Void, air pocket
Most void is created inside thick molding products because the inside part cools and shrinks slow.
The resin freezes on the molding wall firstly, and cools and shrinks to inside. In the process, the inner part cools and shrinks more, and leaves void.
- Cause : Lack of Uniformity of product thickness
- Solution : Maintain the thickness of molding product uniformly and refrain from any sudden change of thickness.
- Cause : Insufficient pressure in mold
- Solution : Raise the holding pressure and holding pressure time.
- Cause : Small size of sprue, runner and gate
- Solution : Expand sprue, runner, and gate. If they are small,
other problems may occur, such as short shot, jetting, lower weld strength,
silver streak, etc.
- Cause : Pressure drop caused by flash
- Solution : You can prevent flash from occurring by lowering the temperature of resin and cylinder or the injection pressure.
However, it may cause short shot, sink mark or void. Therefore, mold adustment is recommended.
- Cause : Moisture (Void occurred out of center.)
- Solution : If void is occurred to other area, not center, moisture might be the cause. Therefore, dry resin and operate again.
- Cause : Gate structure
- Solution : Change the gate structure to tap gate.
- Cause : Multiple pin-point gate
- Solution : The use of multiple pin-point gate may cause stagnant air in the center of product, which may cause void and black spot.
To prevent any stagnant air, change the location of gate and install the air vent.