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Avoiding corrosion when bolting galvanized steel drawer slides to aluminum for camper van bed Answered

Hey guys,

Going to build this bed:

or something very similar. She says she has 6 sliders at 100lbs each, but I imagine she has 6 slides at 100lbs per pair. Either way, I've already purchased 3 pairs of 500lb drawer slides. The problem is, they're galvanized steel. How do I attach them to aluminum L beams? I can use some thick mil rubber tape between the two materials, but what about the fasteners? Some sort of plastic washer and polyurethane sealant around the head and threads touching the galvanized rail side? What should I use to isolate one from the other?

FWIW, I'll probably use 6061 for the frame, which I believe has an anodic index of .9-.95, and the zinc rails are, I believe, 1.25. They're within or close to the .25 threshold so am I worrying about nothing?

Cheers

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withalligators (author)2018-03-12

Thanks guys. I will use some tape and maybe some nylon washers. Seems like it's nothing to get too worked up about. I will be largely in the American southwest, but maybe road trip down to South America some day?

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steveastrouk (author)2018-03-12

Is it going to get wet ?

I built a very large (30 foot, 10 metre) telescope dome nearly 20 years ago which is STILL secured with galvanised steel screws.

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Jack A Lopez (author)2018-03-12

If you want to electrically insulate metal parts bolted together, the insulation layer needed to do this does not need to be thick, or elastic.

You are contemplating using, "thick mil rubber tape", but I think almost any kind of plastic tape would work. For example, clear shipping tape. Actually I think almost any kind of sheet plastic would work. As you have already said, the possible potential difference between these metal pieces is only a few tenths of volts.

Moreover, I think you will get effective corrosion protection, to the extent you can reduce the surface area of places where dissimilar metals are touching. I mean, if the two dissimilar metal pieces want to form a shorted electrolytic cell, the rate of corrosion is going to be proportional to the current that flows, I =V/R. If the current can only flow through very tiny area, then R will be large, and I will be small.

Also this kind of corrosion is worse for assemblies that are underwater, or partially wet, like outdoors in the rain. For something indoors, in moderate humidity, it might not happen, or happen only with geologic slowness.

I should probably point to the Wikipedia article for "Galvanic corrosion",

https://en.wikipedia.org/wiki/Galvanic_corrosion

for anyone who has not already seen that one.

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Yonatan24 (author)2018-03-12

Why do you need to isolate them from one another?

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Yonatan24 (author)Yonatan242018-03-12

How about double sided tape? It's so strong you won't be able to take it apart if you need to...

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