MTFCA Forum

Why is it so hard to weld two broken pieces of cast iron together?

I'm no expert, but several things come to mind: Cast iron can gave different characteristics and levels of quality. It's not all the same.
Cast iron is often oil soaked or rusty. Cast iron is brittle, and it expands a lot when heated to welding or brazing temperatures, which makes avoiding warpage and cracks difficult to avoid. Things like exhaust manifolds are usually heavily oxidized from heat exposure, and can be extra-difficult to weld or braze. If the weld is harder or thicker than the iron being welded, it's likely to cause a crack when the job cools. Specialized welding rods are available for cast iron, and some claim to make the job easy. I have no experience with them.

Shops that specialize in welding cast iron will have specialized equipment like furnaces to heat large parts and methods of slowly and evenly cooling welded objects.

Cast iron has some of the characteristics of glass. It does not take kindly to having heat applied to one area of a casting.

jiminbartow wrote: ↑

Wed Feb 28, 2024 12:46 pm

Why is it so hard to weld two broken pieces of cast iron together?

Technique and your rod is likely where you are struggling. Google 'Muggy Weld' and consider using one of their rods. Depending on what it is that you are working on (-exhaust manifold, engine block, cylinder head, etc.) will dictate what product to use, but we have used it in our shop with great success.

There is a pretty good discussion here regarding cast iron welding with some links:

http://www.locknstitch.com/cast-iron-welding.html

I learned to arc weld cast iron 60 years ago. Don't get in a hurry. Preheat, use soft rod, Weld for a very short time maybe 3 seconds or so, then immediately peen the weld bead with a chipping hammer. Repeat this but allow the weld to cool.
Welding cylinder heads was successful most of the time. Today, I would use an infrared thermometer in order to monitor temperature if I did any cast iron welding. Probably will never try it again unless I wanted to entertain mysellf.

Welding oily iron causes hydrogen embrittlement, which will most likely result in a break.

Art Mirtes

Art Mirtes

The trick to brazing cast iron is to heat it up cherry red with a torch braze your pieces together then keep the torch on and let it cool.with heat very slowly, do not let the cold ambient air hit the hot cast iron.
I have had great success doing it this way.

There you have it. Welding cast iron requires skill in manipulating the heating/cooling, and the impurities in the iron itself, like carbon/oil/rust. The materials need to be as clean as possible. Rust can be ground off, correct heating will largely negate carbon and oil contamination. Slow cooling will reduce cracking at the weld sides.
I don't have these skills, so I use a pro.

Allan from down under.

Some Model T parts are too rare for a novice to practice a repair on. About 10-12 years ago, I had A Waukesha-Ricardo and a Simmons head that both had small cracks. I sent them both to Midwest Cylinder Head Co. in Nevada, IA. for repair. The repairs they made where undetectable when I got them back. I eventually sold both heads and I never had a complaint from the buyers as to the repairs.

About 20 years ago, I had an old timer repair an Edison Standard cylinder phonograph bedplate that had been dropped and broke in two pieces. Before he started welding, he prepared a tray of sand, saturated with oil. When he was done welding the repair, he immediately hurried and covered the bed plate with the oil impregnated sand and let it stay there until cooled. The repair was successful. Once the weld was ground smooth and the bedplate primed and painted, the repair was invisible.

I don’t know why he used the oil saturated sand, but I assume it was to regulate and slow the cooling off of the weld so it would not cool to fast and crack. The important thing is, the repair worked and I’m using the phonograph to this day. Jim Patrick

Welding takes practice to begin with!
After high school in the 60’s I went to a 2 year welding school and have a degree in Welding technology. That was 50 years ago and welding technology has advanced somewhat.

But what hasn’t changed is the techniques and heat control in stick arc, mig, tig and oxyacetylene welding.

Cast Iron welding takes PRACTICE. If you have basic skills such as manipulation, heat control and etc you can weld cast iron. Most of us with Model T’s have junk cast iron T parts such as cracked blocks, transmission covers and a few other cast iron parts.

Use those to PRACTICE on before trying to fix your cast iron part. DO NOT try to repair your part before getting practice on old parts. Before you haul off you cast iron to the scrappers save some for welding practice. PRACTICE MAKES PERFECT.

Many years ago I had the open valve engine on my '10 repaired along the water jacket where it had been weeping in numerous places along a number of spider cracks. The fellow who did it was a true master. He started by cutting away all the damaged area and sent a piece off to be analyzed. He then made up a cast iron patch and obtained cast iron rod that matched the composition of my block. The next step was heating up the block slowly over a number of days to the temperature he wanted. Once it reached the right temperature he made the repair at that temperature working under an insulated blanket and let it cool down slowly over a few days. When he was done you couldn't even see where the repairs had been made. That was over 30 years. Wish he was still around.

For small projects I have had great success with my powder spray torch using a nickel alloy powder. Big stuff like rear main bearing webs ripped out by a broken crank I send out to Lock N Stitch in Turlock. They are the best at what they do.