Foundry
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A foundry is a factory which produces castings of metal, both ferrous and non-ferrous. Metals are processed by melting, pouring, and casting.
Iron is the most common base element processed in a modern foundry. However, other metals, such as aluminium, copper, tin, and zinc, can be processed.
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[edit] Melting
Melting is performed in a furnace. Virgin material, external scrap and/or internal scrap are used to charge the furnace. Virgin material refers to raw materials that are single or limited elements such as nickel or ferro alloys or ingots of standard alloys. External scrap is left over from forming processes such as punching, forging or machining. Internal scrap consists of the gates and risers removed from castings.
The process includes melting the charge, refining the melt, adjusting the melt chemistry and tapping into a transport vessel. Refining is done to remove deleterious gases and elements from the final chemistry. Material is added during the melting process to bring the final chemistry within a specific range specified by industry standards and/or internal aims. During the tap final chemistry adjustments are made and material is added to remove gases.
[edit] Furnace
Furnaces are refractory lined vessels that contain the material to be melted and provide the energy to melt it. Modern furnace types include Electric arc furnaces (EAF), Induction furnaces and channel furnaces. Furnace choice is dependent on the grade and quantities produced.
Furnace design is a complex process, and the design can be optimized based on multiple factors. Furnaces in foundries can be any size, ranging from mere ounces to hundreds of tons, and they are designed according to the type of metals that are to be melted. Also, furnaces are bound by the fuel available that will produce the desired temperature. For low temperature melting point alloys, such as zinc or tin, melting furnaces may reach around 600 Kelvin (327 degrees Celcius). On the high end, from steel, nickel based alloys, tungsten, all the way to other elements with higher melting points, furnaces can reach to over 3600 Kelvin. The fuel used to reach these high temperatures can be electricity, natural gas or propane, charcoal, coke, fuel oil, or wood.
The majority of foundries specialize in particular metals and have furnaces dedicated to these metals. For example, an iron foundry (for cast iron) may use a cupola, similar to a small blast furnace. While a steel, bronze, or brass foundry will normally use an electrical induction furnace. However, in some cases, they may use a gas heated crucible furnace. Most aluminum foundries use either an electric resistance or gas heated crucible furnace.
[edit] Pouring
In a foundry, molten metal is poured into molds. Such molds may be made of sand, metal for permanent molding, ceramic, or refractory materials. The pouring can be accomplished with gravity, or it may be assisted with a vacuum or pressurized gas.
[edit] Casting
Casting is the process of reforming metal into a predetermined shape. This is done by pouring the molten metal into a form or cast and then allowing the metal to solidify. Depending on the conditions of the cast and the casting process, different properties of the final product can be obtained. For instance, if the cast is cooled very quickly, the final metal product will be harder and more brittle than a cast that is cooled slowly.
[edit] Fettling
The solidified metal component is then removed from its mold. Where the mold is sand based this can be done by shaking or tumbling. This frees the cast component, which will still be attached to the metal runners and gates - which are the channels through which the molten metal travelled to reach the component itself. Fettling is the process of mechanically removing these runners and gates. This can be done by sawing, grinding or tumbling.
[edit] Finishing
The final step in the process usually involves finer grinding, sanding, linishing or turning of the component in order to achieve the desired dimensional accuracies, physical shape and surface finish.
[edit] Advantages
The finished product of a foundry can be more versatile than the product of a rolling or machining process. Also, the process of casting molten metal, as is occurs in a foundry, can be far more automated than the labor-intensive machining method. Foundries have been in existence for several millenia, dating back to the ancient Chinese. A foundry is the original way to produce near net shape parts.
