Colorimetry failing on an 8-cavity mold (PA6-GF15). Parts are visually perfect, but fail measurement.
Hi everyone,
I'm an injection molding tech currently fighting a losing battle with colorimetry on one of our projects.
Here is the basic setup:
Machine: Arburg (25 mm screw)
Base Material: PA6-GF15
Colorant: Various masterbatches (we run a full range from light to dark colors)
Mold Setup: 8-cavity mold, hot runners with pneumatic valve gates
The Problem:
Visually, the molded parts look absolutely perfect – there are no visible streaks, spots, or signs of degradation. The issue is purely in the colorimetry numbers, which keep failing QC.
It often happens that out of the 8 cavities, only a single part passes the colorimetry check. We've tested multiple colors from light to dark, and the pass rate is extremely low across the board.
What I've already tried / checked:
Material drying is on point (moisture verified via Aquatrac).
Adjusted back pressure for better melt homogenization.
Tweaked melt temperatures and residence times in the hot runners.
Tuned injection speed profiles and the timing/sequencing of the pneumatic valve gates.
Verified masterbatch dosing times on the unit (proportional dosing).
Has anyone dealt with a situation where the parts look flawless to the naked eye, but the instrument catches such shade differences between cavities that it fails them?