SSkz

What is the best method of protecting cast aluminum from corrosion when it will be attached to stainless steel and dumped into sea water where it would reside for 10 years without any access to it?

Ok, what i am talking about is not part of a boat, but rather a washing machine.
Pic was supposed to go here but this forum wont allow links until i reach 10 posts. So you'll have to Google image "front load washer spider arm corrosion" to get an idea of what it looks like.

I'm posting here because folks at the washer forums haven't come up with a solution yet. I've seen a few posts on boat forums talking about similar problems so i figured you guys might have some experience dealing with these materials in such environments.

The aluminum part i want to treat is called a spider-arm. It's attached to a stainless steel drum. The drum is of course where you put your clothes. This setup is (afaik) always on a front load washer. The thing is, the spider always corrodes and breaks - mine did in just 3 years. It's inevitable. Lots of theories as to why that happens...galvanic corrosion, water PH levels, too little detergent, too much detergent, using cold water, keeping the washer door closed...and so on.
Those who say its NOT galvanic corrosion argue that if it was, the spider would have corroded at the points where it meets the stainless steel drum (the 3 ends), and at the shaft. Although most of the corroded spiders i've seen corrode a few inches from the shaft, i'm yet to see most of the corrosion happening at the spider-arm end joints...or immediately at the shaft. So they are of the opinion that the reason it is corroding is because of soap and high PH water.

In any case, i am getting ready to put in a new spider-arm and i would like to treat/coat it (and/or the stainless steel directly under it) so that i could get at least 10 years out of it.

I am thinking of first etching it with phosphoric acid, then anodizing it, and finally spraying it with a 2 part epoxy primer. What do you guys think?

SB

iTrader: (1)

Hard anodize (military spec) that beatch and see what happens.
You can coat over the hard anodizing with something if you so desire.

class6

Truck Bed-liner coating.

sailtexas186548

Make it out of wood

SSkz

Would that hold up though? And how good is it as a sealer?

Wally

iTrader: (1)

Depending on how crazy you want to go about this....you can go with a type 3 hard coat anodizing and they even have it with a Teflon impregnation now.....you can epoxy paint or powder-coat it as well....you can get a Teflon sheet and put that between the drum and the spider as a barrier...you can bore the holes out bigger that the bolts/rivets attach the spider to the drum with and put in some bushings to isolate it....but any and all of this would be moot if you scratch the spider down to bare metal and expose it...that would set it all off again and you would be back to square one...


if you went with the epoxy paint i would think you would need some sort of etching primer to help it grab on to the anodizing...not sure though as i've never tried painting over anodizing..

jwurl

Most automotive epoxy primers have a ethching property to them . You apply them to bare metal with nothing underneath. I would sand or bead blast the aluminum to roughen it up then apply the epoxy primer. Probably no need to top coat it if it is not contacting anything, but you could paint it for extra protection. Jeff wurl

SSkz

What if i skip the anodizing. How well would the epoxy hold under such conditions (provided i applied it after a good prep)? Another thing i keep hearing is zinc chromate. Any idea on that? I can easily get some here but would it do the job?

Wally

iTrader: (1)

It will all boil down to how well the spider is isolated from the stainless drum..the better you can separate them from touching each other the better chance you have of it not corroding.....and the epoxy should hold up just fine unless you scratch it enough to go down to metal....and exposure to bare metal and it will start corroding again....we had a customer that was buying our pumps and they were lasting 3 months before the environment would eat the aluminum caps off the ends!! we painted them with rattle cans of epoxy paint from HomeDepot and they have not had an issue in 2 years now..they are happy as can be...our distributor who was making good money on replacement parts not so much though
the paint we used was the appliance epoxy paint in rattle cans in the paint dept...only comes in white or black and they use it for spraying ovens and refrigerators so it should be tough enough.
And again try to isolate the spider as much as possible....especially around the mounting/bolt down points as I'm sure there are either rivets or bolts there....

northernoffshore

coal tar epoxy it