TROUBLE SHOOTING GUIDE
FAULTS AND REMIDIES
Fault
Cause
Action
Short ▪ Feed Problems ▪ Check feed to Barrel
(incomplete Moulding) ▪ Check feed from nozzle.
▪ Check screw travel
limit switches
▪ Inadequate flow ▪ Check melt temperature ( may be too low)
▪ Check injection pressure (may be too low)
▪ Check mould temperature (may be too low)

If using hot runners, check their temperature
▪ check the flow path ratio (is not excessive)
Flashing ▪ Worn or damaged mould. ▪ Check for damage at parting line.
Insufficient locking force. ▪ Check for worn mould mechanism.
Increase clamp pressure
Reduce injection pressure.
Reduce melt temperature.
Sink Marks ▪ Insufficient cavity reassure. ▪ Check packing pressure ( may be too low.)
▪ Check mould temperature (may be too low.)
▪ Check shot volume ( may be too low)
Bubbes/mica marks ▪ Volatiles/gases. ▪ Use dry granules
▪ Moisture ▪ Avoid overheating melt.
▪ Degradation products
▪ Volatile additives ▪ Use decompresssion screw
▪ Trapped air (may occur with dry Avoid overheating.
blends) Reformulate if necessary.
Use screw with higher C.R.
Poor finish (dull) ▪ Poor tool quality ▪ Check tool for polish, damage, corrosion
Insufficient pressure in cavity ▪ Check injection and packing pressure.
▪ Check melt temperature
▪ Check mould temperature.
▪ Vary injection speed.
Cold granules (visible ▪ Insufficient melting ▪ Check cylinder temperature
lumps or varying opacity
in moulding) ▪ Check screw speed and screw back pressure.
Fault
Cause
Action
Mertal contamination ▪ Contaminated feed ▪ Check raw material.
▪ Check hopper magnets
▪ or other seperating devices
▪ Machines wear and tear ▪ Check cylinder nozzles etc.
Black marks in ▪ Contamination ▪ Check raw material
moulding ▪ Check barrel and nozzles.
▪ Degraded material ▪ Check for dead spots in system
Black marks in moulding ▪ Air trapped in cavity rapidely ▪ Check air vents clear
(near blind end) compressed and causes burn
mark on moulding
Discolouration near ▪ Excess frictional heating at gate ▪ lower injection rate
▪ Lower melt temperatures.
▪ lower mould temperaturers.
▪ Increase gate section.
Cracked moulding ▪ Too high a cavity pressure ▪ Check injection and cavity pressures.
(often around ejector) ▪ Check melt temperature.
▪ Check mould temperatures
Mould sticking in cavities ▪ Too high cavity pressure ▪ As above
▪ Damaged mould ▪ Check and repair if necessary
▪ Bad mould design ▪ Polish surface of cavity
▪ Increase cavity sidewall tapers.
Delamination near gate ▪ Too high a packing pressure ▪ Reduce packing pressure at the end of
cooling stage.
Higly strained mouldings ▪ Excess orientation in moulding ▪ Raise melt temperature
(e.g. cracking in ▪ Raise mould temperature
certain liquids.)
Drooling between ▪ Failure of nozzle seal ▪ Check that nozzle seal is not jammed
nozzle ▪ Check on seal designed for polymer used
Fault
Cause
Action
Drooling between
▪ Check nozzle setting
nozzle and sprue ▪ Check nozzle/sprue alingement
bush. ▪ Check nozzle/sprue raddi
▪ Check that injection stroke is not
premature
Screw does not return ▪ Check feed from hopper.
▪ Reduce back pressure.
▪ Increase screw speed.