Stuck Carbon Seatpost in Carbon Frame

[Johan Bornman]

Carbon and aluminium actually don't share space well together, and this corrosion of the aluminium is frequently encountered, and is an issue that extends all the way up to the aerospace industry.

 

The solution - titanium. Although I also wonder if there would be an improvement if the aluminium was anodised first...

Titanium definitely is a solution. On my old road bike, I have a ti seatpost and a alu stem. The bike is 19 years old but the stem only three. Every few years when I want to replace the headset I have to saw off the stem. The seatpost comes out without a problem.

 

As for carbon and alu together. I doubt this was carbon. Although it is often called carbon-wrap, I think it is just a carbon sticker like that found on souped-up BMWs in Lenasia. Further, the seat tube is alu on the inside - again not really the carbon's problem.

 

Anodising would work if you could anodize the inside of the seat tube. But I doubt it would work. Christie, can you anodize the inside of a 27mm alu tube?

[Cippo]

@JB, sorry if this has been asked before but how often do you have to clean and lubricate the post with carbon paste? Does the same apply to area between alu stems and carbon bars?

[nolipoli]

As far as I know, the whole anodising process is one of dipping, which should mean the inside if the tube is anodised too. But I do stand to be corrected.

 

Isn't it wierd how aluminium has always been push as a "rust proof" material, which is actually BS.

[Johan Bornman]

As far as I know, the whole anodising process is one of dipping, which should mean the inside if the tube is anodised too. But I do stand to be corrected.

 

Isn't it wierd how aluminium has always been push as a "rust proof" material, which is actually BS.

 

No, It isn't dipping as in hot-dip zinc plating (galvanizing) where you take the object and dip it in a bath of molten zinc. It is a chemical process where you lay a layer of ceramic on top of the alu. Actually, not on top. One half of the layer is on top, one half penetrates the alu. It is an electrolytic process, which is why I question the possibility of plating inside a tube. But, my knowledge of anodizing is limited and I'm assuming that like chrome, you cannot plate inside a Faraday shield.

 

But yes, rust-proof it aint. It's a bitch

Edited June 17, 2013 by Johan Bornman

[Johan Bornman]

@JB, sorry if this has been asked before but how often do you have to clean and lubricate the post with carbon paste? Does the same apply to area between alu stems and carbon bars?

I don't know. As far as I know, carbon paste is simply a friction paste to prevent the carbon seatpost from slipping inside the seat tube (stems etc also qualify). Usually carbon cannot be torqued sufficiently to prevent slip, so they put gritty past in there to prevent slipping.

 

Most of these pastes are actually the cause of the problem. In old-fashioned quill stems, the grease put on there emulsifies and exacerbates the problem since the water cannot evaporate but is still available to do damage.

 

I suspect carbon paste doesn't protect against galvanic action but makes it worse. I may be wrong, but I don't see an ingredients list on my tube of carbon paste to confirm or deny the thought.

 

I'll take it out frequently - once a month, as a precaution. I wish I practice what I preach, then I won't have to saw off those expensive stems.

[Cippo]

 

I don't know. As far as I know, carbon paste is simply a friction paste to prevent the carbon seatpost from slipping inside the seat tube (stems etc also qualify). Usually carbon cannot be torqued sufficiently to prevent slip, so they put gritty past in there to prevent slipping.

 

Most of these pastes are actually the cause of the problem. In old-fashioned quill stems, the grease put on there emulsifies and exacerbates the problem since the water cannot evaporate but is still available to do damage.

 

I suspect carbon paste doesn't protect against galvanic action but makes it worse. I may be wrong, but I don't see an ingredients list on my tube of carbon paste to confirm or deny the thought.

 

I'll take it out frequently - once a month, as a precaution. I wish I practice what I preach, then I won't have to saw off those expensive stems.

 

Thanks, much appreciated.

[Christie]

It would be possible to anodize the inside of a tube - the electrolisis is done in a bath, if the electrolyte can reach it would take. But I have not seen it done on the inside of a frame, Im not sure why it is not done. If I had to guess it would be something to do with the welds. The welds on alu frames are not full penetration welds on the frames I have seen, tubes are just butt welded. Perhaps electrolyte will get trapped inside the frame and behind the welds, and be difficult to wash out completely, which will make a mess of the insides if the welds over time?

[Johan Bornman]

It would be possible to anodize the inside of a tube - the electrolisis is done in a bath, if the electrolyte can reach it would take. But I have not seen it done on the inside of a frame, Im not sure why it is not done. If I had to guess it would be something to do with the welds. The welds on alu frames are not full penetration welds on the frames I have seen, tubes are just butt welded. Perhaps electrolyte will get trapped inside the frame and behind the welds, and be difficult to wash out completely, which will make a mess of the insides if the welds over time?

Duh! I just looked at the insides of anodised nipples and the colour is perfect right inside the thread. A little inspection should have answered that question.

 

Most carbon frames just have a piece of straight alu tubing as the seat tube (with fancy carbon and stuff wrapped around it), so I cannot think of a single reason why not to anodise it. I think it is poor attention to detail.

 

Now if someone can please tell this stupid built-in spell checker that anodise is spelt with an s and not a z, I'll be very happy. Friggin Americans.

[nolipoli]

 

 

No, It isn't dipping as in hot-dip zinc plating (galvanizing) where you take the object and dip it in a bath of molten zinc. It is a chemical process where you lay a layer of ceramic on top of the alu. Actually, not on top. One half of the layer is on top, one half penetrates the alu. It is an electrolytic process, which is why I question the possibility of plating inside a tube. But, my knowledge of anodizing is limited and I'm assuming that like chrome, you cannot plate inside a Faraday shield.

 

But yes, rust-proof it aint. It's a bitch

 

Yeah, I meant dipping as in submerging, as opposed to a spray on process.

BTW, anodising is actually aluminium oxide, not ceramic.