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central heating furnace into a gas forge


santisandreas

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hello everyone i am working on my first gas forge which is a used central heating furnace converted into a forge. my father helped me construct it since he is an engineer and has some experience from working with central heating over the years. now i am starting to doubt my decision to use the furnace since is has a lot of excess metal on it which might absorb a lot of heat from the fire. At the begging we constructed a burner using a video from you-tube from David Hammer which was good for a first one but didn't have the capacity to heat such a large chamber. then we decided to build it from the inside with fire cement and pieces of bricks so it will have better insulation. this is gonna have two burners the one we built and a burner from Rex over at hybrid burners. view the images and tell me what you think, if you please. thanks in advance. keep in mind this is our first attempt in doing something like this. btw does anyone know why the images rotate when uploading them? how to fix this?

 

kind regards,

Andreas Santis.  

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You might be better off building a completely new forge out of a small pipe or cylinder of steel, lined with Kaowool.  Use a firebrick on the bottom.  There are many threads on this forum to check out about building your own forge and burner setup.  It will also be lighter and easier to move around.  Your forge looks like it started out as a boiler or large hot air system.  Very bulky for a blacksmithing forge.

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yeap it is a boiler. but i built it with fire cement to have a smaller chamber and it will include two burners for certain. the burners will be removable to be placed into a smaller forge which i will build later on.but since i had the boiler i thought it would be a good idea to make it into a forge. thanks for your opinion. if this consumes too much gas because of the large chamber i will definetly build a smaller one.. 

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A boiler is not designed to insulate the combustion chamber from the the water jacket or tubes.  A forge is designed to hold the heat inside the combustion chamber to heat up metal that is placed in it.  The refractories you are using do NOT look like insulating refractories.  You can build burners that will heat up the thermal mass; but it will be slow to come up to temperature and use *MANY* time the amount of gas than a simple cheap forge designed to be a forge.

 

This is one of the times when people often say "I wanted to save money so I decided to spend many many many times the cost of buying the right refractories for a forge in gas to run it so I could use refractories not suitable for a forge."

I have seen professional smiths take a roll of Kaowool and put a couple of pieces of wire around it and a burner in the side and use that has a forge---it's the kaowool that makes the forge not  the hard shell we put around it.

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ok thanks for that. the refractory is the one which they use for fireplaces which has some insulation. i would have used kaowool if we had it in my country, Cyprus, but i wasn't able to find anywhere to buy it. i thought of buying it online but it costs 30 euros to buy it and 100 for shipping because of its weight. so i will have to stick with fire bricks and this refractory with the construction of another forge. does anyone have any links for plans here on IFI? thanks in advance

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ok thanks a lot. this has been helpful. i will make another forge using plans i found. Rex has suggested a site where i am gonna buy the kaowool i just don't know which is the one most suitable for a Gas forge because this site has a lot of variety. its a very good site though, it has everything. can you take a look and tell me which one is best suited for a forge?i think the extra high temperature rigid ceramic insulation would be best, i am not sure though. thanks in advance. http://www.mcmaster.com/#standard-ceramic-insulation/=spr5f7

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As has been said I don't know how many times here, 1 ea. well tuned 3/4" naturally aspirated burner will bring approximately 300-350 cu'in. to welding temperature.

 

The mistakes in your boiler conversion forge are sufficient to not want to write a couple pages about. Build a forge from scratch, a scratch purpose built device is almost always less trouble than conversions, forges especially. As Thomas points out a furnace's purpose is exactly the opposite of a forge, a furnace is designed to transfer heat away from the fire efficiently a forge is designed to keep heat as contained as possible.

 

Dave's burner design and instructions make an outstanding burner easy to someone with decent tool skills. His burners are ejector type similar to Mike Porter's and as good or better than Price's not to mention WAY cheaper. They easily live up to the 35- cu/in to welding temperature rule of thumb.

 

All you need to do is build a forge in that range, 1 burner 350 cu/in and it'll easily hit welding temps under the burner, 2 burners and 700 cu/in is near perfect.

 

Frosty The Lucky.

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thanks. sorry for not doing my homework Frosty. i didn't look into it thoroughly before trying to do this forge. i have a bit of a problem with the terminology concerning this matters because english is not my first language, but its getting better with each day. thanks anyway for everything. you have all been really helpful.  

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thanks. sorry for not doing my homework Frosty. i didn't look into it thoroughly before trying to do this forge. i have a bit of a problem with the terminology concerning this matters because english is not my first language, but its getting better with each day. thanks anyway for everything. you have all been really helpful.  

 

No need to apologize to me, rereading what I wrote I came on kind of harsh. Certainly no need to apologize for your English, you speak as well or better than a lot of our native English speakers.

 

Translating terminology is always a problem but we're getting better at it ourselves, have you ever tried figuring out assembly instructions translated from Japanese or Chinese? Compared to them you come across like a charm. We'll get you up and running, if you don't understand something just say you don't we'll reword it or something.

 

Frosty The Lucky.

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You can see the pictures by going to http://hybridburners.com/forge-comments.html then scroll down till you see Dragon Forge from Tennessee.  That is the forge that I have in my shop.  It was made from a 30# propane bottle.  I suggest using either a 20# propane bottle or a Freon bottle.   

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hehehe no Frosty i haven't tried it, didn't come across it actually. thanks anw i am now reading about your forge Wayne and i think i will go for it. what bottle did you use in the end? a 40# or a 30#? because in hybrid burners it says 40#. i will use a 1" burner from Rex and the smaller one i made with the instructions from Dave. and as frosty said earlier 700 cu/in will be good. should i use the 40# or the 30#? thanks anyway for all your help. 

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I used a 30# propane bottle but would suggest a 20# bottle or a Freon bottle and a 3/4" burner.  The larger bottle will require more burners to heat up the entire area and you will only be able to forge about 6" at a time unless you are heat treating swords or twisting pickets.  I believe that one of the biggest mistakes made when building forges is to build to large.  They just burn more fuel and don't get up to welding temps.  Of course, altitude also has an effect on the heat output of a forge.  Higher altitude = less heat.

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ok thanks Wayne, just to clear everything out before i proceed. i already have the 1" burner from Rex and since you said on your website that the 3/4" burner is suitable for 350 cu/in the 1" burner will be sufficient for the 20# bottle which is 583 cu/in? or do you think its not going to reach welding heat with just this burner? if not, because the 1" burner is the one i want to use on this forge how much cubic inches should i look for? 400 or something? thanks in advance and sorry for the trouble, i just want to be sure before i proceed. 

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Did you subtract the space the refractory is going to take up?

 

My quick little playing around forge is made from the small light gauge helium bottles they sell to inflate balloons at parties here in the USA,  for an example: http://www.partycity.com/category/balloons/helium+tanks.do

 

I get them free or at scrap rate as they are discarded when the party is over.

They are easy to cut with an angle grinder and a cutting disk and not too large.  I line with an inch or two of kaowool and place  half thickness bricks on the bottom to provide and armoured floor for work to rest on.

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yes i did Thomas. my fire pot will be 14" depth and 10" wide which is a 5" radius of the whole circle if you do the math this adds up to 1020 cu/in divided in half is 510. Rex suggested that the 1" burner is more powerful than the 3/4" T Rex and will bring a chamber of about 600 cubic inches to welding heat but he said that this is not 100 certain since he is not in the business of making forges. so i thought to make it 500 cu/in to be certain. the forge will not be from a propane bottle because it is illegal in my country. so it will be similar to the forge of Roger Melton with 4" thick insulation. thanks again for all your help   

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The output of a burner is determined by the area of the output nozzle. A 1" burner is twice the area of a 3/4" burner, it's output is 2x. A well tuned 3/4" burner will bring 300+ cu/in to welding heat so a 1" burner will bring 600+ cu/in to welding temp. I find the numbers I get here at 425' above sea level to be 350 cu/in and 700 cu/in respectively.

 

The other factor besides ambient air pressure, elevation, humidity, ambient temperature and such that effects burner and forge volume performance is the forge chamber shape. If the chamber is of equal dimensions within reason the rule of thumb holds very well towards the upper end of the curve. A rough cube of 350 cu/in will be well served with a 3/4" burner. However if it's long and narrow, say 4.5" x 2.25" x 18" it'll be melt your stock hot, under the burner but the temperature will fall off as distance increases till it's in the  mid to low orange range near the far end.

 

If a person needs a long narrow forge then it's going to have a more uniform temperature using two smaller burners spaced equidistant than it will with a single big enough "according to the numbers" burner.

 

Aligning the burners effects the temperature as well. If it is aimed directly at the far face that part of the forge will be the hottest and the far corners will be cooler. If the burner is aimed at an angle to the far face the fire will circulate in a vortex spreading the heat more evenly for a more uniform chamber temperature.

 

Both alignments have pluses and minuses, for instance: A common complaint about gas forges (I know it's my biggest gripe) is whatever is in the forge WILL get HOT making some operations like setting rivets tricky. This means a forge with burners aimed to make vortices is going to really heat everything in it to the same temp. This is good for things like twisting, scrolling, heat treating and the like.

 

A burner aimed perpendicular to the far face will have a really HOT spot under the burner and cooler (that's a relative use of the term!) away from it so it'll be easier to heat only a section of the work in the forge. One part of the work can be melting yellow while the parts out of the direct flame will be in the orange. This is good for things like setting rivets, doing final tweaking on say ram's horns, finial scrolling a long thin taper, etc. I push the thin sections out the far side of the hot spot so the point doesn't melt off while I bring the heavier section to heat.

 

It goes on and on, give you some time and I'll be sponging knowledge from you. I will, I'm like that you know. <wink>

 

Frosty The Lucky.

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hey everyone i have found the refractory to be used for the insulation of the forge and it will be from a company Kerneos Inc. the product is Secar 71 or 80. take a look at their products if anyone is interested in the future to buy from them. i will order it from turkey which is closest to Cyprus to reduce shipping costs.  http://www.kerneosinc.com/secar71.php

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