Page 92 - Injection Molding Advanced Troubleshooting Guide
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76 8 Machine Performance
Figure 8.15 Does everyone understand how each controller works?
Key items to check include the following
Pressure:
Does the machine setpoint match the hydraulic gauge and the displayed pres-
sure on the controller? If not, which one is correct? Use a secondary hydraulic
pressure gauge or a process monitoring system with a hydraulic pressure trans-
ducer to measure the actual value. The gauge on the machine may need to be
replaced, or the pressure output calibrated.
Keep in mind that if the pressure is not accurate second-stage pressure can cre-
ate defects as can back pressure. Pressure should be evaluated throughout the
cycle to determine where variations or accuracy problems are occurring. Back
pressure can result in variation to the melt temperature and viscosity of the
material, which can than impact much of the process.
Temperature:
Are all of the heater zones on the barrel and nozzle working? Look for zones that
are not achieving the required temperature because that is a likely indicator that
the machine may be experiencing heating problems. Also examine the current
draw on the various zones for any zones that are calling for either 100% or 0%
output. A properly working heater zone will cycle on and off as the zone heats
up. Individual heater bands can be checked with an “Amp Clamp” type of tester
to verify if the band is drawing current; if not the band may be burned out. An-
other problem that can occur is when two thermocouples get swapped on zones,
