Azur Jahić

how much air to forge

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how much air need to be to go to forge i heard if you have too much air it will cool of your fire but if you have a small it dont heat enaugh

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The fuel does not control the heat of the fire. You should pile on more fuel than you need to have reserve fuel available (solid fuel forges).

The AIR you supply to the fire determines the heat of the fire. More air equals more heat, less air equals less heat. BUT YOU MUST have the fuel available to burn, and some excess.

Build the fire to match the work you are doing. Big fire for big work and small(er) fire for small(er) work. A piece of 1/4 inch square does not take much heat to get up to high orange or yellow forging heat. There is not much mass and it heats rather quickly.

Larger stock like 1/2 inch square is 4 times the mass, that is 4 pieces of 1/4 in square stock in a bundle. It takes 4 times the heat and 4 times as long to get it up to forging temperature.

Larger stock still, like 1 inch square stock is 16 times the mass, that is 16 pieces of 1/4 inch stock in a bundle. It takes 16 times the heat and 16 times as long to get it up to forging temperature.

To many blacksmiths, 1 inch is considered small because they use 2, 3, 4 inch and larger material. It takes much more fuel and much more air to get the much larger mass up to temperature.

Start with a ball of fire about the size of a melon, with additional fuel on top and to the side. Any given fuel contains only so many BTUs of heat. That heat is released as the fuel burns. The fuel must be replaced to keep the heat being released available as it burns. You control the burn rate and the heat being released and available in the forge by the air. Cut off the air and the fire dies.

How much air is needed? That depends on your fire, your forge, your metal size and the project at hand. You need enough air to get the metal in the fire to the temperature you need.

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I have sorta thought it odd that the very large forges use only a few small holes and the very small forges have many many air holes or use large slotted grates placed at the base.

Never heard of the "too much air" senario.................

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Most of the fires in the large forge I use are about that size. See the bellows that is used.It works swell, but much rather use the 12inch Champion 400

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Sometimes the answer to a question is found in the old reference books. The answer is also related to the forges and work being done at that period of time (before 1945), by blacksmiths that WORKED 10 hours a day, and earned their living by what and how much they produced.


12th ed Machinery's Handbook 1945

Air persssures and pipe sizes for forges

Blacksmith's forges require air pressures varying from 1-1/2 to 6 ounces per square inch. Small forges with the blower close to them are adequately supplied with 1-1/2 ounce pressure. If the blower is some distance away and a long discharge pipe with many bends leads to the forge, even through the latter be small, it may be necessary to carry 3 ounces pressure or more, to overcome the friction of the air ducts. Large forges usually require from 3 to 6 ounces pressure. The table "air pressures and pipe sizes for forges" gives the diameters of discharge mains for various tuyere sizes and numbers of forges.

For a one forge set up the numbers are diameter forge tuyere in inches vs diameter discharge main at the blower in inches.

3/4 forge tuyere......... 1-1/2 diameter discharge main at the blower in inches
1 forge tuyere............ 1-1/2 diameter discharge main at the blower in inches
1-1/4 forge tuyere...... 2 diameter discharge main at the blower in inches
1-1/2 forge tuyere...... 2 diameter discharge main at the blower in inches
1-3/4 forge tuyere...... 2-1/2 diameter discharge main at the blower in inches
2 forge tuyere............ 3 diameter discharge main at the blower in inches
2-1/4 forge tuyere ......3 diameter discharge main at the blower in inches
2-1/2 forge tuyere...... 3-1/2 diameter discharge main at the blower in inches
2-3/4 forge tuyere...... 4 diameter discharge main at the blower in inches
3 forge tuyere ........... 4 diameter discharge main at the blower in inches
3-1/2 forge tuyere..... 4-1/2 diameter discharge main at the blower in inches
4 forge tuyere ........... 6 diameter discharge main at the blower in inches

The book goes on to give forge tuyere sizes and diameter discharge main at the blower for up to 10 forges connected to the same air supply.


I saw nothing related to CFM of air required for the forge, only ounces of pressure.

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Glenn, that's great info. I have an 18th ed Machinery's Handbook and this chart is not in it - but I always thought the older publishings would have included blacksmithing information.

The older electric blowers typically put out 250-400 cfm at 2-3 oz SP. in fact, the larger electrics are quite capable of supplying air to two average forges (such as an 11x14 bottom pot or similar size). To my knowledge, hand blowers were not rated.

Having used both air sources, I'm also reasonably certain that a double chamber great bellows can put out more pressure at a lower cfm than a manual geared blower. My reasoning for this is that blowers allow back pressure to escape thru the inlets but a bellows in good shape will hold a lot of pressure and build up to blow more effectively thru a pile of fuel.

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I have used small squirrel cage blowers on my forges. The cage is 3-4 or so inches diameter by 2 inches wide with a 2 inch or so outlet. I tried one last week that was about 6 inches dia x 1 to 1/4 wide and with a 1-1/2 inch outlet. This blower had a much restricted air inlet (removable housing) so it could draw heat from the machine it was attached to. Worked at my forge as a test, but I have not had it in full operation. These are small units, the whole thing maybe 6 inches in diameter.

What ever the electric blower used I usually vent some of the air before it gets to the forge, otherwise it would be too much air. I also have a large opening in the tuyere, 2-1/2 inch pipe with only a 1/4 inch bar across as a grate. It gets a LOT of air through the fire that way.

My suggestion is to find a squirrel cage fan and build a fire and see how it works for you. There are many machines that use these units for cooling. A bathroom ceiling fan should work. The fan from a heater on a automobile will run on 12v or what ever is used on the electrical system of the car. Just recharge the battery when needed. Use what is available in your local area and make it work.


HWooldridge
I think they dropped blacksmithing information about edition 17. Edition 12 has information on making tongs etc. The dimension of the reins are from end to revet of 14 to 40 inches. The tongs for 1/2 inch stock have 18 inch reins from end to revet. This length does not include the jaws of the tongs.

They suggest the weight for a blacksmiths anvil is 150 to 300 pounds and cautions against getting an anvil that is too light in weight. The heaver weight is suggested. Remember this is a production shop prior to 1945, over 70 years ago.

It is interesting that they list the type of steel used to make many different items such as axle shafts, spring clips, springs, bolts, etc. It is of little use today unless you can locate some steel in use in 1945. Even then it was still mystery metal.

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You can have too much air blast.

There is a balance between the amount of fuel that is burning (the size of your fire) and the amount of air (or oxygen) that is needed to support the combustion. If the oxygen is not being consumed completely you produce scale on your iron because the excess O2 reacts with the hot metal and it will also cool your fire.

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HW: As I recall the 13th edition of Machinerys Handbook is the cut off for a lot of the smithing info...Jock over at anvilfire knows the details...

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You can have too much air blast.

There is a balance between the amount of fuel that is burning (the size of your fire) and the amount of air (or oxygen) that is needed to support the combustion. If the oxygen is not being consumed completely you produce scale on your iron because the excess O2 reacts with the hot metal and it will also cool your fire.


Is this theory or fact?

The more air added to an adequate fuel supply in an open fire will increase the heat level, until the fire becomes physically unstable

In my limited experience, whenever the air blast is increased too high, the hot cokes,ash and molten clinkers start to erupt like a volcano in either side or bottom blast forges.

If your workpiece is being cooled by the air blast, it is probably because it is too low in the fire and too near the tue, this manifests itself in a dull red or darker section with hotter sections at either side of this darker colour, this can also be a sign of excess clinker in a bottom blast forge.

At the other extreme, I have used a 1/50th hp squirell cage motor and succesfully firewelded with it, takes a little patience, but does work.

Air flow control by whatever method is key to fire management

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i have this bellows but i dont know what is purpose of upper tube hand lever i know that down lever push down tube but what is purpose of up tube arm lever

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That info went right into the notebook Glen. Thank you.
I like to think of too much air and not enough fuel like running the AC on cool with the fireplace going. :P It can be hard to tell a hollow fire with a coal shell because it doesn't send coke flying. There is a balance, if the O2 is moving faster than it can burn I can only assume it changes (an under-filled) hearth temperature closer to the ambient atmosphere.. since oxygen isn't the only thing air is comprised of.. at least that's how I interpret a white hot shell with nothing below.

Azur,

If the top tube isn't supported/attached by anything other than the rubber and arm? I'd guess it's just there as a guide.
What is your desired metal size to work with?

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Is this theory or fact?
The more air added to an adequate fuel supply in an open fire will increase the heat level, until the fire becomes physically unstable
In my limited experience, whenever the air blast is increased too high, the hot cokes,ash and molten clinkers start to erupt like a volcano in either side or bottom blast forges.
If your workpiece is being cooled by the air blast, it is probably because it is too low in the fire and too near the tue, this manifests itself in a dull red or darker section with hotter sections at either side of this darker colour, this can also be a sign of excess clinker in a bottom blast forge.
At the other extreme, I have used a 1/50th hp squirell cage motor and succesfully firewelded with it, takes a little patience, but does work.
Air flow control by whatever method is key to fire management


This is fact. Most of what you hear on IFI is from armchair smiths who don't know a xxxx about smithing. Fire management is one of the first things a smith must learn. Let them pontificate on all the ways to eliminate scale or manage a fire but it starts in understanding how the fire works . A balanced fire with the steel in a zero o2 zone is where you have to start.

You can blow all the air you what but if you don't have enough fuel all you are doing is forming scale and cooling your fire.

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i have this bellows but i dont know what is purpose of upper tube hand lever i know that down lever push down tube but what is purpose of up tube arm lever


Hi Azur,
It's difficult to say from your single photo, but the principle with double lung bellows is that the lower part is used like an air pump that inflates the upper part which is an air resorvoir that then feeds the air into the tue iron in a steady flow until the top part totally deflates.

Same principle as an electric motor turns a compressor which supplies air at each stroke,(Lower section) to build up air pressure there is a receiver or tank in which the pumped air is stored (Upper Chamber) to enable it to be efficiently used without having to use the smaller capacity pump all the time

Check that as you pump the arm, the air from the lower chamber inflates the top one, substantially, if so a little more weight on the top board may help in getting a better air flow after it is filled.

With regard to the top linkages, there is a slight possibility that the system is two seperate acting single action bellows that are linked, this would be indicated if the two bellows linkages can be connected to the one long arm extending from the base, I would think highly unlikely, but possible,

Where did you get them from? As I would suggest asking the maker/supplier how they were intended to work if that is at all possible, or see if we can get to see the internal plans for the valving arrangement.

Hope this helps, if not, I have some details of how round chambered double action lung bellows function, the principle is the same as square ones and if you send me a pm with your email address I can send you these details as an attachment, I don't think they will post on here.

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i aking this because i made arm for down tube i dont know purpose of up tube lever arm and i dont make it i heard if you put something heavy on upp tube air will be better

i asking this because i dont make up leaver for up tube i think bellows dont need up lever i dont know how my inner tube double chamber bellows work

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This is fact. Most of what you hear on IFI is from armchair smiths who don't know a damn about smithing. Fire management is one of the first things a smith must learn. Let them pontificate on all the ways to eliminate scale or manage a fire but it starts in understanding how the fire works . A balanced fire with the steel in a zero o2 zone is where you have to start.

You can blow all the air you what but if you don't have enough fuel all you are doing is forming scale and cooling your fire.


I am glad you agree with me re adequate fuel, and fire management, although I think some may take exception to your generalisation on the source of advise being given on the site, my problem was with the "cooling the fire" bit.

There is still heat in the fire, and quite intense heat, but because the viable fuel has been consumed then the fire mass decreases until it is extinguished, not by the excess air, but lack of combustible materials. Normally, correct me if I am wrong, but the workpiece in a solid fuel hearth is in contact or buried in the hot coke rather than being positioned in the direct air blast from the tue,

You can have problems with too much air when starting the fire because the pre ignition materials are either extinguished by too much air blast, or they burn out before igniting the forging fuel, paricularly the metallurgical coke we have in general use here in the UK.

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i asking this because i dont make up leaver for up tube i think bellows dont need up lever i dont know how my inner tube double chamber bellows work


Hi Azur
What exactly happens when you pump the arm up and down once?

And what happens when you pump it a few times quickly?

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whan i pump down it force air from down inner tube to up . when i put rocks on up inner tube all preasure go to the pipe to forge

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whan i pump down it force air from down inner tube to up . when i put rocks on up inner tube all preasure go to the pipe to forge


Hi Azur, That seems to be working like it should, the pipe to the forge is the tue/tuyere

To control the amount of air to the hearth through this tue/tuyere you will have to try different speed and lengths of stroke on the handle to give you the air blast you require.

When starting the fire you will need just a breath of air, increasing as the fire takes hold, and as I mentioned in a previous post,
you can have problems with too much air when starting the fire because the pre ignition materials are either extinguished by too much air blast, or they burn out before igniting the forging fuel, so take your time, and don't pump too fast too quickly,

New fuel is more difficult to light than pre part used fuel, you will probably find that the fire collapses somewhat as the paper and kindling are burnt, which leaves a hollow under your burning fuel

What fuel are you using? And make sure there is adequate to sustain the fire

Keep playing until you get it right, it may take a little time but you will get it eventually,

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Most of what you hear on IFI is from armchair smiths who don't know a xxxx about smithing.

If incorrect information is posted on IForgeIron, the site ENCOURAGES CORRECTION with the very next post. To say most of the now 300,000 posts are from "armchair smiths who don't know a xxxx about smithing" is incorrect.

There are world class blacksmiths on the site, others that have years and in some cases a lifetime of experience, and yet others that although they are young in years, have much experience, skill and expertise. They have studied the craft and KNOW of which they speak, and speak from experience that can only be found at the forge.

IForgeIron is a not a book where you can not question the author, or ask for additional information. IForgeIron is an ongoing discussion about blacksmithing and metalworking. You can talk with the author of the post directly. You can ask for additional information. You can discuss with the author the details of the post and in that discussion benefit from the depth of their knowledge.

You are encouraged to share your skill and expertise with others on the site, and are encouraged to post corrections to those items you feel are incorrect either in information or in technique. But to say "Most of what you hear on IFI is from armchair smiths who don't know a xxxx about smithing" is incorrect.

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In a good fire with heart (i.e., not hollow) a smith can blow a fire too hard and introduce excessive oxygen - similar to an oxy-acetylene torch flame that is too lean. With regard to a solid fuel fire and typical forge welding or heavy forging, I find it useful to raise the temperature quickly with high blast until the material is close to the color of the fire then reduce the blast to almost nothing. The fire will glow very brightly when the blast is reduced and allows the material to soak for a few seconds and get to welding temps without burning the stock. This one detail helped my forge welding immensely because my previous practice was to leave the blast open and yank the material out of a volcano. The problem is that thicker material will be hotter at the surface than the core and can cool off fast enough to thwart a weld. Conversely, this same practice can help keep thinner items from burning when excess O2 is present. Bottom line is that fine blast control is important to the smith.

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The discussion so far has NOT covered the size or configuration of the forge and how much coal is actually been dumped into the forge and onto the table. This is a very important piece of information. For instance my 13 inch diameter brake drum that is 3 inches deep with a one inch extension (now 4 inches deep) and table takes half a 5 gallon bucket to get started. More is added as needed for the size work being done.

I found the following in reference in some of my notes. The source was not listed.

For machine blacksmithing forges should be from 36 to 42 inches in diameter and from 26 to 30 inches high, the top of the tuyere being from 4-1/2 to 7 inches lower than the top of the forge. As there are no standards or definite data for guideance in determining the size of the opening for tuyeres or the depth at which they should be placed below the level of the hearth. The table below gives what the writer considers to be proper dimensions for work varying from i inches to 10 inches in diameter, when the blast is delivered at a pressure of 8 ounces per square inch or over. Work over 10 inches in diameter can be more uniformly and economically heated in a furnace.

Table of sizes and arrangement of the tuyeres.

Size of the opening in tuyere..................................3/4 inch................1 inch
Distance between top of tuyere and top of forge ...4 inch .................5 inch
Size of the supply pipe...........................................1-3/4 inch.............2 inch
Size of the work to be done.....................................1/4 to 1 inch........1 to 2 inches


The forge is 3 to 3-1/2 FEET (a meter) in diameter. The top of the tuyere is lower than the top of the forge by 4-5 inches with additional coal on top of that. The air blast is 8 ounces per square inch or greater.

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