Injection molding

A hot runner is a heating system in an injection mold that keeps the plastic in the runner (the channel through which molten plastic travels from the injection molding machine to the mold cavity) in a molten state at all times. Unlike a traditional cold runner, where the plastic solidifies and becomes waste, a hot runner uses heaters and a temperature controller to precisely regulate temperature, so that each time the mold opens for part ejection, only the product itself is ejected—there is no waste material left in the runner.

How a Hot Runner Works

A hot runner system consists of several core components:

1. Hot nozzle: Extends into the mold cavity to precisely inject the molten plastic.

2. Heater: Installed in the hot nozzles and manifold, continuously heating to prevent the plastic from solidifying.

3. Manifold: Evenly distributes the plastic from the machine's nozzle to each hot nozzle.

4. Temperature controller: Precisely controls the temperature of each heating zone to ensure stable system operation.

Throughout the entire injection process, the plastic inside the hot runner remains molten. After the product in the mold cavity cools and solidifies, the plastic in the hot runner is still liquid. When the mold opens, only the finished product is ejected—no waste material remains in the runner.

A hot runner saves material and shortens the molding cycle. However, the mold cost is higher, and maintenance is more complex.