Introduction

The gating system is the critical flow channel that guides molten material from injection machine nozzle into mold cavity. It mainly consists of sprue, runner, gate and cold‑slug well. Reasonable gating‑system design directly impacts filling performance, product appearance, dimensional accuracy and overall molding efficiency, for both thermoplastic and thermoset bakelite / BMC molds.

1. Four Core Components of Gating System

• Sprue: The initial passage where molten plastic first enters the mold from injection‑machine nozzle.

• Runner: Distribution channel that diverts molten material from sprue toward separate mold cavities.

• Gate: The narrow final passage right before melt flows into product cavity. Gate location, quantity, shape and dimension heavily govern finished‑part appearance, dimensional stability, material performance and cycle time.

• Cold‑slug Well: A reserved cavity for trapping partially cooled, semi‑solidified material generated while melt passes through sprue and runner. It prevents cold material from flowing into product cavity and causing surface defects.

2. Key Design Principles for Gates

Gate size shall be determined by part weight, material characteristics and gate geometry. Within acceptable mechanical performance and molding cycle, gate length, depth and width should be minimized as much as possible.

• Too‑small gate: Triggers insufficient filling, sink marks, poor weld‑line appearance and enlarged molding shrinkage.

• Too‑large gate: Induces excessive residual stress around gate area, leading to part deformation or cracking. In addition, post‑processing for gate removal becomes difficult.

3. Common Gate Types for Injection Molds

Proper gate‑type selection optimizes cosmetic quality, raises production efficiency and cuts manufacturing cost. Main gate styles are listed below:

1. Sprue Gate (Direct Gate): Direct feeding onto part surface, suitable for large‑size heavy components.

2. Edge Gate: Side feeding gate, widely used for general‑purpose plastic parts.

3. Overlap Gate: Overlap‑style side gate, reduces jetting defects.

4. Fan Gate: Wide fan‑shaped gate for thin large‑area parts, delivers uniform melt front.

5. Diaphragm Gate: Diaphragm‑type gate for hollow circular workpieces.

6. Ring Gate: Annular gate for tubular products to obtain circumferentially consistent filling.

7. Pin‑point Gate: Tiny pinpoint gate, auto‑degate upon mold opening, excellent surface finish.

8. Submarine Gate (Sub‑gate): Submerged tunnel gate, automatic gate separation, invisible gate trace on outer surface.

9. Horn Gate: Curved horn‑style gate, commonly applied for special‑structure or thermoset bakelite components.

About Us

Hitech (HK) International Limited develops thermoset molds as well as thermoplastic injection molds. Our engineering team optimizes sprue‑runner‑gate layout according to material property, part geometry and volume requirement, to avoid filling defects and guarantee stable mass‑molding performance.