Framebuilders - Headtube strength: Carbon vs Aluminum

My situation requires fork with uncut alloy steerer for high handlebar height ala Sheldon:
http://www.sheldonbrown.com/images/iro-584-09.jpg

I have this on 2 aluminum-framed bikes with no problems.

I have a carbon frame on order from China.
http://www.hongfu-bikes.com/Upload/Pic/2009719195249274.jpg

It has a nice long head tube (13.5cm on 52cm frame). However, I am wondering belatedly if the carbon headtube can handle the magnified stresses brought about by the long steerer/high handlebars. If it were metal, I'd have no question. But carbon, ???

I assume you guys all work in metal, but I know i can count on you to give me an unbiased, objective opinion, Right?:D

Won't guess .. as I cannot know how many layers of carbon cloth were laid up in the mold, around the headtube ,
or if they wrap around Aluminum reinforcing rings .. and which alloy of aluminum they chose

[I've been informed 7000series aluminum includes Zn, and is a bad combination with carbon , unless you are producing Batteries]

.. from the business minds that paint children's toys with a lead based paint.

so I'll wish you good luck. . :twitchy:

Won't guess .. as I cannot know how many layers of carbon cloth were laid up in the mold, around the headtube ,
or if they wrap around Aluminum reinforcing rings .. and which alloy of aluminum they chose

[I've been informed 7000series aluminum includes Zn, and is a bad combination with carbon , unless you are producing Batteries]

.. from the business minds that paint children's toys with a lead based paint.

so I'll wish you good luck. . :twitchy:

haha--I swear I'm not gonna lick the paint:twitchy: Under normal conditions . . .

So what happened to the custom Ti frame you said you were getting?

So what happened to the custom Ti frame you said you were getting?

Carbon frame is done deal--Ti is more long-term hypothetical deal. Need to always have one in the oven and one on the drawing board.

Carbon frame is done deal--Ti is more long-term hypothetical deal. Need to always have one in the oven and one on the drawing board.

from Hongfu with love.....

all we can give you is uninformed speculation. I doubt that you can cause a problem by adding spacers on an aluminum steerer. All I can say is if you do this, be very careful with the fit of your stem and don't make any scratches on the steerer.

I've been informed 7000series aluminum includes Zn, and is a bad combination with carbon , unless you are producing Batteries


I wouldn't worry so much about that 6% zinc, when the matirx of the alloy is aluminium. The aircraft industry doesn't allow carbon fibre in contact with aluminium alloys of any series, due to the 1V+ galvanic potential difference between them. Admittedly, there are high-reliability, long-lifetime concerns for most plane manufacturers, expecting two parts to mate and behave nicely to one andother for tens of years, but you can basically can consider lifetime in service and stress as reciprocals of one another in the same equation. The reason zinc is used in carbon cells is because aluminium is that much more reactive the battery would blow up.

Long story short: carbon touching aluminium, big no-no.

I wouldn't worry so much about that 6% zinc, when the matirx of the alloy is aluminium. The aircraft industry doesn't allow carbon fibre in contact with aluminium alloys of any series, due to the 1V+ galvanic potential difference between them. Admittedly, there are high-reliability, long-lifetime concerns for most plane manufacturers, expecting two parts to mate and behave nicely to one andother for tens of years, but you can basically can consider lifetime in service and stress as reciprocals of one another in the same equation. The reason zinc is used in carbon cells is because aluminium is that much more reactive the battery would blow up.

Long story short: carbon touching aluminium, big no-no.

Well, you got me thinking, since I forgot everything I knew about galvanic reactions 40 years ago.

When I read your post, I was under the impression that carbon is just a conductor, but other than that it's inert, sort of like wood,

Should not your long story short read: carbon touching aluminum and some other metal, big no-no?

Nope. Carbon fibres conduct just fine, as you're aware, but that's all it takes, otherwise you wouldn't get galvanic corrosion between any two conducting couples, and I'm sure you've seen plenty of it in your life.The corrosion occurs purely because of the voltage difference at the interface and proceeds at the anode, which in this case is the aluminium.

What governs the possibility of the reaction is the potential difference, but what governs the rate of reaction is the current density, and in most mating sleeves or other such high contact areas, this is low. Your problem comes with large slabs of cathode against small slivers of anode, such as a sizeable shaft meeting a thin bearing shell or the like.

My scientific knowledge of these things is practically nil however I have heard that that carbon and aluminum don't work well together but it makes me curious about all those frames that use to have aluminum lugs with carbon tubes. Is the frame life limited on them, are all those older Look frames breaking down as we speak? I just finished a carbon/steel frame and all the information that I collected from different people, builders, companies, etc. basically said so long as everything is cleaned properly and the resin is mixed properly and the tubes have a nice fit there should never be a problem. One guy from one of the larger carbon fiber companies I spoke to said they had some old parts lying around that had been glued for over 30 years and were as strong as ever. Is this possible?

How effective is "carbon assembly paste" at preventing galvanic corrosion?

My scientific knowledge of these things is practically nil however I have heard that that carbon and aluminum don't work well together but it makes me curious about all those frames that use to have aluminum lugs with carbon tubes. Is the frame life limited on them, are all those older Look frames breaking down as we speak? I just finished a carbon/steel frame and all the information that I collected from different people, builders, companies, etc. basically said so long as everything is cleaned properly and the resin is mixed properly and the tubes have a nice fit there should never be a problem. One guy from one of the larger carbon fiber companies I spoke to said they had some old parts lying around that had been glued for over 30 years and were as strong as ever. Is this possible?

He's absolutely right. Aluminium epoxy-bonded to carbon fibre isn't galvanically connected to it. There's a nice (thin) layer of waterproof(ish) electrical insulator between them. The situtations I've been describing aren't where aluminium lugs and carbon tubes are used for structural purposes (I dislike them for *entirely* different reasons). I'm talking about the direct touching of aluminium and carbon fibre.

Also, 'carbon assembly paste' does the same thing as the epoxy in such bonded assemblies :-)

I asked at Calfee, CF frame builder , about 7075 with a carbon thread epoxy wrap to reinforce the edge of my tent poles,
that was where I was suggested not to.. Craig Calfee answered my Email.

Machinery's Hand book lists non ferrous alloys by content, so ,maybe 6000 series would be OK, only 6253 shows a Zn content.
a concencious build may have a Glass fiber layer as a separation insulator , but I doubt ,if lowest cost consideration is paramount, mass mfg. will do that.

Machinery's Hand book lists non ferrous alloys by content, so ,maybe 6000 series would be OK, only 6253 shows a Zn content.
a concencious build may have a Glass fiber layer as a separation insulator , but I doubt ,if lowest cost consideration is paramount, mass mfg. will do that.

I'm not sure where this insistence that zinc-containing aluminium alloys are the devil, in contact with carbon, is coming from here. Yes, zinc is used in batteries with carbon, but so is manganese. It's not the zinc that's the issue here, it's any intermetallic precipitate in aluminium alloys, and the aluminium itself. Copper-containing alloys (2xxx series) corrode even worse than 7000 as their intermetallics are even more anodic to the matrix than 7000 series'. No aluminium alloy, even commericlaly pure 1000/1100/1200 series ones should be allowed in contact with carbon. The galvanic cell still exists with nothign but carbon and aluminium. the presence of intermetallics merely hastens it by increasing local current density.

As for framebuilding with aluminium bonded to carbon, there's no issue. The bonding agent iself, unless by some bizarre happenstance one has selected a conductive, electronics-grade adhesive, will insulate the two.

Thanks for the info!