On Wed, 06 Sep 2006 18:12:39 -0400, Steve wrote:
> It's not out yet!
>
> I am using my first thought of the hacksaw blade, and... I am moving
> VERY slowly! I've taken a rather large pay cut since buying this frame,
> and I cannot afford to replace it. I am lucky in that I have another
> bike to ride, so I can take my time.
>
> It really does seem like it is either wedged in there, or somehow
> 'bonded' in there (I have no idea how either might happen).
>
> Thanks for all of the suggestions!
> Steve
I ran this problem by a friend of mine who works with composites in the
aerospace industry, and he ran it by a few of his colleagues. Between
them, they have *forgotten* more about manufacturing with carbon fiber
than all of the bike builders will ever know. Here is what my friend sent
back:
---begin forwarded message:
Chris,
> A vexing problem. Any ideas on why this would happen or how one would
> fix the problem?
Realize that the information that follows is limited because we only have
a description to work with instead of the actual part. There were three
options that came to mind to explain how the tube became stuck. These are
a fit issue, galvanic corrosion, and spalling or crumbling of the surface
of the seat post.
The fit issue is pretty straightforward. The post was too large for the
frame and has become stuck. Unlikely, but a possibility.
The second option is for the seat post to weld itself to the frame due to
galvanic corrosion. Since the frame is also carbon composite, this is
unlikely unless the top of the frame tube has a metal ferrule that is in
contact with the seat tube. This corrosion mechanism happens to carbon
parts if a glass isolation ply is omitted during construction of the part,
or if the isolation ply is damaged during installation and use. Since we
don't know how old the bike is, or how often it has been used in the rain
or humid environments, or even if it has one of those ferrules on the
frame tube, it is difficult to estimate how much of the carbon tube is
stuck. It is worth noting that the isolation ply is usually made from a
'108' or '120' style glass fabric and is only a few thousandths of an inch
thick. It doesn't take much to perform the isolation function, and being
thin it can be easily damaged.
The third option is likely to occur if the seat tube was prettied up with
a hand-applied layer of resin after the manufacture of the carbon
laminate. This is not uncommon, but it can introduce problems. The resin
may have been cured at room temperature losing toughness (resistance to
cracking) and being left with a low glass transition temperature instead
of being oven cured. The glass transition temperature, or Tg, is a
measure of how well cured or cross-linked the molecules are in the resin.
If the Tg is low as in room temperature cured, then the resin will soften
if it is heated. Even sitting out in the hot sun will be enough to soften
the resin. Since it has low toughness, moving the tube inside the frame
could liberate material from the surface of the tube. Liberate enough
material and it could act as a 'stop' preventing the tube from moving. A
low Tg would allow additional material to be liberated under the right
conditions.
How to get it out? Well, all the options have some degree of risk.
Liquid wrench is basically kerosene with some extras thrown in. It is a
penetrating material, but not the best in its class, and may not be
worthwhile here. If you want to use a lubricant go for ordinary rubbing
alcohol. It wets nicely, evaporates, and doesn't leave any residue.
If Steve goes for the hacksaw method, he should try to avoid breathing the
dust and wear gloves. Keeping the cut area wet with water from a spray
mister applied as needed is really all he needs. A dust mask would be a
good addition. Doing it outside would be preferable. Does he know that
carbon dust is electrically conductive? Just be careful where he blows
the dust.
Steve expressed some concern about what solvents would damage the carbon.
I can appreciate and respect his concern, but the carbon part of the
laminate is relatively immune to solvents. Alcohol, acetone, MEK, and MPK
are routinely used in geographic areas that allow them to be used. As
another example of carbon's durability, when we do the test to determine
resin content of a laminate, we dissolve the sample in hot nitric acid for
a couple of hours. The resin goes away, but the fiber remains! Of
course, I think he means the resin component of the laminate, and that is
a tough call to make. The resin might get a little sticky in the presence
of an aggressive solvent such as acetone or MEK if the laminate was not
fully cured. If we could fully dissolve the resin, then getting the seat
post out would be pretty easy.
Speaking of which, there is a solvent
system that will dissolve some cured resin systems, but IIRC the minimum
buy is several hundred dollars and they don't sell it to just anyone. It
is this stuff here:
http://msds.ehs.cornell.edu/msds/msdsdod/a177/m88362.htm
Again, we'd have to isolate the frame and determine what resin system was
used. Let's continue...
Another couple of options for removing the seat post involve disassembly
of the bike and some light machining. The first one calls for the inside
of the seat tube to be tapped with as coarse a thread as possible. Of
course, this only works if the ID of the tube is round. Thread down the
tube for a few inches with the tap and then thread a suitably sized rod
into it. Put a slide hammer on the rod, or make one from metal barbell
weights and some washers. Drive that sucker out of there. Feel free to
use alcohol on the frame and tube prior to removal, and on the operator
after removal.
The second approach requires removal of the crank set,
and will only work if the frame tube is open to the crank tube. This will
even work if the ID of the frame tube is not round. Machine a threaded
bushing so the OD of the bushing is just a little smaller than the ID of
the frame tube. Install the bushing into the frame tube from the crank
tube. Snake a piece of threaded rod through the center of the seat tube
and thread it into the bushing. Attach a slide hammer to the rod and
drive the seat post out. Feel free to use alcohol as described in the
previous approach.
How to avoid this in the future? Part of the fix would be to inspect the
tube before use to verify the presence of the isolation ply. Sometimes it
is hard to see, so a call or email to the manufacturer may be in order.
IMHO, if a manufacturer is selling this product to the recreational bike
market and has either left this isolation veil ply out by design or
manufacturing error - then you have been sold a defective product. I
might give them some wiggle room if they include a note to grease the tube
to mitigate galvanic corrosion. Further, it is *ssssssssooooooooooooo*
easy to include the isolation ply during manufacture, and glass veil ply
is cheap, cheap, cheap - well - compared to carbon.
One of my coworkers made an additional comment that is worth passing
along. He is the gentleman who when I first met him, made me feel as
though I graduated from university last week and this week discovered the
world of composite materials.
Anyway, he said the cycling community
should consider these composite seat posts to be life-cycle limited items
that would get routinely discarded after x-number of miles. The reason he
said this is that this tube should not have broken during an attempt to
remove it. That it broke indicates it had already accumulated damage and
would have failed during use in the not too distant future. Since you
ride, I'm sure you can estimate the loading that occurs to that tube with
varying levels of extension. I'll note for the record that neither he or
I own any stock in the companies that make and sell these tubes!
Not sure if these comments will shed any light on the subject at hand, or
fuel a flame-fest!
----- end forwarded message
--
Chris BeHanna
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