Setting up a furnace, with a couple questions

[Michael Spaulding]

Crappy picture time!

I did a quick MS Paint mockup of my foundry. I've decided to build it raised, about 3 feet off the ground, on a bed of bricks. This way it'll be about waist height and can be used more easily as a forge as well. Just remove the panel over the air vent, to give it a less direct air path, and to give me enough room to stick blades in to heat 'em up. I don't plan to smelt ingots and forge at the same time, as they require two very different temperatures, but is there any glaring issues with this plan? Anything you would change, or that jumps out at you as a significantly better idea?

Thanks for the input!

[ThomasPowers]

Where is the space for the  cubic yards of charcoal required for melting?  How are you adding it and cleaning out ash?

 

(BTW Unless you are starting with ore you  are *not* smelting)

[Michael Spaulding]

everything will be added by removing the top center piece, ash cleaned out with a spade the size of the vent hole, scraped right out and into the awaiting bucket.

Is there a metric or chart on determining how much charcoal I need to achieve a given temperature with a specific amount of airflow? Or a minimum amount of charcoal I should shoot for? I can easily add to the height of the thing until the necessary volume is achieved. (Taking into account the added volume of the crucibles)

As for smelting, I would like to get to that point eventually, working with raw ores, so this is intended to be a smelter, but until I can reliably source raw iron in reasonable amounts (for a small forge) then I'm stuck melting Steel with known carbon levels (Among other things) and blending with sorel to achieve something like wootz

[ThomasPowers]

well the btu content of charcoal is pretty well known; calculating "how much" to get X temperature can be tricky with all the variables involved.  I am surprised that you will be removing the top and the crucibles so you can shovel out the ash during a run; will really slow things down.  You may want to think about a perforated bottom to let ash drop.

 

Looks to be designed as a forge and not a smelter.  For a quick cheap prototype dig a trench in the ground and try it out with the width and height you plan.

 

Also remember that when forging a blade you only want to heat the part you can work before it cools; heating the rest causes: grain growth, decarburization and scale losses.  Only during heat treat do you want to heat the entire length to temp!

[Michael Spaulding]

I wasn't planning to add any charcoal in the middle of a run. I was mostly using Ric Furrer's sealed crucible furnace as a guide, from his famous video. The goal is to not need to touch the furnace, or its contents, while firing crucibles, and I was attempting to see it up to me cleaned easily between runs.

Also, I plan to only heat the part I'm working on, but with this setup I can put the whole blade in, and move the coals to where I need them.

[ThomasPowers]

Do a simple test run melting some brass with charcoal in a trench the size you plan to use to get a handle on how it works---and double the amout of charcoal for brass to steel.

[Michael Spaulding]

That's a fine idea.

Should I have any worry about keeping it hot long enough? Most texts I've read on Wootz say it needs to be heated to 1260c and kept there for 60-90 minutes. Would that amount of charcoal not only get it to the correct temp, but keep it hot enough for an hour? Or should I compensate with more charcoal and less air flow?

[Michael Spaulding]

Alright, I've made a couple decisions on design.

Instead of converting it from furnace to forge, I'm going to build two separate structures. This way I don't need to make so many compromises to make both, and fight to get it to work as either.

I plan to buy a pallet or two of brick and just go have some fun building the bases. This will change my budget, but hey, that's what budgets are for.