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21.3 Cloudiness Troubleshooting 195
21.3.3 Cloudiness Troubleshooting Machine Issues
The most likely cause of cloudiness relating to the molding machine would be hang
up areas.
21.3.3.1 Machine: Hang Up Areas
If a molding machine has an area where material can be trapped and hang up the
material change process will be more difficult. Hang up areas can be locations of
mismatch between the barrel and end cap, end cap and nozzle, nozzle and nozzle
tip, nozzle tip to sprue bushing, or damaged spots on the screw, barrel, end cap, or
non-return valve.
Looking for hang up areas is a time-consuming process due to the requirement of
disassembling the machine components. To justify the effort and time of looking
for hang up areas it is critical to have exhausted other potential root causes.
Sometimes the actual hang up can be a small step difference between components
that allows wisps of the previous material to drag for extended periods of time.
Figure 21.3 shows an off-the-shelf nozzle and nozzle tip with mismatch; the shiny
inner diameter is a step difference between the nozzle body and the nozzle tip.
Figure 21.3 Hang up step (shiny inner diameter) looking through the end of a nozzle
towards the tip
