Advertising in MoldMaking Technology offers
Issue link: https://mmt.epubxp.com/i/485569
Hot Runners 26 MoldMaking Technology April 2015 variations in melt-front velocity and eliminate the associated cosmetic defects. Varying valve pin opening speeds and strokes. Cosmetic issues, dimensional inconsistencies and melt-front freeze-off (espe- cially in thin-walled parts) result from varying the valve pin opening and closing times. To balance mold families without resorting to different opening and closing times, the molder should vary the valve pin opening speeds and strokes. This enables the same balance adjust- ments to be obtained without the negative effects. This same concept also can be applied to multi-cavity tools that experience consistent imbalances. In those cases, a minor change to the speed or full open position of the pin can bring the tool back into balance. Manipulating valve pin movement. Manipulating the movement of the valve pins in direct-gated cosmetic applications is ben- eficial as well. Controlling the valve pin opening speed, closing speed and stroke yields improved gate-area cosmetics. Cosmetic features that used to be unobtainable are now being realized through pin control. Providing valve pin movement repeatability. Electric, pneumatic and hydraulic valve-gated systems with closed-loop valve-pin position control not only facilitate complex valve pin move- ments, but these advanced systems also provide repeatability of the valve pin movement, which translates into increased repeat- ability of part filling and part consistency. A Powerful Combination Although individual technological advances in cavity sensors and hot runner valve gate control have changed the way parts are molded, combining the two technologies yields some interesting possibilities. As discussed earlier, in sequential molding, slowing the initial opening speed of the valve pin offers cosmetic benefits. Whenever Images courtesy of Synventive Molding Solutions. LEARN MORE Visit our Hot Runners Zone for more information on hot halves, nozzles, gates and temperature controllers. Go to moldmakingtechnology.com/zones for a complete list. Slowing the initial opening speed of the valve pins can eliminate cosmetic defects in sequentially flled parts.