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Molding Defects


Silver Streaks ( Inclusion of air )

Silver streaking form the center gate


Characteristics
  • Relatively few occurrences over a wide area
  • Random occurrence at points removed from the gate
  Molding conditions Die conditions Plastic conditions
Causes
  • 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
  • Cold flow mixing
  • No cold slag well
  • Too few sprues, runners, and gates
  • Gate gas mixing (i.e., tunnel gate restrictions)
  • Insufficient mixing of ground matter
Counter-
measures

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

Examine the die

- Installation of a cold slag well
- Correction of sprues, runners, and gates
- Correction of gate height and angle

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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