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| Cause : |
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Inclusion of air |
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Factors :
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Molding conditions - Low nozzle and cylinder temperatures
- Nozzle-touch molding (i.e., solidification of plastic at the nozzle
tip)
- Excessive metal cooling
- Entry of air into the cylinder
- Excessively high molding temperature, injection pressure, and
injection speed
- Poorly-balanced cylinder temperature settings
- Insufficient back pressure
- Excessive amount of pull back |
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Die conditions
- Cold flow mixing
- No cold slag well
- Too few sprues, runners, and gates
- Gate gas mixing (i.e., tunnel gate restrictions) |
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Plastic conditions
- Insufficient mixing of ground matter |
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Location :
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Random occurrence at points removed from the gate
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Click for enlargement
Silver streaking form the center gate
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Appearance :
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Relatively few occurrences over a wide area |
| Countermeasures: |
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Examine the molding conditions
- Modification of the cylinder temperature setting
- Correction of the screw speed
- Correction of the back pressure
- Correction of the surge back volume
- Correction of the die temperature |
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Examine the die
- Installation of a cold slag well
- Correction of sprues, runners, and gates
- Correction of gate height and angle
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Examine the material surface
- Correction of the mixing of ground matter
- Elimination of dust
Please see our grade-specific molding condition sheet.
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