Chemical Intervention

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Chemical Intervention

Postby Duck! » Fri Aug 30, 2013 2:14 pm

I'm having a major headache at work with a broken alloy seatpost well & truly stuck in a chro-mo frame. Any clues what kind of chemical treatment would work to dissolve the alloy without harming the chro-mo?
I had a thought, but it got run over as it crossed my mind.
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by BNA » Fri Aug 30, 2013 3:12 pm

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Re: Chemical Intervention

Postby Nobody » Fri Aug 30, 2013 3:12 pm

Sorry, can't help you with the chemicals, but have you tried a slide hammer?
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Re: Chemical Intervention

Postby Mulger bill » Fri Aug 30, 2013 3:23 pm

Have not done but have witnessed...
Caustic Soda eats Al and leaves Fe alone. Best introduced via the BB shell IIRC.

Tread very gently, use full PPE and do it outdoors.

Have you tried the cut head of post off-hacksaw blade inside post route?
Last edited by Mulger bill on Fri Aug 30, 2013 3:25 pm, edited 1 time in total.
Reason: Added more emphasis...
...whatever the road rules, self-preservation is the absolute priority for a cyclist when mixing it with motorised traffic.
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Re: Chemical Intervention

Postby Nobody » Fri Aug 30, 2013 3:26 pm

Mulger bill wrote:Have you tried the cut head of post off-hacksaw blade inside post route?
Good idea. Something I'd consider if it was my own frame, but you'd want to be super careful on a customer's frame.
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Re: Chemical Intervention

Postby westab » Fri Aug 30, 2013 4:11 pm

I have had success getting stuck seatposts out by "spraying" compressed air down the inside of the seat post cooling it down as it will absorb the lack of temp and help to allow the seat tube to break loose and come out. Please take care with using compressed air - don't spray it on your skin as it can cause harm & also wear safety glasses / hearing protection for your safety.

If you don't have access to a "normal" air compressor - a mini compressor used in a car will do - just be careful not to overheat it as some are only rated for a short run time.

Hope this helps.
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Re: Chemical Intervention

Postby ProCelebrityGolf » Fri Aug 30, 2013 11:11 pm

I suggest talking to this guy - http://gonzlab.wix.com/gonzlab - if you live in Melbourne he can definitely help.
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Re: Chemical Intervention

Postby human909 » Sat Aug 31, 2013 12:39 am

Duck! wrote:I'm having a major headache at work with a broken alloy seatpost well & truly stuck in a chro-mo frame. Any clues what kind of chemical treatment would work to dissolve the alloy without harming the chro-mo?


Mercury!



Or
Galium!
http://www.youtube.com/watch?v=8jDFx7ye ... mhq3vRibYA
Last edited by human909 on Sat Aug 31, 2013 12:45 am, edited 1 time in total.
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Re: Chemical Intervention

Postby Duck! » Sat Aug 31, 2013 12:42 am

Mulger bill wrote:Have not done but have witnessed...
Caustic Soda eats Al and leaves Fe alone. Best introduced via the BB shell IIRC.

Tread very gently, use full PPE and do it outdoors.

That's been suggested elsewhere as well, and will be followed up next week. :)

Have you tried the cut head of post off-hacksaw blade inside post route?

Yes. Although there was no need to cut the head off the post, that was why it needed to come out in the first place! (Split tube, detachable head.) That method has been taken as far as it can - the top of the remaining post is about 100mm below the collar, and is about another 150mm long. It's royally stuffed. :x

What's the time-lapse of that mercury method? Looks a) slow & b) I'm not all that keen on mercury poisoning thanks..... :|
I had a thought, but it got run over as it crossed my mind.
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Re: Chemical Intervention

Postby human909 » Sat Aug 31, 2013 9:21 am

Gallium isn't poisonous and its better than mecury.

But caustic soda is of cause easier to obtain.


These guys seem to do it more safely.
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Re: Chemical Intervention

Postby John Lewis » Sun Sep 01, 2013 4:21 pm

You need to dissolve the oxide build up that is causing the problem.
I have read that cloudy ammonia will do the job. Might have been on Sheldon Brown. I can't recall.
Caustic soda will most certainly dissolve the aluminium. Be aware though that the bubbles given off are hydrogen and mixed with air might be an explosion risk. Unlikely I think if outdoors and care taken.
I used to etch Ali face panels with caustic to make a nice surface on homemade electronic equipment so am a bit familiar with it.

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Re: Chemical Intervention

Postby Duck! » Fri Sep 06, 2013 2:56 pm

Caustic soda did the trick. Boss took the frame home to do, so I wasn't "in on the act" to witness how it worked. Two goes were required to chew it thin enough, then it was just a matter of carefully levering the remnant with a long, flat screwdriver to peel it away from the frame. :) Thoroughly rinsed the inside of the frame with vinegar to neutralise any soda residue, and job done.

Thanks for all the tips. :)
I had a thought, but it got run over as it crossed my mind.
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Re: Chemical Intervention

Postby QuangVuong » Fri Sep 06, 2013 5:06 pm

Those vids are gonna be useful in the coming months when I get around to removing the seatpost in my Bundy.
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Re: Chemical Intervention

Postby Mulger bill » Fri Sep 06, 2013 5:34 pm

Duck! wrote:Caustic soda did the trick. Boss took the frame home to do, so I wasn't "in on the act" to witness how it worked. Two goes were required to chew it thin enough, then it was just a matter of carefully levering the remnant with a long, flat screwdriver to peel it away from the frame. :) Thoroughly rinsed the inside of the frame with vinegar to neutralise any soda residue, and job done.

Thanks for all the tips. :)

8)

Better to let the boss do it anyway, deniability for you if something gets borked in the process :twisted:
...whatever the road rules, self-preservation is the absolute priority for a cyclist when mixing it with motorised traffic.
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Re: Chemical Intervention

Postby eeksll » Fri Sep 06, 2013 6:33 pm

wow :shock: thats insane.
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