Smelting Steel from iron ore

Nancy Reading wrote:

Do you think that a rocket forge just won't get hot enough Joshua? Or that I won't be able to get the right mix in my crucible? I'd really like to try the 'low tech' approach and not use a blower and charcoal if I can help it. I know that doing something different is sometimes a bad idea, but I can't see an obvious problem at the moment, other than the unknown.

The backyard smelter is really about as low-tech as it gets. You could knock it down a peg or two by digging clay out of the creek bed instead of using bricks, make a bag bellows (or use a foot pump) instead of the blower and get your husband to switch off with you pumping the bellows.
:-)
If we go back to that short video in the post above where they are trying to use a RMH for simply forging mild steel (800-900 deg. C) and see how big a furnace they are using and still struggling, I seriously doubt you can get the RMH up to the temps needed to smelt iron ore (1400-1500 Deg. C).

Toward the end of that video, they are talking about using charcoal inside the RMH over the brick they have drilled holes in to raise the temperature. Charcoal will burn hotter and faster than raw wood, but it needs forced air to do it. The RMH is basically just a fireplace with an elongated draft.  
Considering the size of what they are using in that video, and the little furnace I built in the back yard, I'd have to say my little furnace is a cheaper, faster, better method, but I could be wrong.
You can give it a try, but humans have been smelting all sorts of metal ores with charcoal and a bellows for a couple thousand years. If it could have been done in a simple wood fired hearth, I think we would have invented steel much sooner.

As for using the crucible, I have tried that in very small quantities, like a tablespoon of sand, and made a cast iron button. (https://permies.com/t/270554/permaculture/steel-making-process) It still took a propane furnace with forced air blower to achieve the required temperature to melt the iron out of the sand. I tried it with a larger amount of sand in the crucible and a propane furnace to get to temp and had a disastrous mess. (see above) You may have a different result than I did, but after talking with other smiths doing the same thing, they had the same experience that I had doing what I did.

The ancients who made the first crucible steel in India, made it in huge furnaces with many crucibles stacked up inside it. They then filled the rest of the furnace with wood and/or charcoal and pumped bellows into it for hours. That little backyard furnace I built is just a miniature version of that. If you built a similar furnace, loaded a small amount of sand into your crucible and nestled it inside a load of charcoal, you could probably get up to temp to melt that sand, but you would still need forced air to do it.

I don't want to rain on your parade, but I would like to see you have a successful experiment with as little struggle, work, and mess as possible.

Another YT video of crucible steel making with two renowned smiths added for your viewing pleasure: https://youtu.be/namXt4Etn_o?si=6BpiAKjFv3w7OxtS

My project thread on bladesmithforum They've been very helpful and supportive especially on topics like slag. I'm now a little less hopeful that I will end up with a lump of metal, but still want to procede.

I'm starting to make some progress at getting stuff together. I bought some A5 graphite salamander crucibles. I got three, since I understand that they don't necessarily last long and accidents can happen. They do seem rather large and I'm now thinking (given the expense as well) that I may get a smaller one to do the first trials with.
I've also ordered some powdered clay (and some tongs). The postage costs almost as much as the clay, so I'm feeling quite envious of people who can dig it out of the ground locally! I'm hoping that 25kg will be enough powder to slip seal the bricks and riser in position, plus any lid/modifications to the crucible I may want to experiment with.

I haven't decided yet what sort of firebricks to use. It seems that the hotter I can get it, the more likely the smelt is to go well. I suspect melting steel temperatures are unlikely, but I may get hot enough for the impurities to puddle a bit. I'm thinking that if I use insulated firebrick around the bottom of the riser I may be able to get the temperatures a bit higher.

I'm also wondering where the hottest point in the riser might be.  Does anyone have figures on how hot it is at different points in the riser? I've seen videos and images with flames coming out the top, so there is obviously still combustion going on there. I'm thinking that if well insulated, the closer to complete burn in the channel, the hotter the gases will be. I have some refractory blanket, so was contemplating a 5 minute riser (edit : five minute riser thread link for future ref). But if the temperature nearer the top is hotter, I could make it all in firebrick and wrap with the blanket. Then I can more easily put a door and shelf in near the top for the crucible to sit, maybe even accessing through the top thus avoiding the need for a door.

Nancy Reading wrote:My project thread on bladesmithforum They've been very helpful and supportive especially on topics like slag. I'm now a little less hopeful that I will end up with a lump of metal, but still want to procede.

I'm starting to make some progress at getting stuff together. I bought some A5 graphite salamander crucibles. I got three, since I understand that they don't necessarily last long and accidents can happen. They do seem rather large and I'm now thinking (given the expense as well) that I may get a smaller one to do the first trials with.
I've also ordered some powdered clay (and some tongs). The postage costs almost as much as the clay, so I'm feeling quite envious of people who can dig it out of the ground locally! I'm hoping that 25kg will be enough powder to slip seal the bricks and riser in position, plus any lid/modifications to the crucible I may want to experiment with.

I haven't decided yet what sort of firebricks to use. It seems that the hotter I can get it, the more likely the smelt is to go well. I suspect melting steel temperatures are unlikely, but I may get hot enough for the impurities to puddle a bit. I'm thinking that if I use insulated firebrick around the bottom of the riser I may be able to get the temperatures a bit higher.

I'm also wondering where the hottest point in the riser might be.  Does anyone have figures on how hot it is at different points in the riser? I've seen videos and images with flames coming out the top, so there is obviously still combustion going on there. I'm thinking that if well insulated, the closer to complete burn in the channel, the hotter the gases will be. I have some refractory blanket, so was contemplating a 5 minute riser (edit : five minute riser thread link for future ref). But if the temperature nearer the top is hotter, I could make it all in firebrick and wrap with the blanket. Then I can more easily put a door and shelf in near the top for the crucible to sit, maybe even accessing through the top thus avoiding the need for a door.

I'm happy that you are posting and interacting with the folks over at the bladesmith's forum. There is a lot of knowledge and experience there.

A5 is a pretty big crucible. I'm using A4 and I get a 2kg charge in those with room to spare. The larger crucible may be beneficial in the long run because if you do get hot enough to melt the iron out of the sand and are using a smaller amount of sand, you should have enough room in the crucible to contain the carbon boil. The downsides are that you will need to build a bigger firebox to accommodate the larger crucible. You do want enough room around the crucible for the heat to circulate and heat the crucible evenly. The larger crucible also absorbs more heat than a smaller one.

Fire bricks typically come in two varieties, hard and soft. Hard ones are more durable, reflect more heat, but only after they come up to heat themselves. This robs the furnace of more heat in the beginning. Soft fire bricks take less time to come up to heat allowing the furnace temp to rise more quickly but reflect less heat and often crumble at high temps. Information on UK fire bricks here: https://www.bladesmithsforum.com/index.php?/topic/42090-uk-firebricks-that-are-not-too-thick-for-floor-of-gas-forge/#comment-420268

Are you still planning to use the RMH design for this smelt? If so, I cannot help with where the hot spot in the riser will be. My guess is that the hottest section will be down in the bottom of the firebox where the coals are.

According to the senior rocket scientists, the hottest part of the core tends to be the midpoint of the heat riser. You could see temps in excess of 1200 C there with good, dense, dry fuel. This is about the same range as a charcoal (or coke) fire with forced air.

Phil Stevens wrote:According to the senior rocket scientists, the hottest part of the core tends to be the midpoint of the heat riser.

That's really helpful Phil.
Any hints or tips on maximising the temperature output? Obviously good quality dry hardwood in small bits would be a good start. I've got a lot of alder, which isn't excellent but is home grown....I'm likely to need the riser larger diameter than standard for example to avoid constrictions by the crucible. I may have to do a dwarf brick riser then at least. If I made it taller than standard too is that likely to be a positive, neutral or negative idea?

Joshua States wrote:The larger crucible may be beneficial in the long run because if you do get hot enough to melt the iron out of the sand and are using a smaller amount of sand, you should have enough room in the crucible to contain the carbon boil. The downsides are that you will need to build a bigger firebox to accommodate the larger crucible. You do want enough room around the crucible for the heat to circulate and heat the crucible evenly. The larger crucible also absorbs more heat than a smaller one.

Yes, I think I'll get a cheaper smaller one for my first run, just to avoid throwing money away.

Fire bricks typically come in two varieties, hard and soft. Hard ones are more durable, reflect more heat, but only after they come up to heat themselves. This robs the furnace of more heat in the beginning. Soft fire bricks take less time to come up to heat allowing the furnace temp to rise more quickly but reflect less heat and often crumble at high temps.

Good info thanks!

Information on UK fire bricks here: https://www.bladesmithsforum.com/index.php?/topic/42090-uk-firebricks-that-are-not-too-thick-for-floor-of-gas-forge/#comment-420268

Hmm, they don't rate them much! I may just go for the standard ones and check how much insulation blanket I have to wrap outside them. I have been using vitcas and they seem very reasonable to deal with - not charging excessively for delivery to me for example.

Are you still planning to use the RMH design for this smelt?

See Phil's response. Yes I think I need to do this at least for the first time. Then I may reconsider my options!

Nancy Reading wrote:Any hints or tips on maximising the temperature output? Obviously good quality dry hardwood in small bits would be a good start. I've got a lot of alder, which isn't excellent but is home grown....I'm likely to need the riser larger diameter than standard for example to avoid constrictions by the crucible. I may have to do a dwarf brick riser then at least. If I made it taller than standard too is that likely to be a positive, neutral or negative idea?

I don't know how height adjustments will play out, but I'm tinkering and doing some experiments with this in a biochar retort design. My first go-round was following Kobus Venter's advice and it basically had no riser. The burn tunnel just ejects straight up and the gases hit the bottom of a steel drum filled with feedstock. This was a fail, so my next iteration will be a half-height 5-minute riser in the hopes that I will harvest the highest heat levels and then the volume around the drum will be more of a stack. I'm also going to pipe the evolved gas from the retort back to the start of the burn tunnel for full combustion and better positive feedback once pyrolysis starts. I'm in the process of looking for some pipe lengths that I can cut and thread in order to try this.

Nancy Reading wrote:

Phil Stevens wrote:According to the senior rocket scientists, the hottest part of the core tends to be the midpoint of the heat riser.

That's really helpful Phil.
Any hints or tips on maximising the temperature output? Obviously good quality dry hardwood in small bits would be a good start.

I'm not so sure about the hardwood being hotter. Two historically excellent steel smelting cultures are Japan and the Norse. Both of these used softwood (mostly pine) for their charcoal smelters and forges. Japan's traditional swordsmiths still use softwood charcoal today.
Personally, I use softwood charcoal as well. It is my understanding that softwood burns faster and therefore hotter than hardwood.
In the end, if what you have is Alder, then by all means use it.