(1) Function of the Gating System
The gating system in an injection mold refers to the flow channel for the plastic melt within the mold, extending from the injection machine nozzle to the entrance of the cavity. Its function is to ensure that the plastic melt fills every part of the cavity smoothly and to transmit injection pressure to various areas of the cavity during filling and holding. This enables the production of plastic parts with a compact structure, clear shape, stable dimensions, and excellent internal quality.
(2) Components of the Gating System
The gating system consists of four parts:
1) Main Sprue
The main sprue (also known as the feed gate) is the section of the flow channel from where the injection machine nozzle contacts the mold to the runner. It is aligned with the nozzle, allowing the melt to flow without changing direction. As the first channel through which molten plastic passes, the size of the main sprue directly affects the flow speed and mold filling time.
2) Runner
The runner connects the main sprue to the cavity gate (the inlet to the cavity). It serves as a transition channel through which the melt flows from the main sprue into the cavity. The runner also facilitates the transition in cross-sectional area and flow direction of the melt within the gating system.
3) Gate
The gate is the narrowest section where the plastic flows into the cavity, and it is the shortest segment of the gating system. The narrow and short design of the gate is intended to accelerate the melt from the runner, creating an ideal flow state that allows the cavity to be filled completely and enables easy separation of the molded part from the gate after injection.
4) Cold Slug Well
At the start of each injection cycle, the foremost plastic that comes into contact with the cooler mold surfaces will cool and harden, forming what is called a cold slug. To prevent this cold slug from entering the cavity and affecting part quality in subsequent cycles, a cold slug well is usually located at the end of the main sprue or runner. This serves to store the cold slug, allowing the melt to fill the cavity smoothly.
