Shenzhen Alu Rapid Prototype Precision Co., Ltd.

In injection molding, a sprue is the primary channel or passage that serves as the entry point for molten plastic (or other thermoplastic material) to flow from the injection machine's nozzle into the mold cavity. 

It acts as the initial conduit in the mold's gating system, connecting directly to downstream elements like runners (channels that distribute the material to multiple cavities) and gates (narrow openings into the part cavities).

Key Functions and Design Notes:

1.Material Flow: The sprue ensures efficient, high-pressure delivery of the molten material while minimizing turbulence or air entrapment.

2.Design Considerations: It's typically tapered (wider at the top for easier ejection) and sized based on factors like material viscosity, shot volume, and cycle time—often 4–10 mm in diameter at the base. 

3.Post-Molding: After cooling, the sprue solidifies and becomes excess material (often called "sprue scrap") that is ejected with the part and typically recycled.

In multi-cavity molds, a single sprue feeds multiple runners, optimizing production efficiency. For more advanced setups, hot runner systems can eliminate the traditional cold sprue to reduce waste.