Managing heat and delivering resin at a consistent temperature is the role of the nozzle. There are several features that one should consider before making a nozzle choice.
It is important to maintain consistent heat due to the temperature processing window unique to today’s highly engineered resins. Engineered resins have an ideal target temperature that allows optimal processing. A nozzle that can maintain heat very close to the ideal temperature will allow the hot runner system to operate at a lower temperature. Minimizing heat transfer from the nozzle to the surrounding mold and components will allow for lower operating temperatures, and prevent degrading of the resin during processing.
Maintenance considerations should center on ease of nozzle replacement without disassembling the entire hot half. Front loaded heaters and separate thermocouples make for easy replacement and will minimize downtime while maximizing tool productivity.
The nozzle tip and the resulting vestige can be key when considering the cosmetic design of the part. Valve gates, bush nuts, open nuts and sprue nuts are combined with a nozzle to get the desired vestige. Again, maintaining the desired temperature throughout the nozzle aids in creating the desired vestige.
When choosing a control module a unit that provides process temperature, and also can provide amp draw and set point temperature will give the operator the greatest flexibility. A control unit that provides a choice of Centigrade or Fahrenheit temperature measurements and J or K thermocouple options are preferable, as well as one that has a 100-percent boost power button that directs high heat to the nozzle for a few seconds to melt freeze off and return to free flow of the resin.
A bumpless transfer feature provides backup to the automatic temperature control settings. If a thermocouple should fail, controllers with bumpless transfer will convert from automatic to manual mode, while storing the process settings. This allows tools to continue running until the faulty thermocouple can be replaced.
Hot runner technology, introduced to the plastics industry over 50 years ago, revolutionized injection molding processing capabilities by improving molded part quality, enhancing operational efficiencies, reducing scrap and saving money.
what is a hot runnerA hot runner system is a molten plastic conveying unit used within an injection mold. In other words, a hot runner system consists of heated components (generally via electricity) used inside the plastic injection molds, which brings the molten plastic from the barrel of an injection molding machine into the cavities of the mold. The sizing of hot runner melt channels depends on many factors 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.
Prior to hot runner technology, cold runners were widely used on injection molds. Cold runner molds 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 mold, 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.