The runner system in an injection molding tool distributes the molten material into the mold cavities. Many tools use a simple cold runner system where the material injected solidifies in the sprue and runners and is ejected with the parts resulting in waste and requiring de-gating. An alternative is a hot runner which is a more complex system than using cold runners.
A hot runner system consists of two main sub-systems, the heated nozzles and heated manifold. Each sub-system is made up of a number of components which are detailed in the video below from Shini. The video also shows the installation of a hot runner system into the tool and its operation in the injection molding cycle. You can also see the piston in operation in the valve as it opens and closes the gate.
Some reasons for using hot runners include:
- If products will be molded in various colors on one tool – Hot runners are of great value for tools on which different material colors will be run in batches. Hot runners allow for easy and efficient purging on change over of the material color.
- Where waste reduction is critical – Hot runners improve yield and therefore parts that are small or have expensive materials specified can benefit from being tooled with a hot runner system and avoid the waste generated the gates being part of the molding.