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  • Oxy/Propane?

    I've read that Oxy/Propane silver soldering (brazing, really) is the cats meow.

    I've got two cutting torches, an oxy/acety rig, and the multi-fuel (Kevlar) hoses. Can I use an Acetylene regulator on a propane tank (I know I need the acme adapter)?

    Also, Smith et al sell separate propane tips, which are more expensive than normal acetylene tips. Are they really necessary?

    Thanks!

    Robert
    "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

  • #2
    the only one i changed was the cutting tip the rest worked ok
    jerry

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    • #3
      Robert,

      I'm using an acetylene regulator on a propane bottle - works fine. I had to machine up an adaptor as the threads were different, otherwise no problems.

      I think the propane nozzles have larger gas passages than the equivalent acetylene ones, so yes. you'll need proper propane nozzles. Otherwise, for what I need it for, oxy/propane is brilliant. I'd far rather keep propane in my workshop than acetylene. Cheaper, more widely available, less unstable.

      Ian
      All of the gear, no idea...

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      • #4
        I'm no expert (understatement) but I've used both for cutting and brazing. (Although brazing is still a new "art" for me)

        I always heard that the hottest part of the propane flame is the "sheath" around the inner core. For the acetylene flame, the inner core is hotter. Different tips and slightly different technique are needed.

        I personally prefer propane (of course thats what I learned on) but it can cut much thicker material than O/A and does a better job of heating large items for brazing ... like certain cracked pacemaker castings

        Now before anyone jumps in and starts tossing around the "but acetylene is hotter" gambit, its maximum temperature burning in oxygen is 5720*. However, the maximum temperature of propane burning in oxygen is 5110* (both in Fahrenheit), although most values for the oxygen propane flame put it at about 4200*

        More importantly, however, propane produces nearly 1000 btu/hour more heat than an O/A torch - which means better pre-heat and better heavy cutting. (although arguably less control for those "precise" gas welds)


        Anyhow, looking at the two tips and considering that that stoich ratio for propane is 4.3:1 and the stoich ratio for acetylene is something like 1.2 or 1.3 to 1 (iirc), I think that you really do need the propane tips.


        p.s. - propane can't be used for welding, though. Don't ask me how I know Apparently it doesn't produce as much C02 as Acetylene does, so there is no shielding effect. I couldn't figure out how gas welding was supposed to work when all of my puddles just burned right up, then someone told me about that CO2 thing, and it all made sense!

        Argh - everyone beat me to it!

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        • #5
          Originally posted by lazlo
          I've read that Oxy/Propane silver soldering (brazing, really) is the cats meow.

          I've got two cutting torches, an oxy/acety rig, and the multi-fuel (Kevlar) hoses. Can I use an Acetylene regulator on a propane tank (I know I need the acme adapter)?

          Also, Smith et al sell separate propane tips, which are more expensive than normal acetylene tips. Are they really necessary?

          Thanks!

          Robert
          The propane tips have different orifices than acetylene tips, and I think the mixer is different also . If You can purchase an adapter from Your local welding store than I would say yes to the regulator question. But why buy propane and tips and adapters?
          Mapp gas is right below acetylene (heat wise) and propane and nat. gas are right below that , so to do the same amount of work it takes more gas so why switch? Just use a smaller acet.tip with the rig you already have.

          Steve
          I guess I should learn to type faster and not watch TV at the same time !
          There were no replies when I started.
          Last edited by doctor demo; 07-14-2008, 02:18 AM.

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          • #6
            Propane is the cheapest way to cut scrap,not the neatest cut,but cheapest.It does however cut good in a machine torch application.

            Propane is better on thin materials where you do not need super high heat.Solders,fluxes and braze metals can all easily be overheated.

            Yes the tips are needed since the oxy/fuel mix ratio is diffrent.

            Another handy use for a propane bottle and reg in the shop is crude heat treating.A propane burner and a stack of firebrick makes a good furnace for quickie heat treat jobs.
            Last edited by wierdscience; 07-14-2008, 09:15 AM.
            I just need one more tool,just one!

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            • #7
              I'd far rather keep propane in my workshop than acetylene. Cheaper, more widely available, less unstable.
              One little problem with that. It's illegal to keep propane in your shop. The reason is that propane is heavier than air and when a leak occurs the unmixed propane will collect in the lowest part of the shop. As long as there isn't a good source of ventilation it can lie there for a long time waiting for ignition.

              The instability of acetylene isn't a common source of problems since it is dealt with in the design of the apparatus that uses it. If it leaks it mixes with the air since it is almost the same density (very slightly lighter) and doesn't collect on the floor like a land mine. It take a much larger acetylene leak to pose a problem than it does with propane.

              Propane has several issues besides the safety aspect. It's good for heating but sucks for welding and as Darin said makes a more ragged cut. The reason for that is because the majority of the heat in a propane flame is in the outer envelope instead of the central core. This is what makes acetylene a "hotter" flame than propane. It delivers the majority of it's BTUs in the central flame in a much smaller area than propane can. The reason for that is that acetylene has a very wide range of mixture that will combust whereas propane is limited to a very narrow mixture range. Propane requires much better mixing before it will burn. Propane is not well suited to delivering heat precisely when heating for the purpose of bending for instance.

              That brings up another point. While it is possible to use propane in some unmodified acetylene equipment at sea level such as an acetylene/air torch it stops working with only a minor increase in altitude as the mixture becomes too rich with decreasing oxygen partial pressure.
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              • #8
                Thanks for all the responses guys!

                Originally posted by wierdscience
                Propane is better on thin materials where you do not need super high heat.Solders,fluxes and braze metals can all easily be overheated.
                That's exactly what I'm looking for -- I'm doing fine silver soldering, and even with a number 0 acety tip, it's easy to overheat small parts.

                Yes the tips are needed since the oxy/fuel mix ratio is diffrent.
                OK, that helps a lot. I don't know what a stoich ratio is Fasttrack, but I'll take your word for it
                So is a Number 0 propane tip the same size as a number 0 acety?

                Another handy use for a propane bottle and reg in the shop is crude heat treating.A propane burner and a stack of firebrick makes a good furnace for quickie heat treat jobs.
                That was my other reason for wanting to add propane to the shop: I bought one of Stephen Thomas' prototype camelbacks, and it wasn't stress relieved. The local heat treat shops want $75, so I was thinking of just making a pile of firebrick to heat the casting to 1100F.

                I need to get a Harbor Freight weed burner...
                "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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                • #9
                  Ditch the weed burner,build one of these-

                  http://metalcast.boorman.us/reil_1.html


                  You will also need a high flow regulator,think turkey frier,Homedespot and Lowe's used to sell them seperate.


                  Oh,if you want to stress relieve all you need is a sheet metal box big enough to hold your casting and a roll of Kaowood or Fibrofrax wool.Look up 93315K34 at http://www.mcmaster.com/

                  It's great stuff to have around,checkout Ron Reils freon tank forge-

                  http://ronreil.abana.org/minifor1.shtml
                  Last edited by wierdscience; 07-14-2008, 01:49 PM.
                  I just need one more tool,just one!

                  Comment


                  • #10
                    stoich is short for "stoichiometric" - which is basically the ratio between the two (or more) components in a chemical reaction. For combustion, you might have C3H8 + O2 = CO2 + H2O and then you'd balance the equation, coming up with:

                    C3H8 + 5 O2 = 3CO2 + 4H2O, so the stoich ratio in moles would be 1:5 for propane. The molar stoich ratio for acetylene then, is: 2:5

                    2C2H2 + 5 O2 = 4CO2 + 2H2O

                    Basically, you burn more oxygen per mole (or per any unit quantity) of acetylene than per mole of propane.

                    Acetylene is an interesting gas. With a tripple bond between two carbon atoms it's rather interesting on the atomic level. Incidently, its that tripple bond that makes it unstable.

                    I dunno - maybe you already knew what "stoichometric" was. I don't think stoich is a recognized abbreviation, come to think of it. Just what all the chem guys say 'cause they're too lazy to pronounce "stoichiometric"

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                    • #11
                      nup
                      the stoics use C2H5OH
                      Just got my head together
                      now my body's falling apart

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                      • #12
                        Oh, that's good to know that it's just the fittings that are different
                        for Ace or propane.

                        I was told they needed different regulators but I never thought to ask why.
                        Barb

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                        • #13
                          My gas gauge screws right into a 20 pound tank.

                          While we are on the subject of propane. Has anyone tried it with a fluxer?
                          Gene

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                          • #14
                            Originally posted by Coppretta
                            Oh, that's good to know that it's just the fittings that are different for Ace or propane.
                            Your local welding supply will have the acme thread -> NPS adapter for around $30.
                            "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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                            • #15
                              Oh, that's good to know that it's just the fittings that are different
                              for Ace or propane.
                              Not quite. Brass made for acetylene use must not contain more than 65% copper and only bare steel or the correct brass fittings should be used. In particular, copper plated fittings can cause acetylene to explode at any pressure. While it is safe to use an acetylene regulator on propane it is NOT safe to use anything but an acetylene regulator on acetylene.
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