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Farga catalana: The Catalan forge


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This all started because a fellow bladesmith from Barcelona, Miquel Segura, send a book to me with a compilation of the information available on the Catalan forge. Called “Farga Catalana” by the locals, this forge was capable of continuously processing batches of 500 Kg of raw ore together with a similar amount of charcoal in a space of about 50 x 60 x 90 cm and turn that ore into 150 Kg of iron. Since the ore contained an average of 45% iron, the yield was a very impressive 70%.

 

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My challenge was two-fold. I wanted to try to replicate the process in a smaller size forge and I wanted to use it to make steel and not iron. I also wanted the forge to be reusable with very little repairs before the next run.

 

As it is usual for me, I started at the drawing board. After some thinking, I settled in a set of dimensions of about half the length for all sides. That will give a final volume inside the forge of about an eighth the size of the original forge.

 

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I built the forge out of bricks. Casting the bricks yourself allows to vary the composition to suit your purposes. It is also cheaper than buying the standard refractory and insulating brick. It also allows me to make them in the size that I want. Since I wanted this forge to last, I modified the composition of the materials to allow for that purpose. Mostly fireclay, vermiculite, ash and sand.

 

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At this point I needed to consider how I was going to run the forge. The Catalan process calls for a steel wall to be placed sideways inside the forge. This wall will divide the forge in two sections. A smaller section further away from the air blast is used to charge the ore. The larger section is used to charge charcoal. The wall remains during the first stages of warming up the forge and is later removed. My first run was meant to be a test of the concept. I did not want to use good quality ore so I collected dirt from around the anvil, otherwise known as scale, from forging W2 steel. I had about 5 Kg of this material and it seemed like the appropriate candidate ore for my test run.

 

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I set my steel divider inside the forge and charged 2 Kg of ore together with some silica flux on the chamber furthest away from the tuyere. Then I charged a small amount of charcoal on the other chamber and lit it.

 

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I progressively filled the charcoal chamber to the top and within half an hour of starting the fire the temperature measured in the ore chamber reached 1500 degrees F. In the next half hour the temperature went past 2400 degrees. I was not paying attention and the heat melted my probe. I was using a small 50 CFM blower wide open. I retired my old shop/vac from the smelting job because it was too loud. The blower is nice and quiet. I was not sure if it will produce enough air flow but the proof is in the new probe that I will have to buy for my pyrometer.

 

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At that point I removed the steel plate that I used as a divider for the chambers. I continued to pour charges of about 500 g of ore and 1 Kg of charcoal keeping the ore to the further wall of the furnace. The charges went in at about 15 minute intervals. At the end of the next hour I had run out of junk, I mean scale, to feed the forge.

 

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So within 2 hours I had used up 12 Kg of charcoal and 5 Kg of ore. It was time to let the fire burn down. As the charcoal level lowered I noticed that the walls of the furnace held up well to the heat. Because all the ore went in the forge further away from the tuyere, I did not run into any trouble with clogging of the airflow. I did not use enough ore in this run to create an overflow problem either.

 

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I had tried to probe inside the forge with a long piece of rebar to see if there was anything at the bottom. And yes! There it was a nice lump of something. A mixture of iron, steel, slag and charcoal dust that the Catalan smiths called "masser" and we call bloom. It weighted at 2.5 Kg right out of the forge but after some hammering and cleaning actually contained about 1.125 Kg of metal.

 

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I considered this first run a successful proof of concept. For the next one I will use better ore and more charges and will see what this forge can do. The walls of the forge remained without damage so it is already set to go, I just need to get some charcoal chopped.

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Thanks guys. The steel fracture has a nice crystalline structure. The bloom is not homegeneous and some areas spark around 1%, others lower and there may be some iron in it too. At one point in time I will forge the bloom and I will update the results here.

 

Mike, I find it interesting to experiment with different formats and ideas. That helps keep things interesting. Of course with every new "thing" there is a learning curve. This particular forge has many potentials and could have many different uses.

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Hi Jesus

 

 

I like this project...it´s good thing to try some different styles and ideas.

Forge it self look´s simple, but is actially verry efective.

 

It sure would be nice to know analysis of the bloom...Spark was 0,0 -1% thats good..do you think

there could be some alloys...?? Mn, Cr, V Im just quesing here becourse scale that you used is modern stell scale.

 

Looking FRWD to see waht you create form it.

 

Thanks for great topic Jesus :)

 

Niko

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Darn it, you did it before I did! :angry::lol:

 

I've been wanting to try a Catalan forge run for about a year now, but I'm glad you did it first to smooth the road, so to speak. Much faster and lower maintenence than a shaft furnace, at least with the smaller ones. The old bloomery forges around here were of the Catalan type about four feet square and produced iron blooms up to 30-40 lbs in one go. They also had the big water-powered trip hammers to consolidate the blooms.

 

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These were usually blown by a neat-o thing called a Trompe:

 

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Water-cooled moist compressed air as long as you have even a tiny stream of water flowing.

 

Excellent work, Jesus, and I look forward to seeing much more to come! B)

Edited by Alan Longmire
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Too cool, Jesus. Very nice experiment.

 

And Alan, how is that waterjet supposed to work? You run the upper source until the air in the bottom box is exhausted, then what? Plug the top, drain the bottom, and start over? I would think there should be a shut-off, so you don't squirt water into the forge, either... but that's just me.

 

Looks intriguing, though.

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Sorry to beat you to the point Alan but you are better off letting me do the trial and error. Less work for you.

 

The "trompe" is an ingenious way to pump air into the forge by something similar to the Venturi principle. By having a water reservoir at a higher level and allowing the water to rush down a drain pipe, air is drawn with the water through holes along the way. The wind-chest placed at a lower level is supplied with a mix of water and air coming from the pipe. The water escapes through a side opening set at a lower level in the wind-chest and the air scapes through the tuyere set at a higher level. The water flow is regulated at the top reservoir by a tapered cone introduced into the opening of the pipe. By supplying the water from a nearby river or waterfall of sorts the system will work by gravity at a cost of zero dollars. The same water source powered their hammers.

 

The downside is that the air flowing into the forge through the tuyere contains a significant amount of moisture. One intriguing part of the functioning of these forges is that part of the charges was water. I am still scratching my head to understand the logic of this and it may have to do with saving fuel. A typical charge contained mineral ore, charcoal and water.

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Sorry to beat you to the point Alan but you are better off letting me do the trial and error. Less work for you.

 

I am in your debt, sir! :lol: Thanks, and I really do mean that! Me and my ten pounds of high carbon forge scale. ;)

 

Chris, the tromp(e) is a continuous blast source for the reasons Jesus mentions. The largest on record used an abandoned mineshaft to power the ventilation system for a new shaft in the copper mines of upper Michigan. It is a cold, moist blast, which seems to have the effect of helping produce a "cleaner" bloom. Hot blast has a higher productivity, but when coke especially is the fuel it increases uptake of undesireable elements such as phosphorus and sulfur. They do not produce enough blast for a large (4-6 tons per day) blast furnace for cast iron, but they're great for bloomeries. If I had a small stream on my property I'd build one in a heartbeat. Well, the lottery-win retirement plan is still in effect, so one of these days you may see one, along with a puddling furnace and an iron mine... :rolleyes:

 

Edited to add: I bet the extra water in the blast helped keep the temperature of the charge low enough to produce a bloom rather than cast iron. As we know, when water vaporizes it requires heat to do so and carries said heat away as long as it isn't contained. Thus, you can run the blast stronger with the resulting greater yield without risking a slug of cast iron in the hearth. that's my theory, and I'm sticking to it until proven wrong! :P

Edited by Alan Longmire
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Edited to add: I bet the extra water in the blast helped keep the temperature of the charge low enough to produce a bloom rather than cast iron. As we know, when water vaporizes it requires heat to do so and carries said heat away as long as it isn't contained. Thus, you can run the blast stronger with the resulting greater yield without risking a slug of cast iron in the hearth. that's my theory, and I'm sticking to it until proven wrong! :P

 

Alan,

 

The moisture in the blast does have the effect of cooling the process, the steam generated reacts with red hot carbon to produce hydrogen gas and carbon monoxide (just like the old producer gas generators did). This hydrogen greatly improves the reduction rate of iron oxide to iron (a faster rate than carbon monoxide alone). The catalan forge operators were aware of this phenomenon and could run their process "wet" or not so "wet".

 

Jan

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