# i just bought 2 used kiln what to do with them?



## ericrm (Oct 4, 2012)

i just bought 2 big kiln for ceramic ,very sweet guy who sold them to me i know he wont read but i must say good thing... 

those are the beast


apparently they are rated 2350 f max from the spec, they are huge 2 feet by 2 feet...
anyone have played with those
i intend to melt aluminium copper brass or gold :roll: (if someday i have so much of it, that making a button will no be a option :mrgreen: )
i bougth them because i think they are cheaper to use than gaz fire fondry 
do i need ventilation when melting metal?

what kind of crucible should i use with that ? i remember a post about a guy who was making his own crucible if someone have it on bookmark it would be nice to send me the link.


----------



## MysticColby (Oct 4, 2012)

I haven't played with these, but I'm familiar with them from ceramics classes and I use furnaces for melting my metals.
graphite or silicon carbide (aka carborundum) crucibles are my favorite. clay should also work, especially because you'll be able to very easily control how quickly it heats up.
for melting aluminum, a cast iron pot will also work with great results

I would recommend melting all metals outside, or at least have high air flow. I think that pure precious metals shouldn't have any problems, but metals are rarely 100% pure.

copper and brass may give you some problems with oxidation. I recommend adding something that reacts with the free oxygen before they do. I'm not sure what; I usually just use a reducing flame on my propane burner and have the excess propane react with any spare oxygen. maybe powdered graphite?


----------



## NobleMetalWorks (Oct 4, 2012)

Just be careful with those types of kilns if you plan on melting any metal in them, what typically happens is that as you are removing the crucible, small amounts of metal can spill or splatter. If they get on the coils that run in the channels all around the inside of the kiln, it will ruin it.

Mostly people use those types of kilns for curing, firing clay, molds, etc.

They are work horses though, I know someone that has been running one for over 20 years.

Scott


----------



## etack (Oct 5, 2012)

best thing if you plan on melting large amounts of metal in them is to wrap some kwool on the inside and make a large gas burner for them. The amount of electricity you use will be huge.

The controller boxes are where the money is. Does yours have an automatic or manual temp. yours are probably not digitale so the won't bring that much money, but it will some. Your furniture and shelves will bring you some on the ebay.

There are a ton of these out there so I hope you didn't spend a fortune on it.

For me I want to deconstruct the one I just built and use the brick inside an old microwave housing to make a small melting furnace. I haven't decided on gas or electric.

The brick would have cost me more to ship to my house than what I paid for the whole thing. Plus all the extras I got.

I was wondering if you could take a picture of how the lid is attached to the top of it. mine is not and it looks like an easy fix from here.

also be careful about how you move the if you use a dolly place them on a board that spans the entire kiln if not you will break up the middle bricks on the bottom

Eric


----------



## ericrm (Oct 5, 2012)

i dont understand why poeple always think they will cost a fortune to run... the smaller one is 6900 watt 6.9kwh... at 0.08$ kwh it is 5.50$ for a 10:00 hour run, and for a gaz fired furnace is 40$ for a 10 hour run...........

the only thing i fear is it will take an eternity to melt but once again it is electric i just leave it on the side why i wrok on something else and ding when the time is done my copper is melted and hourray

but maybe i dont think clearly, i dont have much knowledge on that mather


----------



## etack (Oct 5, 2012)

You know when you do the math maybe it works out to be cheaper but not quicker. You need to decide whats best for you situation.

Eric


----------



## etack (Oct 5, 2012)

Thanks for the pics

Eric


----------



## MysticColby (Oct 5, 2012)

It should be cheaper to run for the heat it produces, but that's a huge volume to fill with heat. If you have a crucible and metal that fills a significant portion of it, then great. Otherwise it's inefficient. For large amounts of metal melting, it should be comparable in abilities to gas (and cheaper)


----------



## goldsilverpro (Oct 5, 2012)

There are several problems with electric pot furnaces

If there are any acid residues in the material you are melting (silver crystal, gold powder, etc.), the fumes can attack the elements. Also, the fumes from melting other things, such as ore concentrates, can do the same.

I am assuming the furnaces are lined with soft insulating firebrick, which is readily attacked by molten slag and/or metal. A small slag spill can eat a hole all the way through the brick. Also, if molten slag or metal gets on the elements, it can damage them. Most slag spills occur when the material foams over. This is usually due to using borax or other fluxes that contains waters of hydration. Standard grocery store borax has a formula of Na2B4O7.10H2O, which is 47% water. The water converts to steam, which expands and foams over. Borax is part of most all flux mixtures. Especially in an electric furnace, I would always use anhydrous (meaning no water) borax - Na2B4O7. The other flux ingredients, such as soda ash, should also be anhydrous

When things like the conversion of silver chloride with soda ash or the oxidation of base metals with niter are performed, the crucible can be severely attacked and can develop holes in it and leak slag and/or metal into the furnace. Also, normal melting will attack the crucible and, after a number of melts, it can get too thin and sprout holes.

_______________________________________

I agree with etack and would convert one of these furnaces to gas. I prefer natural gas over propane. Instead of glass wool, though, I would cover the insulating brick on the bottom and sides with about a 1 or 2 inch layer of refractory cement. If the inside is hexagonal or octagonal, I would pour the bottom and then use a plywood form to pour the sides in the same shape. You could use a round form but it would take more refractory, which isn't cheap.You would need a hole for the gas inlet and most gas furnaces have a slanted hole at the bottom to drain out molten slag spills. I would also cut down the soft brick about an inch at the top and, after doing the sides, fill it level with the shell with refractory. You might be able to use the original lid for awhile if you cut about a 3 inch in the center to act as an exhaust. Were it me, though, I would probably cast a new lid out of refractory, inside a metal ring with several pieces of rebar support welded to it. All in all, you could end up with a nice gas furnace.

That is what I would do if I had that furnace. As is, the electric furnace might be somewhat serviceable if you (1) are selective about what you melt, (2) are selective about what fluxes you use, (3) never put any wet material in the crucible (4) don't fill the crucible too full, and (5) don't try to get too much usage from a crucible. Also, if you get it too hot, it can splatter material out of the crucible. Just remember that one good flux spill could wipe out the furnace. I have seen many operating gas furnaces in my life and every one had some slag built up in the bottom of it. Also, even the bottom of a good refractory lid will tend to waste away.


----------



## ericrm (Oct 5, 2012)

that is some badash explanation
i does not intend to use any flux in it , as i intend to use it to make mostly copper anode
very good thing to know about borax witch if i understand you wrote is a probleme with any firebrick insulated fondry
thank you


----------



## butcher (Oct 5, 2012)

If melting copper you would need some type of flux like borax, and a carbon source in the flux like charcoal, flour, sugar, something of carbon that when burned would suck up oxygen and metal oxides from the copper and gas off as carbon dioxide gas.


----------



## ericrm (Oct 6, 2012)

butcher, why is this so important to remove oxygen?


----------



## butcher (Oct 6, 2012)

Many metals lower in the electromotive series than oxygen will oxidize easily in air, or in a melt where the heat can force a slow chemical reaction to speed up, or a chemical reaction to occur that would not normally do so otherwise. 
In a way a melt can be like electrolysis, forcing a chemical reaction to occur that might not occur otherwise with metals and chemicals.

This oxidized metal will not melt into a metal, but would burn off in fumes or go up into the slag of the melt, a flux covering can help to keep oxygen from the surrounding air from oxidizing the metals in the melt and help in making the melt more fluid along with other beneficial properties.

Adding a carbon source will collect oxygen from the oxides of metals or from oxygen that would form metal oxides in the melt (chemical reactions of the melt), removing oxygen formed with the metal you plan to melt (metal oxide), it can also help absorb oxygen from the environment of the melted metals surrounding air or air or oxygen used in the torch or melting process, which are used to generate enough heat to get the metal to melt, the oxides and carbon in the chemistry of the melt can also generate more heat in the melt (carbon a fuel source oxide supplying oxygen and heat from the melt generating a chemical reaction that supplies more heat, as the carbon burns off as carbon monoxide or better yet as carbon dioxide)

I think of the melt is in essence as a chemical reaction, the heat of the melt is only one part of this chemical equation, heat that can also speed a reaction, carbon source in this chemical reaction will collect the oxides in this reaction from the metal, and give back the metal an electron (that oxygen took from the metal to form the oxide metal salt) the metal gaining back its electron will now be an elemental metal and will be so after the melt, the carbon collects oxygen and burns it off as carbon dioxide giving up heat in the process the carbon dioxide leaves the furnace as flue gas, taking the metal robbing oxygen with it.

I do not know if I explained this very well.


----------



## acpeacemaker (Oct 6, 2012)

Is the same thing done when atomizing copper under steams or a high pressure. Being that a constant stream of water would have some form of oxygen?


----------



## butcher (Oct 6, 2012)

I have no clue.


----------



## ericrm (Oct 6, 2012)

what your saying about oxidized metal going off in smoke ,is that what they call the ' melt loss' ?


----------



## goldsilverpro (Oct 6, 2012)

Most of the oxidized copper, etc., will be in the slag. That will result in a weight loss of the metal.


----------



## Westerngs (Oct 6, 2012)

If you are going to melt metallic copper to pour anodes, there is no need to use a flux. Just cover the material with new charcoal every time (do this before you start to melt). The charcoal will keep the oxygen from entering the molten copper. Keep the charcoal in place throughout the melt and pour process.


----------



## philddreamer (Feb 13, 2013)

Werterngs wrote:
"If you are going to melt metallic copper to pour anodes, there is no need to use a flux. Just cover the material with new charcoal every time (do this before you start to melt). The charcoal will keep the oxygen from entering the molten copper. Keep the charcoal in place throughout the melt and pour process."

Westerngs, will that procedure also apply for just Cu ingots?
Thanks!
Phil


----------

