Sprue (manufacturing)

In manufacturing, a sprue is the channel through which molten material (such as plastic, metal, or rubber) is injected into a mold. It serves as the primary conduit, connecting the injection nozzle or pouring basin to the runner system. The runner system, in turn, distributes the material to the mold cavities where the final part shapes are formed.

The sprue is typically a tapered hole or channel to facilitate easy removal of the solidified sprue material after the molding process is complete. The angle and dimensions of the sprue are carefully designed to minimize turbulence, pressure drop, and premature cooling of the molten material.

After the molding process, the solidified sprue material, often referred to as the "sprue," is detached from the molded parts. This sprue material can often be recycled and reused in subsequent molding cycles, although contamination and material degradation must be carefully controlled.

In die casting, the sprue often remains attached to the gate system and the casting itself until it is removed during secondary operations like trimming and finishing. Its size and shape are particularly important in die casting due to the high pressures and temperatures involved.

The design of the sprue is a critical aspect of mold design, impacting the quality, efficiency, and cost-effectiveness of the molding process. Factors considered include the type of material being molded, the size and complexity of the part, the molding machine used, and the desired cycle time.