Jump to content

coatings on aluminum bar stock


Philip Perkins

Recommended Posts

Forgive my ignorance, those of you who are knowledgeable about metals.  When one buys pieces of aluminum bar stock ("HandiMetal" etc), is it coated with something?  I have a slowly evolving cart project that involved stripping some aluminum that had been painted w/ crappy spray paint.  The paint came off, but it looks like what I had assumed was raw aluminum underneath actually had some kind of coating on it, that the paint stripper turned white and patchy.  Should I assume that any new pieces I add to this project, starting as bar stock, will have some kind of coating that will need to be dealt with?  (I want to have the whole deal powder coated, eventually.)

Philip Perkins

Link to comment
Share on other sites

Most aluminum bar stock, channel and tubing that is purchased in hardware stores (as "Handi-Metal" as you say) is coated with a finish that can either be a light form of anodizing (which will not "rub off" but will exhibit some of the things you are talking about if paint stripper, etc. is used) or a varnish, shellack type coating. I have built many parts to many of my carts with this aluminum and it has never been a problem. You can see that there is a coating whenever you cut a piece and examine the cut. Aluminum bought at metal supply (like Industrial Metal here in Burbank) may have an oil based protective coating on it but this is easily cleaned off with any solvent. The aluminum then is un-protected and needs to be anodized or coated with powder coat or something. Something to consider is that part of the powder coating process you can have the do a sandblasting that removes everything and preps the aluminum to accept the charged powder particles that are the painting process.

-  Jeff Wexler

Link to comment
Share on other sites

That's what I figured.  Some pieces of hardware store aluminum stuff have been in use in my studio for many years, one piece as a handrest at the front of a mixer, and in all those years the finish hasn't changed at all, even though it has been touched daily by a sweaty mixer.  I guess I'll do the construction and then have them strip the whole thing again before they coat it.

Philip Perkins

Link to comment
Share on other sites

It's always best to lightly sand or bead-blast (as Glen T. suggests) any industrial Al stock before either painting or powder-coating, to both remove the protective coating and texture the surface. A primer is also well advised as an intermediate step to painting. Coatings present on most Al when initially purchased, whether oil or varnish based are commonly applied to prevent aluminum oxide (Al2O3) build up. Like common rust, Al2O3 is corrosive, but proceeds at a MUCH slower rate and will passivate the material over time, preventing further oxidation. The white-ish powder one may notice on weathered Al is just that, aluminum oxide. If handled a fair bit, the dull Al finish won't change as much as the handler will see black transfer to the hands, which involves another chem reaction. Well prepped Al will be very bright silver. Common anodizing is a process that incorporates the chemistry of aluminum oxidation itself and leaves a nice clean finish while also preventing further oxidation. Any method works...or gojo will easily remove the black from your hands.

HTH,

EB

Link to comment
Share on other sites

Careful with the sandblaster on aluminum. It is easy to get a very ruff finish. Bead blasting or belt sanding works best.

Glen Trew

I'm hoping the bead deal will work here--this is a refurb project of an old cart that is assembled, so I can't get at the parts individually to use a sander--too many nooks and crannies.  The powder coaters weren't bothered by the patchy residue, a good sign, I hope.

Philip Perkins

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...