Technical TOOLS, Welding Cast Iron question

I need to add an extension tube to the drivers side exhaust so the collar will clear the steering box. Headers just won't fit(Sanderson) and $1200-$1500 for custom built headers is not going to work either.

So, I have been looking at the Muggy Weld rods and will most likely order some and give it a go. But before I do, anyone have tips or tricks with welding cast iron exhaust manifolds?
Thanks

 

Preheat them to 400-450 degrees with a weedburner torch... this is a MUST. Make sure they are as clean as possible and go to it.. it will be a weak spot, i have had to reweld the manifold on my 6 a couple times (my own fault for dragging the exhaust) but its always broke at the weld.

 

I have welded cracks up with just my Mig. Never had a complete piece off to reweld though. I sand blast the offending crack ,heat the heck out of it ( VEE it out with the grinder of course) and weld . So far so good.

 

The pre-heat and post heat is critical. The hotter the better, even like 1000F is good. The problem is the very high carbon content of cast iron (approx 3-4%, mild steel is like 0.2% or less) which causes cracking along the fusion line.

If you get it hot enough, a MIG should be OK. Welding cast iron is not easy as mentioned earlier the cracking problems. Slow cool as well.

You can also use a nickel rod and a stick welder, many people have had good luck with that. The nickel helps because it is higher ductility, less likely to crack. Same thing here, more pre-heat is better.

Cast iron can also be gas welded using an oxy-acetylene torch. Requires pre-heating and then slow cooling. Arc welding is going to be easier when handling the hot piece of metal before welding.

See a trend here? Pre-heat is the answer.

 

Preheat and brazing is another solution depending on the strength needed. Brazing does hold well.

 

Sean, do a hamb search on the subject I had to weld a cast iron bellhousing about a month ago.Guys on hamb walked me through it sucessfully .Used muggy rod not sure if any better then nickle ,nickle seemed to well smoother.

 

Thanks for all of the responses!

Terry - I planned on heating the manifold in a gas BBQ to get it up to the 450-500 degree range. Do you think that will be an acceptable temp? Concerning the cool down , should I put it back in the grill and lower the temp over time or just let it cool down in open air?

I'm just wondering if it would be a better idea to farm this out to a pro. Know of anyone in the area that could do this kind of work?
Thanks again.

 

Flatdog - Thanks. I'll do a search.

 

In my shop we weld a lot of cast Iron. Clean,Clean, Clean, Pre-heat and weld with Nickel and stress releive with a needle gun place in Vermeculite or dry sand to cool--TV

 

BBQ is OK, but I would like to see even hotter. Unless you BBQ can really crank, it may need some supplemental heat from a torch before welding. The whole piece does not have to be at the high temp, but make sure there is no sharp temp change, heat it evenly over a wider distance. Your weld will make enough stresses in the piece without adding additional heating/cooling stresses. That is why pre-heat is so much help. For cooling you can just close the BBQ and turn off the heat, that will be fine.

I did forget that to peen the weld is an old trick that helps as well. You can do it manually, but an air tool is really nice.

 

I have found that Stress relieving is just as important as the pre and post heating. I do it with a ball-peen hammer, but I imagine a needle scaler would work pretty good too.

I use a Rosebud on an Acetylene Torch to pre-heat, and I pre-heat a fairly large area around the crack/joint. Immediately after welding with Nickel, I put the rosebud to it again and get a fairly large area around the weld glowing a dull red. I try to keep it that temperature while I am peening the Weld and the surrounding area, then I turn the torch off and continue light stress relief until it cools enough for the color to go away.

After stress relieving, I generally just wrap the part in Refractory Insulation so it cools slowly, but I think regular fibergl*** insulation would probably work.

 

one time we talked about preparing a sand box for the cooldown. basically just bury the thing in sand hot for a day or so.