Problem

Possible Causes

Possible Solutions

Flow Marks

Melt and / or mould

too cold

1. Increase barrel and nozzle temperatures.

2. Increase melt and/or mould temperature.

3. Increase injection rate.

4. Increase screw speed and back pressure.

5. Check suitability of screw.

Mould design

1. Change gate location.

2. Enlarge gates.

3. Enlarge runners.

4. Add additional flow-restricting zones

(e.g. sprue pullers) to runners.

Short Shots/Filling Problems

Air entrapment due to

insufficient venting

1. Check for obstruction of vents.

2. Check vent locations.

3. Enlarge vents.

4. Change filling behaviour by reducing or

increasing injection rate and/or pressure.

5. Add vacuum assist to vents

Runner system

1. Check for obstruction of gate.

2. Enlarge gate.

3. Enlarge runners.

Melt and / or mould

too cold

1. Increase barrel and nozzle temperatures.

2. Increase mould temperature.

3. Increase injection rate.

4. Increase screw speed.

Shot weight

1. Increase shot weight.

2. Increase melt cushion.

Sink Marks

Hold pressure too low

1. Increase holding pressure.

Melt and / or mould

too hot

1. Reduce barrel and nozzle temperatures.

2. Reduce mould temperature.

3. Reduce screw speed.

Burn Marks

Melt and / or mould

too hot

1. Reduce barrel and nozzle temperatures.

2. Reduce mould temperature.

3. Reduce screw speed.

Heater(s) stuck on

1. Check thermocouples and heater bands.

Mould design

1. Enlarge vents.

2. Check for obstruction of vents.

3. Add vacuum assist to vents.

4. Check vent locations.

Odour or yellowing

Melt and / or mould

too hot

1. Reduce barrel and nozzle temperatures.

2. Reduce mould temperature.

3. Reduce injection rate.

4. Reduce screw speed and back pressure.

5. Check temperature of hot runners (if used).

Flashing

Injection pressure /

rate too high

1. Reduce injection pressure / rate.

2. Increase clamp pressure.

3. Reduce injection rate.

Melt and / or mould

too hot

1. Reduce barrel and nozzle temperatures.

2. Reduce mould temperature.

3. Reduce screw speed.

Problem

Possible Causes

Possible Solutions

Part distortion/ Warpage

Too much orientation

1. Increase melt and mould temperature.

2. Reduce injection rate.

Part is over-packed

1. Reduce holding pressure.

2. Match injection time to mould fill time.

Uneven mould fill

1. Change gate locations.

2. Ensure uniform mould temperature.

3. Increase injection rate and  pressure.

Black specks or

undispersed particles

Contamination

1. Purge with low-MFI PP or HDPE.

2. Check that colour concentrate is based on

PP or PE, not PVC.

Sticking in mould

Part is too hot

1. Reduce barrel and nozzle temperatures.

2. Reduce mould temperature.

3. Increase cooling time.

Part is over-packed

1. Reduce shot weight and find correct fill point.

Mould design

1. Increase draft angles.

2. Use non-stick surface treatment.

3. If necessary, erode mould.

Lump formation

at gate

Moisture

1. Dry pellets.

2. If using vented screw, check for obstruction of vent.

3. Add vacuum assist to vents.

Voids

Melt freezes too quickly

1. Increase mould temperature.

2. Increase screw speed and pressure.

Moisture

1. Dry pellets.

2. If using vented screw, check for obstruction of vent.

3. Add vacuum assist to vents.

Holding pressure too low

1. Increase holding pressure.

Insert moulding: Inserted part is too cold

1. Preheat part (caution: heat surface only to approx.

80° C – 100° C.)