A Kaldo converter (using the ''Kaldo process'' or ''Stora-Kaldo process'') is a rotary vessel oxygen based metal refining method. Originally applied to the refining of iron into steel, with most installations in the 1960s, the process is (2014) used primarily to refine non ferrous metals, typically copper. In that field, it is often named TBRC, or Top Blown Rotary Converter.

History and description

Convertisseur Kaldo de Florange - Coupe transversale

Steel production

file:Affinage convertisseur Kaldo.svg, lang=en, upright=1.8, Evolution of chemical composition and temperature of the liquid steel, during the blowing in a Kaldo converter. The iron content is linked with the slag composition, the others elements are taken in the metal. The name "Kaldo" is derived from Prof. Bo Kalling, and from the Domnarvets Jernverk (''Stora Kopparbergs Bergslag'' subsidiary) both key in the development of the process. Research into the use of a stirring to promote mixing, and therefore rate of conversion was investigated from the 1940s, and investigations into the use of

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

began c.1948. The feedstock at the Domnarvet works had a

phosphorus Phosphorus is a chemical element; it has Chemical symbol, symbol P and atomic number 15. All elemental forms of phosphorus are highly Reactivity (chemistry), reactive and are therefore never found in nature. They can nevertheless be prepared ar ...

content of 1.8-2.0% and so the process was developed with one aim being dephosphorisation. The first production unit was installed in 1954 at Domnarvet Jernverk. The converter was a top blow oxygen converter, similar to Linz-Donawitz (LD) type, using a cylindrical vessel; the vessel was tilted whilst conversion took place, with typical rotation speeds of around 30 revolutions per minute; the oxygen was injected via a lance, with slag forming materials added separately. Kaldo converters were relatively common in the 1960s in the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Northwestern Europe, off the coast of European mainland, the continental mainland. It comprises England, Scotlan ...

, during the transition from predominately open hearth process steelmaking to oxygen based steelmaking techniques. Converters were installed at Consett steelworks, Park Gate, Rotherham, Shelton works, Stoke-on-Trent; and Stanton Iron Works. Before the advent of the basic-LD process the Kaldo method was a preferred one in the UK for converting high phosphorus iron. The first unit in the UK was at Park Gate Works,

Rotherham Rotherham ( ) is a market town in South Yorkshire, England. It lies at the confluence of the River Rother, South Yorkshire, River Rother, from which the town gets its name, and the River Don, Yorkshire, River Don. It is the largest settlement ...

. In the USA, the process was installed at the

Sharon Steel Corporation Sharon Steel Corporation was an American steel company. Chairmen included Henry Roemer, Henry A. Roemer and later, Victor Posner. After it went bankrupt in the late 1980s, in late 1992, Sharon Steel Corp. was purchased by Caparo Steel. After a se ...

(c.1962). A plant in Japan was installed for ''Sanyo Special Steel Co.'' (Himejii) in c.1965. A combined type of converter (''LD-Kaldo''), using elements of the Linz-Donawitz (LD) and Kaldo processes was installed 1965 in Belgium at Cockerill-Ougrée-Providence's plant in Marchienne-au-Pont as a multicompany research venture. In France, one Kaldo furnace was also installed (one 160t unit, 1960) at

Sollac Sollac (Société Lorraine de Laminage Continu) was a French steel company formed in December 1948 as a cooperative. It produced steel rolls in Lorraine from steel supplied by several other companies. The company underwent various changes of owners ...

's . It was followed in 1969 by two huge 240t units, the biggest Kaldo converters ever built (two times bigger than the previous bigger ones : 1000t rotating at 30 r.p.m. !), at de Wendel-Sidelor's (later

Usinor-Sacilor Usinor was a French steel making group formed in 1948. The group was merged with Sacilor in 1986, becoming Usinor-Sacilor and was privatised in 1995, and renamed Usinor in 1997. In 2001 it merged with Arbed (Luxembourg) and Aceralia (Spain) to fo ...

) (

Lorraine Lorraine, also , ; ; Lorrain: ''Louréne''; Lorraine Franconian: ''Lottringe''; ; ; is a cultural and historical region in Eastern France, now located in the administrative region of Grand Est. Its name stems from the medieval kingdom of ...

, France); these two converters did not meet expectations and the third additional planned Kaldo unit was not installed, instead two OLP (''oxygène-lance-poudre'') 240t units were used. Disadvantages of the process, compared to non-rotating oxygen furnaces (e.g. LD type) were the higher capital cost, more difficult to upscale to higher outputs, and additional complexity (i.e. rotating parts and loading thereof). Advantages included the ability to use a high proportion of scrap metal, and good controllability of final steel specification. At the Park Gate works conversion time was 90 minutes, with up to 45% scrap loading, with a capacity of 75t in a 500t total, diameter converter, with a rotation speed of 40 revs per minute. Due to high maintenance costs the Kaldo converter did not gain widespread usage in the steel industry, with non-rotating converters being preferred.

Non-ferrous production

Nickel Nickel is a chemical element; it has symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive, but large pieces are slo ...

matte Matte may refer to: Art * paint with a non-glossy finish. See diffuse reflection. * a framing element surrounding a painting or watercolor within the outer frame Film * Matte (filmmaking), filmmaking and video production technology * Matte pai ...

was converted by

Inco Vale Canada Limited (formerly Vale Inco, CVRD Inco and Inco Limited; for corporate branding purposes simply known as "Vale" and pronounced in English) is a wholly owned subsidiary of the Brazilian mining company Vale. Vale's nickel mining and ...

(Canada) in a pilot Kaldo converter in 1959, and

Metallo-Chimique Metallo-Chimique International N.V., based in Beerse, Belgium, also described simply as Metallo, is a privately held metals and mining company. The company was incorporated in 1919. Metallo now specializes in the recycling and refining of metall ...

(Belgium) developed secondary

copper smelting Smelting is a process of applying heat and a chemical reducing agent to an ore to extract a desired base metal product. It is a form of extractive metallurgy that is used to obtain many metals such as iron, copper, silver, tin, lead and zinc. Sm ...

using the Kaldo type converters in the late 1960s. The Kaldo type converted is commonly known as a ''Top-Blown Rotary Converter'' (TBRC) in

non-ferrous metal In metallurgy, non-ferrous metals are metals or alloys that do not contain iron ( allotropes of iron, ferrite, and so on) in appreciable amounts. Generally more costly than ferrous metals, non-ferrous metals are used because of desirable pro ...

smelting Smelting is a process of applying heat and a chemical reducing agent to an ore to extract a desired base metal product. It is a form of extractive metallurgy that is used to obtain many metals such as iron-making, iron, copper extraction, copper ...

terminology. By the 1970s, the Kaldo furnace was in common use for

copper Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...

and nickel smelting. A Kaldo converter for the smelting of

lead Lead () is a chemical element; it has Chemical symbol, symbol Pb (from Latin ) and atomic number 82. It is a Heavy metal (elements), heavy metal that is density, denser than most common materials. Lead is Mohs scale, soft and Ductility, malleabl ...

was constructed by

Boliden AB Boliden AB (stylized as Boliden) is a Swedish multinational metals, mining, and smelting company headquartered in Stockholm. The company produces zinc, copper, lead, nickel, silver, and gold, with operations in Sweden, Finland, Norway, Portugal ...

in Sweden in 1976. Kaldo secondary copper units were still in use worldwide at the beginning of the 21st century, but as of 2011 no new units had been commissioned for around 10 years, suggesting that the process had been superseded.

References

Sources

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External links