Insulated runners are oversized passages formed in the mold plate.
As shown in the following diagram, the oversized passages allow an open, molten flow path to be maintained because of the insulating effect of the plastic that freezes on the runner wall, combined with the heat applied to the system with each shot.
The advantages of an insulated hot runner system include simple design and low mold cost. The disadvantages of this type of hot runner system include the following:
- Unwanted freeze at the gate
- Fast cycle time needed to maintain melt state
- Long start-up periods needed to stabilize melt temperature
- Problems in uniform mold filling