Brazing cast iron

[guineafowl21]

I have a small crack in my spindle moulder fence, which is cast iron. I’d usually use the stick welder with Nikko rods, but fancied a go at brazing. What’s a suitable rod and flux to use? I have some general purpose brazing flux on order. Torch is an oxypropane cutting setup.

 

[Sideways]

I think SIF bronze rods are suitable for the job. I'm aware that bronze rods for gas brazing are not recommended for TIG brazing, I think because the gas rods usually contain a small percentage of Silicon that you don't want when TIGging. Datasheets are on the 'web.
I haven't tried brazing cast yet, but did have success silver soldering a replacement tooth into a cast iron gear. You can see that on my thread about overhauling a Harrison L5. Silver solder is strong if you have a repair tight enough to wick the solder in and don't need to fill a gap. You wouldn't need to push as much heat into the part.

 

[TFrench]

Sound like you've got it covered. Sif bronze rods, vee it out well (drill end of crack to stop it spreading) Preheat it well and cool slowly. I've tried tig brazing and found it tricky, although I think the rods I was using were too small.

 

[Fergie 307]

Agree entirely, most important thing is to get the whole casting good and hot and keep the temperature up while you do the repair. Depending on the size of the part you can have a bucket of sand standing by. Half full it with sand, pop your still hot part in, and fill up with more sand. This will help it cool slowly and avoid stress cracks.

 

[guineafowl21]

Thanks. I’ll try the sifbronze rods, and perhaps do as I would with welding - preheat in the oven, weld, then put back into the oven to cool down slowly.

 

[Fergie 307]

If you are talking about a domestic oven then it's not really hot enough, but hey you have to use what you have, probably ok for what I would assume is a fairly thin casting.
Your other half must be very understanding, not sure I would survive the boss finding bits of cast iron baking in her oven !

 

[guineafowl21]

If you are talking about a domestic oven then it's not really hot enough, but hey you have to use what you have, probably ok for what I would assume is a fairly thin casting.
Your other half must be very understanding, not sure I would survive the boss finding bits of cast iron baking in her oven !

Normal oven seems to work, just to take the chill off.

Do you not put stripped down carburettors in the dishwasher? They come up a treat!

 

[guineafowl21]

Done it! Pics to follow. I put the fence piece in front of the diesel jet heater to pre-heat it, having vee’d out the crack. Then it was a case of heat the rod, dip into flux, heat the part, and gradually build up little blobs to fill the vee.

For what it was worth, I tapped/peened the brazed area as it cooled to help prevent cracking.

Is there a clever way of joining up the little brazing rod stubs so you can keep using them?

 

[Vann]

...Is there a clever way of joining up the little brazing rod stubs so you can keep using them?

You just need a fine flame so that only the very ends melt.

Cheers, Vann.

 

[guineafowl21]

Here it is. I might sand and paint it, or leave it as an honest repair. The threads at the top are slightly stripped, so I guess the best option is a helicoil if I want to keep it 1/2”BSW.

I also made this table insert from a Freelander brake disc, which happens to be about the right size, and cast iron of sorts. Made a filthy mess of my lathe.