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Obtaining wrought iron


Carlos Lara

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On 5/8/2023 at 2:59 PM, Alan Longmire said:

Helpful hint, here:  Try a simple finery forge before going to the trouble of building a puddling furnace.  You don't have the large volume of slag you need to run a puddling furnace.

 

A finery forge is pretty much the hearth-style forge that people are using to make steel in the Bloomers and Buttons subforum, except you're trying to do the reverse, i.e. turn high carbon iron into low carbon iron.  For that you will need to run it oxidizing, with the air blast directly on the iron as it melts.  You'll need slag for this as well, but you can use silica sand to provide that.  This does require charcoal, and a lot of it.  Not as much as if you were trying to make a steel bloom from wrought, though.  Start with the regular seven-brick hearth, but put the air blast about 3 to 5 cm from the floor, entering dead level.  Chop  your charcoal into 2.5cm cubes.  Turn on the blast, get a good bed of coals going all across the forge, then add more charcoal until it's about half full.  Keep the blast moderate to medium-high.  When all the charcoal is uniformly white hot, add a handful of silica sand and then start melting your cast iron directly in front of the tuyere.  Add a little more sand, say until you've added about equal to the weight of the cast iron you're adding. Now comes the fun part: Once all your iron starts melting, stir it into the sand. As it starts forming the puck in the bottom of the forge, keep turning it into the blast and watch the sparks as the carbon burns off.  It's sort of like puddling, except in an open fire.  You don't want it liquid at this point, but try to keep it pasty.  As it decarburizes more fully it will get stiffer and stiffer, and it will have voids and pockets of molten sand that has absorbed some iron and become slag.  This is your bloom.  Keep that moving in the fire, adding charcoal as needed to maintain a white heat, until it's pretty much stopped sparking like high carbon.  If you're working alone, a five pound/2Kg bloom is about the biggest you can handle; try for a 1kg or smaller until you get the hang of it.  Once it's fully decarburized, lift it out, still at a white heat, and gently forge it into a pancake with a large hammer.  This will consolidate the bloom back into a solid lump.  Don't hit it hard until it's solid.  You'll feel it go from spongy to hard.  When it cools below yellow, put it back in the forge and bring it back to a white heat with the blast turned way down from what you used to melt it, then remove and keep hammering it into a hockey puck-sized chunk.  Then, take that puck and gently forge it into a bar.  Add sand as flux if it starts falling apart. When you have several of these bars, you can start welding them up into larger bars, always drawing in the same direction.  This will set up the classic stringy structure of the wrought iron.  The more you do this stacking and welding, the more refined the iron will get.  

 

Sound easy?  ;)  It's a lot of very hard work, but it's the way it was done between around 1450 and 1780 in western Europe, and it's still easier than puddling unless you have large equipment.  Puddling really increased the rate of production, but it relies on those economies of scale.  You need five to ten times by weight of slag to cast iron, and you have to keep the furnace white hot for long periods.  I'm also pretty sure you wouldn't get good results trying to puddle using propane.  

 

Finery forges are much easier and don't demand large scale production to be useful.  Most small ( two to ten tons per tap) blast furnaces supported two to four finery forges for wrought iron bar production, depending on how much of their cast iron was hollow wares versus pig for sale or trade.  They also universally used water-powered trip hammers of 200-700 pound falling weight to consolidate the bloom and draw it into barstock.  It's possible to do it by hand, especially with a team of strikers, but it takes a lot of time.

 

This is a long-winded way of saying it's generally easier to find wrought than to make it from cast or steel.  

 

After you consider the work it takes, check ebay or etsy Canada for anchor chain.  Or call these guys, the links in the bottom right photo are nice: https://www.piecesofship.com/pageShipSalvageAnchorsPropellers.html  Pretty sure those are wrought.  The dogbone in the middle of this type of stud chain link is cast, don't try to forge those.  They fall out when you cut and straighten the iron anyway.  These guys have good wrought chain, but no price listed... https://marinesalvageantiques.com/product/ship-anchor-chains/  These chains are the source of the wrought iron Japanese toolmakers use.  

 

I'm crazy enough that I enjoy the process of making iron.  It's not the most economical way to get the stuff by a factor of at least ten, though... :lol:

hey Alan, first time post/long time reader. Would you add small bits of the cast iron at a time similar to doing hearth steel? Also any good recommendations for silica sand? Does it need to be a specific type? 
thanks for help

anthony 

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Welcome aboard for your first post!

 

Unfortunately, I don't know for sure.  I've done bloom smelts from ore, direct crucible reduction, hearth steel, and wootz, but I have not yet done a finery fire.  I suspect you just feed the cast into the hot spot like with hearth steel, since it was done so regularly as a means of commercial production of wrought between ca. 1450-1790. The slag is going to be the key.  Back in the day the finery fire was a flat-bottomed side-blown square hearth about twice as deep as a regular forge fire, say 18 inches square by 16 inches deep.  Out in the boonies they still used them into the 1860s at places like the Merrimac Ironworks in Missouri, long after the big furnaces in the east had built puddling mills. 

 

I'd try it by making a melting hearth like for hearth steel, maybe a bit bigger if you want a bloom bigger than around three pounds.  You'll need to play with tuyere position to get the best decarburization, too.  Something like a 17 to 20 degree downward angle about 2 to 3 inches from the floor would be a good starting point. If that doesn't form blooms, maybe level the tuyere out a bit more...  Just thinking as I type here, I could be totally wrong.

 

Just going on theory here, I'd say if you don't have any actual bloomery or blast furnace slag to use (and few do!) make the first run using cast iron and a lot of clean white silica sand. Sharp white sand like for masonry work is nice and clean. This will probably result in a nasty mess of slaggy black goo.  This is a good thing.  With the bottom of the fire lined with this goo, melt in more cast iron until you have a pasty mass just below the tuyere. If you've run the blast right you should now have a decarburized wrought iron bloom under there somewhere.  If the blast wasn't hard enough you'll have steely high carbon bloom or even cast iron.  

 

In theory a strong blast will decarb the cast as it melts into the puddle of slag.  Once the iron is coated in slag, the slag itself will prevent further decarb, but may steal iron. Thus the iron as the first step in producing the slag bed.  A good iron-rich slag will prevent further loss of iron while also assisting with decarb via the iron already in solution.  These prills of steely iron will explode in showers of sparks as the blast hits them.  You'll need to keep the bloom turning in front of the blast once it gets big enough to stay together and solid enough to keep from incorporating bits of charcoal into itself.  

 

Aiden is the only one I know consistently running a hearth these days, but he's a little busy with his MS thesis and as such probably doesn't have the time or inclination to do the long period of experimentation it may take. It can't be too hard once you've got some iron-rich slag, it's just going to take experience to know how hard to blow it and for how long.  If I had three months off in the winter and a large supply of charcoal and pig iron I bet I could figure it out.  I have a few cast iron sash weights waiting on that day.

 

 

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Thank you for doing the grunt work!  Do let us know how it works out for you.  I know Lee Sauder has done it in his regular side-blast forge, so it is doable.  But Lee knows far more than us mere mortals about ironmaking.  

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Would that be Ferromancy?

 

Just asking

 

G

  • Haha 4

"The worst day smithing is better than the best day working for someone else."

 

I said that.

 

If a thing is worth doing, it is worth doing badly.

- - -G. K. Chesterton

 

So, just for the record: the fact that it does work still should not be taken as definitive proof that you are not crazy.

 

Grant Sarver

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