Page 149 - Injection Molding Advanced Troubleshooting Guide
P. 149
136 15 Black or Brown Specks
Figure 15.2 Nozzle to nozzle tip mismatch step
Figure 15.3 Non return valve with light buildup
Damage on any of the screw and barrel components can create locations that allow
material to hang up and degrade. Similar to mismatch, these damaged areas can
trap material for extended periods of time, which in turn leads to the risk of degra-
dation and black specks. Worn screws can also create undercuts that will trap ma-
terial and lead to black specks. Verification of all components of the melt delivery
