What is a hot runner in plastic mold?

Hot runner technology which introduced to the plastics industry over 50 years ago, revolutionized injection molding processing capabilities by improving molding part quality, enhancing operational efficiencies, reducing scrap and saving money..

A hot runner system is a molten plastic conveying unit used within an injection tooling. In other words, a hot runner system consists of heated components (generally via electricity) used inside the plastic injection toolings which brings the molten plastic from the barrel of an injection mold machine into the cavities of the mold. The sizing of hot runner melt channels depends on many plants such as the type of resin, the injection speed, fill rate, and the molded part. A temperature controller (standalone controller or controls from the injection molding machine) heats the hot runner system within the injection mold and the resin inside the machine barrel to processing temperature and injects the resin into the mold. The resin travels through the inlet, down into the manifold which then splits to the various nozzles and through injection points (or gates) into the final mold cavity where the final part is formed. Today’s molds can have anywhere from 1 to over 192 nozzles depending on the plastic parts being manufactured in the world.

Prior to hot runner technology, cold runners were widely used on injection toolings. Cold runner toolings faced many challenges in conveying the resin from machine barrel to cavities without affecting the flow and thermal characteristics of the resin. With the advancement of resin types and the complexity in mold and part designs, it became more and more difficult to control the molding process via cold runner molds to produce molded parts of acceptable quality.

However, with the introduction of hot runner technology with advanced thermal controls, processing of wider ranges of resin became more practical and convenient to injection molders. Unlike a cold runner tooling, the hot runner components are individually heated to ensure the resin maintains the temperature continuously through the mold. The temperature of each hot runner heated component can also be precisely controlled to ensure the process is optimized to the requirements of each type of resin delivering the highest possible part quality. Today, hot runners are capable of producing highly complex parts in a wide range of sizes which are utilized in every industry.