Odyssèus - 3-9-2006 at 12:30
Is there much of a difference between propane and acetylene (Burning in the atmosphere, not oxy-acetylene) torches? I have a propane torch and I'm
having trouble melting common metals like copper, aluminum, gold, which have MPs well below the operating temperature of my torch (~1800 C I think). I
would like to try an acetylene bottle with my torch but my parents are worried about safety.
chromium - 3-9-2006 at 12:40
Do not know for sure but i suppose that acetylene does not make much difference. Oxygen is needed for high temperature flame.
I did some tests with burning hydrogen and even it is almost useless without oxygen supply.
[Edited on 3-9-2006 by chromium]
12AX7 - 3-9-2006 at 14:21
Acetylene has a higher flame temp, but it's a lot more expensive.
Use more insulation, I melt copper and aluminum all the time. Heck I did a bunch of silver soldering (on copper) with my propane torch just the other
day.
Tim
Odyssèus - 3-9-2006 at 15:18
What type of setup do you use? Ceramic crucible? What volume can you usually melt at one time?
[Edited on 3-9-2006 by Odyssèus]
12AX7 - 3-9-2006 at 16:44
I have a #6 crucible furnace, lightweight insulating refractory, whatever ceramic or metal crucible I'm using. But in general, heating stuff against
a firebrick or kaowool I could easily melt copper. In the interests of speed and efficiency, I'd put more bricks around something quite that hot, of
course.
Tim
Twospoons - 3-9-2006 at 20:31
The old fashsioned kerosene blow-lamps also put out some serious heat. I can melt copper and silver with mine. And I love the roar it makes when
its running!
12AX7's suggestion is best - use more / better insulation. Without that you need a seriously big torch.
Odyssèus - 14-9-2006 at 13:50
Well, thanks for the help. But...
I surrounded my torch head and ceramic crucible with solid red gardening bricks. The crucible had a good red glow over the entire bottom surface of
it. When I went to look at my copper though a minute later it was only a little oxidised. I blasted it for atleast 10 minutes but it refused to melt.
There wasnt very much contact between the bottom of the crucible and the copper though.
I'm going to try and find some online literature on this... I thought it was pretty straitforward. 
12AX7 - 14-9-2006 at 15:17
Ten minutes? It takes a good two hours to soak up a full furnace. (At full throttle an insulating furnace can do copper in under half an hour.)
To melt copper you really need some sort of furnace. At least stack those bricks so there is very little gap for radiation to pass. They may be
prone to cracking, spalling or melting, being common brick, and will require a lot more fire than insulating bricks.
Copper melts at a good yellow heat, almost twice what you were at (maybe only 30% more, if you were viewing in sunlight).
Tim
Odyssèus - 14-9-2006 at 16:00
Oh, wow. I suppose I had a few misconceptions about this. I'm going to see if I can find some insulating bricks and try again.
Thanks for your help.
BioChemMajor - 16-9-2006 at 08:08
MAPP gas i believe burns hotter than propane, and will work with most propane torches, and i saw that a local hardware superstore has small oxgen
bottles and a oxygen/MAPP torch setup (says it can cut 1/4" steel) while this probably isn't as good a oxy/acetelyne you could get the heat from using
oxygen AND fuel, yet not have to have an expensive torch, and big oxy/acetelyne cylinders. (the cylinders were the same size as the propane cylinders
used for small torches)
not_important - 16-9-2006 at 08:16
If you can find local pottery makers, they may have some old insulating firebricks from thier kilns that you can get for little cost or free. You can
simply stack them to form a small enclosure that will greatly reduce heat loss. I've reached cone 10, 1250 C or so, with a propane tourch in such.
Odyssèus - 16-9-2006 at 10:47
Well, I would use MAPP/acetylene and even oxygen, but for some reason my parents think it would be much more dangerous than propane. The only reason
they let me use a propane torch is because a relative gave me the torch tip/head that you screw onto the bottle. They suggested I ask about melting
stuff here before they would let me buy something besides propane.
[Edited on 16-9-2006 by Odyssèus]
froot - 16-9-2006 at 11:14
Acetylene is being slowly phased out in industry here because of it's hazardous properties. If I remember correctly, 5% acetylene contamination in air
in a confined space can explode violently if sparked. I used to mix acetylene with air in plastic bags and set them off, made the most wicked bangs!
The stuff is nasty. There have been accidents in the past where oxygen from full bottles would leak back into empty acetylene bottles, turning them
into deadly bombs. There was an instance near where I live where an entire house was removed from its foundations from one of these.
Propane on the other hand is alot safer, but burns colder. They are now mixing propane with additives, such as butane in order to achieve a hotter
burn.