Crazy information...

Anonymous-0 · Nov 28, 2010

I was looking for a chart with flame temperatures and came across a site that states some interesting pressures for cutting steel with acetylene and oxygen. All are in PSI:

1/4" Oxy 30 to 35 Acet 3 to 9
1/2" Oxy 55 to 85 Acet 55 to 85
1" Oxy 110 to 160 Acet 7 to 15

Those are the most ridiculous figures I've ever seen. 35 Oxy and 3 Acet would cut 1" if you went a little slower. The only good thing it says is to check torch manufacturers data for optimum settings. They won't even be close to ones listed. Dave

60 acre hillside · Nov 28, 2010

160 Oxygen PSI would send fire all over the shop area. Catch everything on fire

JOHNNY from MI · Nov 28, 2010

Acetylene @ 55 - 85 psi ?
Not good for your health!

PJH · Nov 28, 2010

I barely remember learning that Acet should never be set higher than 15?? Something about it being unstable above 15. . . From a welding class that I took 35 years ago.

25 and 5 cuts anything I fool with.

Paul

Ken-Pa · Nov 28, 2010

My advice would be to ignore that chart . Check with your welding supplier . I usually set my accetylene at 5 lb & oxy at 10 lb to start . Than you can adjust the flame up as needed . You want just enough oxy to blow the hot slag away from the cut . Keep metal red & melting ahead of flame by a slow movement . Makes a nicer smooth cut .I've been told 1 bottle of accet will last through 2 bottles of oxy if adjusted correctly . Another thing I learned is when using my torches , open the valve on the tank all the way to avoid leaking .I find that very true since I was loosing a lot of fuel until the distributor told me that . HTH ! God bless

Anonymous-0 · Nov 28, 2010

I made a mistake and listed the O2 pressures twice. It should be Acet 6 to 12. Still more than needed. Dave

Anonymous-0 · Nov 28, 2010

I think it would almost be like trying to hold back a jet engine. That's a lot of pressure out of a small opening. Dave

Stan in Oly, WA · Nov 28, 2010

Hi Ken,

Your conservative approach to gas pressures is intelligent, but rare. I find that students and artists who have the experience to know better almost always use far more pressure than necessary, particulaly oxygen. And turning up the oxygen pressure is generally the only thing anyone tries when they have a problem cutting---no metal cleaning, tip cleaning, preheating the metal, changing travel speed, etc. Just crank up the oxy.

Opening the valve all the way only applies to high pressure bottles, not to acetylene or other fuel gases which are supplied at 100's of psi rather than 1,000's. High pressure gases are supplied in bottles which have valve seats at both the top and bottom of the valve stem. The one at the bottom seals the bottle, and the one at the top seals the valve against leaking when it is open, as you noted. Traditionally, acetylene valves are opened only 1/4 to 1/2 turn so that they can be shut off quickly if there is a problem with a flame where there shouldn't be one.

All the best, Stan

BDT in Minnesota · Nov 28, 2010

na, I think I will just pick up a few more hack saw blades.. those numbers are a little too wild.

JD Seller · Nov 28, 2010

I have Smith torch sets. We usually run 35 psi on the Oxygen and 5-7 on the Acetylene. That will cut up to 1 1/2 easy.

135fan How is the lad who was hit by the car????

Crem · Nov 28, 2010

Stan,
That is one thing that I remember from a class at vocational school back in the sixties. Like you said open the oxygen valve all of the way to back seat and the acetylene valve a little over 1/4 turn so that it can be turned off quickly if needed.

Anonymous-0 · Nov 28, 2010

Lad who was hit by a car? I think you have me confused with someone else. Dave

Ken-Pa · Nov 28, 2010

Hi Stan , as to my opening the main valve all the way was what my supplier instructed me to do . You see I was experiencing leakage somewhere & could smell accet & my tank didn't last as long . He explained just what you said & then said the valve has to seat when opened also . That's what I've been doing & now don't have that smell anymore . I also had all my torches rebuilt just in case they were leaking somewhere also . I take any & all precautions (the best I can)with those explosives in my garage .Thanks though . God bless, Ken

Anonymous-0 · Nov 28, 2010

If you smell acetylene, take the cylinder back. Acetylene should never be opened more than 1 1/2 turns. Your supplier gave you wrong information if he told you to open the acetylene all the way. That's a dangerous situation and is clearly printed on any cylinder lease or sale agreement. If the leak doesn't stop with the valve off, put the cylinder outside and call the welding supply. Oxygen should be fully opened but a lot of people don't without any problems. It's not as big of a concern as acetylene being opened too far. Dave

NCWayne · Nov 28, 2010

Funny thing about the whole deal is that on thicker material, say 1" and up, you could shut the acetylene completely off after you get the cut going and keep it going with the oxygen alone. The only thing you need the aceteylene for is the initial preheating of the material to get the cut started. It's sort of like blowing on glowing coals in a fire and watching them heat up, once the metal starts to flow/burn the oxygen blowing against it perpetuates the burn and effectively preheats the material in front of the cut to a point that the acetylene/preheat flames are no longer needed. Give it a try sometime, it's real easy to go too slow or too fast but given the right speed it works like a charm.

Anonymous-0 · Nov 29, 2010

On 1/4" you could continue the cut for a short distance. 1" plate would cool too quickly. The steel has to be at certain temperature for the oxidation process to work. If it worked that good, cutting machines would shut off the preheat after the cut was started to save a lot of gas. On thicker plate it's common to have to preheat the plate and also use another torch to heat ahead of the cutting torch. Bevel cutting often uses an extra preheat flame. Dave

Tramway Guy · Nov 29, 2010

More important than the pressures is to use the right tip. There are several sizes, optimized for different thicknesses of material!

NCWayne · Nov 29, 2010

I've personally seen it done on plate as thick as 2 inch and it worked just fine. Thing is you have to be using a big tip, like #7, and you have to crank the oxygen pressure up around 70 plus to do it. Still I too understand what your saying about using another torch to preheat ahead of another torch on really thick material. When cutting a bevel I can see where this would particularly be needed as the preheat flames from the cutting head aren't directed completely at the plate but rather at an angle to it which cuts the heat input from them tremendously. As far as an actual flat cut on a cutting table goes, if you watch many of them after the preheat phase is complete the torch head will actually rise up from the plate before starting the cut. In rising like this, even though they don't cut the gas off, this removes the small, blue preheat flames from the process as they aren't needed until starting the next cut. Like I said the main thing when trying this is to be able to maintain the correct cutting speed as too fast or too slow will easily kill the cut.

Bspauld · Nov 29, 2010

Where I used to work they cut 13 in plate, They would get the cut started,(in the center) and take a long peice of regular 1/4 in pipe hooked up to Oxygen and keep the cut going with that,It would melt of course but it got the cut through so they could use a cutting tip to finish the hole

Anonymous-0 · Nov 29, 2010

Even on a hand torch, they say to raise the torch when doing things like cutting holes. This is so that if any slag blows back, it doesn't get on the tip. The preheat flames shouldn't touch the steel. I read about the temp the steel has to be for it to cut but don't remember where. On thick plate, propane or natural gas is often better than acetylene because most of the heat(btu's) is in the outer flame enveleope and acts to preheat the plate ahead of the cut better. Acetylene has more btu's in the inner flame. Unless I was cutting 2" thick plate and up, I much prefer acetylene for cutting. Dave

Anonymous-0 · Nov 29, 2010

I think that's an oxygen lance used for cutting thick sections and scrap. Dave

Ken-Pa · Nov 29, 2010

Oh I did take it back at that time & he tested it & found no leaks . I even took my torch & hose with guages attached . With the tanks valve opened part way , it seemed to leak . Opened all the way , it showed no leakage at all . Thats when he said that they need to be opened all the way in order to seal off properly . There's 2 suppliers here so maybe I'll ask the other one about it . I like to be safe . God bless

Anonymous-0 · Nov 29, 2010

A lot of people working in welding supplies nowadays, don't know as much as they should. Look in a manual for a torch or a book like the O/A handbook, even a cylinder lease, and show it to the person telling you to open it all the way. Unless it's a special type cylinder 1 1/2 turns is the most it should be open. Dave

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