mobile welder - newtownabbey area

Coog

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Didn’t AvE extract one just using acid or alkali? Little bath made out of a yogurt pot taped to the head covering the stud and left it a few days. Whatever he used dissolved the steel but left the alloy untouched. Thought it was genius.
 

pablo

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I’ll be using this precision jig lads

1641973308812.jpeg
 

andy9eleven

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I’ll be using this precision jig lads

View attachment 346458
Then can you do mine pretty please?!



Didn’t AvE extract one just using acid or alkali? Little bath made out of a yogurt pot taped to the head covering the stud and left it a few days. Whatever he used dissolved the steel but left the alloy untouched. Thought it was genius.
I looked at this before but had forgotten about it I have to admit.

It's potassium aluminum sulfate - or alum - the same stuff as the antiseptic blocks the barbers use on your skin after a shave iirc. From memory it dissolves the steel but only adds a crust to the aluminium. I guess if it eroded the bolt enough to allow you to break/crumble it out without damage, that would be a good, and safe result.

Edit to add: Google tells me:

"Does alum powder dissolve metal?

It turns out that a hot solution of alum (ammonium aluminum sulfate), which is available in the spice rack of your local supermarket, will dissolve the steel drill bit without reacting with the brass."

May be worth looking in to this...
 
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pablo

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not sure how youd get the fluid to go vertically up to get the sunk part of the bolt
 

andy9eleven

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not sure how youd get the fluid to go vertically up to get the sunk part of the bolt
I think it's the fumes though. So as Coog says if it was in a cup underneath it could work. Again it was a while ago when I looked at this, but some people heat it slightly with a candle (something like a 10 degree increase in temp speeds up the reaction nicely). Some folk add a peroxide of some sort that generates heat from chemical reaction.

There looks to be stuff on YouTube about it, but I'm in office atm so can't really watch it presently.

Actually quite curious about this now. Found this web snippet saved in my OneNotes:

Armwave: Raising the temperature 10 degrees C (18 F) roughly doubles the speed of any simple chemical reaction.
(so sez 55-year old memory of junior high chem class)
BUT: further digging coughs up that warming is needed... if only to dissolve enough alum in the water to reach a decent concentration (another thing that speeds up the reaction)
The 1st video mentions hydrogen peroxide... its effect is to generate heat.
Suggested amounts are 4 tablespoons of alum to 1 cup of water. Expect it to take 12 hours to dissolve the stud.
Alum is potassium aluminum sulfate (KAl(SO4)2), but the same name can apply to aluminum ammonium sulfate, or even simply aluminum sulfate. (there are many others: Alum - Wikipedia )
... i'm still trying to find the actual reaction chain.
One explanation was: "The alum oxidizes the metals. Both metals ‘rust’ but for most brasses and aluminums the oxides act as protective layers. For ferrous metals the iron oxides flake off rather than stay bound to the metals underneath." ... another site properly used the word "passivates" to describe what was happening to the aluminum.
As the 2nd video shows, acids (nitric or sulfuric) also work. Same passivation effect. Alum's safer.
This EPA wastewater-treatment document describe's alum's action as "...when dissolved in water produces acidic condtions."
...so i assume the black chunk left at the end is iron sulfate.
 

variant

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Sounds like something with hug potential to go horribly wrong in an engine bay

(and i'm a man who's not afraid of a wee chemical reaction to solve a mechanical issue)
 

Coog

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Was more from interests sake than anything else. Thought it was pretty cool. IIRC he lifted out a shard of metal (formerly the stud) after a couple of days and all the threads were immaculate. A nice idea. Not sure I'd attempt it though lol
 
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