Any metallurgists out there?

Jimfrandisco

I'm pretty sure there's someone on here can answer this in layman's terms...

I have a steel frame with an alloy post seized in it. Everything has been tried to remove it but now the only option left is to melt it out - something that Argos, Dave Yates, Roberts etc are all able to do.

That's straight forward enough as i assume the alloy melts at a lower temp than the steel - but what about the brazing used to make the frame? I'd have thought that too would have a lot lower melting point than the steel it joins?
It's a fillet brazed frame and i'd have no idea what metal is used to braze/weld it together..

so can anyone tell me - what material the frame is likely to be welded with and what would be the relative melting points of the steel frame, the welding/brazing material and the alloy seat post.

The reason for asking is that i know a local bloke that makes custom motorbikes so can probably melt out the post but want to make sure there's not something specific to bike welds that could mean it all goes wrong..

cheers

Jim

ballspondroad

http://www.sheldonbrown.com/stuck-seatposts.html

Melting out the seat post seems a bit drastic - cutting it out would surely be easier, see XVI in the above.

ugo.santalucia

This is the most ridiculous thing I've heard...

Surely there are better ways, including cutting it off as a last resort.

Besides, I don't think anyone in the business has a furnace capable of reaching in excess of 600 degrees and large enough to fit a frame in it...

Metallurgy issues, just for curiosity... the paint will go, the braze material will go, the steel itself might undergo phase transition to an austenite phase and the result upon cooling will be a different material (probably softer as not martensitic)

Ben6899

I have to agree with the two posts above. You'll end up tempering the frame material and melting the brazes.

Jimfrandisco

I know how it might sound taken out of context - but this is something that Dave Yates, Roberts Cycles and Argos Cycles (and several other bike frame builders that I've spoken to) do on a regular basis.

All the above frame builders are long established experts in the business, so clearly it is possible to do it....quite how they do it, I don't know - hence the question.

As for other suggestions for removing....everything on Sheldon's list has been tried and exhausted and tried again......anyone that says "surely there are better ways" clearly hasn't had the misfortune of being stuck with a properly seized seat post!!

ugo.santalucia

I don't believe for a minute that they melt it out... it might be that they use heat treatment to get it out, meaning different dilation coefficients of the two alloys might help to get it out...

Monty Dog

I've never heard of anyone 'melting' a seatpost out - maybe the selected application of heat. Heat 'soaking' the whole frame to melt the post would be ridiculous - you could probably buy a new frame for the cost of the re-braze and respray.

Jimfrandisco

I'm sure that heat soaking the whole frame is ridiculous as well and no-one is suggesting that happens, i'd assume it's local heat from a torch inside the frame...

- i'm just quoting the frame builders when they say they can 'melt' the seatpost out.

There must be some frame builders on the forum that can comment on this?

mostly harmless

The area covered in red hammerite was the result of a frame builder melting the previous post out.

I'm not sure whether it was physically melted out or just gotten hot enough to be extracted but the frame builder said "melted". The brazing is fine.

Jimfrandisco

Thanks for posting the picture...out of interest who did you get to do it? I'm based in Reading so looking for someone as close as possible to avoid having to post the frame.
cheers

mostly harmless

IIRC it was Argos (Bristol). Think it was £30 but it was six years ago.

I only used hammerite as I was skint, budget for proper painting if you can afford it. It should be getting powder coated soon but then I say that every winter.

ride_whenever

It's easier to cut it out instead of doing the heat game mainly due to frame damage from the heating.

alan_sherman

I don't think it is melted in a temperature style - more dissolved with acids and a bit of temperature. Or using electrical resistance / arcing or something (vague recolections there - sorry). Either way it will damage the frame finish.

There must be a business opportunity for someone with a saw, a jig and a 27.2mm drill!

Jimfrandisco

ride_whenever wrote:

It's easier to cut it out instead of doing the heat game mainly due to frame damage from the heating.

I think it would've been...but it was a long seat post with too much in the frame to get a hacksaw the length of. Unfortunately the last person that had a go cut the seat post off almost flush with the frame - which means even with a hacksaw down the tube there's not enough above the frame to get mole grips on etc.

Alan Sherman - exactly.... one big jig and one big drill bit would do the business!...But no luck finding one yet!

ballspondroad

Acid would be a bad idea on a steel frame I think but sodium hydroxide would dissolve the aluminium whilst preserving the steel and with care you could avoid damaging the paint. Removing the bottom bracket and pouring it down the seat tube would be the way to do it. Depending on the strength of the hydroxide solution this can get quite hot, so you may want to cool it with ice or water. Do take care though, hydroxide burns are not nice.

kettrinboy

just a thought but if aluminium expands faster than steel then it must also contract faster so perhaps freezing it with something like liquid nitrogen would loosen it , i wonder if anybodys tried it.

Buckled_Rims

If you have to have the last resort method - and it's certainly not melting! - then get the alloy post reamed out. carefully done I believe no harm will be done to your frame.

mercurykev

You can apparently melt out an alloy seat from a steel frame by using Caustic Soda (Calcium Hydroxide) - it just eats the aluminium while leaving the steel intact. Takes about a week.

Jimfrandisco

Buckled_Rims wrote:

If you have to have the last resort method - and it's certainly not melting! - then get the alloy post reamed out. carefully done I believe no harm will be done to your frame.

I would if i could, but it's been impossible so far to find anyone that can/will do it - if melting out is a service that someone like Argos offers then i'm reasonably happy they know what they're doing!

mercury kev - as for caustic soda, i did try that for a few days to try and dissolve the bond between the alloy and the steel...but if it takes about a week then maybe i should give it another go. I've heard mixed reports but if you're talking from experience could you tell me any more - eg what concentration?

cheers

dmch2

Did you try it in a *big* vice mounted on a solid workbench? It'll come out eventually if you twist hard enough. Took two of us to get mine out.

bill57

mercurykev wrote:

You can apparently melt out an alloy seat from a steel frame by using Caustic Soda (Calcium Hydroxide) - it just eats the aluminium while leaving the steel intact. Takes about a week.

Mercury kev means Sodium Hydroxide, which is what Caustic Soda is. It would need to be very concentrated and is very hazardous to use. Even dissolving the solid pellets generates large amounts of heat, enough to boil the water and spit it back in your face.

Have you thought of trying a slide hammer?

Stellite

kettrinboy wrote:

just a thought but if aluminium expands faster than steel then it must also contract faster so perhaps freezing it with something like liquid nitrogen would loosen it , i wonder if anybodys tried it.

I would imagine the heat used would just be enough to cause the frame and the seat post to expand at different rates and break the corrosion, as you use on seized nuts and bolts.

I remember once using heat on a large coupling and R22 freon to shrink a shaft prior to assembly. Unfortunately when the freon burn it produced Phosgene gas and nearly killed the lot of us.

Stay safe!

pmysgar

I had this problem recently. Told that heating would distort the frame. Tried ammonia (dissolves aluminium oxide), but that didn't seem to do much. May have more luck immersing the frame, but the aluminium post will be compound and not purely aluminium.
I eventually managed to get it out using hand reamers but it took a long time....

RIKO

Some thing you could try is drill a hole through the seat post this will allow you to slide a bar through the hole. You can then clamp this in a vice and use the frame as a lever to rotate it and try and release it

ugo.santalucia

RIKO wrote:

Some thing you could try is drill a hole through the seat post this will allow you to slide a bar through the hole. You can then clamp this in a vice and use the frame as a lever to rotate it and try and release it

THis sounds like a sensible solution

beatsystem

I would have thought a hacksaw blade used to cut a slot in the post down its length after cutting it off at about an inch from the frame, then twist it with a big wrench would do the trick.

bill57

Jimfrandisco wrote:

Unfortunately the last person that had a go cut the seat post off almost flush with the frame

Don't you guys read?

Bar Shaker

Its caused from Bi-metalic action.

If you ride a steel bike, go the whole hog and use a steel seat post.

Chris James

Bar Shaker wrote:

Its caused from Bi-metalic action.

If you ride a steel bike, go the whole hog and use a steel seat post.

Mmm, or grease the seat post regularly. Still it's easy to be wise after the event.

mmacavity

Yes liquid nitrogen works, and does not damage the frame or the paint.
Loctite freezeandrelease, Wurth Rostoff, etcetc, can also work.

Jimfrandisco

In the end i decided to give the Caustic Soda another go - the only cost being some a couple of quid and a bit of time...rather than the expense and risk of having it melted out.
(although if Argos etc tell me this is perfectly possible/done regularly then i still have a tendency to believe them).

Caustic Soda is definitely working - If there was any of the post sticking out of the frame to grab hold of then i'm sure it would be out by now, but as there isn't i'm just having to dissolve the whole lot.

When i last looked this morning the post was pretty much paper thin.

Anyways, cheers all for your suggestions - and yes, next time i will be greasing on a more regular basis...