Brass panel artwork : circle

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Spesification : 
  1. Circle Medal 
  2. Material : Brass
  3. Production : Handmade
  4. Size : Custom
  5. Color : Custom

Joe McCabe's picture

Bronze Welding Question

Hello, I have enjoyed and benefited from the great collection of info on this site and am posting for the first time. I started bronze casting about two years ago and have had  an issue with welding smaller pieces. I am using a Miller Syncrowave 250 TIG machine. The piece I am currently trying to weld ( to fill imperfections) is 1/4" to 3/8" round at the narrowest. I cannot seem to get it up to temp to flow without burning through. I have tried 1/16 and .040 tungsten and set at low amps DC. The piece is Everdur and I am using bronze fill rod. Any suggestions or alternatives to welding small imperfections would be appreciated. Thanks!


Rich Waugh's picture

Filling Everdur

Joe,

Welcome to ArtMetal! I would suggest, in the future, you post questions such as this in a stand-alone blog post so they don't get missed.

To answer your question - If your Syncrowave is one of the newer ones with pulse capability, I suggest you try that at a fairly low pulse frequency. If you don't have pulse, use a small tungsten like the 1/16", either ceriated or thoriated, and taper it to about 2x-3x the diameter with a sharp point. Make sure, of course, that the grinding lines run with the length of the tungsten, not across it. I chuck my tungsten in a cordless drill and use a small belt sander with a 180 grit belt and then finish up by just barely rounding off the point on a diamond whetstone.  I find this gives me a very stable arc.

Use a larger gas cup with a gas lens if you have one.  Set your pre-flow gas for about a half second or so, and post flow for maybe three or four seconds.  Pure argon, of course.

Now - here's one trick most people don't ever try but that works a treat for filling little imperfections.  Use AC, instead of the normal DCEN.   Yep, I did say AC.  I know the conventional wisdom is that AC  is just for aluminum, but it has an advantage over DC in this case.  AC allows the reverse current flow to heat the filler more than the work, and that's what you want in order to fill little pits and such without melting the piece.  A 50/50 balance is good at 120Hz (or whatever your Syncrowave can do).  Again, pulse if you have the capability.  I'm now using an inverter TIG so I can play with all these variables, but my older Syncrowave 250 doesn't have them.

What you want to do is to heat the filler rod primarily and let the torch heat "wash" the work piece to keep it just below the fluidus point.  The plasma path should carry the molten filler right onto the work and flow it smooth.  You should be able, with a bit of practice, to get the filler to flow nicely and "wet" onto the work without collapsing the work. 

Of course, everything must be clean and shiny to start with if you want good wetting and flow.  I use a stainless steel wire brush reserved exclusively for Si Bronze and then wipe with acetone.  On really thin stuff where the work is thinner than the smallest filler rod I have, I will sometimes use a chunk of copper as a heat sink behind the workpiece.  My copper heat sink pieces are all old and oxidized so nothing sticks to them, not even the SiBronze filler.

Hope this helps you out!


Joe McCabe's picture

re: filling everdur

Rich, that is extremely helpful information! I have an older syncrowave that does not have pulse so I will work with what I've got.. AC huh? interesting. I will give it a shot. It has been frustrating to watch a piece I have so much time invested in melt before my eyes when I try to fill a little imperfection. Thank you so much. I will let you know how it turns out!


Rich Waugh's picture

That's what we're here for

That's what we're here for Joe, and happy to help!


Joe McCabe's picture

AC issues

Rich,  I gave the AC welding a go this afternoon on some scrap pieces to test it out. I was having problems maintaining a stable arc and it was "pulsing"pretty bad. I did get the filler to flow nicely but the arc was so erratic I could not see what I was doing.I mainly weld mild steel and stainless so I am not sure what to expect with AC. I used 1/16 tungsten, thoriated , set to 130 amps AC , gas lens and sharpened as you explained in your last post. What am I missing?


Rich Waugh's picture

AC does make for an unstable

AC does make for an unstable arc, no question about it. One thing that sometimes helps is to do what you do for welding aluminum - ball the tungsten. Put a chunk of heavy copper on the welding table and strike an arc on it with the tungsten, maintaining the arc as you increase amps with the foot pedal until the end of the tungsten melts into a ball. That ball shape will hold a more stable arc on AC and be less prone to getting pitted out from the reverse flow part of the AC cycle. You might also try using a pure tungsten electrode and a short point (or ball) and see if that improves your results.

This sin't a real elegant process, but it does work. You just have to practice. Does your Syncrowave allow you to vary the AC balance? If so you might try shifting the balance so it is a bit biased toward electrode negative. That is, more heat into the work and a bit less into the tungsten. With practice you'll find the method that works best for you.

Another tip for welding silicon bronze (and aluminum) is to keep in mind that it does transfer heat faster than steel so you kind of have to start out hotter than you'd think and then back off the instant you start to get a puddle. I pretty much stomp the pedal down to start and then back down to the lowest amperage I can that will maintain a puddle. Again, this one takes practice to get right.


Joe McCabe's picture

Good to know

Like I said I have very little to no AC welding experience. It is good to know that it is inherently unstable. Now I will tweek my settings until I get an arc I can live with. I'm heading to the metal recycler this week and will look for a good hunk of copper. As far as stomping the pedal and backing off I have tried this and had  results. I need more practice to back off before disaster strikes.