Water-Powered Projectile Injection Molding
The Institute for Plastics Processing (IKV), Aachen and Wittmann Battenfeld, Kottingbrunn, have developed a water-powered projectile injection molding process (PIT) for manufacturing plastic liquid-conveying conduits. With this technique, a projectile is first place on an injector and, after the mold is closed, overmolded with the polymer melt. Then, water is injected under high pressure, driving the projectile through the molded part. The still-molten core is forced into an adjacent cavity that is opened by hydraulically actuated slides following initial filling of the mold with polymer.
The process operates fully automatically, i.e. the projectiles are picked up by a part-handling device and placed on the injector. The part molded in the preceding cycle is removed and deposited on a conveyor belt. By using a projectile, the resultant wall thickness becomes practically independent of the rheological properties of the material. The process is characterized by reliability as well as a high degree of reproducibility of the channel formed.
The projectile injection technique was developed by Röchling Automotive using inert gas a few years ago. In this approach, the cavity is filled initially with melt either completely or partially, and then the projectile is shot through the plastics melt. The cooling time, part weight and wall thickness are controlled via the projectile diameter. The process yields liquid-conveying conduits with very uniform wall thickness. This translates into reduced molded part weight and material consumption. Thanks to the constant inside diameter and the smooth inside surface, there is only little pressure loss in the conduits.
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