Forge welding
Encyclopedia
Forge welding is a solid-state welding process that joins two pieces of metal
by heating them to a high temperature and then hammer
ing them together. The process is one of the simplest methods of joining metals and has been used since ancient times. Forge welding is versatile, being able to join a host of similar and dissimilar metals. With the invention of electrical and gas welding methods during the Industrial Revolution
, forge welding has been largely replaced.
Forge welding between similar materials is caused by solid-state diffusion. This results in a weld that consists of only the welded materials without any fillers or bridging materials.
Forge welding between dissimilar materials is caused by the formation of a lower melting temperature eutectic between the materials. Due to this the weld is often stronger than the individual metals.
The temperature required to forge weld is typically 50 to 90 percent of the melting temperature. Steel
welds at a lower temperature than iron
. The metal may take on a glossy or wet appearance at the welding temperature. Care must be taken to avoid overheating the metal to the point that it gives off sparks
from rapid oxidation (burning).
blades. During the process a billet of steel is repeatedly drawn out, folded back and welded upon itself. Another lesser known application was the manufacture of shotgun barrels. Metal wire was spooled onto a mandrel
, and then forged into a barrel that was thin, uniform, and strong. Often such objects are acid etched to expose the underlying pattern of metal which is unique to each item and adds to their aesthetic appeal.
is used to keep the welding surfaces from oxidizing, which would produce a poor quality weld. The flux mixes with the oxides that do form and lowers the melting temperature and the viscosity
of the oxides. This enables the oxides to flow out of the joint when the two pieces are beaten together. A simple flux can be made from borax
, sometimes with the addition of iron filings.
Early examples of flux used different combinations and various amounts of iron
fillings, borax, sal ammoniac
, balsam of copaiba
, cyanide
of potash
, and soda phosphate
. The 1920 edition of Scientific American
book of facts and formulae indicates a frequently offered trade secret as using copperas, saltpeter
, common salt
, black oxide
of manganese
, prussiate of potash, and "nice welding sand" (silicate).
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
by heating them to a high temperature and then hammer
Hammer
A hammer is a tool meant to deliver an impact to an object. The most common uses are for driving nails, fitting parts, forging metal and breaking up objects. Hammers are often designed for a specific purpose, and vary widely in their shape and structure. The usual features are a handle and a head,...
ing them together. The process is one of the simplest methods of joining metals and has been used since ancient times. Forge welding is versatile, being able to join a host of similar and dissimilar metals. With the invention of electrical and gas welding methods during the Industrial Revolution
Industrial Revolution
The Industrial Revolution was a period from the 18th to the 19th century where major changes in agriculture, manufacturing, mining, transportation, and technology had a profound effect on the social, economic and cultural conditions of the times...
, forge welding has been largely replaced.
Forge welding between similar materials is caused by solid-state diffusion. This results in a weld that consists of only the welded materials without any fillers or bridging materials.
Forge welding between dissimilar materials is caused by the formation of a lower melting temperature eutectic between the materials. Due to this the weld is often stronger than the individual metals.
The temperature required to forge weld is typically 50 to 90 percent of the melting temperature. Steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
welds at a lower temperature than iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
. The metal may take on a glossy or wet appearance at the welding temperature. Care must be taken to avoid overheating the metal to the point that it gives off sparks
Ember
Embers are the glowing, hot coals made of greatly heated wood, coal, or other carbon-based material that remain after, or sometimes precede a fire. Embers can glow very hot, sometimes as hot as the fire which created them...
from rapid oxidation (burning).
Applications
One of the most famous applications of forge welding is in the production of pattern-weldedPattern welding
Pattern welding is the practice in sword and knife making of forming a blade of several metal pieces of differing composition that are forge-welded together and twisted and manipulated to form a pattern. Often called Damascus steel, blades forged in this manner often display bands of slightly...
blades. During the process a billet of steel is repeatedly drawn out, folded back and welded upon itself. Another lesser known application was the manufacture of shotgun barrels. Metal wire was spooled onto a mandrel
Mandrel
A mandrel is one of the following:* an object used to shape machined work.* a tool component that grips or clamps materials to be machined.* a tool component that can be used to grip other moving tool components.- Variants :...
, and then forged into a barrel that was thin, uniform, and strong. Often such objects are acid etched to expose the underlying pattern of metal which is unique to each item and adds to their aesthetic appeal.
Flux
Often a fluxFlux (metallurgy)
In metallurgy, a flux , is a chemical cleaning agent, flowing agent, or purifying agent. Fluxes may have more than one function at a time...
is used to keep the welding surfaces from oxidizing, which would produce a poor quality weld. The flux mixes with the oxides that do form and lowers the melting temperature and the viscosity
Viscosity
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...
of the oxides. This enables the oxides to flow out of the joint when the two pieces are beaten together. A simple flux can be made from borax
Borax
Borax, also known as sodium borate, sodium tetraborate, or disodium tetraborate, is an important boron compound, a mineral, and a salt of boric acid. It is usually a white powder consisting of soft colorless crystals that dissolve easily in water.Borax has a wide variety of uses...
, sometimes with the addition of iron filings.
Early examples of flux used different combinations and various amounts of iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
fillings, borax, sal ammoniac
Sal ammoniac
Sal ammoniac is a rare mineral composed of ammonium chloride, NH4Cl. It forms colorless to white to yellow-brown crystals in the isometric-hexoctahedral class. It has very poor cleavage and a brittle to conchoidal fracture. It is quite soft, with a Mohs hardness of 1.5 to 2, and has a low specific...
, balsam of copaiba
Copaiba
Copaiba is a stimulant oleoresin obtained from the trunk of several pinnate-leaved South American leguminous trees . The thick, transparent exudate varies in color from light gold to dark brown, depending on the ratio of resin to essential oil...
, cyanide
Cyanide
A cyanide is a chemical compound that contains the cyano group, -C≡N, which consists of a carbon atom triple-bonded to a nitrogen atom. Cyanides most commonly refer to salts of the anion CN−. Most cyanides are highly toxic....
of potash
Potash
Potash is the common name for various mined and manufactured salts that contain potassium in water-soluble form. In some rare cases, potash can be formed with traces of organic materials such as plant remains, and this was the major historical source for it before the industrial era...
, and soda phosphate
Phosphate
A phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Organic phosphates are important in biochemistry and biogeochemistry or ecology. Inorganic phosphates are mined to obtain phosphorus for use in...
. The 1920 edition of Scientific American
Scientific American
Scientific American is a popular science magazine. It is notable for its long history of presenting science monthly to an educated but not necessarily scientific public, through its careful attention to the clarity of its text as well as the quality of its specially commissioned color graphics...
book of facts and formulae indicates a frequently offered trade secret as using copperas, saltpeter
Potassium nitrate
Potassium nitrate is a chemical compound with the formula KNO3. It is an ionic salt of potassium ions K+ and nitrate ions NO3−.It occurs as a mineral niter and is a natural solid source of nitrogen. Its common names include saltpetre , from medieval Latin sal petræ: "stone salt" or possibly "Salt...
, common salt
Salt
In chemistry, salts are ionic compounds that result from the neutralization reaction of an acid and a base. They are composed of cations and anions so that the product is electrically neutral...
, black oxide
Oxide
An oxide is a chemical compound that contains at least one oxygen atom in its chemical formula. Metal oxides typically contain an anion of oxygen in the oxidation state of −2....
of manganese
Manganese
Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...
, prussiate of potash, and "nice welding sand" (silicate).