Foundry Technology Review Questions 1 Identify some of the...

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Foundry Technology Prepared by S. Kimutai Review Questions 1) Identify some of the important advantages of shape casting processes. Answer . Advantages include (1) complex part geometries are possible; (2) some casting operations are net shape processes, meaning that no further manufacturing operations are needed to accomplish the final part shape; (3) very large parts are possible; (4) they are applicable to any metal that can be melted; and (5) some casting processes are suited to mass production. 2) What are some of the limitations and disadvantages of casting? Answer . Disadvantages include (1) limitations on mechanical strength properties; (2) porosity; (3) poor dimensional accuracy; (4) safety hazards due to handling of hot metals; and (5) environmental problems. 3) What is a factory that performs casting operations usually called? Answer . A foundry. 4) What is the difference between an open mold and a closed mold? Answer . An open mold is open to the atmosphere at the top; it is an open container in the desired shape which must be flat at the top. A closed mold has a cavity that is entirely enclosed by the mold, with a passageway (called the gating system) leading from the outside to the cavity. Molten metal is poured into this gating system to fill the mold. 5) Name the two basic mold types that distinguish casting processes. Answer . The two mold types are (1) expendable molds and (2) permanent molds. 6) Which casting process is the most important commercially? Answer . Sand casting is the most important casting process. 7) What is the difference between a pattern and a core in sand molding? Answer . The pattern determines the external shape of the cast part, while a core determines its internal geometry if the casting includes a cavity. 8) What is meant by the term superheat? Answer . Superheat is the temperature difference above the melting point at which the molten metal is poured. The term also refers to the amount of heat that is removed from the molten metal between pouring and solidification. 9) Why should turbulent flow of molten metal into the mold be avoided? Answer . Turbulence causes the following problems: (1) it accelerates formation of oxides in the solidified metal, and (2) it causes mold erosion or gradual wearing away of the mold due to impact of molten metal. 10) What is the continuity law as it applies to the flow of molten metal in casting? Answer . The continuity law, or continuity equation, indicates that the volumetric flow rate is constant throughout the liquid flow. 11) What are some of the factors that affect the fluidity of a molten metal during pouring into a mold cavity? Answer . The factors include (1) pouring temperature above the melting point, (2) metal alloy composition, (3) viscosity of the liquid metal, and (4) heat transfer to the surroundings.
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