Sprue (molding)
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A sprue is the vertical passage through which liquid material is introduced into a mold and it is a large diameter channel through which the material enters the mold. It connects the pouring basin to the runner. In many cases it controls the flow of material into the mold. During
casting Casting is a manufacturing process in which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a ''casting'', which is ejected ...
or molding, the material in the sprue will solidify and need to be removed from the finished part. It is usually tapered downwards to minimize turbulence and formation of air bubbles.


Casting

In
casting Casting is a manufacturing process in which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a ''casting'', which is ejected ...
, a sprue is the passage through which a molten material is introduced into a
mold A mold () or mould () is one of the structures certain fungi can form. The dust-like, colored appearance of molds is due to the formation of spores containing fungal secondary metabolites. The spores are the dispersal units of the fungi. Not ...
, and the term also refers to the excess material which solidifies in the sprue passage.


Function

Sprues can serve as filters, as
heat sink A heat sink (also commonly spelled heatsink) is a passive heat exchanger that transfers the heat generated by an electronic or a mechanical device to a fluid medium, often air or a liquid coolant, where it is dissipated away from the device, th ...
s, and as feeders. Bronze, in particular, has a high shrinkage rate as it is cooling. A sprue is tapered with its bigger end at the top to receive the liquid metal, the smaller end is connected to the runner.


Sprue design

The design of the sprue gating and runner is also essential for casting. The design can incorporate either bottom or vertical gating. For bottom gating :t_f = \frac where: :t_f = Time for filling :A_m = Area of mold :A_g = Area of gate :g = Acceleration due to gravity :h_t = Total height :h_m = Height of mold cavity This equation may change if the height of gating is equal to height of casting material. Then the equation will be: :t_f = \frac or, simplified, :t_f = \frac where: :t_f = Time for filling :A_m = Area of mold :A_g = Area of gate :g = Acceleration due to gravity :h_t = Total height (Height of gating + height of mold cavity) :h_m = Height of mold cavity


Injection molding

In injection molding, sprue refers to the passage through which a liquid material (such as polystyrene or polyvinyl chloride) flows into a die, where the material solidifies to form parts. ''Sprue'' also refers to the material that solidifies in these passages, forming a framework that attaches the parts in a roughly planar arrangement.


Sprues, runners, and gates

Some moldmakers distinguish the sprue, the gate, and the runner. The sprue is a large-diameter channel through which plastic flows, usually around the edges of the part or along straight lines. The runner is a smaller channel from the sprue to the individual part. An analogy may be found in a water system that employs a water main (sprue) and smaller pipes (runners) to individual houses. The gate is the location at which the molten plastic enters the mold cavity and is often evidenced by a small nub or projection (the "gate mark") on the molded piece. Many scale-model kits are made from injection-molded plastic. Hobbyists typically remove the parts of a model kit from the runner using a sharp
craft knife A utility knife is any type of knife used for general manual work purposes.Peterson, Harold L., ''Daggers and Fighting Knives of the Western World'', London: Herbert Jenkins Ltd., , p. 1 Such knives were originally fixed-blade knives with du ...
or
razor saw A backsaw is any hand saw which has a stiffening rib on the edge opposite the cutting edge, enabling better control and more precise cutting than with other types of saws. Backsaws are normally used in woodworking for precise work, such as cutti ...
. The sprues usually form a rectangle with the runners and parts inside which makes them easier to box. Model makers sometimes use sprues or runners as raw material to fabricate additional parts, such as railings on
model ship Ship models or model ships are scale models of ships. They can range in size from 1/6000 scale wargaming miniatures to large vessels capable of holding people. Ship modeling is a craft as old as shipbuilding itself, stretching back to ancient t ...
s, antenna wires on
airplanes An airplane or aeroplane (informally plane) is a fixed-wing aircraft that is propelled forward by thrust from a jet engine, propeller, or rocket engine. Airplanes come in a variety of sizes, shapes, and wing configurations. The broad spectr ...
, or
greeble A greeble ( ), or "nurnies", is a part harvested from plastic modeling kits to be applied to an original model as a detail element. The practice of using parts in this manner is called " kitbashing". Etymology The term "greeblies" was first us ...
s on fictional spacecraft. Sprues in model kits often include engravings to identify the parts by number.


See also

* Chvorinov's rule


References

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