Why am I failing at alumnium brazing?

[skotl]

Success!

Test piece:

Folded box, that's going to be part of the extraction duct on the belt sander:

Just goes to show you get what you pay for - this is with the lumiweld rods.


As noted earlier, it needs a lot of heat. I wasn't getting anywhere on the box, then swapped to a newer calor bottle and it all came good.
Probably time to get a mapp torch...

 

[Mr Roo]

Wahey!

Success!

Test piece:

View attachment 258837


Folded box, that's going to be part of the extraction duct on the belt sander:

View attachment 258840

Just goes to show you get what you pay for - this is with the lumiweld rods.


As noted earlier, it needs a lot of heat. I wasn't getting anywhere on the box, then swapped to a newer calor bottle and it all came good.
Probably time to get a mapp torch...

 

[Turbo]

I found that the hotter more compact flame of an oxy propane welding torch was better than a mapp gas torch.

 

[skotl]

I found that the hotter more compact flame of an oxy propane welding torch was better than a mapp gas torch.

Yeah, but that means having big cylinders of oxygen, propane/acetelyne in the garage, which scares the poop out of me

Meanwhile... I hadn't realised how (relatively) expensive mapp torches are! I'll persevere with the cheapo propane torch for now...

 

[Robert Mullins]

I've used utectic 555 low temperature alloy, we used oxy-acetylene carburising flame, as the heat was/is somewhat localised and allowed the rebuilding of bearing surfaces and reclamation of stripped threads:

 

[Matchless]

I too have used this Duraweld or whatever it masquerades as with some success. It is not ally welding as such but what a terrific get out of jail card the few times I have used it.

What I cannot understand is how you can get it to fully penetrate say 3mm alloy sheet when you are nowhere near the melting point of the alloy???? I have found with mazac repairs it pays to place the original part into a mould made out of say plaster as the melting point of the mazac and lumiwled are only a few degrees apart and the mazac part does start to grow!

 

[northwest]

What I cannot understand is how you can get it to fully penetrate say 3mm alloy sheet when you are nowhere near the melting point of the alloy???? I have found with mazac repairs it pays to place the original part into a mould made out of say plaster as the melting point of the mazac and lumiwled are only a few degrees apart and the mazac part does start to grow!

Just imagine two pieces of copper sheet and you solder them together, it is a similar process. You don't actually melt the copper but you bond the two pieces together.

 

[Hopefuldave]

What I cannot understand is how you can get it to fully penetrate say 3mm alloy sheet when you are nowhere near the melting point of the alloy???? I have found with mazac repairs it pays to place the original part into a mould made out of say plaster as the melting point of the mazac and lumiwled are only a few degrees apart and the mazac part does start to grow!

The alloy in the rod does mix with the base metal, and the zinc? in it lowers the base metal's melting point (like tin/lead solder, the combination has a lower melting point than either pure metal - it's called an eutectic alloy). So... the base metal will actually puddle and fuse with the rod, for filling voids and fat joints (far out, man...) I've got started with the rods then fed in more ally and the chemistry means the ally melts into the puddle too, sort of half and half has worked ok *but the puddle melting point starts getting hotter as it's diluted by the ally*. I did section and polish/etch a fillet "test joint" I'd done (caustic soda) and could see the toe had penetrated the work, it wasn't just lying on top of it. YMMV, of course!

Dave H. (the other one)

 

[Seadog]

The alloy in the rod does mix with the base metal, and the zinc? in it lowers the base metal's melting point (like tin/lead solder, the combination has a lower melting point than either pure metal - it's called an eutectic alloy).

Something that was demonstrated to me when doing Engineering Science.

If you've time to spare, a thin piece of aluminium rod, and a scrap piece of copper, heat the copper until it's barely a dull red and then rub the end of the rod against it. A eutectic alloy will be formed locally and you'll find that you can push the rod through the copper.

 

[Matchless]

I still think it is some sort of magic!

 

[Pigeon_Droppings2]

This forum really is a wealth of knowledge...I was totally unaware of the science behind how these rods work.

The mapp gas torches aren't big money unless they've suddenly gone up. I use an unbranded copy torch...am sure I paid £20 for it...I'll check and report back.

This is like mine...mine is the benzomatic which is identical to the Rothenberger...now £48...I paid £20...but similar can still be had for £28. You want the one with the flow control...the brass twiddle on the top of the body.

 

[skotl]

Made an over-the-top locking mechanism for my anti-dog letter catcher, with my new found aluminium brazing skills

This was lathed out of a 50mm rectangular block, then brazed together:

Yep - that should be strong enough to keep the dog out...