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Moisture streaks

Author : Date : 4/21/2013 5:34:18 AM

Moisture streaks

Moisture streaks are distinct streaks appearing on the surface of plastic mouldings, usually radiating from the gate and caused by excess residual moisture in the

polymer granules.

Many plastics absorb moisture from the atmosphere; how much they absorb depends on the type of resin.

Moisture in the granules, even if it is only surface condensation, can cause problems in parts including, poor surface finish, processing issues, increased flash or

loss of mechanical properties such as impact and tensile strength in some materials.



Solution:
  
         1. Check the mould cooling circuit for leaks onto the mould face.

         2. Check the packaging of the plastic granules damage.

         3. Check the moisture content of the granules.

         4. Ensure pre-drying at recommended temperature and time.

         5. Reduce the quantity of granules held in the feed hopper.

         6. Check raw material storage conditions.

         Most enginnering materials require between 2 and 4 hours drying to reach typical acceptable moisture content for moulding: 0.02%. Hot air dryers are not always effective especially in a humid environment; therefore dehumidified-air drier systems are the preferred method.

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