From the link I posted on alternate fuels -
"The real reason is that alternative fuels don't create any shielding gas. Conversely, a proper mixture of oxygen and acetylene with a neutral flame produces CO2, which in turn shields the molten weld puddle from atmospheric contamination."
Actually, since the definition of a "neutral flame" is one that has neither excess oxygen NOR excess fuel, ANY fuel is capable of a neutral flame. This is whether it takes a 1:1 ratio or a 1:15 ratio to accomplish neutral conditions.
Some fuels (like acetylene) make it easier to get to a neutral flame, since acetylene has quite a bit wider range of "richness" vs. flammability - this means that you can set the flame where you want it with fuel only, then add oxygen til the "feathers" go away and STOP, giving you a neutral flame. I was taught to turn up the gas til the flame separates from the tip, then back it down til it "re-connects", then add oxy til the feathers go away. Naturally it helps if you know how MUCH of a flame you want and set pressures close to what you want FIRST (experience helps here)
Other gases require that you "sneak up on it" by lighting a gentle fuel/oxy mix, then alternately turning up gas then oxy, and repeating til you get the flame size you want, finally "tuning" the "feathers" out. No "feathers" on the end of the flame means you are no longer "rich", but if you keep adding oxy past that point, you get a REDUCING flame (oxygen-rich), which is usually a "no-no".
As to acetylene making nicer cuts, I have no firsthand experience with alternate fuels for cutting - out of the 20-odd weldors in our weld shop at work, only about 3-4 of them made the effort to adapt rather than *****, and a couple of those told me they'd found several differences in each of the several gases they tried that required changes in technique in order to get best results. A couple of them told me that once they "got the hang of it", propane was about the same as acetylene (results, NOT technique)
Functionally, propylene looks to be the closest to acetylene for cutting/heating (definitely NOT welding), and maybe even BETTER for HEATING, but after seeing those fire/explosion vids of Praxair and Air Liquide plants, I'm more than nervous about going there, at least until I've had time to explore whether that OP valve issue is now dead.
Now that I have plaz for up to 1" and stick, mig and tig capabilities, heating would be my main use for gas except for the rare occasion when I'd need to cut more than 1", so if I find that it's very expensive to convert to propane, I'll probably do as you and "bite the bullet" once every 4 years or so and refill my #5 acetylene bottle.
I'm sure my choice would be affected if I were in the salvage biz, and went thru a tank or two a week, but I'm not. (In fact, I'm no longer in ANY biz by the end of this month, (retirement) but that's another (joyful) story... Steve
