Bessemer Process - Process by which high quality Steel is produced from molten Pig Iron. Now superseded by other methods, the process was patented by Henry Bessemer is 1856. The molten iron is poured into the 'Bessemer Converter' which is then tilted while air is blown at high pressure through the bottom of the converter.
The process was completely superceded by 1974.
The modern equivalent is the 'BOS' process where pure oxygen is bubbled though the iron in a vessel with a solid bottom. A Bessemer converter is preserved at Kelham Island Museum, Sheffield.
The Bessemer Process Explained
Blister Steel - First type of steel that was commercially produced. Process took place in a Cementation Furnace and produced a bar that had a high carbon content on the surface and a low Carbon content in the centre. Process resulted in a blistered appearance to the bars, thus the name. Not much use in this form until processed into Crucible Steel or Shear Steel.
Blast Furnace - Furnace built like a tower for reducing ore into metal. Can be used as part of non ferrus metal reduction, but is normally associated with iron production. Ore (Iron Ore for Iron production), Coke (originally Charcoal) and a flux (typically limestone) and tipped into the top.
Molten Pig Iron and Slag are removed periodically from the base of the furnace.
After 350 years, Blast Furnaces remain the only way to economically produce large quantities of Iron.
Description of the Blast Furnace Process
Bloomery - Very early type of Furnace for reducing Iron Ore directly into Wrought Iron. Product was of poor quality as it was never molten. Slag was generally removed by hammering, but some was inevitably left behind and trapped within the product. Superseded by Finery and Chafery Process
Description of the Bloomery Process
Carbon Steel or Mild Steel - Most common and generally useful form of Steel. Contains 0.3% of Carbon.
Cast Iron - Iron with a high Carbon content (above 2%). Identical, in most cases, to Pig Iron, it is easily cast to almost any shape and melts at a lower temperature to other type of iron and steel. Traditionally melted in a Cupular Furnace (a tall cylindrical structure but much smaller than a Blast Furnace).
Cast Iron is extremely hard and brittle. Machining is difficult and it is easily shattered, revealing its crystalline structure. Chilled Cast Iron is even harder and is produced by cooling the castings to increase the speed at which the iron solidifies. Cast Iron is still is wide use for numerous casting, from drains covers through to engine blocks and water pipes. Can be Grey, White or Malleable.
Cementation Furnace - A furnace (more of a kiln) in which wrought iron bars and Charcoal were heated for up to two weeks, until the carbon had been absorbed into the surface of the iron. The resulting Blister steel could be further processed into Shear Steel or Crucible Steel
Crucible Steel - High Quality steel created by melting Blister Steel in a covered crucible using a coal fire. After the slag was removed, the resulting steel had consistent properties throughout. Process was superseded by Bessemer Process but crucible melting did not stop until after World War II.
Drop Hammer - A forging hammer that drops vertically onto the work piece. Usually relying on a powered cylinder to lift the hammer head and then adding to the force of the downward stroke. Originally steam powered (developed by James N??) but most now using compressed air. Steam hammers converted to air are generally not as good following conversion as the air does not expand in the same way as steam leading them bouncing off the work piece where a hit the work piece and continue to be forced down by the expanding steam.
Electric Arc Furnace - Since the second World War, this has been the standard furnace for melting steel in large quantities. Typical Capacities are 80 to 120 Tonnes. They were generally used as direct replacements for Siemens Open Hearth Furnaces.
Low Voltage, High Current electricity arcs between three large electrodes hung from the lid of the furnace and the metal on the furnace hearth. This produces very intense heating in the centre of the furnace, in a similar way to arc welding.
The heating can be very accurately controlled and as there are no 'products of combustion' (smoke and flame) within the furnace high quality steels are easily produced.
Finery and Chafery - Two stage process that was developed from the Bloomery Process
Description of the Finery and Chafery Process
Forge Welding or Fire Welding - The first process by which separate pieces of iron were joined together into a single piece. The process is still used by blacksmiths to join Wrought Iron and Mild Steel. Unlike Gas or Electric Welding the work pieces are heated in a fire or furnace until they are the correct temperature (1300°C for Wrought Iron). The joint is then hammered together until the pieces have been merged. Several heating may be needed to complete the process.
Helve Hammer - Name given to the heavier types of water powered forging hammer. The Helve is the Main Beam of the Hammer pivoted at the tail end, with the hammer head or Tup at the nose. Helve Hammers can be 'Belly Helve' where the hammer is lifted at the mid point of the helve beam, while a 'Nose Helve' is lifted from in front of the Tup. Both Wortley Top Forge hammer and the surviving Low Forge hammers are 'Belly Helve' type. Lighter Hammers tended to be 'Tail Helve' being lifted by a cam pushing down behind the pivot. Examples of this type are at Abbeydale Industrial Hamlet.
Iron - Metallic Element - Symbol = Fe; Atomic Number = 26; Atomic Weight = 55.847; Specific Gravity (Solid) = 7.85; Melting Point = 1533°C; Boiling Point = 2840°C
Iron Ore - Form in which iron occurs naturally. Ores are primarily iron and oxygen but may include phosphorous, and ??. Before the development of the Basic Bessemer Process, only high quality ores (typically Swedish) could be used for the production of iron, as high phosphorous caused numerous problems. Typical British Ores contained ??% iron but production of these generally stopped when imported ore containing up to ??% iron became available. Ore used in the U.K. is generally imported from ??
Pig Iron - the name used for the iron directly produced from a blast furnace. Originally cast into 'pigs' around the base of the furnace, lasted casting machines were developed to produce pigs but iron is now generally transported while still molten and converted into steel on the same site. The name is derived from the impression given of piglets feeding from the sow by the iron being run off the furnace into the original style of sand moulds. Pigs were traditionally sized to be manhandleble. Pig Iron changes its name to Cast Iron when remelted, although no actual processing takes place. Iron casings can be created directly from the blast furnace.
Press - machine tool for forming forgings but relies on a slow powered push rather than the series of heavy blows from a Drop Hammer. Hydraulic presses can easily have a capacity to produce several thousand tons of force.
Puddling - Last and most widespread of the ways to produce Wrought Iron from Pig Iron. First devised by Henry Cort in 1784, but later revised by Joseph Hall in 1816.
Solid iron, be it fresh Pig Iron or scrap Cast Iron, was first melted and then refined. Once the iron was molten in the bottom of the hearth, it was stirred with a long pole. This brought the carbon in contact with the air where it burn off. However as the carbon content reduced, the melting point increased and the iron became a lump of sticky Wrought Iron. The Process was sometime known as 'Pig Boiling' as the iron tended to bubble as the carbon was removed. Last Commercial Puddling took place in the U.K. in the mid 1970s.
Hammering (under a ShinShinglingdling Hammer) and rolling followed puddling in order firstly drive out the slag, weld the iron into a homogeneous lump and lastly produce a saleable product.
Puddling had to take place in a Reverberatory Furnace in order to avoid contamination of the Iron.
Description of the Puddling Process
Reverberatory Furnace - Type of Coal fired furnace in which the flame and gases passes across the top of the enclosed hearth, heat being reflected down onto the hearth proper. The principle advantage of this type of furnace was that poor quality fuel could be used without the risk of contamination of the work piece. Puddling was one of the major process that required a Reverberatory Furnace.
Shear Steel - Before the development of Crucible Steel, Blister Steel was forged by repeated folding and forge welding to mix the areas of high and low carbon steel. Shear Steel was the lowest quality generally created and further folding and welding created Double Shear Steel. Long regarded as ideal for blades and cutting edges, primarily because the slag trapped within the steel lead to a serrated edge without it being purposely formed.
Siemens Open Hearth Furnace - Following the sucessful introduction of the Bessemer Process for producing Steel, the Siemens Process was devised. It can be regarded as an updated and enlarged version of the Puddling Process but producing Steel rather than Wrought Iron. Gas or Heavy Oil were used as fuel and these and the combustion air were preheated using the exhaust flue gases. The flame is directly above the hearth and is fired from alternative directions in order to make best use of the preheaters. A Siemens furnace can be charged with molten Pig Iron, Solid pigs or Scrap Steel. Alloying and refining can take place before the Steel is teemed and cast.
The majority of the structure of a Siemens 'Open Hearth Furnace' is fire brick. This required total replacement on a regular basis. Although long since replace in the U.K. by BOS and Electric Arc Furnaces, other countries, such as the USA seem to have perpetuated their use.
Description of the Siemens Process
Slag - By-product of heating / melting iron and steel. Consists of oxides and other impurities that are not generally wanted. The process of forming a slag is essential to remove impurities at almost every stage of iron and steel production. A flux such as lime, limestone or fluorspar is added to the furnace and this attracts many of the impurities from the metal. Types of slag are currently used in road surfacing.
Steel - Compound of Iron containing between 0.15 & 1.35% of carbon. Modern alloys include Chromium, Lead, Manganese, Molybenum, Nickel Vanadium & Tungsten to give varying properties. Can generally be hardened and welded with ease. Produced from Pig Iron by the Bessemer or Siemens Process since 1856, now replaced by BOS Process. Before that time, Shear Steel and Crucible Steel were produced in very small quantities
Wrought Iron - Iron that is almost pure (less than 0.15% carbon). Can be shaped and forge welded with ease, but is soft and does not harden in the same way as Steel. Wrought Iron is rarely seen in molten from as it has a high melting point and there is no advantage in melting it as part of a process. Part of the properties of Wrought Iron are attributed to the Slag inclusions that result from Puddling and Forge Welding. Widely used in Bridges, Axles and Ships plates before the development of Bessemer and Siemens Steel. The last commercial production of Wrought Iron in the U.K. ceased in 1976
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