Sandblasting before Anodizing -- Q&A, Problems & Solutions

A. This is VERY simple, follow this instructions :

1) etch in your caustic for 10 sec,
2) 20 sec deoxidize,
3) approx. 45-60 sec in ABF solution.
4) flash anodize for 10 min.
5) GO BACK TO YOUR CAUSTIC ETCH, STRIPPING THE ANODIZE
6) deoxidize the same as before 20 sec.
7) go back to your ABF solution same time
8) anodize for normal time w/your dye and seal

And that's how you get rid of the streaks from any blasting

A. Poor Bead Blasting is poor bead blasting. Excessive pressure and uneven blasting produces uneven appearing parts. The solution is to decrease pressure, use the proper media and blast with even movement. Aluminum will "burn" otherwise. Few people know how much art is involved in cosmetic beadblast. To correct the problem a strip, light & even beadbast, and anodize.

Good Luck.

A. If you are unhappy with vibratory wait until you try blasting. Abrasive blasting methods will leave you too rough of a surface and your plating processes will be not be uniform, and/or subject to failure. For good protection plated surfaces need to a be about 18 RMS or finer (lower). About the best blasting can achieve is about 35RMS. Probably your vibratory problem is that the media composition is too rough (coarse) and therefore you may have to do a multi-step operation.

A. In your other post you were talking about bright anodizing. Is this another product? If you are using the vibratory tumbler to deburr and then doing a light etch, you should get the desired uniform (satin-like) finish on your parts. What is the product?

A. With a hand held wand it is absolutely impossible to get a "uniform" finish on (soft) aluminum. This is because anyplace that gets 3 seconds longer blasting then an adjacent place will have a "shelf" and hence never uniform.

Further, any kind of blasting makes the anodizing non-uniform because the metal is soft and you are pounding it with a hard substance backed up by strong force. You will be pounding all sorts of non-aluminum junk into the surface. Some of this junk can be removed in the alkaline etch. Hey, why not just alkaline etch (after thorough cleaning) and get a uniform finish to start with?

A. If the parts can handle the dimensional change, you can etch it, then anodize it, then remove the original anodize in the etch, then anodize it again.

That would probably work, a lot of parts look a lot better the second time around - most of the impurities/stains are incorporated into the original oxide layer and removed when you remove it.

Don't try this with castings though, I imagine it would result in a very poor second anodize due to the other casting constituents.

Good luck.

A. It has been my experience you need to deox or desmut the part first. If you anodize over a water stain it will set the pattern, and then only mechanical means can remove it.Sometimes it has helped us if we also flash anodize the part .To do this we desmut , rinse, anodize for five min., rinse and then go back through your regular process.

A. Mr. Hankins in completely correct - a deox step is necessary after the etch and prior to the anodize. I've become so accustomed to the two baths always being used together that I just think of it as one process, hope it didn't cause any confusion.

Good luck.

A. Since I can not observe the process, it is difficult to blame any one thing. My guess is the cause is in the blast process as it is terribly difficult to blast two parts identically, even with excellent automation. A factor might be media break down giving different roughness as the process proceeds through the day. Minor angle and pressure differences make a huge variance in the cosmetics of the part. Have you tried using one level finer blast media?
Mark a couple of parts for the top of the rack and a couple for the bottom of the rack to see if you can find a difference there, since the bottom gets a minor amount longer etch than the top does.

A. There are media deposited in the surface.
Reduce your Blasting time (Ra too)and use and angle 60 to 90.