Why would carbon fiber rust steel? It’s basically just plastic.
Galvanic corrosion in the presence of an electrolyte (sweat in this case)
It’s right at the opposite end to aluminium so they don’t get on well. Steel is roughly central.
I have a feeling the scale is related to the number that they give the alloy (4140, 7005) but that might be just coincidence or i’m talking shit.
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Sweat is bad for steel with or without anything, and carbon fiber is just plastic so I don’t see why it would affect anything.
Aluminum part should be anodized to protect against corrosion, if the corrosion resistance needs to be strong then it should be hard anodized (this limits color choice to black or olive green but it makes it impervious to corrosion).
You gotta do whatever it takes to prevent sweat from coming into contact with any steel part because it WILL corrode it no matter what. Either with oil or something.
If you want to really protect steel from corrosion then have it nitrided.
Have a look on google for galvanic corrosion on carbon bike frames. Sweat on steel wouldn’t rust it away in the space of a year, it’d affect it for sure, but the galvanic effect accelerates the process dramatically. It’s the carbon in carbon fibre, which is graphite strands, which causes the effect. Lots of spare electrons floating about makes it very conductive.
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So can you put coatings on the carbon fiber to stop this? I mean carbon fiber is basically covered in epoxy so the epoxy would prevent conduction…
What is done to mitigate this? Surface treatment of steel/aluminum parts (nitriding, hard anodizing)?
I mean bearings have to be steel no matter what.
Yeah you can paint it but bike manufacturers aren’t gonna do that on the inside of their head tubes. The bearings are lubricated with dialectric grease to prevent this from happening but as someone else said the newer design isn’t as watertight so it needs regreasing often.
I’d not be surprised if the bearings were aluminium on a bicycle as in engineering terms it’s not doing a lot of rotations, but they do wear out fast
I had ceramic bearing set in my crankset bottom bracket.
Highly rated and they cost a lot!
Why can’t they for example use a plastic insert around the bearing housing to prevent such a corrosion? How much is a piece of plastic cost? Carbon is already expensive as it is.
Steel is a great material if you think about it… it’s cheap, plentiful, and strong when the right kind/right engineering is used.
This is considering that in ancient times steel was more expensive than gold! they used wrought iron more often than not to make tools, and raw iron for pots and pans.
Graphite/carbon is a lubricant so the plastic insert would either slip with rotation, or snap with the flex force of general riding. Even the carbon wears out and fails on recent high end models, there was a big recall about it.
In bike land, weight saving sells, and they don’t really have to give many fucks about safety, that’s why the UCI weight limit was introduced, to try to ensure manufacturers didn’t make shitty weak frames for the purposes of weight saving.
Hambini explains it:
Here what a bike mechanic says about headsets with cables going through bearings (did not mention galvanic corrosion, but it is implied):
Are you having to charge your customers extra (or more often) for headset bearing replacements, brake bleeds, cable replacements, etc?
Yes, all is more expensive and I recommend to customers on new bikes to change sub-optimal headset bearings (BMC on so expensive bikes use headset bearings for $10 with a horrible lifetime) for stainless steel bearings with good quality seals. If you need to change bearings, it’s a horrible job when you must cut brake hoses, sometimes change one hose (you can usually use the old rear for front brakes and you need new one for rear). Changing the rear brake hose is sometimes not easy (it’s a question about the BB area). If you need to change headset bearings, it’s sometimes a harder job than building a new bike (you must clean up everything, take it all off, and then build again from zero.
Link: The Jury's In: What Bike Mechanics Really Think About Internal Cable Routing Headsets - Bikerumor
As in this table
Stainless steel is closer to graphite (carbon fiber) so both materials together are less prone to galvanic corrosion than others.
It just occurred to me that my pedals are magnesium alloy. For a spectacular burn when the bike catches fire obviously
To be fair, you need to aim a blowtorch at a sharp corner on it and keep at it until it starts to melt… but once it burns… man it’s hard to put out. Blowing on it will only make it burn hotter (the CO2 and water vapor in your breath certainly does not help), and DON’T even think about pouring water on it. Water makes it worse. Best thing to do is pour sand on it, just make sure it’s NOT carbonate sand (like the kind on the cliffs of Dover), because that will make it burn hotter.
Magnesium is fun stuff, it’s also incredibly light too, at half the density of aluminum but being almost as strong. This is why they are used on bikes. They are also used on scooters/motorcycles/cars too. But seriously in solid form it really isn’t going to burn in a normal fire. You need VERY hot fire for this. Shaving and powder on the other hand…
say what?
Do you know what FRP is? It describes fiberglass, kevlar, and carbon fiber. It stands for fiber reinforced plastic. Because that is what it is.
Carbon fiber is basically epoxy (which is a plastic) reinforced with carbon fiber.
Unless you are talking about carbon carbon composite, like the ones used on the space shuttle. That stuff is so exotic and expensive that no consumer products use it.
yes, fiber reinforced plastic is, well, plastic reinforced with fiber. and no, FRP doesn’t describe fiberglass, kevlar, and carbon fiber - those are types of fibers (the F) that might be in FRP.
Yes, carbon fiber is often combined with plastics, and what’s described as carbon fiber is often FRP, but you can’t just call carbon fiber (even FRP) a plastic and dismiss galvanic corrosion, as it may have conductivity closer to pure cf than the pure plastic (I’m not sure of the actual conductivity (which will vary), but I do know that it’s enough to be a concern).
Ok, I just figure that since the fiber is covered in the resin that it would block any conductive action.
By the way I don’t know if you could make a bike frame out of carbon carbon composite, but if you are a billionaire I’m sure you could get an aerospace company to do it… it would probably cost about 100,000 US, and it would also be really fragile (Columbia found that out the hard way…)
But it would be great for riding through say a blast furnace.
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What about Taiwan in July at 1pm?
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Carbon carbon composite is great for heat where most common materials just melts… You know when stuff glows red hot. It’s just not all that good at resisting impacts of foam at 500mph.