Thomas method

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Thomas converter from Hörder Kesselschmiede from 1954. In use until 1964 in the Thomas steel works in Phoenix-Ost . The Thomas pear is 7 meters high and weighs 64 tons.

The Thomas process or completely Thomas-Gilchrist process describes a process for steel production and was named after the British metallurgists Sidney Thomas (1850–1885) and Percy Carlyle Gilchrist (1851–1935). The steel produced in this way is called Thomasstahl .

Procedure

Chemistry in the Thomas process

The Thomas process (also called the basic wind freshening process ) is a so-called blowing or wind freshening process, in which air is blown into the liquid pig iron through the bottom nozzles of the converter , the Thomas pear.

The oxidation process , which lowers the carbon content ( freshening ), provided enough heat in this process to keep the steel liquid, so an external heat supply was not necessary in the converters.

The Thomas pear was lined with a basic dolomite stone or dolomite tar mixture and was particularly suitable for processing iron rich in phosphorus.

The phosphorus oxidized to phosphorus pentoxide was slagged with the limestone added as an additive (Thomas slag) and was marketed finely ground under the name Thomas flour as a phosphate fertilizer .

Thomasstahl served the production of rails, profile iron and sheet metal. Almost all steel structures from the 1950s to 1970s are made of this steel.

history

The Thomas process itself is only a minor modification of the Bessemer process , for which only the lining of the converter had to be converted to dolomite and a system for adding lime had to be purchased. In the early 1880s, almost all German smelting works therefore started tests in disused Bessemer converters in order to be able to evaluate the new process or to apply for circumvention patents. For Germany, on the initiative of Gustave Léon Pastor and Josef Massenez, the Rheinische Stahlwerke and the Hörder Bergwerks- und Hütten-Verein jointly bought the patent rights and licensed them to other German smelters, but above all to the smelting works of Lorraine , which are based on rich, phosphorus-containing minette deposits sat.

Disadvantages of the procedure

Thomas pear, detail of herringbone tilting drive
Thomas pear, details riveted vessel, screwed retaining ring

Wind freshening has the metallurgical disadvantage that inevitably large amounts of nitrogen ( air contains around 78% nitrogen) and hydrogen are dissolved in the steel. In steel, nitrogen and iron and other alloying elements form hard, brittle nitrides that make the steel less tough. In addition, over the years there is additional nitrogen embrittlement in the steel.

It was preferred to refine iron ores rich in phosphorus in the Thomaskonverter. Phosphorus is a companion to steel that greatly reduces toughness, especially at low temperatures.

Thomas steels are considered to be difficult to weld. The high hydrogen content favors cold cracks, which is particularly important when welding old steel structures. As a preventive measure, filler materials with high toughness are used during welding.

In the middle of the 1970s in the Federal Republic of Germany , since the beginning of the 1980s in most countries, the production of Thomasstahl was stopped and the Thomas process itself was replaced by the Linz-Donawitz process .

Known claims

Thomasstahlprodukte came into the public eye again due to the Münsterland snow chaos , when 82 high-voltage pylons buckled under the multiple increased ice load (approx. 18.9 kg / m) in November 2005 during unusually heavy snowfall and storms  . However, the operators, especially RWE , did not consider the masts to be at greater risk of brittle fracture . RWE argued that in this natural disaster, not only were old masts made of Thomasstahl kinked, but also newer masts made of modern materials. According to a report by the Federal Institute for Materials Research and Testing , which was commissioned by the Federal Network Agency , the cause of the damage was the simultaneous occurrence of a total of eight damage triggers:

  1. strong wind
  2. very heavy snowfall
  3. Freezing temperatures
  4. wet and therefore heavy snow
  5. onset of rain
  6. unilateral load on the guy lines
  7. Cross wind
  8. individual rotating conductors

In particular, no areas of corrosion were found.

Thomasstahl has not been used for high-voltage pylons since the late 1960s, but pylons built before 1940 are still in use today .

In June 2006, RWE representatives in the economic committee of the state parliament of North Rhine-Westphalia said they wanted to repair or replace 28,000 (of 42,000) masts (by 2015), invest 550 million euros in the renovation and primarily renovate masts in the vicinity of residential areas and roads. The NRW Minister for Economic Affairs, Christa Thoben , urged RWE to act more quickly and also criticized the attitude of the VDEW ( Association of the Electricity Industry ) and the VDN ( Association of Network Operators ).

Web links

Commons : Thomas Converter  - collection of images, videos and audio files

swell

  • Ulrich Wengenroth: Corporate strategies and technical progress of the dt u. British steel industry 1865–1895. Vandenhoeck & Ruprecht, Göttingen 1986, ISBN 3-525-36302-8 , especially Chapter V.

Individual evidence

  1. Federal Network Agency : Investigation report on the supply disruptions in the network area of ​​the RWE in the Münsterland from November 25, 2005.  ( Page no longer available , search in web archivesInfo: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. dated June 2006 (accessed on May 6, 2011)@1@ 2Template: Toter Link / www.bundesnetzagentur.de  
  2. ↑ Electricity pylons - pressure on RWE.  ( Page no longer available , search in web archivesInfo: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. In: Rheinische Post. June 14, 2006.@1@ 2Template: dead link / local-wirtschaft.rp-online.de