: injection troubleshooter :

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plastic part voids

• Voids - plastic injection troubleshooter


• Description:
Vacuum hollows (‘empty bubbles’) in the moulding, due to thermal shrinkage that draws material away from the fluid core of a part.

• Causes:
machine
· injection pressure too low
· injection pressure time too short
· injection speed too high
· back pressure too low
mould
· mould temperature too low
· incorrect material flow
· part wall too thick
material
· melt too hot
· wrong material grade: some PC resin types more sensitive


• Actions:
1st
decrease injection speed to medium range
2nd
increase holding time
3rd
reduce melt temperature
4th
increase mould temperature
5th
check gate size: too small results in freezing at gate
with voids and sinks in other areas of the part
6th
increase gate size and reduce gate land length
7th
increase nozzle size and/or runner system
8th
redesign part to obtain equal wall sections


contact: jmfalcao@moldplast.com