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Green Sand Metalcasting Foundry News

"R" - Glossary of Foundry Additives

Posted by Hill and Griffith Company on Jul 3, 2018 9:58:52 AM

R - Foundry Additives Glossary


Any substance which resists high temperatures is called a refrac­tory. They are generally used for lining melting furnaces, pouring ladles and metal pots. Clay minerals are the oldest and most commonly used refractories. Natural refractories are ceramic materials such as fire clay, bauxite, ball clay, kaolin, zircon, silica, chromite-spinel, olivine, magnesite, and hundreds of others. Refractories are usually classified as being acid, basic, or neutral. The silica refractories are called "acid," the "basic" refractories are magnesite, dolomite and a few others. The "neutral" refractories are chromites, graphite and alumina. A product is not considered "refractory" unless it withstands at least 2806°F (1541°C). High grade refractory materials should withstand at least 3100°F. (1700°C.) and should resist slag, metallic oxide and chemical attacks. Refractories are prominently used in the foundry industry in every operation where heat is applied.

Kerosene and light oils containing waxes are used as release agents with most green sand mixtures. Silicone type release agents appear to be very effective for use with furan no-bake binder mixtures, hot box and shell applications. There are many commercial types and grades. 



Various solids or semi-solid organic substances obtained from the extractions of chiefly trees and vegetables are called, "Resins." Resins may be transparent or translucent and non-conductors of electricity. They are soluble in ether and alcohol. Some are only soluble in a few commercially accepted chemicals. Resins are insoluble in water. For example, "rosin" is the resin left after the distillation of the volatile oil of turpentine. Resins are a group of substances from tree gum extractions to those manufactured commercially such as the phenol resins, or the casein resins. Resins are complete compounds composed of carbon, hydrogen and some oxygen. Natural resins are soluble in alcohol and similar organic solvents. Resins are used in foundry coatings, com­pounds, and certain core additives. Oleoresins are natural resins containing essential oils of that plant. The commercial resins besides­ rosin are: lac, dammar, mastic, anime, sandarac, frankincense and others. Gum resins that are not entirely soluble in alcohol are rubber, myrrh, gamboge and a few others. Resins are used in coatings, sprays and refractories to adhere the substances to the molds and cores. Resins, and their uses, are well known to commercial mold and core wash producers. The thermosetting phenol-formaldehyde resins may be a 1-stage or a 2-stage setting resins. These resins may be partially reacted with hexamethylene-tetramine. 

Hot Box Resins

Hot boxes used for making cores are generally heated from 450 °F. (232°C.) to 500°F. (260° C.) and the cured sand mixture is held in the heated core box between 8 to 25 seconds, depending on the size and design of the cores. The use of the hot box processes con­tinues to grow and to improve in large productive foundries. Improve­ments in core making production are continually being researched. Cold-Set Resins and Methods Sand, resin binder and catalyst are mixed or mulled together. The coated mixture is then introduced into the core box and allowed to cure in the box, which is the pattern. Setting time, bench life, and cold or cured strengths are determined from a number of factors. The furfuryl alcohol modified ureas and phenol formaldehyde are the popular foundry choices for this process. Acidic conditions of most of the basic binders enable the completion of the curing. Any item in the mixture which contains minerals that form a salt when combined with the acid used, affects the curing performance of the resin. This, in turn, affects the proportion of catalyst used and may completely inhibit the curing reaction. The composition of the base sand may require special attention, if excessive mineral matter is present to affect the pH of the mixture.

Cold set resins

The amount of binders used is generally between 1.75% to 3.5%. The catalyst is generally 40% to 50% of the weight of the resin binder in the mixture. Cold curing mixtures have found a place in the production of large steel, ductile or gray iron castings such as those used for paper making machinery, lathe beds, milling machines, and others. Cold curing is less popular in the malleable and non-ferrous foundries. The resin industry is truly changing much of today's foundry core practices.

There are two kinds of rosins, "wood rosin" and "gum rosin." Rosin may be a common resin obtained from many varieties of trees which exudes as a dripping from that tree. The viscous liquid resin of the pine tree is distilled to remove turpentine and the residue formed is the rosin used in the foundry. It is flammable and easily fusable. Its formula is [C19H29COOH] and it is one of the less expensive organic acids available. Its specific gravity is generally 1.08 and it melts at approximately 212 °F (100°C), or slightly higher. Rosin is soluble in alcohol, turpentine and the alkalies. Rosin has various commercial gradings, but only the less expensive gradings are used in the foundry. The dark grades of wood rosin are considered inferior, but they do fulfill their purpose as foundry binders. Rosin oil is used, in foundry core oils, coatings, washes and refractory compound.

Is an oil produced from the distillation of rosin in retort furnaces. Two qualities of rosin oil are generally produced. One is a light spirit called "pinolin" which forms from 1% to 5% of the rosin. There is a heavier oil attached which forms about 80% to 84% of this distil­late. The coke-like residue left, is about 10% to 15% and consists of gas and water. Crude rosin oil has a specific gravity of 0.986 to 0.995. 

It contains abietic acid. Crude rosin oil can be purified by neutraliza­tion, or by the injection of air. It can be refined to a commercial liquid and is used as an adulterant of turpentine. The lighter distillate is used by the foundry as a "blended rosin oil" and is a mixture of about 35 % rosin oil with added mineral oils. It is frequently used with tung oil in the foundry for use as a core oil. It is also blended with many com­mercial core pastes and used in various refractory coating pastes. These refractory pastes may contain rosin oil, western (Volclay) ben­tonite, zircon flour, silica flour, plumbago, water and other ingredients mixed to an emulsified form to be further blended into a wash or coat­ing. Rosin oil is also used as an additive in slurries to aid suspension and to give adherence to sand mold surfaces. Also see: CORE OILS.)

Latex is a milky substance found in many plants. It is a com­plexed emulsion in which such substances as proteins, alkaloids, starches, sugars, oils, tannins, resins, and gums are found. Rubber is obtained from the latex of many plants. Chicle used as the base for chewing gum is another latex product. Several core pastes and core compounds have been made with latex. It is the base ingredient in solutions of alcohol which acts as the carrier.

The grain is very similar to that of wheat in structure. It is long and slender and is pulverized into flour by special grinding mills. Rye flour and its use in the foundry is more common in Europe and abroad than in America. Rye flour is used as a corn flour and wheat flour replacement in various foundry sand mixtures such as those common in making molds and cores. 

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

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