Cycleops
Legendary Member
- Location
- Accra, Ghana
Whatever happened to Yellow Saddle? Some useful posts but very prickly.
Stuck seat post
- Thread starter gazza19
- Start date
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newts
Veteran
- Location
- Isca Dumnoniorum
Maybe repairing an undertensioned spoke somewhere in the wilderness?
Ajax Bay
Guru
- Location
- East Devon
Bowed out of CycleChat a few years ago, but we exchanged messages last year: he's still beside a (sea) loch.
GuyBoden
Guru
- Location
- Warrington
I've removed stuck seatposts in the past with caustic soda.
From my posts:
"When aluminium posts are stuck into a steel frame, the caustic soda technique does work, but it takes about 4 to 7 days. Aluminium "welds" itself to the steel, it's a chemical reaction over time. WD40 won't do anything in this situation. I've used caustic soda, but it ruins the paintwork near the top of the seat post.
Procedure:
Cut the seat post off about 3inch from the top and pour in caustic soda into the seat post hole, alternatively remove the BB and pour caustic soda in from the bottom (block all holes up first). leave and top up every day until the Aluminium has gone. (Wear gloves and goggles.)"
https://www.cyclechat.net/threads/peugeot-competition-cp10-work-so-far.209068/#post-4523963
https://www.cyclechat.net/threads/what-have-you-fettled-today.87079/page-362#post-4742595
From my posts:
"When aluminium posts are stuck into a steel frame, the caustic soda technique does work, but it takes about 4 to 7 days. Aluminium "welds" itself to the steel, it's a chemical reaction over time. WD40 won't do anything in this situation. I've used caustic soda, but it ruins the paintwork near the top of the seat post.
Procedure:
Cut the seat post off about 3inch from the top and pour in caustic soda into the seat post hole, alternatively remove the BB and pour caustic soda in from the bottom (block all holes up first). leave and top up every day until the Aluminium has gone. (Wear gloves and goggles.)"
https://www.cyclechat.net/threads/peugeot-competition-cp10-work-so-far.209068/#post-4523963
https://www.cyclechat.net/threads/what-have-you-fettled-today.87079/page-362#post-4742595
Ajax Bay
Guru
- Location
- East Devon
Tell us more. What is the chemical reaction which 'welds' the aluminium to the steel?
GuyBoden
Guru
- Location
- Warrington
Yes, thanks @midlife I was alluding to Galvanic Corrosion, we don't really need to be too technical, it's only a bike seat post.
For the pedantic amongst us:
"Galvanic Corrosion is the chemical reaction of a metal, galvanic corrosion creates the largest number of corrosion problems for aluminum alloys. Galvanic corrosion, also known as dissimilar metal corrosion, occurs when aluminum is electrically connected to a more noble metal, and both are in contact with the same electrolyte."
I am an engineer, but do we really need to over complicate a simple matter. I don't think so, personally.
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Ajax Bay
Guru
- Location
- East Devon
Great to hear you're an engineer too: we can both 'appeal to authority'.
But as as you have subsequently implied, the chemical reaction is not between Al and Fe, as 'weld' implies [you said "Aluminium "welds" itself to the steel"], so maybe using 'weld' actually misinforms, rather than simplifying imho.
Al2O3 [edit - thank you @faster, valency fail] is created between the two metals, and this molecule is way larger: hence the seat post sticks.
Btw avoid the temptation to use of grease which merely keeps H2O in the interface for longer (in emulsion) and gives the galvanic corrosion longer to operate.
Periodic removal, wipe clean and reinstall is the sensible maintenance regime requiring a minute's effort every 3 months (say).
But as as you have subsequently implied, the chemical reaction is not between Al and Fe, as 'weld' implies [you said "Aluminium "welds" itself to the steel"], so maybe using 'weld' actually misinforms, rather than simplifying imho.
Al2O3 [edit - thank you @faster, valency fail] is created between the two metals, and this molecule is way larger: hence the seat post sticks.
Btw avoid the temptation to use of grease which merely keeps H2O in the interface for longer (in emulsion) and gives the galvanic corrosion longer to operate.
Periodic removal, wipe clean and reinstall is the sensible maintenance regime requiring a minute's effort every 3 months (say).
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So we can have:
1. the aluminium "welds" itself to the steel
OR
2. due to galvanic corrosion, aluminium oxide forms between the two metals which, due to the larger size of the oxide molecule vis a vis the molecule it replaces, causes the seat post to stick
...think I'll go with the former
1. the aluminium "welds" itself to the steel
OR
2. due to galvanic corrosion, aluminium oxide forms between the two metals which, due to the larger size of the oxide molecule vis a vis the molecule it replaces, causes the seat post to stick
...think I'll go with the former
Great to hear you're an engineer too: we can both 'appeal to authority'.
But as as you have subsequently implied, the chemical reaction is not between Al and Fe, as 'weld' implies [you said "Aluminium "welds" itself to the steel"], so maybe using 'weld' actually misinforms, rather than simplifying imho.
Al3O2 is created between the two metals, and this molecule is way larger: hence the seat post sticks.
Btw avoid the temptation to use of grease which merely keeps H2O in the interface for longer (in emulsion) and gives the galvanic corrosion longer to operate.
Periodic removal, wipe clean and reinstall is the sensible maintenance regime requiring a minute's effort every 3 months (say).
Whilst we're down at this level of pedantry, 'weld' doesn't imply any sort of chemical reaction between the two surfaces being joined.
Also, it's Al2O3.
