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Injection Moulding Trouble Shooting

Problem Possible Cause Suggested remedy
Sink marks Material too hot Reduce cylinder temperature
Insufficient material shot into cavity Increase feed
Insufficient dwell time Increase cylinder heat
Gate freezing off too early Increase mould temperature
Piece ejected too hot Increase dwell time
Insufficient effective pressure in cavity Increase mould temperature
Increase cooling time in mould
Increase pressure
Reduce heating
Voids Gas developed by too hot material Pre-dry
Condensation of moisture on granules Increase pressure,
Shrinkage due to delayed solidification Increase mould temperature
of the core in thick sections

Surface defects Cold mould Increase pressure, injection speed
around gate Increase mould temperature
Hot mould Cool mould near gate

Flash formation Excessive injection pressure Reduce pressure,
Material too hot Check sprue runners and gates
Mould faces out of line Reduce heating
Insufficient clamp pressure Realign mould faces
Foreign material of ace of mould Increase clamp pressure
Restriction to flow in one or Clean mould faces
more cavities on multi cavity mould Find and remove restriction

Poor welds Material too cold Increase heating
Flow marks Injection pressure too low Increase injection pressure
Poor finish Inadequate venting Give enough venting
Dirty cavity surface Clean
Mould temperature too low Increase mould temperature
Excessive use of mould Use of mould surface
surface lubricant lubricant not recommended

Brittleness Material cold Increase heating
Mould cold Increase mould temperature
Material degraded(Yellow specks) Decrease heating
Contamination Check cylinder and hopper
Excessive regrind Reduce percentage of regrind

Warping Moulded in stresses due to: (a) Increase heating
(a) Material cold (b) Check feed. Reduce
(b) Overpacking in vicinity of gate injection pressure and heating.
Reduce injection time.

Silver streaking Part ejected too hot Increase cooling time
Material cold / Mould cold Increase heating
Condensation of moisture on mould Increase mould temperature
Entrapped vapour Dry and heat mould
Pre-dry material

Burn marks Improper venting Clean vents

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