Brazing cast iron

[tcianci]

What should I be doing to get a cast iron piece from a Delta Unisaw to braze.

I cleaned both halves with a sandblaster, heat cherry red with an oxy acetylene torch, use fluxed rod, used bare rod with dip flux, and it won't take, save a few small areas.

I'm open to instruction.

 

[The Cobbler]

Keith Fenner has some you tube videos on brazing cast might help to look them up & watch them
he uses bronze rod and dip flux. maybe you need higher heat on the base metal?

I just watched a new vid of his brazing ductile iron hubs, he makes it look so darn easy LOL

 

[matt_i]

I'd heat the base workpiece on a gas grill, all burners wide open for at least an hour to get heat into the metal. Then I think you'll have enough heat added by oxyacet.

Keep in mind the bronze doesn't flow/wick thru the joint like a soldered joint in copper plumbing. It is often advisable to create a shallow "V" on the surface, half on each side of the crack, in order to capture the molten bronze. And use gravity so the V- fills up and the molten bronze doesn't run down the side. Back to the grill and then do the other side.

 

[gearhead1]

Do you have a mig welder (with gas, not flux core)?

My friend owns an automotive machine shop, he turns an old kitchen oven on as high as it will go and heats up the part (cast iron intake for example). Then he welds it with his mig welder, then puts it back in the oven and turns the oven off and lets it cool overnight.

A customer brought a Massey Ferguson 3 cylinder diesel tractor which threw a rod through the block. It didn't hurt the cylinder or anything else, but put a hole through the side of the block. He made a cardboard template, then cut out a piece from a plate of steel. He welded the steel into the cast iron block with the mig welder. He ground the weld with a grinder, then used a flap disc. After it was painted, you couldn't tell from the outside it was ever repaired!

He's had several people tell him that you can't weld cast iron with a mig welder, then he says, I'll show you......Then he says guess how many have cracked and guess how many have come back......

 

[The Cobbler]

the problem with mig & and arc welding on cast is where the molten puddle of cast was, it becomes very hard and brittle

 

[jsaw]

I wish Granddad was still around to ask. He used to do lots of brazing in his day. I'm sure he told me many times what the trick to brasing cast iron was, but I cant remember.

 

[Bclinehand]

There are ways to improve your chances of successfully welding cast iron.

As has been said pre-heat is required.
It can be mig welded with a high nickel welding wire.
Using a ball peen hammer on the weld while still red hot helps stress relieve the repair to increase your success rate
Post heat is as important as pre heat...burying the part in kitty liter overnight will hold the heat in the part

When I cracked the trunion on my cast Beaver -Rockwell knock off I did a lot of YouTubing and was successful .

 

[jsaw]

I have welded cast with regular rod. But, it was in a non critical situation.
You can get nickel rod for welding cast.
I dont know if silicon bronze everdur would work or not.
Maybe ask at your local welding supplier if they know of any old timers that know how to braze.

 

[jsaw]

I do remember that when brazing, you want to get the base metal hot enough to melt the filler, but not too hot. To hot and the filler rod melts and balls up and rolls right off of what you are trying to braze.

 

[royce]

What should I be doing to get a cast iron piece from a Delta Unisaw to braze.

I cleaned both halves with a sandblaster, heat cherry red with an oxy acetylene torch, use fluxed rod, used bare rod with dip flux, and it won't take, save a few small areas.

I'm open to instruction.

A couple thoughts;

Regrind your pieces with rounded bevels because if you heated it cherry red and the braze would not take, it's a sure bet they scaled.

Make sure your welding tip is set with a neutral flame.

Introduce flux long before the work is up to temp, to keep them from oxidizing.

I hope that helps.

Royce

 

[tcianci]

Thanks Guys! I checked out some Youtube videos and tried a few different things. Finally I found a different rod in some stuff my Dad left me. It was pre-fluxed and I'm guessing a lower temp rod. It worked pretty well. I don't think this is a high stress application, the saw was actually working fine cracks and all. My earlier problems were surely from the metal oxidizing. The lower heat rod got me by that problem.

 

[Crazyjake8493]

I don’t do any gas welding or brazing, but I have TIG brazed cracked cast iron with aluminum bronze rods. Silicon bronze would work too but I prefer aluminum bronze for cast iron.

 

[theoldwizard1]

Keith Fenner has some you tube videos on brazing cast might help to look them up & watch them
he uses bronze rod and dip flux. maybe you need higher heat on the base metal?

I just watched a new vid of his brazing ductile iron hubs, he makes it look so darn easy LOL

Yep, saw the same videos !

He saved those hubs. Of course, Keith could have made him new ones !

On one of his old videos he put the piece of cast iron that was going to be brazed in his wood stove and open the air feed wide open. After about an hour, he pulled it out and started to braze.

 

[BLB]

The secret to successfully brazing [bronze welding] cast iron is to FILE the surfaces to be brazed. sandblasting/grinding etc permits abrasive particles to penetrate the surface of the iron which prevents the molecular bonding we wish to occur from taking place. By all means, grind, sandblast, whatever, but before attempting to braze, file all the surfaces where the brazing will take place. I like a nice deep 90 degree vee. Preheat casting and using cast iron tinning flux [a brown flux], tin all the surfaces. Apply the tinning flux liberally; you need to protect the heated iron surface from oxidising. Once all surfaces are tinned, use regular pink/white flux and build up and fill the vee-ed out section. Allow to cool slowly out of draughts.

 

[Firstram]

The secret to successfully brazing [bronze welding] cast iron is to FILE the surfaces to be brazed. sandblasting/grinding etc permits abrasive particles to penetrate the surface of the iron which prevents the molecular bonding we wish to occur from taking place. By all means, grind, sandblast, whatever, but before attempting to braze, file all the surfaces where the brazing will take place. I like a nice deep 90 degree vee. Preheat casting and using cast iron tinning flux [a brown flux], tin all the surfaces. Apply the tinning flux liberally; you need to protect the heated iron surface from oxidising. Once all surfaces are tinned, use regular pink/white flux and build up and fill the vee-ed out section. Allow to cool slowly out of draughts.

^This^ Use a die grinder with a carbide bur to remove the contaminates and grind a V most of the way thru.

 

[BLB]

Yes, indeed, you can use a carbide burr instead of a file. The important thing is to have absolutely no abrasive lodged into the prepared surface.

 

[amason3]

And to use Nickel rod.

 

[KMScott]

I brazed a broken foot a while back on a Rock Island 6" vise. I thought about welding but felt the strongest method would be silver soldering. I used Easy Flow 45, stuff I have had for many years. I machined out a pocket added a couple small screws and bolted the foot I made from cast material. Before bolting the foot in place I had some .005 Silver solder sheets and sandwiched the insert with the flux. I am a fan of the Stay Silv water based flux and found on e-bay easily.
I preheat like mentioned earlier before adding the braze rod and have found that you have to be real patient and heat the area all around the braze since the piece draws the heat, using a oven is a great idea but I did not have one close. I like to sand the braze rod before using to remove the oxide. This braze came out pretty good but I could have taken more time and used less braze material after soaking the braze in water to remove the hard flux. Just thought I would add my 2cents and show a few pic;s. Good luck with your's and post your results. Kevin

 

[Jim greengo]

I have welded cast with regular rod. But, it was in a non critical situation.
You can get nickel rod for welding cast.
I dont know if silicon bronze everdur would work or not.
Maybe ask at your local welding supplier if they know of any old timers that know how to braze.

 

[Jim greengo]

I don’t do any gas welding or brazing, but I have TIG brazed cracked cast iron with aluminum bronze rods. Silicon bronze would work too but I prefer aluminum bronze for cast iron.

Nickel welding rod works also,just knock flux off off it.

 

[NASTYZEN]

A bit late to the party but here's a link to my brazing 101 thread. Hope it can help someone.
https://www.garagejournal.com/forum/showthread.php?t=120122


KMScott, brilliant casting repair! Very well done!

 

[larry4406]

A bit late to the party but here's a link to my brazing 101 thread. Hope it can help someone.
https://www.garagejournal.com/forum/showthread.php?t=120122


KMScott, brilliant casting repair! Very well done!

I agree!

Someone 50-100 years from now will be trying to take those screws out and be cussing and moaning!