Best method of sealing aluminum to prevent corrosion?

[Radkeyz]

The aluminum part i want to seal is part of a washing machine. It's called a spider-arm, and it's attached to a stainless steel drum. The drum is of course where you put your clothes.

This setup is (afaik) only on front load washers. 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, not using bleach...and so on.

Those who say it's 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 up 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. Zinc chromate is also an option, since it's readily available here. What do you guys think? Would that work? Any other suggestions? Many thanks for any point in the right direction!

Click here for more pics (Google image)

 

[Ron]

Your corrosion is generalized. There might be some galvanic influence but not the issue.

It is likely a result of the harsh environment.

Your proposed methods will help, but will likely result in a change in the type of corrosion you'll see. Most likely you will get filiform corrosion and the coating will start flaking away. You'll get a longer life but 10 years might be a stretch.

Change the spider material to stainless steel for long term service

 

[Radkeyz]

Ron...
Question: How would any corrosion (filform) develop if the part is properly sealed?

 

[Ron]

Under your premise if something were coated, it would last forever. Unfortunately, coatings fail as well. Small aberrations in the coating such as pinholes, sharp edges and other issues will allow filiform corrosion to develop in aluminum.

 

[Radkeyz]

Forever might be a stretch. I just want to give the arm the longest possible life, even if the longest feasible is 4 years (since 3 years seems to be the current deal). And i would like to accomplish that in the form of a coating. That way at least i can say i did the best i could.

 

[Ron]

Then coat in the manner you proposed. It is a good system and will increase the longevity.

 

[3DDave]

Most dissimilar metal corrosion is localized because the moisture and conductivity is localized. High pH (alkaline) conditions will tend to damage anodizing, which it does by stripping the ordinary protective aluminum oxide film.

I'd look to find a powder coater. Go over the part and round any sharp corners at least a little bit before coating. The ideal is if the film thickness is uniform. I think alodine/conversion coat is recommended before powder.

 

[rb1957]

how would you recoat in-service ? AFAIK all corrosion coatings need inspection and reapplication if required to maintain the protection.

If the part is cheap to replace then live with it.
If the part is expensive, make your own part out of stainless, and sell as an unlimited life part.

I would why this part of the drum gets wet ? I mean, the washing is on the opposite side, no?

another day in paradise, or is paradise one day closer ?

 

[drawoh]

Radkeyz,

What will it cost you to coat this thing? What will it cost you to replace your washer with a washer that is known to be reliable, i.e. non-corroding, among other things? Check the reliability ratings in Consumer Reports.

--
JHG

 

[Radkeyz]

rb1957,

If the part is cheap to replace then live with it.
If the part is expensive, make your own part out of stainless, and sell as an unlimited life part.

Not cheap, and above all, a PITA to replace. I really dont want to have to open it back up again. I wish i could make my own spider but just no time...i need this thing operating ASAP.

I would why this part of the drum gets wet ? I mean, the washing is on the opposite side, no?

The arm and drum are enclosed in a plastic tub. The tub fills with water, so the arm gets wet.

drawoh,

What will it cost you to coat this thing? What will it cost you to replace your washer with a washer that is known to be reliable, i.e. non-corroding, among other things? Check the reliability ratings in Consumer Reports.

Except for a Speed Queen (which is mainly commercial) and an Australian brand i've seen on Youtube, ALL front loads are made of the same materials...thus the same structural failures.

 

[drawoh]

Radkeyz,

I am very happy with my front loading Whirlpool washer. Why does it have to be top loading?

--
JHG

 

[cvg]

we have had front loaders for probably 17 years (two different units during that time) and so far have no problem with the spiders. at least, it has not broken yet. we do have some disgusting goo in the front door seal, but that's another issue. so it seems that the problem is likely caused by environmental conditions in your installation such as water quality or perhaps but not likely you are using some sort of extra strong detergent that is very hard on aluminum. so coating may help the spider, but addressing the water quality issue might be a better long term solution.

goo

http://cf.cleanandscentsible.com/wp-content/uploads/2013/09/Resized-Washing-Machine-Before.jpg

 

[hokie66]

Why is this a structural issue? Another forum, perhaps?