Welding Repair,... Cast Iron?

The OP said he had a smithy forge. If it were me, I would tin some more brass onto the area he has already brazed to get it high and proud above the crack. Then fire up the forge with the piece inside it as it comes up to temperature and "sweat" in the eisiting brazing to insure a proper bond was achieved, then turn the forge off and let the piece anneal back to room temperature over the next 3 to 4 hours.
 
Thats a very good way,,,
Not saying anything bad about Robo Pi, but the integrity of that weld just might no hold up...most of the brass is just sitting on top.

Practice, got to make sure its a dull red preheating, and because its a small crack does not mean to use a small tip, you will loose heat to fast, need a bigger tip to keep it hot and kinda wipe and smear the fluxed rod until it flows, (tinning) then you will have it..
I have a habit of brazing the part in a angled vertical position or from the bottom up, that way your brass will roll out untill you have it tinned then it will flow, reduce your heat a bit by moving tip away and get a shelf of brass formed, then just keep building on top of that, you will then have a good sound weld.
Its hard to really explain how to do it,, I bet if you watched it being done at a welding shop, looking over the welders shoulder, you would say "I Think I Got It" Then a little practice and you'll have it..
Everyone has a different way of brazing.
 
horty said:
Not saying anything bad about Robo Pi, but the integrity of that weld just might no hold up...most of the brass is just sitting on top.
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Actually that's not the case. The first half of the crack brazed up very well with very deep penetration. I was very pleased with the first couple inches. Unfortunately I had to stop at that point to reposition the workpiece in the vice. And during that process it cooled down a bit and I wasn't able to get it back up to a reddish glow at that point. So yes, the latter part of the job did not achieve good penetration. In some places it did, but in other places all it would do is ball up on the surface. So clearly those spots were not good. But I'm very happy with the repair overall. The first couple inches that went very well was probably good enough for this repair even if I had stopped there.

I don't believe that I had a flux problem. I used coated rods, but I also dip them into additional flux. The main problem I had at the end was not being able to get it hot enough. I think part of the problem at that point was that the crack was getting closer to the mass of the vice jaw and that was acting like a heat sink. I think I would have been just fine with a hotter torch. Lack of heat at the end of the job was the most likely culprit. It just refused to glow red at that point. And I know that's not going to work, but I didn't have a bigger torch. So I just let it go at that point. Like I say, the first couple inches went really well. So well, that that alone was probably a sufficient repair anyway. I feel pretty good about it. It's not a perfect repair, but I think it will do the job. A hotter torch is what I needed. I have a bigger torch around here somewhere but I haven't found it yet. It's not where it belongs so where it might be is anyone's guess.

I have a cast iron tractor pulley that needs to be brazed up next I'm going to either find my larger torch or pick one up somewhere. In fact, I have an old set of oxy-act torches that have larger tips. I think the torch body needs new O-rings. I'll have to look into refurbishing that old torch.
 
No problem. I just wanted to clarify that it wasn't as bad at it might have sounded. I'm happy with the repair. It's just not perfect. And I do like for things to be perfect. But let's face it, they seldom are. :grin:
 
horty said:
the flux is most important, I used a general 1/8" or 3/16" bronze rod, with a #1, 2, 3 peterson flux, The #1 is blue can not shown, they sell small cans.......................Dont use coated rods, you want to use a little of each flux as your brazing, and your surface needs to be tinned or else it will just be a glob mess and will never hold any strength,
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@horty
Hey Tim, how do YOU use the three different fluxes?
1) Is it a fixed ratio mix used thru-out the braze process?, if so what's your recipe?
2) Do you use one type for "tinning" and then another during filling?
3) is ther some visual trigger that makes you switch between them?

Thanks for any additional pointers.

-brino
 
cbellanca said:
I have done both. I depends on how much stress the part sees in service. As thin as the part is stick welding would be at real chore with an AC welder. Getting the heat right presents an undercutting problem. Brazing is much easier. I would follow the prep, preheat and cool down advice above for ether process. I don't think a hole at the end of the crack will help in this case.
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The main reason for the hole is on cast iron parts when there in temperature changes like a car exhaust or cylinder head. The thought on that is the expansion and contraction of the two metals , from my understanding.
 
brino said:
@horty
Hey Tim, how do YOU use the three different fluxes?
1) Is it a fixed ratio mix used thru-out the braze process?, if so what's your recipe? NONE
2) Do you use one type for "tinning" and then another during filling? YES & NO, Us #1 Blue Most Of The Time.
3) is ther some visual trigger that makes you switch between them? YES
Just a Note:
I use #2 and #3 Hi-Heat for some exhaust manifold work, or use cast Iron rod with #2 and #3, I sometimes grind out crack but usually dont, I use excess heat and melt out the crack as I go,, Different Process.

Thanks for any additional pointers.

-brino
Click to expand...
I'll do the best I can, haven't felt well for a few day, old ticker problems..

No special recipe.

During tinning, I will use a little of each, just a touch on the rod, sometimes the impurities in the cast will cause problems tinning, so to be sure the tinning takes place, It's a habit for me to use a little of all three.
You can tin the area to be welding all at one time if you want, or just go ahead a little bit, I usually go ahead a little bit and then do some filling, then some of that process is done, then you can concentrate on filling that area, if at any time you see that the brass is not flowing smoothly, a touch of all should take care of the problem.

If you see the part is cooling down to fast, heat it back up, I always use a big tip, bigger than you would think for some parts, that way the heat is always there, and by manipulating the temp at the tip, (which is done constantly, for me, by and moving the flame quickly in and out of the area also controls the heat/temp. What ever you need to do to keep a nice red heat or close to red heat and to keep the brass flowing nicely, dont try to fill a spot that wont tin, its possible to cover that area up to not be seen with brass but there will be no tinning underneath, I just concentrate on the area I'm filling.

Use to weld 4 ft cracks, 3" wide after ground out, in giant earth moving equipment transfer cases, what a very hot job, sometimes face shield would melt and face would blister, that was in the early 70's, but then It was hard to find anyone to do that type of work, so $4-5 thousand dollars was nothing to an oil field company for 2 days work, when the new part was 15-25 thousand dollars and 2 months to get it from overseas.

That's about it, and don't breath in the fumes to much, could cause some health problem, for me it made me drink alot of cold beer after a days work, or if I had sore arms and shoulders I would rub alcohol on them from the inside out.

If somethings don't make sense to you I apologize, this is the best I can do considering how I feel.

If you trust me and want to send me your private email, I might have some stuff to send you...

Hope this helps you
Have a good day,
Tim
 
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