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HOT RUNNER DESIGN CONSIDERATIONS
(as seen in Mold Making Technology)
Evaluating system design can help avoid potential problems down the road
By Sal Benenati
Hot runner systems are such a common part of injection molds that hot runner suppliers must adjust component designs in order to meet increasingly stringent requirements in performance and materials often adding to system complexity.
For instance, some designs use stepping motors to operate valve gates, others use special heaters, and still others require special tolerances in the mold for it to function properly.
When selecting a hot runner system, however, keep in mind that oftentimes, with each increase in complexity or sophistication, comes a decrease in utility that is not always obvious.
As you evaluate options for an appropriate hot runner system for your next job consider every feature's positive and negative aspects, and then carefully determine if the benefits outweigh the drawbacks.
For example, a special nozzle heater may be a good solution for stabilizing the nozzle's heat profile (which otherwise may not work well with sensitive resins), but you also may face restricted availability, high cost, durability challenges, and difficult heater replacement. With a little investigation, you'll find out that the clearance between the nozzle body and the heater is prone to oxidation, which bonds the heater to the nozzle body and makes removal without damage almost impossible. If the chosen nozzle is the only type that will work with the required resin, the use of a special heater may be justified. However, if other nozzles fit the available mold space and can do thejob without employing a special heater then exposure to the drawbacks of such a heater would be unjustified.
The question is, how can one know about potential problems before they occur? The design looks sleek the product data is appealing, and the manufacturing methods and materials used seem high-tech and sophisticated.
The nozzle's design objective was easy maintenance and improved functionality. The unit's parts are effectively produced and can be easily replaced using standard tools. Heat equalizing occurs internally allowing the use of a simple coil heater.
Size flexibility is an important consideration. These nozzles can be used on a mini manifold that is 3 inches in diameter or in a large, multi-cavity system.