Fluid-Conducting Hollow PU Parts
Researchers at the Institute for Plastics Processing (IKV) in Aachen have developed a new processing method that combines the projectile injection technique (PIT) with reaction injection molding of PU. Using this new method, it is possible to produce fluid-conducting hollow parts with complex geometries from PU. The objective of the new process combination is to marry the good mechanical properties of elastomeric, continuous fiber-reinforced parts with the volume production capability and cost-lowering potential of injection molding.
The experiments employed a modular mold in the cavity of which a round mesh of glass or aramid fibers was held. A plastic projectile was placed on the cavity-side injector. Once the mold is closed, the reaction mixture enters the cavity between the fiber reinforcement and injector, forming a cushion of melt above the injector. Next, the gas-driven projectile passes through the cavity, forming the hollow part. In the newly expanded version of the process, the projectile used employs flow effects to center itself automatically in the middle of the part. The advantage here is to ability to use faster reacting PU systems.
In fluid-conducting lines, the quality of the inside surface has a direct effect the flow characteristics. Microscopic examinations have shown that the molded PU parts have a smooth inside surface. The continuous fiber reinforcement is not visible at the inside surface, since the fiber filaments lie close to the outer edge of the part.
To determine the stability of the hollow parts, the burst pressure of individual test specimens was measured. PU pipe with a round mesh of glass fibers was able to withstand pressures of 90 bar. The PU pipe reinforced with round aramid fiber mesh achieved mean burst pressures of more than 140 bar.
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