Foundry1 Foundry A foundry is a factory that produces metal castings. Metals are cast into shapes by melting them into a liquid, pouring the metal in a mold, and removing the mold material or casting after the metal has solidified as it cools. The most common metals processed are aluminium and cast iron. However, other metals, such as bronze, steel, magnesium, copper, tin, and zinc, are also used to produce castings in foundries. In this process, parts of desired shapes and sizes can be formed. Process From Fra Burmeister og Wain's Iron Foundry, by Peder Severin Krøyer, 1885. In metalworking, casting involves pouring liquid metal into a mold, which contains a hollow cavity of the desired shape, and then allowing it to cool and solidify. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process. Casting is most often used for making complex shapes that would be difficult or uneconomical to make by other methods.[1] Melting Melting is performed in a furnace. Virgin material, external scrap, internal scrap, and alloying elements are used to charge the furnace. Virgin material refers to commercially pure forms of the primary metal used to form a particular alloy. Alloying elements are either pure forms of an alloying element, like electrolytic nickel, or alloys of limited composition, such as ferroalloys or master alloys. External scrap is material from other forming processes such as punching, forging, or machining. Internal scrap consists of gates, risers, defective castings, and other extraneous metal oddments produced within the facility. The process includes melting the charge, refining the melt, adjusting the melt chemistry and tapping into a transport vessel. Refining is done Melting metal in a ladle for casting to remove deleterious gases and elements from the molten metal to avoid casting defects. Material is added during the melting process to bring the final chemistry within a specific range specified by industry and/or internal standards. Certain fluxes may be used to separate the metal from slag and/or dross and degassers are used to remove dissolved gas from metals that readily dissolve certain gasses. During the tap, final chemistry adjustments are made. bronze. The fuel used to reach these high temperatures can be electricity (as employed in electric arc furnaces) or coke. induction furnaces. Reverberatory and crucible furnaces are common for producing aluminium. Modern furnace types include electric arc furnaces (EAF). cupolas. If the hydrogen concentration in the melt is too high. Electricity. To do that. reverberatory. Furnaces are refractory lined vessels that contain the material to be melted and provide the energy to melt it. melting furnaces may reach around 500° C. . They are designed according to the type of metals that are to be melted. Furnace choice is dependent on the alloy system quantities produced. and the design can be optimized based on multiple factors. or EAF. EAFs. ranging from small ones used to melt precious metals to furnaces weighing several tons. cupolas. Most aluminium foundries use either electric resistance or gas heated crucible furnaces or reverberatory furnaces. When the bubbles go up in the melt. propane. For example. An efficient way of removing hydrogen from the melt is to bubble argon or nitrogen through the melt. while a steel foundry will use an EAF or induction furnace. Bronze or brass foundries use crucible furnaces or induction furnaces. the resulting casting will be porous as the hydrogen comes out of solution as the aluminium cools and solidifies. A metal die casting robot in an industrial foundry Furnace design is a complex process. the furnace must be designed for temperatures over 1600° C. For high melting point alloys such as steel or nickel based alloys. they catch the dissolved hydrogen and bring it to the top surface. The majority of foundries specialize in a particular metal and have furnaces dedicated to these metals. such as zinc or tin. the density of the aluminium sample is calculated to check amount of hydrogen dissolved in it. Degassing In the case of aluminium alloys. For low temperature melting point alloys. or natural gas are usually used to achieve these temperatures. Furnaces must also be designed based on the fuel being used to produce the desired temperature. Furnaces in foundries can be any size. induction furnace. and crucible furnaces. Porosity often seriously deteriorates the mechanical properties of the metal. porosity sealing can be accomplished through a process called metal impregnating. several different types of equipment are used by foundries. For ferrous materials. Alternatively.Foundry 2 Furnace Several specialised furnaces are used to melt the metal. and brass castings. In cases where porosity still remains present after the degassing process. a degassing step is usually necessary to reduce the amount of hydrogen dissolved in the liquid metal. and induction furnaces are commonly used. designed to melt hundreds of pounds of scrap at one time. There are various types of equipment which measure the amount of hydrogen present in it. an iron foundry (for cast iron) may use a cupola. gates. The molds are constructed by several different processes dependent upon the type of foundry. Pouring can be accomplished with gravity. Ceramic mold casting — Plaster mold. Investment casting — Wax or similar sacrificial pattern with a ceramic mold. This frees the casting from the sand. Where the cope and drag separates is called the parting line. using the ancient lost-wax casting process Degating Degating is the removal of the heads. Cores are used to create hollow areas in the mold that would otherwise be impossible to achieve. When making a pattern it is best to taper the edges so that the pattern can be removed without breaking the mold. clay or resin is needed for sand to retain shape. Pouring In a foundry. runners. which is still attached to the metal runners and gates . Shakeout The solidified metal component is then removed from its mold.A diagram of draft on a pattern . • Die casting — Metal mold. Runners. called a cope. Bronze poured from a ladle into a mold. The opposite of draft is an undercut where there is part of the pattern under the mold material. making it impossible to remove the pattern without damaging the mold. A split pattern has a top or upper section. quantity of parts to be produced. For some metal types. This is called draft. metal to be poured. Both solid and split patterns can have cores inserted to complete the final part shape. plastic or metal. Lost-foam casting — Polystyrene pattern with a mixture of ceramic and sand mold. gates.A diagram of an undercut in a mold In the casting process a pattern is made in the shape of the desired part. Simple designs can be made in a single piece or solid pattern.which are the channels through which the molten metal traveled to reach the component itself.Foundry 3 Mold making . These mold processes include: • • • • • Sand casting — Green or resin bonded sand mold. size of the casting and complexity of the casting. and risers may be removed using cutting torches. The pattern is made out of wax. and with some gating . or it may be assisted with a vacuum or pressurized gas. More complex designs are made in two parts. Many modern foundries use robots or automatic pouring machines for pouring molten metal. molten metal is poured into molds. wood. called split patterns. • Billet (ingot) casting — Simple mold for producing ingots of metal normally for use in other foundries. this can be done by shaking or tumbling. V-process casting — Vacuum is used in conjunction with thermoformed plastic to form sand molds. and a bottom or lower section called a drag. molds were poured by hand using ladles. Traditionally. and risers from the casting. Where the mold is sand based. No moisture. bandsaws or ceramic cutoff blades. [2] More and more the process of finishing a casting is being achieved using robotic machines which eliminate the need for a human to physically grind or break parting lines. sometimes collectively called sprue. other metal alloys. baking powder among others. walnut shells. The reason for this is that these processes have better dimensional capability and repeatability than many casting processes. properties of a material. gating material or feeders. or may be hurled using a shot wheel. The most common application is metallurgical. glass beads. Heat treatments are also used in the manufacture of many other materials. These processes are used because their material removal rates are slow enough to control the amount of material. and sometimes chemical. any surfaces that require tight dimensional control are machined. Other foundries weld multiple castings or wrought metals together to form a finished product. The media may be blown with compressed air. including heads. to achieve a desired result such as hardening or softening of a material. 4 Heat treating Heat treating is a group of industrial and metalworking processes used to alter the physical. iron. that can exceed 50% of the metal required to pour a full mold. the sprue. Numerous materials may be used as media. or machining the component in order to achieve the desired dimensional accuracies. A few foundries provide other services before shipping components to their customers. called a gate stub. including steel. case hardening. Heat treatment techniques include annealing. it is not uncommon today for many components to be used without machining. such as glass. Many castings are machined in CNC milling centers. sanding. The introduction of these machines . aluminium oxides. heating and cooling often occur incidentally during other manufacturing processes such as hot forming or welding. This means a granular media will be propelled against the surface of the casting to mechanically knock away the adhering sand. physical shape and surface finish.Foundry system designs. precipitation strengthening. Surface cleaning After degating and heat treating. and thus melting costs. slag) from the casting surface. risers and sprue. to minimize the cost of excess sprue. Finishing The final step in the process usually involves grinding. tempering and quenching. Some foundries will assemble their castings into complete machines or sub-assemblies. sand. normally to extreme temperatures. Since this metal must be remelted as salvage. The blasting media is selected to develop the color and reflectance of the cast surface. Terms used to describe this process include cleaning. sand or other molding media may adhere to the casting. Risers must usually be removed using a cutting method (see above) but some newer methods of riser removal use knockoff machinery with special designs incorporated into the riser neck geometry that allow the riser to break off at the right place. To remove this the surface is cleaned using a blasting process. It is noteworthy that while the term heat treatment applies only to processes where the heating and cooling are done for the specific purpose of altering properties intentionally. runners and gates can be removed by breaking them away from the casting with a sledge hammer or specially designed knockout machinery. the yield of a particular gating configuration becomes an important economic consideration when designing various gating schemes. and sand blasting. After grinding. Shot peening may be used to further work-harden and finish the surface. The media strikes the casting surface at high velocity to dislodge the molding media (for example. Painting components to prevent corrosion and improve visual appeal is common. is usually done using a grinder or sanding. These steps are done prior to any final machining. Removing the remaining gate material. Heat treatment involves the use of heating or chilling. However. bead blasting. The gating system required to produce castings in a mold yields leftover metal. Oxford. Castings (2nd ed. Paul. J T. John (2003). Wiley.Foundry has reduced injury to workers.. UK: Butterworth-Heinemann. With a change of tooling these machines can finish a wide variety of materials including iron.org/) American Foundry Society (http://www.[3] 5 References [1] Degarmo. costs of consumables whilst also reducing the time necessary to finish a casting.com/) Photographic documentation of the founding process (http://herold-gefrees. Ronald A.). [2] Beeley. p.org/) World Foundry Organization (http://www.de/en/foundry/process) . Foundry Technology (2nd ed. It also eliminates the problem of human error so as to increase repeatability in the quality of grinding. Peter (2001).).indianfoundry. ISBN 978-0-7506-4790-8 External links • • • • The Institute of Indian Foundrymen (http://www. Materials and Processes in Manufacturing (9th ed.afsinc. Black. (2003). 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