# trouble furnace



## Dlog Renim (Jun 27, 2012)

Hi all..

i did a furnace (mini one) to melt small batch.. it seem to heat.. but cant melt aluminum.. well maybe i have problems with my propane tank.. the gas flow regulator seem to malfunction .. when i put the propane bottle side way.. the gas flow boost by it self and the flame shut off 

here picture of what i did..

i crunched fire brick into powder to fill all the inside of the biggest can... and on top i made about 2 inch of that powder into cement



























this last picture it what i get from a foil paper after 15min in my little furnace...

some advise ???


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## jimdoc (Jun 27, 2012)

I hope you don't plan on melting any precious metals in that metal crucible.

Jim


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## Dlog Renim (Jun 27, 2012)

not for precious..

i wanna melt aluminium from radiator heater on GPU board


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## jeneje (Jun 27, 2012)

The type of torch you are using will not do what you want. You will need a bigger furnance and at least a 20lb tank with enought pressure to push the heat. You will need a complete burn(Blue-green flame) to achaive melting temp. The firebrick will have to reach temp first and then the chamber will rise in temp to begain the melting. Hope this helps you.
Good luck with your project.
Ken


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## MysticColby (Jun 27, 2012)

I believe that torch can adequately melt aluminum in a furnace of that size. But 15 min is probably too short, as the torch is smaller than ideal.
I think what the main problem is is furnace design. Currently, you seem to have the fire directed at the furnace wall below the crucible, expecting the heat to rise to the crucible. That is inefficient. Most of the heat will be absorbed by the furnace wall.
The more efficient setup would have the flame directed at a 45º angle onto the side of the crucible so it circles around the entire crucible.
check out this thread: http://goldrefiningforum.com/phpBB3/viewtopic.php?f=56&t=13162
It's intended for melting PMs, but will work for aluminum (wouldn't need quite as big of a torch for the lower temperature)

A few things on melting aluminum:
steel or iron crucibles work very well when melting aluminum. But they have limited uses (the high heat causes rapid oxidation (rusting) on the outside of the crucible).
melting aluminum foil as-is won't get you a pool of molten aluminum. The high surface area will cause nearly all of the metal to oxidize as it's in the process of melting. A successful technique is to melt some more substantial aluminum, then add the cans or foil (crumpled into tight balls), and push the foil ball under the surface of the molten aluminum with a long metal or graphite rod (I use a fireplace poker). I get about 82% recovery, the other 18% being lost as aluminum oxide (slag), which floats on top of the aluminum and can be scrapped off or aluminum poured from beneath it if it's not too much.

hmmm, re-reading your post, you might not be trying to get the aluminum, but rather get the aluminum off. If that's the case, it's worth noting that aluminum will get very malleable when it's hot but below it's melting point. Might be possible to heat to that point then scrape it off with a screwdriver.


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## Dlog Renim (Jun 27, 2012)

all i wanted to do..

is to lurn how those litle kind of furnace work..

by building one.. i taught it would be the good way..

So far what i know is my source of fire (the torsh) seem to be broken.. ill try with a other one..

I wanna melt those just for fun.. and make litle ingot to get the technich to manipulate blah blah blah..

i took the concept from youtube.. some does the same thing but with a air drier and some charcoal instead of propane... and some use the yellow gas bottle..

heres a vid of what i did exactly.. except i dont have the same flow of gas

[youtube]http://www.youtube.com/watch?v=NZZPXU02iJE&feature=related[/youtube]


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## jeneje (Jun 27, 2012)

The last 30 seconds say it all!! Check out the heat source. Propane want work in his design.
Ken


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## publius (Jun 27, 2012)

First, you don't need the can with the holes in it as in the original. A simple cylinder of fireclay and sand with a plinth block on the the bottom to keep the crucible up off the floor. The next thing is to set the tuyere at an angle so the flame swirls around the crucible. When you set the crucible on the plinth put down a piece of cardboard so the crucible does not stick to the plinth.

The torch should not be laid on its side. The fuel is liquid inside the tank and needs to expand in the upper portion of the bottle so it can burn well, so keep it vertical to leaning more than 30 degrees off vertical. I have used propane to melt small quantities of Aluminum in a furnace like this. MAPP gas and acetylene are much faster.

Others here have given you good advice. Look for a book At the Lindsey Publications web site (http://www.lindsaybks.com/dgjp/djgbk/found/index.html) where you will find "Building a Gas Fired Crucible Furnace" for about $13 USD plus shipping. This, by the way, can be adapted as a assay furnace. [/hint]

Robert Jeffery, CWI


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## Dlog Renim (Jun 27, 2012)

cool.. tank you all for the advise..

ill go read this and give a other try


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## MysticColby (Jun 28, 2012)

it's true you don't need an inner can container to act as the wall of the foundry when you use fireclay. But he said the walls were filled with crushed fire brick, so you would need something to keep it from caving in. For this type of furnace, I would recommend going the fireclay route.
But personally, I prefer using whole fire brick arranged into walls. Just seems cleaner and like it would last longer (also easier to fix: just take out broken brick and put in a new one).

charcoal with an air blower can be used to melt aluminum. the coals should be below and around the crucible (the more surface area that's in contact with the coals, the better) with air being blown in somewhere near the bottom.

I want to share 
My big aluminum furnace runs on coal simply because coal is cheaper for the same weight and produces more heat for the same weight.
I was able to design mine so there is a cylinder of dense fire brick on sides and floor (yellow in picture), surrounded by perlite (white in picture). Air is blown in through multiple holes in the floor. It even allows for spilled aluminum and ash to fall through the holes onto the gravel road below for easy cleanup. The holes are actually drilled into the dense fire brick, and the brick is held up by a grate made of aluminum I made. The bars of the grate are spaced perfectly so they are exactly between each hole. Air flowing through the holes is enough to cool the bottom brick so the aluminum grate doesn't melt, and being completely hidden protects it from IR heat.  The walls are a 25 gallon metal trash can (brown in the picture), the floor that the air tube goes through is cement and perlite (black in picture), the lid is fire clay / cement / sand / perlite slab I made a while ago for another furnace (black in picture).
After some use, there are a couple holes that are plugged by molten iron from a crucible that failed, but there are still like 100 good ones, so it'll be a while before I need to replace those bricks. It would be too hard to melt the iron out, but maybe I could rapidly oxidize or dissolve with chemicals... HCl maybe? would that react with the fire brick?
The outer walls do get hot, but it seems to happen from the top down, meaning it gets hot because the fire touches the top of the can (around the rim) and travels down, not because heat is lost through the walls. Perlite is VERY insulating, but melts at high temps (well above the melting temp of aluminum, but the coal/charcoal can get hot enough), hence the fire brick.
Everything except the cement floor is loose. The perlite keeps the bricks in place, and each brick has a beveled edge that keeps it from falling in. If a brick breaks, I'll probably leave it in place. If several break or perlite starts falling in, I can take everything out and replace the broken parts with spares I made. The floor, being the most delicate and with the most strain on it, can be replaced without taking anything else out.
Overall: The inside diameter of the cylinder is 31 cm (12 inches). The inside height of the cylinder is 42 cm (16 inches). The cylinder is a decagon (10-sided), 2 bricks tall. The whole thing can be picked up and moved by 1 person awkwardly or 2 people easily, maybe 25 kg (55 lb). Crucible is a 4 quart cast iron pot, can hold about 9.5 kg (20 lb) of aluminum. Takes about 60 minutes of preheating before it starts melting.


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## Dlog Renim (Jun 28, 2012)

so today i cut the first can floor.. so now i can put my crucible right at the good place.. so far in 10min.. i did a little puck hehe

i would need a better air intake.. i think ill give a try with some charcoal


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## Dlog Renim (Jun 28, 2012)

second try.. seem i get a better heat now.. i can fill up to half the crucible.. but pass that not enough heat 
as i have no mold to pour in.. i leave it cool down in my crucible (tomato can) 
i can see less default to in the block.. guess its because my heat was higher than the first try

so ill build the same one.. well sorta.. and will put a real burner on a BBQ tank this time.. i got the book to about how to build your own blah blah blah.. this should help out..

ill keep this one as a souvenir and for small batch or demo for friend.. now my GPU rad are taken less place.. need to give a try on casting with black sand hehe

tank you all for the help on this one


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## MysticColby (Jul 3, 2012)

It looks like you do have aluminum there, but also a lot of slag (aluminum oxide). If you want useful metal, pouring into an ingot mold is required.
cheap ingot mold ideas:
cast iron or steel muffin tins
old metal cooking pot with tapered edges
green sand (sand + clay. google it for details)
You can even scoop a small hole out of a gravel driveway and pat it smoothish. You'll pick up some rocks, but those can be picked off once cool. Make sure it isn't damp at all (liquid metal + moisture = steam explosion), and do NOT do any of this over concrete.

Picture is me, crucible is cast iron pot, molds are cast iron, about 2 lb (1 kg) aluminum when full (about $10 each from some sort of online casting supply store, I forget where but could find it if you want). You can see the aluminum oxide in the crucible (rough part), and how the smooth, clean, aluminum pours out from beneath it.
That metal was pretty clean to begin with... probably part of my brother's engine I melted down after he destroyed it.


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## BAMGOLD (Jul 3, 2012)

Can I ask what the point in melting down a 50cent per pound metal is?


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## MysticColby (Jul 5, 2012)

Fun
Though I will agree that it does cost more to melt than the metal is worth
I make aluminum castings (art)
It adds some intrigue to never have to buy the metal


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## Dlog Renim (Jul 5, 2012)

Hi well the point is :

- i get to understand better how the furnace work... try and mistake and apply the good solution for further construction

- i get use to handle hot melting metal.. so later when i will work with more precious one.. i will have little experience

- also aluminium is waaaay easy and free to me to get .. also remember i live in a apartment.. so i don't have much space to work with a bigger furnace that could probably melt better metal..

For the swag.. i discover (well not me but here on the forum) how to remove it.. by adding salt and bicarbonate ... 

i did a little try to make a mold .. for a little gift to my girlfriend.. i took all the block to remove the swag (you can see the piece at the bottom was way much cleaner aluminium)

here what it give


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## publius (Jul 5, 2012)

Great try. I like the idea of small steps before moving on to the real precious metal. Keep up the good work!


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## BAMGOLD (Jul 5, 2012)

Point taken.

I may be interested in the aluminum your pouring actually, I don't know much about the alloys and such of Aluminum, but I love making things out of aluminum, and would like bricks of aluminum to mill down.

let me know what you have, and I may be able to help you gain some money back if you choose.


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## MysticColby (Jul 6, 2012)

that does look a lot cleaner, good job!
salt and bicarbonate to remove slag... never heard of it, but it does sound similar to other fluxes. I'll have to try it. Where did you discover that? what proportions?


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## rewalston (Jul 6, 2012)

If working with molten aluminum, a good drossing flux is equal parts of sodium chloride and potassium chloride. It looks almost like water when molten, cleans all of the dross right out. And if you want to recover any alumina that is in the dross, just drop the whole thing (the dross or slag) into a bucket of water, the two salts dissolve leaving the alumina behind. You can then evaporate the water and recover the salts to be used again.

Rusty


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## goldpete (Jul 6, 2012)

Dlog Renim said:


> all i wanted to do..
> 
> is to lurn how those litle kind of furnace work..
> 
> ...


i built mine in a similar way except i used cement, sand and perlite mix for the walls and also made a lid to match with a small hole in the middle . and i use bbq heat beads(coal) and a hair dryer on an angle to make the heat circle . and omg it gets so hot


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## Dlog Renim (Jul 6, 2012)

exactly what rewalston say... i dint have exactly the good thing hehe but yeah that's what they use to cast aluminium car part.. they add those 2 thing one a the time getting the swag out between and after.. and in the video they told it help when time for pouring into the cast and wont make bubble ... i took a cookie mold .. they use black sand so cant tell about the bubble ..


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