Removing an aluminium seat post from a steel frame with caustic soda
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- Опубликовано: 5 июл 2012
- My first experimentation of using sodium hydroxide (caustic soda) to remove a stuck aluminium seat post from a steel bike frame.
Build thread for the bike here:
www.retrobike.co.uk/forum/view... 
Хобби
An old skool approach to health and safety .... I love it !
Seal the seatpost / Turn the frame upside down / pour in soultion through bottom bracket - that way you don't need to keep toping up and risk covering yourself in caustic soda
I just did this for the 1st time on a 1950s racing frame and it works. Took about 5 refills over the course of a few days - leaving it overnight. It takes off paint as well.
I used this method after trying everything - everything! It worked perfectly to the amazement of the bike shop (one of many) that tried to get it out after my attempts failed. My only note is that my frame was steel but the cable stays were aluminum, so make sure to either mask it well or ensure you don't have any aluminum parts that you don't want vaporized exposed.
I had to do this on a tandem. Both seatposts were deep and completely stuck. It didn't hurt the paint, just ate up the aluminum.
Wow, I know it's been years since this was uploaded, but holy shit what a scary set of choices surrounding super-dangerous chemicals.
Hopefully anyone intending to do something similar can assess the risks I took and make the adjustments they feel necessary to make it safer.
Have a six pack of beer with you while doing this. Not to drink, but to splash on your body that might get hit with that caustic soda mix. Caustic soda will burn your skin very very quickly but the beer is at the opposite end of the pH scale (beer is somwewhat acidic) and will neutralize the nasty caustic and just might save your skin. Of course, any beer left over after finishing this project can then be consumed in celebration!!
The reaction is so violent it vaporizes the water, which is carrying the hydroxide ions. That's why the fumes are noxious, you're sniffing real basic vape.
A good idea that would make for easy work as long as you could isolate all of the fluid in the seat tube. What I could not overcome was how to stop all leaking into adjacent tubes and out of the frame itself. I used uninflated balloons stretched over either side of the BB shell which worked really well. It ran through the holes for the BB cable guide which I successfully plugged with chopsticks. Great. But then it found its way out the chain stays at the dropouts and out the headset, out the stem. Everything is open inside the frame to some degree. Then I flipped the frame, plugged the top of the seat tube and tried filling through the BB shell. Ultimately the same problem. It ended up getting so messy (and dangerous) that I had to stop. If it was just a matter of plugging the BB shell and fill the seat tube it would be a certain fix for all bikes. But you must have a bike with isolated tubing? I can't emphasize enough how gnarly this stuff is. Extreme caution required.
It's important to say that ALL vestiges of the caustic soda must be cleaned out of the seat tube before fitting your new seatpost. If you don't do this, the remnants of the old caustic soda will soon make the new post corrode into the seat tube. It happened to me!
Thanks for your concern, you're absolutely right and I would suggest anyone else attempting this pays heed and is more careful than I am when I do it.
DO NOT QUESTION THE KING OF FOOTBALL
Thanks for posting this. I'm currently soaking a front fork in casutic soda to dissolve the remainder of a very stuck handlebar stem. I started working with a much weaker solution and it was slow. I've bumped it up now that I see your frame didn't melt or the gas didn't cause an explosion! I will pass on the bare flame and bottle-shaking steps though!
Good stuff. Good luck with the renovation of the fork!
Thanks for your concern - I did get a little on my arm, but it didn't burn that much.
I'd recommend that anyone else trying this does take more safety precautions than I do, including a mask and long sleeves.
Thanks for the video!! I was almost giving up, this method saved my day!
I'm glad it was helpful :)
I'm pretty sure it's just hydrogen gas released, as the chemical reaction is:
2Al + 2NaOH + 2H2O → 2NaAlO2 + 3H2
but I would suggest anyone trying it at home takes full precautions.
To be fair, I took more precautions than I would have if it hadn't have been filmed.
I'm on step 4 to remove a stuck aluminum post, if it doesn't work, I now have a step 5. XD
I didn't have the equipment to drill it out accurately enough. Plus this way was more fun.
I think it was a couple of hours in total - I left it for a bit, hence getting dark, but the reaction slows quite quickly after the initial burst, so it's a lot quicker if you continually add more caustic soda.
Works great for dissolving rust without harming the steel at all but destroys aluminium.
That was VERY RISKY shaking /opening the bottle like that those goggles wouldn't help much ....
You could try gently heating the seat tube with the frame upside down, so it expands quicker than the seat post. Alternatively you may be able to use a puller to get it out, depending on how far down it is.
Thanks for the video, I'm about to do the same to mine. Can I ask where you get your frame powder coated? and how much it costs? this is my first frame restoration and i'm unsure whether to get it sprayed or powdercoated.
I was expecting a volcano type explosion of caustic soda anytime. Please, if you attempt this, find a way to not loose your face. A weaker solution over a longer time comes to my mind.
Hi mate, I want to try this however by bottom bracket is also seized and im not sure how i can block off the bottom of the seat tube without removing it. I could try removing it with caustic soda too however one side is steel and ive tried my best on removing both cups however they wont budge
What kind of tape you use to sealed bottom of the frame??
how did you seal the bottom bracket?
Wtf ? I put mine upside down in a vice and twisted the bike worked a treat but I am more physics than chemistry
This one was already sheared off inside the frame when I bought the bike.
I try it but i used caustic soda flakes and its is to hard to dissolve or i just wait it to dissolve the aluminum
Interesting, but messy stuff! Was just proving it could be done, or did you actually use the bike frame after that?
Hello. Yes, it's a great frame. After removing the seatpost I had it powdercoated, built it up and rode it. I did eventually sell it, because I had two very similar frams, both from 1993, and I slightly prefer the other.
Sorry for the slow reply - test it with a magnet and if there's an attraction it's steel and otherwise it's likely to be aluminium (assuming it's not titanium or carbon!).
or. water in , pour it out to measure how much soda needed , two thirds back in , add soda into frame . or , weaker solution longer time safer . unless ppl come to it when our gone .
Any left over spray it on your weeds kill them off. I was 2 hour removing a seat post last week WD40 did the job
If the seatpost fell completely into the bikeframe's post and is lodged completely in there, seat not attached and it is not sticking out whatsoever. How would I go about getting it out? ..Without destroying it?
I have stuck aluminium seatpost in carbon frame. if i will use your method in carbon frame will it work? Or sodium will damage carbon? Will i need to do something after reaction will end like to clean parts of alluminium from frame? Thank you
Carbon fibre is rated as having good resistance to sodium hydroxide (caustic soda) chomarat.com/wp-content/uploads/2011/06/CHO-3265-Chemical-Resistance-Guide.pdf but it is quite an extreme solution, so always best to make sure you've tried easier methods first. It would also be worth consulting an expert in carbon to back up the carbon's resistance as I am no expert.
I rinsed the frame out and dried it afterwards, but so long as you use sufficient caustic soda all the aluminium alloy will have reacted away and the product tends to drain out pretty easily.
Good luck with getting that post out.
Where is the removing of the seat post?
How long did it take??
Always wondered how they made Thomas the Tank Engine's steam!
All part of the science :)
I did it in about 2 x 1 hour session if I remember correctly
LIGHT IT!
Guts!
But did the weeds on your terrace survive?
Added bonus of clearing weeds from the patio :D
Caustic soda mixture will eat anything organic. That's why they use it to clean drains. But it doesn't hurt steel or even paint.
If the aluminum seatpost and aluminum frame are stuck, how do you remove it?
That's certainly more difficult. Firstly, soaking it as much as possible in a dismantling lubricant like Plusgas is a good step. After that, if it is not sheared off then you can try to get it moving clamped in a vice, but otherwise I would try using a slide hammer, or as a last resort cutting it from the inside using a saw blade with a handle attached.
Sodium hydroxide (caustic soda) reacts with aluminium, but doesn't react with steel, so you can only use this approach with an aluminium alloy post in a steel frame. For a steel post in a steel frame I'd soak it in a penetrating fluid like Plusgas.
To find a recommended powdercoater I'd advise looking on this thread on Retrobike:
www.retrobike.co.uk/forum/viewtopic.php?f=1&t=232111
I wouldn't really recommend the place I used for this frame as I wasn't entirely happy with the job they did.
Caustic soda wicked stuff great when ever you need to play a nasty prank because this stuff acts like acid if you don't clean up the parts your parts will start to melt
jonathan oxlade it's a very powerful base, natriumhydroxide :)
+Jeppe Løger no. Na means sodium
+Elements & Science Na in periodic system of elements represents Natrium (which is also called Sodium). The same is for K, Kalium (also called Potassium).
BAK87 yes, however those were the old names, now they are always called sodium or potassium
What effect would the cosmic soda have on a carbon fibre frame
I don't know for certain, but I'd be concerned it might compromise the carbon fibre.
how many 500ml bottles have you used?
I only needed one. Still have the others for future projects!
where did you buy the caustic soda?
I just bought it at my local convenience shop, but they should also stock it in DIY stores etc.
kingoffootball yeah thanks, with a little more research i found that out for myself! lol..thanks for this post.. its saved me a lot of hard work.. first time i tried it i made the solution too weak, so back again with a stronger solution.. left it overnight... cleared by morning.. amazing results.. and no hassle or hazard really, as long as you are sensible about it, its fine
Shaking the bottle into direction of face. Hmm
will it ruin the paint?
Different people seem to have had different experiences. I used quite a strong concentration and the paint was definitely faded where I had spilt the mixture on it, but I didn't really take care because I knew I was repainting it. I think it is possible to do it without damaging the paint if you are careful.
I,ve found a bottle of spirits of salt in the shed. Will this work as well or better?
HCL also reacts with aluminium and not steel, so as far as I know that should also work, but I haven't tried it myself. You may also need to be even more careful with it than sodium hydroxide.
Would it work on a steal post I tried everything I broke the top and it still didn't come out but its a steal frame and steal post will it damage the frame?
So not a good idea for corrosion on vintage Campagnolo chainring then ?? Good job I checked 😲😀
did you coat the inside of the frame with anything after flushing all of the caustic soda out with water?
Yeah, I sprayed some Waxoyl inside all the tubes just to help protect it once it was thoroughly dry. Not specifically because I'd used caustic soda on it, just because I would have done that to help protect the steel frame before I rebuilt it anyway.
How long ??
I just left it until it seemed to have stopped reacting and then changed the caustic soda. I think I left it about an hour before I added new caustic soda.
Dude, wear a mask and long sleeves...
Hahaha 00:36 Amazing straight after saying that just looking straight into the corrosive reaction with no mask😆
When I tried this it just filled up the rest of the bike and not the tube with the seat post :s
Mmmmmmm, Soda.
I don't understand it. My caustic soda does not react that strongly at all. Just a bit of prickling and that's it. Had it for hours in the seat post .... no visible effect.
Is it definitely an aluminium seat post? If so and it's not really reacting then it's most likely to be the strength of the caustic soda solution. Dissolving the caustic soda is exothermic, so the solution should get quite hot - so if it's not heating up much maybe it's not strong enough. Best to be careful and start with a weaker solution anyway and then get more concentrated until it's effective.
kingoffootball Hey man,
thanks for getting back at me. I followed your adivice and spiced things up a bit. I bet the main reason was, that the soda did not stay in in place for a long time. I now turned the frame upside down and it certainly does work, unfortuneatly, I assume due to temperate, it quite hard to properly seal the tube. But I am getting there ;)
Good work. I sealed off the bottom of the seat tube using an old inner tube and electrical tape, so I could keep it filled up.
Wont the caustic soda start rotting away at the frame aswell, why didn't it, is the frame aluminum?
the frame is steel
just pee down the tube
“Some chemical reaction is taking placre...” that is an understatement....the whole bicyclre is getting cooked not only that you guys are breathing all the fumes...is that how you guys do things in ...wherever you come from?
get a new frame and throw away that shitty piece of junk
I once had an aluminium paint spray pot and I thought it was a good idea to clean it with a caustic soda mix, so I put it on the floor in the garage and came back after a couple of hours and all that was left of the post was the rim and a small part of the top end.