amounts and have limited foundry use. Clays containing high lime are not completely acceptable for refractory purposes. Most clays when wetted and kneaded with the hand have sufficient plasticity and cohesion to form shapes. When clay is mixed with sand or other aggregates, tempered and mulled, they must develop proper bonding properties to be accepted by the foundry. Clays are not only used as sand binders and refractories, but are also present in foundry compounds, mold washes, core washes, coatings, pastes, cope and drag seals, patches, and for use in many phases of the foundry.
COAL (See ANTHRACITE COAL-BITUMINOUS COAL-CARBON-COAL DUST--COKE-LIGNITE-SEACOAL) Coal is a general name for a black mineral which is largely composed of carbon but containing smaller amounts of hydrogen, nitrogen, oxygen and sulphur in it. Coal was formed by deposits of ancient vegetable matter while under pressure. By aging, coal developed into a natural product that could be employed as a fuel. It gives combustible gases and carbohydrate products. Peat is a form of coal in its first developing stage, followed by lignite, bituminous coal, and finally harder anthracite coal with various intermediate grades between. Coal deposits are widely distributed in many parts of the world. Its value is judged on its contained fixed carbon content, volatile matter and ash content. It is graded into many screened sizes for acceptance by the foundry industry. A good grade of coal for foundry use generally contains 55% to 60% fixed carbon, 30% to 37% volatile matter, and one which does not exceed 8% of ash content (lowest is preferred). The B.T.U. value should be a minimum 13,500 to 14,000 per pound. Coal can absorb large amounts of water, which is not recommended for foundry use. For foundry use in sand mixtures, it is also known as "coal dust" and "seacoal." Composition of Coals (See: BITUMINOUS COAL)
COAL DUST (See: SEACOAL) Is the European name given ground coal used principally in British and Continental European molding sands. It is the same type coal termed, "Seacoal" in the U.S.A. and other North American foundry practices.
COAL OIL (See: FUEL OIL-KEROSENE-OIL-PETROLEUM An oil used as fuel oil, also an oil used in certain liquid partings.
COAL MEASURE CLAY (See: CLAYS-FIRECLAY-KAOLIN) The geologists adopted the word "fire clay" as being the same as a "coal measure clay." Many "coal measure clays," however, are no longer considered fire resistant. Fire clay is not necessarily a refractory clay, or one resistant to the action of fire. Usually, coal measure clays are deposited below a coal seam, hence they were named accordingly. A coal measure clay is a sedimentary clay having a low flux content. Many fire clays are used in the foundry industry as bonding clays when they are ground quite finely and have good plasticity. They are also used as binders for refractories, or ladle and furnace linings when blended with other aggregate materials.
COAL TAR (See: ASPHALT-COAL TAR PITCH-TAR) Is used for many purposes in the foundry, but one use is to help bind refractories such as basic refractories, which are used in basic cupolas, basic electric arc or oxygen furnaces, or ladles.
COAL TAR PITCH (See: ASPHALT-COAL TAR-PITCH-TAR) In the destructive distillation of coal, coal tar pitch is produced by the coking action, as coal is heated under a controlled atmosphere. Coal tar, benzene and toluene are further extracted from the coal gas and coal tar pitch. Ammonia is condensed and recovered from the coal gas and water condensate. Bituminous coals are found to be most suitable for this purpose. Coal tar pitches are used widely in the foundry industry where skin-dried molds are made and where dry sand molds are preferred. (See: pages 164-166, 214-216)
COBALT NAPHTHENATE (See: DRIERS, CORE-DRYERS) Is the reaction product between a cobalt salt and naphthenic acid. It is used to accelerate the rate of "drying" of a core oil.
COKE (See: CARBON-COAL-PETROLEUM COKE) One of the basic raw materials used in the foundry is coke. It is a porous, infusable black residue which remains after the volatile matter is driven away from the bituminous coal, which has been heated to a temperature between 2192° F. (1200°C.) to 2552° F. (1400°C.) without allowing air to burn it. The volatile is expelled. This coke residue which is mainly fixed carbon and ash is a porous, cellular material. It has a fixed carbon of about 86%. The ash is generally less than 12 % and the sulphur content should not exceed 1 % . The volatile matter should be less than 2 % by weight. The apparent specific gravity should never be less than 0.8. The true specific gravity varies between 0.8 to 2.10 for acceptable foundry use. A typical foundry coke for melting metal has an ignition point of about 1000°F. (538° C.). The sulphur should be less than 0.8%. Coke is screened for melting purposes as a fuel, or ground to various sizes where it is used in many ways in the foundry. A finely ground, sand-sized coke is used as an addition to molding sand. Coke is used as bedding sand for venting very large castings produced in dry sand molding. Fine coke and charcoal are used as parting material, or as blacking ingredients for mold or core wash coatings. Very finely ground coke and charcoal are used as dust-on facings for molds and cores. Besides melting metal, coke is used in many other foundry areas.
COLD BOX CORE BINDERS Several patented processes exist. One has two liquids added to a core sand mixture. About 2 % binder is used. One liquid is phenolformaldehyde resin in an organic solvent. The second is polymethylene polyphenol isocyanate. After flowing the sand mixture into the core box, a gas vapor of triethylamine is forced thru the formed core. The residual vapor and air are passed thru a dilute phosphoric acid scrubber for safety purposes. A hard core is formed without heat.
COLD CURED RESINS (See: RESINS) May be a chemical self-curing urea-formaldehyde furfuryl alcohol liquid resin which does not require subsequent baking. Cold cured resin may also be an oil binder with sodium perborate to activate. Cold curing synthetic resins, such as furan base resins, do not require heat to develop their bonding and hardening properties. Curing is accomplished by acid such as phosphoric, or gaseous methods. Also, a cold curing resin may be an alkyd resin which cures at room temperature when mixed with an activator. These may be a linseed oil base using isocyanate, aromatic poly, or methylene diphenyl-dinaphthenate and/ or cobalt.
COLD-SET RESINS (See: COLD BOX-COLD CURED RESINS-RESINS-SELF-CURING BINDERS)
COLLOID (See: SODIUM ALGINATE-VOLCLAY. Colloidal particles are invisible under the average foundry microscope. Their diameters are less than one-tenth (0.1) of a micron. Particles of smaller diameters are of molecular dimensions. Albumin, glue, starch, gelatin and the mineral, "bentonite" are typical colloids used· commercially within the foundry. A colloidal state is a dispersed mixture of two substances in which one substance, called the "dispersed phase" is uniformly distributed in a very finely divided state of less than 0.1 microns in the dispersion.
COLLOIDAL BOND (VOLCLAY) (See: CLAYS) Volclay bentonite is a colloidal substance which can be readily dispersed in water. As a colloidal dispersion or suspension, there is a continuous random motion which occurs in the so-called, "Brownian Movement" and the true clay particles do not settle.
COLLOID OIL-Nos. 500-501 (See: CORE OILS) A complete family of proprietary core oils developed and tailored to fit the requirements for binding foundry cores.
COLLOID RELEASE AGENT A commercial release agent or pattern spray developed for, and by, the foundryman.
COLLOIDREZ 7104 A liquid phenolic resin of high solid content. It is a high temperature resin, used principally by the steel foundry industry for binding cores. It is used as a refractory binder, a coating additive and as an ingredient for core or mold sprays.
COMPO (See: CHAMOTTE) The name is derived from an English Sheffield composition which is an intimate mixture of sand, crushed firebrick, clay, and water. These are prepared by mulling and tempering. Compo is then made into a mold facing, usually covering a back-up brick frame so as to improve the casting's surface.
CORE BINDERS (See: AIR-SET BINDERS-CORE OILS-FURAKE BINDERS-HOT BOX BINDERS-LINSEED OIL-NO-BA BINDERS-OILS-SELF CURING BINDERS) 1. Core binders are classified according to their composition: a) Organic b) Inorganic 2. Core binders are classified by their hardening or curing temperatures: a) Freezing cores by using water as the binder • b) Curing cores at room temperature with binders such as: sodium silicate, ethyl silicate, other silicates, oxychloride, Portland cement, Hi-early cement, rubber cement • c) Curing cores by baking, and using binders such as: 1) Core oils (linseed, polymers, cottonseed, corn, china, fish, soybean, perilla, others) 2) Cereals ( corn, wheat, rye) ; starch, dextrin 3) Gelatins 4) Resins (urea, phenolic, modified or unmodified) 5) Rosin, sulfite, protein, gums, others 3. Core binders cured by baking: a) Those that harden on cooling, after being heated, i.e., Coal tars such as pitch or natural asphaltum minerals such as gilsonite, and coal tar resins. Waxes such as carnauba, paraffin, carbo wax, beeswax, spermaceti, bayberry, others. b) Binders that dry, oxidize, polymerize and harden on heating such as core oils, resins, or rosins. Synthetic resins such as urea formaldehyde, phenolic formaldehyde, modified oils such as vegetable oil, modified with resin. Gum rosins such as ester gum, gum arabic, gum tragacanth, gum ghatti, locust bean gum, and less popular gums. Wood rosins such as pine gum or the distillate from turpentine oils. Specially processed rosins. Rosin oils, or synthetically produced rosin oil. Petroleum resins or oils that require polymerization. Stearate which may be stearic acid, a fatty acid-but not widely used as a core binder. c) Those binders that exhibit adhesion when the water solvent is evaporated, such as dextrin and cereals. Polyvinyl alcohol is also one which is a latex type binder. 4. Drying type core binders: a) Vegetable oils (linseed-cotton-tung-china-soy bean) are more widely used oil binders b) Polymers, either mineral or vegetable, are the faster baking oils c) Marine or animal oils such as whale, menhaden, sardine, or other type fish oils which have lesser baked tensile strengths 5. Binders that evaporate moisture to give adhesion: a) Sulfite cellulose, lignin sulphite, calcium sulphite, others b) Proteins c) Cereal (wheat-rye-corn), gluten flour d) Dextrin, molasses, sugars, gelatins e) Starch ( corn or potato) f) Cellulose acetate (methyl cellulose) 6. Mineral Binders (inorganic type binders) a) Bentonite (Volclay or Panther Creek) b) Fireclay (Kaolinite) c) Ball Clay d) Cement 7. Chemical Type Core Binders a) Sodium silicate gassed with CO2 to harden b) Rubber with the proper evaporated solvent c) Oxychloride d) Silicon esters e) Many resin types of the synthetic family f) Ethyl silicate 8. Catalyzed Binders a) Acid setting binders-no-bake type resins b) Gas setting binders-sodium silicate type binders and more recently the isocyanate activated gas binders 9. Ai Setting (curing) Binders which require no baking a) No-bake type using sodium perborate as an activator b) No-bake self curing type using phosphoric acid as an activator
CORE DRIERS (See: DRIERS, CORE) An additive to hasten the baking and curing of a core.
CORE OILS (See: COLLOID OIL-CORE BINDERS - DRYING OIL- EMULSIFIED OIL- OILS-SPERM OIL) Some liquid organic binders used for making sand cores in the foundry are called "core oils." The base formulation for foundry core oils originally was 55% to 60% linseed oil, 20% drying oil such as kerosene and 20% to 25% of a natural resin. Various hydrocarbons, vegetable oils and marine oils gradually replaced linseed oil, as technology advanced. For years, linseed oil was claimed to be the best liquid-core binder, however in many cases the baking required was too expensive for ordinary foundry use. Vegetable oils, hydrocarbons, and solvents were added to core oils to give different core properties. Marine, various fish oils and rosin oil were introduced. Molasses, dextrin and sulphite liquors were gradually included in many commercial core oils. Earlier, AFS had specifications for recommended core oils according to the percentage of raw linseed oil which the core oils contained. This also regulated the amount of gum rosin present in the core oil. In fact, the minimum of 25 % linseed oil regulated the amount of white kerosene added. It was also specified that no fish oil adulterant be added unless specified. The viscosity, specific gravity, flash point, iodine number, baked strength at specific temperatures, and collapsibility at specific temperatures are all important in selecting a foundry core oil. Drying oils such as perilla oil and corn oil have been used in many commercial grades of core oil. From 15% to 35% drying oils replaced the amount of linseed oil with various degrees of success. Soybean oil was gradually blended with linseed oil in early foundry core practices. There was actually no specification on grades of core oils produced by commercial manufacturers other than by agreement between the manufacturer and the foundry. Foundries specified core oil properties that proved best for the castings they produced. There are innumerable commercial and proprietary core oils available for today's purchase. Over the years, core oils have gradually given way to synthetic resins, but not to the extent that the industry advertises. Core oils still lead all other core binders and are still the basic binder of the foundry core room. Core oil is specifically a binder for cores, yet it is added to many molding sand mixtures for special applications. One pint of core oil added to one thousand pounds of molding sand is common practice in many manganese steel foundries, so as to improve casting finish and prevent metal oxide attacks on the silica base core or mold. It is common for various core oils to be added to molding sands in different percentages. To help hold mold edges and to give added dry strength-to molding sand surfaces some core oils have been used. For further data on core oils, composition and their uses.
CORE PASTES (See: ADHESIVE-CEMENTS-GLUE-GUMS)
Are commercially prepared adhesives used to join core parts and assemblies. Most core pastes are mixtures of one, or several blends of clay, bentonite, dextrin, cereal, lignin sulphide, proteins, starch, gums, and resins. Usually core paste is sold in a dry powder, or semi-paste form which may be mixed further with water or a recommended lubricant to form an adhesive paste. This core paste is to cement sections of molds or core assemblies together. Due to variations in foundry practice, it is difficult to predict which core paste is best suited for the particular mold or core being made. The base sand also dictates the best paste to use when it is applied. Core pastes are formulated to meet specific conditions throughout the entire range of foundry practice. One of the earliest core pastes was a mixture of fire clay, bentonite, and dextrin in about equal parts. This clay paste was mixed by the foundry with water to achieve their desired consistency. Cereals of various natures were later used with this clay mixture. Still later, caseins were added, then numerous glues and resins were adapted into various commercial formulations for foundry use.
CORN FLOUR (See: CEREAL) A cereal flour used as an addition to sand mixtures to give specific properties in the casting of metals. It is used in both core and molding mixtures. Gelatinized corn flour is made from the dry milling of hominy grits, or meal for foundry use. It is produced in several grades; such as, light weight, intermediate weight and heavy weight.
CORN OIL (See: CORE OILS-OILS) It is also known as "maize oil," a bright yellow oil obtained by pressing the germ portion of the grain and collecting the oil. The grain contains about 20% of corn oil and is a by-product in the manufacture of corn starch and glucose. Corn oil is also obtained in the manufacture of alcohol from corn grain and consists largely of oleic and linoleic acids. It has been used in the foundry as a liquid parting agent when blended with kerosene and as a blended core oil to obtain specific properties. CORN STARCH (See: STARCH) CORUNDUM (See: ALUMINA-ALUMINUM OXIDE -ALUNDUM-BAUXITE) Corundum is an oxide of aluminum with the chemical composition [ Al203]. While it is found in the natural state, the small amount of the corundum used as foundry sand is artificially manufactured. Artificial corundum is made on a large scale and sold under various trade names. It is made by fusing bauxite in an electric furnace in the presence of carbon. The Moh hardness of corundum is 9. Its specific gravity is 3.93 to 4.10. The word "Corundum" is Hindu. The word applies to gem stones or opaque stones and is widely used to describe most stones of this type. The foundry uses the largest amount of corundum as grinding wheel aggregates, but because of its expense it is used sparingly as a refractory aggregate. It is used in many mold and core coatings. Corundum finely ground is used in refractory washes to replace silica sand fines, as well as silica flour for specific foundry molding and core purposes.
COTION SEED OIL (See: CORE BINDERS-CORE OIL-OILS) The kernels of the cotton seed themselves are heated and press·ed to remove the oil from the seeds. During this pressing, the kernels are wrapped in cloth to prevent anything but oil from being expressed. The'-oil is purified to a soft white substance very similar to lard in appearance. Cotton seed oils are used in many core oils for foundry use and in many cases they have been replacing the more expensive oils in commercial compounded core oils.
CREOSOTE Creosote is often referred to as a "pitch oil" or "dead oil." It is a yellowish, oily, highly viscous, tarry liquid obtained from the distillation of coal or wood tar during the manufacture of gas and coke. It is an antiseptic liquid with a smoky, burning taste and used as a deodorizer. Its specific gravity is between 1.07 and 1. 1. The foundry type creosote contains the three cresols; ortho, meta, and para. It is a complex mixture of various phenols and their esters, principal constituents being guaiacol, cresol, phloral and methyl cresol. Creosote is used with tar or gilsonite as a coating on some cast metal ingot molds to separate the cast steel ingot from the iron mold. It is used as a coating on permanent molds in combination with various asphaltum products, gilsonite, or pitch-like materials. This use is gradually declining, as less expensive commercial blackings and coatings are offered as substitutes. Creosote has been used by foundries for coating chills. It is gradually being replaced by other materials due to its release of irritating gases which are products of its decomposition. For this same reason, creosote as a molding sand additive has never attained popularity in the foundry.
CRUDE OIL (See: FUEL OIL) CRUDE SAND (See: SAND)
Sand which is mined and not further processed.
CUMERONE RESINS (See: CORE BINDERS-RESINS-SYNTHETIC RESINS) Are synthetic resins having great solubility in many organic solvents and are used as foundry type resins to some degree. Resins, as a binder group, are slowly replacing core oils in the core room. However, their growth has leveled off considerably since their conception only a few years ago. Cumerone resin is not the most popular foundry type resin.
CYANITE OR KYANITE (See: KYANITE) The mineral cyanite is an aluminum silicate, corresponding to the formula [ Al2SiO5]. Its Mob's hardness varies from 5 to 7.5, depending on the crystanographic direction. Its specific gravity is 3.56 to 3.67. Cyanite is found associated with various type of rocks and is generally not found in its pure form. Cyanite derives its name from the Greek word meaning "blue," in reference to the delicate blue of the inner portions of the bladed crystals. Cyanite or kyanite is a refractory that is used in many mortars or cements of the foundry. It is also calcined to form mullite, which has greater volume stability as a refractory of high temperatures. Kyanite is also used in some investment molding for casting metals. It is considered a refractory and many foundries incorporate it in various furnace applications as well as foundry sands for specific cases.
Review of "Glossary of Foundry Additives" by Clyde A. Sanders, American Colloid Company