Sheffield Steel
Like Rome, Sheffield is built on 7 hills. The similarities do not extend much beyond that fact, but the topography of the city gave it an advantage and led to its industrial development over hundreds of years. The rivers flowing through the city provided power for waterwheels that drove machinery in hundreds of workshops. The area is a source of iron ore and coal which led to the steel industry and which put the city on the map as a major industrial centre. Sandstone quarries provided grinding wheels used for polishing steel, particularly in the cutlery trade which has existed for 800 years.
Sheffield has an international reputation for metallurgy and steel-making. Many innovations in these fields have been made in Sheffield. Benjamin Huntsman discovered the crucible technique in the 1740s at his workshop in Handsworth. This process was made obsolete in 1856 by Henry Bessemer's invention of the Bessemer converter. Thomas Boulsover invented Sheffield Plate (silver-plated copper) in the early 18th century. Stainless steel was invented by Harry Brearley in 1912, and the work of F. B. Pickering and T. Gladman throughout the 1960s, '70s, and '80s was fundamental to the development of modern high-strength low-alloy steels.
Benjamin Huntsman and crucible steel
Benjamin Huntsman, a noted clockmaker in his own right, was the inventor of the crucible steel process. What motivated Huntsman to develop an improved type of steel is not known for definite, though the most popular theory states that he was dissatisfied with the quality of steel then available for watch-springs - then usually made of German steel.
After almost a decade of experimentation, Huntsman had achieved a scale and quality of production that was commercially viable. In 1751 he established his first purpose-built works at Attercliffe, a village on the outskirts of Sheffield, at a time when his process had become one of the most sought after industrial secrets of the eighteenth century. Numerous attempts were made to discover it both at home and from abroad, and by the 1760s his first serious commercial competitors were operating furnaces in Sheffield.
The theft of Huntsman's secret is represented by two distinct traditions. Of these, the best known is the story of the shivering beggar who arrived at Huntsman's furnaces on a freezing winter night in search of shelter and warmth.
Steel melting was at that time covertly carried out during the hours of darkness, and the sympathetic furnace-men on duty allowed the stranger to rest in the warmth of the melting shop. However, the beggar was in reality one of Huntsman's competitors, Samuel Walker, and by feigning sleep he observed the whole process, learning enough that on his departure the following morning he took the secret with him. He immediately set to work building his own furnaces and was soon producing steel to rival Huntsman's.
This oral tradition is supported to a certain extent by documentary evidence. In 1750, Samuel Walker built a "House and Furnace for refining steel in at Grenoside", taken to be the result of his subterfuge. However, it was not until 1771 that any further furnaces were built by Walker which suggests that the original furnace had met with limited success.
On the other hand, the date of 1750 or earlier would locate the espionage at Handsworth, where the furnaces directly adjoined Huntsman's cottage, making it less likely that such a simple ruse could have succeeded, particularly as the furnace hands had all been "pledged to inviolable secrecy".
The second lesser-known but more sinister account portrays Huntsman as the recipient of the secret and first appeared in a short book Essays on Iron and Steel (1773) by Henry Horne, a London cutler. Surprisingly he made no mention of Huntsman's name in connection with crucible steel, but instead ascribed the invention to a mysterious "gentleman residing in the Temple" who subsequently passed on the secret to a gold lace maker, "one Waller from London", who employed it to make improved steel rollers for flattening gold wire.
Dissatisfied with success in his own trade, Waller contracted a cutler of Covent Garden to manufacture cast steel razors. Due to the high mirror polish of the steel, these proved popular and Waller soon acquired "a pretty large number of customers at the west end of the town, where he became a considerable hawker". His unexpected success alarmed the other razor manufacturers, and a number of them conspired to build their own steel furnace and break Waller's monopoly.
The book's author, Henry Horne, took up the challenge and, despite considerable difficulties, claimed to be soon producing steel "vastly superior" to Waller's, with which he supplied the London cutlers "at a very moderate price".
Faced with this competition, Waller left for the North of England with the intention of selling the secret at the highest price. Finding no takers at Birmingham, he continued to Sheffield where after several rejections, he met "some keen friends" who extracted the secret from him for a sum of money, and were soon producing superior steel to Waller. It was not long before Horne found his customers turning to Sheffield, where they could purchase steel from eight to ten pence a pound, undercutting his own trade.
With a clear interest in the affair, Horne's version of events cannot be regarded as impartial, and as such has been often discredited. Horne certainly manufactured cast steel, although there is nothing in his account to suggest a date earlier than 1765, by which time others in Sheffield were also practising the art.
John Waller himself published a pamphlet in which he claimed to have discovered the steel casting process towards the end of 1737, some years prior to Huntsman. Although his account betrays a practical appreciation of the problems that he would have encountered in attempting the process -- including the identification of crucible manufacture as a key secret -- most of his claims are unsupportable. Waller claimed to have presented his findings before the Royal Society, although no records survive to confirm this. However, it does correspond to another oral tradition in the Huntsman story, in which Huntsman is said to have turned down the offer of a Fellowship by the Royal Society due to his Quaker principles.
The truth probably incorporates elements from all of the above stories. It is likely that the Royal Society, having heard of Huntsman's invention, invited him sometime around 1750 to present his findings with the possibility of a fellowship. At this stage, some details of the process may have been transmitted in confidence to a small group of Fellows, including the "gentleman residing in the Temple" who later passed them on to Waller for his own use. Subsequently Waller, realising the value of the process, attempted to market it elsewhere and published his own version of its discovery in order to conceal the subterfuge. Finally, the "keen friends" who Horne claimed extracted the secret from Waller may well have been Huntsman's rivals, the Walker family.
What is certain is that the controversy over cast steel was real, and that much was at stake. Waller's appeal obviously fell on deaf ears, as Huntsman continued to increase his trade and reputation, while the name of John Waller and the London cutlers faded away.
Henry Bessemer
The Bessemer process was the first inexpensive industrial process for the mass-production of steel from molten pig iron. The process is named after its inventor, Henry Bessemer, who took out a patent on the process in 1855. The process was independently discovered in 1851 by William Kelly.The process is a development of a practice known in China as early as the 200s. The key principle is removal of impurities from the iron by oxidation through air being blown through the molten iron. The oxidation also raises the temperature of the iron mass and keeps it molten.
The process is carried on in a large ovoid steel container lined with clay or dolomite called the Bessemer converter. The capacity of a converter was from 8 to 30 tons of molten iron with a usual charge being around 15 tons. At the top of the converter is an opening, usually tilted to the side relative to the body of the vessel, through which the iron is introduced and the finished product removed. The bottom is perforated with a number of channels called tuyères through which air is forced into the converter. The converter is pivoted on trunnions so that it can be rotated to receive the charge, turned upright during conversion, and then rotated again for pouring out the molten steel at the end. The oxidation process removes impurities such as silicon, manganese, and carbon as oxides. These oxides either escape as gas or form a solid slag.
The refractory lining of the converter also plays a role in the conversion - the clay lining is used in the acid Bessemer, in which there is low phosphorus in the raw material. Dolomite is used when the phosphorus content is high in the basic Bessemer (limestone or magnesite linings are also sometimes used instead of dolomite) - this is also known as a Gilchrist-Thomas converter.
In order to give the steel the desired properties, other substances could be added to the molten steel when conversion was complete, such as spiegeleisen (an iron-carbon-manganese alloy). When the required steel had been formed, it was poured out into ladles and then transferred into molds and the lighter slag is left behind. The conversion process (called the "blow") was completed in around twenty minutes. During this period the progress of the oxidation of the impurities was judged by the appearance of the flame issuing from the mouth of the converter: the modern use of photoelectric methods of recording the characteristics of the flame has greatly aided the blower in controlling the final quality of the product. After the blow, the liquid metal was recarburized to the desired point and other alloying materials are added, depending on the desired product.
The Bessemer process revolutionized the world. Prior to its widespread use steel was far too expensive to use in most applications, and wrought iron was used throughout the Industrial Revolution. After its introduction steel and wrought iron were similarly priced, and all manufacture turned to steel.
Created on 11/01/2006 07:50 PM by admin
Updated on 11/05/2006 02:27 PM by admin
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