- molds and plastics  injection troubleshooter -

• Dimention Changing- plastic injection troubleshooter

• Description:

Excessive shrinkage means part dimensions differing from expected ones; amorphous resins behave differently to semi-crystalline materials.

• Causes:
machine · injection pressure too low
· injection hold pressure time too short
· overall cycle too short
· back flow valve cracked
· excessive cylinder clearance
· heater bands burned out
mould · too hot
· gates too small (related to inadequate pressures)
· gating in the wrong place
· mould too small

• Actions:

1st. increase injection pressure
2nd. increase cooling time
3rd. increase mould temperature
4th. maintain uniform cycle time operation
5th check machine for erratic operation
6th check the percentage regrind to virgin material
7th increase gate size
8th reduce gate land length
9th relocate gate if glass-filled compounds
10th balance runner and/or gate system
11th reduce number of cavities to balanced system

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