[TheForge] Forge welding

[Chuck Robinson]

20 Mule team borax has, in addition to water of crystallization, an anti 
caking additive that melts at a higher temp than the borax, and can 
slightly decrease the quality of the weld.
Anhydrous borax is a better flux.
Chuck
On 7/26/2011 2:19 PM, Mike Spencer wrote:
> Roger Degner wrote:
>
>> I use anhydrous boarax which comes from a chemical supply house not
>> 20 mule team that was boiled and then ground which still has water
>> in it or absorbs water.
> Laundry borax -- the 20 Mule Team stuff -- contains 10 (!) molecules
> of water for each molecule of borax (sodium tetraborate) as "water of
> hydration".  That is, it's not wet or even slightly damp in the usual
> sense.  The configuration of the borax molecule is such that those
> molecules of water bind to it very tightly even when the borax seems
> to be powdery dry.  Toasty-warm won't drive off that water but the
> temp of orange- or yellow-hot iron will.
>
> When you put such hydrated borax on a piece of hot iron, it writhes,
> froths and foams as those 10 molecules of water are driven off.  Maybe
> that doesn't matter if you're welding anchors or axles but for
> smallish or very delicate work, lots of the borax just falls off (into
> the fire if you apply it with a spoon in the fire) and fails to melt.
>
> I put a bunch of 20 Mule Team borax in a long-handled iron ladle and
> melt it in the forge.  As the water is driven off, I add more borax
> until the ladle is half full or so. Then I pour the melt out onto a
> steel slab where it hardens into a brittle, greenish-black, glass
> puddle.  Break it up a bit with a hammer and run it through an old
> food grinder to get a gritty powder of -- ta-DAH! -- anhydrous borax.
>
> That powder sticks to hot iron real good, melts quickly at orange heat
> and wicks into joints pretty well.  Doesn't foam and froth.  And
> it doesn't seem to pick up water from the air, either, so it keeps
> indefinitely.
>
>
> FWIW,
> - Mike
>