Twinshot Technologies has changed the design on its lower-cost coinjection molding technology. Instead of two screws, one inside another, Twinshot's new Version II uses a single screw with a two-stage design similar to a vented barrel, running through a single barrel.
The ratio of material is controlled externally by starve-feeding one or both of the screw stages.
Twinshot Technologies markets the process for Community Products LLC of Rifton, N.Y., which developed it for its own injection molding operation.
The initial method used one screw inside another, hollowed-out screw. Depending on whether one or both screws turned, the injection unit delivered one shot, then the second. That process no longer will be used, officials said.
Twinshot II uses two hoppers at different points along the screw. The first material enters the screw at the first-stage section. At the transition point to the second stage of the screw, the melt moves into a channel through the core of the second section, and at that point, the second material enters the outside, flighted part of the screw.
Twinshot inventor Joel Thompson said the new method offers several advantages. “Recovery time is much quicker — even faster than an equivalent conventional screw — because both materials extrude simultaneously. Independent heat control on two melting zones also is possible. Overall cost is reduced because one simple screw replaces two more-complex ones.”
Twinshot II can be retrofitted to all injection presses, regardless of injection piston design. The new method also can be scaled down to much smaller screws than the original process.
Spirex Corp., a Youngstown, Ohio, screw and barrel maker, is selling Twinshot to the retrofit market.
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