Propane or acetelyne?

[KennyG]

Hey Northernlights,

Thanks for the links. They were good reads.
Ken

[david_r]

NL,
Thanks for the good info. Unfortunately, the math isn't that simple. When you are actually cutting, you should be using a similar amount of oxygen with either fuel.

[chris88]

You can weld with propane. Throw your parts in the forge, get them to welding temp, flux and hammer weld them


Forge welding doesnt work to good with propane. With coal its a **** of alot easier. Coal is nicer to use too. I have an acetelene regulator on my bottle.

I probably wont have to gas weld so i think i'll go with the propane and just wait a little longer to get the steel up to temp. Can you get a carbon arc torch for any welder? What do you need to do? Do they work good and clean? If i get my Miller running which im getting today ill get a carbon arc torch if its cheap/good.
Chris

[MAC702]

NL,
Thanks for the good info. Unfortunately, the math isn't that simple. When you are actually cutting, you should be using a similar amount of oxygen with either fuel.

Actually, the math really is that simple. While many weldors set the gauge pressures to read the same for the supply, the actual amount fed to the flame is controlled by the needle valves. And you will burn the stated ratios of fuel gas to oxygen, which means you will have to buy them in the same ratios.

Also something not mentioned yet, is that the typical torch set-up has hoses that are NOT rated for use with propane as the fuel gas. It will eventually corrode the hose unless specifically made for propane use.

Propane will work for cutting because once preheat is accomplished it is the oxygen that does the cutting, using the steel as the fuel. Heating and welding rely on the heat accomplished by the fuel gas burning in the oxygen, and propane just can't compete.

[TheDjost]

The different burn ratio of propane vs acet. is true for the preheat flame only (wich does use some oxy, but not the majority of what's used for normal cutting). The preheat's job is to bring the steel up to the right temp. What cuts the steel is the oxygen jet. The oxygen reacts with the hot steel and oxidizes it rapidly (thus producing lots of heat) and expels it from the cut. So the only difference in oxygen usage is a bit more for the preheat and for a bit longer, but once the cut is started, it's almost the same. You can't just estimate the amount of steel you would cut with acet. and divide by 3, or even by 2. It mostly depends on how much time you spend preheating and/or heating steel vs actual on trigger cutting time. Lots of small cuts will affect oxy usage comparison much more than fewer long cuts.



In any case, my vote goes to propane, for a lot of reasons. To list a few: price, convenience, safety...

-Justin

[TRG-42]

When people complain about how cold propane is versus acetylene they are not really giving it a fair and proper test ( more on that later )

FACT : Max Neutral Flame Temp of Acetelyne in oxygen iis about 5620deg F
Max Neutral flame temp of propane in oxygen is about 5090degF

In reality this is a small difference because flame temperature is not really going to make as big a difference as themal output ( BTUs )

FACT : BTU of Acetlyne is about 1470btu/ cu ft
BTU of Propane is about 2500btu/cu ft

So really to say acetlyne gives off less heat is not entirely correct ( plain wrong actually )

In the welding industry the vast majority of preheating is done with oxy propane . This is a fact . They don't do it because its cheaper but rather for preheating the available heat from propane is much higher

FACT : If you look at any torch manufacturers catalog, you will see propane / propylene / MAPP heating heads of 250,000 btu/hr to 1,000,000/hr ( pretty scary actually ) .

But if you look at the Acetylene heating tips the max you see in the Harris catalog is a relatively small 240,000 btu/hr . The largest Smith Acetylene heating tip is only less than 200,000 . The largest Victor is about 300,000 . These are all far less than what they make for Oxy Propane

Please see this link for the BTU data ( bottom of page )

http://www.thermadyne.com/vec/litera...57_65-2007.pdf



Back to the Unfair Comparison

For years I professed that Acetylene was way hotter for cutting than Propane . Made the mistake of saying that to cutting table expert . He had me "show" him how much slower it was. When he told me I was cutting with propane incorrectly I was actually offended !

The mistake I was making was I was cutting with Propane like I was cutting with Acetylene. Turns out "where" the heat is in the propane preheat flame is nowhere near where it is with Acetylene !

FACT : Propane releases a freakishly small proportion of heat in the inner flame ( less than 10% ) so most of the heat in the flame is in the outer cone . Acet releases almost 40% of its heat in the inner cone

Problem with where the heat is in the flame

If you cut with acetylene you are use to putting the tip of the inner flame on the plate. If you do the same with propane you will be waiting a long time

Back to me looking silly

He then showed me just by raising the torch so I was in the secondary flame the preheat started WAAAAY faster . Is it necessarily as fast a preheat as Acetylene...no but it is nowhere as poor as most people think

FACT : just about all industrial plate cutting operations nowadays ( CNC tables ) are done with oxy propane or propane derivatives ( except for plamsa tables obviously )

If you watch these tables cut, it will simply amaze you how quickly they can start a cut on 1"+ plate with the lowly propane

Stochiometric Ratios of Burning Gas

Everyone states that Propane "uses" more oxygen ( 4:5 ) vs Acet ( 1:5 ) . This is true but remember when cutting there is far more oxygen being used in the cutting orifice than there is being fed into the preheat mixer of the tip

So yeah numbers look in favour of Acet but it is not as bad as you would initially be lead to believe

Welding with Propane

Lots of conjecture out there on why you cant weld with propane. Always here how its not hot enough. Nothing to do with that. You can take a big huge #7 oxy propane tip and compare it to a tiny #1 welding tip. Even thought he propane tip has far more heat you will still not get good weld

The reason Propane ( and other alternative fuels ) is not suitable is that Acetylene when buring with Oxygen will creat a cone of CO2 shielding gas to shield the weld zone. Propane does not do this




Bottom Line : There are may people will will not be conviced Propane is a good cutting fuel gas which is fine, but the performance difference is not as bad as some of Acetylene advocates would lead you to believe

Poke you head into a scrap yard or a plate shop and it will amaze you how quickly they start a cut with propane ( with the right gear and settings and techniques )

[tooldude56]

WOW.That surely answered a lot my my questions on this subject.I think that was the most information that I have ever gotten from one post.Obviously you have lit more than a few torches in your time.Thanks for your post..........

tooldude56

[truckinmach1]

Thanks TRG-42,
You sure gave us alot of good info. Answered alot of questions I have had. It would have taken me ALL DAY to type that much
Thank again,
Bret

[david_r]

Mac,
First of all, welcome back.

There was a third sentence to my post. "When you are actually cutting, you should be using a similar amount of oxygen with either fuel." Maybe I'm doing it wrong but when I'm cutting, I spend more time with the lever depressed than with it not.

[Piper106]

TRG-42; excellent post about the difference between acetylene and propane.

You say that with propane you need to lift the torch up let the secondary flame flame do the work. Can you give us any help on how far beyond the end of the propane primary flame the surface of the plate should be to get good pre-heating??

Piper106

[BKD]

I've got a question too...

I grew up on Acetylene, but when I got my own setup, I went with propane. Even got the Type T hose. Cutting and heating is all I do with it.

My question is this: How do you properly "set" the flame? No problemo with Acetylene, but the propane tips are a little different, and I don't know any "experts" personally to show me how to set the flame (am I using enough oxygen/too much oxygen??) with propane. It's just different. And I'm the only oddball around this area that is using Propane that I know of. That being said, I've cut quite a bit with it already, but I'm still not confident that I'm getting the flame set the way it should be.

Any helpful hints/suggestions?

Thanks!!

[Sberry]

I did a job of my own a while back and just kind of started, used my service truck to cut from and I dont really know why I didnt set a 100#r in the back instead of using acet. It would have saved about 200$ just for the effort. Something that is a major waster of O2 is dirty or eroded tips. I talked to the scrap guy and he said he was paying only 6 or 7$ for Victor Journeyman tips. Next time I run into him I am going to see if he will part with a couple just to have new ones on hand.