Page 429 - Injection Molding Advanced Troubleshooting Guide
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428 42 Splay
contaminant may degrade at a different temperature, which results in outgassing
causing bubbles in the plastic melt stream. Also contamination by foreign mate-
rials may cause a surface that delaminates giving an appearance similar to splay.
Material contamination can come from anywhere along the feed stream of the
material including at the supplier, in the tanker truck, in the silo, in the gaylord, in
the drying hopper, or at the machine hopper. Always take precautions to avoid
cross contaminating material when loading it into a silo or hopper.
Figure 42.5 Open gaylord: potential for contamination
42.3.4.2 Material: Excessively Wet
Excessively wet material can lead to severe problems. Even non-hygroscopic mate-
rials can have splay problems when molded with a large enough amount of surface
water. Reach your hand down into the material; if it is wet enough you will feel the
moisture. Even though you normally would not dry this material (polypropylene
for example) it will need to be dried to get rid of this surface moisture.
