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Acetylene dirty?


#1

Was: Is propane safer than acetylene?

In the ongoing comparison of the virtues of propane and acetylene,
it has been said that acetylene is “dirty” because of a sooty flame.
I have never understood this – I use one of the ordinary
air-acetylene arrangements and never have gotten a sooty flame. If I
hook it up with the oxygen tank, then I do get a sooty flame – I
almost never do this because the oxy-actylene flame is too hot for
anything but casting (which I don’t pursue).

I guess what I’m saying is that, IMHO, in deciding what fuel to use,
acetylene shouldn’t be omitted because one thinks it has a dirty
flame.

Judy Bjorkman


#2
I almost never do this because the oxy-actylene flame is too hot
for anything but casting 

Well I have to disagree with this as I don’t do any casting but I
have been using (exclusively) an oxy/acetylene torch for the last 30
years for all of my work. It’s not too hot for anything if you know
how to use it.

Daniel R. Spirer, G.G.
www.spirerjewelers.com


#3

Oxygen with acetylene was used for many years by Pt specialists.
With the proper stoichiometric considerations, it is NOT dirty. If
you don’t know what you’re doing it can be dirty and cause lots of
problems.

Eddie Bell gave an excellent exposition on this very topic at one of
Brad Simon’s Bench Conferences a couple years back.

Wayne


#4

Hi Wayne,

Oxygen with acetylene was used for many years by Pt specialists.
With the proper stoichiometric considerations, it is NOT dirty. If
you don't know what you're doing it can be dirty and cause lots of
problems. 

The idea that a stoichiometric reaction between acetylene and oxygen
(2 H2C2 (g) + 5 O2 (g) --> 4 CO2 (g) + 2 H2O (g)) does not leave any
free carbon available is correct if you only look at the end product
of the reaction. That reaction takes a certain amount of time and in
a torch flame distance to complete so there are a range of partially
reacted gases in that flame so it is possible to have heated un-
reacted acetylene available in the flame to be ready to react with
the platinum or palladium.

If you have your torch adjusted to a strongly oxidizing flame you
are less likely to have any free acetylene in the flame and it takes
a certain amount of carbon to create a problem. So if you always use
an strongly oxidizing flame you are likely to never have a problem
when working platinum, palladium is another story as it also reacts
with oxygen and so an oxidizing flame is not such a good idea.

Regards,

Jim

James Binnion
@James_Binnion
James Binnion Metal Arts


360-756-6550


#5
I guess what I'm saying is that, IMHO, in deciding what fuel to
use, acetylene shouldn't be omitted because one thinks it has a
dirty flame. 

The only place where the “dirty” nature of acetylene is truly a
problem is platinum and palladium work. Both of these metals will
absorb carbon and turn brittle. While a complete reaction between
acetylene and oxygen will not leave any un-burned carbon a flame is
an ongoing reaction and there is always gas in various stages of
reaction in the flame so you can indeed have carbon available to
react with the platinum in the flame and since acetylene has so much
in it you are more likely to run into problems with it. Acetylene
C2H2 has more carbon in it than any other fuel gas Propane C3H8 and
Natural Gas which is mostly methane CH4 are both less likely to
provide unreacted carbon to be adsorbed by the platinum or
palladium. While a complete reaction between acetylene and oxygen
will not leave any un-reacted carbon a flame is an ongoing reaction
and there is always gas in various stages of reaction in the flame so
you can indeed have carbon available to react with the platinum in
the flame and since acetylene has so much in it you are more likely
to run into problems with it. So as long as you are working with
anything but those two metals you will have no problems with "dirty"
acetylene and your work.

James Binnion
@James_Binnion
James Binnion Metal Arts


360-756-6550


#6

With the proper stoichiometric considerations, it is NOT dirty

Wayne is correct in the above statement. Judy said that if she hooks
acetylene up with her oxygen tank, then the flame is sooty, but not
when she burns acetylene in atmospheric air. That doesn’t make sense.
A dirty flame is due to incomplete combustion, ie not enough oxygen
for the fuel to burn completely, so the acetylene needs at least as
much oxygen as it needs to react/burn (stoichiometric equivalent) and
then it will burn cleanly. IOW, supply the flame with enough oxygen
to completely burn the acetylene and you cannot possibly get the
sooty carbon deposits that some people experience.

Helen
UK
http://www.hillsgems.co.uk


#7

Judy,

The reason you don’t see a sooty flame with your air/acetylene torch
is that there are the little holes at the base of the torch tip that
correctly mix ambient air into the acetylene pre-ignition. If you
cover those holes with your fingers with the torch lit, you’ll see a
"pure" acetylene flame, which is a white/yellow in color and very
sooty due to incomplete ignition. This technique is actually quite
handy if you want to soot up some steel nails to use as positioning
jigs, or to soot up an ingot mold to prevent the precious metal
sticking to it.

When you first light an oxy-acetylene rig, you’re lighting the
acetylene only, and that torch doesn’t contain the ambient-air holes
that pre-mix the acetylene. Therefore, you get those little sooty
"floaters" that fly around the studio.

That being said, I use an air-acetylene rig for 90% of my
fabrication/soldering (on silver), oxy-acetylene for most of my
casting. Oxy-propane is my choice for reticulation and fine detailed
fabrication work, but I have yet to get someone to come out and
properly install lines from an outside propane tank into my “new”
(remodeled) studio. Soon, I hope!

Hope this helps!
Karen Goeller
No Limitations Designs
Hand-made, one-of-a-kind jewelry


#8

when you heat a hydrocarbon fuel (oil or gas) you first break off
the hydrogen which don’t all combust without excess air and good
fuel air mixing. Breaking the acetylene triple carbon to carbon bond
gives free carbon which doesn’t totally burn with insufficient
oxygen and poor fuel air mixing.

Acetylene gets the the high combustion temperatureheat from the
breaking triple bond.

Lampblack was made by burning natural gas in insufficient air. In
soot houses that collected the lampblack. This has been replaced by
heating fuel oil and flashing the hydrogen off leaving the soot
called carbonblack. Used as a pigment in newspaper ink. and a filler
in rubber products.

this is done in a few places in West Texas particularly in and near
the town of Big Spring.

jesse


#9

Thanks, Karen, for that explanation of why the air-acetylene flame
does not produce those dreadful sooty floaters that oxy-acetylene
does. I also enjoyed seeing your web-site! Great jewelry!

Judy Bjorkman