Four Components of Injection Mold Gating System
The gating system of an injection mold serves as the critical channel connecting the injection machine nozzle to the mold cavity. Its design directly impacts the flow behavior of molten plastic, filling efficiency, and the final product quality. The gating system typically consists of four core components: the sprue, runner, gate, and cold slug well, which work together to transport, distribute, and control the molten plastic during molding.
1. Sprue
As the starting point of the gating system, the sprue directly connects the injection machine nozzle to the runner entrance. It features a tapered design (with a taper angle of 2°–5°) to facilitate the smooth removal of the solidified sprue material during demolding. The sprue diameter is determined by the product weight and injection machine specifications, typically ranging from Φ3–8 mm.
Key Design Considerations:
Use a sprue bushing (gate sleeve) to enhance wear resistance.
Insufficient taper may cause demolding difficulties.
2. Runner
The runner distributes molten plastic from the sprue to multiple cavities. It can be categorized into:
Conventional runner systems: Suitable for multi-cavity molds.
Hot runner systems: Maintain molten state via heating.
Common cross-sectional shapes include circular (most efficient), trapezoidal, and U-shaped.
Design Guidelines:
Adopt a balanced layout to ensure simultaneous cavity filling.
Runner diameter is generally 1.5–2 times the product’s maximum wall thickness.
3. Gate
The gate is the precision channel linking the runner to the cavity. Its core functions include:
Controlling molten plastic flow speed and direction.
Regulating holding pressure for shrinkage compensation.
Determining surface quality and appearance of the final product.
4. Cold Slug Well
Acting as a safety mechanism, the cold slug well performs the following roles:
Trapping leading cold material to prevent it from entering the cavity.
Providing a buffer zone for molten plastic flow.
Assisting in breaking off the solidified sprue during demolding.
