# Need to Build Furnace to get hot enough to melt copper



## greatgems (Mar 22, 2012)

I need to make a furnace affordably that can melt about 10 kilos of copper at a time would like for it to get to 1400C or higher would be great to get to 1900C any advice and plans would be great


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## martyn111 (Mar 22, 2012)

http://www.artfulbodgermetalcasting.com/


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## MysticColby (Mar 22, 2012)

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=56&t=13162

I've successfully melted copper in this. It'll take up to a size B2 graphite crucible (4-1/2 height : 3-7/8 diameter), which holds 2 pounds of aluminum (907 g Al or 3009 g Cu or 3523 g Ag or 6490 g Au) though I wouldn't want to fill it to capacity. better to do less than 2/3 so you have a rim to hold onto. Anyways, 10 kg of copper would require a B8 crucible (B10 crucible to be safer).
As it happens, I'm currently working on a big brother furnace to this one that will accommodate a B10 or B16 crucible (/maybe/ a B20, but that'd be a tight fit) ^_^. The one in that link has 6 bricks on the wall (hexagon) and half a brick on the floor. The one I'm making (which will be for aluminum) will have 20 bricks on the wall (2 sets of 10 bricks stacked on top of each other = decagon), and 2 layers of 2 bricks on the floor. I doubt I could melt PM in it with the torch I have in any reasonable time, but with a bigger torch, it could be done. All I have so far is a design, plans, jigs, bricks. Need to cut bricks, arrange, assemble.
cost of bricks = $72. cost of wood for jigs = $2. cost of metal clamps = ~$15. Then there's non-consumables like a wood shop, carbide hacksaw, circle saw.
One could probably be made for cheaper with a recycled water heater and insulating blanket, but I like the feeling of durability and solidity of these style furnaces.


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## greatgems (Mar 23, 2012)

Really nice design. Anyone have one using acetoleen to get there tempatures higher? Any advice on getting a furnace like this to 1800c i also want to treat sapphires thanks.


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## jimdoc (Mar 23, 2012)

Forget about punctuation already?


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## greatgems (Mar 23, 2012)

for a quick forum post? Didn' feel perfect grammer was need, but answers would be awesome.


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## Oz (Mar 23, 2012)

greatgems said:


> for a quick forum post? Didn' feel perfect grammer was need, but answers would be awesome.


Just don’t be in a hurry and sloppy with a crucible of molten metal or you may pour it down your boot.


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## Harold_V (Mar 24, 2012)

greatgems said:


> for a quick forum post? Didn' feel perfect grammer was need, but answers would be awesome.


Yes! Awesome! And possibly totally wrong. Don't be afraid to use proper English and punctuation on this board. It's expected. Each of them help avoid misunderstandings. They also display respect for those from whom you hope to get those awesome answers. 

Harold


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## MysticColby (Mar 25, 2012)

I would image you could simply substitute acetylene for propane without difficulty (but do be aware of maximum working temp of your furnace and crucible - most have a max temp around 1500 C). That said, I think acetylene is too expensive to use on something this large, especially when not necessary. I feel that most people use acetylene because it's so quick and easy. They like the ease of a melting dish (propane in air on melting dish takes too long for it to be of use). adding oxygen to propane would be the next thing I'd consider if propane in air wasn't good enough.
Silver: 961 C
Copper: 1083 C
Iron: 1539 C
Propane in air: 1980 C
Propane in oxygen: 2526 C
Acetylene in air: 2500 C
Acetylene in oxygen: 3480 C


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## Geo (Mar 25, 2012)

acetylene does not burn as clean as propane.this is from a lifetime of observation.the heavier the fuel, the hotter it burns or i should say the more carbon it contains.acetylene will create soot if not added to oxygen.when combusting acetylene, it either needs oxygen added or introduced to enough heat to oxidize the carbon into carbon dioxide. you would have to heat the furnace first or create a thick black smoke.its almost the same as using oil to fire the furnace, which burns much hotter than either gas simply because it contains more carbon.


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## depperl001 (Mar 25, 2012)

greatgems said:


> Really nice design. Anyone have one using acetoleen to get there tempatures higher? Any advice on getting a furnace like this to 1800c i also want to treat sapphires thanks.




Hi, 
Treating sapphires does not require that much heat, if you get a sapphire to a pale yellow heat you would have lost the colours and be left with only yellows. The trick is to get them to about 900 degrees and let them cool slowly.

Regards,

Josef Vavryn


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## DONNZ (Mar 26, 2012)

Don't know if this will help, but I'll throw it out there:

*LB White Industrial 400 Industrial and Special Purpose Torch*

http://www.bedroomfurniture.com/LB-White-Industrial-400-Industrial-and-Special-Purpose-Torch-Industrial-400-LBW1094.html#overview


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## butcher (Mar 27, 2012)

That is one expensive weed burner.


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## MysticColby (Mar 27, 2012)

Geo said:


> acetylene does not burn as clean as propane.this is from a lifetime of observation.the heavier the fuel, the hotter it burns or i should say the more carbon it contains.acetylene will create soot if not added to oxygen.when combusting acetylene, it either needs oxygen added or introduced to enough heat to oxidize the carbon into carbon dioxide. you would have to heat the furnace first or create a thick black smoke.its almost the same as using oil to fire the furnace, which burns much hotter than either gas simply because it contains more carbon.



Sorry, but the recent O-chem student in me is screaming here. Propane is heavier than acetylene, but acetylene burns hotter. weight does not dictate heat. It is true that larger molecule creates more heat per molecule burned, but it's also spread over more products. The most heat is generated from highest energy with lowest number of products.
Propane: CH3-CH2-CH3 + 5 O2 --> 3 CO2 + 4 H2O (1 mole + 5 mole -> 7 mole + 2.2187MJ heat) (316.9kJ heat per mole)
Acetylene: CH≡CH + 5 O2 --> 4 CO2 + 2 H2O (1 mole + 5 mole -> 6 mole + 2.598MJ heat) (433kJ heat per mole)
by comparison, octane (gasoline): 2 C8H18 + 25 O2 --> 16 CO2 + 18 H2O (2 mole + 25 mole -> 34 mole + 5.33MJ heat) (156.7kJ heat per mole)
as you can see, acetylene produces more heat per number of molecules than propane, which is why it burns hotter.
Incidentally, this also explains why burning both of these with pure oxygen instead of air makes a hotter flame:
Air is ~21% oxygen, so for every 21 oxygen atoms, there are 79 other atoms (mostly nitrogen, which is essentially inert)
Propane in air: CH3-CH2-CH3 + 5 O2 + 18.8 other --> 3 CO2 + 4 H2O + 18.8 other (1 mole + 5 mole + 18.8 mole -> 25.8 mole + 2.2187MJ heat) (86kJ heat per mole)

Flame temperatures: http://en.wikipedia.org/wiki/Adiabatic_flame_temperature
My favorite is the Dicyanoacetylene ^_^ now THAT sounds poisonous. Take a look at it and you'll understand why acetylene has so much heat in those triple bonds


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## Geo (Mar 27, 2012)

thats why i corrected to say the more carbon it contains. its seems the harder it is to combust a fuel, the hotter it is.like diesel fuel, it takes a lot of pressure or heat to make it decompose but it generates more heat than gasoline.


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## goldsilverpro (Mar 27, 2012)

The melting point of copper is about 2000F. A typical gas fired furnace will run about 2400F, max, without forcing it. That's plenty for copper. I've melted many tons of it at that temperature.


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## Lou (Mar 27, 2012)

Natural gas ought to do that fine.

Copper is a bastard to melt without it oxidizing. Invest in some graphite plates to float on the top and some phosphorus to deoxidize if you plan on making any castings!


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## greatgems (Mar 29, 2012)

Thank you everyone. I found my solution and its propain with oxygen being added in. To the Sapphire treating 900c is far to low to do anything. I have treated all kinds of gemstones for a while now, and sapphires need about 1600 -1800c to treat to nice blue aspecially ones from africa. 

thanks


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