Hi folks, the final head scratcher (I hope) in putting together my forge is that the exhaust cowling is cracked in several places.

Any tips on the best way to fix it? I was planning on drilling the end of the cracks (if I can find them!!!), then grinding out the cracks, doing a little preheat with the propane torch and arc welding it together with some nickel / iron rods, followed by a little peening from an air needler, and a slow cool down (not sure how yet!).

Does that sound about right to you?

Anyone know how I can get it onto my work bench without it breaking under its own weight?

Cheers, Al.

Yup, sounds good but I've been known to build a wood fire in the barnlot to pre-heat cast iron stuff...a good bed of coals heats a general area fairly well after a couple of hours. good luck!

What you propose is a sound procedure for attempting to repair cast, so long as your rods are compatible with the metal, note I said "attempt" as it might not work even then. Take dimensions in case you want to fab one similar in mild steel. In a last try scenario you could stitch across the cracks with heavy wire or tack up with the mig after turning the amps up and cleaning out the cracks with the grinder. Whichever method you attempt to weld with just try a series of tacks evenly spaced to keep the HAZ small as possible. good luck.

As David points out trying to weld cast iron is a bit of a 'Yoda' job (Do or do not, there is no try ) Preheating is important, the right welding rods are crucial, and letting it cool evenly and slowly is paramount. I welded a piece of cast iron on the arms of an old drill press that went brilliantly right up to letting it stand and cool, at which point it went 'plink' and cracked. Second time I left the arm in the fire on a bed of yellow/orange coals (without any air) and welded it, then let the lot slowly die down until the fire was cold. No 'plink' and the drill press is now in daily use. Oh, by the way, I did say weld IN the fire, coke, coal, and charcoal are excellent conductors. (Another gem from Dale Russell)

Thanks guys.

David - what is the advantage of tacking with the Mig? Its 400 amps, so I'd better not turn it up too far!

My alternative method was to either mig it or tig it with maybe 309 or 312 stainless? I hear that can work. Any thoughts?

The arc rods I was considering using are for cast iron (high nickel content).

Cheers, Al.

Al, as I said the procedure you propose has as good a chance as any, go with that first.You will find out fairly quickly If the rods are compatible, short runs only, each end, then in the middle,then split the difference until you have it done without too much heat build up but cooling it as slowly as possible and gently peening as you go, just as you said. If the rods are not compatible then grind away any deposit and try stitching it with the mig, just little tacks, the mig is cooler. the 309 for dissimilar metals might be worth a try with the tig. good luck.

I have had good luck taking old blankets of fiberglass insulation and laying over the part to keep an even and slow cool down process making sure the whole part is covered and holding in the heat.

I don't know if it would apply to a firepot, but machinable (high nickle ) rods do not stick well to an automobile manifold. The cheaper non machinable cast rods do better. Whether it's the repeated heating and cooling or some chemicals from the exhaust gas, I do not know. I have welded some cast iron bath tubs as you suggest with decent results - plugging the holes for use as a livestock water tank.

JWBIRONWORKS gave me an old rivet forge that had a crack through the entire pot; he brazed it back together. Its traveled from Indiana to Georgia and been kicked around a good bit and still holding together. I've also had pretty good luck using Rockmount's Jupiter rod., and once I even managed to get some Lincoln/Electric 7018 to work...only once though. Preheat, weld and inch or so, let it cool a bit, weld and inch on the other side, repeat ad nauseaum. It still might 'pop' on you though. Cast iron is a pain.
Mickey

Al:
You might also use a technique used on cracked engine blocks where you can't preheat. You take all day (or two), vee out the crack, weld a half an inch and peen. Then go do something else. Come back in a half an hour and do it again. Don't let it get hot. Go have another cup of coffee. Good luck. Either method should work.
Warren

Take your cast rods nock of the flux sand them clean and tig it up. Heatit up v it out and you should be fine. I do it quite often with cast iron pumps.
Travis

i used to weld up broken casting using oxy acetylene we veed out the crack and pre heated the casting and used a cast iron filler rod with a flux coating once welded the casting was post heated to prevent fast cooling which would cause a fracture and then we linished the casting to smarten it up . all the best

If you can tig, as you said in your post, get some tig brazing rod and use that combined with Warren's timing suggestions. However, your hood will remove more smoke if you get rid of that old one and make a sheet metal one with a 12 inch dia. stack on top of it. At the very least you will want to add a back panel and some partial sides to that antique hood to improve draw.

Brazing would be my first choice as the success rate is usually higher (unless you are quite familiar with welding cast). If you do decide to weld, it helps to strap it with steel if the design will allow it. Imagine stitches across a cut - short pieces of flat steel (perhaps 3/4x3/16?) spaced regularly and welded using Ni rod.

My Beaudry hammer ram is cast iron and was broken in half across the middle when I bought it; I cut a piece of 1/4 plate to size and welded it to the front of the ram using short stitch welds followed by peening. This repair has held up to regular use for 20 years and shows no signs of letting go.

I have welded cast iron using 55% nickel rod many a time. These electrodes are expensive, it might be cheaper to buy some thick plate and weld up a new firepot.
Just a thought. If you do go with the cast firepot weld, I recommend preheating, peening and dont bother grinding the finished weld.

Finaly breaking my lurking you might look up a welding shop that specalizes in Flame Spraying Here is a link to read up on the processes : http://www.aa1car.com/library/ar497c.htm

I have seen this done in a few of the machine shops I worked at in the oil patch in the past. It was amazing the first time I saw this.