粘弹性硅橡胶成型过程中的层流与背皮形成
Laminar Flow and Backrind Formation in Molding of Viscoelastic Silicone Rubber
摘要：
当热固性聚合物在高温下在封闭模具中固化时，热膨胀可在成品中产生缺陷。当内部压力上升将模具推开，固化的聚合物通过分型线处的间隙流出时，就会出现这些缺陷。这种缺陷被称为背皮，在压缩成型中特别常见，其中被捕获的不可压缩聚合物的压力增加可以压倒模具上的夹紧压力并将聚合物从模具袋中排出。如果喷出的材料已经固化，它会留下结构损坏，从而在成品中留下缺陷。背壳通常在固化聚合物退出模具的间隙附近表现为参差不齐的接缝线。它的外观通常是不规则的和碎片状的，这表明生产它的过程中没有特定的图案或均匀性。在这种情况下，固化的聚合物在被驱动朝向和通过分型线时主要充当粘弹性固体。后果皮的不平整是由于固体的撕裂和破碎造成的。然而，固化的聚合物在其朝向分型线流动并通过分型线时可能主要充当粘弹性液体。由于雷诺数较低，流动是层流，并且后壳见证了该层流。更具体地，所观察到的后壳形状对应于朝向分型线的层流中的等值线轮廓，该轮廓可以使用计算流体动力学来预测。
英文摘要：
When a thermoset polymer is cured at elevated temperature in a closed mold, thermal expansion can produce flaws in the finished product. Those flaws occur when rising internal pressure pushes the mold open and cured polymer flows out through gaps at the parting lines. Known as backrind, such defects are particularly common in compression molding, where the increasing pressure of a trapped, incompressible polymer can overwhelm the clamping pressure on the mold and expel polymer from the mold pocket. If that ejected material has already cured, it leaves behind structural damage and consequently a flaw in the finished product. Backrind usually appears as a ragged seam line near the gap where cured polymer exited the mold. Its appearance is typically irregular and fragmented, suggesting no particular pattern or uniformity to the process that produced it. In such cases, the cured polymer acts predominantly as a viscoelastic solid as it is driven toward and through the parting line. The backrind's ragged character results from tearing and fragmentation of that solid. It is possible, however, for the cured polymer to act predominantly as a viscoelastic liquid as it flows toward and through the parting line. Since the Reynolds number is low, the flow is laminar and the backrind bears witness to that laminar flow. More specifically, the backrind's observed shaped corresponds to isochronous contours in the laminar flow toward the parting line, contours that can be predicted using computational fluid dynamics.
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