20.6.3 Flow Marks
The nished product exhibits blush and ow marks, due to variations in
material temperature from gradients between the machine nozzle and mold
sprue bushing. Cold material in the nozzle tip section results in a halo around
the direct sprue.
Probable Cause:
1. Molding Machine
• Wrong injection speed
• Wrong injection pressure
• Hold pressure too long
2. Mold
• Insucient mold cooling
• Temperature of mold too high around the gate
• Temperature of mold too cool
• Gate size is too small
• Gate is in wrong location
• Land length of gate is too long
• Incorrect Hot Runner system
3. Material
• Melt temperature is too low
Solution (in sequence):
1. Adjust injection speed
2. Add a large cold slug area
3. Add cold wells at the end of the runner system
4. Use hot sprue bushing
5. Identify and eliminate dead pockets / sections
20-7TROUBLESHOOTING
Hot Runner User Manual
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