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Smelting Steel from ore

Nancy Reading

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I've been considering the possibilities of making steel from raw materials. Mostly because I think it would be amusing. Our rock here is basalt, the remnents of an ancient volcano that straddled the Irish sea. I believe I can collect black sand from our local beach as a starting material. Ihave no idea what sort of quality metal I may end up with, but there is a local knife maker who may be interested in making something if I come up with something useable.

This thread then is a project thread to collect together some resources and report on progress as and when any is made. I'm happy for people to chip in if they are also either succeeding in smelting, or wishing to have a go too.

I found this article on iron processing on britannica.com fairly useful as an overview. It seems that a katana furnace, which is used in Japan to make steel is pretty similar to a bloomery furnace. This 'blog post about Japanese swords going a little into the metallurgy of the swords. I went down a few youtube tunnels and found a few that are of interest:

A little delving into the metallurgy suggests that the simple bloomery furnace gives a metal that is easier to work with if you have an unknown ore, because more of the impurities (Phosphorus and Sulphur) are able to escape during the smelting process. When heated in a crucible (known as wootz steel) the post smelt process is more involved to get a fine quality steel.
I'm interested in seeing whether somehow the crucible process could be adapted to let the impurities out as obviously this will be easier to adapt to the rocket stove as per Uncle Mud's furnace. Otherwise there will be a lot of charcoal involved.

Questions:
Would the j tube (or batch) get hot enough to smelt steel without forced air? The video of the natural draft furnace implies this is the case, although their yield was rather low. How hot does it need to be for how long?
Could an open crucible let the impurities escape? I'm thinking load a crucible with ore, appropriate amounts of iron sand, charcoal and maybe some oyster shells to promote cleaning, and heat up in reducing atmosphere in the riser as per Uncle Mud's rocket forge from the low tech jamboree.
How do I tell what sort of quality steel I have (assuming I get any!)? Spark test shows carbon content, but what about the Phosphorus and Sulphur impurities?

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Joshua States

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Nancy,
You are embarking on a journey that will take you down many rabbit holes. I was about to direct you to https://permies.com/t/240809/tech/DIY-Steel-melting-foundry, but I see you have already been there.
The links and reference materials I posted there are excellent places to start. I am not familiar with any of the videos you posted and cannot comment on the reliability of any info they provide.
If I can be of any help along the journey, please reach out to me. I will be following this thread as well.

What I can recommend is using the iron sand in your area rather than the basalt. Extracting iron from ore is a rather tedious process with good quality limonite or bog ore. Extracting it from basalt is another thing entirely. Sifting and sorting the high iron sand out of the batch is an easy process and will help reduce the slag (impurities) in the smelt. Just get one of those big pickup magnets and pull out anything that sticks to it, discarding what doesn't.

A supercharged location of smelting information from modern-day people who are actively pursuing the craft requires you to join Facebook, if you haven't already done so. There is a FB group called "Iron Smelters of the World". and you should join. They keep an online library of historical documents that you can download, and people post frequently when they do smelts, discuss results, and are generally very enthusiastic about sharing information and helping others to learn. I also have some documents you might want to read, which I can send you via email.

Crucible steel and bloomery are very different products with very different processes. While you can put ore into a crucible and make steel, (this was how Pulat or Wootz was made) I would not recommend putting iron sand into a crucible. It boils out of the crucible and makes a gigantic mess in the furnace. Ask me how I know.

I can try and answer some of your questions:

1. Would the j tube (or batch) get hot enough to smelt steel without forced air?
Traditional methods used bellows to stoke the fire to achieve the temperatures required to melt iron. This is roughly 1540 degrees C. Failure to achieve and hold this temp results in an incomplete melt and inferior product because the impurities do not separate from the iron. The airflow doesn't have to be excessive. A hairdryer will work on a small smelter. A shop vac is better though. It must be able to fluctuate speed so you can reduce the flow when adding ore and fuel to the smelter without stopping airflow altogether.
2. How hot does it need to be for how long?
As stated above you are looking at 1540C for long enough to reduce the amount of ore to melt it down. That depends on how much ore you have in your run. In a crucible furnace like mine, I use a propane burner with a blower, and it takes about an hour to reach temperature and about 20-30 minutes of hold at temp per kg of material in the crucible.
3. Could an open crucible let the impurities escape?
Whether you use an open top crucible or a closed crucible, the impurities rise to the top of the melt and can be discarded. Most of the people I know (myself included), making crucible steel use a layer of crushed glass on the top of the charge inside the crucible. This serves a number of purposes. It melts pretty quickly compared to the iron/ore/charge materials and makes a sealed layer that prevents oxidation. It also collects the impurities out of the charge leaving the iron or steel at the bottom. The glass layer is then chipped out with a chisel to release the puck from the crucible.
4. I'm thinking load a crucible with ore, appropriate amounts of iron sand, charcoal and maybe some oyster shells to promote cleaning, and heat up in reducing atmosphere in the riser as per Uncle Mud's rocket forge from the low tech jamboree.
I have not watched said low-tech jamboree, but it sounds dicey to me. If I were to suggest a method for you, it would be to build a small smelter to reduce the sand into iron bloom. Refine the bloom through a subsequent melt and start forging it into bars. Stack, forge weld, repeat as needed to homogenize the material. If it proves to be low grade steel or pure iron, you could refine it in more melts or use it as stock in a crucible melt. The iron needs carbon to become steel. The only way to do that is to melt it in the right atmosphere with a carbon source and pray to the smelting gods that the iron absorbs enough carbon. If it absorbs too much carbon, you get cast iron, which is not a forgeable material. It can be used in a crucible with lower carbon content material to "even out" the carbon content and make it useable.
5. How do I tell what sort of quality steel I have (assuming I get any!)? Spark test shows carbon content, but what about the Phosphorus and Sulphur impurities?
The spark test will give you a rough idea of the carbon content. At least it tells you the carbon content of the area held against the grinder...... To tell what other elements have alloyed with your product requires sending it out to a lab for testing. Bloomery is not a homogenous material. Carbon and other alloying are not uniform across the entire bloom. It takes refinement to create a uniform material, or a contained and complete melt in a crucible.

Some other reputable online information sources:
Crucible steel making: https://www.wootzsmithforum.com/forum-2/
Bloomery and crucible steel making: https://www.bladesmithsforum.com/index.php?/forum/25-bloomers-and-buttons/

I belong to both of these forums and one of your local knifemakers is a frequent visitor on the second forum, but not in the Bloomers and Buttons section.

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Kevin Olson

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Nancy Reading wrote:I've been considering the possibilities of making steel from raw materials. Mostly because I think it would be amusing. Our rock here is basalt, the remnents of an ancient volcano that straddled the Irish sea. I believe I can collect black sand from our local beach as a starting material. Ihave no idea what sort of quality metal I may end up with, but there is a local knife maker who may be interested in making something if I come up with something useable.

Nancy -

You've received a very helpful reply from Joshua, but I'll stick my oar in these waters, just a bit.

I have a coworker who is a custom knife maker. I've bought a couple of his Slojd blanks. He mostly makes knives by stock removal (milling and grinding) and uses a lot of fancy sintered powder metal tool steel alloy blanks. He makes both fixed blades (the Slojd knives or other wood carving specialty blades, or kitchen knives and butcher knives), and folding blades (high end liner lock pocket knives). He also makes sheathes for his knives from vegetable tanned leather. He also does some hand forging, and has built a hydraulic forging press.

One of his ongoing projects is to try to make Wootz steel, using magnetite sand collected from a local beach. We, too, have a lot of basalt around, but not exclusively; it's also interbedded with conglomerates, mud stones or shales (and even a bit of true metamorphic slate) and sand stones. I know of only one small outcrop of limestone (called Limestone Mountain, locally, but it's just a hill, really). As far as I am aware, our local basalt doesn't have a high iron content. There are iron mines (historical and currently operating) within a hundred miles or so of where I am located, but that was exploiting specular hematite (early) and iron oxides (current). My coworker used a magnet, as has been suggested by Joshua, to separate the magnetiite from other material. Where we are, most of the beach sand is actually a fairly "blonde" quartz sand, so the layers of black sand are very distinct, visually. He has collected several 5 gallon buckets (US gallons) of this sand. He is also patient and methodical. He designed and built a high powered inductive power supply to run the furnace. That's beyond what most people could do, but high speed switching power supply design is his "thing", so this is right in his wheelhouse. He's tested the power supply by heating steel bar forging stock. It will make the end of a bolt or bar hot enough to forge pronto - in a handful of seconds - using a properly sized coil. He also has a rolling mill mostly designed, so that he can more easily make bar stock from the eventual Wootz melts. He chose the induction furnace approach because he can more carefully control the melt feed stock and atmosphere (and, he knows a lot about making and building inductive power supplies).

I can ask him if he has any suggestions for you, beyond what Joshua has already provided.

I am interested in the forging aspect of J-tubes, myself. I had recently collected an old hand cranked forge blower in usable condition, and was intending to build a forge pot out of an old heavy truck brake drum from the salvage yard, at least for starts. But, a J-tube rocket (considering I have a collection of salvaged brick, and can get fire brick from a local brick yard) might be a straighter path to the goal, which is to heat ferrous alloys sufficiently that they can be hot worked rather than cold worked. A bit of heat treating, too. Among the projects I have in mind is a shingle froe, for which I have collected a piece of broken truck leaf spring from the side of the road. Though I am not much of a welder (but I am mean with a grinder!), I could try to arc weld the froe blade to a sleeve of pipe or tubing, but I'd still need to flatten the arch out of the spring. I could do that with a charcoal fire in a pit, but I think I'd prefer to have the handle socket integral with the blade, rather than relying on my as-yet dubious arc welding skills.

I'll see what my suggestions my buddy may have. If he has anything additional to Joshua's info, or at variance to it, I'll pass it along. I'm not very knowledgeable about steel smelting and forging.

Michael Cox

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Interesting project. It looks like fun.

One suggestion, if you plan on using black sand, is to separate it from the other minerals first. Black sands tend to be more dense as they contain more iron. The techniques that gold prospectors use for gravity separation can help you out. For small batches you could use hand panning, for larger batches you may want to try some kind of sluice.

While you beach sand looks "black" I would expect it to have lots of other mineral grains as well which can be separated out.

[youtube]https://youtube.com/shorts/mBVwSN-0VBY?si=wfI2lp9uSDNQCJZv[/youtube]

Can can also try using a magnet system like this:

[youtube]https://youtube.com/shorts/FsTKm1wcPww?si=dD_aFpULsbEG4CRG[/youtube]

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Kevin Olson

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Michael Cox wrote:The techniques that gold prospectors use for gravity separation can help you out. For small batches you could use hand panning, for larger batches you may want to try some kind of sluice.

The black magnetite sand we have around here also has a (very) small amount of fine gold in it - more nearly the same densities, I suppose, so laid down together, but that's just a guess. A few hobby prospectors are "washing" these black sand deposits using small portable sluice boxes - on the order of the size of a rain gutter - with silicone riffle mats laid in the bottom. The riffle mats have special (and proprietary) molded patterns, because the gold is such small particles ("flour gold"). The flow rate of the water, and the slope of the sluice box, must be carefully controlled to separate the gold. Even then, I'm pretty sure the gold collected would barely cover costs. But, they have fun doing it. I've thought about getting a small sluice setup for my wife, since she's actually the rocks and minerals enthusiast in our household. Come to think of it, Christmas is coming...

Joshua States

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Michael Cox wrote:I am interested in the forging aspect of J-tubes, myself. I had recently collected an old hand cranked forge blower in usable condition, and was intending to build a forge pot out of an old heavy truck brake drum from the salvage yard, at least for starts. But, a J-tube rocket (considering I have a collection of salvaged brick, and can get fire brick from a local brick yard) might be a straighter path to the goal, which is to heat ferrous alloys sufficiently that they can be hot worked rather than cold worked. A bit of heat treating, too./quote]

Building a simple forge from bricks is not that difficult. https://permies.com/t/179207/pep-metalworking/Basic-backyard-forge
I used to have a tire rim forge. I traded a small anvil for it some years ago. It had a real coal forge duck nest (fire pot) installed in it and an electric blower with variable speed. The outside of the fire pot was packed with some sort of white clay for insulation. You could build a similar forge using the hand crank blower you have. You might want to create a firepot out of some clay or castable refractory.

I pulled the fire pot out and bult a solid fuel forge around it.

Joshua States

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I thought about another method of reducing black sand to extract the iron that I have done and can share. I will let @Nancy Reading decide if I should post that process in pictures here, or create a separate thread for it.
It involves direct reduction of black sand into small (2-3oz) cast iron buttons. These are then folded into a strip of wrought iron. The process is repeated until the heating effect of carbon migration provides for a usable and hardenable steel that you can forge into a knife or other tool.

Nancy Reading

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Thank you all for your comments!
I'm happy for you to post your button making method here Joshua. Or you can make a new one. It's handy for me to have all the information in one place, but a new thread (link it here please!) is also fine.
We have had a go at crushing the basalt. Some of it (called 'rotten rock' locally) really looks like it is nodules of iron, you break it and it has a shiny purple metallic look. However it is the harder building grade rock that seems to be more magnetic. This is one of my crap videos, but I think you can see the way the compass needle moves towards the rock face. It does something similar around our house. (edit: You might want to mute the soud out - it was a bit windy!)

Since nature seems to have done most of the work in separating out the magnetite out in the sands that using that does seem to be the easiest way forwards for me. I thought I had some pictures of our trials - but I seem to remember about half the beach sand would cling to a strong magnet. Here's a picture of some 'rotten rock' from when we were making the driveway - it looks a lot more iron rich than I think it actually is.

driveway_rotten_rock.jpg

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Joshua States

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Nancy Reading wrote:Thank you all for your comments!
I'm happy for you to post your button making method here Joshua. Or you can make a new one. It's handy for me to have all the information in one place, but a new thread (link it here please!) is also fine.
.

Done. Here is the link: https://permies.com/t/270554/permaculture/steel-making-process

Kevin Olson

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Joshua States wrote:Building a simple forge from bricks is not that difficult. https://permies.com/t/179207/pep-metalworking/Basic-backyard-forge
I used to have a tire rim forge. I traded a small anvil for it some years ago. It had a real coal forge duck nest (fire pot) installed in it and an electric blower with variable speed. The outside of the fire pot was packed with some sort of white clay for insulation. You could build a similar forge using the hand crank blower you have. You might want to create a firepot out of some clay or castable refractory.

I pulled the fire pot out and bult a solid fuel forge around it.

Joshua -

Thanks for the photos of your old setup. Yes, that's more or less what I was thinking, but I'll need to make the duck nest from fire brick or something, I imagine. I was intending to use a brake drum, because I know that cast is more heat resistant than high carbon steel.

Another acquaintance built what he styled a "Viking forge", which was basically a wooden box, with a thick lining of wood ashes. He claimed that this was typical for iron age Norse forges. I don't know much about the history, so I was happy to take his word for it, at least provisionally. His master's degree was in industrial archaeology, and he was "into" experimental archaeology (attempt to replicate past historical technological achievements, I think - that's based on my observation of his activities). In any case, he made this setup work for a number of years, though he eventually switched over to a propane forge when his life got busy with a wife and children. Unlike coal or charcoal, propane heats up pretty quickly, and is cools off quickly, too. So, I know simple can work, if the operator is skilled (or maybe just determined), but given my lack of skill, I am hoping a slightly more auspicious setup will sooner yield acceptable results!

My end goal is to be able to do minor tool building and repairs, and make use of a lot of metal which gets sent out for scrap. A lot of springs, broken axles and the like just get hauled off to the big scrap recyclers. That's fine, but I figure it's better to try to use some of that stuff one or two more times before is gets turned into some commodity melt, somewhere.

Joshua States

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Kevin Olson wrote:

Joshua -

Thanks for the photos of your old setup. Yes, that's more or less what I was thinking, but I'll need to make the duck nest from fire brick or something, I imagine. I was intending to use a brake drum, because I know that cast is more heat resistant than high carbon steel.

Another acquaintance built what he styled a "Viking forge", which was basically a wooden box, with a thick lining of wood ashes. He claimed that this was typical for iron age Norse forges. I don't know much about the history, so I was happy to take his word for it, at least provisionally. His master's degree was in industrial archaeology, and he was "into" experimental archaeology (attempt to replicate past historical technological achievements, I think - that's based on my observation of his activities). In any case, he made this setup work for a number of years, though he eventually switched over to a propane forge when his life got busy with a wife and children. Unlike coal or charcoal, propane heats up pretty quickly, and is cools off quickly, too. So, I know simple can work, if the operator is skilled (or maybe just determined), but given my lack of skill, I am hoping a slightly more auspicious setup will sooner yield acceptable results!

My end goal is to be able to do minor tool building and repairs, and make use of a lot of metal which gets sent out for scrap. A lot of springs, broken axles and the like just get hauled off to the big scrap recyclers. That's fine, but I figure it's better to try to use some of that stuff one or two more times before is gets turned into some commodity melt, somewhere.

My understanding of a typical Viking age forge is little more than two semicircles of fired clay stood on the flat sides parallel to each other with a bellows pump that blew air into the charcoal fire burning between the two semicircles. You can see this setup toward the end of the video linked in this thread: https://permies.com/t/55079/Community-production-iron#2837396.

Based on what you described as the work you are interested in doing, you should probably look at what is called a Rivet forge and try to model your setup after that. A typical rivet forge is small, portable, and can be used with either coal, coke, or charcoal.
https://www.centaurforge.com/Centaur-Forge-Rivet-Forges/products/385/

Nancy Reading

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Lots of good thoughts!
I have no idea if there is likely to be gold in our sand. I suspect not, but you never know. I'm now more interested in iron than gold anyhow at the moment.

Joshua States wrote:I would not recommend putting iron sand into a crucible. It boils out of the crucible and makes a gigantic mess in the furnace. Ask me how I know.

Now I have to ask! I'm suspecting it went horribly wrong for you? - but if you tell me what you did, I may see another way around it :)

Separating the sand with a magnet is a pretty easy first step. At this point I'm more interested in achieving a metal, than what to do with it afterwards. Maybe it will be a knife blade (that would be pretty cool) but to be honest, I'd be pretty happy with a paperweight at this point. It depends on what I can achieve.

I'd really like a low tech approach and the bloomery process is pretty basic. I think the temperatures typically achieved do not go high enough to melt the iron, and I suspect that the 1100 C of a rocket stove will be enough heat to get a lumpy mass like a bloom or tamahagane.

tamahagane

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Nancy Reading wrote:

Now I have to ask! I'm suspecting it went horribly wrong for you? - but if you tell me what you did, I may see another way around it :)

Separating the sand with a magnet is a pretty easy first step. At this point I'm more interested in achieving a metal, than what to do with it afterwards. Maybe it will be a knife blade (that would be pretty cool) but to be honest, I'd be pretty happy with a paperweight at this point. It depends on what I can achieve.

I'd really like a low tech approach and the bloomery process is pretty basic. I think the temperatures typically achieved do not go high enough to melt the iron, and I suspect that the 1100 C of a rocket stove will be enough heat to get a lumpy mass like a bloom or tamahagane.

tamahagane

After my successful reduction of black sand in small quantities and subsequent folding those little buttons into an iron bar (https://permies.com/t/270554/permaculture/steel-making-process) I got the not-so-bright idea of putting a kg of sand and some charcoal into a crucible to see what happened.
What happened is called a "carbon boil" where the sand starts to melt rapidly and all the various stuff that isn't iron starts turning to gasses and liquids. It came out of the crucible (open top) and I shut down the furnace. You may have better luck at lower temps.
Anyway, I removed what was left in the crucible with a chisel and now I have a few hundred grams of chunky partially reduced magnetite.

They will stick to a magnet, so they are ferrous.

I intend to take these, and possibly make more at a lower heat, combine them all into a short stack furnace to refine the iron out of it.

I just haven't had the time. We moved recently and the shop has been packed away for 7 months. Now that I am set up again, I will try and get back to making steel, but it probably won't be until springtime.

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Joshua states wrote: I got the not-so-bright idea of putting a kg of sand and some charcoal into a crucible to see what happened.
What happened is called a "carbon boil" where the sand starts to melt rapidly and all the various stuff that isn't iron starts turning to gasses and liquids. It came out of the crucible (open top) and I shut down the furnace. You may have better luck at lower temps.

The reaction for the reduction of ore into steel produces carbon dioxide gas, so I can imagine that it it reacts too quickly you will get it boiling. The hotter the temperature the quicker the reaction. If you were 1400C that is way hotter than I think I will achieve in a simple rocket j tube. I do need to get a feel for what may be workable parameters still.

To make the process as 'sustainable' and Skye based as possible, I'd love to be able to produce the heat from my coppice wood. Making lots of charcoal, just to burn it off to produce the heat, is the known bloomery method, and I may fall back to that, but it will mean a lot of charcoal making (buying it is a fall back possibility).

I think what I will start with is making a rocket forge - similar to the one made by Uncle Mud at the low tech jamboree (here's another video from the kickstarter):

I'll get a moderate sized crucible. I guess I'm not aiming to make more than 200g (6-8Oz) of metal at a time. Charcoal is pretty bulky, the ore is only 30% yeild at best, so (thinks) maybe a 3 pint crucible may be big enough? I'll then experiment to see what temperatures I see in the crucible, maybe melting different compounds - sand, lower melting point metals. I'm not sure how high a temperature our FLIR camera goes, but that might tell me the temperatures I am reaching. If I can't get to 1100C ish then I wonder whether burning Charcoal in the rocket may be an option to increase the temperature? Otherwise it is stepping down from my aspirations and, yes a propane, or electric furnace might have to be considered. I'm short of clay here, so I don't really want to purchase tonnes of clay to make a chimney for a traditional bloomery furnace and buying more refractory sruff is maybe an extravagance I can't afford since I'm spending all my pocket money on a new polytunnel frame.

There is a quite a bit of 'playing' to scope out the possibilities yet!

I did look on the bladesmith forum (my registration still worked) but it doesn't look like anyone has tried a j tube rocket forge for smelting as yet. I'm staying away from Facebook as I dislike it and it is very difficult to use it as a reference. Duck duck doesn't throw up anything, although I did find this old permies thread, looking at smelting and forging other materials such as glass, although there is no follow up on it as yet.

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Question: How are you planning to measure the temperature in the furnace/crucible?

Nancy Reading

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I suspect there is a band of temperatures that will be suitable for smelting - slower at lower temperatures and quicker (as you maybe found) at higher temperatures. It looks like our FLIR camera doesn't go up that high so my plan at the moment is to build the rocket forge and play with it for a while - put different things in the crucible and see what happens.

Some melting points(degrees Celsius) from engineering toolbox:

Lead 327.5
Zinc 419.5
Aluminum 660
Glass 700
Copper 1084
Iron, Gray Cast 1127 - 1204
Iron, Ductile 1149
Silicon 1411
Steel, Carbon 1425 - 1540
Iron, Wrought 1482 - 1593
Steel, Stainless 1510
Sand 1550

So if I can get copper to melt I know I'm getting about the required temperatures. It looks like there is not much in between various cast irons and silicon (asbestos at 1300 C).
I'm interested to see that stainless steel has a pretty high melting point. That suggests that I could make a stainless bar support for the crucible rather than a brick one, which might then provide less obstruction to the hot gas flow and more heat transfer into the vessel.

I'm suspecting that with experience one will be able to tell by the glow and the chimney flume, how hot the forge chamber is getting.

I'm hoping I'm right that 1100-1200 C will be hot enough. this reference suggests that 1300 C was a temperature for a Roman bloomery, so maybe the temperatures in a normal rocket won't be high enough?

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I suspect that a rocket forge may struggle with smelting. The temperature will be fine, but the smelting from ore is as much about ensuring that the atmosphere is reducing (high carbon, low oxygen) as it is about temperature. In a traditional bloomery, powered charcoal or coal is added in layers with powdered ore. The close physical mixing in the hottest part of the bloomery ensures that the reaction completes for convert your iron oxides/iron sulphides etc... to metallic iron.

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Nancy Reading

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I'm sort of hoping that by mixing charcoal and ore sand in the crucible I will get the mixing and the atmosphere. According to engineering toolbox again the spontaneous ignition temperature of charcoal is 349 C . Hmm, maybe that means it will all have burned away before the iron compound is hot enough to react with the Carbon Monoxide? Alternatively, the CO might be heavy enough to stay in the crucible. Maybe I'll need a lid, maybe it won't work. As I wrote above, I couldn't find references to anyone who has tried smelting in a rocket. When people use crucibles they usually get hot enough to melt the iron, so closer to 1400C than 1100C, so it might be I'll end up with nothing more than hot sand

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Nancy Reading wrote:I'm sort of hoping that by mixing charcoal and ore sand in the crucible I will get the mixing and the atmosphere. According to engineering toolbox again the spontaneous ignition temperature of charcoal is 349 C . Hmm, maybe that means it will all have burned away before the iron compound is hot enough to react with the Carbon Monoxide? Alternatively, the CO might be heavy enough to stay in the crucible. Maybe I'll need a lid, maybe it won't work. As I wrote above, I couldn't find references to anyone who has tried smelting in a rocket. When people use crucibles they usually get hot enough to melt the iron, so closer to 1400C than 1100C, so it might be I'll end up with nothing more than hot sand

If you are going to use an air-draft rocket stove with a crucible, you should seal that crucible to create an oxygen-free atmosphere inside the crucible. That will keep the charcoal from burning out before the ore starts to react.
When smelting in a crucible with a propane furnace, we can adjust the atmosphere inside the furnace by changing the propane to air ratio. That leaves the inside of the furnace with no oxygen left over to burn the charcoal.
You can seal the crucible with some refractory cement or clay. I don't know what is available where you are, but you could ask those knifemaker guys where they get the stuff they line the insides of their forges with.
Here, I can get five pounds of Satanite refractory for 16 USD. I can make dozens of crucible lids from that much refractory. They are only about 1/2-inch thick.

I think what you will get will be more than hot sand, if you set it up right. You may not get enough heat to melt the iron out of the sand, but you just might get enough to melt all the other stuff off.
Some crushed glass over the top of the sand & Charcoal would also help to isolate the slag from the iron.
The glass melts pretty quickly and is lighter than the sand so it floats on top. There are a couple of videos of an open-top crucible in my furnace at this link: https://drive.google.com/drive/folders/1O7d9C1EAGKvgq4UqjYcd7wgDcOfEshis?usp=sharing
You can see the molten glass is bubbling as the gasses from the melting charge escape through the glass.

Nancy Reading

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Joshua States wrote: There are a couple of videos of an open-top crucible in my furnace at this link: https://drive.google.com/drive/folders/1O7d9C1EAGKvgq4UqjYcd7wgDcOfEshis?usp=sharing
You can see the molten glass is bubbling as the gasses from the melting charge escape through the glass.

That is so cool (hot!) thank you!

I've been doing more reading round the subject and sometimes I'm full of confidence, and at other times I think it will never work. I feel that I need a really good book, so that is probably going to be my birthday present to myself...

According to Erica and Ernie's The Rocket Mass Heater Builder's Guide 1 6in j tube in a moderate climate can get to 1100-1300 oC an 8in in a super cold climate to 1350 oC plus. The temperature needs to be above about 1100 oC to get a 'bloomery' style reduction going on - a bit hotter probably better for yield. For true steel making (as opposed to a mixture of different carbon concentrations) it seems you need to get hot enough to melt iron - approaching 1500 oC.

image source

From the Iron-Carbon phase diagram you can see that as the carbon content increases the melting point decreases, which is why it is easier to make cast iron than steel.

Some other interesting references:

Apparently the Haya people may have been smelting steel in a bloomery near West Lake Tanzania 2000 years ago: ref: Complex Iron Smelting and Prehistoric Culture in Tanzania, Author(s): Peter Schmidt and Donald H. Avery The main aspects that made it possible seem to be long tuyeres (the blower nozzles) that went right into the furnace so preheating the combustion air, a fine charcoal strata made from reeds which gave a good carbon surface and (my thought) possibly flux, roasting the ore for the next batch inside the furnace providing extra Carbon as it cools in a Carbon dioxide rich atmosphere.

I found a nice little article on a simple way of assessing ore for commercial exploitation, which might be a starting point - A crucible melt at 1250 oC for one hour with the powdered ore laid in between layers of Charcoal.

Assessing the Quality of Iron Ores for Bloomery Smelting, Ivan Stepanov et al.

Here is a thread from bladesmithforum on a crucible smelt.

If I get pure iron then the Georgian method seems a possibility for converting it to a good steel in a crucible in a second melt process:
Half the iron is placed in the crucible bottom, then a layer of glass or sand, then carbon and the rest of the iron in layers, finally a lid with hole. At 1200 oC the sand/glass melts and provides a barrier between the iron at bottom and the carbon layers. The upper iron absorbs Carbon and starts to melt at 1500 oC it falls through the molten sand and mixes with the iron layer which also starts to melt. After 1.5 hrs at 1500 oC it ends up as a steel nugget under a glass layer (sound simple (!) )

It seems that impurities of Sulphur and Phosphorus are the main problematical ones from a functional metal point of view. I found a breakdown of the raw basalt from this area (Eocene basalt of Isle of Skye (average of 14 analyses, Tompson et al., 1972)

:
SiO2 47.24
TiO2 1.84
A12O3 15.73
Fe2O3 1.86
FeO 10.63
MnO 0.2
MgO 9.17
CaO 9.7
Na2O 2.94
K2O 0.48
P2O5 0.22
Which shows no sulphur and little Phosphorus in the raw rock - what it is in the magnetite rich portion (that 1.86% Fe2 O3) that I can easily get out of the sand, is another matter of course! I hadn't appreciated how much FeO there seems to be - I guess that is what is giving the rotten rock it's rusty appearance.

My thought at the moment is to try something very basic along the lines of Ivan Stepanov's process and see if I can get any metal, and then tweak the process from there. Don't expect it to happen anytime soon though! Since I will be working outside I need a period of dry weather; but maybe in April we might get a chance. There are a few essentials on my shopping list too. I'm OK for safety gear, due to my husband's welding hobby, but a crucible, tongs, clay and more firebricks are almost certainly required.
Methods will depend on what sort of temperature I can achieve. Even if I can't get the full conversion to steel, I'd be pretty happy with a metal nugget that could be worked and converted to something useful elsewhere.

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Joshua States

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Oh no! Nancy is staring down a rabbit hole and is about to jump in!

About getting a book on the subject, most of the books about this type of smelting are long since out of print. However, there are a decent number of academic papers on the subject that you can download for free at https://www.academia.edu/. (if you can tolerate reading a PDF document rather than a real book).
Lee Sauder is an American blacksmith and possibly the foremost expert on the subject of bloomery iron and steel smelting still alive today. (https://independent.academia.edu/LeeSauder)
You can also find his videos on YT and there was one he did in Africa in a village once renowned for their steel production from ore. Search YT for Lee Sauder smelting in Africa
Other names from history on the subject of crucible steel are Al Pendray and John D. Verhoeven. They were mostly concerned with recreating the fabled Wootz, or Pulat steel from antiquity. They started with ore in a crucible furnace.

Sometime in April sounds like the same time I will probably start making crucible steel again. This winter has been pretty dry and unusually warm though. I could start up sooner!
Excited for you to give it a go.

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