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I Forge Iron

Repair to a Firepot


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Old cast iron is almost impossible to weld with nickel rods....even with pre and post heat they still crack and crackle into more pieces than you started out with!!....brazing is iffy unless you coat the inner pot with refractory.to help keep the heat down. Best luck ive had is with straps of mild steel being bolted across the cracks in several spot to hold it all together. prebend the straps to match the firepot radius and use grade 8 bolts. for the last forge i rebuilt i had a "donut" cut at my fab shop and using another forge dished it out to match the inside contour of the original pot and bolted in place. (see my rebuild post "whats missing on this forge " and "its not missing now" to see what im talking about. Good luck and i hope you manage to save the pot.

MMM Fab & Forge

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For welding it, 3/32 nickle 99 rod. Preheat the iron, use short (1") beads 6" apart to help even out the heat. Normally peining is necessary, but that may cause further cracks and brakes. After you are finished bury it in something to slow the cooling rate (sand, ashes, vermawatsits :wacko: ). It's a 50/50 shot that you'll put it off. Those rods run 25 to 30 a pnd.

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I wouldn't touch it with a welder unless you're really good. And even then you have to wonder if it would just be easier/cheaper to fab up a new firepot or buy one from Centaur Forge. Bolting straps across the crack and then covering those straps with fire cement would be the easiest, cheapest method, and would have a good chance of working.

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I'll be back shortly with a mix from an old blacksmithing source that might actually help you fix this ...

From a long time back in an old blacksmithing archive article..


A cement for stopping clefts or fissure of iron vessels can be made of the following: Two ounces muriate of ammonia, I ounce of flowers of sulphur, and I pound of cast-iron filings or borings. Mix these well in a mortar, but keep the mortar dry. When the cement -is wanted, take one part of this and twenty parts of clean iron borings, grind- together in a mortar. Mix water to make a dough of proper consistence and apply between the cracks. This will be useful for flanges or joints of pipes and doors of steam engines.

Yet another formula...

Iron-Rust Cement

The iron-rust cement is made of from fifty to one hundred parts of iron borings, pounded and sifted, mixed with one part of sal-ammoniac, and when it is to be applied moistened with as much water as will give it a pasty consistency. Formerly flowers of sulphur were used, and much more sal-ammoniac in making this cement, but with decided disadvantage, as the union is effected by oxidizement, consequent expansion and solidification of the iron powder, and any heterogeneous matter obstructs the effect. The best proportion of sal-ammoniac is, I believe, one per cent of the iron borings. Another composition of the same kind is made by mixing four parts of fine borings or filings of iron, two parts of potter's clay, and one part of pounded potsherds, and making them into a paste with salt and water. When this cement is allowed to concrete slowly on iron joints, it becomes very hard.
******************************************* Below formula
The following link might be better suited to your particular repair (scroll down to the mixture) Brimstone=sulphur & Black lead=graphite

Cement For Cast-Iron Tanks - Cement For Heated Objects Cement For Cast-Iron Tanks The following is recommended for damaged places in cast- tanks, cisterns, etc.: Five parts brimstone, 2 parts black lead, and 2 parts of cast-iron filings, previously sifted. Melt together, taking care that the brimstone does not catch . The damaged place, perfectly dry, is well heated by laying a piece of red-hot upon it, and is then stopped with the cement previously heated in a melting ladle until it becomes Read more:

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