The traditional iron industry in Sichuan

The southwestern province of Sichuan was in pre-modern times quite isolated from the rest of China. It communicated with eastern China via the Yangzi River through a series of dangerous gorges (which since 2003 have been flooded by an enormous dam), and with Shaanxi via a famously arduous mountain road. On the other hand transport conditions within the province were good. The name means ‘four rivers’, and transport on these rivers bound the province together to form an economic whole. The soil is fertile and the climate reliable, and these factors have made Sichuan one of China’s breadbaskets. The province has attracted immigrants throughout Chinese history, and its population density is extreme. In 1997 Sichuan was divided into two, Sichuan and Chongqing; see the map.

Drawing and section through a water-powered blast furnace in Yingjing amt, Sichuan, ca. 1877. (Béla Széchenyi, Die wissenschaftlichen Ergebnisse der Reise des Grafen Béla Széchenyi in Ostasien, Vol. 1, Wien 1893, p. 678).

Blast furnace in Sichuan, photographed ca. 1936. (Luo Mian, Zhongguo Gongchengshi Xuehui Sichuan Kaochatuan baogao, no. 15: Gang tie, 1936, p. 19).

Section through a blast furnace in Qijiang amt, Sichuan, 1936. (Luo Mian, p. 20).

One consequence of these geographic factors is that the iron industry has had good market conditions: demand from a large population, with excellent transport, and isolation from outside competition. There has been considerable production of iron since ancient times, and in recent centuries the traditional blast furnaces used in Sichuan have been the largest in China. The images on the left show some of these.

The oldest description of a blast furnace in Sichuan, from 1877, is by the Hungarian traveler Béla Széchenyi. The ore is blackband, which consists largely of FeCO₃. It is calcined (roasted) to remove sulphur and transform the carbonate to an oxide (e.g. by the reaction FeCO₃ → FeO + CO₂ ↑). The calcined ore is charged into the top of the blast furnace together with charcoal and – probably – limestone as a flux. The blast comes from an enormous windbox (1 m in diameter, 3.5 m long), driven by water power. The iron is tapped regularly, forming large slabs, weighing ca. 100 kg. Liquid slag is tapped through the same hole as the iron, and there is therefore some mixing of the slag and the pig iron, resulting in ‘slaggy’ iron. This mixing is not too important, however, since the slag is easily removed in the next step, in which the pig iron is either cast or converted to wrought iron.

Section through a puddling furnace in Sichuan, ca. 1936. It is built of a type of refractory sandstone which is common in Sichuan. a. firebox, height 93 cm. b. puddling hearth, diameter 67 cm. c. blast pipe. d. flame channel. (Luo Mian, p. 24).

Two photographs (back and front) of a puddling furnace in Sichuan. (Luo Mian, p. 24).

Conversion to wrought iron is done in a puddling hearth like that shown above on the right. It resembles the simpler fining hearth used in Dabieshan, with the difference that the fuel and the iron are separated. The fuel, either charcoal or mineral coal, burns in the firebox. Air is pumped in, and the flame proceeds downward and melts the iron in the puddling bed. The puddler stirs (‘puddles’) the molten iron until the carbon is burnt out of it and it can be removed as a pasty lump of wrought iron. The separation of the fuel from the iron simplified the work and made it possible to use mineral coal as the fuel without adding too much sulphur to the iron.

Modern times gradually reduced Sichuan’s isolation, especially after steamship transport became common on the Yangzi River in the 1920s, and this had major consequences for the iron industry. Besides competition with foreign iron, there was also a new competition with other industries for raw materials and capital, while labour costs appear to have fallen.

It became necessary to adapt the technology to the new economic conditions. The use of water power became uncommon, and the blast furnaces were more often driven by manpower. This reduced capital costs, not only because the blast apparatus was simpler, but also because of an extra degree of freedom in the location of an ironworks: it was no longer necessary to place the works on an expensive site with access to water power.

The use of a limestone flux in the blast furnace also became uncommon. An increased production of cement in these years had made limestone more expensive, and another reason was that the blast furnace could function longer without limestone. Limestone made the slag alkaline, so that it attacked the furnace shaft, which normally was of sandstone and therefore acid. It may be that the omission brought a reduction in the quality of the iron, since limestone removes sulphur as well as making the slag less viscous.

On Sichuan during World War II, see Barbara W. Tuchman, Stilwell and the American experience in China, 1911-45, New York 1970 (many later reprints, some with altered title, Sand against the wind).

In 1938, after the Japanese occupation of eastern China, the Chinese government under Chiang Kai-shek relocated to Sichuan and established its capital in Chongqing. The province was now again isolated, and the entire civilian demand for iron could only be supplied by the traditional industry. A great deal of experimental work was done to improve the traditional technology using modern scientific knowledge; the experiments continued after the war and up through the 1950’s, seemingly with some success. The positive results of these experiments may have contributed to the optimistic approach to the traditional technology which characterized the period of the Great Leap Forward, 1958–60.

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