Page 214 - Injection Molding Advanced Troubleshooting Guide

22.3 Color Swirls Troubleshooting 205

Figure 22.2 Volumetric additive feeder

Be sure to understand the impact of different auger sizes. This is a volumetric rela-
tionship so the ratio in settings between a ½″ and a 1″ auger is not 2 : 1. To deter-
mine auger output consult the manual of the additive feeder for settings as well as
minimum and maximum throughput rates.

Case Study: Color Concentrate

This case involved a PP automotive molding. The part ran in three different
colors, black, gray, and tan, and only had issues when running with the tan
color concentrate. Careful review of the data showed that this problem
showed up virtually overnight and could generate over 20% scrap. Many
things were tried to determine the cause of this issue including pulling and
cleaning the screw and barrel. The color concentrate supplier was convinced
that there was contamination coming from the barrel; however, running
highly loaded white concentrate did not replicate the defect, and it would
only show with the tan color concentrate. After convincing the color con-
centrate supplier that the defect was not caused by the machine (the mold
also ran in a secondary press), the supplier conducted an in-depth investi-
gation into their raw components. They determined that one of the raw pig-
ments used in the tan concentrate was actually clumping together, which ▸