# Simple large furnace DIY



## kjavanb123 (May 22, 2017)

Hi,

Came across the following video, made by the same guy who created a mini arc furnace, might be useful,

https://youtu.be/y2RYYBRFu1A

Here is a link by the same guy on how to make the propane burner,

https://youtu.be/eO8NwseRxSA


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## Lightspeed (Aug 23, 2017)

For doing small pours with a 1kg crucible I built one of these, but use it laying down as the example is shown for a Blacksmiths forge. I built this way because I simply hate the idea of vertically lifting a crucible full of 1200 deg C molten metal and double handling, switching to another set of tongs to pour, so its a kind of furnace/forge/kiln crossover. I use it for silica melt dishes when I need to and silica or clay graphite crucibles.

https://www.youtube.com/watch?v=EFKoGZkUQt4

For safety reasons I started with a new store bought empty cylinder which is not a 9kg cylinder its actually 11kg, same diameter just longer/taller. I use a JF#1 burner which is 3/4 inch made by Thermal Art Design in the U.S.A. this burner is made from Stainless and has a replaceable flare when needed and adjustable choke, which is absolutely necessary for tuning your burner for Oxidising, Neutral or Reducing flame. I run a C.I.G. Edge regulator to a 9kg propane cylinder for fuel. A gas ball valve sits just before the burner fuel input line, No idle circuit or secondary needle valve.


The Refractory lining is Ceramic fibre in my case made by Unifrax, Durablanket Zirconium 2400f high density 1" thick, but 2 layers, so 2" total. I do suggest you put your money into buying the best grade ceramic fibre you can source. I also use a bubbled alumina firebrick as a base. Contrary to many instructions all over the web I did not use Sodium Silicate as a bonding and surface sealant. The reason being it was simply not necessary in my case as I was sealing the ceramic fibre with a wash coat internal layer refractory, in fact every exposed ceramic fibre surface(Ceramic fibre is dangerous when exposed please research this before using and constructing) In my case I used a locally made product called RTZ wash coat which is a highly reflective ceramic zircon coating applied in a thin layer by brush or sprayed on. In the United states the most highly acclaimed wash coat is called ITC 100 HT, I can get this into Australia though it is extremely difficult to source and is Ex United States only, the product is expensive and the single reason I did not use it is the cost of postage combined with the initial product price, if you can get it use it. 

This furnace is a simple project within the bounds and reach of the majority using this forum, it will melt a 1kg Salamander charged with Silver Cement to the top in around 5-7 mins once the refractory is up to temp along with the Crucible, depending on your output fuel pressure, I currently use around 10-15p.s.i. for silver and 20-25p.s.i. for gold. It is a brilliant and quite handy addition to your refining workshop, compact and very effective. I could easily fit/use a larger crucible but simply have no need for small melts.

You may choose to build as you would a normal vertical furnace, building this way you could fit a much larger crucible and even boost it with a blower, but you will need a larger burner in the 1" range, Hybridburners make such an item for those for whatever reason need an insane amount of heat, these are also engineered burners made in the United States and are amongst the absolute best available for temperature attainable by BTU output and economy. 

** Note There is no point having a Saturn 5 type burner if your refractory is not up to scratch, nor is it of any purpose spending your money on the best refractory if your burner does not have the BTU output necessary for your size chamber. There is an abundance of information on the web regarding this.
visit http://www.hybridburners.com/ and research, this site has an abundance of information regarding forge construction, it will need to be adapted to suit your own application. Don't try and re-invent the wheel, use what is proven and works. Beware of building burners out of bits of pipe fitting from idiots posting on youtube, the large majority have no bloody idea what they are doing or any comprehension of the danger through their inept stupidity they are peddling to the public.

If you are so inclined to do a Furnace for yourself, as in the other areas of our selected hobby/profession, your personal safety is an absolute priority, there are no second chances here when you have a full molten charge at up to 1300 deg C. If any of your appendages get into contact with the melt they are gone....instantly..... and gone for good. If you get molten flux on you it produces extremely Toxic burns that will poison your body, flux burns are worse than molten metal burns. Spend as much or more on safety gear as you do on your furnace build. I use elbow length, foil backed, internally wool lined, Kevlar stitched Aramid Gloves, if you think you can use welding gloves when extracting a crucible from this setup.......you are wrong!! Once leather is hot it will burn you, use a face shield, thick leather boots, molten splash resistant apron. This is a recommended minimum. Your safety gear should reflect your respect for ones life.

Best regards to all, just wanted to share a small project that works for me.


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## goldsilverpro (Aug 23, 2017)

I've built quite a few gas fired pot furnaces but never one with a kaowool type lining. Personally, I would never use it except for a one shot emergency, since I doubt if it's any more resistant to slag than insulating firebrick. I've always used at least 2" of castable refractory that's good to about 3000F. In refining, slag spills are quite common and I want to be prepared for them.

When I had my last refinery, I had a #16 furnace that I used daily. I had no pouring tongs, so all handling of the crucible, including charging, removal of the crucible from the furnace, and pouring was done with a single set of charging tongs - no changing to pouring tongs. I felt that, with proper technique, I could safely handle anything up to a #16 if the crucibles were store under dry conditions. Also, I used bilge type SiC crucibles almost exclusively. I used clay/graphite for pure silver.* I'm not recommending that you don't use the safer pouring tongs or even the most safe 2 man tongs. I'm just saying how I did it. *


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## snoman701 (Aug 23, 2017)

goldsilverpro said:


> I've built quite a few gas fired pot furnaces but never one with a kaowool type lining. Personally, I would never use it except for a one shot emergency, since I doubt if it's any more resistant to slag than insulating firebrick. I've always used at least 2" of castable refractory that's good to about 3000F. In refining, slag spills are quite common and I want to be prepared for them.



The slag spills are so so for the kaowool. You really have to give them a good coating of a refractory cement, preferably a rammable castable.

Insulating fire brick is also pretty prone to pitting with the castable refractory. Less so that just straight kaowool, but not nearly as good as a good dense castable.

In practice, it's best to use a hard refractory interior, with an insulating fire brick or kaowool lining. Both have their own purposes. Often the best way to do this is to create a shell with the fire brick, then create an interior liner with the castable. 

Look to glass working furnaces for great examples if you are looking to create a furnace that is economical to fire. If you just want to melt stuff and don't really care about the fuel useage, just use the castable.


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