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In praise of SiB

Silicon bronze (SiB) has become the favorite rod in my arsenal. It’s been around for a loooooong time, and yet every time I post a sculpture or a weld I did using it, I get a chorus of “What kind of filler are you using?” And after I answer, the chorus sings, “What? Why? How?”

SiB is a pretty versatile filler material. With a TIG torch you can use it on a lot of junky stuff that would cause traditional steel filler to snap crackle and pop. In my art I love it for attaching zinc-coated nuts and bolts to each other. The SiB melts at a lower temperature than the coating, so it doesn’t “explode” when welded.

Of course, it’s not exactly welding. You’re not joining metal to metal with a similar rod, you’re technically brazing—electric brazing.

The lower melting point makes it ideal for joining galvanized metal, because you burn up less of the coating. It’s also great for sheet metal work because lower melting temps equal less heat equals less warping, and you can still sand and paint it.

SiB actually has outstanding wear properties too. My dad had some worn cast-iron gears that needed the teeth built up. I didn’t have the time to do a preheat/postheat, so I decided to “weld” it cold instead, getting the material just warm enough to take the SiB. He filed them down to fit, and they’ve been working perfectly in his snowblower for the past three or four seasons.

It’s also terrific for joining dissimilar metals. For my sculptures, it opened up a new world to me years ago when I found I could use it to attach copper to steel. The contrast in colors, the tactile difference in materials, it all adds to the character of the pieces.

In reality, I do go back and forth between calling it TIG brazing and welding. It’s too easy to call it welding, because it’s essentially the same process as GTAW. The differences in how the filler reacts to the base metal are subtle. You have a smaller window for the rod to melt into the puddle; if you’re too cold the joint won’t accept the filler and the end will ball up. If you’re too hot you melt into the base metal too much and find out the hard way why it’s called a “hot cracking” rod.

Melting into the base metal a little is OK, but excessive melting will fracture the joint down the middle. But overall, it’s a heckuva lot like TIG welding steel when it comes to machine settings, consumables, and hand-eye coordination. The filler is pretty much the only variable that changes from a process standpoint.

I should note that while I typically use DC negative polarity (just like I’d use on steel) to weld/braze with SiB, you can use AC. Alternating current’s cleaning process helps when brazing some materials.

An important thing to keep in mind when using SiB rod is that it’s made up of a lot of stuff, chemically speaking. There’s a little lead, a little zinc, a little of this, and a little of that. The fumes don’t leave you feeling great. It’s not as bad as brazing bronze rod using flux with an oxyacetylene rig, but it’ll give you a nice headache. A fume extractor is ideal, but even a box fan to suck away the nasty fumes is a smart plan of action.

SiB build up on snow blower gears.

If you can TIG weld and want to try TIG brazing, just grab some SiB and go to town. You’ll notice the slight differences in laying a bead that I mentioned earlier, but overall it’s a pretty simple process.

All images courtesy of Brown Dog Welding.

About the Author
Brown Dog Welding

Josh Welton

Owner, Brown Dog Welding

(586) 258-8255