Forging and Blacksmiths
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Wikipedia-Article "Forging"
- This article is about smithing. For more uses of the word forge, see forge (disambiguation).
The forge or smithy is the workplace of a smith or a blacksmith. "Forging" is the term for shaping metal by use of heat and hammer.
A basic smithy contains a forge, sometimes called a hearth for heating the metals (commonly iron or steel) to a temperature where the metal becomes malleable (typically red hot), or to a temperature where work hardening ceases to accumulate, an anvil (to lay the metal pieces on while hammering), and a slack tub (to rapidly cool, and thus harden, forged metal pieces in). Tools include tongs to hold the hot metal, and hammers to strike the hot metal.
Once the final shape has been forged, iron and steel in particular often get some type of heat treatment. This can result in various degrees of hardening or softening depending on the details of the treatment.
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Forging
Forging is the working of metal by plastic deformation. It is distinguished from machining, the shaping of metal by removing material (drilling, sawing, milling, turning, grinding, etc.), and from casting, wherein metal in its molten state is poured into a mold, whose form it retains on solidifying. The processes of raising, rolling, swaging, and drawing are essentially forging operations although they are not commonly so called because of the special techniques and tooling they require. Some of these techniques are shown in this animation of the forging of simple flat firetongs.
Forging results in metal that is stronger than cast or machined metal parts. This is because during forging the metal's grain flow changes, making it stronger and more ductile.
Many metals are typically forged cold but iron and its alloys are almost always forged hot. This is for two reasons: firstly, if work hardening were allowed to progress, hard materials such as iron and steel would become extremely difficult to work with; secondly, most steel alloys can be hardened by heat treatments (i.e. by the formation of Martensite) rather than cold forging. Alloys that are amenable to precipitation hardening (such as most structural alloys of aluminium and titanium) can also be forged hot, then made strong once they achieve their final shape. Other materials must be strengthened by the forging process itself.
Forging was done historically by a smith using hammer and anvil, and though the use of water power in the production and working of iron dates to the twelfth century CE the hammer and anvil are by no means obsolete.
In modern times, industrial forging is commonly done either with machine presses or with hammers powered by steam or compressed air. These hammers are very large, having reciprocating weights in the thousands of pounds. Smaller power hammers (500 pounds or less reciprocating weight) and hydraulic presses are common in art smithies as well.
In industry a distinction is made between open- and closed-die forging. In open-die work the metal is free to move except where contacted by the hammer, anvil, or other (often hand-held) tooling. In closed-die work the material is placed in a die resembling a mold, which it is forced to fill by the application of pressure. A great many common objects (wrenches, crankshafts...) are produced by closed-die forging, which is well suited to mass production. Open-die forging lends itself to very short runs and is appropriate for art smithing and custom work.
Closed-die forging is more expensive for mass production than is casting, but produces a much stronger part, and is therefore used for tools, high-strength machine parts and the like. One particular variant, drop forging, is often used to mass produce flat wrenches and other household tools.
Types of forges
Coal/coke/charcoal forge
A forge which typically uses bituminous coal, industrial coke or charcoal as the fuel to heat metal.
The designs of these forges have varied over time and circumstances for thousands of years but whether the fuel is coal, coke or charcoal the basic design has remained the same. The illustration at the beginning of this article shows a coal forge in operation.
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 metalurgical effects (hardening, annealling, and drawing temper as examples).
The forge fire in this type of forge is controlled in three primary ways: 1) the amount of air, 2) the volume of fuel, and 3) the shape of the fuel/fire.
These factors have determined over time 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 air to be forced into the tuyere
- 'fire pot' or 'hearth' a place where the burning fuel can be contained over or against the tuyere opening.
In practice fuel is placed in or on the 'hearth' and lit. The 'bellows' are worked to introduce additional air (oxygen) into the fire through the 'tuyere'. With the additional oxygen the fire can consume more fuel and burn hotter.
In practice a blacksmith will balance the fuel and oxygen in the fire to suit particular kinds of work and 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. When 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, and surrounding all will be a ring or horseshoe shaped layer of raw coal usually kept damp and tightly packed to both 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 will increase the air into the fire and feed and deepen 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 coal is used in although since there is no need to convert the raw fuel into something more refined at the heart of the fire as with coal, the fire is handled differently.
Individual smiths and specialized applications and needs have led to the development of a variety of forges of this type, from the commercially available coal forge described above to simpler constructions amounting to little more than a hole in the ground with a pipe leading into it.
Gas forge
A forge which typically uses propane or natural gas as the fuel to heat metal. 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 through use of a mechanical blower or by taking advantage the Venturi effect.
Gas forges vary widely in size and construction, from very 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-powered forge lies in its ease of use, particularly for a novice smith. A gas forge is very simple to operate compared to coal forges, and the fire produced will be clean and consistent. They are however less versatile as the fire cannot be reshaped to accomodate large or unnusually sized 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 ennable forge-welding, but a well designed forge will easily run hot enough for any task.
Drop forge
The workpiece, say a spanner, is created by hammering a piece of hot metal into an appropriately shaped die. The metal (in some default, easily produced shape like a rod or brick) is heated and placed on the bottom part of a die. The top part of the die then drops onto the piece. The die may drop under gravity or be powered, but in all cases drop forging involves impact. The force of the impact causes the heated metal to flow into the shape of the die, with some metal squirting out of the thin seams between the die covers. This thin metal is called flash and has to be cut away in the next stage of processing. The drop-forged pieces usually also need further processing (like machining and polishing of working surfaces) in order to comply with stricter tolerances than forging alone can provide, and to present a good finish.
Drop forging: From BYU, with a nice crosssectional diagram.
Hydraulic Press Forge
In hydraulic press forging the work piece is pressed against the two die halves with a gradually increasing force, over a period of a few seconds. The quality of the pieces is better than drop forging as there is more control over metal flow, but the process takes longer and requires more energy.
See also
- solar forge
- Manufacturing techniques: Washington university site.
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Wikipedia-Article "Blacksmiths"
- For other uses, see Blacksmith (disambiguation).
A blacksmith is man or woman designing, making and hot shaping metal products, such as wrought iron gates, grills, railings, light fixtures, furniture, sculpture, tools, decorative and religious items, cooking utensils and weapons. Generally, blacksmiths do not work the non ferrous metals (tin, brass, bronze,copper etc.). These require a separate set of skills and require their own specialists. Blacksmiths do not usually make things that are purely decorative in fact most of the time they are highly functional too.
Ferrous metals will rust quickly if not protected with some coating. For interior metalwork it is ok to polish them and treat them to a coat of wax or laquer. Some blacksmiths have their own secret concoctions to give the required finish. Outdoors the steelwork needs to be primed, undercoated and painted. Or a more durable but less environmentally friendly finish is hot zinc spraying or hot dipping.
Blacksmiths work by heating pieces of metal (wrought iron or steel) with a forge until the metal becomes malleable enough to be shaped to a desired outcome via repeated manipulation with a hammer, punch or other tooling against an anvil. Heating is accomplished by the use of propane, natural gas, coal, charcoal, or coke. Modern blacksmiths may also employ oxyacetalene torches and electric induction furnaces as a heating medium. The other reason for heating the metal, other than for increasing its malleability, is for metallurgical purposes. The metal can be hardened, tempered, normalized, annealed, case hardened, and other more exotic processes that change things like the grain structure.
Specific to the craft of the blacksmith, when working with steels, the metal can be heated and then quenched. The purpose of this is to produce rapid cooling to generate specific microstructures in the metal. A quench generally results in steel that is hard and brittle, so a tempering process takes place to increase the toughness of the alloy and reduce the hardness. This involves heating the material to a specific temperature. With most tool steels, this tempering process can be gauged by the appearance of a coloured oxidation tint on the metal surface. Different uses require different hardness and toughness combinations, and so receive different temperings. It is possible to temper different parts of an object to different levels, which is one area where the skill of the blacksmith comes into play. For example, the face of a hammer is often left as a harder material than the main body, giving a blend of the hard wearing face with a resilient and tough tool. Japanese samurai sword makers were particularly adept at making their weapons very hard on the cutting edge while keeping the main body of the blade tough to support the cutting edge in powerful jarring blows.
Blacksmiths work with 'black' metals, especially iron (see wrought iron), while whitesmiths work with 'white' metals (such as tin and lead), although such artisans are more commonly called tinsmiths. The word 'whitesmith' also traditionally refers to a smith who, instead of leaving the finished product black, files and polishes his products to a reflective, or "white" luster. The term 'black' metals arises from the layer of oxides that form on the surface of the metal during heating (called fire scale). The black metals have a dark firescale, whilst the white metals show a light coloured firescale, if any. The art of working with the precious metals (gold and silver, primarily) is known as goldsmithing. The term "Smith" originates from the word "Smite", which means to hit. Thus, a blacksmith is a person who smites the black metals. (The suffix "-smith" has since come to refer to other crafts. For instance, a woodworker is sometimes called a "woodsmith", though hitting wood is only a marginal part of his craft.) In recent years the forging of stainless steel has given rise to a fresh approach to architectural blacksmithing. The work of Giusseppe Lund illustrates this well.
Mass production techniques have reduced the marketplace for blacksmith work except in Africa, India, Southeast Asia, and South America where large numbers of artisans remain doing traditional work. The great demand for custom metalwork has given rise to a new breed of smiths commonly known as Artist-Blacksmiths. A famous pioneer of this type of artisan is Philip Simmons of Charleston, South Carolina.
One very famous blacksmith was Hephaestus (Latin: Vulcan). He was the blacksmith of the gods in Greek and Roman mythology and constructed all of their weapons and, especially, the lightning bolts that Zeus (Latin: Jupiter) threw at the Earth.