Page 215 - Injection Molding Advanced Troubleshooting Guide
P. 215
206 22 Color Swirls
in turn led to areas of dark pigment that in turn became color streaks/swirls
when processed. After the issue with the raw pigment had been corrected
the problem was completely resolved. This was a case that took an extra
amount of time to resolve because the color concentrate supplier had to be
fully convinced that there was an issue with the material. Much waste could
have been eliminated if the supplier had been more open-minded to the
potential root cause.
22.3.4.2 Material: Contamination
Many common defects can occur when material is not protected from contamina-
tion (see Figure 22.3). There are many potential sources of contamination in a
molding shop. Some general rules of thumb to help avoid contamination are:
Keep material containers covered.
Make sure that all hoppers, conveying lines, and feeders are thoroughly cleaned
whenever materials are changed.
Clearly label all materials to reduce the opportunity to mix materials. This can be
everything from hoppers to gaylords to silos. Switching materials in a silo with-
out a thorough clean out can lead to a long-term contamination issue that can
lead to a variety of defects including color swirls.
Figure 22.3 Color swirl from contamination
Keep in mind that one pellet of contamination can lead to a color swirl in the
molded part creating scrap. When troubleshooting a color swirl problem, it is well
worth inspecting the material for contamination.
