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Do I Need Forced Air?

Discussion in 'Working the Steel' started by Tom Stegner, Aug 20, 2019.

  1. Tom Stegner

    Tom Stegner New Member

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    Hi, I am new at this and my ultimate goal is to make a damascus sword. I have melted copper in my forge so I guess I am getting around 2000 degrees F out of a single burner propane forge. Can I get another 200 degrees out of it without doing the forced air thing? And, if not...could someone show me a plan for adding a reliable forced air setup that won't burn down my home? My wife is a little concerned about that...lol.
     
  2. dancom

    dancom Dust Maker Best Shop Tool

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    Hi Tom,

    Many ways to skin that cat. A sword would benefit from a longer (read larger volume) forge. Do you know the volume of the forge? Plan for one naturally aspirated 3/4" burner for about 300 cubic inches of interior forge volume. Some say 350 but I'd err on the lower. Forge geometry and construction play their parts too. I see some forges with huge openings front and back, just leaking precious heat. Making firebrick baffles to close off the chamber a bit can really help keep the heat in.

    What type of burner do you have? Burners can be tweaked, however, typically homemade naturally aspirated ones are not very efficient. Adding a couple of PSI to the air intake will certainly give it a boost in temps. I've seen everything from dried compressor air jetted in from a regulator set at a few PSI, to low volume furnace exhaust fan, 12 V heater blower from a car etc., anything to give a small boost.

    As far a not burning down the house: Never leave the forge unattended. Have a fire extinguisher handy. Best if you can wheel it outside. It's good for fresh air, but noisier for the neighbours of you are banging on an anvil all day.

    Dan
     
  3. Tom Stegner

    Tom Stegner New Member

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    Hi Dan and thx for the reply. I converted a propane tank...fire brick cemented to the insides 1.5" and then I put in 2 layers of 1" ceramic fibre insulation giving me a working forge area of 376 cubic inches. I have a 5.75" opening at each end and a metal plate that I can put a fire brick on and block off either the front or back or both. My burner is homemade. I use a 1" pipe with a 1" to 1.5" coupling as the burner. Pipe is black, coupling is stainless and at the gas end I have a 1.25" stainless T with the gas jet mounted in the middle of the top pointing straight down the nipple. One side of T is blocked off with a plug. The other has a flap in front that lets in the air. When I open that up all the way, I get a nice flame. I am using a 20psi regulator on the prone tank.
     
  4. dancom

    dancom Dust Maker Best Shop Tool

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    Sounds like you have 1" sidearm burner. Ideally you would have a much larger intake for the 1". I would shoot some air in and see how hot it will get. Cal @FORGE used to use low PSI compressed air with his naturally aspirated venturi burners.
     
    Last edited: Aug 20, 2019
  5. Mythtaken

    Mythtaken Staff Member CKM Staff

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    FYI: A vertical forge tends to generate more heat where it's needed than a horizontal one (heat rises). Plus the design is better suited for dealing with all the drippy schmutz (technical term :)) from borax, if you're using flux for making your damascus. You may find you don't need to add air at all with a vertical forge.

    When it comes to swords, remember that you only work a small area at a time, so there isn't a great need to heat the whole length of the blade at once. The exception is for the heat-treating process. For that, you can build a separate tube forge with a ribbon burner that will distribute heat along the whole length.
     
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  6. Tom Stegner

    Tom Stegner New Member

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    Hey Dan, thanks for the info. I will start getting things together for a forced air setup. Back to the drawing board lol.
     
  7. dancom

    dancom Dust Maker Best Shop Tool

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    I love your ambition. Sword! I'm still trying to dial in a chef's knife. ;-)

    What Tim says. You only need a longer forge for heat treating and at that stage you won't be working at forging temps.

    I wish I could point you to the photos of Cal's forge and the little air injectors he added. It appeared to be a simple and precise way to boost the air to the burner. Unfortunately, these photos went bye-bye when Photobucket pulled a fast one.

    Here is a page in the forum where adding some compressed air was discussed. https://canadianknifemaker.ca/index.php?threads/problem-with-not-getting-enough-heat.2993/

    Dan
     
  8. Tom Stegner

    Tom Stegner New Member

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    I read that link you sent me and perhaps I am doing the wrong thing. I add more oxygen until that orange flame goes away from the openings. I will back off on it and we will see what that does. Thank you very much you have been very kind.
     

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