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Reference · Gates & Runners

Mold flow.
Gate. Runner.
Material delivery.

Gate and runner design reference. Where plastic enters cavity. Gate type affects appearance, properties, processing.

01 · Key principles

Key principles.

Cold runner

Standard

Plastic in runners cools, ejected with part. Trimmed.

Hot runner

Premium

Heated runners keep material molten. No waste. Faster cycle.

Edge gate

Standard

Gate at edge of part. Visible mark on edge.

Tunnel gate

Hidden

Tunnel through mold to cavity. Mark hidden inside.

Pin gate

Hot runner

Small precise gate from hot runner. Auto-trimmed.

Submarine gate

Buried

Gate buried, breaks off cleanly. Low scarring.

FAQ

Gate placement rules?

Avoid cosmetic surfaces. Allow uniform fill. Far from mating surfaces. Discuss with tooling engineer.

Hot vs cold runner?

Hot: $5-20K premium tool. No runner waste. Faster cycle. Cold: cheaper, slower, runner becomes scrap.

Gate scarring?

Cold runner gates leave visible mark. Hot runner pin gates almost invisible. Tunnel/submarine gates hide.

Material flow analysis?

Mold flow simulation predicts fill. Identifies issues before tooling. Premium service for complex parts.

Gate size selection?

Smaller gate: more shear, faster cooling, harder to fill. Larger gate: easier fill, slower cycle, larger scar.

Multi-cavity gating?

Balanced runner system equal flow to all cavities. Critical for consistent parts.

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