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plastic flow marks

• Flow Marks - plastic injection troubleshooter


• Description:
Blush and flow marks are the result of variations in material temperature, caused by the temperature gradient between machine nozzle and mould sprue bushing. A halo around the direct sprue is the result of cold material in the nozzle tip section. Eliminating the temperature gradient will minimize the blush and halo effects.

• Causes:
machine
· injection speed too slow or too fast
· injection pressure too low
· hold pressure too long
mould
· inadequate mould cooling
· mould too hot around gate
· mould too cold
· gate too small
· wrong gate location
· gate land length too long
· wrong hot runner system
material
· melt temperature too low


• Actions:
1st
adapt injection speed
2nd
add a large cold slug area
3rd
add cold wells at the end of runner systems
4th
control nozzle heat better: if necessary add beryllium copper tip (not recommended for FR resins)
5th
shorten or eliminate standard sprue bushing, use a hot sprue bushing
6th
clean flow must exist from the cylinder, adaptor, nozzle and tip. Avoid and eliminate any dead pockets or sections


contact: jmfalcao@moldplast.com