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  • Gas welding

    Question on gas welding. Why would it not be possible to gas weld with regular air from a compressor, instead of buying oxygen in tanks. Just trying to find away to save money.


  • #2
    The oxygen you buy in tanks is close to pure oxygen the stuff we breathe is only a small percentage oxygen. Here are some numbers I pulled off the Internet. "Oxygen includes 21% of the atmosphere at all altitudes. The remaining atmosphere consists of 78% nitrogen and 1% traces of other gases." As you can see the stuff we breathe only has about 21 % compared to 99.9 for technical oxygen. You can get set-ups the use acetylyne and suck in reguler air but I don't beleive they get hot enough or can pin point the flame well enough for welding. I suggest you get some books or take a class on welding before you attempt it or buy equipment because it can be very dangerous inthe hands of novices.



    • #3
      I have a partial answer:
      The oxygen in a tank is just that - oxygen.

      From you compressor you get atmospheic air: nitroge,oxygen, carbon dioxide, and other elements.

      When you adjust an oxy/act flame to weld with, you typically want a neutral flame. Both gasses are completely burned. With shop air you will have other elements besides oxy. Adding these elements to a weld joint is not a good idea.



      • #4
        You can get air/acetylene torches. Plumbers use them for soldering copper tubing, and they would likely be a good choice for silver soldering or brazing. They put out significantly more heat than a propane torch, but I don't think they get hot enough (for the reasons others have given) to weld steel. You're talking about a quantum leap from brazing heat to welding heat.

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        • #5
          You can also buy your oxygen and use propane for the fuel,a bit slower than actylene,but lots cheaper.
          I just need one more tool,just one!


          • #6
            Air fuel works very well for soldering, heating, steel cutting, and brazing provided the torches are suited for the combination.

            You can weld steel with some fuel/oxygen combinations but while I've used a few I don't prefer them. For that reason I've paid the extra cost and for years suffered the inconvenience of replaceing empty gas cylinders for oxy acetylene.

            The best gas welding combination is oxygen/acetylene because it has both the highest flame temperature by far (5720 F) and the best flame chemistry for welding steel. It's the high carbon monoxide content of the acetylene flame envelope that reduces oxides and speeds the welding process producing clean, tough, well penetrated welds. Oxy/propane (I tried it and the books were right - not reccommented) makes a weld but a poor and brittle one.

            As for your question using air as the oxidizer gas for welding. It was pointed out earlier that air contains 78% nitrogen. It contributes nothing to the welding process and because of its presence it absorbs heat from the combustion of the fuel gas reducing its temperature and interfering with the flame chemistry in sone way I can't recall.

            Oxy/acetylene burns at 5720 degrees F. Oxy/propane at 5090.

            Air/acetylene burns at 4252. Air/propane at 3596. No comparison in temperature. Oxygen makes all the difference in the world.

            Oxy Vs air as a welding fuel gas oxidizer is one of those "you and run but you can't hide" issues. If you're going to weld you need ozygen and acetylene. I suggest you bite the bullet and get the gasses you need to gas weld properly.

            Here's some links:




            • #7
              Damnit Forrest, you are way too pendantic. And yes, there is no substitute for Oxy/Actelyne. I have tried propane as fuel gas and find that it is a pain in the ass. It has a very narrow mixture range and is very prone to blowing out. It is ok for heating large parts but then you really need two torch setups to make good use of it.
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              • #8
                How about oxy / propane for cutting steel, instead of oxy / acetylene? Any experiences with it?
                All of the gear, no idea...


                • #9
                  Once the metal is hot, the oxy is what causes the cutting action. You are basically burning the metal away.

                  I have toyed with all of the other methods listed and found that oxy/acetylene to the best for cutting and welding metals in my shop as far as gas units. The big expense is not the cost of the gas, thats relatively cheap, it's the cost of the bottles.

                  Let me say this, there is the right way to do things, and all of the other ways. When you try to get by with less expensive equipment or doing "quick and dirty"methods, you end up with poor quality.



                  • #10
                    I use Oxy/Propane for cutting all the time and it works just fine. Just make sure you buy the cutting tips that are made for it.


                    • #11

                      [This message has been edited by pgmrdan (edited 09-02-2004).]


                      • #12

                        You have it right. Carbon monoxide is the product of incomplete combustion. If there is enough oxygen present then the reaction will produce carbon dioxide.
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                        • #13
                          Pgmrdan, I'm more than a little vague about combustion chemistry; what I know I read in the weld engineer's office from their references. I do recall the several envelopes comprising a stable fuel gas flame each have their own conbustion chemistry. The outermost pale blue envelope is CO2, superheated steam and carbon monoxide which is burning at its interface with atmospheric oxygen.

                          It's in this outermost envelope that the superheated carbon monoxide performs a powerful reduction function. Heat up a piece of copper or brass to where it shows colors and play the outermost envelope on them. Note how the colors (thin layers of oxides instantly reduce to show the color of bare metal.

                          What happens at the tip of the innermost cone to make a 5700 degree termperature, I'll never know. Nor do I understand the nature of the intermedate cone that I adjust to a mere "feather" when welding and its even more powerful reduction properties.

                          But I am aware of the shielding and reduction properties of the oxy/acetylene outer flame envelope and how it's far superior in its effect to that of an oxy/propane flame.

                          It's sufficient that it works and that I have the "monkey see, monkey do" know-how to take advantage of its properties.

                          [This message has been edited by Forrest Addy (edited 05-24-2004).]


                          • #14

                            [This message has been edited by pgmrdan (edited 09-02-2004).]


                            • #15
                              When I had the dental business we had a small welder which used Hydrogen Peroxide,and propane gas.This machine converted Hydrogen peroxide into oxygen and was very good and became really hot.Unfortunately I bought a large volume of the Hydrogen peroxide in gallon plastic containers.
                              No one told me it had a short shelf, life and most of it was useless when I came to use it the machine .
                              It is still here under my house in the basement these were very popular at one time about twenty years ago but you never see them now Alistair
                              Please excuse my typing as I have a form of parkinsons disease