# Mini firebrick furnace



## rfd298 (Jun 22, 2010)

I had to build my own mini firebrick furnace because I busted the awesome one that LaserSteve created. Unfortunately Steve has not been producing them lately and I needed to have a working furnace. Soooooooooooo I acquired some 2300 degree firebricks. I used my drill press to carve out the brick. Well I put three relief slots in to cut down on blow back; it was better but I believe it could be improved. In addition I also tiered it slightly as opposed to a giant bowl. Since I dumped the contents of my first ever melt into my original furnace, I tried to design it so that wouldn't happen again. I'll tell you what it melted the three buttons I put into it real quick.


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## chemist (Jun 22, 2010)

Very nice design! 
When you use it, do you place another brick on top of the crucible to cut down on heat loss?


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## rfd298 (Jun 22, 2010)

chemist said:


> Very nice design!
> When you use it, do you place another brick on top of the crucible to cut down on heat loss?



Absolutely. Like I said before, since Steve has temporarily stopped production of his furnace, I had to improvise, though pretty much it is his design slightly tweaked. So when he is back online, please purchase one of his mini-firebrick ovens because they really work well.


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## HAuCl4 (Jun 23, 2010)

Simplicity is a beautiful thing!.


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## rfd298 (Jun 23, 2010)

I decided to modify the design I made to improve heating times and blow back. This design may or may not work better. I did set this brick up to work with the 3" melting dish that Steve sells and another type that are a little smaller but have a pour spout. Anyway, I have a few more bricks and a couple of designs in my head. More to come.


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## HAuCl4 (Jun 23, 2010)

You may want to try a design with the torch hole tangent to the crucible, and only one exit (You can carve more exits later if it doesn't work :shock: ). Like this picture:


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## rfd298 (Jun 23, 2010)

I'll try that design next. Thanks


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## lazersteve (Jun 23, 2010)

A few key factors when designing the mini's:

1. The more brick you remove away from the bottom of the dish, the quicker the dish will cool when the torch is off.

2. The flame should hit the dish near the bottom center in the thickest part of the dish for fastest heating.

3. The flame should lick around the dish evenly on all sides to insure the entire dish gets hot all the way up to the rim. If the rim is not hot the gold powder will form a ring around the upper cool rim and the gold will not melt.

4. The furnace should have small exits around the top rim of the dish to allow the flame to escape. If the flame back washes out of the inlet hole the furnace will be very slow to heat and you will use more gas to melt the gold. You will also tarnish the torch tip shortening the life of your torch.

5. The furnace should be operated with a clean brick on top for fastest heat times. The more you peak, the longer it will take for your gold to melt.

6. The top rim of the lower brick should have a small indention in it that will allow you to grasp the lip of the dish with a pair of bent needle nosed pliers for pouring and casting.

7. The dish should ride in the lower brick touching around the upper portion of the rim. If the dish does not fit flush against the top inner rim of the brick, heating will be slower. The bottom of the dish should have about 1/4 to 1/2" clearance to the bottom of the furnace dimple.

8. The inlet hole should be large enough to allow the flame to enter in without striking the brick before it hits the dish. 

9. The torch should be positioned between 0 and 3/8" from the inlet hole. Adjust for best flame and least blow back out of the inlet. You want a good flame shooting out of the rim holes for fastest heat up time.

10. Preheat the dish from above. Preheat until a tinging or creaking wood sound is heard. This is the moisture escaping from the dish. Keep the torch from 6-8" away from the dish during this time. Slowly ease the torch closer as the noise is heard. Sprinkle with powdered borax when the dish glows a red color when under the torch flame.

Steve


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## samuel-a (Jun 23, 2010)

i never built one or owned one, but i would have give this design a try.


add 4-6 small outlets where the crucible and brick meet, place a shallow carved top and... viola....


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## lazersteve (Jun 23, 2010)

Sam,

That design is similar to how I make them except:

1. The inlet hole is level with the bottom of the cavity.

2. The inlet hole is angled up towards the bottom of the dish.

3. The cavity is not so round. It's more elliptical so more of the brick makes contact with the dish around the top. 

Steve


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## Dragnfly1 (Dec 5, 2022)

A couple questions I have are, does this work with propane alone or Mapp gas tanks? Has anyone tried using this with the microwave transformer that is converted into an arc with carbon rods from a 6v battery like they show on YouTube? I tried it like this but failed to get it hot enough , fast enough to actually melt PMs. My firebrick is different though. So I'm wondering if I should order this type of firebrick instead.


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## Yggdrasil (Dec 5, 2022)

Dragnfly1 said:


> A couple questions I have are, does this work with propane alone or Mapp gas tanks? Has anyone tried using this with the microwave transformer that is converted into an arc with carbon rods from a 6v battery like they show on YouTube? I tried it like this but failed to get it hot enough , fast enough to actually melt PMs. My firebrick is different though. So I'm wondering if I should order this type of firebrick instead.


I think you misunderstand. You can use a Microwave to melt metals inside refractory insulating firebricks.

And you can use carbon rods to create an arc to melt metals by a welding machine or other electrical power supply.

I never heard about doing both. The microwave will heat the conductors and thus increasing resistance decreasing efficiency, so it is counter intuitive in my world.


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