Forges

What is a forge?

The forge is the hearth upon or inside of which the fire is kept for the purpose of heating the iron. The forge provides a safe fire resistant structure in which to keep the fire, and to which a source of air blast can be piped to increase the heat of the fire. Most modern shop forges incorporate a chimney structure to remove smoke from the fire, out of the shop safely. The blast of air raises the heat of the fire in the same way as blowing softly on a small flame to help light a campfire.

The blacksmith's forge has remained similar in design and purpose for millenniums. Some of the differences being in the materials we now use to build our forges and the source of air supply and delivery. Despite its modern look, the modern forge works exactly the same as those of its predecessors.

A forge fire for hot working of metal

Over thousands of years of forging, these devices have evolved in one form or another as the essential features of this type of forge:

During operation, fuel is placed in or on the hearth and ignited. A source of moving air, such as a fan or bellows, introduces additional air into the fire through the tuyere. With additional air, the fire consumes more fuel and burns hotter.

A typical Scottish smithy at Auchentiber, North Ayrshire, Scotland.

A blacksmith balances the fuel and air in the fire to suit particular kinds of work. Often this involves adjusting and maintaining the shape of the fire.

In a typical, but by no means universal, coal forge, a firepot will be centered in a flat hearth. The tuyere will enter the firepot at the bottom. In operation, the hot core of the fire will be a ball of burning coke in and above the firepot. The heart of the fire will be surrounded by a layer of hot but not burning coke. Around the unburnt coke will be a transitional layer of coal being transformed into coke by the heat of the fire. Surrounding all is a ring or horseshoe-shaped layer of raw coal, usually kept damp and tightly packed to maintain the shape of the fire's heart and to keep the coal from burning directly so that it "cooks" into coke first.

If a larger fire is necessary, the smith increases the air flowing into the fire as well as feeding and deepening the coke heart. The smith can also adjust the length and width of the fire in such a forge to accommodate different shapes of work.

The major variation from the forge and fire just described is a 'back draft' where there is no fire pot, and the tuyere enters the hearth horizontally from the back wall.

Coke and charcoal may be burned in the same forges that use coal, but since there is no need to convert the raw fuel at the heart of the fire (as with coal), the fire is handled differently.

Individual smiths and specialized applications have fostered development of a variety of forges of this type, from the coal forge described above, to simpler constructions amounting to a hole in the ground with a pipe leading into it.

http://www.beautifuliron.com/smithforge.htm

Standard coal forge

A forge typically uses bituminous coal, industrial coke or charcoal as the fuel to heat metal. The designs of these forges have varied over time, but whether the fuel is coal, coke or charcoal the basic design has remained the same.

A forge of this type is essentially a hearth or fireplace designed to allow a fire to be controlled such that metal introduced to the fire may be brought to a malleable state or to bring about other metallurgical effects (hardening, annealing, and drawing temper as examples). The forge fire in this type of forge is controlled in three ways: 1) amount of air, 2) volume of fuel, and 3) shape of the fuel/fire.

Charcoal
Charcoal is the blackish residue consisting of impure carbon obtained by removing water and other volatile constituents from animal and vegetation substances. Charcoal is usually produced by slow pyrolysis, the heating of wood, sugar, bone char, or other substances in the absence of oxygen (see pyrolysis, char and biochar). The resulting soft, brittle, lightweight, black, porous material resembles coal and is 85% to 98% carbon with the remainder consisting of volatile chemicals and ash.
Coal
Coal is a readily combustible black or brownish-black sedimentary rock normally occurring in rock strata in layers or veins called coal beds. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure. It is composed primarily of carbon along with variable quantities of other elements, chiefly sulfur, hydrogen, oxygen and nitrogen.
Coke
Coke is usually produced from coal; the process is called coking. Volatile constituents of the coal—including water, coal-gas, and coal-tar—are driven off by baking in an airless furnace or oven at temperatures as high as 2,000 degrees Celsius. This fuses together the fixed carbon and residual ash.
Clinkers
Clinker is a general name given to waste from industrial processes — particularly those that involve smelting metals, burning fossil fuels and using a blacksmith's forge which will usually result in a large buildup of clinker around the tuyère. Clinker often forms a loose, black deposit that can consist of coke, coal, slag, charcoal, grit, and other waste materials. Clinker may be reused to make hard paths. It is laid and rolled, and forms a hard path with a rough surface. Clinker often has a glassy look to it; also note that it is much heavier than coke.

A clinker is coagulated slag or metal impurities that "melt" from the coal as it becomes coke. Most clinkers consist of pyrites that are naturally included in coal seams. Using "metallurgical" grade coal (met coal) greatly reduces clinkers. Clinkers will block air flow from the tuyere and that is why the firepot has a clinker breaker. Large clinkers will have to be removed with a poker.

Firepot with Tuyere, Clinker Breaker, and Ash Dump http://www.blacksmithsdepot.com/Templates/cart_templates/cart-detail.php?theLocation=/Resources/Products/Forges_and_Parts/Fire_Pot_with_Tuyere_and_Ash_Dum


Clinker breaker

Breakes up clinkers so they can be removed from the firepot.

Grate

The grate allows the coal ash to fall through the tueyre into the ash dump while keeping the burning coke and clinkers in the firepot.


Tueyre
From Wikipedia, a tuyere is a tube, nozzle or pipe through which air is blown into a forge. Air or oxygen is injected into a forge under pressure from bellows or a blower into thte firepot. This causes the fire to be hotter in front of the blast than it would otherwise have been, enabling metals to be smelted or melted or made hot enough to be worked in a forge. This applies to any process where a blast is delivered under pressure to make a fire hotter.
Blower
Bellows
There are several different types of bellows, but they all work according to the same concept. There are single-chambered bellows (made out of two teardrop shaped boards), hand-operated bellows (made out of leather and wood) and double-chambered bellows (the most efficient type and constructed out of two airtight chambers instead of one).
Firepot
fire pot

Gas Forges
http://www.statemaster.com/encyclopedia/Forge

A forge typically uses propane or natural gas as the fuel. One common, efficient design uses a cylindrical forge chamber and a burner tube mounted at a right angle to the body. The chamber is typically lined with refractory materials, preferably a hard castable refractory ceramic. The burner mixes fuel and air which are ignited at the tip, which protrudes a short way into the chamber lining. The air pressure, and therefore heat, can be increased with a mechanical blower or by taking advantage of the Venturi Effect.

The Venturi effect is an example of Bernoulli's principle, in the case of fluid flow through a tube or pipe with a constriction in it. The fluid velocity must increase through the constriction to satisfy the equation of continuity, while its pressure must decrease due to conservation of energy: the gain in kinetic energy is supplied by a drop in pressure or a pressure gradient force. The effect is named after Giovanni Battista Venturi, (1746–1822), an Italian physicist.


Gas forges vary in size and construction, from large forges using a big burner with a blower or several atmospheric burners to forges built out of a coffee can utilizing a cheap, simple propane torch. A small forge can even be carved out of a single soft firebrick.

The primary advantage of a gas forge is ease of use, particularly for a novice. A gas forge is simple to operate compared to coal forges, and the fire produced is clean and consistent. They are less versatile, as the fire cannot be reshaped to accommodate large or unusually shaped pieces;. It is also difficult to heat a small section of a piece. A common misconception is that gas forges cannot produce enough heat to enable forge-welding, but a well designed gas forge is hot enough for any task.

A forge typically uses propane or natural gas as the fuel. One common, efficient design uses a cylindrical forge chamber and a burner tube mounted at a right angle to the body. The chamber is typically lined with refractory materials, preferably a hard castable refractory ceramic. The burner mixes fuel and air which are ignited at the tip, which protrudes a short way into the chamber lining. The air pressure, and therefore heat, can be increased with a mechanical blower or by taking advantage of the Venturi effect. Propane is a three-carbon alkane, normally a gas, but compressible to a liquid that is transportable. ... For other uses, see Natural gas (disambiguation). ... The term refractory can refer to multiple things: A refractory clergyman is one who refused to swear an oath to the French Revolution-era French state under the Civil Constitution of the Clergy. ... The term refractory can refer to multiple things: A refractory clergyman is one who refused to swear an oath to the French Revolution-era French state under the Civil Constitution of the Clergy. ... This article is about ceramic materials. ... A Venturi meter is shown in a diagram, the pressure in 1 conditions is higher than 2, and the relationship between the fluid speed in 2 and 1 respectively, is the same as for pressure. ...



Fire Tools: You will need certain tools to manage the fire.


What fuels are used for the fire?

Charcoal was the original forge fuel. A beginner will immediately ask the question here "can I use bar-b-que charcoal?" The answer is no, not bar-b-que charcoal. Charcoal is made from plant material (usually wood and/or straw and clay or some other filler material) that has been heated to drive off volatile matter with almost pure carbon left behind. By a process of distillation in which wood is heated hot enough to burn, but starved of oxygen, most of the compounds in the wood are driven off in the form of vapors or smoke leaving carbon behind. Before the industrial era this was accomplished by stacking logs in a pile and burying with dirt. A small fire was built at the bottom of one end and a hole opened in the top of the mound to vent the vapors or smoke. The air supply was restricted to allow the fire to burn hot enough to literally char the wood into 'coal', but at the same time starving the wood pile inside the mound from getting enough oxygen to burn completely. The idea was to put out the fire after the wood was converted to charcoal. After the burn most of the wood was recovered in the form of charcoal with only minor losses due to some wood being closest to the fire. Visitors to this website will need to search elsewhere for instructions on making charcoal.

Between approximately the 15th and 18th centuries, blacksmiths gradually began the change to coal as their primary source of forge fuel. Not all coals are suitable for forge fuels, and the lack of access to a source of good coal and the lack of success with coal slowed its adoption as the primary fuel for blacksmiths. Even today blacksmiths must be very picky about how and where they obtain their coal, and most smiths locate good sources by word of mouth. In some regions of the world, coke is easier to obtain.


Coke: Coke is usually produced from coal; the process is called coking. Volatile constituents of the coal (including water, coal-gas, and coal-tar) are driven off by baking in an airless furnace or oven at temperatures as high as 2,000° F. This fuses together the fixed carbon and residual ash.

The Fire

Here are several pages to help the new smith learn to use the fire. Beginning with The Fire, an amateur smith or beginning smith can learn how the fire is used and troubleshoot problems he may be having with his fire. With all the misinformation spreading through the small blacksmith chapter groups it appears that a good source of info from someone who has actually used a blacksmith's fire to produce ironwork, is in order.

The another link here Lighting the Fire is written for beginners. This page written exclusively for beginners, details several different methods of lighting the blacksmith's coal fire. Look for a few photos to be placed on that page soon.

The next page is Using the Fire which describes the theory of the blacksmith's coal fire and details how to maintain and use the fire to heat iron for forging and welding. Photos will be added to this page a few at a time as I have time to shoot them. Heats and colors are described on this page along with fire tool use so the beginner can better understand what he or she needs to get off to a good start.

Forge Design.

The Forge Design pages (now numbering 15 separate pages and more material is being added) offer lots of ideas to help in the design and construction of good custom built forges. Lots of pictures of real-life pictures of the forges built by professional and historical blacksmiths from around the world. The style and method of constructing the shop forge is a matter great consideration and individual preference to the blacksmith who will be using it everyday. A blacksmith cannot use 'just any ol forge'. Placement of the fire, chimney, size of hearth, height, and materials and construction considerations are discussed. This series has become a great companion resource to The Coal Forge pages.

Here I need to make the point that time and again, amateur smiths too often build their forges with little or no knowledge of what they are doing. Worse yet, they usually build another forge to replace the first failed attempt, and again they fail to learn from previous mistakes.

These pages were created to share all of my sources of forge design. The smith that fails to understand these fundamentals will ultimately fail to build a good forge the first time and probably ever time if they also fail to learn from their mistakes. Let me give these readers a hint. See how the professionals build their forges. Learn from the mistakes of others and see what they did to design the most practical forges for their shops. Forges must be designed with careful consideration to the work they will encounter throughout the life of the forge. This design aspect which is so often unknown or overlooked by beginners and first time forge builders, has a strong impact on the productivity and effort to produce ironwork. The Forge Design pages - and the Coal Forge pages- were published specifically to help new smiths start out with the best forges possible.

Gas Forges

What about natural gas and Propane?

Blacksmiths today now have access to gas-fired forges and furnaces as well as coal and coke forges to heat the iron. Gas forges offer the convenience of not having to worry about where to buy good smithing coal. Gas forges are not as hot as coal forges and take longer to heat the iron to a forging temperature. In all cases the lower heat value of gas means longer heat times and more oxidation. However the size and capacity of the gas forge allows a much larger number of straight un-worked, or nearly straight bars to be placed in the fire at one time, and therefore can heat more un-worked bars over a longer period of time than the coal forge. This last point is the reason why a business needing forgings is more likely to have a gas forge than a coal forge. On the other hand the coal forge is still king when higher heats on larger and heavier bars are needed, and fewer bars are to be heated for work, and for heating work of more complex shape which cannot be placed inside the limited interior area of the gas forge. Each type of forge (coal or gas) has its advantages and disadvantages, and this is why each shop must choose what type of setup works best in their situation. Many shops employ both gas and coal forges and use them each for specific tasks such as-coal for heavy bars and gas for large numbers of small work.

Most gas forges never get up to welding heat.

Contrary to what most hobbyists are claiming today, most factory-made gas forges cannot reach welding heat. Don't be fooled by the claims of amateurs that they forge weld all the time with this or that forge. Most amateurs are simply boasting of being able to do something that they have never actually done. Most factory-made gas forges cannot reach welding heat, and the few that can, will heat the iron much more slowly. During the last 25 years, a new welding flux was introduced specifically for allowing gas forges (those forges that are actually capable of reaching welding heat) to be used for welding. This special flux is formulated for the increased scaling that results from longer heat times when using the gas forge.

The lower temperature and slower heating associated with the gas forge is actually helpful to most beginner smiths and those with poor fire skills because, a cheap gas forge will not heat the iron to a sizzling white heat- suddenly destroying the iron. Instead the iron will waste away (slowly burning) in the fire over a long period of time, but the inexperienced smith need not worry about suddenly destroying his iron by accidentally leaving it in the fire too long. On the other hand...

Some gas forges CAN get hot enough to fire weld!

There are some homemade and custom designed gas forges that can reach this higher heat. If the reader is going the gas forge route, I recommend visiting Ron Reil's website to see how to design the hotter custom-made forges at http://ronreil.abana.org/design1.shtml . Ron has compiled a large collection of designs both of his own and those sent to him by friends. Lots of designs of burners, insulation, most are inexpensive. These guys keep adding more stuff.

Special fluxes needed for fire welding with gas forges.

Since gas forges will take longer to heat iron, more oxidation will develop during the extended heating period. Special fluxes are used to deal with the additional scaling which results from this oxidation. Centaur Forge sells these fluxes.

 



Coal Forge Vs. Gas Forge

The Question:

Part of this question is which fuel is more available in your area? If you've never used a coal forge before and have no one to teach you, go with gas. My reasoning is that coal, in general, produces a hotter fire and one of my first tries resulted in the "infamous" sparking steel. At that point it was pretty much worthless, having been burned. I've rarely had a similar problem with the gas forge getting it too hot before I got back to the metal and started working it. You can pick up or make a coal forge generally cheaper than a gas forge. This is because the burners and insulation of a gas forge generally cost a lot more than the "pan" and plumbing for a coal forge. Coal forge's generally need a blower, but a cheap hair dryer will work in a pinch. I first bought a gas forge. After the mice used the kaowool for a nest, I had to reline it. It's worked fine ever since and taught me how to apply rigidizer and ITC refractory. I recently was given an old coal rivet forge. It needs to be replumbed and I've got a source for an old blower. It just needs to soak for awhile in diesel fuel to loosen it up and then disassembled and rebuilt (hopefully not).

Okay, here are a few pros and cons for coal vs gas forges:
(http://www.spaco.org/Blacksmithing/CoalForgeVsGasForge.htm)

Type of Forge Pro Con
Coal
  • coal forges get hotter than gas forges
  • coal forges are more traditional
  • coal forges with blowers can use hand cranked blowers, meaning that you can forge in places that don't have electricity available
  • coal forges present less of a CO hazard than gas forges might. It's not a zero hazard, however.
  • coal forges don't require pressurized gases
  • coal forges don't make any noise when idling and they make very little noise when being blown
  • coal forges don't use much fuel when idling
  • coal forges, when run improperly can be smoky and maybe smelly. Could produce a problem with neighbors
  • coal forges take more expertise to run. We teach fire management first because of this
  • coal forges indoors require a well designed chimney (10 inch min diameter)for proper operation
  • coal forges are dirtier to operate
  • coal forges have to be cleaned out and have clinker, coal and coke separated after each use
Gas
  • gas forges are relatively clean to operate
  • gas forges don't take a lot of training to use
  • gas forges are more neighbor-friendly
  • gas forge fuel, usually propane, is all contained in a pressurized cylinder so no mess
  • gas forges usually don't need a chimney; but they DO need ventilation
  • gas forges don't require constant maintenance while they are running

  • gas forges are noisy, whether in use for heating or when idling, because they usually (but not always) idle at full power
  • gas forges radiate a lot more heat at the operator and into the room than coal forges do
  • gas forges have been around a long time in industry, but the "public" doesn't see the gas forge as the tool of the "smith under the chestnut tree"
  • gas forges can be sources of carbon monoxide poisoning, so ventilation is always a vital concern
  • gas forges can be cantankerous. One can forge weld in some of them but not in others

Coal Forges



Forge terms

Coal/coke/charcoal forge (Standard coal forge)

A forge typically uses bituminous coal, industrial coke or charcoal as the fuel to heat metal. The designs of these forges have varied over time, but whether the fuel is coal, coke or charcoal the basic design has remained the same.

A forge of this type is essentially a hearth or fireplace designed to allow a fire to be controlled such that metal introduced to the fire may be brought to a malleable state or to bring about other metallurgical effects (hardening, annealing, and drawing temper as examples). The forge fire in this type of forge is controlled in three ways: 1) amount of air, 2) volume of fuel, and 3) shape of the fuel/fire.

A forge fire for hot working of metal
Over thousands of years of forging, these devices have evolved in one form or another as the essential features of this type of forge:
  • Tuyere -- a pipe through which air can be forced into the fire
  • Bellows or blower -- a means for forcing air into the tuyere
  • Firepot or hearth -- a place where the burning fuel can be contained over or against the tuyere opening.

During operation, fuel is placed in or on the hearth and ignited. A source of moving air, such as a fan or bellows, introduces additional air into the fire through the tuyere. With additional air, the fire consumes more fuel and burns hotter. A typical Scottish smithy at Auchentiber, North Ayrshire, Scotland.

A blacksmith balances the fuel and air in the fire to suit particular kinds of work. Often this involves adjusting and maintaining the shape of the fire.

In a typical, but by no means universal, coal forge, a firepot will be centered in a flat hearth. The tuyere will enter the firepot at the bottom. In operation, the hot core of the fire will be a ball of burning coke in and above the firepot. The heart of the fire will be surrounded by a layer of hot but not burning coke. Around the unburnt coke will be a transitional layer of coal being transformed into coke by the heat of the fire. Surrounding all is a ring or horseshoe-shaped layer of raw coal, usually kept damp and tightly packed to maintain the shape of the fire's heart and to keep the coal from burning directly so that it "cooks" into coke first.

If a larger fire is necessary, the smith increases the air flowing into the fire as well as feeding and deepening the coke heart. The smith can also adjust the length and width of the fire in such a forge to accommodate different shapes of work.

The major variation from the forge and fire just described is a 'back draft' where there is no fire pot, and the tuyere enters the hearth horizontally from the back wall.

Coke and charcoal may be burned in the same forges that use coal, but since there is no need to convert the raw fuel at the heart of the fire (as with coal), the fire is handled differently.

Individual smiths and specialized applications have fostered development of a variety of forges of this type, from the coal forge described above, to simpler constructions amounting to a hole in the ground with a pipe leading into it.
Coal
Coal is a readily combustible black or brownish-black sedimentary rock normally occurring in rock strata in layers or veins called coal beds. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure. It is composed primarily of carbon along with variable quantities of other elements, chiefly sulfur, hydrogen, oxygen and nitrogen.
Coke
Coke is usually produced from coal; the process is called coking. Volatile constituents of the coal—including water, coal-gas, and coal-tar—are driven off by baking in an airless furnace or oven at temperatures as high as 2,000 degrees Celsius. This fuses together the fixed carbon and residual ash.

Charcoal

Charcoal is the blackish residue consisting of impure carbon obtained by removing water and other volatile constituents from animal and vegetation substances. Charcoal is usually produced by slow pyrolysis, the heating of wood, sugar, bone char, or other substances in the absence of oxygen (see pyrolysis, char and biochar). The resulting soft, brittle, lightweight, black, porous material resembles coal and is 85% to 98% carbon with the remainder consisting of volatile chemicals and ash.

Clinkers
Clinker is a general name given to waste from industrial processes — particularly those that involve smelting metals, burning fossil fuels and using a blacksmith's forge which will usually result in a large buildup of clinker around the tuyère. Clinker often forms a loose, black deposit that can consist of coke, coal, slag, charcoal, grit, and other waste materials. Clinker may be reused to make hard paths. It is laid and rolled, and forms a hard path with a rough surface. Clinker often has a glassy look to it; also note that it is much heavier than coke






mouse
    Gee Mom, look what else I've found!




"We all do better when we all do better."
       - Paul Wellstone, US Senator from Minnesota (1944-2002)

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