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I Forge Iron

need help with burners


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Hey guys, quick question.....right now i have a small forge with a 3/4 in. venturi burner (side arm style) I also have another venturi style burner that is a bit smaller that i had started with before getting the bigger one. any way i have been making knives using the stock removal method and using the forge to heat treat them. Now that the weather is nice (i dont have a big shop so my forge needs to be kept outside) i want to learn how to forge some blades during the summer. So i have decided to build a bigger forge. so what i really want is to have it set up with a forced air or blown burners. however funds are kinda tight right now. so i was thinking of getting one blown burner made and a blower and then for now also have the bigger venturi burner i have. so the forge would have 1 blown burner, 1 3/4 sidearm venturi burner, and if i need it i have the smaller venturi burner. then down the road when i get some more money to spend switching to all blown burners. so my question is will that work? i have never seen a forge with both blown and venturi style burners  some one told me that the blown burner MIGHT effect how the venturi burner will work. Has any one done this? does any one see any reason it will or wont work very good for the time being???? Thanks guys i really appreciate it i havent been able to find much info on this.

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Not completely sure why you think you need more than a 3/4" Venturi burner for a knife making forge.  A forge only used for knife making doesn't have to be very large at all.  Remember that you can only beat on about 6" of knife length during any heat in any case, and with a pass thru door you can make a pretty long knife in a forge that has a 6" internal diameter and is around a foot long.  If you build yourself a 3/4" Frosty T-burner  (the parts for which are pretty darn cheap if you already have  a ball valve and propane regulator) you should be fine if the forge is properly insulated and has a good door.

Needless to say a single, well designed blown burner will also serve such a forge well.  If you want to optimize the efficient heating of the blown burner, probably the best avenue for doing this is to build yourself a ribbon burner to get even heating to the walls ASAP so they can reflect the same back onto your stock.

While you can combine naturally aspirated (NA) burners with blown burners in a single chamber, it will make tuning the former much more difficult.  The NA burner will be very sensitive to whether the blown burner is on and how you deal with your door openings.  If the NA burner is idle, and you don't have it's opening into the forge plugged, you will heat that burner up quite a bit since there will be no air going thru it and the blown burner's exhaust gasses will in part be exhausted thru the port. Actually, on reflection, I wonder how forges with multiple NA burners get away with this without overheating their inactive NA burners.  Probably not as big an issue since there is less outlet pressure from the burner assembly?

In any case, I also would not recommend combining burner types as you are proposing.

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ok thanks....is there any rule of thumb how much space a blown burner will heat up to forge welding temps? (say the one on hightemptools.com that has a 2in body with a 1in burner tube)

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Not to mention what you are planning on forge welding.  If high carbon steel only you need to get up to the high yellow/orange range.  If wrought iron you need to be in the white hot range.  Low carbon steel somewhere in between.

The other side of the equation is how massive your billet will be inside the forge, and how long you will take to heat it up each time.  While a light weight fiber blanket forge will get up to temperature quickly, when you put a massive colder billet into it, it will cool it down quite a bit faster than a forge with some thermal mass.  Of course the latter forge will take a lot longer to get up to temperature, provided it has the same insulating value in its walls.

I assume that you are planning on forge welding up some patterned billets of high carbon and nickel.  I'm not the best person to answer that as I have only limited direct experience.

Remember that if you plan on using flux on your billets you need to build a forge that can handle more flux contact.  It will eat through any soft brick or refractory blanket insulation in a hurry.  That is why most folks have a separate forge body for welding verses the one used for forging.

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