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Thread: Help with brazing with MAP
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5th Nov 2006, 12:23 AM #1Member: Blue and white apron brigade
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Help with brazing with MAP
I bought a MAP torch about a year ago mainly for soldering and I noticed recently that the instructions say it is capable of brazing so I thought I'd have a go at turning two 100 mm long bits of 3mm thick brass angle into a square tube. So basically I need to braze 2 x 100 mm long seams.
I started by cleaning the brass with emery paper. Then I built myself a small firebrick hutch and bought some flux covered brazing rods supposedly suitable for brass. I managed to get the brass up to red heat but when the rods entered the flame the rod did not melt and the flux caught fire and burned away.
Then I tried ordinary thin (1mm) bronze brazing wire and some brass/copper flux. All I managed to do here is deposit little blobs of bronze all over the place.
Then I tried some silver + something brazing wire and used borax as the flux. This worked a little better but there were still a lot of gaps and it's a along way from what one would call "neat" because it seems like the brass takes so long to heat up that it oxidizes and then the brazing wire does not stick to the brass. The angles have also twisted quite badly.
Any suggestions and to what I might be doing wrong?
Someone suggested using plain brass wire as the brazing rod, can anyone comment on this before I buy it?
I could just take it to work and use the oxy but I'd like to be able to do some brazing jobs at home without having to lug the piece to the bottles or vv.
Thanks
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5th Nov 2006, 02:33 PM #2
Brazing or braze welding
Its all in the terminolgy and understanding what it means and what it can and can't do
You are applying brazing procedures to a piece that should be
Tig welded or Silver soldered.
To explain, brazing is the mechanical bonding of a low temp melting metal to another,as in traditional tin soldering.
Brazing rod is essentially brass, so you are trying to weld three low melting temperature pieces ie.2 parent metal units and a filler metal unit together - result - problems you are suffering.
Silver solder (blue tip ) may work if -
Emery the surfaces to be joined
Apply GP.Silver solder Flux (yes Borax is the basis-but not the only active constituant of the flux.It should be mixed with water if it dries out -to a thick cream consistantcy
Heat the flux until it dries (it will look like dried toothpaste)
Keep heating until flux turns to water like appearance.
About that point the brass will be up to red temp.Only then stroke the tip of the silver solder into the joint. The silver solder rod is not melted by the flame but by the heat of the parent metal.As the filler runs in heat along the desired fill area to keep the parent metal hot enough.
That should get you on track.
Manufacturere tend to make rather broad general statements.The trouble is that diy guys mistake them as specific.
In fact you will get better results taking the whole shebang to work and doing it with the oxy.
Grahame
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5th Nov 2006, 03:28 PM #3Member: Blue and white apron brigade
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Thanks Graeme, that's very helpful.
The MAP torch with the Bernzomatic silver solder and flux works fine, I thought brazing might produce a stronger joint.
Cheers
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