Where the
world gathers for metal finishing
Q&As since 1989


-----

White film or "dust" on anodized parts

Current question & answers:

August 18, 2021

Q. We have a black dye tank and are getting a copper/bronze film on the tank. It is on the parts after they are anodized but wipes off easily. What is weird is that even though it wipes off the rag is still white, like nothing was on it. A few months ago we ran some castings in the dye, I know, not too smart, and I was thinking that once they hit the dye after anodizing the heat opened the pores and the dye got contaminated? Any suggestions? I have attached some photos.

           

Henry Conway
- Joppa Maryland

---

⇩ Closely related postings, oldest first ⇩

---

Q. Our black anodize is coming out with a red tint to it. Has anyone come across this problem before? Please help.

Randy A. Mattson
- Seattle, Washington
2002

---

Q. Also some of our black parts have a white film on them. They are easily wiped off with MEK / methyl ethyl ketone. What causes this?

Randy A. Mattson [returning]
- Seattle, Washington
2002

---

---

Q. We are having difficulty anodizing (especially black dye) aluminum parts. There appears to be, for lack of a better term, "dust" or "sand" on the parts. Originally we thought the problem only existed on black dye parts and eventually determined that the dye was contaminated. We have changed the dye bath as well as the seal (nickel acetate). We then were informed that our sulfuric bath was too low in concentration and increased it to 230 gm/l. Still have the same problem except the "dust" is smaller, but more prevalent. Sometimes we can wipe the "dust" off after dye and then seal resulting in a okay finish, but sometimes we end up with white spots in place of the "dust". We are wondering if we should approach the sulfuric bath, or move to the front of the line and examine the clean, etch or desmut bath. Any ideas?

P.S. 14 amps/sq. ft. and 720 rule for soak time. All alloys, with most of the problems arising with 2024.

Thanks in advance for the help.

Mike Shiver
anodizing shop junkee - Mulberry, Florida, USA
October 14, 2009

---

A. I think that your problem is not having a dedicated desmut tank after the etch step. Some combined ones work when the tank is new, but get worse as they age. You say that 2024 is a problem . 7075 is probably as bad or worse (guess). Both are high alloy, mainly copper, and will smut a lot, giving the dust like parts as the aluminum around the smut anodizes and the smut does not. James Watts - Navarre, Florida October 16, 2009 A. 1. Check for galvanic voltage (about 1.08 volts) between the titanium rack and the stainless steel dye tank. Find a way to reverse it or come back and I will write it out again. 2. After anodizing (preferably with 180 gm/L free acid and dissolved aluminum under 12 gm/L) rinse once in water, then dip in 5%/vol Nitric Acid then rinse again in another water tank. Let us know what happens. Robert H Probert Robert H Probert Technical Services Garner, North Carolina October 16, 2009 October 17, 2009 A. You probably are in a dusty environment. I advice setting up a small clean room with air purifier to isolate exposure to dust as the metal surface becomes vulnerable because of charge/ions diffusion it has went through while the plating process. Hope this helps. Ammar Jangbarwala, Process Scientist - Gilroy, California

---

Q. If I didn't mention before, we do have a dedicated desmut tank. Each tank is followed by a dedicated rinse tank.

The dye tank is poly-pro, not stainless, so I am not having that issue.

The shop is very clean, but we had the thought of dust contamination at first also. We dumped and recharged the dye and seal because that was our first thoughts. That did not help at all. We are climate controlled and have only been in this facility for several months. I don't think dirt is our problem, but we have not completely ruled out that possibility.

We have had great success for some time now and then things slowly started getting worse. Does copper contamination cause any of these issues? We had a long hook on one rack that was in the bath and caused the cathodes to take on a copper color. This is the reason we are now dumping the entire acid bath and restarting. We originally had around 120 gm/L, but were told to charge the tank up to 230 gm/L. We noticed a big difference in the color of the parts after anodizing. We are planning on recharging at 165 gm/L, but Mr. Probert says 180 gm/L. Which is best when we anodize a little bit of everything. We are also wanting to change the cathodes (which brings up another questions). We were told that the original cathodes were 1100 alloy, but are trying to locate 6063-t6 because of all the chatter leading us that way. So far we have had no luck in locating them locally. Will another temper or alloy work?

Thanks for the help.

Cheers

Mike Shiver [returning]
anodizing shop junkee - Mulberry, Florida, USA
October 20, 2009