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Molding Defects: Silver Streaks
Thermal decomposition and deterioration
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| Cause : |
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Thermal decomposition and deterioration |
| Factors : |
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If bubbles are formed during blank purging:
- Faulty heater band (i.e., localized heating by the nozzle heater)
- Excessively high nozzle temperature, cylinder temperature, injection speed,
or screw speed
- In-cylinder retention |
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If bubbles are not formed during blank purging:
- Poor nozzle contact
- Too few sprues, runners, and gates
- Bad gate positioning
- Retention inside hot runners |
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Location :
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| Occurs over the complete
molding immediately after passage through the gates
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Click for enlargement
Silver streaking from the center gate
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Appearance :
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Thin, long sparkler-type pattern |
| Countermeasures: |
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If bubbles are formed during blank purging:
- Heater band repair
- Optimization of the nozzle temperature, cylinder temperature,
injection speed,
or screw speed
- Optimization of the balance between molding machine capacity and molded
component capacity |
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If bubbles are not formed during blank purging:
- Examination of nozzle contact
- Repair of sprues, runners, and gates
- Correction of gate positions
- Review of hot-runner temperature setting and injection speed
Please see our grade-specific
molding condition sheet
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