Stealthsilent
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Can’t do brazing
I’m trying to melt some metals into other metals and I’m trying a bunch of different reducing agents, but none of them work. I used sodium
carbonate, sodium bicarbonate, 50/50 sodium chloride and pottasium chloride, resin, and borax.
I didn’t mix the reducers onto any kind of solvent and just heated them up with a gas torch. They all first balled up(with exception of the tree
resin) then got to around 700C(idk, what temp do things start getting red hot?), then they lost all adhesiveness to themselves and spread across the
plate I was heating them on, to form a glassy, waxy kinda substance. Any kind of metal I put on them doesn’t bond with that melted reductant, it
just balls up and rolls/slips away.
The metals I’m using are probably tin, and copper. Zinc won’t ball up when I heat it up(I’m melting pennies).
The two metals I’m melting start to shine when I heat them up to 700c under the gas flame, but when I remove the flame, it starts to turn
wrinkly(which I think is the oxide layer).
After I reach 1200C(I’m guessing) the two metals do the same thing as the reducers and start “wetting” the surface of the iron plate I placed
them on
What is happening when I heat up the metal? Why does it start to shine and there is no oxide sheathe? Does the tin oxide get dissolved into the tin?
Also, why don’t any of the reducing agents bind with the metals I’m melting? And why do the metal balls and the reducing agents lose self cohesion
at around 1200C?
I’d you want pictures I can post them.
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XeonTheMGPony
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Most brazing rod is a brass alloy and the fluxes contain a flouride salt that activates between 500c to 780c ruffly
Surface prep is very important for good adhesion. If you want to get a job don just buy the proper materials other wise you'll be spending the next
couple years perfecting your own to see that's what they all ready have on the store shelf!
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Heptylene
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I believe certain metals shine when heated because the flame contains unburnt reducing species (carbon monoxide, and possibly hydrogen) that reduce
the oxide. Another possibility is that the oxide is not thermodynamically favored at high temperatures.
The brazing flux I have states that it contains 25-50% potassium tetrafluoroborate.
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Stealthsilent
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Interesting, thank you for your responses. I want to understand what is going on, that’s why I’m asking questions and doing expiernments.
I will post pictures and videos on everything so it is more clear
[Edited on 9/15/2018 by Stealthsilent]
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Stealthsilent
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So this is me melting tin, ignore the audio, it’s just me babbling.
You’ll notice the tin glow red then start to shine a color of silver. Then it stops adhering to itself and falls flat on the steel tray.
https://vimeo.com/291640374
And this second video is how the tin looks after it cools down. I’m guessing it is oxidized.
https://vimeo.com/291640898
So my questions are why did the tin shine, and why did it lose adherence to itself. Why didn’t it look oxidized when I was heating it? was it
absorbing any gasses? Thanks
[Edited on 9/25/2018 by Stealthsilent]
[Edited on 9/25/2018 by Stealthsilent]
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Deathunter88
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Quote: Originally posted by Stealthsilent  | So this is me melting tin, ignore the audio, it’s just me babbling.
You’ll notice the tin glow red then start to shine a color of silver. Then it stops adhering to itself and falls flat on the steel tray.
https://vimeo.com/291640374
And this second video is how the tin looks after it cools down. I’m guessing it is oxidized.
https://vimeo.com/291640898
So my questions are why did the tin shine, and why did it lose adherence to itself. Why didn’t it look oxidized when I was heating it? was it
absorbing any gasses? Thanks
[Edited on 9/25/2018 by Stealthsilent]
[Edited on 9/25/2018 by Stealthsilent] |
You're brazing technique needs some work. The goal is not to get the tin as hot as possible, but rather to get the substrate to the melting point of
the tin (or whatever else you're using as the 'solder'.) Heating the tin directly with the torch will just form a passivating layer of oxide that wont
allow it to wet the surface you want to braze. The reason that the tin appears shiny is because you are using a reducing flame, and so the un-burnt
gas helps reduce the oxide back to tin metal, but this is only really an illusion and you will not get a good bond heating the tin directly. Go watch
some youtube videos explaining proper brazing.
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Stealthsilent
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Please read what I was trying to do.
Are you sure it’s shiny because it’s being reduced by the carbon in the flame? Let me redo the expirment, but this time, heat the tin from under
the steel plate.
Okay I did it and the tin turned really grey, so I guess he’s right. But does the oxygen dissolve into the metal when I heat it up? That question is
one I want to know.
I guess all of the ingredients I’ve been using aren’t very pure, so that’s why it doesn’t react with the SnO2
[Edited on 9/26/2018 by Stealthsilent]
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Stealthsilent
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I figured it out, that guy was right when he said the flame was reducing the metal. I understand that the small crystals are the unmelted metal. But
don’t understand why it loses cohesion above ~800c
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