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View Full Version : Silicon Bronze TIG cracking, why?



bryanmartin
01-10-2016, 05:20 PM
I'm practicing silicon bronze TIG on some scrap, but I keep getting cracks in the weld. Anyone know why? I know it's not a very strong form of weld, but the part isn't stressed, it's just some scrap sheet metal. Welding on DC with 1/16 tungsten and filler, straight argon. I don't know how many amps because my machine only allows you to dial in the max, then adjust with the pedal. I was barely on the pedal, only enough to keep an arc.
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That Guy There
01-10-2016, 05:29 PM
Maybe because you are diluting the base metal? With SiBr you want to tig braze, very similar to brazing copper etc. Try not to dilute the base metal. Just melt the SiBr

thegary
01-10-2016, 05:30 PM
It has been years since I did much with silicon bronze but I can tell you this, you are way too hot. You really do not even need to melt the base metal. I would also look at your gas flow. You need to strike an arc and gradually increase the amps till the rod melts and flows onto the base metal. In the past I have had this problem when using silicone bronze to weld bronze because of needing to melt into the base metal. In that case I needed to gradually decrease amps to 0 over a minute or so. That will not help here though. I do not know what machine you have but you need more control. On that thin of sheet metal it will not take much to melt the rod.

Louie1961
01-10-2016, 05:32 PM
I think you are getting the base metal too hot. When the base metal mixes with the silicon bronze it makes it brittle.

njs552
01-10-2016, 07:08 PM
Everyone else has it pretty well covered. In the pictures it looks like you have too much heat and are melting quite a lot of base metal.

If this is your first time using SiBr I would suggest practicing on thicker material before that thin stuff. You want to start the arc, and when a puddle starts to form back off the pedal a bit and start adding filler. The weld should be a shiny gold color when your done with no coloring/tinting from base metal dilution.

WNY_TomB
01-10-2016, 08:03 PM
forget the foot pedal. if .050 metal start at 25 amps and try it, if you feed you can increase try 5 amps more at a time
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you are not suppose to melt the steel. sharp tungsten and travel fast enough adding enough silicon bronze. if hot (melting steel) stop arc wait for metal to cool. kind of basic start at end weld toward middle. if you weld to end probably burn through at end. did i mention use a sharp tungsten. no point on tungsten will make a mess for that reason alone.
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i have worked with dozens of tin knockers making sheet metal fabrications and none used a foot pedal.

motolife313
01-10-2016, 09:00 PM
Looks like it's from crater crack. Taper off the pedal at the end

bryanmartin
01-10-2016, 11:02 PM
See? That's why I love this forum. Thanks guys! I had no idea I wasn't supposed to melt the base metal. I am taking a TIG class, but it doesn't start until next week, in the mean time I can't resist playing around. I appreciate your help.

thegary
01-10-2016, 11:12 PM
In some cases I have melted the base metal but the trick is to melt as little as possible. If you are using too large of filler rod you will have a hard time since the base metal will want to melt easier than the filler. You need to get the filler rod into the arc as soon as you get the arc established so it can heat up and take most of the heat from the arc. You kind of put the rod between the arc and the base metal. A small amount of base metal dilution does not bother the weld most of the time . The thinner the metal the more critical the dilution problem is. On that thin of metal I would use 1/16th filler at most and if I had some SB mig wire I would us it.

bryanmartin
01-10-2016, 11:14 PM
forget the foot pedal. if .050 metal start at 25 amps and try it, if you feed you can increase try 5 amps more at a time
.
you are not suppose to melt the steel. sharp tungsten and travel fast enough adding enough silicon bronze. if hot (melting steel) stop arc wait for metal to cool. kind of basic start at end weld toward middle. if you weld to end probably burn through at end. did i mention use a sharp tungsten. no point on tungsten will make a mess for that reason alone.
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i have worked with dozens of tin knockers making sheet metal fabrications and none used a foot pedal.

What do you mean by forget the foot pedal? Will the torch trigger work better? Thanks.

shovelon
01-10-2016, 11:45 PM
What do you mean by forget the foot pedal? Will the torch trigger work better? Thanks.

I myself that question too. You are lucky to have a pedal, use it. There may be cases where a pedal is cumbersome but benchwork affords you the luxury to use your pedal. It's nice sometimes to taper off the arc when terminating and not leave a crater.

But then if you don't have remote current control you make do.

motolife313
01-11-2016, 11:07 AM
Silicone bronze is much better with a foot pedal. I'm not the greatest with SB because I don't practice with it much but what I do is get the base metal too puddle just a little bit( small puddle) then that's when I know to start adding filler. If you don't let it puddle just a little bit on the start the rod will ball when you try and add filler. Maybe practice on 1/8" base metal. Set the machine to 90 amps but you prolly wouldn't need it all. If your on under 1/16" base metal I would think 25 at the low end and try 45 amps that should be about perfect. But 1/16 might be a hair big, which means it should be a slow go from you quenching the metal so much with the big filler. Have fun also I always where cheater lense, helps see the puddle a lot. I used to just wear reading glasses but that's annoying getting those on all the time so I finally got some 3-0 cheaters.

Rick Finsta
01-11-2016, 12:15 PM
I've had success getting nice joints so far by heating the base metal to the point it is really shiny and a couple of tiny little puddles start to form then get at the filler metal ASAP; if this makes sense you can almost see the surface imperfections (like grinding marks, etc.) "pop out" visually when the puddle is *just* about to form. For thinner stuff I was told to actually start the arc on the filler but I haven't tried it at all with anything anyone here would call "thin..."