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Molding Defects


Uneven-thickness type flow marks

 


Characteristic

Uneven luster in locations where the material thickness varies.

Cause

Immediately after molten plastic has passed through a change in die thickness, factors such as the flow speed, cooling speed, and pressure applied to the die surface will change, and luster differs as a result of this.

Countermeasures
  • Raise the die temperature
  • Increase the speed of the injection flow
  • Raise the runners and gates
  • Review the shaped of the molded component and round off corners on steps between areas of different thickness so that smoother flow may be realized.

Condition of flow mark occurrence due to
  Filling speed   Molding temperature
Filling
direction
Die
Filling
direction
Die
240℃
Low speed
220 deg.C
240℃
Intermediate
speed
240deg.C
240℃
High speed
280 deg.C


 Apply colored ink to the die to ascertain the condition of flow mark occurrence.

Result of examining flow-mark start point as caused by level differences: The corner edge at the level-difference exit constitutes a start point for shear.


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