What was the output of a Bessemer Converter?

What was the output of a Bessemer Converter?

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Henry Bessemer's Bessemer converter is generally understood to be the technology that created the concept of industrial-scale steelmaking, but what constitutes "industrial-scale"? The Wikipedia page says that a Bessemer converter could process batches of 5 to 30 tons at a time, and that one stage of the process lasts 20 minutes, but that's as far as the information goes.

If I was a steelsmith in the 1860s with a single Bessemer converter (original model) and access to an unlimited amount of raw materials, how much steel could I make each day at a sustainable pace?

According to "Iron And Steel In 19th Century America: An Economic Inquiry" by Peter Temin, in 1867 a pamphlet claimed…

The cost of a plant with 2 three‑ton converters was given as $80,000; of a "five‑ton plant" with steam power, $125,000; and of first‑class apparatus with fireproof buildings and duplicate machinery making 50 tons of ingots in twenty‑four hours, $200,000. It cost only two‑thirds as much for a Bessemer plant as for a crucible steel, charcoal bloom, or puddled bar plant of the same capacity, the trustees asserted, and it took only 30 men to run a five‑ton Bessemer plant.

"The Albany and Rensselaer Iron and Steel Works, Troy, New York" by A. L. Holley is an excellent source. Holley licensed the technology from Bessemer and set up the Troy mill. His book, published in 1881, has extensive detail about the plant. It used three 7-ton vessels.

As the departments grew gradually and experimentally, and were not expected to exceed 60 tons of product per day, the buildings are not the size and arrangement that would now be made; but by means of convenient transporting apparatus, 400 tons of hot ingots per 24 hours are delivered by power into the blooming furnaces, and are rolled, cut up, and chipped, under a 7-ton hammer, and loaded hot on the rail mill cars with reasonable facility.


Two copulas running together can melt 500 tons per 24 hours.

I'm no steel maker, but from reading Holley's accounts it seems the limiting factor was not the size of the converter but many, many others. He spends very little time on the converters and much more on blowing engines, pressure pumps, boilers, blooming trains (whatever that is), power feeding tables…

Troy had three 7-ton vessels in a mill able to deliver (not just melt) 400 tons per day. A single vessel would likely be less efficient. For example, with three one could be melting, one pouring, and one being cleaned.

The use of the converter did not really ramp up until about 1867. In 1868, the best performing mill had two 5-ton converters that produced 500 tons per month combined. By 1876 various improvements and mastery of the process resulted in typical production for a single 5-ton converter at a good mill averaging around 3800 tons per month. The best mills are reputed to have done as much as 4200 tons per month in a single 5-ton converter.

Thus, by the mid-1870s good mills were doing 750 to 800 heats a month, or perhaps about 32 heats every work day. Note that the nominal 5-ton capacity of a converter could be exceeded by a good crew, so they might be doing heats of 5.5 tons or more.

At that time 5-ton converters were the norm. Giant 30-ton converters did not come until later. In 1877 there were two converters as large as 10 tons in Britain, and there were numerous 2 and 3 ton converters.

The history of Swedish iron and steel industry

The Swedish iron and steel industry has a long history beginning in the Middle Ages.

The Period of Osmund

It was merchants from Lübeck who, in the Middle Ages, began to interest the kings of Sweden in the export of iron on a large scale. It was also at that time that German mine owners and merchants acquired the rights to run their own operations in Sweden's mining areas and trading communities.

Mining and foreign trade thereby paved the way for the integration of Sweden into the mainstream of European civilisation. The consequence was a new economic structure and the emergence of a broader society in the formerly agrarian Sweden.

The Swedish iron exports during the Middle Ages comprised so-called osmunds &ndash a standardised format of high-grade forged iron with a weight of just 3 hectograms.The osmund was an accepted object of barter both in Sweden and abroad and was also used as a form of payment with its value being determined by the Crown.

In the 14th century, a large amount of Sweden's iron production was exported, mainly to Lübeck and Danzig. The entire annual production at this time has been estimated at 2,000 tonnes, less than a third of the production from the German forges.

Since the cogs (trading vessels) from Lübeck were not able to enter Lake Mälar, Stockholm was established as a transhipment centre, customs station and port of shipment for iron and copper exports from Närke, Västmanland and Dalarna.

In the 1420's the Scandinavian king, Erik of Pommern, granted preference to Swedish seamen and merchants over their counterparts from Germany and barred Öresund to the cogs fiom Lübeck. This was devastating for Swedish iron exports and led to peasant miners fiom Dalarna and Västmanland - together with merchants in Stockholm, all under the leadership of the peasant miner Engelbrekt - breaking out of the union with Denmark and Norway.

Lübeck, which helped Gustav Vasa gain power - this in exchange for the sole rights to trade in Sweden - saw itself defeated by the united forces of the Swedish and Danish kings. The trading monopolies enjoyed by other Hanse cities would also later be abolished following the expansion of Dutch and English shipping in the North Sea and the Baltic.

The price of Swedish osmund iron started to decline around the mid-14th century and continued to fall during the 15th century. The reasons were to be found on both the producers' and consumers' side. In Europe, the more blast furnace technology was used the more iron production increased, thereby putting pressure on Swedish products. Even though the price fell, Swedish exports of osmund iron to Danzig increased during the 16th century. Here, Swedish iron was used as a basis for the manufacture of a more workable forging iron, which was turned into long bars - known at the time as bar iron - by water-powered iron hammers. This was then sold on under the designation, 'bar iron from Danzig', mainly to Holland and England.

Bar iron takes over

During the 16th century, the kings of Sweden realised that Sweden, too, had to modernise its iron production and start producing bar iron. In order to handle the difficult technical changeover, the involvement of expertise and finance from foreign countries was required.

The decisive modernisation of the Swedish iron industry in fact took place at the beginning of the 17th century. Then Spain recognised Holland's its dependence in 1609, the Dutch started to plan for their future defence partly through importing iron cannons from Sweden. A large number of forgers who had emigrated to Holland from Spanish controlled Wallonia were now recruited to work in Sweden at the Royal ironworks and armouries, modernised by engineers such as Willem de Besche and financed by businessmen such as Louis De Geer.

The doctrine that dominated trade policy in Sweden in the 17th century was mercantilism which stated that a country's economy should be strengthened through high protective tariffs. In addition, exports should be favoured and imports restrained in order to establish a trade surplus. The fact that in international trade finished products commanded a better price than raw materials led to a prohibition, introduced in 1604, on exports from Sweden of osmund iron. In the future, only Sweden's processed bar iron could be exported.

In the 1640's, Sweden's exports of bar iron amounted to around 11,000 tonnes a year. Fifty years later, the average was about 27,000 tonnes a year and in the 1740's an average of 40,000 tonnes a year was achieved.

The large increase depended almost wholly on the emergence of new markets, firstly in Holland and then in England. Nevertheless, most of the armaments produced remained in Sweden and the production of nails, plate, tools and utensils was mainly for the home market.

During the 18th century, Sweden's iron production virtually doubled due to the increased demand for bar iron from abroad, particularly England, which had a large need for high-quality, so called Oregrund iron, as an input for its steel industry. Bar iron gradually came to comprise no less than three-quarters of the total Swedish exports, creating for the Crown much needed revenues in the form of taxes and export duties.

In England, the charcoal forests had been stripped to such an extent that the country had become strongly dependent on iron imports from Sweden. England's imports in the 1730's totalled about 25,000 tonnes of which Sweden's contribution was nearly 20,000 tonnes. From Russia came about 5,000 tonnes but Russian iron, some twenty years later, would rise to 15,000 tonnes hich would then equal Sweden's share.

At the end of the 18th century technology in England had been developed enabling the use of fossil coal in metallurgical processes.

In addition, it was increased competition from Russian bar iron that caused the crisis for Sweden's iron industry which in turn was a crucial factor in the establishment of Jernkontoret in 1747. The increasing utilisation of coal and coke would subsequently lead to a radical change in the competitive status of Swedish iron, and during the 19th century Europe's iron production gradually switched to countries with ample resources of fossil coal.

Forging regulations

The strong growth of bar iron exports had aroused concern that the competition of the bar mills for charcoal and pig iron would lead to increased production costs. It was for this reason that a limitation on forge production was introduced whereby it would also be possible to influence the prices on the international markets. The owners of the bar mills were successful in implementing a forging regulation in the Riksdag of 1746-47 which effectively obstructed an increase in bar iron exports over the long term. It was not until the 1830's that the regulation was wholly abolished.

However, a significant upturn in the value of the composition of exports took place during the latter part of the 18th century. Exports of iron, which had undergone further processing following forging under the heavy bar iron hammers, increased sharply. With the help of the lighter and faster iron hammers it was possible to produce thinner bars, or strips, which were then bound together and exported in bundles. Forged plate and steel was also exported to a greater extent than before.

Sweden's bar iron exports during the 18th century - as previously mentioned - were very much focused on the British market. This was complemented by a stable and significant export to the Baltic Sea countries and, in the latter part of the century, by increased exports to France, Portugal and the Mediterranean lands. At the same time the former large-scale sales to Holland diminished. Trade policy considerations were to be of major importance for Sweden's foreign policy during the coming revolutionary and Napoleonic periods.

The Napoleonic wars ushered in a serious crisis for the Swedish iron industry. The reasons were &ndash inter alia &ndash that the custom tariffs on Swedish bar iron to Great Britain were raised sharply. From just over 52,000 tonnes of bar iron per year during the 1790's, the total Swedish export fell to less than 30,000 tonnes for the lowest year, 1808. The losses in the British market could, however, largely be compensated by the newly emerging US market. Thus, in the early 19th century, the USA became an important market and was, right up to the First World War, the largest importer of Swedish bar iron.


At this time many people in the Swedish iron industry realised that the solution to the crisis lay in improving the quality of Swedish charcoal forging. The Walloon forge retained its position on the market in Sheffield. Others recommended going over to the use of coalfired puddling furnaces &ndash invented in England &ndash for the production of forgeable iron and complementing this with rolling mills. This was to be delayed, however, until 1845 when the mill owner, Gustaf Ekman, solved the problems of adapting a Lancashire forge to Swedish conditions using charcoal instead of coal as an energy source. In the Ekman furnace the frayed surfaces on the puddle bars could be effectively welded together. Ekman's furnace thereby became the mainspring in the development of the rolling mill of that period. An added advantage was that fuel consumption was sharply reduced.

The improved quality now made it possible to recover a large part of the lost market in Sheffield. When furnaces adapted to Swedish conditions had been developed and rolling mills set up, iron of high quality could be produced in large quantities. Also, with rolling mills the expensive hammer working in the forge could be replaced. The expansion of the Lancashire forge resulted in a sharp increase in the demand for pig iron and overall production increased to about 180,000 tonnes per year by the start of the 1860's.

The technical advances resulted in more concentrated operations, and smaller mills were now being closed down to the advantage of larger and more dynamic units. This process, known as 'the great mill shutdown', meant that the number of smelting furnaces in Sweden declined from 220 in 1840 to less than 160 by 1880 (despite the fact that many new furnaces were opened during this period).

The Bessemer process

The need for steel increased strongly in the mid-1800's. For industries and means of transport steel of high quality was required in large quantities. Both in Europe and the USA assiduous efforts were made to replace the old craft methods of steel production with processes that better responded to the growing demand. One such was the Bessemer method, introduced by Henry Bessemer in 1855, a system whereby air blown into smelted pig iron made it possible to produce steel directly in the furnace.

The desired carbon content was obtained by breaking off the process at appropriate intervals. At the time it was an epochal discovery. Before, in the finery processes the product became a softer, carbon-lacking iron which had to be carburised through special processes and at a high cost in order to become hardenable steel. Using the Bessemer process this was now no longer necessary. Bessemer himself did not succeed in producing any ingots of satisfactory quality.

When, in 1858 at Edsken, the Swede, Göran Fredrik Göransson became the first person in the world to successfully apply the Bessemer process on a practical scale and produce ingot steel of good quality, this was an industrial exploit of historic importance with international ramifications. It marked the start of the modern steel age by enabling the economic production of high-quality steel products such as rails, railway wheels, ship plate and so on. Now, for example, the great railway construction in Europe and the USA could begin.

The successful introduction of the Bessemer method in Sweden led to its implementation in many Swedish steelworks at the start of the 1880's. It would be some time, however, before the production levels exceeded 50,000 tonnes and not until 1895 that production of 100,000 tonnes would be exceeded for the first time. However, in Sweden the Bessemer process never became the major production method for ordinary steel as it did in other countries. This was mainly because of the expensive charcoal pig iron required to charge the Bessemer converter.

Instead, it was the other great ingot steel method, the Siemens-Martin method, which was to lead the Swedish steel industry into its great era of expansion. A characteristic of the method was that the steel smelting took place in a furnace designed by the Siemens brothers in 1861. Pierre Martin was the first person to successfully produce ingot steel in a furnace of this type.

It would take some time &ndash not until the latter part of the 1880's &ndash before the open-hearth production of steel in Sweden would become widely established but by 1895 it had already exceeded that of Bessemer steel. Not until then did the volume of ingot steel production exceed that of the wrought iron production, meaning that the Lancashire method maintained its position as the most important for production of iron and steel during most of the 19th century.

The introduction of ingot steel processes represented a major upturn in the Swedish steel industry. Both production and exports were doubled during the period from the 1870's up to the First World War. At the same time, the export of Lancashire iron increased at the same rate as ingot steel, at least until the turn of the century. Particularly in the most important export markets - Great Britain and the USA &ndash the Lancashire bar iron continued to predominate. After 1900, however ingot steel took an increasingly larger share of the market whilst the so-called wrought iron methods, based on the Lancashire and particularly the Walloon forge, declined in importance.

A precondition for the geographical concentration of the iron and steel industry at the end of the 19th century was the development of communications &ndash particularly the railways. Steelworks demanded a cheap supply of materials &ndash coal, ore, etc. &ndash as well as good transportation facilities to the export harbours for the finished steel.

The start of the 20th century saw a breakthrough for electric steel &ndash a process which, as a consequence of advantageous electricity prices, was to enjoy a rapid expansion in Sweden. Together with the acid open-hearth process the electric-steel process was to have great significance for the development of Sweden's quality steel.

The advance of free trade

The breakthrough to a more liberal trade policy did not take place until J.A. Gripenstedt a supporter of free trade - became the Minister of Finance in the mid-19th century. As late as 1850 there was a ban on exports and imports of pig iron, an export ban on iron ore and an import ban on bar iron. In 1865, however, thanks to Gripenstedt's authority Sweden became a member of the international free trade system which emerged along the lines of the so-called Cobden treaty between France and Great Britain.

Gripenstedt was also behind the national railway policy, the reforms in the banking sector and the introduction of freedom of trade in 1864. He has come to personify the deregulation and liberalisation which took place in Sweden in the mid-19th century.

There was certainly no question of introducing a complete freedom of trade without protective tariffs. A number of important products enjoyed complete tariff exemption whereas others were subject to relatively modest duties. Iron and steel was on the exemption list up until 1888 when tariffs were re-introduced. For its time, the Swedish customs tariff was fairly sensitive to free trade.

In 1934, a change in American trade policy took place. The Americans realised that to increase their exports they must also be prepared to increase imports. It was this perception that lay behind a liberalising tariff agreement America completed with a number of countries including Sweden. From the 1930's and to the period just after the Second World War, security policy considerations came to play an increasingly important role in shaping trade policy. It was essential for individual countries to make themselves self-supporting with regard to the most important commodities.

&lsquoA steel for every purpose&rsquo

During the 1930's the steel industry made rapid strides. The rationalisation and modernisation which had taken place during the 1920's led to an increase of steel production by about 60 per cent. This increase was almost wholly due to ingot steel. Pig iron production grew during the same period by about 30 per cent but did not attain the peak figures recorded during the First World War. During the 1920's production of wrought iron had declined to insignificant quantities. Important progress in the production of specialty steels was also achieved, a large part of which were exported. At the same time the production of ordinary steel had also considerably increased.

During the Depression years of the 1930's, the Swedish steel mills managed to recover a significant share of their home market from foreign steel producers. Sweden's steel industry also developed over this period, greatly diversifying its product range. Fagersta Bruk's advertising slogan - 'A Steel for Every Purpose' - is well-known. This led to increased competition between the individual companies but paid off during the blockade of Sweden during the Second World War and greatly facilitated Swedish rearmament.

After the Second World War

During the immediate post-war years, a large number of regulations remained in force - not least in the area of foreign trade. Here there was a jungle of bilateral trading agreements, mostly with different countries, and the price situation with both imports and exports varied sharply. Payment difficulties were a regular occurrence. Gradually, however, these regulations were abolished. Through the Bretton Woods system a stable currency order was created meaning that world trade could start to expand again. A strong contributory factor was the more or less contemporary agreement reached between the world's leading industrial nations on customs tariffs and trade: The General Agreement on Tariffs and Trade (GATT).

After the Second World War, several organs were created in western Europe for economic and political co-operation the main purpose of which was to reduce the future risk of war. The most important of these was the European Coal and Steel Community (1951) &ndash the embryo of the European Union. From this first step, which was primarily intended to strengthen co-operation between France and West Germany, there subsequently grew the EEC (1957) which came to embrace other industries, including agriculture.

Central to this co-operation was the establishment of a customs union entailing common external custom tariff for all member states. The co-operation was developed gradually towards the creation of a single internal market embracing fifteen conntries which we now know as the EU. Sweden's entry as a full member on 1st January 1995 enabled Swedish industry to participate fully in the EU's integration work.

For Sweden's steel industry, membership in itself has not brought major changes. The industry has long been closely tied to the Coal and Steel Community with Swedish steel companies applying the price and market regulations which relate to steel trading in the union. However, an important advantage of membership is participation in the decision-making institutions and the removal of costly frontier controls on trade.

The Bessemer converter

The Bessemer converter was a machine and surrounding process that involved the removal of impurities from pig iron (a type of iron with a high carbon content) and its conversion into steel – a material that had historically been costly and time consuming to manufacture. The key principle behind its operation was the removal of impurities such as silicon, manganese and carbon through oxidation, turning the brittle, largely unusable pig iron into very useful steel.

The oxidation of impurities occurred in a Bessemer converter, a large egg-shaped container in which the iron was melted. The solid iron was inserted through a hole at the top and heated from the bottom. Once the converter had melted the pig iron, pressurised air was injected through and across the liquid metal, forcing the unwanted silicates to react with oxygen and convert into gas and/or solid oxides (ie slag).

Once the oxidation process had taken place, the usable molten steel could be poured out from the container directly by tipping it on a central pivot – the container was suspended off the ground by a pair of large struts – while the slag could be skimmed off the surface for reuse or disposal. The steel was emptied into large moulds, where it could be set into a wide range of products.


Bessemer Hall of History Founded in 1886 by industrialist Henry Fairfield DeBardeleben, Bessemer is the third largest city in Jefferson County. It is located in central Alabama in the southern part of Jones Valley, an area rich in iron ore and limestone. Famed football and baseball star Bo Jackson and actor Glenn Shadix were both born in Bessemer. World-renowned artist Thornton Dial spent most of his life in the city. Residents Keith and Donna Barton gained fame in the mid-2000s for their hen, Matilda, the "World's Oldest Living Chicken." The city has a mayor-council form of government. Downtown Bessemer After becoming president of the Bessemer Land and Improvement Company in 1886, Henry Fairfield DeBardeleben bought 4,000 acres of land for a planned new town that would be associated with his iron and coal businesses. He named the new city after Sir Henry Bessemer, inventor of the most prevalent steel-making process of the time. DeBardeleben sold the first commercial lots in April 1887 by June 1887, the town had a population of about 1,000 and had established a court and jail. That same year, the citizens of Bessemer chose Robert M. McAdory as the first mayor and elected eight councilmen. The mayor and councilmen voted to incorporate the city of Bessemer on September 9, 1887. Debardeleben also purchased buildings from the 1884 Cotton Exposition in New Orleans for use in Bessemer and had them shipped to Alabama via railroad. The Mexico building became the Montezuma Hotel and served as Debardeleben's home initially in 1896, it became the Montezuma University Medical College, operating until it burned in 1900. The Jamaica building was used as part of a mill. Neither building still stands. Two years later, the city constructed a city hall that also housed the fire department the building was destroyed by fire in the mid-1930s, and a new structure was built at the same location in 1937. The city also built a library with funds obtained from industrialist and philanthropist Andrew Carnegie in 1906. Owen House Bessemer's early economy centered primarily on mining and steel manufacturing, which attracted many laborers to the city, but the city's economy often suffered during economic downturns because of resultant high unemployment in the labor sector. During a recession in 1907, the Tennessee Coal, Iron, and Railroad Company, a major employer in the city, sold stock to United States Steel to relieve debt. U.S. Steel aided Bessemer by establishing a welfare program for sick and injured employees, improving infrastructure, and investing in education for children. To supplement Jefferson County's main courthouse in Birmingham, the county constructed a satellite courthouse in Bessemer in 1915 to serve the needs of the Bessemer area. The county built a new courthouse in October 2009. After the decline of the mining and steel industry during the last two decades of the twentieth century, the city diversified its economy to include industrial parks, professional offices, retail centers, and recreational facilities.
  • Educational services, and health care and social assistance (20.4 percent)
  • Retail trade (15.0 percent)
  • Manufacturing (14.7 percent)
  • Arts, entertainment, recreation, and accommodation and food services (12.5 percent)
  • Professional, scientific, management, and administrative and waste management services (7.4 percent)
  • Construction (6.7 percent)
  • Transportation and warehousing and utilities (5.7 percent)
  • Other services, except public administration (5.6 percent)
  • Finance, insurance, and real estate, rental, and leasing (5.0 percent)
  • Public administration (3.4 percent)
  • Wholesale trade (1.5 percent)
  • Information (1.3 percent)
  • Agriculture, forestry, fishing and hunting, and extractive (0.8 percent)

Historic Furnaces at Tannehill Attractions in Bessemer include Alabama Adventure theme park, which features a traditional amusement park with rides and a water park WaterMark Place Outlet Shopping Center and a city-owned civic center that hosts live theater, sporting events, concerts, banquets, and expositions. Bessemer is also home to Tannehill Ironworks Historical State Park, located on the site of a historic foundry that operated from 1829 to 1865 and served the Confederacy during the Civil War this site also is home to the Iron and Steel Museum. Other historic sites include the McAdory Plantation House and the Owen Plantation House, two of the three homes that comprise the nineteenth-century West Jefferson County Pioneer Homes. The century-old Bright Star, a five-star restaurant named an American classic by the James Beard Foundation, is located in downtown Bessemer. The Bessemer Hall of History Museum contains artifacts and displays related to Bessemer's industrial and cultural history it is housed in the former Alabama Great Southern Railroad Depot and is on the National Register of Historic Places. Watercress Darter National Wildlife Refuge is located just outside of Bessemer and protects the habitat of the endangered watercress darter, a small freshwater fish.


Input voltage Edit

A typical power inverter device or circuit requires a stable DC power source capable of supplying enough current for the intended power demands of the system. The input voltage depends on the design and purpose of the inverter. Examples include:

  • 12 V DC, for smaller consumer and commercial inverters that typically run from a rechargeable 12 V lead acid battery or automotive electrical outlet. [3]
  • 24, 36 and 48 V DC, which are common standards for home energy systems.
  • 200 to 400 V DC, when power is from photovoltaic solar panels.
  • 300 to 450 V DC, when power is from electric vehicle battery packs in vehicle-to-grid systems.
  • Hundreds of thousands of volts, where the inverter is part of a high-voltage direct current power transmission system.

Output waveform Edit

An inverter may produce a square wave, modified sine wave, pulsed sine wave, pulse width modulated wave (PWM) or sine wave depending on circuit design. Common types of inverters produce square waves or quasi-square waves. One measure of the purity of a sine wave is the total harmonic distortion (THD). A 50% duty pulse square wave is equivalent to a sine wave with 48% THD. [4] Technical standards for commercial power distribution grids require less than 3% THD in the wave shape at the customer's point of connection. IEEE Standard 519 recommends less than 5% THD for systems connecting to a power grid.

There are two basic designs for producing household plug-in voltage from a lower-voltage DC source, the first of which uses a switching boost converter to produce a higher-voltage DC and then converts to AC. The second method converts DC to AC at battery level and uses a line-frequency transformer to create the output voltage. [5]

Square wave Edit

This is one of the simplest waveforms an inverter design can produce and is best suited to low-sensitivity applications such as lighting and heating. Square wave output can produce "humming" when connected to audio equipment and is generally unsuitable for sensitive electronics.

Sine wave Edit

A power inverter device which produces a multiple step sinusoidal AC waveform is referred to as a sine wave inverter. To more clearly distinguish the inverters with outputs of much less distortion than the modified sine wave (three step) inverter designs, the manufacturers often use the phrase pure sine wave inverter. Almost all consumer grade inverters that are sold as a "pure sine wave inverter" do not produce a smooth sine wave output at all, [6] just a less choppy output than the square wave (two step) and modified sine wave (three step) inverters. However, this is not critical for most electronics as they deal with the output quite well.

Where power inverter devices substitute for standard line power, a sine wave output is desirable because many electrical products are engineered to work best with a sine wave AC power source. The standard electric utility provides a sine wave, typically with minor imperfections but sometimes with significant distortion.

Sine wave inverters with more than three steps in the wave output are more complex and have significantly higher cost than a modified sine wave, with only three steps, or square wave (one step) types of the same power handling. Switch-mode power supply (SMPS) devices, such as personal computers or DVD players, function on modified sine wave power. AC motors directly operated on non-sinusoidal power may produce extra heat, may have different speed-torque characteristics, or may produce more audible noise than when running on sinusoidal power.

Modified sine wave Edit

The modified sine wave output of such an inverter is the sum of two square waves one of which is phase shifted 90 degrees relative to the other. The result is three level waveform with equal intervals of zero volts peak positive volts zero volts peak negative volts and then zero volts. This sequence is repeated. The resultant wave very roughly resembles the shape of a sine wave. Most inexpensive consumer power inverters produce a modified sine wave rather than a pure sine wave.

The waveform in commercially available modified-sine-wave inverters resembles a square wave but with a pause during the polarity reversal. [5] Switching states are developed for positive, negative and zero voltages. If the waveform is chosen to have its peak values for half of the cycle time, the peak voltage to RMS voltage ratio is the same as for a sine wave. The DC bus voltage may be actively regulated, or the "on" and "off" times can be modified to maintain the same RMS value output up to the DC bus voltage to compensate for DC bus voltage variations. By changing the pulse width, the harmonic spectrum can be changed. The lowest THD for a three-step modified sine wave is 30% when the pulses are at 130 degrees width of each electrical cycle. This is slightly lower than for a square wave. [7]

The ratio of on to off time can be adjusted to vary the RMS voltage while maintaining a constant frequency with a technique called pulse width modulation (PWM). The generated gate pulses are given to each switch in accordance with the developed pattern to obtain the desired output. Harmonic spectrum in the output depends on the width of the pulses and the modulation frequency. It can be shown that the minimum distortion of a three-level waveform is reached when the pulses extend over 130 degrees of the waveform, but the resulting voltage will still have about 30% THD, higher than commercial standards for grid-connected power sources. [8] When operating induction motors, voltage harmonics are usually not of concern however, harmonic distortion in the current waveform introduces additional heating and can produce pulsating torques. [9]

Numerous items of electric equipment will operate quite well on modified sine wave power inverter devices, especially loads that are resistive in nature such as traditional incandescent light bulbs. Items with a switch-mode power supply operate almost entirely without problems, but if the item has a mains transformer, this can overheat depending on how marginally it is rated.

However, the load may operate less efficiently owing to the harmonics associated with a modified sine wave and produce a humming noise during operation. This also affects the efficiency of the system as a whole, since the manufacturer's nominal conversion efficiency does not account for harmonics. Therefore, pure sine wave inverters may provide significantly higher efficiency than modified sine wave inverters.

Most AC motors will run on MSW inverters with an efficiency reduction of about 20% owing to the harmonic content. However, they may be quite noisy. A series LC filter tuned to the fundamental frequency may help. [10]

A common modified sine wave inverter topology found in consumer power inverters is as follows: An onboard microcontroller rapidly switches on and off power MOSFETs at high frequency like

50 kHz. The MOSFETs directly pull from a low voltage DC source (such as a battery). This signal then goes through step-up transformers (generally many smaller transformers are placed in parallel to reduce the overall size of the inverter) to produce a higher voltage signal. The output of the step-up transformers then gets filtered by capacitors to produce a high voltage DC supply. Finally, this DC supply is pulsed with additional power MOSFETs by the microcontroller to produce the final modified sine wave signal.

More complex inverters use more than two voltages to form a multiple-stepped approximation to a sine wave. These can further reduce voltage and current harmonics and THD compared to an inverter using only alternating positive and negative pulses but such inverters require additional switching components, increasing cost.

Near sine wave PWM Edit

Some inverters use PWM to create a waveform that can be low pass filtered to re-create the sine wave. These only require one DC supply, in the manner of the MSN designs, but the switching takes place at a far faster rate, typically many KHz, so that the varying width of the pulses can be smoothed to create the sine wave. If a microprocessor is used to generate the switching timing, the harmonic content and efficiency can be closely controlled.

Output frequency Edit

The AC output frequency of a power inverter device is usually the same as standard power line frequency, 50 or 60 hertz. The exception is in designs for motor driving, where a variable frequency results in a variable speed control.

Also, if the output of the device or circuit is to be further conditioned (for example stepped up) then the frequency may be much higher for good transformer efficiency.

Output voltage Edit

The AC output voltage of a power inverter is often regulated to be the same as the grid line voltage, typically 120 or 240 VAC at the distribution level, even when there are changes in the load that the inverter is driving. This allows the inverter to power numerous devices designed for standard line power.

Some inverters also allow selectable or continuously variable output voltages.

Output power Edit

A power inverter will often have an overall power rating expressed in watts or kilowatts. This describes the power that will be available to the device the inverter is driving and, indirectly, the power that will be needed from the DC source. Smaller popular consumer and commercial devices designed to mimic line power typically range from 150 to 3000 watts.

Not all inverter applications are solely or primarily concerned with power delivery in some cases the frequency and or waveform properties are used by the follow-on circuit or device.

The runtime of an inverter powered by batteries is dependent on the battery power and the amount of power being drawn from the inverter at a given time. As the amount of equipment using the inverter increases, the runtime will decrease. In order to prolong the runtime of an inverter, additional batteries can be added to the inverter. [11]

Formula to calculate inverter battery capacity: [12]

Battery Capacity (Ah) = Total Load (In Watts) X Usage Time (in hours) / Input Voltage (V)

When attempting to add more batteries to an inverter, there are two basic options for installation:

Series configuration If the goal is to increase the overall input voltage to the inverter, one can daisy chain batteries in a series configuration. In a series configuration, if a single battery dies, the other batteries will not be able to power the load. Parallel configuration If the goal is to increase capacity and prolong the runtime of the inverter, batteries can be connected in parallel. This increases the overall ampere hour (Ah) rating of the battery set.

DC power source usage Edit

An inverter converts the DC electricity from sources such as batteries or fuel cells to AC electricity. The electricity can be at any required voltage in particular it can operate AC equipment designed for mains operation, or rectified to produce DC at any desired voltage.

Uninterruptible power supplies Edit

An uninterruptible power supply (UPS) uses batteries and an inverter to supply AC power when mains power is not available. When mains power is restored, a rectifier supplies DC power to recharge the batteries.

Electric motor speed control Edit

Inverter circuits designed to produce a variable output voltage range are often used within motor speed controllers. The DC power for the inverter section can be derived from a normal AC wall outlet or some other source. Control and feedback circuitry is used to adjust the final output of the inverter section which will ultimately determine the speed of the motor operating under its mechanical load. Motor speed control needs are numerous and include things like: industrial motor driven equipment, electric vehicles, rail transport systems, and power tools. (See related: variable-frequency drive ) Switching states are developed for positive, negative and zero voltages as per the patterns given in the switching Table 1. The generated gate pulses are given to each switch in accordance with the developed pattern and thus the output is obtained.

In refrigeration compressors Edit

An inverter can be used to control the speed of the compressor motor to drive variable refrigerant flow in a refrigeration or air conditioning system to regulate system performance. Such installations are known as inverter compressors. Traditional methods of refrigeration regulation use single-speed compressors switched on and off periodically inverter-equipped systems have a variable-frequency drive that control the speed of the motor and thus the compressor and cooling output. The variable-frequency AC from the inverter drives a brushless or induction motor, the speed of which is proportional to the frequency of the AC it is fed, so the compressor can be run at variable speeds—eliminating compressor stop-start cycles increases efficiency. A microcontroller typically monitors the temperature in the space to be cooled, and adjusts the speed of the compressor to maintain the desired temperature. The additional electronics and system hardware add cost to the equipment, but can result in substantial savings in operating costs. [13] The first inverter air conditioners were released by Toshiba in 1981, in Japan. [14]

Power grid Edit

Grid-tied inverters are designed to feed into the electric power distribution system. [15] They transfer synchronously with the line and have as little harmonic content as possible. They also need a means of detecting the presence of utility power for safety reasons, so as not to continue to dangerously feed power to the grid during a power outage.

Synchronverters are inverters that are designed to simulate a rotating generator, and can be used to help stabilize grids. They can be designed to react faster than normal generators to changes in grid frequency, and can give conventional generators a chance to respond to very sudden changes in demand or production.

Large inverters, rated at several hundred megawatts, are used to deliver power from high voltage direct current transmission systems to alternating current distribution systems.

Solar Edit

A solar inverter is a balance of system (BOS) component of a photovoltaic system and can be used for both grid-connected and off-grid systems. Solar inverters have special functions adapted for use with photovoltaic arrays, including maximum power point tracking and anti-islanding protection. Solar micro-inverters differ from conventional inverters, as an individual micro-inverter is attached to each solar panel. This can improve the overall efficiency of the system. The output from several micro-inverters is then combined and often fed to the electrical grid.

In other applications, a conventional inverter can be combined with a battery bank maintained by a solar charge controller. This combination of components is often referred to as a solar generator. [16]

Induction heating Edit

Inverters convert low frequency main AC power to higher frequency for use in induction heating. To do this, AC power is first rectified to provide DC power. The inverter then changes the DC power to high frequency AC power. Due to the reduction in the number of DC sources employed, the structure becomes more reliable and the output voltage has higher resolution due to an increase in the number of steps so that the reference sinusoidal voltage can be better achieved. This configuration has recently become very popular in AC power supply and adjustable speed drive applications. This new inverter can avoid extra clamping diodes or voltage balancing capacitors.

There are three kinds of level shifted modulation techniques, namely:

  • Phase Opposition Disposition (POD)
  • Alternative Phase Opposition Disposition (APOD)
  • Phase Disposition (PD)

HVDC power transmission Edit

With HVDC power transmission, AC power is rectified and high voltage DC power is transmitted to another location. At the receiving location, an inverter in a static inverter plant converts the power back to AC. The inverter must be synchronized with grid frequency and phase and minimize harmonic generation.

Electroshock weapons Edit

Electroshock weapons and tasers have a DC/AC inverter to generate several tens of thousands of V AC out of a small 9 V DC battery. First the 9 V DC is converted to 400–2000 V AC with a compact high frequency transformer, which is then rectified and temporarily stored in a high voltage capacitor until a pre-set threshold voltage is reached. When the threshold (set by way of an airgap or TRIAC) is reached, the capacitor dumps its entire load into a pulse transformer which then steps it up to its final output voltage of 20–60 kV. A variant of the principle is also used in electronic flash and bug zappers, though they rely on a capacitor-based voltage multiplier to achieve their high voltage.

Miscellaneous Edit

Typical applications for power inverters include:

  • Portable consumer devices that allow the user to connect a battery, or set of batteries, to the device to produce AC power to run various electrical items such as lights, televisions, kitchen appliances, and power tools.
  • Use in power generation systems such as electric utility companies or solar generating systems to convert DC power to AC power.
  • Use within any larger electronic system where an engineering need exists for deriving an AC source from a DC source.
  • Frequency conversion - if a user in (say) a 50 Hz country needs a 60 Hz supply to power equipment that is frequency-specific, such as a small motor or some electronics, it is possible to convert the frequency by running an inverter with a 60 Hz output from a DC source such as a 12V power supply running from the 50 Hz mains.

Basic design Edit

In one simple inverter circuit, DC power is connected to a transformer through the center tap of the primary winding. A switch is rapidly switched back and forth to allow current to flow back to the DC source following two alternate paths through one end of the primary winding and then the other. The alternation of the direction of current in the primary winding of the transformer produces alternating current (AC) in the secondary circuit.

The electromechanical version of the switching device includes two stationary contacts and a spring supported moving contact. The spring holds the movable contact against one of the stationary contacts and an electromagnet pulls the movable contact to the opposite stationary contact. The current in the electromagnet is interrupted by the action of the switch so that the switch continually switches rapidly back and forth. This type of electromechanical inverter switch, called a vibrator or buzzer, was once used in vacuum tube automobile radios. A similar mechanism has been used in door bells, buzzers and tattoo machines.

As they became available with adequate power ratings, transistors and various other types of semiconductor switches have been incorporated into inverter circuit designs. Certain ratings, especially for large systems (many kilowatts) use thyristors (SCR). SCRs provide large power handling capability in a semiconductor device, and can readily be controlled over a variable firing range.

The switch in the simple inverter described above, when not coupled to an output transformer, produces a square voltage waveform due to its simple off and on nature as opposed to the sinusoidal waveform that is the usual waveform of an AC power supply. Using Fourier analysis, periodic waveforms are represented as the sum of an infinite series of sine waves. The sine wave that has the same frequency as the original waveform is called the fundamental component. The other sine waves, called harmonics, that are included in the series have frequencies that are integral multiples of the fundamental frequency.

Fourier analysis can be used to calculate the total harmonic distortion (THD). The total harmonic distortion (THD) is the square root of the sum of the squares of the harmonic voltages divided by the fundamental voltage: THD = V 2 2 + V 3 2 + V 4 2 + ⋯ + V n 2 V 1 >=<^<2>+V_<3>^<2>+V_<4>^<2>+cdots +V_^<2>>> over V_<1>>>

Advanced designs Edit

There are many different power circuit topologies and control strategies used in inverter designs. [17] Different design approaches address various issues that may be more or less important depending on the way that the inverter is intended to be used.

Based on the basic H-bridge topology, there are two different fundamental control strategies called basic frequency-variable bridge converter and PWM control. [18] Here, in the left image of H-bridge circuit, the top left switch is named as "S1", and others are named as "S2, S3, S4" in counterclockwise order.

For the basic frequency-variable bridge converter, the switches can be operated at the same frequency as the AC in the electric grid (60 Hz in the U.S.). However, it is the rate at which the switches open and close that determines the AC frequency. When S1 and S4 are on and the other two are off, the load is provided with positive voltage and vice versa. We could control the on-off states of the switches to adjust the AC magnitude and phase. We could also control the switches to eliminate certain harmonics. This includes controlling the switches to create notches, or 0-state regions, in the output waveform or adding the outputs of two or more converters in parallel that are phase shifted in respect to one another.

Another method that can be used is PWM. Unlike the basic frequency-variable bridge converter, in the PWM controlling strategy, only two switches S3, S4 can operate at the frequency of the AC side or at any low frequency. The other two would switch much faster (typically 100 KHz) to create square voltages of the same magnitude but for different time duration, which behaves like a voltage with changing magnitude in a larger time-scale.

These two strategies create different harmonics. For the first one, through Fourier Analysis, the magnitude of harmonics would be 4/(pi*k) (k is the order of harmonics). So the majority of the harmonics energy is concentrated in the lower order harmonics. Meanwhile, for the PWM strategy, the energy of the harmonics lie in higher-frequencies because of the fast switching. Their different characteristics of harmonics leads to different THD and harmonics elimination requirements. Similar to "THD", the conception "waveform quality" represents the level of distortion caused by harmonics. The waveform quality of AC produced directly by H-bridge mentioned above would be not as good as we want.

The issue of waveform quality can be addressed in many ways. Capacitors and inductors can be used to filter the waveform. If the design includes a transformer, filtering can be applied to the primary or the secondary side of the transformer or to both sides. Low-pass filters are applied to allow the fundamental component of the waveform to pass to the output while limiting the passage of the harmonic components. If the inverter is designed to provide power at a fixed frequency, a resonant filter can be used. For an adjustable frequency inverter, the filter must be tuned to a frequency that is above the maximum fundamental frequency.

Since most loads contain inductance, feedback rectifiers or antiparallel diodes are often connected across each semiconductor switch to provide a path for the peak inductive load current when the switch is turned off. The antiparallel diodes are somewhat similar to the freewheeling diodes used in AC/DC converter circuits.

Fourier analysis reveals that a waveform, like a square wave, that is anti-symmetrical about the 180 degree point contains only odd harmonics, the 3rd, 5th, 7th, etc. Waveforms that have steps of certain widths and heights can attenuate certain lower harmonics at the expense of amplifying higher harmonics. For example, by inserting a zero-voltage step between the positive and negative sections of the square-wave, all of the harmonics that are divisible by three (3rd and 9th, etc.) can be eliminated. That leaves only the 5th, 7th, 11th, 13th etc. The required width of the steps is one third of the period for each of the positive and negative steps and one sixth of the period for each of the zero-voltage steps. [20]

Changing the square wave as described above is an example of pulse-width modulation. Modulating, or regulating the width of a square-wave pulse is often used as a method of regulating or adjusting an inverter's output voltage. When voltage control is not required, a fixed pulse width can be selected to reduce or eliminate selected harmonics. Harmonic elimination techniques are generally applied to the lowest harmonics because filtering is much more practical at high frequencies, where the filter components can be much smaller and less expensive. Multiple pulse-width or carrier based PWM control schemes produce waveforms that are composed of many narrow pulses. The frequency represented by the number of narrow pulses per second is called the switching frequency or carrier frequency. These control schemes are often used in variable-frequency motor control inverters because they allow a wide range of output voltage and frequency adjustment while also improving the quality of the waveform.

Multilevel inverters provide another approach to harmonic cancellation. Multilevel inverters provide an output waveform that exhibits multiple steps at several voltage levels. For example, it is possible to produce a more sinusoidal wave by having split-rail direct current inputs at two voltages, or positive and negative inputs with a central ground. By connecting the inverter output terminals in sequence between the positive rail and ground, the positive rail and the negative rail, the ground rail and the negative rail, then both to the ground rail, a stepped waveform is generated at the inverter output. This is an example of a three level inverter: the two voltages and ground. [21]

More on achieving a sine wave Edit

Resonant inverters produce sine waves with LC circuits to remove the harmonics from a simple square wave. Typically there are several series- and parallel-resonant LC circuits, each tuned to a different harmonic of the power line frequency. This simplifies the electronics, but the inductors and capacitors tend to be large and heavy. Its high efficiency makes this approach popular in large uninterruptible power supplies in data centers that run the inverter continuously in an "online" mode to avoid any switchover transient when power is lost. (See related: Resonant inverter)

A closely related approach uses a ferroresonant transformer, also known as a constant voltage transformer, to remove harmonics and to store enough energy to sustain the load for a few AC cycles. This property makes them useful in standby power supplies to eliminate the switchover transient that otherwise occurs during a power failure while the normally idle inverter starts and the mechanical relays are switching to its output.

Enhanced quantization Edit

A proposal suggested in Power Electronics magazine utilizes two voltages as an improvement over the common commercialized technology, which can only apply DC bus voltage in either direction or turn it off. The proposal adds intermediate voltages to the common design. Each cycle sees the following sequence of delivered voltages: v1, v2, v1, 0, −v1, −v2, −v1, 0. [19]

Three-phase inverters Edit

Three-phase inverters are used for variable-frequency drive applications and for high power applications such as HVDC power transmission. A basic three-phase inverter consists of three single-phase inverter switches each connected to one of the three load terminals. For the most basic control scheme, the operation of the three switches is coordinated so that one switch operates at each 60 degree point of the fundamental output waveform. This creates a line-to-line output waveform that has six steps. The six-step waveform has a zero-voltage step between the positive and negative sections of the square-wave such that the harmonics that are multiples of three are eliminated as described above. When carrier-based PWM techniques are applied to six-step waveforms, the basic overall shape, or envelope, of the waveform is retained so that the 3rd harmonic and its multiples are cancelled.

To construct inverters with higher power ratings, two six-step three-phase inverters can be connected in parallel for a higher current rating or in series for a higher voltage rating. In either case, the output waveforms are phase shifted to obtain a 12-step waveform. If additional inverters are combined, an 18-step inverter is obtained with three inverters etc. Although inverters are usually combined for the purpose of achieving increased voltage or current ratings, the quality of the waveform is improved as well.

Compared to other household electric devices, inverters are large in size and volume. In 2014, Google together with IEEE started an open competition named Little Box Challenge, with a prize money of $1,000,000, to build a (much) smaller power inverter. [22]

Early inverters Edit

From the late nineteenth century through the middle of the twentieth century, DC-to-AC power conversion was accomplished using rotary converters or motor-generator sets (M-G sets). In the early twentieth century, vacuum tubes and gas-filled tubes began to be used as switches in inverter circuits. The most widely used type of tube was the thyratron.

The origins of electromechanical inverters explain the source of the term inverter. Early AC-to-DC converters used an induction or synchronous AC motor direct-connected to a generator (dynamo) so that the generator's commutator reversed its connections at exactly the right moments to produce DC. A later development is the synchronous converter, in which the motor and generator windings are combined into one armature, with slip rings at one end and a commutator at the other and only one field frame. The result with either is AC-in, DC-out. With an M-G set, the DC can be considered to be separately generated from the AC with a synchronous converter, in a certain sense it can be considered to be "mechanically rectified AC". Given the right auxiliary and control equipment, an M-G set or rotary converter can be "run backwards", converting DC to AC. Hence an inverter is an inverted converter. [23]

Controlled rectifier inverters Edit

Since early transistors were not available with sufficient voltage and current ratings for most inverter applications, it was the 1957 introduction of the thyristor or silicon-controlled rectifier (SCR) that initiated the transition to solid state inverter circuits.

The commutation requirements of SCRs are a key consideration in SCR circuit designs. SCRs do not turn off or commutate automatically when the gate control signal is shut off. They only turn off when the forward current is reduced to below the minimum holding current, which varies with each kind of SCR, through some external process. For SCRs connected to an AC power source, commutation occurs naturally every time the polarity of the source voltage reverses. SCRs connected to a DC power source usually require a means of forced commutation that forces the current to zero when commutation is required. The least complicated SCR circuits employ natural commutation rather than forced commutation. With the addition of forced commutation circuits, SCRs have been used in the types of inverter circuits described above.

In applications where inverters transfer power from a DC power source to an AC power source, it is possible to use AC-to-DC controlled rectifier circuits operating in the inversion mode. In the inversion mode, a controlled rectifier circuit operates as a line commutated inverter. This type of operation can be used in HVDC power transmission systems and in regenerative braking operation of motor control systems.

Another type of SCR inverter circuit is the current source input (CSI) inverter. A CSI inverter is the dual of a six-step voltage source inverter. With a current source inverter, the DC power supply is configured as a current source rather than a voltage source. The inverter SCRs are switched in a six-step sequence to direct the current to a three-phase AC load as a stepped current waveform. CSI inverter commutation methods include load commutation and parallel capacitor commutation. With both methods, the input current regulation assists the commutation. With load commutation, the load is a synchronous motor operated at a leading power factor.

As they have become available in higher voltage and current ratings, semiconductors such as transistors or IGBTs that can be turned off by means of control signals have become the preferred switching components for use in inverter circuits.

Rectifier and inverter pulse numbers Edit

Rectifier circuits are often classified by the number of current pulses that flow to the DC side of the rectifier per cycle of AC input voltage. A single-phase half-wave rectifier is a one-pulse circuit and a single-phase full-wave rectifier is a two-pulse circuit. A three-phase half-wave rectifier is a three-pulse circuit and a three-phase full-wave rectifier is a six-pulse circuit. [24]

With three-phase rectifiers, two or more rectifiers are sometimes connected in series or parallel to obtain higher voltage or current ratings. The rectifier inputs are supplied from special transformers that provide phase shifted outputs. This has the effect of phase multiplication. Six phases are obtained from two transformers, twelve phases from three transformers and so on. The associated rectifier circuits are 12-pulse rectifiers, 18-pulse rectifiers and so on.

When controlled rectifier circuits are operated in the inversion mode, they would be classified by pulse number also. Rectifier circuits that have a higher pulse number have reduced harmonic content in the AC input current and reduced ripple in the DC output voltage. In the inversion mode, circuits that have a higher pulse number have lower harmonic content in the AC output voltage waveform.

Other notes Edit

The large switching devices for power transmission applications installed until 1970 predominantly used mercury-arc valves. Modern inverters are usually solid state (static inverters). A modern design method features components arranged in an H bridge configuration. This design is also quite popular with smaller-scale consumer devices. [25] [26]

Taming a volcano

The first time he tried the new process, Bessemer would discover just how violent this reaction could be. He wrote: “All went on quietly for about ten minutes sparks such as are commonly seen when tapping a cupola, accompanied by hot gases, ascended through the opening on the top of the converter, just as I supposed would be the case. But soon after, a rapid change took place in fact, the silicon had been quietly consumed, and the oxygen, next uniting with the carbon, sent up an ever-increasing stream of sparks and a voluminous white flame. Then followed a succession of mild explosions, throwing molten slags and splashes of metal high up into the air, the apparatus becoming a veritable volcano in a state of active eruption. No one could approach the converter to turn off the blast, and some low, flat, zinc-covered roofs, close at hand were in danger of being set on fire by the shower of red-hot matter falling on them. All this was a revelation to me, as I had in no way anticipated such violent results. However, in ten minutes more the eruption had ceased, the flame died down, and the process was complete. On tapping the converter into a shallow pan or ladle, and forming the metal into an ingot, it was found to be wholly decarburised malleable iron.”

All attempts to make the reaction less fierce failed and Bessemer concluded that speed (the whole process was complete in around 20 minutes), extreme heat and violent eruptions were all the necessary hallmarks of successful steel production. Instead, he devoted considerable time and thought to designing a reaction vessel that would contain the process as safely as possible.

After some experimentation, he designed the reaction vessel as a long ovoid with plenty of headroom for molten metal to spark and erupt without leaving the converter, and the characteristic offset outlet, or ‘mouth’. The converter was pivoted on trunnions so that it could be tilted to receive the charge and pour the molten steel into ladles or moulds. The capacity varied between 8–30 t of molten iron, though most converters were designed to carry a charge of 15 t.

The process was patented in 1855, though iron companies initially failed to produce the high-quality steel they’d expected excess oxygen left the steel brittle and it was difficult to retain the right quantity (of between 0.2–2.1% by weight) of carbon in the steel. Bessemer’s solution, which was to stop the airflow before all the carbon was converted, took a lot of trial and error to perfect. An easier solution was proposed by the metallurgist Robert Mushet, who suggested burning off all the carbon and then adding a precise quantity of Spiegeleisen, an iron-carbon-manganese alloy. This made it relatively straightforward to ensure the steel contained precisely the right quantity of carbon, while the manganese removed excess oxygen from the steel. This improved Bessemer process was first licensed in 1865, to the Dowlais Iron Company in Wales.

How Henry Bessemer Changed the Steel Industry

Sir Henry Bessemer was an English inventor and engineer that is popularly known for being the first to develop and process steel inexpensively, later contributing to the invention of the “Bessemer converter.” Sir Henry changed the steel industry in a way that no one ever had, and no one has since. He was an inspiration to the entire steel industry, especially during the Industrial Revolution.

Bessemer is known for other inventions as well, and his persistence and perseverance should be duly noted if you are looking for inspiration to become an inventor. Looking into Bessemer’s life and inventions should inspire you to take a look into your creative side as well, as we could all use some inspiration from this amazing English inventor.

Sir Henry Bessemer (19 January 1813 – 15 March 1898)

Henry Bessemer’s Early Life

Bessemer was born in 1813, in Hertfordshire, England, raised by an Engineer and Typefounder, showing his creative side at a very early age. Being that his father was an inventor, it was apparent that Henry wanted to follow suit, becoming an inventor like his father. Unfortunately, their family was not exactly rich, and this forced Henry out of school and into work to help his family survive. But he didn’t let that stop him in fact, this was the very spark that he needed to start bringing out his own ideas and inventions. Much of the inventions and creations from Henry all came about due to his transgressions, for if not for his troubles, it would have never pushed him to create and invent some of the most important products of all time.

Working with his father, Henry learned about metallurgy, and while most of his education was informal, he certainly learned just what he would need to know to help his inventions in the future. Knowing that his family needed help financially, and being an inventor at heart wanting to follow the footsteps of his father, he began tinkering with items and products around the home.

Perhaps one of the most interesting facts about Henry Bessemer is in his last name – over generations, it seems as if the last name was corrupted into Bessemer when originally it was spelled with an A, BA-ssemer. It continued to be Bassemer for some generations, but over the years, it was changed to an E, and they just never corrected it.

Anthony Bessemer – Henry’s Father

By the age of twenty, Henry’s father Anthony had helped in the construction of the first steam pumping machine to run in Holland. At the age of twenty-one, he fled to Paris, France, with nobody and no money. Destined to fail, he proved everyone wrong, becoming a part of the French Academy of Sciences within just five years.

At Paris mint, Anthony obtained a lead position, which eventually led to him inventing the copying machine, and as you can imagine, this brought him much popularity and abundance. However, this did not last long. This was, unfortunately, when the French Revolution began, and when they came for Anthony, he fled to England.

This was the start of Henry’s life, had Anthony not fled, who knows if Henry would have ever even been born.

Early Inventions

Before Henry Bessemer changed the steel industry, he had other ideas and creations in mind. Many people say that he was inspired to start inventing things so that he and his family didn’t have to struggle during the financial issues they were having.

His earliest invention was the very first movable stamps, used to date documents. He then updated the typesetting device, creating a machine that produced graphite for use in pencils.

From 1838 to 1883, Henry held about 129 patents for his inventions, becoming a prolific inventor. Here is a list of all of the creations and inventions Bessemer came up with during the 1800s.

  • Moveable stamps
  • Moveable dyes for embossed postage stamps
  • Military ordinance
  • A screw extruder used to remove sugar from sugar cane
  • A graphite producing machine
  • Upgrading the typesetting machine

Bessemer dreamed up many other inventions within the iron, steel, and glass industries.

SS Bessemer

Also known as the “Bessemer Saloon,” the SS Bessemer was a passenger steamship that helped fight against seasickness. Henry invented this ship in 1868 after experiencing his own issues with seasickness, so being personally affected, he created a ship with gimbals that were designed to stay level. The hydraulics were controlled by the steersman who would watch the leveling, making sure that everything worked without having problems. Unfortunately, the ship was always in a trial version and never received the proper tests that it needed to become an actual ship on the sea, and eventually, the idea was canned and put away, and the ship was scrapped.

Trials and Tribulations

The SS Bessemer didn’t just “get put away and scrapped,” but it actually destroyed some of the Calais piers on its voyage, and this put Henry’s confidence at an all-time low. This only shows that it doesn’t matter how talented you are at creating and inventing products. Even if your ideas could potentially benefit the world, you can still get turned down, turned away, and rejected. Instead of allowing this to end your career, however, we could all take notes and learn a little from Sir Henry and let the failures push us forward – not backward.

In fact, Henry was born during one of the hardest moments of his father’s life during the French Revolution. Anthony Bessemer (father) escaped from the reverses during the revolution and fled to Hertfordshire, England, from Paris, France. He had no money to his name at all, but he knew that he had to make this work, not only for him but now for baby Henry on the way. So Henry’s story started out during trying times. His family always seemed to be in a financial crisis, so he left his studies behind. His childhood consisted of being in the workshop every day with his father, Anthony.

Henry Bessemer and his inventions thrived off of trials and tribulations. This just proves to you that even during the darkest of days, we all need to keep trying.

Manufacturing Bronze Powder and Gold Paint

Henry Bessemer changed the steel industry many times during his life. His popularity and fortune grew after he first created the system of manufacturing bronze powder that aided in the production of gold paint. This process had been around for some time, especially in China and Japan, but he succeeded in making it much more affordable.

This creation consisted of six steam-powered machines, making a bronze powder that he examined from Nuremberg, but improving the product at a much lower price than anywhere else. This bronze powder aides in producing gold paint as well, and Henry was one of the first persons to use reverse engineering in this process. This was, in fact, one of the earliest uses of reverse engineering ever implemented, which is basically deconstructing a product to find out as much information as you can, then copying that information but also improving it as you reconstruct and put it back together.

The process was always kept a secret, with only some of his family members knowing the ins and outs of manufacturing bronze powder, and this secretive process is actually still used today. Henry made this invention and product so cheap for consumers that he made a huge profit from it, aiding as the start of many other inventions.

Napoleon, the Emporer

Napoleon Bonaparte was a French military leader who led many successful campaigns during the Revolutionary wars, rising in his popularity each time he was successful. So what does Napoleon have to do with Sir Henry Bessemer? Meeting with this Emporer was quite possibly the most important beginning of Henry’s career, as it was the very start of the Bessemer converter – it at least sparked the idea and contributed to the creation of it.

During the Crimean War, there were many imperfections in the British army’s artillery, which Bessemer continued to point out to his generals. One of his early proposals was to fire an elongated shot from a smooth-bore gun, but the British office was not hearing any of this. The only encouragement he received was, in fact, from Napoleon Bonaparte, the Emporer. Napoleon encouraged him so much that he invited Henry to Vincennes where they produced experiment after experiment, testing this method of an elongated shot through a smooth-bore gun, and helping the rotation by grooving the projectile of the shot. However, during these experiments, Bessemer found that the material was just too weak, and he had to find a to make the material stronger, leading him to fuse cast iron with steel and create a strong metal material. This combination led to Bessmer patenting the process in 1855, the first of many patents over the next 15 years.

As we mentioned before, even trials and tribulations have a place in our lives, and an accident during one of these experiments led Henry in a different direction. He began trying other experiments that he hadn’t thought of yet, which led to a second steel patent. This patent consisted of melting pig iron, through which steam was blown, and allowed you to use a large furnace containing many crucibles. These experiments led him to patent what we now know as the “Bessemer Converter.”

The Bessemer Process and the Bessemer Converter

Before we had the open furnace, Sir Henry Bessemer invented the Bessemer Converter, which led to changing to the steel industry forever. This process consisted of melting pig iron while air or steam was blown through it. This aeration aided in removing any impurities by oxidizing, which also helped the mass of the iron, and keeping it molten longer. This process had been used outside of Europe for many years but never on such a large industrial scale.

Bessemer Converter inveted by Sir Henry Bessemer

This process resulted in mass production and was also simultaneously the cheapest way to produce steel, making Sir Henry Bessemer one of the most honorable inventors of all time. He changed the steel industry by storm because if not for him, railroads, skyscrapers, and stronger metal machines might not be here today. One of the best factors of this game-changing steel production idea is the fact that it was the highest quality steel but at the lowest rates possible.

Although the Bessemer Converter is considered Sir Henry’s invention, there was an inventor by the name of James Nasmyth, who had actually been working on this idea for some time. However, he abandoned the project, and even when Henry tried to give him some of the credit and profits, Nasmyth refused them because he was already in retirement. This was when Sir Henry Bessemer became known as the “Man of Steel” or the “Inventor of Steel.”

What can we learn from Sir Henry’s life and inventions?

Sir Henry might have passed away in 1898, but his legacy lives on forever. Henry Bessemer changed the steel industry and many other industries during his life. His passion and persistence are instilled in the hearts of inventors and creators everywhere. Henry was brought up into a tough world and was considered almost destined to fail, yet these challenges seemed to drive him. The fact that he pushed through and allowed the trials to make something great of himself is a story and a legacy that all of us should take notes from.

If you’re a creator or an inventor, we can take Sir Henry’s life as inspiration. Even if you don’t plan on creating or inventing the next big thing, no matter what the love of your life is, you can take his trials and tribulations that he went through and used as a positive thing and make those positive thoughts your own.

If someone like Henry Bessemer changed the steel industry, then which industry can you have an impact on? He was born into adversity and poverty, yet he used those struggles as reasons to make something of himself. He actually took the cards he was dealt with and built something from them. This proves that anyone can overcome their problems and make a difference in the world, especially as an inventor.

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Getting your idea out of your head and into your hands is only the first in a long set of steps towards becoming a successful inventor.

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Modern steel is made using technology based on Bessemer's process. On the making of the first steel ingot, Bessemer said:

Bessemer was knighted in 1879 for his contributions to science. The "Bessemer Process" for mass-producing steel was named after him. Andrew Carnegie greatly advanced the steel industry in America after studying the Bessemer process and the British steel industry in the late 1800s.

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From Graces Guide

The Bessemer process was the first inexpensive industrial process for the mass-production of steel from molten pig iron.

1855 The process is named after its inventor, Henry Bessemer, who took out a patent on the process in 1855.

A similar process was claimed to have been discovered in 1851 by William Kelly. The process had also been used outside of Europe for hundreds of years, but not on an industrial scale. 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 out 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, after Sidney Gilchrist Thomas who had invented a process for dealing with the phosphorus with the help of his cousin, Percy Gilchrist Ώ] .

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 moulds 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.

Before the Bessemer process Britain had no practical method of reducing the carbon content of pig iron. Steel was manufactured by the reverse process of adding carbon to carbon-free wrought iron, usually imported from Sweden. The manufacturing process, called the cementation process, consisted of heating bars of wrought iron together with charcoal for periods of up to a week in a long stone box. This produced blister steel. Up to 3 tons of expensive coke was burnt for each ton of steel produced. Such steel when rolled into bars was sold at £50 to £60 a long ton. The most difficult and work-intensive part of the process was however the production of wrought iron done in finery forges in Sweden.

This process was refined in the 1700s with the introduction of Benjamin Huntsman's crucible steel making technique, which added an additional three hours firing time, and additional massive quantities of coke.

In making crucible steel, the blister steel bars were broken into pieces and melted in small crucibles each containing 20 kg or so. This produced a higher quality crucible steel, and increased the cost. The Bessemer process reduced by about ½ the time to make steel of this quality, while requiring only the coke needed initially to melt the pig iron. The earliest Bessemer converters produced steel for £7 a long ton, although they priced it initially at around £40 a ton.

Both Bessemer and Huntsman were based in the city of Sheffield. Sheffield has an international reputation for steel-making, which dates from 1740, when Benjamin Huntsman discovered the crucible technique for steel manufacture, at his workshop in the district of Handsworth. This process had an enormous impact on the quantity and quality of steel production and was only made obsolete, a century later, in 1856 by Henry Bessemer's invention of the Bessemer converter which allowed the true mass production of steel. Bessemer had moved his Bessemer Steel Co to Sheffield to be at the heart of the industry. The city's Kelham Island Museum still maintains one of the UK's last examples of a working Bessemer converter [from Workington, Cumbria] for public viewing.

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.

The Bessemer process was so fast (10-20 minutes for a heat) that it allowed little time for chemical analysis or adjustment of the alloying elements in the steel. Bessemer converters did not remove phosphorus efficiently from the molten steel as low-phosphorus ores became more expensive, conversion costs increased. The process only permitted a limited amount of scrap steel to be charged, further increasing costs, especially when scrap was inexpensive. Certain grades of steel were sensitive to the nitrogen which was part of the air blast passing through the steel.

Watch the video: How It Works - Steel Production