/diy/ - Do It Yourself

[Anonymous No.1106120]

What's the trick to attaining very high temperatures with a furnace?
I'm curious as to whether I can make a wood-fired oven capable of either cooking pizzas or melting metal.

[Anonymous No.1106124]

>>1106120
Two very different functions. An oven for cooking, you want to be fairly large to accommodate whatever you want to cook, and also large to give a more even heating temperature across your food so you don't get burned areas and undercooked areas in the same piece of food.

For a forge, you want as small an area as feasible compared to what you want to heat up or melt, and get it as hot as you possibly can in that small area regardless of how hot the rest of the forge gets.

Also, while you can cook just fine with wood, wood itself is not a great substitute for charcoal in a forge. The refining process of turning the wood into charcoal makes it a much better fuel for reaching the highest temperatures you can get to. Luckily if you're a poorfag, you can turn wood into charcoal yourself. There are a bunch of ways, the easiest being to just shove as much wood into a metal can as you can fit and throw the whole thing into a fire.

[Anonymous No.1106127]

>>1106124
What about an oven of this shape, with the cooking/smelting area in red and the air intake in blue?

[Anonymous No.1106128]

>>1106124
A proper wood-fired pizza is hot enough to melt zinc. You are correct though. A pizza oven at 800F that has a lot of zinc chucked in will instantly go down in temps and stay down as it tries to heat up the zinc. That length of time may be too long and the masonry's stored heat will peter out before the metal is melted. Thus, an actual furnace is needed, because a pizza oven use residual heat to cook, not applied heat.

[Anonymous No.1106132]

>>1106127

a dual use metal melting furnace/food oven seems like a pretty good way to ingest weird toxic shit

[Anonymous No.1106133]

>>1106132
this

[Anonymous No.1106134]

>>1106120
>>1106127
Why do you want one oven to do both? It will be much easier, more effective, and safer to make a separate oven and forge.

[Anonymous No.1106136]

>>1106132
>>1106127
>>1106120
Do it this way. Fire in bottom that melts the metal in the furnace above. Waste heat from the furnace goes up inside the wall of a double walled pizza oven. No gases enter the pizza oven to touch the pizza, they go around the pizza oven's inner shell.

Melt aluminum, zinc, lead, and other low temp metals while cooking food.

[Anonymous No.1106161]

>>1106120
My gf begs me to cum inside her, and she always cums when I do it. Says it's the best part.

[Anonymous No.1106243]

>>1106136
I was hoping to have a single-opening furnace, if I'm going to have a large structure in the back yard it might as well be decorative, so I was thinking it'd be cool to make a dragon popping out of the ground.
Could probably make local news if I made it look like Smaug, given that I'm in New Zealand and nothing ever happens here.

[Anonymous No.1106658]

>>1106243
I'm not sure how serious you are so I'll keep it short.

he gave you the best answer. i once knew a guy who worked glass out of a wood fired furnace in italy. its close to what he drew. you can look up glass wood furnace/ crucible and probably find the information you are looking for. the key is insulation/refractory material. Those temps would require a lot of hot burning wood as a given. Probably a low roof in the burn area. you should build a few small gas ones to get the general idea first.

[Anonymous No.1106692]

>>1106658
Pretty serious, it'd be a fun project.
The problem is, it seems like no matter what I'm going to need one or two extra openings.

[Anonymous No.1106710]

>>1106692
The openings don't need to look like openings.

[Anonymous No.1107125]

>>1106710
Hmm, how about this then?
>mouth for both inserting fuel and for cooking
>openable belly for melting metal, hook for hanging crucible
>grate for ash to fall through into a pit as wood burns

I wonder if I can make everything, including the crucible, out of clay?

[Anonymous No.1107126]

>>1107125
forgot sketch of rough form

[Anonymous No.1107136]

>>1107125
It won't last very long, made of only of clay. Clay-base only for the pizza oven, but thick refractory inside and clay-base outside for the furnace.

[Anonymous No.1107206]

>>1107136
What is clay-base?
Also, what can I make refractory out of?

[Anonymous No.1107214]

>>1106120

Have we decided to just give that starting image a free pass?

[Anonymous No.1107217]

>>1107214
Yes

[Anonymous No.1107220]

>>1107217

Fare enough.

OP, is this for a temporary setup? That's what it's sounding like.

[Anonymous No.1107223]

>>1107220
Permanent.
I have plenty of space to build a big thing, so I might as well build a big thing, but I don't want to create clutter by building multiple smaller things.

[Anonymous No.1107224]

>>1106120
Coal logs for pottery khelms, they burn white hot with a little bit of airflow

[Anonymous No.1107231]

>>1107223
>Permanent

You can have a permanent pizza oven but you can never ever have a permanent metal foundry furnace. This is because the refractory deteriorates and you much rebuild the furnace over time. You could just make the furnace section removable in some way so you can replace only the refractory and perhaps a metal shell it is in.

[Anonymous No.1107233]

>>1107231
What is the refractory though?
What is it made from that makes it need to be replaced?

[Anonymous No.1107237]

>>1106120
>What's the trick to attaining very high temperatures with a furnace?
A combination of several factors: choice of fuel, ample and well-controlled air flow, insulation of hot areas, recapturing heat from exhaust to preheat incoming air, careful arrangement of flame to effectively deliver heat to the item to be heated.

>whether I can make a wood-fired oven capable of either cooking pizzas or melting metal.
As with many such inquiries, it's possible, but practicality is a very different question. In particular, "metal" is a rather broad category, much of which requires hotter temperatures than a pizza oven operates at, and much of which produces toxic fumes that should be kept away food and food preparation equipment. If you want to melt lead-free pewter, it shouldn't be difficult. If you want to melt iron, you're going to have trouble.

[Anonymous No.1107242]

>>1107237
I don't see why a furnace+cooker like >>1107125 would have a disadvantage over a regular furnace though.
Wouldn't the main problem be that the difference between iron melting point and clay melting point is only 200'C?

[Anonymous No.1107246]

>>1107214

Face it, bro: Everyone wants to fuck that bunny.

>>1107233

"Refractory", in this case, is simply referring to the insulating structure that keeps the heat in the furnace.

It's basically a consumable. There just isn't any material that is the right combination of heat tolerant, insulating, and durable. The high required temperatures and mechanical stress of the heating/cooling cycle degrades it over time, and its replaced as necessary.

That being said, good refractory material does last more-or-less indefinitely when working relatively low-melting-point metals (such as aluminum or zinc). Anything involved in melting any sort of iron alloy, however, will need regular maintenance.

[Anonymous No.1107248]

>>1107242
>Wouldn't the main problem be that the difference between iron melting point and clay melting point is only 200'C?
That's a deal-breaker (metals need to be rather above their melting points to be practically castable, the oven has to be rather hotter still to heat the metal to that temperature in a reasonable amount of time, and 200 degrees from their melting point most materials are sagging from heat-induced loss of strength), but it's not the only one. Another is that wood doesn't burn hot enough to melt iron. Period. The kinds of flames used to melt iron are typically nearly-pure carbon fed with preheated forced air wrapped tightly with a refractory enclosure. An open naturally-ventilated furnace like that wouldn't even get hot enough to forge iron, let alone melt it.

[Anonymous No.1107249]

Over here where u live everybody has some kind of fireplace they use to heat their home. I live close to the arctic circle.
The way people use a fireplace is to have a "baking oven" meaning a large brick fireplace where you heat the bricks by burning wood, remove the ashes and the embers from the fireplace, close the dampers(s) and put the food in the fireplace. It has a constant heat for a long time thanks to the large thermal mass. It also serves as a heater for the home as one can store heat in it, meaning one can heat it just a once/twice a day and save on heating.
This is the way I'd do a oven that works with wood. As a foundry can be built from scrap anytime id build another one for melting metal. I'd never ever mix these two. But it's OP's choise, obviously, I just wouldn't do a dual thingie. Just not worth it. A proper wood fired oven is good for both heating and cooling and a foundry is good for melting metal.

[Anonymous No.1107251]

>>1107246
Objection!
I do not wish to fuck the bunny, 3 is my limit.

So, is clay suitable refractory?
Because that'd be convenient, since it can be pasted on as it wears away.

[Anonymous No.1107255]

>>1107251
>So, is clay suitable refractory?
Suitable for what? What kind of clay? Are you slapping it on and letting it dry, or are you firing it into bricks?

[Anonymous No.1107256]

>>1107255
Whatever I find in the river, there used to be a brickworks in my area so I want to find out where it was so I can collect clay.

[Anonymous No.1107258]

>>1107256
Suitable for what? Are you slapping it on and letting it dry, or are you firing it into bricks?

[Anonymous No.1107262]

>>1107258
Slapping it on and letting it dry, I want a nice smooth form.
Unless bricks offer an advantage, in which case it will be partially brick.

[Anonymous No.1107266]

>>1107262
Suitable for what?

[Anonymous No.1107267]

>>1107266
Oh, suitable refractory for a furnace.
Well, I suppose it's suitable for aluminium and stuff, but I guess I mean "what metals is it suitable up to?"

[Anonymous No.1107275]

>>1107267
>aluminium and stuff
If you fire it into bricks, it might work for aluminum, if you use a cooler flame than is usually used for aluminum. Though with wood fuel that shouldn't be a problem. Copper and its alloys might work for a single firing. Iron is right out.

Fired bricks have structural strength. Dried clay turns to powder under any stress. Unless you sculpt the entire refractory vessel and bake it in a kiln, a single smooth piece won't hold together.

[Anonymous No.1107283]

>>1107275
So what about this plan?:
The exterior of the walls will be smooth pasted clay, the core of the walls will be fire brick, and the interior will be ablatitive pasted clay which is replaced occasionally.

[Anonymous No.1107397]

>>1107283
Inner pasted clay falls down when you first fire up the furnace, outer pasted clay falls down the first time it rains, and the fire bricks fall down soon after that because there's nothing holding them in place. Fire bricks are typically supported by steel or conventional brick. And if you want to melt iron, you'll need special high-temperature fire bricks, since conventional fire bricks can't handle that temperature for long.

[Anonymous No.1107398]

>>1107397
So what would work then, if I wanted a pasteable inner and a pasteable outer?

[Anonymous No.1107407]

>>1107398
Inner shell of fire brick and fire mortar, with inner coating of fire mortar. Outer shell of brick and mortar, with outer coating of cement render. Concrete slab foundation. Steel doors/fixtures bricked in place, previously coated with high-temperature paint/enamel.

[Anonymous No.1107414]

>>1107407
I don't have fire mortar or cement render.
Are they common?

Also, if I can fire bricks out of clay, why would pasted clay fall apart when the furnace is fired up?

[Anonymous No.1107440]

>>1107414
>Are they common?
Cement render is cement applied as an external covering to masonry. Since you're posting this here, you probably have cement locally. Fire mortar is something of a specialty product, kinds suitable for an iron-melting enclosure rather more so. You might not find it locally in retail, but it can be bought online. e.g. https://www.amazon.com/Rutland-12-5-lbs-Castable-Cement/dp/B000H5T5EA/ref=sr_1_4?ie=UTF8

>why would pasted clay fall apart
Kilns slowly raise dried clay to a precisely controlled firing temperature and hold it there for a long time, then slowly cool down. This reduces thermal stress, steam explosion risk, and inconsistent vitrification, while allowing the clay to shrink slightly from firing. Pasting clay on bricks, then baking it with the fire it contains would produce fast, uneven heating, cold spots that never vitrify (these would be on the border between the pasted clay and brick, preventing a structural bond), and any vitrified sections would pull away from the sides when they cool and shrink. The movement and thermal stress would help convert the merely dried clay back into powder even if you avoided bumping the sides as you add fuel / heat things.

[Anonymous No.1107451]

>>1107397
In my experience, clay is more resilient than that.
I have unfired clay stuff which handles water just fine.

[Anonymous No.1107454]

>>1107451
>unfired clay stuff
You mean "unglazed" right? Because without being fired, dry clay absorbs water and becomes wet clay. That is, mud.

[Anonymous No.1107458]

You should not melt metal and prepare food in the same oven. You'll create a serious heavy metal poison hazard.

Don't do it, you'll end up poisoning yourself and your loved ones.

[Anonymous No.1107590]

>>1107454
No, I mean unfired.
I have an ornament outside I made myself which is designed so a small fire can be prepared in it, and neither the fire inside nor the rain outside has harmed it in the slightest, even the fine details of it are intact; and I live in a place where the weather is incredibly unpredictable: Strong wind, rain, and sun can all occur in a matter of several hours.

So I have a hard time believing what you say about pasted clay being destroyed by rain and fire.

[Anonymous No.1107606]

>>1107590
That's because you inadvertently made earthenware without realizing it. A furnace, for melting metal, will need refractory insulation; which will prevent the clay outside; turning into earthenware when the furnace is fired.

[Anonymous No.1107770]

>>1107606
What's wrong with earthenware?
If it resists fire and rain, it's good enough for me.

[Anonymous No.1107771]

>>1107770
The fucking distinction here is proper terminology. Earthenware isn't raw clay.

[Anonymous No.1107777]

>>1107771
So it doesn't matter if I have an earthenware furnace?

[Anonymous No.1108618]

this depends on the clay in your area. it is unlikely it is suited for your purpose. commercial refractory material is made under tremendous compression. the reason all those build your own forge people posting questions about their shit not working is usually placed the torch where it doesn't get enough fresh air or poor refractory material. honestly you can build a hot ass furnace with a small torch if you know what you are doing. i nobody just builds a perfect earthen furnace their first try. their are many variables. if your clay is suited for such you may have a fire brick manufacturer near you. this is without question your best chance for success.

[Anonymous No.1108777]

>>1108618
You can easily DIY your own refractory mix and bricks at home in your backyard. People do it all the time. You don't need "good" clay either. You can slip some bad clay to refine it.

[Anonymous No.1108823]

>>1108618
There used to be a brick manufacturer at a nearby river. I don't know if they produced fire bricks though, the only info I can find is a short article from over a century ago.

>>1108777
What would a refractory mix be though?

[Anonymous No.1108831]

>>1108823
https://www.google.com/search?q=refractory+mix+recipe
https://www.google.com/search?q=diy+fire+bricks

[Anonymous No.1108843]

>>1106120
oxygen line and or turbo