- molds and plastics  injection troubleshooter -

• Burn Marks- plastic injection troubleshooter

• Description:

Burn marks are (often) brown streaks. They are usually caused by overheating the material due to entrapped air (diesel effect) that causes the darkening in colour and carbon buildup.

• Causes:
machine · problems with back flow valve
· injection speed too fast
· back pressure too high
mould · inadequate venting, entrapped air
· frictional burning
· check sprue diameter
material · melt too hot or too cold. May create shear

• Actions:

1st. check venting channels for dirt
2nd. decrease injection speed
3rd. decrease injection pressure
4th. use programmed injection steps
5th check for heater malfunctioning
6th reduce screw r.p.m.
7th decrease nozzle temperature
8th reduce melt temperature
9th improve mould cavity venting
- add vents to ejector pins
- add vents to parting line of part
10th enlarge gate to reduce frictional burning
11th change position and/or increase gate size

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