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152 17 Brown Streaks
17.2 Brown Streak Troubleshooting Chart
Table 17.1 shows the brown streak troubleshooting chart.
Table 17.1 Brown Streak Troubleshooting Chart
Molding Process Mold Machine Material
barrel temperatures thermocouple location heater bands wrong material
hot runner temperatures manifold leaks thermocouples contamination
residence time lubricants machine performance color concentrate
back pressure bleeding of mold saver hang up areas, screw,
barrel, etc.
recovery speed hot runner insulator gap screw design
sprue bushing seat
17.3 Brown Streak Troubleshooting
Brown streaks are usually a sign that the material has been exposed to either ex-
cessive temperatures or elevated temperatures for extended times. Based on this
fact it is critical to review all of the heat sources that the material is exposed to
during processing. Also, closely examine any potential areas that material may
hang up and experience extended time at temperature.
As with many common defects the location of the brown streak can be an indicator
of where the problem is occurring. If the brown streaks occur just inside the gate
area of the part it is a sign that the overheating or hang up area is most likely
occurring toward the end of the melt control process.
17.3.1 Brown Streak Troubleshooting Molding Process Issues
The main process-related causes of brown streaks are:
Barrel temperatures
Hot runner temperatures
Residence time
Back pressure
Recovery speed
