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A sprue is a large diameter vertical channel through which liquid material is introduced into a mold. It connects the pouring basin to the runner. In many cases it controls the flow of material into the mold. During casting or molding, the material in the sprue will solidify and need to be removed from the finished part. It is usually tapered ...
Injection moulding (U.S. spelling: injection molding) is a manufacturing process for producing parts by injecting molten material into a mould, or mold. Injection moulding can be performed with a host of materials mainly including metals (for which the process is called die-casting ), glasses , elastomers , confections , and most commonly ...
Sprue puller pin—The sprue puller pin pulls the sprue from the sprue bush. It is usually made of CHMCS; Core back plate—It holds the core insert in place and acts as a "stiffener". It is usually made of mild steel. Guide pillar and guide bushing — The guide pillar and guide bush align the fixed and moving halves of a mold in each cycle.
The metal is poured into the mold through a hollow channel called a sprue. The metal and mold are then cooled, and the metal part (the casting) is extracted. Casting is most often used for making complex shapes that would be difficult or uneconomical to make by other methods. [1]
The pattern is lifted from the sand, leaving a molding cavity. A passageway for metal to enter the mold, called a "gate", is then cut from the sprue hole to the void left by the pattern, and a runner is cut from the sand to allow metal to flow into the riser. The flask is then put back together, and metal can be poured into the mold.
A bronze casting showing the sprue and risers. A riser, also known as a feeder, [1] is a reservoir built into a metal casting mold to prevent cavities due to shrinkage.Most metals are less dense as a liquid than as a solid so castings shrink upon cooling, which can leave a void at the last point to solidify.
The person designing the mold chooses whether the mold uses a cold runner system or a hot runner system to carry the plastic and fillers from the injection unit to the cavities. A cold runner is a simple channel carved into the mold. The plastic that fills the cold runner cools as the part cools and is then ejected with the part as a sprue.
The sprue and risers must be arranged to allow a proper flow of metal and gasses within the mold in order to avoid an incomplete casting. Should a piece of core or mold become dislodged it may be embedded in the final casting, forming a sand pit, which may render the casting unusable. Gas pockets can cause internal voids.