D - Foundry Additives Glossary
DEXTRIN (DEXTRINE) (See: CEREAL-CORE BINDERS STARCH)
Foundry dextrin is usually a bright yellow or white color. It is completely water soluble and forms a syrup. It is a concentrated starch product. Dextrin is produced by the acid digestion of pure corn starch. When used in molding sands it adds little green compression strength to the sand mixture, but as the temper water migrates to the mold's or core's surface when left standing, dextrin adds exceptionally high dry surface strength. Usually the amount of temper water in the sand mixture determines the dry compression, or shear strength. It is common in the foundry to use dextrin where inner dry compression strength is required, and where dry compression strength is necessary to hold and provide detailed edges of the mold or core. Dextrin weighs approximately 1.3 to 1.4 lbs. per quart, or 39 to 42 lbs. per cubic foot when purchased as a foundry additive. Cereal and dextrin are widely used in the foundry industry as binders. The steel foundry has practiced the use of dextrin perhaps more widely than other foundries. It gives very high skin hardness to molds or cores which contain it. The higher the moisture content of molds bearing dextrin, the harder the surface of the molds and cores, particularly if they are later baked in an oven. Dextrin is a powerful binder and is made by moistening starch or cereal with a mixture of dilute nitric and hydrochloric acids, then exposing this mixture to a temperature of 212°F. to 259°F. (100°C. to 125°C.) for a given period. Dextrin varies in grades due to differences in the starch from which it is made. Dextrin has been called "British Gum" and "Amylin." There is a group of compounds which have the same formula as starch [C6H10O5J.
DIATOMACEOUS EARTH (See: KIESELGUHR-TRIPOLI)
Although diatomaceous earth is not widely used in the foundry, it is a hydrated silicate of the same composition as the opal. At times it has been referred to as a clay, but it is mostly like Tripoli and Kieselguhr. It is sometimes called "Diatomite" and 90% of its volume is porous. It has great absorptive powers and most often holds five times its volume of water. The apparent density of diatomaceous earth in the commercial form occasionally used in the foundry is approximately 12 lbs. to 17 lbs. per cubic foot. It is very light and has been used for insulating purposes in the foundry. It is used in some insulating cements, mortars and mold coatings. It can withstand temperatures up to 1900°F. ( 1038°C.). Diatomaceous earth has functioned as a replacement for asbestos fiber for insulating purposes in the foundry but has limited use as an additive in molds or cores at present.
DIATOMITE (See: DIATOMACEOUS EARTH)
DIETHYLENE GLYCOL (See: ETHYLENE GLYCOL)
DRIED SAND (See: SAND)
Any sand which has been dried mechanically to remove its water before commercially used in the foundry.
DRIERS-CORE (See: AMMONIUM NITRATE-COBALT NAPHTHENATE-DRYER)
Ammonium nitrate, cobalt salts, iron salts, potassium permanganate and a few others are added to core oils to hasten baking time.
DRYER-CORE (See: AMMONIUM NITRATE-DRYER)
DRYERS OR DRIERS (See: AMMONIUM NITRATE-COBALT NAPHTHENATE-DRIER, CORE)
A few dryers used in certain core mixtures are: ammonium nitrate, cobalt salts, iron salts, and potassium permanganate. These hasten baking time of core oil binders.
DRYING OIL (See: CORE BINDERS-CORE OIL-LINSEED OIL - OILS)
1) Vegetable oils such as linseed, tung*, chinawood and soybean are drying oils. 2) Polymers, either mineral or vegetable, are the faster drying oils in core mixtures. 3) Marine, fish, and animal offer the lesser baked tensile strengths. * Tung and china wood oil are synonymous.
DRY PARTING (See: LIME-LYCOPODIUM-PARTINGS TALC)
Dyes or "dye stuffs" are substances which give color to various molding sand and core sand mixtures in the foundry. The dyes may be mineral, animal, or vegetable dyes. The artificial dyes are mainly derived from coal-tar residues, whereas vegetable dyes are watersoluble and are made from woods, flowers, leaves, barks and such. Mineral dyes are extracted from such natural minerals as hematite, ochre, limonite, and others. Marine dyes are obtained from various snails, conchs, and many forms of marine life. Small amounts of dyes color sand mixtures to any degree desired.
Review of "Glossary of Foundry Additives" by Clyde A. Sanders, American Colloid Company
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