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plastic burn marks

• 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


contact: jmfalcao@moldplast.com