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How to treat/coat cast aluminum to prevent corrosion?

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  • How to treat/coat cast aluminum to prevent corrosion?

    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. I'm posting here because folks at the washer forums haven't come up with a solution yet. I've seen a few posts here 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 protect is called a spider-arm, and it's attached to a stainless steel drum. The drum is of course where you put your clothes. It spins at speeds of 1200rpm. The load (clothes) can be unevenly distributed in the drum, therefore it could be put through high stress. This setup is (afaik) only on front load washers. The aluminum part 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?

    Appreciate any help i can get!


  • #2
    Ayuh,..... Yer Best bet would be anodizing, or powder coatin' the piece,.....

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    • #3
      What vintage and brand of washer are we talking about?

      We have two washing machines. Both are early to md-90's models. Neither have corrosion issues.

      Stainless and aluminum play pretty well together unless stray voltages are introduced into the mix.

      Looking at the pictures I doubt part is aluminum. Looks to be die cast. Most likely pot or white metal with a high zinc content.

      Pop, pop, fizz, fizz in a number of scenarios
      Last edited by dingbat; August 13th, 2017, 10:39 AM.
      ....

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      • #4
        Originally posted by Bigjj View Post
        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?
        simple, dont use aluminum.

        in salt water - dont let aluminum and stainless touch.....ever.

        hard anodizing the aluminum helps a bit, however galvanic corrosion eats that too.

        there needs to be an isolator material between them, or you have a battery. if you add a bit of copper, you can call it an eveready or duracell. however if you want 10 years of life without access to it, make everything out of 316L stainless, (not the 304 that is common in washing machine parts) dont have any crevices (look up crevice corrosion) and never use aluminum with it.
        1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - http://forums.iboats.com/forum/owner...988-rogue-2420

        Past Boats
        1970 Wooster Hellion - Merc 9.8
        2002 SeaRay 190BR - 5.0 - A1G2 - "Cheasheads in Paradise"
        1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

        What’s behind you doesn’t matter.Enzo Ferrari

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        • #5
          Originally posted by dingbat View Post
          What vintage and brand of washer are we talking about?

          We have two washing machines. Both are early to md-90's models. Neither have corrosion issues.

          Stainless and aluminum play pretty well together unless stray voltages are introduced into the mix.

          Looking at the pictures I doubt part is aluminum. Looks to be die cast. Most likely pot or white metal with a high zinc content.

          Pop, pop, fizz, fizz in a number of scenarios
          It's a Samsung. That's the thing...mid-90's means you got a quality washer. The new ones are notoriously called glitter boxes. Just Google "front load washer spider arm" to get an idea.

          It's a washer...so water can definitely act as stray voltage.

          I wasn't able to find info on what it's made out of. Most of the stuff online says it's cast aluminum. Any idea how i can test it? Who does these kind of tests?...i'm thinking hooked-up-to-computer-for-a-reading kind of deal, if there is such a thing,

          Meanwhile though. How well would an epoxy primer work in sealing this thing from corrosion?


          Originally posted by Scott Danforth View Post

          simple, dont use aluminum.
          Easier said than done. I have no option. It only comes in aluminum (or die cast like dingbat is saying).

          Originally posted by Scott Danforth View Post
          in salt water - dont let aluminum and stainless touch.....ever.
          Again...no choice.

          Originally posted by Scott Danforth View Post
          hard anodizing the aluminum helps a bit, however galvanic corrosion eats that too.

          there needs to be an isolator material between them, or you have a battery. if you add a bit of copper, you can call it an eveready or duracell. however if you want 10 years of life without access to it, make everything out of 316L stainless, (not the 304 that is common in washing machine parts) dont have any crevices (look up crevice corrosion) and never use aluminum with it.
          I really don't have any choice short of fabricating the whole thing. I just want to be able to coat or treat the spider arm (the thing that's corroding)...or/and the immediate area it sits on, which is stainless steel. Therefore, i would like to know what the best coating for this application is. So many out there.
          Forget 10 years. I'd be happy if i could give it the longest possible life, even if the longest feasible is 4 years (since 3 years seems to be the current deal). At least i did the best i could,

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          • #6
            if there is an electrical path between the drum and the spider arm, the spider arm is going to dissolve in anything other than distilled water. any minerals in the water (like soap) and say good by. it gets worse if you add bleach.

            find a stainless fabrication shop and fabricate one out of stainless. or replace every few years.
            1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - http://forums.iboats.com/forum/owner...988-rogue-2420

            Past Boats
            1970 Wooster Hellion - Merc 9.8
            2002 SeaRay 190BR - 5.0 - A1G2 - "Cheasheads in Paradise"
            1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

            What’s behind you doesn’t matter.Enzo Ferrari

            Comment


            • #7
              Up until 4 years ago I was your local "connect it to a computer" metal analyzer salesman among other things... You can own one too for just $39,760

              Having it powder coated Is your best shot. Use nylon washers under the hardware. Gives you less contact area but more importantly causes a gap between the spider and drum for air to circulate
              ....

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              • #8
                You guys seem to not be for epoxy primer. Any reason why?

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                • #9
                  I would use phenolic vs nylon washers. nylon has a low compression strength

                  you can use epoxy primer and paint, however your going to need to get a brand new part, sand down (or bead blast) to remove the surface oxidation that has already started and immediately apply the zinc self-etching primer, then the epoxy primer, then an epoxy top coat.
                  1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - http://forums.iboats.com/forum/owner...988-rogue-2420

                  Past Boats
                  1970 Wooster Hellion - Merc 9.8
                  2002 SeaRay 190BR - 5.0 - A1G2 - "Cheasheads in Paradise"
                  1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

                  What’s behind you doesn’t matter.Enzo Ferrari

                  Comment


                  • #10
                    Originally posted by Bigjj View Post
                    You guys seem to not be for epoxy primer. Any reason why?
                    Up until a few yeas ago, we painted our equipment with a Sherwin Williams acid catalyzed wash primer (P60G2) and a paint formulated specifically for industrial metals applications. Mixing components was pain staking and cleaning the equipment after use required chemicals that had the makings of an EPA Super Find site, but the stuff worked very well.

                    I would highly recommend the material or something similar for your application, but I doubt your going to find anything close to an equivalent formulation at a VOC compliant big box store. You can't use an epoxy paint formulated for a garage floor and expect good results on metals.

                    On top of that, prep work and painting skills play heavily on the integrity of the coating. Both variables are negated going with power coating


                    ....

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                    • #11
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                      You can't really anodize the part because it looks like they are pressed onto a stainless shaft, plus anodizing doesn't really work well on cast aluminum because they have a very high silicone and zinc content.

                      Powdercoating is an option but you would have to mask the shaft which is definitely doable. May not hold up forever to the corrosive chemicals and other things tho.

                      In my opinion, your best bet would be to take the whole assembly to a plating shop and have them do a electroplated nickel over copper strike. We nickel plate die cast aluminum parts all the time where I work.
                      1995 Stingray 606zp - 4.3LX
                      1996 Bayliner Capri 2050 40th Anniv Edition - 5.7 Merc

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