Keywords: Watermill, investigation, China

1 Introduction

      Ancient Chinese people invented a lot of machinery, much of which played an important role in social development and has been handed down in the respects of principles, structures and manufactures, and is now named "traditional machinery" to be differentiated from the modern machinery.

2 The Records of Watermill in the History of China

    Chinese water-powered machinery was invented in the Western Han Dynasty (206 B.C.~25 A.D.). There were watermill (water-wheel-powered mills) in the Northern and Southern Dynasties (420 A.D.~589 A.D.)[1]. Since the Tang Dynasty, watermills were applied widely. A watermill was depicted by a traditional Chinese painting dated in the Five Dynasties (907~960 A.D.) or in the Northern Song Dynasties (960~1127) (figure1). This painting is collected Shanghai Museum.


                         Figure 1 a watermill in ancient China

3 A Watermill in Lijiang County of Yunnan Province

    Generally, ancient records and drawings of machinery were very sketchy. In order to get a clear understanding of traditional watermills, the author of this paper went to Lijiang County in Yunnan Province in June of 1993, and investigated a watermill nearby small Shigu Town (figure 2) and drew it in the light of mechanical engineering (figure 3 and figure 4).

                          Figure 2 A watermill in a log cabin

1. vertical shaft, 2. vanes of oblique-shot water-wheel, 3. chute, 4. lower millstone, 5. iron tee-key, 6. upper millstone, 7. ropes, 8. hopper, 9. bottom tray, 10. stick, 11. pin, 12. adjusting wedges, 13. pull rod, 14. pin, 15. lower beam, 16. wedges, 17. iron and bearing (including bowl-shaped plate with a hole, hexangular part, flat with a hole), 18. stone block

                        Figure 4 left view of Shigu's watermill

    The watermill was built nearly a small village of Shigu Town, Songpingzi, which is about 4 milles away from Shigu Town of Lijiang County beside Jinsha River. Its principles and structures were special. The millstones in a log cabin are over a small stream (figure 5). The lower millstone is static. A vertical shaft is erected through the lower millstone, and fixed to the keyseat of the upper, movable millstone by an iron tee-key. A water-wheel is built on a hub which is at the end of the shaft. In addition, there are three iron parts under the hub. These parts form an end bearing of the shaft. The round hole of the lower millstone becomes a journal bearing of the shaft. The flow of stream is led into a chute and lashes at the vanes of water-wheel, thereby rotates its shaft that drives the upper millstone. The flow of water is regulated with a sluice-gate to control the rotational speed of water-wheel. The average speed is about 30 rpm. While the chute is closed off, the water-wheel stops.

                            Figure 5 millstones and the hopper

    There is a hopper over the millstone (figure 6). Grains are fed into the hopper, and then pour into the entrance of the upper millstone through the side hole of bottom tray. The flow of grain is controlled by adjusting the gradient of bottom tray that is hung by two ropes, the lengths of which can be changed to adjust the position of bottom tray. A short stick, which is tied to the bottom tray and touches the rough surface of the rotating upper millstone, makes the bottom tray and the hopper shake, thus causing the grains to flow easily (figure 7). In the end, the grains are crushed into small pieces or powder by the millstone. The size of powder depends on the chink between two millstones. With the help of a lower beam, a pull rod and a set of wedges, this chink can be controlled by adjusting the height of wedges (figure 8). In fact, the lower beam is burdened with the shaft and the upper millstone. The narrower the chink is, the smaller the powder is.

                                      Figure 6 Hopper

                          Figure 7 bottom tray, stick and upper millstone

                            Figure 9 a set of wedges and millstones

4 The Water-wheel of the watermill

    The horizontal oblique-shot water-wheel has no rim, and slightly resembles an upside-down umbrella in shape (figure 9). There are water-wheels of this kind at two villages, Fengyang nearby Dali City and Yunhe of Tengchong County in Yunnan Province. Such water-wheel is used to drive a rotary double edge-runner mill at Yunhe. The bigger the diameter of water-wheel is, the more vanes it needs. While the diameter is small, α, the acute angle between a vane and the shaft, is small. In figure 2, αequals 82°. The author thinks that such structure can make a small water-wheel have long vanes. The flow of water lashes at the upper end of vanes, and then runs down along the vanes. Therefore, much force makes water-wheel rotate. If A is the plane formed by the center line of shaft and the lower edge of a vane, and B is the plane lashed by the flow of water, then there is β, the acute angle between A and B. The angle, β, makes the flow of water force the vanes effectively. The water-wheel is also rotated by a horizontal component of gravity of water. Sometimes, the plane B becomes somewhat hollow, which may improve the function of water-wheel. Because we have not found any record or drawing of such device as Shigu's water-wheel, we cannot have a clear and unambiguous understanding of its origin, but the author thinks that it is older than water-wheel with rim that is drew in figure 1.

    The parts of Shigu's watermill except the millstones and a few iron parts are usually made of high-quality wood.

    Interestingly, there is a water-powered trip-hammer about 80 meters away from the above-mentioned watermill. The flow of stream from the watermill rotates the vertical undershot water-wheel of the trip-hammer.There are similar watermills in Sichuan Province and Tibet (figure 10), which are close to Yunnan Province.


                                  Figure 10 the water-wheel

5 Conclusions

    Through the investigation, the author acquired detailed knowledge about the structures, manufacture, cooling and lubrication system, control and adjustment of a kink of traditional or even ancient watermill. The above details were not recorded in ancient books. It is thus clear that the existing traditional machinery and other technologies are very valuable living historical materials. With the modernization of science and technology, many of traditional technologies will gradually be eliminated in China, so it is urgent for us to investigate and research them[2].

Acknowledgements

    This research is sponsored by the NSFC(Grant No. 50075006) and Institute for the History of Natural Sciences, Chinese Academy of Sciences (1994). I would like to thank Prof. Tan Derui and Dr. Yi Hua. Prof. Tan, who works at Shanghai Museum, presents me a copy of figure 1. Dr. Yi, who works at Institute for Nationalities of Chinese Academy of Social Science, presents me figure 10.

References

1. Zhang, B., Traditional Chinese Water-wheels and the Machinery Driven By them, Zi Ran Ke Xue Shi Yan Jiu (Studies in the History of Natural Sciences), Vol.13, No.2, pp.155-163; No.3, 254-263, 1994
2. Zhang, B., A Review and Thinking of Studies in the History of Chinese Machinery, Kexue Jishu yu Bianzhengfa (Science, Technology and Dialectic), Vol.11, No.3, pp.36-38, 1994

See: Proceedings of the 11th World Congress in Mechanism and Machine Science. Beijing: China Machine Press, 2004, edited by Tian Huang. pp.921-923.