Protecting non aluminum metals when anodizing

A. Hi D. Although some plastics and some glues can resist the cleaning, etching, desmutting, anodizing, and sealing steps involved, as a practical matter you'll have to remove them. First, because you won't know whether it will damage your particular plastic and glue. But secondly, even if you say you don't care, the anodizer will almost surely say they don't want that stuff dissolving or falling off into their tanks. Sorry for the bad news :-(

Luck & Regards,

A. The best answer, if at all possible, is to anodize first and install the steel inserts after,

There are masking materials - tapes, paints, plastics, waxes, etc which can be used to protect the steel inserts during anodizing, but they are difficult to do a leak proof job with. If you can use an alternate finish, you could chromate the assembly, and with some care on the part of the finisher, the steel will not be damaged, but neither will it be protected.

A. Steel inserts should be installed after the anodizing process, for the reason you mentioned. If its a press fit, or threaded hole that your inserts are being installed in, have your coater mask that hole. Inserts can be paint masked, but all it takes is one bare spot, and the insert will be destroyed. Mil 8625F states that:

In the long run, its much safer to install the inserts after the coating process.

A. As Jeffrey stated, it is very difficult to get perfect seals on a masking job.
Some shops would not put in the helicoils until after anodizing, which meant that the holes had to be plugged. One shop would make the hole one drill size undersized and not have it masked and would redrill the hole. This frequently caused chipping of the anodize around the hole. It also meant that cutting fluid other than water could not be used. It also meant that clamps had to be lined with cardboard or plastic to prevent scratches.

A. Hi George.

We appended your inquiry to a similar thread that pre-answers it.

If this is one single part that is already built, although success might not be likely, maybe you have little to lose by trying precision masking.

If these are parts that you are designing, change the design, as the tiniest defect in masking will destroy the part and possibly upset the process line chemistry as well. Good luck.

Regards,

A. Your fasteners should be installed after the coating processes, period. At a bare minimum, after the anodizing process.

With that being said, there are ways to protect the fasteners during the anodizing process (Ti screw/nut/washer/o-rings come to mind), however they wouldn't be fool-proof, and could very well have undesirable cosmetic results, or even worse as Ted stated, destroy the part.

I would seriously consider re-engineering your process steps, they seem completely backward to me, especially if this is a high volume production job.

A. Hi Pravin. You can try pre-anodizing and dyeing the rivets; but considering the brittleness of the anodized coating, plus the flaking and decrease in saturation of the black color as they are stretched during installation, I'm not very confident. Your only option may be to paint the rivets.

I may be misunderstanding, but assembling steel components with aluminum rivets in the severe service usually associated with automotive application doesn't sound practical because of the large galvanic currents that will be at work trying to dissolve the aluminum rivets. Good luck.

Regards,

A. Hi Edward. We appended your inquiry to a thread which answers it. The anodizing process will destroy the brass unless you are able to fully mask it, which sounds improbable. Sorry, but the brass inserts probably need to come out first. Good luck.

Regards,

A. Sorry Matt, no chance whatsoever of it working. If it's a relatively inexpensive clock, you can make the whole face, including the numbers out of aluminum, anodize the whole thing and mask it to dye the dial black and the numbers brass colored. Or you could anodize the whole thing, dye it black, engrave the numbers back to the aluminum, and anodize them and dye them gold. Otherwise, you're stuck with attaching the brass numerals after the anodizing.

Regards,

A. Stainless Steel or any most other metals, if made anodic in sulfuric acid, dissolves. Your masking is leaving some SS exposed.

A. Hi pankaj. The steel will be okay if you're sure the plastic is free of pinholes and of an acid resistant type (vinyl or teflon). Some plastics like nylon might not hold up.

Regards,