Term
| Identify some of the important advantages of shape-casting processes. |
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Definition
| 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. |
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Term
| What are some limitations and disadvantages of casting? |
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Definition
| 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. |
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Term
| What is a factory that perfoms casting operations usually called? |
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Definition
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Term
| What is the difference between an open mold and a closed mold? |
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Definition
| 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 closed 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. |
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Term
| Name the two basic mold types that distinguish casting processes. |
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Definition
| The two mold types are (1) expendable molds and (2) permanent molds |
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Term
| Which casting process is most important commerically? |
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Definition
| Sand casting is the most important casting process. |
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Term
| What is the difference between a pattern and a core in sand molding? |
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Definition
| The pattern determines the external shape of the cast part, while a core determines its internal geometry if the casting includes a cavity |
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Term
| What is meant by the term superheat? |
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Definition
| 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. |
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Term
| Why should turbulent flow of molten metal into the mold be avoided? |
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Definition
| Turbulence causes: (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 |
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Term
| What is the continuity law as it applies to the flow of molten metal in casting? |
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Definition
| The continuity law, or continuity equation, indicates that the volumetric flow rate is constant throughout the liquid flow |
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Term
| What are some of the factors that affect the fluidity of a molten metal during pouring into a mold cavity? |
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Definition
| 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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Term
| What does heat fusion mean in casting? |
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Definition
| Heat of fusion is the amount of heat energy required to transform the metal from solid state to liquid state. |
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Term
| How does solidification of alloys differ from solidification of pure metals? |
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Definition
| Pure metals solidify at a single temperature equal to the melting point. Most alloys (exceptions are eutectic alloys) start to solidify at the liquidus and complete solidification occurs at the solidus, where the liquidus is a higher temperature than the solidus. |
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Term
| What is a eutectic alloy? |
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Definition
| A eutectic alloy is a particular composition in an alloy system for which the solidus and liquidus temperatures are equal. The temperature is called the eutectic temperature. Hence, solidification occurs at a single temperature, rather than over a temperature range |
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Term
| What is the relationship known as Chvorinov's rule in casting? |
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Definition
| Chvorinov's rule is summarized: Tts = Cm(V/A)^n, where Tts = total solidification time, Cm is the mold constant, V is the volume of casting, adn A is the surface area of casting |
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Term
| Identify the three sources of contraction in a metal casting after pouring. |
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Definition
| The three contractions occur due to: (1) contraction of molten metal after pouring; (2) solidification shrinkage during transformation of state from liquid to solid, and (3) thermal contraction in the solid state |
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Term
| What is a chill in casting? |
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Definition
| A chill is a heat sink placed to encourage rapid freezing in certain regions of the casting |
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