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Hot Runner Technology OCT 2017

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4 Hot Runner Technology F E AT U R E By David Hoffman Six Key Factors for Evaluating a Hot Runner System Details matter when it comes to selecting and integrating a hot runner system. This guide makes that process easier by covering those details thoroughly. This four-drop hot runner system has pressed-in tubular heaters. Mold builders and injection molders have different requirements when it comes to hot runner systems. Mold builders are often con- cerned about price, delivery and quality, while the molder is concerned with operation, per- formance and ease of maintenance. However, both moldmaker and molder must be part of the decision-making process when considering a hot runner system and supplier to guarantee the best selection from available system op- tions and to optimize integration of the system into the mold. Here are six important items to consider when evaluating a hot runner system: 1. Manifold heaters. For installation, most manufacturers use a press. If the heater con- tact with the manifold is not uniform, there will be hot spots created in the heater element, which causes premature failure and non-uni- form heating of the manifold itself. Also, process capability can be affected especial- ly with some engineering materials, as their viscosity may be more temperature sensitive than commodity resins like polypropylene and polyethylene. 2. Nozzle heaters. Measuring the ohm resistance for each nozzle heater can provide good information when troubleshooting the hot runner system. Too great a variance may prevent uniform temperature profiles and the potential for process variation will increase. Additionally, the life of a heater with less efficiency is reduced because of the required increase in workload. 3. Nozzle tip orifice. Pressure differences in plastic injection molding are defined in the Hagen Poiseuille equation, where (Q) is the flow rate, (l) is the runner length, (n) is the material viscosity and (r) is the radius of the flow channel: The equation shows that any slight differ- ence in "r" value, which includes the orifice in a hot runner nozzle and gate tip, is affected to

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