Summary for anodized thread porosity Discussion
Odd porosity on anodized threads is the issue Todd Brueckmann raises for a black type II anodizing process: after sealing, one specific form-tapped part develops tiny white specks or “lice-like” growths on the threads, even though the defect is not visible after dye and rinse and does not occur on other form-tapped parts. He says the sealant has been checked repeatedly, the pH is correct, and changing sealant has not solved it. The part is run on aluminum racks with titanium hangers. Chris Jurey, Past-President of IHAA, suggests the most likely cause is not the seal itself but small voids and/or burrs left by thread forming, which can trap sulfuric acid electrolyte. Over time, that trapped chemistry can bloom out as white aluminum sulfate, creating the appearance of porosity after sealing.
Q. I’m type 2 anodizing black and I have been having this problem when sealing this particular part that has threads that are form tapped. It looks as if there are little specs of lice growing off of the threads and this was not there after the dye and rinse cycle. The odd part is that we do not have this problem with any of the other parts that we use form taps on. This is the only part. Yes, I’ve tested the sealant. The pH is right on the money and I’ve changed the sealant several times and it does it on the first or 15th run.
I’m hoping someone has run into this. I’m using aluminum racks with titanium hangers for the parts.
Todd Brueckmann
– ASHLAND [Virginia]
August 15, 2024
A. I would guess that there are little voids and/or burrs left from the thread forming. This traps sulfuric acid electrolyte which blooms out over time as white aluminum sulfate
Chris Jurey, Past-President IHAA
Luke Engineering & Mfg. Co. Inc.
Wadsworth, Ohio
