The Composition of A Pouring System
A common runner system is also known as a gating system or a pouring system, which is the only channel for molten plastic to flow from the nozzles of injection machines to mold cavities. A runner system includes a main runner, a sub-runner and a pouring gate.
1. Main Runner
A main runner also known as a main pouring gate, a sprue or a down gate, which refers to the flow path from nozzles of injection machines and parts near the bushings of main runners to sub-runners. This is the first part where the molten plastic flows into the molds.
A sub-runner is also known as a branch runner. It can be divided into the first and the second runner due to different mold
designs. A sub-runner is the transition area between a main runner and to a pouring gate, which can make the flow of the molten plastic smooth; for molds with multiple cavities, a sub runner has a function of evenly distributing the molten plastic to each mold cavity at the same time.
3. Pouring Gate
A pouring gate is the narrow channel between that connects the sub-runner and the mold cavity, which is also the smallest and thinnest part. The pouring gate uses the narrow flowing surface to achieve the purpose of acceleration, and high shear rates can make the plastic have good fluidity(due to the characteristic of getting thinner by shearing; the heated stiction viscous heating also has have functions of increasing the materials' temperature and decreasing viscosity.
The pouring gate firstly solidifies its seal so as to prevent the plastic flowing back to the pouring gate, to avoid the mold cavities' pressure dropping too fast, and to make the shaped products have function of shrinkage pools. After the plastic products are shaped, they are easy to be cut off in order to be separated from runner systems and the plastic products.
4. Cold Slug Well
A cold slug well is used to store, complement and fill relatively cold plastic wave in the initial phase so as to prevent cold slugs directly getting into the mold cavities, affecting the filling quality or blocking the pouring gate. A cold slug well is often located at the end of the main runner, and there should be another one at the end of the sub-runner when the sub-runner is long.