Meaning
Injection moulding components utilize unheated channels to transport molten resin from the sprue to the cavity. Within this setup, a cold runner solidifies at the same rate as the moulded item and requires mechanical removal during the ejection phase. The channel geometry dictates the pressure drop and cooling duration required for the material to reach structural stability.
Practitioners specify these systems for low-volume production or when processing resins that are susceptible to thermal degradation in heated environments.
System Design
Geometry selection determines the efficiency of the filling stage. Circular profiles minimize the surface-area-to-volume ratio to maintain heat better than trapezoidal cuts. These selections affect the clamp force needed to hold the tool closed against high injection pressures.
Operational Consequence
Cooling requirements are determined by the thickest section of the system which is typically the sprue. If the cold runner remains molten while the part is ready, the entire cycle slows down. This creates a production bottleneck that increases the hourly machine cost per unit.
Material Utilization
Regrind processing allows operators to reclaim the excess plastic generated by the sprue and gates. Using a cold runner introduces a recycling step where the solidified channels are granulated and mixed with virgin material. Careful management of this ratio prevents the loss of mechanical properties during subsequent cycles.
