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  • #16
    In high school we had a small foundry furnace and a small forge to do casting and heat treating. Both were fueled by either propane or natural gas, I am not sure which. Anyway, the furnace if we were casting aluminium or brass we would fire it up with a blower feeding air into the fuel stream and it would work great. On the rare occasions we were allowed to attempt to cast iron the instructor would unlock a special valve that allowed the welding oxygen supply to be injected into the fuel stream along with the blower air. Holy $hit. When that happened you would swear that a jet engine had started in the foundry room and the temperature in the room would noticeably go up within a minute. Within 10 minutes the door had to be left open and all vent fans turned on. In any case the little brick foundry furnace would be glowing orange/yellow within 20-30 minutes and a 20 pound crucible of iron melted to casting temperature within an hour or so. The forge was plumbed the same way and the oxygen used only if someone wanted to do forge welding or needed a LOT of heat for some special purpose. In most cases the blower was more than enough to do simple heat related projects or aluminium/brass castings. Iron and steel required MUCH more heat!!
    Robin

    Happily working on my second million Gave up on the first

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    • #17
      I use a shop built forge lined with ko-wool and a non- blown burner to weld damascus . I have welded dozens of billets
      with out a single fail. I use propane and I run it at about 10psi

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      • #18
        The burner is only half the tool. If your enclosure is not sufficient, you are just heating your shop. You must contain the heat you generate in a small space, only then can you get that heartwarming glow. Your only other option is to use outrageous amounts of fuel, as in a rosebud oxy-fuel torch.

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        • #19
          Yep, you need a good burner and good kiln or furnace with proper insulation to keep the heat that gets put in from getting out. I can get pretty close to white hot with a makeshift plumbing fitting propane torch and some firebrick.

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          • #20
            I'm using a "soup can forge" made using a soup can (DUH! ) lined with a mix of plaster of paris, sand and vermiculite along with a one of the common every day swirl or "turbo" style propane torches. Just the other day I heated up a 10mm allen key and forged the short end on the "anvil" of my bench vise to make a cutting blade for a wood working router plane. The whole short end allen key was bright cherry red in under a minute and I had the forging done in four heats then one more for the hardening quench. Super simple, super cheap but a good match for the torch head I'm using by being small. The working area for the torch I'm using is only 1.5D x 4L inches. Much bigger and I think it would not be as effective. I've used it for hardening some other O1 drill rod specials with great results too. With the torch I could heat up about 3/4" of 1/2" diameter drill rod to hardening temperature in free air. With the little soup can forge I can get a good 2 to 2.5" of the same 1/2" rod up to a bright cherry hardenable temperature.

            Granted the Turbo or swirl style torch is better than the other styles. But I'd say that if you have that many propane bottle screw on burners or a combination of screw on and forge style burners and none of them are good at heating the metal that perhaps it's the body of the forge which is at fault.

            Or if you are using an adjustable burner perhaps you're making the mistake of trying to run them too far open? If you open up past what the burner needs for some amount you'll get a hot oxidizing flame. But anything more than that is going to result in a cooler rather than hotter temperature. It might sound more energetic but that's the sound of all the excess air rushing in and cooling down the area in the forge. Perhaps it just needs to be tuned to find the peak temperature setting?
            Chilliwack BC, Canada

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            • #21
              I melted the aluminum out of a rotor one day with just propane. But I built a brick chamber around the set-up to contain the heat. Now I have some left-over kiln brick which works even better than the hard brick. It's very light so it allows a high temperature to build up quickly. That's the stuff you want. Just build a lego oven to suit the size of the workpiece.

              I cut these bricks with a table saw. Once you start getting into smaller pieces, it becomes quite brittle, but you can easily cut strips to use to support something that you want to heat. This works great for silver soldering.
              I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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              • #22
                a lot of input, thanks, but i still have no idea what im doing wrong or what problem my friend has.

                some more info:

                - my "forge" is an itong block with a volume of 0.6 liters (think a pint). the flame comes from above directly on the piece. after 10 min. the outside is just a litle warm.
                - the burner that fits best is putting out 20-25 kw (at least by my calculation). lambda can be adjusted and i tried all possible settings. its a roaring, blue flame comming out from a 21 mm id pipe.
                - i tried different door openings as well.

                so i reckon isolation and power deficiency can be excluded.

                can we agree on the following?

                - cast iron can be melted with a venturi propane burner in a furnace. not sure about steel. (plenty of "evidence" on youtube.)
                - it doesnt make sence to use oxygen
                - a forced air burner is no hotter than a venturi burner (its a matter of power)

                so where do i go next? do i get some exotic, reflecting alumina-zirconia refractory? work on the burners? if the commercial ("turbo" or whatever) ones provide the same flame temp. as my bigger ones (medium orange) what can i do? even my forced air burner is the same (the thing must be puttin out over 100 kw). still no idea why the "2000° flame" doesnt heat up a small piece of steel to at least white (without a furnace).

                the only thing that comes to mind is to try to position the burner higher in the furnace to make sure the piece is not in the cooler central part of the flame (the hottest are with propane is further away from the tip than with oxy-acet.).


                edit: i would post some pictures, but the stuff is outside under a tarp covered with snow right now.
                Last edited by dian; 01-07-2021, 03:00 AM.

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                • #23
                  Originally posted by metalmagpie View Post
                  Just because you have a lot of burners doesn't mean that any of them are efficient at getting every bit of BTU out of your propane. I suggest you go read up on blacksmith forge burners. Here is a site you can get started:

                  https://hybridburners.com/products.html

                  Red heat is what, 1300F? And a propane/air flame is 2000F? There's plenty of temperature there, especially for sheet metal. I completely agree with the posting above about using firebricks to build temporary furnaces.

                  metalmagpie
                  i think i have seen and built all the possible burner combinations possible. i just wonder if there are proprietary secrets after all. i mean why would people pay $200 and more if you can assemble the same with $10 of components. but what might these secrets be?

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                  • #24
                    Originally posted by Butcher View Post
                    I use a shop built forge lined with ko-wool and a non- blown burner to weld damascus . I have welded dozens of billets
                    with out a single fail. I use propane and I run it at about 10psi
                    thats what my friend has, exept that he bought it for $1000+. so what do you think makes the difference? he even has two burners.

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                    • #25
                      We need to see what you've got for a torch setup. The venturi burner I made is just some plumbing pipe and fittings with a welded mount for the gas jet - for that I used a .030" (I think, don't remember for sure) MIG nozzle and made a mount so it could be slid back and forth to fine tune position. I run mine about 10-12 psi at the max also. Even using just the open firebrick I have enough heat to forge pretty easily, this ¾" steel bar got up to temp for bending in a matter of minutes.

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                      • #26
                        i have no problem with forging (of small pieces). thats more or less the color that i call medium orange above. i have problems getting higher.

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                        • #27
                          Yeah that's after it's been out of the heat for some time, gotten bent and laid on the cold cement floor to be checked against the layout for the bend. I can get way hotter than that. It sounds like your torch isn't up to temp, maybe bad mixing or something. The position of the venturi on mine makes a big difference. Is yours adjustable?

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                          • #28
                            all of the ones i made are adjustable. as i said, i can lean most of them out until the flame separates and goes out. i whish i had a s-type thermocouple and box. so your torch gets steel to white heat? im beginning to think we have a low oxygen level in the air around here .

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                            • #29
                              Yes, it does. I'm pretty sure it would easily melt a small piece of steel even in the open firebrick setup.

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                              • #30
                                Don't most of the furnaces use a weed burner type of heat?
                                I've made a few burners and found it easy and super cheap. For me it was a lot of trial and error to get the mixture proper. I've never made one for a foundry burner. If I did it I'd copy my weed burner.

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