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Bicycle Parts: Chains, Gears & Ball Bearings : Corrosion Resistant Bicycle: Parts

Bicycle Parts: Chains, Gears & Ball Bearings : Corrosion Resistant Bicycle: Parts


Charles McMahon for Expert Village. We are
talking about how bicycles are put together and the materials. If you want more information
you an look at a college level text book, on merionmedia.com. Obviously you are using
a bike out of doors in all weather, so the components have to resist corrosion. While
the rims are made from a high strength aluminum alloy, actually by an extrusion, extruded
through a die, it has got a very funny cross section, so it is an aluminum alloy, the spokes
are normally stainless steel although you can get carbon steel spokes. Now the aluminum
doesn’t corrode, no aluminum doesn’t rust, the reason is it has a very thin oxide layer,
so thin you see through it, so what you see is the aluminum underneath. But this oxide
layer is so complete and tenacious that it separates the aluminum metal from the oxygen
in the air and the water vapor and so on. So that’s why aluminum doesn’t corrode.
It is passivated by this oxide. The stainless spokes don’t corrode, because they have
enough chromium atoms mixing with the iron to form an oxide that is chromium rich. And
that oxide acts the same as the aluminum oxide it passivities the stainless steel with this
chromium rich oxide and therefore the metal underneath can’t rust. So they both have
the same principles in both cases. Both passivated the rim by aluminum oxide and the stainless
steel spokes by a chromium rich oxide, the hub is normally also aluminum Now the reason
you like aluminum out here is obviously it is lighter. So you would rather have aluminum
than steel out here. If you use steel, you probably use chromium-plated steel and that
will last for while, but the chromium plating gets pits and then you can get corrosion in
the pits. You can use carbon steel spokes, they have to be coated with either zinc or
cadmium a sacrificial layer, as long as that layer is on that will protect them but when
that layer is gone they will rust. So best is aluminum rims, stainless steel spokes.

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