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Air Compressor Forge


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I am a newbie blacksmith and want to build my own propane forge. To do so I recently aquired a air compressor that is 16 inches wide and ablut 24 inches long. I want to insulate it with 2inch ceramic blanket, cover that with a half inch of refractory cemnt and line the bottom with fire bricks. The problem is I do not know if I will be able to reach forge welding temp with how bug of a space I will have? Any I deas on how I might redesign are much appreciated. 

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Welcome to IFI... I always suggest reading this to get the best out of the forum. READ THIS FIRST

You will undoubtedly need at least two burners. Not knowing where in the world you are located or what type of work you are planning it's hard to give you an answer. For ideas on how to redesign it you need to read through the Forges 101 sticky.

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If you are planning to pattern-weld for smaller projects (like blades), I would take 4 inches off the bottom side of the tank and weld a flat piece there. Then you would have a nice flat surface to facilitate a floor without using fire bricks, and you would decrease the internal volume. This may prove more efficient during heating. You could use the extra blanket to decrease the width of the internal volume too. A 16 inch diameter tank is pretty big, but then I do bladed things, so you may need bigger.

 

Also, read the consolidated notes for beginner forge builders (sticky). In my opinion, that's a really great place to wet your feet.

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Yes, No, Maybe depending on information you have not provided: Like size of burners, number of burners, type of fire brick, etc.

They reach forge welding temperatures in forges big enough to fit a rail car into; it's how big/how many burners you have and how much money you are willing to spend in fuel to run it at forge welding temps.

Can you tell us why you need so large a forge?  Generally when a new smith tells us they want a large forge, they actually need a much smaller forge with a pass through out the back:  Example Sword Forging; you DON'T want to heat more metal than you can work before it passes out of forging temperature. Doing so results in decarburization, scale losses and grain growth.  So for a sword forge 9" of heated interior is fine; any more you are throwing away money heating it and damaging your steel.  Billets for forge welding are generally fairly compact as that is easier to weld without flaws---note a piece of round stock 2" in diameter and 4" lpng should have more than  enough steel in it to forge a sword even expecting 50% loss in forging and grinding!

Having more than one forge of different sizes/uses is often the cheapest way to go'---my analogy is: would you buy a dumptruck as your daily driving vehicle because once or twice a year you need to haul a load of gravel?

So more details on what you are trying to accomplish please!

 

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On 3/26/2019 at 7:18 PM, MCalvert said:

If you are planning to pattern-weld for smaller projects (like blades), I would take 4 inches off the bottom side of the tank and weld a flat piece there.

Thank tou for the advice. This is probably what I will do. Would you suggest 2, 3/4 in burners? 

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That's still enormous, at 16" long with an internal diameter of 11" you will have a volume of about 1520cubic inches, a well built 3/4" burner heats 350cubic inches to welding temps which means you will need 4 3/4 inch burners. That will be a gas hog. Now if you are set on a forge this size you can build an internal baffle wall to reduce the internal volume when you only need half of the forge, but even then it's still quite large.

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Thank you for this advice! I have decided that I will then insert the 2in kaowool into the now cut tank  I will then insert a fire brick bottom and place a wood box that is the same size chamber that I have settled on(7in by 4.5 in tall by 16 in long) and fill any gaps between this box and the  kaowool with refractory cement. 

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So you plan to waste a lot of gas that will cost much more to buy than making a heat treating forge---why?

Did you skip the post about:  " Example Sword Forging; you DON'T want to heat more metal than you can work before it passes out of forging temperature. Doing so results in decarburization, scale losses and grain growth.  So for a sword forge 9" of heated interior is fine; any more you are throwing away money heating it and damaging your steel.  Billets for forge welding are generally fairly compact as that is easier to weld without flaws---note a piece of round stock 2" in diameter and 4" lpng should have more than  enough steel in it to forge a sword even expecting 50% loss in forging and grinding!"

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As usual, Thomas is right.  MCalvert’s suggestion of cutting off a section of the bottom and welding flat floor on is a great idea.  The mailbox style forge seems to be well loved.  It would be easier to line as well.  You don’t want a forge that is 16” in diameter unless you are making small anchors or something.   Right now you are looking at a four or five burner forge. Many people build three burner forges only to end up blocking off a section and using only one or two burners at a time.  

Every professional shop I have visited has run a small, one burner forge for their daily work.  The guys at Dragon’s Breath Forge near me weld massive Damascus billets fluxless on a Nazel 4B powerhammer that shakes your bones....and they do it all on a tiny forge with one ribbon burner heating it.  That shop sports two Forged in Fire winners.....

I know you just want to get the burners locked down, but we don’t want to send you off buying or making a load of burners that you don’t need.

 

Lou

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Thank you all for the great advice! I am going to take your suggestions and do the mailbox type-ish forge and will be cuting the length down to about 12inches. Like you guys have mentioned I took my plans for the forge and made myself think that I needed this monsterous thing. I will be postibg pictures of the finished produbt in about a month or two once I find the time to finish the forge.

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Don't expect your first forge to be your last.  Just like one's first "learner car" is probably not the one you will stay with your entire life. Make the forge the one you need now and plan to change it out as needed. I know one pro smith who needed a large forge for a specific use and took a roll of kaowool and rolled out a length and fastened it with baling wire---no shell at all!.

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I don't see anyone giving actual dimensions.  So....

On 3/28/2019 at 12:50 AM, Mikey98118 said:

A BIG forge is made from a five gallon propane cylinder, a daily use forge is made from a two gallon Freon or helium cylinder

i.e. 5 gal propane tank has 12.5" diameter, 2 gal has 9" diameter.  With 2" of ceramic fiber that makes the large one 8.5" diameter interior, and the smaller one a 5" diameter interior.  Use that as guidelines.  Cut a slot out of your 16" diameter to make it smaller - with ceramic fiber make your inside diameter between 6 and 8".  The formula for interior volume is 3.14 x interior diameter x length.  As stated above, 1 3/4" burner per 350 cubic inches.

Good luck!

Dan R

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18 hours ago, D.Rotblatt said:

The formula for interior volume is 3.14 x interior diameter x length.  As stated above, 1 3/4" burner per 350 cubic inches.

Uhhhh? :blink:

Pi x d = circumference doesn't it? The two formula I know for area of a circle are: Pi x r squared or (my personal favorite) .7854 D squared.

3.14 is Pi rounded off.

Volume of a cylinder being area of the circle x length. Yes?

Frosty The Lucky.

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My, you have a tolerant idea of even "roughly" spherical. :huh: 

V=(4/3)πr^3 is one I use more often that I thought I would and about as deep into math as I go.  To be honest if I needed to figure the volume of a brain and can't just measure how much water it displaces I'd go with "roughly spherical" and fudge some with my fingers crossed. :) I have no idea how to calculate the volume of the flappy part that makes the brain fart sound.

Frosty The Lucky.

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