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Old 01-19-2005, 02:08 PM
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Welding cast iron exhaust manifolds

I need to cut and modify the outlet on a '49 Cad exhaust manifold. How do you MIG weld these things?

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Old 01-19-2005, 03:21 PM
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Preheating them and using oxyacetylene would be the best way.

Something that rare I think you should practice on some junk stuff first. Unless its something minor like building an ear back up exhaust manifolds are hard to weld and not have them crack or warp.
You would be better off taking them to a pro and even then theres no guarantee.
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Old 01-19-2005, 03:26 PM
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I do not know about mig welding cast but you can stick weld it. I have seen a exhaust manifold and two construction compressor air outlet manifolds welded with success. We used welding rod from Certainium Alloys, a old timer that was a salesman would come around the shop, the guy could weld most anything, the knowledge he had was amazing.
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Old 01-19-2005, 03:27 PM
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The only wire that I could ever get to work correctly on cast iron was Linde "Easy grind" it left a soft bead compared to the "harder than the hinges of heII" beads normal with mig. Unfortunately they no longer market it.

You might try brazing wire in the mig. I have had limited success with it welding ends and edges of blocks and corners of manifolds. Heat the iron well with a torch, braze a short bit and repeat heat, braze again, etc. Then let the piece cool VERY SLOWLY! I then mill the faces and USUALLY hve a good repair. Cast Iron is tricky!!
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Old 01-19-2005, 04:23 PM
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Some good information about the specifics of cast iron welding is here
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Old 01-19-2005, 07:47 PM
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Cast iron rods

A buddy of mine who has been a welder for 25yrs. welded a casting for me for my milling machine. He "V" ground the break and then heated the pieces to 500 deg. in a old oven I have in the shop. He then used a "cast iron rod" that came from the welding supply. He'd weld a little and put it back in the stove, then move to the other side and weld a little. When he finished it he went around it tapping on it with a small hammer. Then put it back in the stove and turned the temp down to 450 deg. and let it bake for about 30 min. Took it back out and tapped it then turned it down to 400 deg. Did this dropping the temp gradually till he got it back down to about room temp.
It didn't crack and is still working fine.
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Old 01-19-2005, 08:05 PM
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I am familiar with the method Capt. Zorro is talking about, real close to the way I did it. You have to let it cool slowly to keep it from cracking. An old timer trick is to bury it in sand when you are done.

You have to grind off the oxides just like with aluminum. You will see the iron form a pool underneath the oxides and you can peel them off like a skin with the filler rod. This is if you don't remove them well enough.
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Old 01-19-2005, 08:45 PM
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To actually properly cast weld cast iron, the pre-heat should be done at 1000 degrees F. The part that is to be gas welded is kept hot while it is welded. The base material is liquified and the filler material is added.

This is a highly skilled operation, and to properly heat the part, you need a firebrick oven and ceramic wool blankets to cover the part while welding.

This is the only proper way to weld cast and avoid any stress in the welded material.

The part must be heated and cooled off slowly.

Powder welding is another method, and only requires a pre heat of 700 degrees the welded area is heated up with a rosebud type tip to a dull red and molten metal powder is sprayed into the crack. The big advantage to this method is that the intense localized heat of electric welding is avoided, reducing the chance of stress forming around the welded area.

Electric welding of any type should only be used on corners or ears of cast parts. It applies too much heat into a localized area, creating stress in the iron and inducing more cracks.

A corner piece can be stick welded because the the material can expand to the outside, thus avoiding the stress crack.
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Old 01-19-2005, 09:08 PM
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Nickle Rods are made for welding on cast iron, mild steel-nickle alloys. I run them at 90-100 with a 1/8" rod. It is hard to weld with and get it to keep from craking. I have only done it a few times and it was hard to do
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Old 01-20-2005, 08:15 AM
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I've welded cast iron with a torch and iron filler rod and just heated it up with a rosebud, welded it, then wrapped it in a fire blanket. This worked wonderfully.

If you have a larger weld to make then it would be a good idea to hit it with the rosebud a few times while welding to keep the entire casting up to temp.

There is also a special flux to use with the rod.


Steve
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Old 01-20-2005, 09:48 AM
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Be forewarned! Some cast iron manifolds can be next to if not impossible to weld due to the carbon and graphite content. Some people will tell you one way is the best and then someone else will tell you something different. The truth is that cast iron grades and types are so varied that there is just no blanket do-all method for welding all cast iron. NEVER try to weld it with an alloy steel or mild steel rod or mig wire! There are several types of nickle welding rods(electric) available and some can be quite costly running about $30 or more a pound but more expensive does not translate to better in the sense that they would be stronger or less likely to crack. The expensive rod has more nickle(about 99% or higher) and is used when the weld area must be machined or drilled and tapped. You can use the cheaper rod to attach parts but if you need threaded holes in the weld area you MUST use the high nickle machinable rod. Also some may tell you to use stainless steel rod or wire DON"T DO IT! if it worked there would be no need for nickle rod. If you have even a tiny amount of steel rod or high iron content cast rod in the weld then the transition area between weld and parent metal will be harder than a tap and therefore cannot be even drilled much less threaded. I have been a certified welder in the mining industry since 1968 and I have tackled a lot of cast iron but I tend to avoid it when possible as some castings can be a real bear. Most manifolds are difficult but some will weld quite easily and the only way to find out is to try but I would suggest checking with someone who has experience welding cast iron before cutting on them.
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