HotRunner

Hot runner systems, often referred to as hot runners, are used in injection molding to keep the plastic in the runners and gates molten as it flows to the cavities. By eliminating solidified runners, they reduce material waste and allow more precise control of melt temperature and flow. They are widely used in high-volume production of plastic parts with complex geometries.

A hot runner comprises heated channels within a stainless steel manifold, nozzle heaters, and a temperature control system, often including valve gates or needle gates to regulate each cavity. The melt is supplied by the injection molding machine nozzle, travels through the heated channels, and exits through the gates. Temperature control, nozzle sealing, and channel design are critical to prevent scorching, burn-on, or clogs and to avoid leakage at the gate.

Advantages include reduced scrap, shorter cycle times, improved color and material consistency, and the ability to produce parts with more consistent cosmetic finishes. Disadvantages include higher capital cost, greater mold complexity, additional maintenance, potential hot runner failures, and the need for specialized process knowledge and startup/shut-down procedures.

In practice, hot runners are common in automotive, consumer electronics, packaging, and medical device manufacturing, especially where high volumes and consistent quality justify investment. They may use valve gates for precise shut-off or open gates for simpler designs. See also injection molding, cold runner systems, and valve-gate technology.