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Molding Defects: Flash (fins or spew)
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The terms "flash", "fins", and "spew" are used to
refer to excess molding material that penetrates into mold gaps
(i.e., between parting faces, slide push-out faces, and inserts,
etc.) in a molten state.
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Normal
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Flash
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| Molding machine : |
- Causes
- Insufficient mold clamping pressure in the molding machine.
- Aging of the die.
- Countermeasures
- If there is insufficient clamping pressure, estimate the correct
pressure using the following equation and choose an appropriate
molding machine.
Die clamping pressure = Projected surface area x die-internal
effective injection pressure / 1,000 kg
In the case of ABS, a rough value for 400 kg/cm2 can be used
in this calculation for the die-internal effective injection
pressure
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| Die : |
- Causes
- Insufficient mold clamping pressure.
- Insufficient precision at the die's mating faces
- The molded product is arranged in a cantilever-type setup
as a result of die design.
- Countermeasures
- Switch to a suitable molding machine.
- If the problem is related to mating faces, a joint examination
must be carried out with the die machining company.
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| Material : |
- Causes
- Plastic has low viscosity.
- Countermeasures
- If the problem is related to the plastic's viscosity, either
lower the temperature of the plastic or switch to a grade with
higher flowability.
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