Seized alloy seatpost in a carbon frame

[Hairy]

With carbon and aluminium as the two things? Surely it can only ever happen between two metals?

 

Is this bloke's "carbon" frame one of those ones we see in the classifieds here with the welds on them?

 

How would an alloy seatpost get stuck in a carbon frame anyway?

Carbon + Alum left to their own devices without anything like copper slip between them = potential issues down the road

[TNT1]

I dont know anything about this, but from watching Mike Patey on youtube building a bush plane out of carbon fibre, he mentioned the corrosion a few times where he used Aluminium and as such he put and insulating layer between the carbon and aluminium so they are never in direct contact.

Oh, who knew. I Binged it:

 

 

Does carbon fiber react with aluminum?

The issue with using carbon fiber materials for fastener applications is that carbon fiber is electrically conductive, thus making it more susceptible to galvanic corrosion. ... Aluminum and plain steel, when coupled with a carbon composite, are both highly susceptible to galvanic corrosion.

 

 

 

And:

 

Edited April 28, 2021 by TNT1

[Hairy]

With carbon and aluminium as the two things? Surely it can only ever happen between two metals?

 

Is this bloke's "carbon" frame one of those ones we see in the classifieds here with the welds on them?

 

How would an alloy seatpost get stuck in a carbon frame anyway?

https://www.corrosionpedia.com/galvanic-corrosion-of-metals-connected-to-carbon-fiber-reinforced-polymers/2/1556#:~:text=The%20carbon%20fibers%20in%20CFRPs,more%20susceptible%20to%20galvanic%20corrosion.

 

Carbon Composites' Drawbacks

Despite all of the excellent properties of CFRCs, there are issues with using carbon fiber reinforced composites and metals together. The carbon fibers in CFRPs cause this material to become electrically conductive. The carbon fibers are electrically conductive and electrochemically very noble. Therefore, when a metal is electrically connected to a CFRP, it is more susceptible to galvanic corrosion. (To learn more about galvanic corrosion, read An Introduction to the Galvanic Series: Galvanic Compatibility and Corrosion.)

There are five conditions which need to be met for galvanic corrrosion to occur between a metal and the composite material:

1. An actively corroding metal
2. An electrically conductive composite (usually carbon fiber)
3. An electrical connection between the composite and the metal
4. An electrolyte (usually salt water)
5. The presence of oxygen

[DieselnDust]

use a extinguisher with co2 around the frame where seatpost is stuck , it freezes the area and seatpost comes out quite quickly

 

 

How does freezing the frame release the seat tube? Are you hoping that the higher wall thickness seat post will shrink more than the thin tubed seat tube?

[Hairy]

How does freezing the frame release the seat tube? Are you hoping that the higher wall thickness seat post will shrink more than the thin tubed seat tube?

Seen it done on the world wide web before ... can't recall where, but it worked for that person.

[Alouette3]

How does freezing the frame release the seat tube? Are you hoping that the higher wall thickness seat post will shrink more than the thin tubed seat tube?

The heating and cooling trick, relying on the difference in clearance with expansion and contraction is quite a common trick used to fit bearings etc. This might just be an option to help loosen the corrosion bond, had some luck with it in other applications. Not sure what the effect would be on the Carbon though. Would still use some penetrating oil of sorts.

[JCA12]

Similar topic (but different problem) I have an alloy seatpost with a carbon frame which sometimes slips when riding trails.

What would you guys use to stop it slipping. The seatpost clamp is torqued correctly.

[RobertWhitehead]

Reduce the amount of lubrication and possibly get a new clamp. I have had this in the past as well. I used an alu post on a carbon frame, then I sold the frame and transferred the post to an alu frame but kept the carbon paste on the post. The post kept dropping until I cleaned all the paste off the post. 

 

 

Similar topic (but different problem) I have an alloy seatpost with a carbon frame which sometimes slips when riding trails.
What would you guys use to stop it slipping. The seatpost clamp is torqued correctly.

[Martin PJ]

Similar topic (but different problem) I have an alloy seatpost with a carbon frame which sometimes slips when riding trails.

What would you guys use to stop it slipping. The seatpost clamp is torqued correctly.

Coke can shim.

[Alouette3]

Similar topic (but different problem) I have an alloy seatpost with a carbon frame which sometimes slips when riding trails.

What would you guys use to stop it slipping. The seatpost clamp is torqued correctly.

There is a special carbon friction paste made for this. Rapide cycles always advertises little sachets.

[droo]

If they're round and either 30.9 or 31.6 I have the tools to get them out for you, but you'll have to get the bikes to me.

 

Otherwise your most reliable method is to cut the post off and use a hacksaw blade to cut vertically through the seatpost from the inside in two or three places and pull the remains out in bits.