Cast iron is a material that is used in farm and automotive applications. It is a great material but sometimes failures require dramatic repairs. In this article I'll tell you about a repair I made on the head of an old tractor using a stick welder.
Step 1: Research
I'm not much of a welder, though I wish I was. So a project like this was kicked off with a lot of research on the interwebs/intertubes. Use the Google machine, watch videos, read a book, talk to old people. The standard research bit, but without note cards.
However, too much research can be a problem. If your research gets in the way of actually starting the work, stop, get out of your armchair, and do something.
Welding tips and tricks is a good YouTube channel. He even has a video on welding cast iron.
Cast iron comes in many grades. Some are easily welded. Others are more difficult and require local pre-heating. Sometimes the whole casting must be placed in an oven and brought to something like 900 oF. So you may have to try other methods if welding doesn't work. Alternatives are buying a new casting or consider stitching or other obscure repair technology.
The success of your repair depends somewhat on the location of the repair and the geometry of the situation. The tab I'm welding onto the head is about the best possible situation because it's small, connects only at one end, and the alloy is easy to weld. It has to do with how the metal shrinks and which directions that the casting and weld material pull at each other.
One technique that's all over the internet is the peening method. With the casting at room temp, weld about 1" and peen it with a slag hammer while it's red hot. Apparently it relieves stress in the weld as it cools and reduces the chances of cracking. I didn't need to do this for my project but there are so many people who advocate this methods that I thought it should be mentioned.
Step 2: Disassembly and Fit-up
There's a variety of advice about how to weld cast iron but they all agreed on preparation. Degrease and remove paint. Grind edges back so there's space for the electrode as it melts into the material.
My brother is a real welder and he insists on removing the flammable materials within 3 meters and have a 6-hour fire watch. I couldn't do all that but I did remove the fuel line and tank. I also cleaned all of the oil and other residue from the area where I was welding and constructed a spark shield out of aluminum flashing. I still had a fire because I didn't clean the oil far enough back. It was small and I caught it right away but it shows that there's real risk.
Step 3: Welding
Actually start to weld. The electrode starts easily enough but it burns a lot different from 6011. I had very little spatter.
I used Hobart brand high-nickle electrodes. It was whatever Fleet Farm was selling. The pack only has a few rods and it's expensive--more than 10 $.
Oh, and this project is your excuse to buy an LCD welding helmet if you don't have one already.
Step 4: Finishing
I'm not very good at welding so it was a mess when I finished. Going uphill was the worst. After grinding down the welds, it looked OK. There is some porosity but it's OK because this weld is only holding up part of the battery, some of the sheet metal, and instruments. If it breaks, no one is going to die.
I think it took 4x as long to clean up the welds as it did to make them. Fit-up took longer than that.