[Captainbeaky]

Having some problems tig brazing today.

Tig brazing on thin steel - the part is an old rare and expensive VW exhaust, and has rusted very thin In several areas, so I am re-welding the flanges, and I want to reinforce a couple of really thin bits with braze - basically butter it with braze, rather than plate it up. Yup, it's a dodge, but it's very thin, and expensive to replace, so i want to get a few more miles out of it...

Welding went fine - no problems - other than my lack of skill - I started at too low a current for the flange thickness, as I was being cautions, but after a little practice, I got the knack.

The part was sandblasted just prior to welding.

This time around, it's simply not wetting out.
Normally, I strike the arc, and feed a little rod in, and she wets out.
This time, no joy, I had a ball of bronze that refused to wet out.
I add heat, and it eventually wets out, but it's so hot that the braze is spattering and loads of white powder is left around the bronze ( so I'm overheating it).

It's not the base material, because I tried it with another test piece and a cast pulley I am repairing - I get the same results.
These are the same rods I've used before - so it's not the rods.

I was getting tired, running low on gas and wanted my supper, so I've packed up for the night, but I'm surprised it didn't work.
When I've used the silicon bronze rod in the past, it's always gone in smooth as silk, and I've been very happy with the result.

What am I doing wrong?
Why is it not wetting out?

Thanks in advance,

Mike.

[Tom Osselton]

I'm a nubie to this and I've picked up some silicon bronze to try and have been wondering if I need some flux to use as the rods are not flux coated are you using any flux?

[Otto Nobedder]

Mike, one possibility comes from your statement, "...running low on gas."

There are several threads here, including a recent one, regarding low gas and the conditions that can arise. If you can try again with a fresh full bottle, you may find a big difference, as gas pressure seems to be your only variable.

It seems the solubility of water in welding gas is inversely proportional to the gas pressure. Each time a bottle is refilled, the procedure calls for it to be evacuated so that moisture is removed (like evacuating an air conditioner before adding Freon), but this step is often skipped for the sake of production. If the same bottle has been refilled without evacuation several times, you get moisture in the gas as your pressure drops.

Steve S

[sedanman]

What are you using for filler metal and what are your machine settings and polarity?

[Captainbeaky]

Mmmmm. That sounds very possible & plausible.
As pressure reduces, any water in the gas cylinder will tend to evaporate, as the overall pressure drops.
Increasing pressure does the opposite ( as proven by the water that gathers in a compressor air tank!)
The cylinder was standing in the sun too....and my mild steel welds weren't stellar either, so you could be onto something....

Also, in the arc, water will break down to hydrogen and oxygen. The oxygen won't do the steel any favours, and will form an oxide very quickly (and I'm pretty sure the hydrogen would do something to the copper too..)

And on reflection, the arc was not very stable and didn't always form properly.

Thanks for that - while it was on my list to try the other (full) cylinder, I hadn't thought of the moisture issue being linked to pressure... Perhaps it's time to try out the dessicant gas drier I bought a while back, but never got to fit!

I was tired before I started ( it was the last job of the day), and just wanted to get it done, so didn't do much fault finding before I stopped for the night because I was getting ratty ( let's face it - TIG welding problems and a bad mindset don't go together)

I'll keep you all posted...

Oh - nearly forgot to answer the last question...
Silicon bronze suitable for cast iron made by SIF ( I can't remember the exact composition).
RTech 161 AC/DC tig, air cooled 26 torch, red thoriated tungsten, DCEN, argon shield. Machine was set to 120amps ( I was using stainless filler rod for some other bits of the job) , but I was using the pedal very softly on the brazing, not melting the base metal at all - I estimate 40 to 60 amps on the brazing.

[kiwi2wheels]

In addition to the new bottle, try using the machine on AC rather than DC.

The ACHF acts like the flux in gas brazing.

[Captainbeaky]

Ok, all sorted now - I had a few issues, all stemming from the first.

Moisture in the gas.

I fitted a gas drier to the gas line - I'll pop a photo up here when I get a moment- and ran the dregs of the old cylinder through it.
The dessicant just started to turn from blue to pink, showing the presence of water.

I changed the cylinder for a fresh one.
But the arc still didn't form nicely.
Things were a little better on steel, but no go on the bronze.
I cleaned the rods down again, cleaned the workpiece, but no change.

The arc looked as though I had poor gas coverage - wandering around, and not stabilising.
And was very poor on AC.

So I took apart the torch, and the gas lens had a "spattered" appearance.
Also, the inside of the ceramic was jet black - carbon?

I fitted a new gas lens, new ceramic, new tungsten, wiped all the torch head parts down with acetone.

All sorted, the bronze is now wetting out properly...

What a carry on...

[Poland308]

Heavy black inside the cup screams gas issue. Get a flow meter with a ball that you stick on your cup. Check the flow and then you may need to verify there giving you the gas that the label says.

[Otto Nobedder]

Actually, the black residue and speckles on the lens screen can speak to the moisture issue that may have started this ball rolling. Consider the behavior you were experiencing... The last time I had this issue (carbon steel) I was getting "sparkles" from the arc that crapped up the screen and discolored the inside of the cup.

Steve S

[Captainbeaky]

I've been thinking about getting a pea shooter flow gauge for a while... Will go and get one...

I'm down to my last set of consumables for the 26 size torch too, so I think it's time to upgrade to a wp20 - I'm getting tired of the huge "euro" style torch...

Next project - a water cooler!


Thanks for the help guys, I was a bit lost at first...

[Otto Nobedder]

You'll love the -20 torch after working with a -26. It's like comparing a pocket knife to a hatchet.

Steve S

[Captainbeaky]

Yeah, my scratch start inverter has a wp9, and it's lovely and small!
I need to think carefully about leads and pipes, so it stays small, light and flexible.

[Bill Beauregard]

You've got me wondering about rust. In my youth, it seems like a hundred years ago, but is less than half that, I did a great deal of auto body rust repair. Rust is never in a convenient place. The convolutions of where rust happens are endless. Welding, (or brazing) rusty steel doesn't work. Sand blasting rust equates to a dentist fixing a cavity with a toothbrush. Only heat will drive it out of the hole. Most rusty steel evaporates before the rust goes away. My technique in the day was to heat to molten, and melt it to a place where solid. Then I would decide whether to fill with filler, or fit a patch. If your exhaust rusted where the heat was concentrated you may stand a chance. Those areas likely are an ant hill of unsound metal. Get rid of them. Shape fresh metal to reach where it isn't as rusty.

Check the internet. I've recently been using cathodic cleaning to rid myself of rust. Put two pieces of steel in water. Connect the negative clamp of a battery charger to the piece you want to save, positive to the sacrificial scrap steel. Add 1 TBS per gallon washing soda. It is amazing how this works! You then need to vigorously wire brush the loosened rust away.

[MosquitoMoto]

You've got me wondering about rust. In my youth, it seems like a hundred years ago, but is less than half that, I did a great deal of auto body rust repair. Rust is never in a convenient place. The convolutions of where rust happens are endless. Welding, (or brazing) rusty steel doesn't work. Sand blasting rust equates to a dentist fixing a cavity with a toothbrush. Only heat will drive it out of the hole. Most rusty steel evaporates before the rust goes away. My technique in the day was to heat to molten, and melt it to a place where solid. Then I would decide whether to fill with filler, or fit a patch. If your exhaust rusted where the heat was concentrated you may stand a chance. Those areas likely are an ant hill of unsound metal. Get rid of them. Shape fresh metal to reach where it isn't as rusty.

Check the internet. I've recently been using cathodic cleaning to rid myself of rust. Put two pieces of steel in water. Connect the negative clamp of a battery charger to the piece you want to save, positive to the sacrificial scrap steel. Add 1 TBS per gallon washing soda. It is amazing how this works! You then need to vigorously wire brush the loosened rust away.

Yes - cathodic cleaning is a wonderful thing. There's nothing like it for getting the rust out of a motorcycle fuel tank!


Kym

[Captainbeaky]

Yes, I agree.
Normally, I'd grind out and weld back in - but it would be easier to re-fabricate.

But in this case, the exhaust coupling isn't "lace curtains", it's serviceable - just very thin.
So "buttering" the thinnest bits with bronze is a way I can thicken up the thin bits until I fabricate new parts.
I want to test your it the system first, to see if I like the fit and sound.

The part is a y-piece, and short (5"), so I can sandblast thoroughly inside and out.

Not tried electro stripping the rust. Have used chemical dips - very good results.