Runner System
Last updated
Definition of Runner System
The runner system connects the machine nozzle to each cavity gate. In a cold-runner mold, runners solidify with the part and are ejected as scrap or regrind. Hot-runner systems keep runners molten for direct gating with less material waste per cycle.
Runner layout must balance fill time, pressure drop, and shear heating across all cavities. Symmetrical layouts help multi-cavity molds fill evenly; asymmetry can cause size or weight variation between cavities.
Why It Matters for Plastic Injection Molding
Runner volume adds to part cost on high-volume programs. AMP evaluates cold vs. hot runner economics based on annual volume, material price, and gate-quality requirements.
Runner size and routing affect which cavity fills first. Flow simulation and in-cavity pressure sensors help validate balance before production release.