Weld dilution - techniques.

[Drains]

What techniques do people use to maximise or minimise dilution?

I'm laying aluminium bronze onto EN19, and amongst other things, need to keep dilution to an absolute minimum, as post weld, the EN19 is removed to leave a completely non-magnetic area (of a valve).

As there are size constraints, it's not possible, or at least easy, to allow a large dilution zone for removal.

Any suggestions therefore in technique to limit the dilution zone, gratefully received!

 

[hotrodder]

I normally use a lay wire technique when brazing with TIG, sometimes with a slight weave (more like the oscillation that you get when walking the cup than a deliberate weave) as i find it easier to avoid melting the base material. Talking much thinner material than the valves you posted pics of in the other thread about ally bronze though. Not really done any jobs that similar but given the joint geometry am thinking playing with pulse settings. Is it the sharp corners where dilution is the issue? Could they be radiused or at least broken when prepping the joint?

 

[Drains]

This is really a weld rather than a braze HR. at least I've not managed to do a strong braze type joint, only a weld, so there is inevitably some dilution. I've ended up using the Lorch MACS setting, using DC with a pulsed ac component. This seems to work better than DC and far, far better than AC (which UTP seem to recommend). The DC applies the weld and the AC knocks off the oxides on the bronze. A pure AC weld is rubbish- the steel doesn't like it at all, no surprise there, though didn't stop me from trying.

I'm really looking at the number of runs to do. I want to do multiple runs, but I'm not sure if that will increase dilution? A thin buttering layer first followed by a cap, or do I fill in a one-er....?

Which would minimise dilution? Or would it make no odds?

The sharp corners are not a problem. It's the base of the weld where I need to keep dilution down. In fact that bit doesn't need to weld at all as the material underneath it is bored out... Hmm, that's given me a thought... Time for a ponder...