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Hot Runners 28 MoldMaking Technology April 2015 FOR MORE INFORMATION: Synventive Molding Solutions / 800-367-5662 brousseau@synventive.com / synventive.com CONTRIBUTOR Bill Rousseau is director of applications and technical services for Synventive Molding Solutions, a business of Barnes Group Inc. a pin speed adjustment is made, the timing of the sequence also needs to be adjusted to compensate for the change in volumetric flow throughout the part. Using a cavity sensor to trigger the valve pin to open when the flow front reaches a specified position eliminates the need to adjust the sequence separately when pin speed changes are made. This reduces the time required to set up the process and creates a more robust process when the timing of the pin opening in rela- tion to the flow front position is critical. In addition to simply triggering the opening of the hot runner valve gates based on flow front position, more advanced valve gate control systems can initiate other events as well. For example, valve pins can be moved to interme- diate stroke positions to increase or decrease flow from a specific gate when the melt flow front reaches various points throughout the fill. This is useful for complex parts as it essentially allows the creation of separate injection profiles for each hot runner gate. Going a step furher, cavity sensors combined with full pin control allow fully closed-loop pressure control. Instead of the pin making predetermined movements based on various triggers, the molder can set a desired pressure curve for a sensor near the hot runner gate and have the hot runner valve pin auto- matically adjust to maintain that target pressure curve. This combination of technology effective- ly allows each hot runner nozzle to control an individual injection unit at each gate. Individual closed-loop pressure control at each gate can be used for extremely complex parts, family tools with drastic part weight differences, higher cavitation of preci- sion parts and modular tooling. Although cavity sensor and hot runner valve gate control technologies individually offer impressive advantages for mold- ing, even greater gains can be achieved by combining these two technologies. In addition, new applications for these smart tools are being developed that will allow stable processes to be created for even the most challenging applications. Top Image: Full control over pin movement helps the molder affect balance and improve cosmetics. Bottom Image: Cavity sensors combined with full pin control can create independent closed-loop pressure control at each gate.