Hot runner

Where it comes up

• Plastic injection moldingMolten thermoplastic injected into a steel or aluminum mold. Lowest piece price for plastic parts at 5,000+ a year.

Related terms

Cold runner

A cold runner is an unheated channel system in an injection mold that carries molten plastic from the sprue to the gates. The runner solidifies with each shot and is ejected with the parts, then scrapped or reground. Cold runner molds cost less than hot runner molds but waste more material.

Gate

A gate is the opening where molten plastic or metal enters the mold cavity from the runner. Gate type, size, and location affect fill, knit lines, sink, and the mark left on the part. Common types include edge, submarine, pin point, and valve gates.

Cycle time

Cycle time is the time needed to complete one full production cycle, such as one mold shot, one press stroke, or one machined part. It sets machine hours per part, so it is a primary input to piece price. In injection molding, cooling usually takes most of the cycle.