Sprue:-
It is a channel through which molten metal is pours into the parting plane where it enters into the runner and gates to reach the mould cavity. When molten metal is moving from top to the cope, it gains velocity and requires a smaller amount of area of cross-section for the same amount of metal to flow. If the sprue is straight and cylindrical, then a low pressure area will be created at the bottom of the sprue. Since the sand is permeable, it will aspire atmospheric air into the mould cavity causing defects in the casting. That is why the sprue is generally made tapered to gradually reduce the cross-section.
It is a channel through which molten metal is pours into the parting plane where it enters into the runner and gates to reach the mould cavity. When molten metal is moving from top to the cope, it gains velocity and requires a smaller amount of area of cross-section for the same amount of metal to flow. If the sprue is straight and cylindrical, then a low pressure area will be created at the bottom of the sprue. Since the sand is permeable, it will aspire atmospheric air into the mould cavity causing defects in the casting. That is why the sprue is generally made tapered to gradually reduce the cross-section.
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