Page 240 - Injection Molding Advanced Troubleshooting Guide
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24.3 Cracking Troubleshooting 231
Nylon is a material that has very different properties in a dry-as-molded (DAM)
condition versus its normally moisture-stabilized condition. When molding nylon
that has been dried extremely well there may be cases of parts acting brittle and
cracking during ejection or handling. In most cases as long as the material was not
damaged exposure to moisture will allow the material to achieve its conditioned
physical properties. Do not over-dry nylon and ensure proper tooling and process
conditions to minimize the impact of nylon in a dry-as-molded state.
See Chapter 9 on drying for more information
24.3.4.2 Material: Contamination
The most likely culprit for material-related cracking or breaking is contamination.
Contamination of the intended raw material with an alternate material can yield a
nonhomogeneous mixture that is severely compromised. Most of the time if con-
tamination is the root cause there will be other visual defects on the part such as
splay, delamination, streaking, etc.
It is crucial to avoid situations that can cross contaminate materials. Preventative
measures include keeping all material in closed containers, ensuring adequate
cleanout of any storage bins, hoppers, or silos, clear labeling standards, education
of employees on handling regrind, education of employees that the same color does
not mean the same material, etc.
Make sure that when using color concentrates that the concentrate is intended for
use in the base resin. Also maintain clear labeling and protocol to ensure that no-
one grabs just any box of concentrate that appears to look like the right color. Not
all concentrates are compatible with all base materials. In STOP troubleshooting it
is critical to Think about possible sources of contamination.
24.3.4.3 Material: Regrind
If regrind is handled well it can perform as well as virgin material. However, re-
grind can create issues if the following occurs:
Contamination with other materials
Not drying if the regrind becomes wet
Heat histories can lead to components in the additive package burning after
reuse
24.3.4.4 Material: Manufacturing Issues
Material suppliers typically do an excellent job of manufacturing the materials
that they produce. However, like any manufacturing process there will be variation
and mistakes. If a component is left out of the formulation or not added at the cor-
rect level the material could create issues. Two possible culprits could be impact
