Best Masking Materials & Methods for Aluminum Anodizing

A. One could write a book about the best masking techniques and materials and still not answer your questions. I worked in a shop that did selective hardcoat for IBM, Boeing, and others, and we usually found that each part had its own quirks and oddities. This is one area that is more art and intuition than science. We usually had a few women who did masking almost all the time (sorry guys, women did a better job than men, since they had more patience and better dexterity). These employees made more than the standard rackers, since their work required more skill.

As to who makes masking materials, there are several firms who make a living selling plugs, tapes, paints, even plastic screws for masking. Some are probably listed in the suppliers' section of this site, and "Products Finishing" now has their suppliers' Directory at their site. We used to like to visit the masking vendors' booths at the Trade Shows such as SurFin, and with just a little bit of talking, they become most willing to send samples of the masking devices which they sell, and they would also express their willingness to make custom masking if the volume warranted it. We ended up using several suppliers, because we would find one plug from one vendor, and another plug or tape from another vendor.

One trick we learned when using tape or paint, whether it was required or not, was to give the parts a light conversion coating prior to application of paint or tape. It dramatically improved the chances that the tape or paint would stick through the whole process without undercutting or even lifting off the surface, which can be a disaster, of course.

Phil Johnson
- Madison Heights, Michigan

Ed. note: We can't compare brands & sources on this advertiser-supported, no-registration-required (and therefore largely anonymous) site (huh? why?), so thanks for your deft handling of the question, Phil.

A. The most common methods are tape, liquid masking (paint like) and solid masking methods like plugs.

A. Hi Tony,

Since this guy is roaming around here and he keeps tabs on my posts *GRIN*. Call Mark at U.S. Specialty Color. They sell a liquid maskant that can be purchased in 1 gallon and 5 gallon containers; I've got a 1 gallon can myself and it will probably last me a very long time, and its relatively inexpensive, around $35-40 for a 1 gal. container. If you're looking for something more along the lines of caps, plugs or tapered masks, well take your pick. There's no less than 10-12 that I can think of.

"Internet advertising demand curve: infinite demand at zero cost, zero demand at infinitessimal cost" -- TJ Pullizzi, 1995

A. The best way depending on the flatness of the area is the liquid maskant. I use about 1 gallon per week for flat surfaces and it works faster and cleaner than tapes, but if you want to use tape C.S. Hyde have a green poly tape, inexpensive and can be dye cut to the right size with a release liner, we're talking pennies here for over 5K. Liquid mask is best put on by silk screen (you can get a cheap one from a PCB supplier if they have some around and screens are also low cost.

A. Hi Tyler. Because chromic acid is highly corrosive and extremely oxidizing, I'd probably be happy that all the other sizes are holding up well. Per some chemical resistance charts I've looked at, there is no non-exotic elastomer that holds up as well -- neoprene, vinyl, and silicone all rank worse. Fluoropolymer plugs (Viton, PVDF, Teflon) would be more resistant but I don't know if they are available.

Luck & Regards,

A. Hi Tyler. You may want to establish a process you can determine the life of the plug then rotate them out based off your study. For example. Have 10 bins. New plugs go in first bin. After first use, they go in to the second bin so on and so forth. Once determined how many cycles they can go through, discard them prior to that cycle.