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Internal pressure


Bryan Davis

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Hey everyone! This is my first post, and I am making it as I ramp up towards my first smelt.

 

I have been going over the posts here and have been able to get a lot of the details of my first smelt down, like ore type, flow rates, charcoal creation, furnace design, etc...

 

What I haven't seen though is any talk about the internal pressure of the furnace and what effect it has on a bloom. I was thinking of modifying one of the Rockbridge furnaces to increase the internal pressure as a way of increasing the temperature.

 

Has anyone tried doing this? If so, was it helpful? Hurtful? Aside from a different way to regulate temperature, I'm speculating that the rate of reactions inside the furnace would increase at a higher pressure, so I wanted to try it to get a better yield.

 

 

Anyways, thanks for all the great info so far!

 

-Bryan

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Hi Bryan,
I think I have seen Lee Sauder, and, or, Darrell Markewitz , have some drawings/charts about this.
Pressure is very important. ........ I have smelted many kinds of ore, in many different smelters, and the one thing that seems the most important is the air pressure.

The guys using very low pressure devices, like old bag bellows and such have a very hard time getting solid compact blooms. Lower pressure, can make good iron/steel, but imo, it takes a good flow of air to keep a good centered bloom mass.
I have used bellows, that push the same amount of air, pressure, and Vol. ( as the shop vac.), and have made fine solid bloom with these.
Your best bet in smelting air, is a cheap shop vac. I have been using a 29$ shop vac for many years now. Or a bigger one with a variac to slow it down.
With the basic vac. I use a ball valve, ( mostly wide open) which lowers the pressure.
I have found that it doesn't take a whole lot of pressure, but sometimes the forge, squirrel type fans have a hard time pushing enough air.

It's about having enough air to move the reduction zone as high as it can be on the size smelter you are using. I have found the 8-10 in. internal dia. stack smelter to be the best all around.
It is easy to get a basic shop vac. (adjusted) to raise the reduction zone well near the top of a 40 in high stack. Plus the return on product, for the amount of charcoal/ore seems the best.
https://www.facebook.com/groups/361798240526981/

That is our FB page. Lots of info there. And people from all over the world, willing to help.
https://picasaweb.google.com/lh/myphotos

That is my Picasa page, with about a hundred smelts of info.

Don't worry about temps. That is a very hard thing to judge. All ores are different. As long as it is hot enough to reduce your ore, and get a good liquid slag, your likely doing fine.

Like anything, it can take some practice. I've lost count of how many smelts I have done, and I still learn something new every time.

What is you ore??


Have big fun !!

Mark


Mark Green

 

I have a way? Is that better then a plan?

(cptn. Mal)

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Thanks for the reply Mark.

 

I wasn't clear in my post, but what I was referring to was a furnace where you could regulate the internal pressure, not air pressure of the forced air. After I posted, I realized that this really just isn't possible because of many, many reasons (I had just been thinking on the theory for a while - basically a practical application of Boyle's Law - and hadn't thought of practical construction of the thing yet). Ha. But I hadn't yet looked into which shop vac I was going to be using, so your reply was still helpful! I've been working my way through both Lee's and Darrell's posted material. The amount of info they've gathered since starting this is staggering.

 

Unfortunately, there is no natural source of iron near me so I'm going to buying some hematite commercially. However, Kaolin is plentiful around me, so I got lucky there and I can create my own charcoal. I'm going to be following Lee's recommended design for my first smelt ( this one: http://leesauder.com/pdfs/furnace%20construction.pdf) so I can get the process down before experimenting with custom furnaces. I joined up on the linked Facebook group, thanks for the link.

 

I'm expecting to actually get out there and smelt in about a month and a half (rather than over-thinking it) and I'll definitely return here with some pics! I'm near Atlanta, Ga - if anyone wants to stop by just send me a message and I'll let you know the details.

 

Bryan

 

PS - Your Picasa link was a relative link rather than an absolute link so I couldn't follow!

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Bryan: go prospecting along the bypass around Cartersville. There was a HUGE iron industry there once upon a time, lots of hematite in the clay. Find one of the old pits and dig away, with permission of course. Also search mindat.org for iron minerals in Georgia. There should be magnetite up in the northeast corner, I already mentioned the hematite northwest of Atlanta, and there's an excellent chance of goethite/limonite along the western slopes of the mountains in the northeast. Check the state geological surveys as well. Who knows, you might even strike gold (literally!) if you look for magnetite around Dahlonega. Mountains mean minerals, and iron is fairly abundant. It's just finding it and getting permission that's the hard part.

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That Sauder's construction method is the same as I make mine. 90% of the time.
Best way I have found. It's all about that plinth !!!

 

https://picasaweb.google.com/106800196895572422821/BloomFurnaceConstruction

 



Mark Green

 

I have a way? Is that better then a plan?

(cptn. Mal)

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Bryan (and everyone else)

 

since I was implicated...

 

My team here has made some input pressure readings. Honestly using fairly cobbled together instruments. This primarily to counter criticisms (largely from theoretical academic commentators) that all the current work is not 'scientifically rigorous' enough.

(But like Lee says 'If you don't get any iron - whatever you have done *has* to be wrong'.)

 

The first thing we tried (cheap and only a relative measure) was a simple U tube with water in it attached to the tuyere side. This gave us some rough ideas - at least between individual smelts.

Eventually I got a small guage (off E-bay) that measured 0 - 30 psi range. (The trouble I had was finding something in the right range, at a price I could manage.)

Some of the individual smelts in our series here have the input pressures measured. You would have to check through the individual 'smelt data' records one by one - there is no centralized table with all the variables charted from all the experiments. (Neil and I am working on that however - with plus 60 smelts, and so many measurement points, its pretty ugly.)

see : http://www.warehamforge.ca/ironsmelting/index.html

Overall, the average we recorded for input pressure at the tuyere was 3 - 5 PSI.*

 

We also were using a rough guage for input volume. This consisted (budget again) of a wind surfer's speed guage placed across the input pipe. The volumes were calculated mathmatically from the flow speed. Again not the ideal, and it turned out fatigue in the vanes at the high speeds measured really effected instrument performance with time.

 

gage185.jpg

 

I have been using a different method than Lee uses for controlling the input air from the electric blower. (I've managed to purchase one of the same high end blowers he uses by the way). You can see the sliding plate gate (from a dust collection system) located just at the exit from the blower. So I'm limiting the amount of air into the entire downstream system. (Lee uses a moveable plate just in front of the tuyere set up, venting off excess air.) Both of us have some rough calibrations on these valves that let us have some rough approximation of the air we are providing to the overall system. Mine is marked (very rough approximations!) of 100's of litres / minute (based on earlier measurements). Lee's (was) marked in fractions of total possible (1/4 - 1/2 ...)

 

My smelting partner, Neil Peterson, is driving an experimental series investigating Viking Age glass bead making furnaces. (Even *less* archaeology than for iron smelting furnaces!). He has deeper pockets than I certainly do (!) and has recently invested in a multi input data recorder system. Along with high temperature probes, he has purchased some modules that will record pressure, and a better quality vane type air speed (so volume) instrument. We still have to assemble the fittings and run some tests, but we have good hopes for better (more consistant) measurements into the future.

 

You may have gathered from all that - my thrust here has been to researching possible historic *process* - with less concentration on *product*.

I have to agree with what Mark has said : That historic air delivery systems may not result in the most efficient utilization of ore = not the best quality blooms. You most certainly can *make* iron in lower air systems (and this most certainly was the method for much of human made iron production). What many researchers miss is the second stage - of bloom to bar. What you may gain in simplicity from ore to bloom is competely lost by the extra labour / materials converting a lacy bloom into a working bar.

Lee has much better experience / notes / observations about this aspect.

 

Ok

 

Lee and Skip experimented and documented and then introduced to all the concept of high volume air = better ore to bloom conversion, both in terms of size and density. (Historic note, look at the impact of water powered systems circa 800 - 1100 AD in Europe - pretty much the same thing!)

 

Although some experimenters have produced measurements of input air pressures, I am uncertain that anyone has attempted to measure pressures inside the actual furnace itself.

 

As Mark as mentioned, delivery air needs to be considered in terms of not only *volume* but also in terms of *pressure*.

This is why people attempting to use rotory blacksmith's forge blowers as air sources often have less than the best results. Those equipments produce a large volume - but at virtually no pressure. The air simply does not penetrate through the tuyere diameter into the charcoal mass. Increasing the diameter of the tuyere might assist this. Using multiple tuyeres would certainly help (and both methods are seen in historic systems.)

 

But in actual fact, none of us need to really worry so much about absolute pressure measurements, or even with measuring air volume. The best 'working' measurement is via charcoal consumption. Rate of charcoal consumption is also the effect of internal temperature and size of the effective heat zone. Bigger and hotter = faster charcoal burning.

 

Most of us are working on some variation of the 'Sauder System', what historically I would call the 'short shaft' furnace. Most typically our working furnaces have an internal diameter of closer to 10 - 12 inches.

This is quite important when discussing measurements and working methods.

As you have seen, there is a dance between ore / charcoal / furnace / air. My own experience is that there is no *absolute* 'perfect' furnace. Any basic design will have to be modified based on changes to those four primary elements. Hematite will not produce the same results, even in identical furnaces and method, as the bog iron ore analog I typically use here.

 

I'm (educated?) guessing that any attempt to modify the internal gas pressure in what is a very rough and simple furnace will prove far more effort than effective in result.

Past experience has proved the simplest way to effect the reaction ability of a furnace is just to increase the total stack height. (Nice example there, Mark gave 40 inches as his ideal stack height - I usually build for closer to 24 - 30 inches. My standard furnace diameter is larger, rarely below 10 inches, to his reported 8 inch minimum. I know we are working with quite different ore types, and maybe charcoal as well.)

There are just too many other variables (things that can, and often do, go wrong!)

 

I'd be interested in what results you come up with / records generated.

 

Darrell

website: www.warehamforge.ca
Blog : http://warehamforgeblog.blogspot.com
(topics include iron smelting, blacksmithing, Viking Age)

NOTE : Any posted comments may be converted into a future blog article!
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Bryan: go prospecting along the bypass around Cartersville. There was a HUGE iron industry there once upon a time, lots of hematite in the clay. Find one of the old pits and dig away, with permission of course. Also search mindat.org for iron minerals in Georgia. There should be magnetite up in the northeast corner, I already mentioned the hematite northwest of Atlanta, and there's an excellent chance of goethite/limonite along the western slopes of the mountains in the northeast. Check the state geological surveys as well. Who knows, you might even strike gold (literally!) if you look for magnetite around Dahlonega. Mountains mean minerals, and iron is fairly abundant. It's just finding it and getting permission that's the hard part.

 

Do you just kind of call up the owner of the property and ask them ever so politely if you can take ore off the land? How do you identify who owns the property? I looked around mindat.org (this is really cool - didn't know it existed!) and found a few places closer to where I live (Gwinnett) that I'd be able to swing by, but don't know how to interpret the results. That is, I don't know how to find out who to call. This one in particular: http://www.mindat.org/loc-72214.html

 

I do know there are no active iron mines in Ga, so I don't actually expect a problem once I get in contact with the right person, but I'm finding it difficult to find out who that is.

 

 

Worked!

 

That Sauder's construction method is the same as I make mine. 90% of the time.

Best way I have found. It's all about that plinth !!!

 

https://picasaweb.google.com/106800196895572422821/BloomFurnaceConstruction

 

Some good instructions and step-by-step directions on there, thanks. Question - you used 12 inch tubing for the column. Did the clay shrink significantly when it set/hardened? From what I've read around here and through the various person sites, 10 inches seems to be yielding the best results. Another question is - I've seen that Lee has done some experiments regarding angle of the tuyeres, but has there been any proposed reason for why some angles work better than others?

 

I still haven't really grasped what the purpose of the "door" at the base is. Is it just to help extracting the bloom? Is it to help detach the bloom from the walls? Something to do with tapping slag (I thought we wanted a slag bath in the bottom for most of the process?)?

 

Sorry for all the questions, but the more I read/learn the more questions I seem to have. Also, nice sculpting on the back :)

 

I'm (educated?) guessing that any attempt to modify the internal gas pressure in what is a very rough and simple furnace will prove far more effort than effective in result.

Past experience has proved the simplest way to effect the reaction ability of a furnace is just to increase the total stack height. (Nice example there, Mark gave 40 inches as his ideal stack height - I usually build for closer to 24 - 30 inches. My standard furnace diameter is larger, rarely below 10 inches, to his reported 8 inch minimum. I know we are working with quite different ore types, and maybe charcoal as well.)

There are just too many other variables (things that can, and often do, go wrong!)

 

I'd be interested in what results you come up with / records generated.

 

 

I do plan to go into this more when I get some experience. This post was a bit premature for me, but I had just been thinking about it for a bit. In addition to extending the stack up, I'm going to have to reinforce the structure on the outside because any success in actually increase the pressure will put more strain on the clay and I'm worried it will crack/break.

 

Also, have you and the others ever put your recorded data into a database somewhere? Or, if you haven't, would you mind if I started consolidating all of your public data with others in a central searchable/queryable system? It would help with comparing results and finding patterns.

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To find the owner, find the street address if possible and see if your county has a property tax GIS system. These are usually online amd freely searchable. Once you have a name then you can call, send a letter, knock on the door, or whatever.

 

In the unlikely event Gwinnett County does not have a GIS database, go to the tax assessor's office and ask to see the tax maps of the area in question.

 

Also keep in mind many of these old prospect's mineral rights are owned by corporations like Virginia Iron, Coal, and Coke, not the actual landowner. I have had no luck trying to go through these companies, since many of them no longer exist. Since it's just iron, I would not expect any problems if they find out anyway. Unless you start full-scale commercial extraction, that is!

 

People skills help, and I am somewhat lacking in that department.

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A couple of things

 

On Tuyere angles

The Smeltfest Group (Primaries Sauder, Williams, McCarthy, Markewitz) undertook a specific series in 2005 to test just this aspect. A number of similar furnaces were constructed, varying the tuyere angle.

 

The ideal angle for the tuyere is between 20 - 25 degrees down from horizontal (Sauder and Williams 2002). Less angle, and the developing slag bowl sits too high and shallow, and will quickly engulf and ‘drown’ the tuyere. Too steep, and there is not enough room for the growing bloom, and the air blast will actually cut into and erode its surface. Set the tip of the tuyere roughly 5 cm beyond the interior wall. Further in than that, and the heat of the furnace simply erodes the tip off. Less, and the air blast tends to roll back over and errode the inner wall. (Any working furnace tends to modify itself internally to its ‘ideal’ configuration as a smelt progresses.)

 

(from 'If you don't get any iron' - EXARC, 2012-1)

http://exarc.net/issue-2012-1/ea/if-you-dont-get-any-iron-towards-effective-method-small-iron-smelting-furnaces

 

 

That is obviously the short form. Refer back to one of Lee's (or one of my own) formal papers if you want all the details on what we *think* is going on inside the furnace. For practical purposes, an tuyere angle of between 15 - 25 downwards angle has proven most effective with these short shaft furnaces.

 

Also, have you and the others ever put your recorded data into a database somewhere? Or, if you haven't, would you mind if I started consolidating all of your public data with others in a central searchable/queryable system?

 

 

At core this is the balance between doing, recording - and analyzing (!!)

Most all reading here are *doing*.

I have put together some overall charts of my own experimental work

http://www.warehamforge.ca/ironsmelting/smeltvariables.html

(only to 2007)

http://www.warehamforge.ca/ironsmelting/index.html

(at the top there are a set of 'point form main variables', each with images)

That web site also has all the data individually from all the smelts so far (although I'm a bit behind on the most recent ones).

 

I did start a larger project attempting to pull in all the data I could find, from individuals undertaking 'Dark Ages' period equipments and methods (c 450 - 1100). Since the explosion of interest in Early Iron, (and my own life, the universe) I have pretty much given up on that project (at least for now).

 

Right now Neil Peterson and I are attempting to get more data collected on all the blooms we have made and have on hand here. Primarily to get accurate weights and undertake very (!!) rough carbon content via simple spark testing. I freely admit the problems with sparking blooms, and my own limits on observations.

 

I remain (pitifully!) behind in the 'bloom to bar' conversion phase. Right now I'm trying to get some data together on loss rates at that step, especially as it relates back to the ore to bloom phase.

 

Oh, yea.

Should be making some more actual *objects* out of all this bloomery material too!

 

Darrell

website: www.warehamforge.ca
Blog : http://warehamforgeblog.blogspot.com
(topics include iron smelting, blacksmithing, Viking Age)

NOTE : Any posted comments may be converted into a future blog article!
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Bryan-

Tuyere angles vary with furnace design, but for a shaft furnace, I usually try to start with 17 degrees, and then alter in subsequent smelts if necessary. If the angle is right, the bloom will have a nice bowl shape with a continuous rim. If it's too shallow, the rim will cut under the tuyere, and lead to a kidney bean shaped bloom. If the angle is too steep, the bloom tends to be more ball shaped ( if there's plenty of room below the tuyere).

But that's detail stuff, You have to make a bloom before you can start worrying about its shape.

 

You might save yourself some confusion and questions if you buy a copy of "Ore to Axe"- just the price of 2 bags of charcoal.

https://www.createspace.com/336053

Trailer is on my website--

 

Lee

 

Lee

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Bryan-

Tuyere angles vary with furnace design, but for a shaft furnace, I usually try to start with 17 degrees, and then alter in subsequent smelts if necessary. If the angle is right, the bloom will have a nice bowl shape with a continuous rim. If it's too shallow, the rim will cut under the tuyere, and lead to a kidney bean shaped bloom. If the angle is too steep, the bloom tends to be more ball shaped ( if there's plenty of room below the tuyere).

 

But that's detail stuff, You have to make a bloom before you can start worrying about its shape.

 

You might save yourself some confusion and questions if you buy a copy of "Ore to Axe"- just the price of 2 bags of charcoal.

https://www.createspace.com/336053

Trailer is on my website--

 

Lee

 

Lee

 

You're late. I did like a week ago :)

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  • 2 weeks later...

To find the owner, find the street address if possible and see if your county has a property tax GIS system. These are usually online amd freely searchable. Once you have a name then you can call, send a letter, knock on the door, or whatever.

 

In the unlikely event Gwinnett County does not have a GIS database, go to the tax assessor's office and ask to see the tax maps of the area in question.

 

Also keep in mind many of these old prospect's mineral rights are owned by corporations like Virginia Iron, Coal, and Coke, not the actual landowner. I have had no luck trying to go through these companies, since many of them no longer exist. Since it's just iron, I would not expect any problems if they find out anyway. Unless you start full-scale commercial extraction, that is!

 

People skills help, and I am somewhat lacking in that department.

 

And when people skills fail, social camouflage comes in really handy.

 

Oh, and check your email, man.

The Tidewater Forge

Christopher Price, Bladesmith

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And when people skills fail, social camouflage comes in really handy.

 

Oh, and check your email, man.

Therein lies a story....

 

And I do check email, just not at 2 A.M...

 

Edit: sorry, didn't know gmail was not working if I didn't allow autosynch. Haven't gotten anything since who knows when? Just use the other one.

Edited by Alan Longmire
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