This will describe the sprue and runner system of molds. More comprehensive reference can be found in Runner and Gating Design Handbook: Tools for Successful Injection Molding

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• Gate system
• Product/Part design

Sprue

A sprue is a channel through which a molten plastic material is being injected from the nozzle of the injection machine into the mold. It has a smooth, round, tapered wall to allow smooth material flow.

Runner System

Runners are channels where material flows from the sprue to the cavities.

Conventional Runner:

Improved Runner:

Balanced Runner: Resin is evenly distributed throughout the cavities. Volume and condition is the same. There is more material used because the total runner length is longer compared to the other two.

Hot Runners or sometimes called runnerless, can be more economical in high volume injection molding.