20.6.2 Blisters or Bubbles
The nished product contains small gas or air lled pockets or cooling voids.
Probable Cause:
1. Molding Machine
• Low injection pressure
• Back ow valve malfunctioning
• Decompression cycle too long
• Rapid plasticizing
• Trapped air in feed
• Feed error
2. Mold
• Trapped or volatile gas
• Low mold temperature
• Poor thin/thick transition phase
• Inadequate venting
3. Material
• Overheating of resin
Solution (in sequence):
1. Verify control and / or holding pressure
2. Increase back pressure
3. Increase mold temperature
4. Inspect back ow valve
5. Ensure proper venting
6. Increase gate size
7. Decrease vent land length
20-6
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