Page 444 - Injection Molding Advanced Troubleshooting Guide
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444 44 Stringers
44.2 Stringers Troubleshooting Chart
Table 44.1 shows the stringers troubleshooting chart.
Table 44.1 Stringers Troubleshooting Chart
Molding Process Mold Machine Material
high nozzle temperature hot tip temperature nozzle heater setup moisture content
low decompression tip-bearing surface machine performance volatiles
high melt temperature lack of cooling nozzle tip
valve gates
tip orifice size
44.3 Stringers Troubleshooting
Typically, stringers appear due to too much heat at a nozzle or hot tip. An import-
ant factor to consider with stringers is that they can lead to parting line damage
over time. Stringers on the mold surface will actually create a hobbing of the steel
resulting in mold repairs.
44.3.1 Stringers Troubleshooting Molding Process Issues
Potential processing-related concerns are:
High nozzle temperature
Low decompression
High melt temperature
44.3.1.1 Molding Process: High Nozzle Temperature
If the nozzle temperature is set or running too high the material will remain mol-
ten at the nozzle tip, which will allow a stringer to be pulled as the mold opens. The
plastic at the very tip of the nozzle must freeze off enough to create a break point
for the material that will not be molten.
When experiencing stringers review the actual nozzle temperature against the
specified set point. If the nozzle is running over the set temperature investigate
why. Try reducing the nozzle temperature to see if the stringers are reduced. Fig-
ure 44.2 shows a thermal image of a nozzle and adapter.
