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Blacksmithing and metalworking questions answered.

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coal, charcoal, fuel

Coal Forge Fires :

Management and Cleanliness

Carbón, charbon à bois, Holzkohle, Kohle, kol / stenkol, houtskool, koolstof

Coal Fire management

Fire management can only be described in very general terms because of the variables which include infinite grades of coal and nearly infinite variations in forge design and construction. The general process follows.

  • You start the fire with fresh coal using a torch or a wad of paper and a little kindling. In a good forge with good coal you can start a fire with a sheet of newsprint alone. The air blast should be very gentle when starting a fire. If you listen to the paper or kindling burning the least blast that creates the most fire noise is the best. Too much blast cools the fire and can put it out just like blowing out a candle.

  • Once the fire is going you shovel on more fresh coal making a mound over the center. This will create thick yellow smoke at first. As the coal cokes down and the fire builds the smoke reduces and the remainder will be burnt off.

  • Once the fire is going good you reduce the air, pile on more coal and let the heat build as coke forms (assuming good coal). I poke a vent into the pile with a gently curving poker with a straight point. This reduces the spread of the fire and helps create a hot spot around the vent.

  • Once the fire is burning clean and hot you can bury a piece of steel in the fire. Use as little air as is needed to keep the fire hot. When working alone using a bellows or hand crank blower you generaly use as much air as possible to build the fire back up between heats tapering off as needed depending on the size of the work. If you have a helper than they must control the air and not be too slow or too fast. Motorized blowers should be adjusted to a low steady blast.

  • As you work the center of the fire becomes hollow. Pat down or push the surrounding coke and coal toward the center. Add coal to the reserve area in the forge. Feeding coal to the center is a continous job. I work the fuel in while pulling the bellows and waiting for the steel to get hot.

  • In forges using hand crank blowers or bellows it is easier to use a beehive type fire where you keep a roof of fresh coal on top of the fire and vent it out the front where you are putting the work in to heat it. Maintaining this fire shape is a little more difficult than an open fire and requires close attention. It is nearly impossible when more than one person is using the fire.

  • When doing large or odd shape work the fire breaks up using more fuel and air. When feeding an open fire push the surrounding coke into the center and replace it with fresh coal. This is constant movement from the outside in. Do not put fresh coal into the cneter of the fire. This creates more smoke and cools the fire. Coke makes the hot clear fire at the center and is created in the area surrounding the center.

  • Open fires are hard to supply sufficient air without a helper or powered blower.

  • Both type fires tend to spread and need to be controled. A spreading fire is an inefficient fire. Only the heat concentrated in the center is useful. A little water from a sprinkling can will put out the excessive fire outside the center and usualy leave coke. Sometimes at the end of the day you have a huge mound of coke. Most smiths pick this out and use it for welding fires or to feed the next days fire using just the minimum fresh coal to start the fire, then piling on the coke THEN surrounding that with fresh coal.
The above assumes a good coking grade of bituminous coal and a fairly normal bottom blown forge with fire pot.

Coal Reserve:

This is the area of the forge where extra coal is kept. Technicaly the center of the forge and firepot is only about a foot square or less. This is all that is needed for a very small forge like a brake drum forge. However, during the day a smith may burn as much as a bushel of coal. Full size forges are usualy about 30" by 40" (750 x 100mm) with the firepot centered toward one end. All this excess area is primarily for fuel storage so that the fire can be convieniently fed as needed.

Some may argue that the larger area is to support larger work. This is true but it is a secondary purpose or benifit of the first. With large and small forges alike we often need stock supports for long or unweildly work. Wheelwrights often had supports on the front of the chimney to hang tires so they did not settle too deep into the fire.

Wet Coal, Dry Coal, Dirty Coal:

Depending on the type dry coal starts easier. Some coal absorbs moisture and is thus harder to start. But in general coal is coal and what moisture it has was bound into it in the ground eons ago. However, I like having some dry coal to start a fire.

Dirty coal is a different thing. Dirty coal is hard to get started, hard to keep burning, causes more scale on metal and is nearly impossible to weld with.

If coal has been dumped out of a forge where much of it was burnt then you have, coal, coke, clinker and ash. When smiths dump their forges they generally pick out the larger lumps of coke to use for welding fires, the obviously clean coal that can be easily shoveled and scrap the rest that is mixed with ash and clinkers.

Coal that has been shoveled off the ground or the bottom of the pile at a coal dealers graveled lot is often full of dirt that is just as bad as the ash above. Gravel often gets coated with enough coal that you cannot tell the difference without a sharp eye for shape and texture. Sandy soil causes excessive clinkers, clays deaden the fire and gravels do not burn making cold spots in the fire.

References and Links

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