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| {{unreferenced|date=November 2008}}
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| {{expert-subject|date=December 2011}}
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| [[File:BronzeSprueRisersSideView.jpg|thumb|Bronze casting showing sprue and risers]]
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| A '''sprue''' is the passage through which liquid material is introduced into a mold. During [[casting]] or [[Molding (process)|molding]], the material in the sprue will solidify and need to be removed from the finished part.
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| ==Casting==
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| In [[casting]], a sprue is the passage through which a molten material is introduced into a [[molding (process)|mold]], and the term also refers to the excess material which solidifies in the sprue passage. In [[sand casting]], the sprue is formed by a [[dowel]] which is removed from the sand to make the hole into which the metal is poured.
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| ===Function===
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| Sprues can serve as filters, [[heat sink]]s, and as feeders. [[Bronze]] in particular has a high shrinkage rate as it is cooling; a sprue can continue to provide molten metal to the casting, provided it is large enough to retain its heat and stay liquid, as metal in the main casting cools and shrinks. The design of the sprue and runner system can be also utilized to trap unwanted [[dross]] and sand from continuing into the main cavity; this may include adding porous material to the runners, or designing the sprue to eject the dross to the side of the sprue using [[cyclonic separation]].
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| ===Sprue design===
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| The design of gating and runner is also essential for casting. The design can be done by using vertical and bottom gating.
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| For bottom gating
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| :<math>t_f = \frac {2 A_m(\sqrt {h_t}-\sqrt {h_t-h_m})} {A_g \sqrt {2g}} </math>
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| where:
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| :<math>t_f</math> = Time for filling
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| :<math>A_m</math> = Area of mold
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| :<math>A_g</math> = Area of gate
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| :<math>g</math> = Acceleration due to gravity
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| :<math>h_t</math> = Total height
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| :<math>h_m</math> = Height of mold cavity
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| This equation may change if the height of gating is equal to height of casting material.
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| Then the equation will be:
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| :<math>t_f = \frac {2 A_m\sqrt {h_t-(h_t-h_m)}} {A_g \sqrt {2g}} </math>
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| or, simplified,
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| :<math>t_f = \frac {2 A_m\sqrt {h_m}} {A_g \sqrt {2g}} </math> | |
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| where:
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| :<math>t_f</math> = Time for filling
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| :<math>A_m</math> = Area of mold
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| :<math>A_g</math> = Area of gate
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| :<math>g</math> = Acceleration due to gravity | |
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| :<math>h_t</math> = Total height (Height of gating + height of mold cavity)
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| :<math>h_m</math> = Height of mold cavity
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| ==Injection molding==
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| In [[injection molding]], the term '''sprue''' refers to the passages through which a liquid material (such as [[polystyrene]] or [[polyvinyl chloride]]) flows into a [[Die (manufacturing)|die]], where it solidifies to form parts. It also refers to the material which solidifies in these passages, forming a framework attaching the parts together in a roughly planar arrangement.
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| ===Gates and runners===
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| Some moldmakers make a distinction between three separate entities: the gate, the runner, and the sprue. Certainly in the plastics injection moulding industry, the gate is the location at which the molten plastic enters the mold cavity and is often seen as a small nub or projection (the "gate mark") on the molded piece. The sprues are large-diameter channels through which plastic flows, usually around the edges of the part or along straight lines. Finally, in this naming scheme, the runner represents only the smaller channels that divert from the sprue to the individual part. An analogy to the sprue/runner system might represent the sprues with city water mains, and runners with the smaller pipes leading to individual houses.
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| Many [[scale model]] kits are made from injection-molded plastic. Hobbyists, such as builders of [[scale model]]s, typically remove the parts of a [[model kit]] from the runner using a sharp [[craft knife]] or [[Backsaw|razor saw]]. They may also use the sprue or runner as a raw material to fabricate additional parts, such as railings on [[model ship]]s, or [[Antenna (radio)|antenna]] wires on [[model airplane|airplanes]].
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| Sprues in model kits often include engravings to identify the parts by number.
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| ==See also==
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| *[[Chvorinov's rule]]
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| {{Metalworking navbox|castopen}}
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| [[Category:Casting (manufacturing)]]
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| [[Category:Plastics industry]]
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