Page 416 - Injection Molding Advanced Troubleshooting Guide
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42.3 Splay Troubleshooting  415



          42.3.1„ Splay Troubleshooting Molding Process Related Issues

          The following sections will deal with potential splay causes in the process in-
          cluding:
             ƒ Drying
             ƒ High melt temperature
             ƒ Decompression
             ƒ Back pressure
             ƒ Residence time
             ƒ Screw recovery
             ƒ Feed throat temperature
             ƒ Inconsistent material feed

          42.3.1.1„  Molding Process: Drying
          One of the most common causes for splay is excess moisture in the material. This
          moisture will turn to gas when the material is subjected to molding temperatures.
          Figure 42.2 shows a magnified picture of splay on a part surface. This gas will be
          contained in the plastic melt until the plastic enters the mold, where the depres-
          surization on the melt stream will allow the gas bubbles to reach the surface of the
          mold leaving behind the streak of splay. Hygroscopic materials, such as ABS, poly-
          carbonate, nylon, TPU, polyesters, or PC/ABS, absorb moisture from the environ-
          ment and require drying.































          Figure 42.2  Splay magnified
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