DIY aluminum anodizing for anti-corrosion benefits?

[BradH]

I have a number of plain / polished aluminum fuel bowls on hand and know already what the exposure to E10+ fuel does to untreated aluminum when it's left to sit for any extended amount of time. There are some DIY aluminum anodizing products and a number of YT vids on DIY anodizing, but they seem aimed primarily at the variety of colors that can be created. None of this stuff is Type III hard-coat anodizing, but would it still have anti-corrosion benefits, especially from ethanol?

I suppose another alternative is checking w/ a local metal finisher who offers a variety of anodizing options, including hard-coating. However, I've got a pretty small collection of parts to which this would apply, and my thought on this approach is whether it's even close to being cost effective. These bowls could be replaced by either factory hard-coated or Nitroplated parts for $60 to $80 each, depending on the fuel bowl style.

Thanks - Brad

[ijames]

One of my responsibilities at my last job was getting some of the parts we made anodized, so I spent a fair amount of time finding and talking with metal finishers about what they offered and what they charged. Most do their pricing based on a minimum lot charge for a small number of items, or a per piece price for recurring large orders so long as the minimum is also met. In the Baltimore area the lot charge for various plating and anodizing jobs is in the $100-150 ballpark, including natural finish type III hardcoat anodizing. That was the only anodizing we used, and on 5056 and 6061 it comes out a dark gray, almost greenish color. We used Eastern Plating in Baltimore for anodizing. They sometimes were slow, but the quality was good for the most part and the price was the best. Call around and find out what the lot charge is, then gather up all of the pieces you can for one load to get the price per piece down as low as you can. Ask if you need to separate by alloy as they might want to run each alloy in a separate load which will drive up your price. Sounds like you could maybe save 50% by anodizing what you have, over buying new.

[BradH]

Good info, thanks.

I'm in northern Virginia, about 45 minutes (no traffic) from Laurel. The place I have in mind to check with is Alexandria Metal Finishers, although they've relocated to Lorton since a friend of mine worked there years ago.

[ijames]

Hey, almost a neighbor although that "no traffic" is a fantasy . Heading south to visit family, if I use I495 and I95 and go through the Mixing Bowl in the morning so against traffiic my average the last few years is 3 hours Laurel to Quantico (20-25 mph for 65 miles). Job was also in Laurel so given the traffic patterns I never dealt with any Virginia metal finishers so can't recommend anyone down that way. Oh, I almost always go I495 to Route 5 to US301 in Waldorf then down to VA207 to get back to I95. There's a toll at the bridge but I get past Fredericksburg in half the time. You're on the west side so not nearly as bad, I just had to vent .

One thing to watch out for is how they hang and clamp your parts. They use a big crossbar that sits on the top edges of the tank, then hang vertical 1" square bars off of that that go down into the liquid, then put clamps on the vertical bars to hold the pieces to be anodized. Ever seen ring clamps in a chemistry lab? That's kind of what the clamps look like. They have a slot with locking screw to attach to the vertical bar, then at the other end they may have just a simple groove or they may have some pinch fingers. With the groove type they put one clamp above and one clamp below the piece and squeeze them together as they tighten the clamp to secure the piece. The finger type is used for small pieces and uses either a spring or screw to clamp down on the piece. All this fixturing is aluminum so it gets anodized each run, then chemically stripped before reusing it. The anodizing leaves an insulating surface so if the stripping isn't perfect you can get poor electrical connections that lead to arcing and erosion on your piece. Also, the clamps cover up the contact spot with your piece so you will get a small defect there. And if the clamp isn't clamped tightly enough you can still get an arc even if the metal prep is perfect. All that is a long-winded way of saying that you need to go over your parts with them to make sure that the clamping is done on non-critical surfaces. You don't want to get a burr on a gasket surface or venturi, for example. Also, holes will close up a bit. The etch removes a bit of material but then the hardcoat anodizing adds about 0.001" to each surface so a hole will tighten up 0.001-0.0015". I remember our machinist having to tweak some hole sizes that got bearings pressed in, and some that got threads. I'll try to drop in and visit with him late next week, and if I do I'll post any tips he gives me.

It's fun watching some of the anodizing process. At Eastern Plating the tanks were about 2' wide by 8' long by 30" deep and they had about 15 of them lined up side by side. The big crossbar I mentioned was about 4" by 4" by 10' long and had hooks where an overhead crane grabbed it. Anodizing is a multistep process where the parts go through a rinse tank, an etch tank, the anodizing tank, maybe a dye tank, and a sealant tank, with various rinse tanks and others between each of those. There are counterelectrodes in the anodizing tank and what looks like a giant booster cable gets clamped to the crossbar when it is in the anodizing tank. Picture a foot long alligator clamp with 0000 sized wire leading off to a 10,000 amp power supply - big manly stuff .

[BradH]