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  • #31
    There is no "exact temperature" that can be said to be "where propane burns". That may be where it burns in a particular condition, but change conditions and you get a different result.

    If you light gasoline in a pool, it burns, but not really hot. If you blow air in, it burns hotter. If you atomize it, and burn it in a cylinder, it can burn VERY hot, somewhere above 2300 deg, because that is where you start getting NOx.

    Same for propane.... force air in, it will be hotter. Force air in that has been preheated, and it will be hotter than plain air.

    A blast furnace melts iron, but it needs forced air, that has been preheated, do do it well.

    If you were to do preheated air, using your furnace exhaust, as a blast furnace does, It would surprise me if you could not get a lot hotter than the numbers quoted in earlier parts of the thread.
    3751 6193 2700 3517

    Keep eye on ball.
    Hashim Khan

    If you look closely at a digital signal, you find out it is really analog......

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    • #32
      what Doozer said.

      You've never never seen what happens to the end of a piece of small binding wire into the flame of the smallest of propane torch - quickly gets bright orange or white hot. Propane/air can easily achieve orange hot and white hot temps with steel - just look up the temp of the flame and the temp of steel at orange heat.

      For a given torch size, its a matter of 1) how much heat is going into the work vs environment and 2) hot big is the work. Work on 1) to achieve the goal, if that fails, you need a bigger torch or something burning at even a higher temp - e.g. propane/oxygen or O/A

      For a given size torch, it is not about how much air is put through - the size of the torch determines how much fuel there is and it needs a certain amount of air to combust. Force more air through and it will just blow out the flame. Want a bigger flame, i.e. more heat (same temp), use a bigger torch

      Here's a shot getting a stack of old files up to forging temps - easily done with a medium propane/air torch and a bunch of IFBs to direct more heat to the work. It would be hopeless with that torch and thermal mass of the work without the IFBs

      Last edited by Mcgyver; 01-08-2021, 08:37 PM.
      in Toronto Ontario - where are you?

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      • #33
        Dian, You haven’t mentioned what size regulator your using, I think you need about 10 psi ( or more). BBQ grill regulators are much lower.
        When I get Time... I'll...

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        • #34
          The "more air", is not putting in an excess, but putting in what is needed with better mixing, starting with a rich mix and adding the secondary air. If the burner does a good job, then forget the air mix and go with the preheating of the air.

          But watch out that you do not get the burn back into the burner body. Preheated air will probably need a different nozzle/burner.
          3751 6193 2700 3517

          Keep eye on ball.
          Hashim Khan

          If you look closely at a digital signal, you find out it is really analog......

          Comment


          • #35
            regulator is 0-60 psi.

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            • #36
              mcgyver said:

              "You've never never seen what happens to the end of a piece of small binding wire into the flame of the smallest of propane torch - quickly gets bright orange or white hot. Propane/air can easily achieve orange hot and white hot temps with steel - just look up the temp of the flame and the temp of steel at orange heat."

              now thats pretty weird. if i hold a wire into the flame of any of the torches (yes, also the commercial ones and mapp) it only gets to orange heat. never see any really yellow or even whitish color.

              i tried measuring a sheet metal strip with an infrared gun and max was 650°c, gun probably showing wrong.

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              • #37
                Originally posted by dian View Post
                now thats pretty weird. if i hold a wire into the flame of any of the torches (yes, also the commercial ones and mapp) it only gets to orange heat. never see any really yellow or even whitish color.
                I just went a tried it to make sure my memory wasn't exaggerating things. Colour gets somewhat subjective and depends on ambient light, but I couldn't get it white hot. I wasn't too hard to get it a very light yellow. So maybe a bit of exaggeration, but definitely more than orange. This is with a turbotorch and #4 tip, propane air. No idea the PSI, no gauge on the regulator.

                To your Q, where are people melting steel and getting to welding temps with propane? Assuming you mean propane/air? The temp is hot enough but the challenge as discussed is getting enough heat into the work

                edit...after trying it in the air, I placed the piece on an IFB with another IFB as a backstop. Colours are hard to accurately photography, but after it cooled, I looked at it again....seems like I melted steel with a propane/air set up





                Last edited by Mcgyver; 01-09-2021, 09:55 AM.
                in Toronto Ontario - where are you?

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                • #38
                  youtube is full with people getting steel up to welding temp. and melting cast iron in crucibles with venturi torches. not sure i saw steel being melted in crucibles, as mentioned, but they get white hot.

                  i joined a forging forum and there too they forge (and weld) damascus with venturi forges. forced air is only needed when the forge is larger, like for an anvil, its a matter of btu. im only reading so far, but will report what i learn. im sure there are some tricks. they also use alumina and alumina zirconia coatings, because "regular" refractory grout (usually 1280°c) melts. i know at least one member over on pm casts staightedges "at home", might ask him too.

                  im actually doing this research for my friend, its pretty disappointing he cant get damascus up to heat in his small $1000+ forge. my equipment is still covered with snow, so i cant do much.
                  Last edited by dian; 01-09-2021, 11:16 AM.

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                  • #39
                    A "propane torch flame" is not one thing...... it has a variety of temperatures in it. you see this as the blue, yellow and orange parts of the flame, if it has all those. Usually the inner blue cone has the hot spot at the end of it. So where the item is in the flame makes a big difference as to how hot it gets.

                    Ideally, you would have a setup where the entire flame is like the hottest part.

                    The "propane flame temperature" that you end up with inside the furnace is pretty much the average of the entire flame, plus mixing with outside air that comes in. To get hotter, you would first get rid of outside air leakage, and then work on the flame temperature.
                    Last edited by J Tiers; 01-09-2021, 11:45 AM.
                    3751 6193 2700 3517

                    Keep eye on ball.
                    Hashim Khan

                    If you look closely at a digital signal, you find out it is really analog......

                    Comment


                    • #40
                      Dian what is the altitude where you are?
                      --
                      Tom C
                      ... nice weather eh?

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                      • #41
                        im at 300m, so that should not be the problem. i also inquired about the gas im using. its 96% propane (the rest being mainly butane and ethane). so thats not the issue either. i tried heating a thin wire against an isolating brick in the horizontal position with several torches. again, orange heat, wire doesnt bend by its weight, it still needs some force. its snowing, so still no further experiments.

                        maybe i need to build a torch like this:

                        https://youtu.be/NlBNDRcWGig?t=220

                        no idea if hes injecting liquid propane, but the whole contraption gets to yellow heat. i have to watch some more of his vids. interestingly he mentiones its hard to get much over 1900°f with conventional torches. the "official" flame temperatures must be measured under weird circumstances.

                        mcgyver, are you sure that wire melted? it might have rather oxidised. but yes, it looks melted and if it really melted then this it a mystery to me.

                        Comment


                        • #42
                          Originally posted by dian View Post
                          im at 300m, so that should not be the problem. i also inquired about the gas im using. its 96% propane (the rest being mainly butane and ethane). so thats not the issue either. i tried heating a thin wire against an isolating brick in the horizontal position with several torches. again, orange heat, wire doesnt bend by its weight, it still needs some force. its snowing, so still no further experiments.

                          maybe i need to build a torch like this:

                          https://youtu.be/NlBNDRcWGig?t=220

                          no idea if hes injecting liquid propane, but the whole contraption gets to yellow heat. i have to watch some more of his vids. interestingly he mentiones its hard to get much over 1900°f with conventional torches. the "official" flame temperatures must be measured under weird circumstances.

                          mcgyver, are you sure that wire melted? it might have rather oxidised. but yes, it looks melted and if it really melted then this it a mystery to me.
                          I think the missing variable in your analysis is size of the torch - just how much propane is being burned between different set ups will be major factor. Propane/air is hot enough, i.e. the temp of flame.
                          in Toronto Ontario - where are you?

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                          • #43
                            Originally posted by dian View Post
                            im at 300m, so that should not be the problem. i also inquired about the gas im using. its 96% propane (the rest being mainly butane and ethane). so thats not the issue either. i tried heating a thin wire against an isolating brick in the horizontal position with several torches. again, orange heat, wire doesnt bend by its weight, it still needs some force. its snowing, so still no further experiments.

                            .......
                            What part of the flame was on the wire?
                            3751 6193 2700 3517

                            Keep eye on ball.
                            Hashim Khan

                            If you look closely at a digital signal, you find out it is really analog......

                            Comment


                            • #44
                              again, i tried every possible mixture. i have burners that run on 1/3 of the opening in free air, because they will take much more air in the furnace. of course i tried every part of the flame. the guy above puts thermocouples in the flame and shows the temp. of each torch. hes getting from 1900 - 2200°f (his torches). unfortunately he works with compressed air. even hight carbon steel will not melt under 2600°f, so i dont think there is a way to melt it with apropane flame.

                              it seem that on the forums every beginner has the same problem*. it somehow gets solved over time by kiln design, re-emissive zircopax coatings and burner modifications. im just not there yet. every forum has its own go to burner design, so its a bit complicated.

                              *reaching forging temp.

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                              • #45
                                I have heard the blue cone in the propane torch is hotter but in my experience you get more heat into the work if you dont let that blue cone touch the work. In fact the blue cone will cool off the work, while the outer edges of the flame heat it, try heating up a thin strip of steel near to the point it burns and bring the torch closer and where the blue cone touches it, the steel will drop below orange heat.
                                Last edited by johansen; 01-23-2021, 02:57 PM.

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