Porosity on silicon bronze cast iron brazing

[Andy Somogyi]

Tried practicing some SIB braze on cast iron, and got massive porosity.

Made some coupons out of an old brake disk, cleaned off most of the rust by soaking in phosphoric acid and hit the belt sander to give a bevel.


First try was DC, 150A and the top of the bead didn’t look terrible, sure had some holes.

Tried AC on the other side, 10% cleaning and that was a disaster. It seemed to pull all sorts of crap out of the cast iron and contaminate the tungsten right away.

Gave it a break test and OMG, whole thing full of holes.

One guess is I didn’t clean the middle lands where the parts touched, and they still had the black phosphate from the acid clean, IDK, maybe this was contaminating the weld???

So what settings do you guys like for cast iron TIG braze?

Here’s the disastrous first attempt:





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[danielplace]

Never had any bgreat luck with tig brazing cast iron. Gets to hot too quick and cools too quick.

Brazing cast is a slow process of bringing up to temp and getting penetration as it wicks into the crack and wets out in the pores then cools slowly since large area is brought up to high temps.

It doesn't really take to the casting when casting is only heated locally with tig. Oxy-Acetylene is more user friendly for brazing cast.

[Kelvin]

It doesn't really take to the casting when casting is only heated locally with tig. Oxy-Acetylene is more user friendly for brazing cast.

I've never had much luck tig brazing with SiB, either, although I may have given up on it too fast. O/A with borax flux works way better IME.

[Country Metals]

Your also trying to weld something together that has crap impregnated inside of it. Things like oil pans, heads, all cast items from china, and such usually dont weld at all because when you heat it up, you will the crap out if them.

Things like hydraulic cylinders, mill tables, and anything smoothly built will weld just fine because it was designed to block out all instances of crap impregnating them.

Use a better piece of steel and your results will greatly improve.

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[Kelvin]

Some kinds of cast iron are slam-full-up with carbon/graphite. Don't know whether that's the case here, but I suspect if so, it wouldn't help.

[danielplace]

Your also trying to weld something together that has crap impregnated inside of it. Things like oil pans, heads, all cast items from china, and such usually dont weld at all because when you heat it up, you will the crap out if them.

Things like hydraulic cylinders, mill tables, and anything smoothly built will weld just fine because it was designed to block out all instances of crap impregnating them.

Use a better piece of steel and your results will greatly improve.

I realize he has that option since this is practice metal pieces but was thinking he wants to learn to tig weld/braze cast iron not steel or cast steel.

I believe the cast iron may be the challenge he is trying to solve.

[Andy Somogyi]

When you have something cast to fix you can't just turn it to something it isn't.

I think he wants to weld cast iron not steel or cast steel. The cast iron is the challenge he is trying to solve.

Yes, I’ve got a broken part of a press that I have to fix, so I’m trying to learn the technique by practicing on scrap cast iron.


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[Bob]

As the cast iron heats up, impurities are pulled out into the weld. My only luck with tigging it would be to grind almost all of the weld out, leaving just enough to hold the pieces stuck together. Reweld it a second time and most times it will be a good weld. Like others have said, torch brazing it would be the best.

[LtBadd]

Can you post a pic of what you want to repair?

[MinnesotaDave]

I like tig brazing, but the guys are right - preheat it first.

Always clean the weld area. You have to bevel to get all the way through anyway.

So far, in my somewhat limited experience, I've like aluminum-bronze better.

I recently had a sil-bronze repair end up with some hard spots during drilling and a few pinholes. I didn't experience that with al-bronze.

[danielplace]

Dave is correct on the filler. The silicone bronze is hard and solidifies so quickly you don't get the liquid flow and penetration you do with al-bronze or with the nickel rods.

[smithdoor]

I seen that type of porosity in pass.
Seen on repair work, I do not how it happens.

The fix was to use a O/A torch and work down to the base metal (typically cast iron) with flux.

Dave

Tried practicing some SIB braze on cast iron, and got massive porosity.

Made some coupons out of an old brake disk, cleaned off most of the rust by soaking in phosphoric acid and hit the belt sander to give a bevel.


First try was DC, 150A and the top of the bead didn’t look terrible, sure had some holes.

Tried AC on the other side, 10% cleaning and that was a disaster. It seemed to pull all sorts of crap out of the cast iron and contaminate the tungsten right away.

Gave it a break test and OMG, whole thing full of holes.

One guess is I didn’t clean the middle lands where the parts touched, and they still had the black phosphate from the acid clean, IDK, maybe this was contaminating the weld???

So what settings do you guys like for cast iron TIG braze?

Here’s the disastrous first attempt:





Sent from my iPhone using Tapatalk Pro