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17.3 Brown Streak Troubleshooting 159
17.3.3 Brown Streak Troubleshooting Machine Issues
The main machine-related causes of brown streaks are:
Heater band
Thermocouple
Machine performance
Hang up area
Screw design
Machine temperature control is critical to avoiding material degradation. The three
main components of temperature control of a machine are the heater bands, the
thermocouples, and the controller. Any of these three items can lead to problems
with material overheating and degrading.
17.3.3.1 Machine: Heater Bands
The first part of the machine temperature control is the heater bands on the ma-
chine. All bands must be working to provide even distribution of the heat to the
barrel. If a zone is burned out the resulting lack of temperature control will create
a location on the barrel that could result in material degradation. Some machines
have heater band burnout detection to automatically detect when a heater has
burned out. If you need to verify heater bands on a machine without burnout detec-
tion the best method is to use an “Amp Clamp” style meter to verify that the zone
has electrical current flowing to it. If the heater is burned out there will be no cur-
rent present. When replacing heater bands make sure to use the correct width and
wattage. Also, heater bands must be mounted tightly to the barrel because if they
are loose there will be poor heat transfer.
17.3.3.2 Machine: Thermocouples
Thermocouples are responsible for providing temperature feedback for the pro-
cess. If the thermocouple is not providing accurate information the temperatures
will also not be accurate. The first thing that can go wrong with thermocouples
would be using the wrong type, so if the machine is supposed to have a type “J”
thermocouple do not replace it with a type “K”. Another problem that can occur
with thermocouples is when they are not inserted correctly into the thermocouple
well on the barrel or nozzle. If the thermocouple is not located to the correct depth
it will provide a lower temperature reading than it should and will tell the control-
ler to continue to heat when it should not be heating.
17.3.3.3 Machine: Machine Performance
See Chapter 8 on machine performance.
