Traditional blast furnaces in Sichuan
and Chongqing

Description of a blast furnace in Sichuan, by the Hungarian traveller Béla Széchenyi, 1877

Hoani-pu [Huangnipu 黄泥铺, a village in modern Yingjing County 荥经县] lies in a narrow valley, and bears throughout the stamp of a typical mining district. Everything here is black with coal dust from coal mining and iron industry. In the neighbourhood chain bridges cross over the streams. Coal and iron occur together in the immediate vicinity.

On the opposite bank is a blast furnace, ca. 8–9 m high and 5.5–6 m broad at the base. In form it is quite similar to a European blast furnace; it is built of stone and held together by an external wooden construction.

The blast is provided by a [piston-]bellows 1 m in diameter and 3.5 m long. This bellows, or rather, cylinder, is constructed on the same pattern as the common Chinese kitchen blowing cylinder, except that the piston is driven by a water-wheel. For the tapping of both iron and slag there is only one opening, at least I did not see a special opening for the latter.

The ore smelted here is an ironstone (blackband) with 40–60 per cent iron which occurs between the coal measures. Next to the shaft of the blast furnace the ore is first mixed with charcoal and roasted. As the works stood empty and out of operation, I was unable to obtain further data on the smelting process. I give the construction of the furnace in [the illustration above].

In the storehouse of the works was a large number of cast iron slabs measuring 1 m long, 0.60 m broad, and 0.02 m thick. [These would weigh about 100 kg each.] The surface of this cast iron is very slaggy because of the lack of a separate outlet for the slag; its fracture is steel-grey and full of blow-holes throughout.

Next to the blast furnace was the foundry, which however was also out of operation.  . . .

Translated from Béla Széchenyi, Die wissenschaftlichen Ergebnisse der Reise des Grafen Béla Széchenyi in Ostasien, Bd. 1: Die Beobachtungen während der Reise. Wien 1893, pp. 678–679.

Description of blast furnaces in Sichuan in the 1930s,
by Luo Mian 羅冕

The smelting furnace

The dimensions of the furnace are different in different places. Usually the height is 2 zhang 丈 4 chi 尺 [8 m], mouth [diameter] 2 chi 8 cun 寸 [93 cm], [inner diameter of the] belly at the widest point [the boshes], 5 chi 8 cun [193 cm], bottom [diameter] 9 cun [30 cm]. The interior has the shape of a vase [tanzi 罈子] of the above dimensions, widest in the middle and diminishing toward the top and bottom, as in [the figure on the right], which shows a section of the smelting furnace at the most recently built ironworks in Qijiang 綦江 . The mouth is a round hole into which wood, charcoal, and ore are charged and from which smoke escapes. The taphole is ca. 6 cun [20 cm] higher than the bottom; it has diameter 8 cun [27 cm, surely a typographical error for 8 fen 分, 2.7 cm], and is used for tapping both iron and slag.

The exterior of the furnace is square. It is narrowest at the top, ca. 1 zhang 4 chi [4.7 m], and widest at the bottom, 1 zhang 8 chi [6 m]. [The figures on the right] give an overall view. The work area [the tapping arch] looks like a city gate. The place where blast is blown in [the blowing arch] is at the side or the back, and has the same form as the work area [tapping arch]. The mouth [tuyère] of the pipe from the windbox [fengxiang 風箱, double-acting piston bellows] is inserted into the furnace at a height of ca. 1 chi [33 cm]; it has an adjustable prop, so that the height can be varied as desired. The blast is operated either by human power or by water power. The blast is cold, though some ironworks in Qijiang have recently changed over to hot blast.

The furnaces are built of refractory sandstone, which is acidic. In the interior, above and below the tuyère, it is plastered with a mixture of salt, loam, and sand to prevent the corrosion of the sandstone by basic materials. The plaster is usually composed of ca. 1 part salt, 4 parts clay, and 5 parts sand; some use danba 胆巴 (a magnesium salt) mixed with salt and clay.

The sandstone is supplied seasonally by stoneworkers. The furnace as a whole can last more than 200 days, but it is never worked for more than 200 days in a year. The next year it is rebuilt. The expenditure [per year] for the furnace and tuyères is somewhat over 1,000 yuan 元. Assuming the worst case, a production of only 250 tonnes of pig iron per year, then the cost of the furnace is about 4–5 yuan per ton, which is not expensive; the disadvantage of this type of furnace lies rather in the quality of the pig iron produced.

Production of pig iron

After the bottom of the smelting furnace has been dried, a layer of 400 jin 斤 [240 kg] of semi-charred charcoal is laid out on the bottom, followed by 600 jin [360 kg] of calcined ore. Further layers are added, alternating in the same way, until the top of the furnace is reached, giving a total of about 14,000 jin [8.4 tonnes] of ore. Then the bottom layer is ignited and the blast is started to maintain combustion. After about a day [morning to evening] the molten iron begins to flow. Outside the taphole the workers prepare a bed of fine sand which they rake to form a mould for a flat plate. The taphole is opened by striking with an iron rod, and iron and slag flow out together. As they flow into the mould the rake is used to remove the slag; the iron left behind in the sand mould, when it has cooled, is the cast-iron plate [the pig]; it is ca. 2 chi 5–6 cun [ca. 85 cm] long, 1 chi 4–5 cun [ca. 50 cm] wide, and weighs ca. 100 jin [60 kg]. [The thickness of the plate would then be ca. 1.8 cm.] After the first day, tapping can be done from time to time as convenient. The quantity of iron tapped is highly dependent on whether the temperature is sufficient; therefore it is important not to neglect the temperature. After the first tapping, fuel and calcined ore continue to be charged alternately as described above. As a general rule more than 4,000 jin [2.4 tonnes] of cast iron can be produced from 12,000–13,000 jin [7.2–7.8 tonnes] of calcined ore. By custom more than 5,000 jin is considered excellent, 4,000 jin normal, and 3,000 jin inferior. [These quantities are 3, 2.4, and 1.8 tonnes respectively, presumably per day.]

Translated from 中国工程师学会四川考查团报告之十五，钢铁，1936年，第18–21叶。

Last edited by DBW 28 February 2023
Stylistic changes 6 June 2024