Hot runner systems keep the plastic in the runner system molten throughout the molding cycle, eliminating the need for cold runners. They offer significant advantages for high-volume production but come with higher initial cost and complexity.
Hot runners eliminate runner waste, reduce cycle time (no runner cooling), enable automatic operation, allow smaller machine selection (less shot weight), provide better control over gate quality, and enable multi-cavity and family mold designs that would be impractical with cold runners.
Manifold is mounted outside the mold. Easy maintenance, but longer flow path and higher heat loss. Suitable for simple multi-cavity layouts.
Manifold is integrated into the mold plate. More compact, better temperature control, but harder to service. Most common configuration for production molds.
Two manifolds on separate parting lines for stack molds. Doubles output without increasing clamp tonnage requirement. Best for thin-wall parts in high volumes.
Hot runner systems add $2,000-15,000 per cavity depending on complexity and brand. ROI calculation should include: runner waste savings (material cost), cycle time reduction, and labor savings from automatic operation. For production runs under 50,000 parts, cold runners are typically more economical.