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  1. #1
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    Default Aluminum Disc with Stainless Steel Rope Rigging

    Hi All, hoping some of you experts can advise on best course to maximize longevity of a public art piece.

    Details:
    I have a 1/8" thick x 14" diameter aluminum disc suspended between a concrete floor and metal post above, using 1/8" metal cable. The disc has a 3/8" hole at top and at bottom, to thread the cable through. The disc's entire surface including the holes is sealed by powder coated paint.

    This is part of an outdoor public art piece in Texas with extreme humidity, rain, sun, all weather. Eventually, the powder coating will probably get worn away where the cable thimble rubs against it. When that happens, I'm concerned about corrosion at those points of contact.

    I initially planned on using stainless steel wire-rope, stainless thimble, and aluminum crimped sleeve. An engineer told me under non-marine outdoor conditions, it would take decades for noticeable corrosion to happen between aluminum and stainless. But after researching online, I'm not so sure.

    What's your experience with stainless hardware contacting a small point of aluminum?

    Rather than using stainless thimble, I could use a coated wire rope, but that too will eventually wear out as the artwork blows in the winds and friction eats the coating. I've also been reading a bit about Tef-gel, lanolin or other insulators, but have zero experience with them.

    Any recommendations for how to best protect contact points between aluminum & stainless steel? Also, any estimates on how many years it would take for corrosion to set in?

    rigging-detail.jpg

  2. #2
    BobL is offline Member: Blue and white apron brigade
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    Does the disc have to be Al ? - even if it's powder coated it will eventually, to use a local expression, go "manky"
    The main wear and corrosion will be at the contact point between the stainless rope and disc. This will chip teh paint off in a few days/weeks and the corrosion will spread from there.
    Long term the wear could eat right thru those holes to the outside of the disc.
    The easiest solution would be to replace the Al disc with a Stainless one.

    Its not much use to you but as it so happens, our local steel merchant has heaps of these on his scrap pile which he sells for $6/kg but I get them for $1kg
    If weight is an issue, a 1mm disc could be used as it should be just as strong as the original 3mm Al one.

  3. #3
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    Quote Originally Posted by BobL View Post
    Does the disc have to be Al ? - even if it's powder coated it will eventually, to use a local expression, go "manky"
    The main wear/corrosion will be at the contact point between the stainless rope and disc. This will chip teh paint off in a few days/weeks and the corrosion will spread from there.
    The easiest solution would be to replace the Al disc with a Stainless one.

    Its not much use to you but as it so happens, our local steel merchant has heaps of these on his scrap pile which he sells for $6/kg but I get them for $1kg )

    Unfortunately, it must be aluminum discs. Any thoughts on best way to mitigate the corrosion?

    I could use aluminum thimble, so the disc would be directly touching an aluminum thimble in stead of stainless steel thimble. The thimble could be sacrificial, that is, replaced once a year. Would that protect the aluminum disc? I'm not clear on whether the corrosion would quickly spread from the thimble to the disc itself.

  4. #4
    BobL is offline Member: Blue and white apron brigade
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    It's not just the corrosion but wear that needs mitigation - any paint or plastic sheathing will just wear through in that situation.
    This is because of the flexible nature of the wire going through the hole in the Al means it will continually rub against the Al.
    One possibility would be to firmly affix a stainless eyelet over the powder coated hole so the SS wire rubs on the SS eyelet rather than the Al disc.
    Attaching the eyelet without cracking the powder coating won't be easy.

  5. #5
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    Quote Originally Posted by BobL View Post
    It's not just the corrosion but wear that needs mitigation - any paint or plastic sheathing will just wear through in that situation.
    This is because of the flexible nature of the wire going through the hole in the Al means it will continually rub against the Al.
    One possibility would be to firmly affix a stainless eyelet over the powder coated hole so the SS wire rubs on the SS eyelet rather than the Al disc.
    Attaching the eyelet without cracking the powder coating won't be easy.
    I edited my prior reply, but am guessing you didn't see it. So let me ask you here:

    I could use aluminum thimble, so the disc would be directly touching an aluminum thimble in stead of stainless steel thimble. The thimble could be sacrificial, that is, replaced once a year. Would that protect the aluminum disc? I'm not clear on whether the corrosion would quickly spread from the thimble to the disc itself. Using a coated stainless rope will also help a bit, especially since the thimble will reduce fraying.


  6. #6
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by Deefer View Post
    I edited my prior reply, but am guessing you didn't see it. So let me ask you here:

    I could use aluminum thimble, so the disc would be directly touching an aluminum thimble in stead of stainless steel thimble. The thimble could be sacrificial, that is, replaced once a year. Would that protect the aluminum disc? I'm not clear on whether the corrosion would quickly spread from the thimble to the disc itself. Using a coated stainless rope will also help a bit, especially since the thimble will reduce fraying.

    By thimble I assume you mean an eyelet?
    Like this?
    Screen Shot 2021-03-03 at 9.51.35 am.png

    Is the thimble fixed firmly in the hole? - if not it will still wear though the powder coat on the disc.

    If yes then you might as well use a stainless eyelet as it will not need to be replaced.

    Either way the eyelet will need to be applied careful so as not to crack the Al disc's powder coasting.

  7. #7
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    Quote Originally Posted by BobL View Post
    By thimble I assume you mean an eyelet?
    Like this?
    Screen Shot 2021-03-03 at 9.51.35 am.png

    Is the thimble fixed firmly in the hole? - if not it will still wear though the powder coat on the disc.

    If yes then you might as well use a stainless eyelet as it will not need to be replaced.

    Either way the eyelet will need to be applied careful so as not to crack the Al disc's powder coasting.
    No, not an eyelet. I'm talking about cable-rigging thimbles like this:
    thimble.png
    The wire rope fits inside the thimble groove, so the stainless steel would have no direct point of contact with the disc. But I don't understand how quickly the corrosion would move through the thimble and into the disc. I'm wondering if the thimbles were replaced once a year, would that prevent corrosion of the disc.

  8. #8
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    It seems to me that the al disc will wear at the point of contact and the whole thing will fail.
    Even in light winds this would not take long.
    The best way would be to use a crimped lug on the stainless cable and bolt it securely to the al disc, because it is then solidly bolted it removes the wear point and should increase it's life significantly.
    Regards
    Bradford

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    What about a cable fixed with some type of epoxy, into two holes drilled in edge of disc?
    Nev.

  10. #10
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    Quote Originally Posted by SurfinNev View Post
    What about a cable fixed with some type of epoxy, into two holes drilled in edge of disc?
    I'm guessing the epoxy would wear out soon enough. Unless there's a super strong one I'm not aware of.

  11. #11
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    Aluminium can be anodised in various colours.
    It eventually fades in the sun but does protect from corrosion though maybe not so well in marine environments.
    Powder coating, if (when?) it fails loses all ability to protect anything, and cannot be readily touched up like paints.
    "Two pack" paints might be worth investigating.
    Too bad a stainless steel or bronze disc can't be used.

  12. #12
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    Quote Originally Posted by nadroj View Post
    Aluminium can be anodised in various colours.
    It eventually fades in the sun but does protect from corrosion though maybe not so well in marine environments.
    Powder coating, if (when?) it fails loses all ability to protect anything, and cannot be readily touched up like paints.
    "Two pack" paints might be worth investigating.
    Too bad a stainless steel or bronze disc can't be used.
    It's a special process where digital imagery can be printed using dye-sublimation onto powder coated paint. The process only works on non-anodized aluminum.

    I did have a different thought. Perhaps there's a super strong synthetic fiber rope I could use instead of steel cable. But it would need to be tough enough someone couldn't cut it with scissors or a knife. Any recommendation?

  13. #13
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    Welcome to the forum Deefer.

  14. #14
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    Quote Originally Posted by Deefer View Post
    It's a special process where digital imagery can be printed using dye-sublimation onto powder coated paint. The process only works on non-anodized aluminum.

    I did have a different thought. Perhaps there's a super strong synthetic fiber rope I could use instead of steel cable. But it would need to be tough enough someone couldn't cut it with scissors or a knife. Any recommendation?
    Kevlar rope is very difficult to cut with normal scissors or knives but can be cut with special ceramic blade tools I believe.
    A yacht rigging business should be able to give you good advice and carry out the work. And you will have someone to blame if it doesn't work.
    Bill

  15. #15
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by Deefer View Post
    No, not an eyelet. I'm talking about cable-rigging thimbles like this:
    thimble.png
    The wire rope fits inside the thimble groove, so the stainless steel would have no direct point of contact with the disc. But I don't understand how quickly the corrosion would move through the thimble and into the disc. I'm wondering if the thimbles were replaced once a year, would that prevent corrosion of the disc.
    I reckon the corrosion is later least of your problems, It's any connection in contact with the powered coated hole that will wear out the powder coat and even through the Al disc. What needs to be made more rugged is the hole in the disc, If this is converted to a fixed connection such as a stainless eyelet then the wear becomes "stainless on stainless" which will be far less than "anything on powder coated Al".

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