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  • Writer's pictureHill and Griffith

"I" - Glossary of Foundry Additives (Green Sand Additive Products)

I - Foundry Additives Glossary


INDUSTRIAL ALCOHOL (See: ETHYL ALCOHOL) INHIBITORS Are agents which prevent decomposition, or retard decomposition rates to acceptable levels. They are widely used in magnesium molding sands to diminish oxidation rates which can cause severe fire conditions or explosions. Materials such as boric acid, sulphur or a fluoride are used to prevent the burning of molten magnesium alloys when poured in foundry molds, and are called inhibitors. These inhibitors restrain an undesirable mold-metal chemical reaction generally due to the oxygen reaction in the mold cavity when the hot metal enters the mold.

INORGANIC BINDERS Binders such as clay, bentonite, cement, sodium silicate, silicon esters, and others are classified as inorganic binders. Some metallic salts are so classified in the foundry. Usually, foundry binders of this type are more refractory than the organic type. They do not decom­pose as fast and have more durability.

INVESTMENT COMPOUND A refractory mixture used for molds or cores which is formed around wax patterns in investment casting, or the "lost wax process."

IRON ORE OXIDE (See: FERRIC OXIDE-HEMATITE-IRON OXIDE-KLEAN SURF) The principal iron ore additives used in the foundry are generally those ground from hematite (Fe2O3 ); magnetite (Fe3O4); limonite (Fe2O3 •3H2O); and siderite (FeCO3). Most of the ground iron oxide used in foundry sand mixtures as green sand additive products is hematite (Fe2O3 ). The iron content varies from 30% to 55 % iron (Fe). Ground hematite is not only used for coloring the core or molding sand mixtures, but it is also used as an additive to prevent metal penetration, burn-on and/or pinholing of the casting from incorrect foundry molding and core sand mixtures. Iron ore oxide blended with other oxides or binders is one of a group of proprietary binders or compounds used in the foundry. They are formulated to promote a specific function, or meet a certain set of conditions demanded of a foundry sand, or refractory mixture. The FeO-SiO2 eutectic, which is found when silica reacts with iron oxide, melts about 2150°F. (1178 °C.). This leads to one explanation for the efficacy of iron oxide towards increasing hot compression strength and hot plasticity of a sand core mixture. The iron oxide forms a glaze when heated, which is compressed on a flat plane just beneath the interface of the sand's surface, thus lowering the hot permeability sufficiently to retard metal penetration. Since the iron oxide acts as a flux, the coefficient of expansion of the sand mixture is lowered and the tendency for a defect, such as a scab, buckle, or rat­tail is minimized. Hot compression strength of the sand mixture increases as a result of the glaze caused by the fusion of the iron oxide additive. Certain wood flours containing iron oxide are also available to the foundry. Iron oxide proportions in the compounded wood flour range from two to three percent by weight. However, in most cases, iron oxide is used as only a coloring agent, which enables the foundry­man to identify each sand mixture being used. Foundries producing ferrous or nonferrous castings find the use of a good quality iron oxide as an aid in promoting easier cleaning of the castings which sharply reduces cleaning costs.

In specific applications iron oxide is used to: (1) Improve surface finish of the casting. (2) Decrease veining of the casting. (3) Reduce metal penetration of the casting. (4) Increase hot plasticity of the sand mixture. (5) Reduce burn-on of the casting. (6) Increase glazing of the sand mixture. (7) Reduce or eliminate pinhole porosity in castings.

Iron oxide in combination with silica flour in core or mold facings improves the sand surface to such an extent that in many cases a mold or core wash may not be required. Klean Surf iron oxide is a well known commercial grade that furnishes this property to a sand mixture. Iron oxide is compatible with practically all of the core binders, especially sodium silicate. One to three percent Klean Surf iron oxide is recommended for general use in the CO2 sodium silicate molding process. If this amount is insufficient for a specific application, fire­clay, or western bentonite may be used in conjunction with the oxide. When iron oxide is used in ladle lining mixtures, it is sometimes re­ferred to as a "mineralizer or plasticizer." If iron oxide is mixed with siliceous materials, it tends primarily to reduce the sintering point of the mixture, hence this increases the vitrification or glazing at the mold-metal interface. However, caution must be exercised so as not to impair the refractoriness of the mixture to any great extent. IRON OXIDE (See: IRON ORE OXIDE-IRON OXIDE-KLEAN SURF) There are many grades of iron oxide used as a foundry additive in both core and molding sand mixtures. Iron oxide is added to foun­dry sand mixtures, principally to color the mixtures but also to improve the hot plastic deformation. A few iron oxides do this; some don't. Klean Surf is the most popular and successful foundry grade iron oxide. Types Many foundrymen believe that an iron oxide containing the highest percentage of iron (Fe) is best for use. In a few minor cases, this is correct, in most major cases, it is incorrect! Some grades of iron oxide are prepared by calcining or roasting them in various heaters, ovens or dryers. These roasted iron oxides are principally used as coloring agents for cement products, aggregate compounds, dog foods, cattle or animal feeds. Iron oxides are also used as additions for low priced paint pigments. Many foundrymen have purchased these iron oxides without fully realizing that the roasted types are difficult to melt, or fuse, after the ores are oxidized by heat. Their only value is in the coloring which they furnish. When certain iron ores are roasted so as to increase their (Fe2O3) content, a highly oxidized condition of all the associated minerals develops. A very high percentage of ferric oxide (Fe203) may act as a refractory which offsets its low eutectic value in a mold or core sand mixture. Some commercial foundry grades of iron oxide may contain a small percentage of added carbonaceous materials. When these oxides are added to a core or mold mixture, the carbon slightly delays. fusion by offering a reducing atmosphere before the final oxidation occurs. Great claims are made for certain of these iron oxides, but they are also economically limited. The delay of oxidation is often is a dis­advantage. A third foundry type of oxide which has been found to be the most satisfactory, and the most popular, foundry accepted is Klean Surf Iron Ore Oxide. It contains the best overall properties for foundry mold or core use.



ISOPROPYL ALCOHOL (See: ALCOHOL -ETHYL ALCOHOL) It is used in many light-off sprays and washes. It is also known as "2-Propanol" and is prepared from propylene, a by-product of a petroleum cracking solvent. It is miscible with water. Isopropyl alcohol is a low cost alcohol solvent widely used in the foundry indus­try as the light-off fuel in coatings and sprays.

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


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