brazing dam

I'm filling up the bottom of a cast iron exhaust port with braze, I want to
build a damn at the end of the port to stop the brass from falling out
(something similar as you can do copper when mig welding mild steel). Any
ideas?
thanks
Simon
Reply to
Simon
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I'd expect that the plaster like "investment" material used for lost wax casting should work. Check with a jewelry supply place. You could mold it into place, wait for it to dry and then bake any remaining moisture out of it with a little heat before starting the brazing job.
Back when I was a kid hanging around my dad's jewelry shop we cast white hot molten platinum into molds made of that stuff and it sure took the heat. The first few thou of the investment material next to the platinum glassified, but we got that off by soaking the castings in open wax pots of hydroflouric acid. OSHA would have had a field day checking out dad's shop if they were around back then.
If it was soft solder, you could use a "tinkers dam". Tinker was the olde name for a tinsmith. Their dams was just bits of clay used to keep solder from spreading where it wasn't needed. They salvaged scrap tin since it was quite valuable then, but they threw away the clay dams when they'd done their job because of the negligible value of a tiny bit of dried clay.
Hence the expression "Not worth a tinker's dam."
Jeff
Reply to
Jeff Wisnia
Eastwood sells a ceramic putty that works well for this. It's kinda pricey, but it's reusable.
If you know anyone who does casting, a bit of petrobond sand would work. You could probably make up some "green sand" out of silica sand (sandbox stuff) and some bentonite clay. Some kittylitter is bentonite.
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Reply to
Don Foreman
You thought about what will happen if the port gets hot from the exhaust? You did. OK. :-)
Additional to the other suggestions: How about tack welding a dam out of sheet metal. Not so sure wether surface tension is high enough that the braze does not escape through a little gap. I have the impression that you do have to get the brass to final shape anyhow.
And completely different (but more expensive): Do it with MIG. You get bronze (CuAl, CuMg) wires, but they cost. Might save you some time because it is easy to model with MIG/MAG. If you can reach the place.
Nick
Reply to
Nick Müller
Carbon block is often used as a dam. Why not try a piece of sheet metal blackened with acetylene soot? As long as you don't put direct heat against the black plate the alloy will not stick. Randy
I'm filling up the bottom of a cast iron exhaust port with braze, I want to build a damn at the end of the port to stop the brass from falling out (something similar as you can do copper when mig welding mild steel). Any ideas?
thanks
Simon
Reply to
R. Zimmerman

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