Advantages to the gating method drawn here are automatic degating. Gating from the bottom up aids venting, and gating into ribs, bosses, and no show areas improves cosmetics. The part is sheared from the gate when the ejector pins force the part and runner system out of the mold. The tunnel gate/runner must flex enough to pop out of its restricted area.
The small cross-sectional opening of the submarine gate becomes a problem with respect to resin filled plastic. This style gate could be a problem with low viscosity, long fiber, or bead filled resins. The small gate restriction could raise the melt temperature and affect heat sensitive resins. Ignoring these factors could result in high mold maintenance.
Submarine or tunnel gates leave a very small gate scar on the part (Approximately .020 to .060 in diameter) making them highly desirable. In addition, the submarine gate creates an opportunity to locate on a non-cosmetic surfaces. By design, the scar is sheared clean, automatically.
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