2022年毕业设计方案中起重机的英文翻译2.docx

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1、精选学习资料 - - - - - - - - - The Use and History of Crane Every time we see a crane in action we remains without words, these machines are sometimes really huge, taking up tons of material hundreds of meters in height. We watch with amazement and a bit of terror, thinking about what would happen if the

2、load comes off or if the movement of the crane was wrong. It is a really fascinating system, surprising both adults and children. These are especially tower cranes, but in reality there are plenty of types and they are in use for centuries. The cranes are formed by one or more machines used to creat

3、e a mechanical advantage and thus move large loads. Cranes are equipped with a winder, a wire rope or chain and sheaves that can be used both to lift and lower materials and to move them horizontally. It uses one or more simple machines to create mechanical advantage and thus move loads beyond the n

4、ormal capability of a human. Cranes are commonly employed in the transport industry for the loading and unloading of freight, in the construction industry for the movement of materials and in the manufacturing industry for the assembling of heavy equipment. 1. Overview The first construction cranes

5、were invented by the Ancient Greeks and were powered by men or beasts of burden, such as donkeys. These cranes were used for the construction of tall buildings. Larger cranes were later developed, employing the use of human treadwheels, permitting the lifting of heavier weights. In the High Middle A

6、ges, harbor cranes were introduced to load and unload ships and assist with their construction some were built into stone towers for extra strength and stability. The earliest cranes were constructed from wood, but cast iron and steel took over with the coming of the Industrial Revolution. For many

7、centuries, power was supplied by the physical exertion of men or animals, although hoists in watermills and windmills could be driven by 1 / 21 名师归纳总结 - - - - - - -第 1 页,共 21 页精选学习资料 - - - - - - - - - the harnessed natural power. The first mechanical power was provided by steam engines, the earliest

8、 steam crane being introduced in the 18th or 19th century, with many remaining in use well into the late 20th century. Modern cranes usually use internal combustion engines or electric motors and hydraulic systems to provide a much greater lifting capability than was previously possible, although ma

9、nual cranes are still utilized where the provision of power would be uneconomic. Cranes exist in an enormous variety of forms each tailored to a specific use. Sizes range from the smallest jib cranes, used inside workshops, to the tallest tower cranes, used for constructing high buildings. For a whi

10、le, mini - cranes are also used for constructing high buildings, in order to facilitate constructions by reaching tight spaces. Finally, we can find larger floating cranes, generally used to build oil rigs and salvage sunken ships. This article also covers lifting machines that do not strictly fit t

11、he above definition of a crane, but are generally known as cranes, such as stacker cranes and loader cranes. 2. History Ancient Greece The crane for lifting heavy loads was invented by the Ancient Greeks in the late 6th century BC. The archaeological record shows that no later than c.515 BC distinct

12、ive cuttings for both lifting tongs and lewis irons begin to appear on stone blocks of Greek temples. Since these holes point at the use of a lifting device, and since they are to be found either above the center of gravity of the block, or in pairs equidistant from a point over the center of gravit

13、y, they are regarded by archaeologists as the positive evidence required for the existence of the crane. The introduction of the winch and pulley hoist soon lead to a widespread replacement of ramps as the main means of vertical motion. For the next two hundred years, Greek building sites witnessed

14、a sharp drop in the weights 2 / 21 名师归纳总结 - - - - - - -第 2 页,共 21 页精选学习资料 - - - - - - - - - handled, as the new lifting technique made the use of several smaller stones more practical than of fewer larger ones. In contrast to the archaic period with its tendency to ever-increasing block sizes, Greek

15、 temples of the classical age like the Parthenon invariably featured stone blocks weighing less than 15-20 tons. Also, the practice of erecting large monolithic columns was practically abandoned in favor of using several column drums. Although the exact circumstances of the shift from the ramp to th

16、e crane technology remain unclear, it has been argued that the volatile social and political conditions of Greece were more suitable to the employment of small, professional construction teams than of large bodies of unskilled labor, making the crane more preferable to the Greek polis than the more

17、labor-intensive ramp which had been the norm in the autocratic societies of Egypt or Assyria. The first unequivocal literary evidence for the existence of the compound pulley system appears in the Mechanical Problems Mech. 18, 853a32-853b13 attributed to Aristotle 384-322 BC, but perhaps composed at

18、 a slightly later date. Around the same time, block sizes at Greek temples began to match their archaic predecessors again, indicating that the more sophisticated compound pulley must have found its way to Greek construction sites by then. Ancient Rome The heyday of the crane in ancient times came d

19、uring the Roman Empire, when construction activity soared and buildings reached enormous dimensions. The Romans adopted the Greek crane and developed it further. We are relatively well informed about their lifting techniques, thanks to rather lengthy accounts by the engineers Vitruvius De Architectu

20、ra 10.2, 1-10 and Heron of Alexandria Mechanica 3.2-5. There are also two surviving reliefs of Roman treadwheel cranes, with the Haterii tombstone from the late first century AD being particularly detailed. 3 / 21 名师归纳总结 - - - - - - -第 3 页,共 21 页精选学习资料 - - - - - - - - - The simplest Roman crane, the

21、 Trispastos, consisted of a single-beam jib, a winch, a rope, and a block containing three pulleys. Having thus a mechanical advantage of 3:1, it has been calculated that a single man working the winch could raise 150 kg 3 pulleys x 50 kg = 150, assuming that 50 kg represent the maximum effort a man

22、 can exert over a longer time period. Heavier crane types featured five pulleys Pentaspastos or, in case of the largest one, a set of three by five pulleys Polyspastos and came with two, three or four masts, depending on the maximum load. The Polyspastos, when worked by four men at both sides of the

23、 winch, could already lift 3000 kg 3 ropes x 5 pulleys x 4 men x 50 kg = 3000 kg. In case the winch was replaced by a treadwheel, the maximum load even doubled to 6000 kg at only half the crew, since the treadwheel possesses a much bigger mechanical advantage due to its larger diameter. This meant t

24、hat, in comparison to the construction of the Egyptian Pyramids, where about 50 men were needed to move a 2.5 ton stone block up the ramp 50 kg per person, the lifting capability of the Roman Polyspastos proved to be 60 times higher 3000 kg per person. However, numerous extant Roman buildings which

25、feature much heavier stone blocks than those handled by the Polyspastos indicate that the overall lifting capability of the Romans went far beyond that of any single crane. At the temple of Jupiter at Baalbek, for instance, the architrave blocks weigh up to 60 tons each, and one corner cornice block

26、 even over 100 tons, all of them raised to a height of about 19 m. In Rome, the capital block of Trajans Column weighs 53.3 tons, which had to be lifted to a height of about 34 m see construction of Trajans Column. It is assumed that Roman engineers lifted these extraordinary weights by two measures

27、 see picture below for comparable Renaissance technique: First, as suggested by Heron, a lifting tower was set up, whose four masts were arranged in the shape of a quadrangle with parallel sides, not unlike a 4 / 21 名师归纳总结 - - - - - - -第 4 页,共 21 页精选学习资料 - - - - - - - - - siege tower, but with the c

28、olumn in the middle of the structure Mechanica 3.5. Second, a multitude of capstans were placed on the ground around the tower, for, although having a lower leverage ratio than treadwheels, capstans could be set up in higher numbers and run by more men and, moreover, by draught animals. This use of

29、multiple capstans is also described by Ammianus Marcellinus 17.4.15 in connection with the lifting of the Lateranense obelisk in the Circus Maximus ca. 357 AD. The maximum lifting capability of a single capstan can be established by the number of lewis iron holes bored into the monolith. In case of

30、the Baalbek architrave blocks, which weigh between 55 and 60 tons, eight extant holes suggest an allowance of 7.5 ton per lewis iron, that is per capstan. Lifting such heavy weights in a concerted action required a great amount of coordination between the work groups applying the force to the capsta

31、ns. Middle Ages During the High Middle Ages, the treadwheel crane was reintroduced on a large scale after the technology had fallen into disuse in western Europe with the demise of the Western Roman Empire. The earliest reference to a treadwheel magna rota reappears in archival literature in France

32、about 1225, followed by an illuminated depiction in a manuscript of probably also French origin dating to 1240. In navigation, the earliest uses of harbor cranes are documented for Utrecht in 1244, Antwerp in 1263, Brugge in 1288 and Hamburg in 1291, while in England the treadwheel is not recorded b

33、efore 1331. Generally, vertical transport could be done more safely and inexpensively by cranes than by customary methods. Typical areas of application were harbors, mines, and, in particular, building sites where the treadwheel crane played a pivotal role in the construction of the lofty Gothic cat

34、hedrals. Nevertheless, both archival and pictorial sources of the time suggest that newly introduced machines like treadwheels or wheelbarrows did not 5 / 21 名师归纳总结 - - - - - - -第 5 页,共 21 页精选学习资料 - - - - - - - - - completely replace more labor-intensive methods like ladders, hods and handbarrows. R

35、ather, old and new machinery continued to coexist on medieval construction sites and harbors. Apart from treadwheels, medieval depictions also show cranes to be powered manually by windlasses with radiating spokes, cranks and by the 15th century also by windlasses shaped like a ships wheel. To smoot

36、h out irregularities of impulse and get over dead-spots in the lifting process flywheels are known to be in use as early as 1123. The exact process by which the treadwheel crane was reintroduced is not recorded, although its return to construction sites has undoubtedly to be viewed in close connecti

37、on with the simultaneous rise of Gothic architecture. The reappearance of the treadwheel crane may have resulted from a technological development of the windlass from which the treadwheel structurally and mechanically evolved. Alternatively, the medieval treadwheel may represent a deliberate reinven

38、tion of its Roman counterpart drawn from Vitruvius De architectura which was available in many monastic libraries. Its reintroduction may have been inspired, as well, by the observation of the labor-saving qualities of the waterwheel with which early treadwheels shared many structural similarities.

39、Structure and placement The medieval treadwheel was a large wooden wheel turning around a central shaft with a treadway wide enough for two workers walking side by side. While the earlier compass-arm wheel had spokes directly driven into the central shaft, the more advanced clasp-arm type featured a

40、rms arranged as chords to the wheel rim, giving the possibility of using a thinner shaft and providing thus a greater mechanical advantage. Contrary to a popularly held belief, cranes on medieval building sites were neither placed on the extremely lightweight scaffolding used at the time nor on the

41、thin walls of the Gothic churches which were incapable of 6 / 21 名师归纳总结 - - - - - - -第 6 页,共 21 页精选学习资料 - - - - - - - - - supporting the weight of both hoisting machine and load. Rather, cranes were placed in the initial stages of construction on the ground, often within the building. When a new flo

42、or was completed, and massive tie beams of the roof connected the walls, the crane was dismantled and reassembled on the roof beams from where it was moved from bay to bay during construction of the vaults. Thus, the crane grewand wanderedwith the building with the result that today all extant const

43、ruction cranes in England are found in church towers above the vaulting and below the roof, where they remained after building construction for bringing material for repairs aloft. Less frequently, medieval illuminations also show cranes mounted on the outside of walls with the stand of the machine

44、secured to putlogs. Mechanics and operation In contrast to modern cranes, medieval cranes and hoists - much like their counterparts in Greece and Rome - were primarily capable of a vertical lift, and not used to move loads for a considerable distance horizontally as well. Accordingly, lifting work w

45、as organized at the workplace in a different way than today. In building construction, for example, it is assumed that the crane lifted the stone blocks either from the bottom directly into place, or from a place opposite the centre of the wall from where it could deliver the blocks for two teams wo

46、rking at each end of the wall. Additionally, the crane master who usually gave orders at the treadwheel workers from outside the crane was able to manipulate the movement laterally by a small rope attached to the load. Slewing cranes which allowed a rotation of the load and were thus particularly su

47、ited for dockside work appeared as early as 1340. While ashlar blocks were directly lifted by sling, lewis or devils clamp German Teufelskralle, other objects were placed before in containers like pallets, baskets, wooden boxes or barrels. It is noteworthy that medieval cranes rarely featured ratche

48、ts or brakes to forestall the load from running backward. This curious absence is explained 7 / 21 名师归纳总结 - - - - - - -第 7 页,共 21 页精选学习资料 - - - - - - - - - by the high friction force exercised by medieval treadwheels which normally prevented the wheel from accelerating beyond control. Harbor usage According to the present state of knowledge unknown in antiquity, stationary harbor cranes are considered a new development of the Middle Ages. The typical harbor crane was a pivoting