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10t桥式起重机的总体结构及运行机构设计[7张CAD图纸+文档]

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摘要

　　　本次毕业设计是针对毕业实习中桥式起重机所做的具体到吨位级别的设计。我国现在应用的各大起重机还是仿造国外落后技术制造出来的，而且已经在工厂内应用了多年，有些甚至还是七八十年代的产品，无论在质量上还是在功能上都满足不了日益增长的工业需求。如何设计使其成本最低化，布置合理化，功能现代化是我们研究的课题。本次设计就是对小吨位的桥式起重机进行设计，主要设计内容是10t桥式起重机的结构及运行机构，其中包括桥架结构的布置计算及校核，主梁结构的计算及校核，端梁结构的计算及校核，主端梁连接以及大车运行机构零部件的选择及校核包括: 轮压计算及强度验算, 运行阻力计算,选择电动机,减速器的选择验算,运行速度及实际功率,选择制动器,选择联轴器,低速浮动轴的验算,缓冲器的选择等计算。还有小车的运行和起升机构零部件的选择及校核包括: 运行阻力计算，选电动机，选择减速器验算起动时间，按起动工况校核减速器功率，选择制动器，选择高速轴联轴器及制动轮，验算低速浮动轴强度，钢丝绳的选择，滑轮、卷筒的计算，联轴器的选择。

　　　关键词: 起重机；大车运行机构；小车运行结构；小车起升结构；桥架；

主端梁

Abstract

　　　The graduation design is aimed at the graduation fieldwork medium-sized crane do specific to tonnage level of design. Our country is the application of the big crane or counterfeit foreign backward technology out of manufacture and has within the plant for many years, some even application or the 70s and 80s products, both in quality and in on the function can't satisfy the growing industrial demand. How to design makes it the lowest cost, decorate rationalization, functional modernization is our topic. This design is on small tonnage design of bridge crane, the main design content is 10t bridge crane structure and operation organization, including bridge structure arrangement calculation and checking the structure of the girder, the calculation and checking, calculated and checked the beam structure, the main girders connection and cart mechanism parts selection and checking including: wheel pressure calculation and intensity checking, running friction calculation, the choice of motor, gear reducer is checked, choose speed and actual power, choose brakes, choose coupling calculating speed floating axis, buffer choice calculation, etc. And car running and lifting mechanism parts selection and checking including: running friction calculation, choose motor, choose reducer, by starting checked start-up time check reducer power, choose working brakes, choose high-speed couplings and brake wheel, the checking low-speed axial intensity, the wire rope floating choice, pulley, drum calculation, coupling choice.

　　　Keywords: cranes; During operation organization; Car running structure; Car hoisting structure; Bridge; Main girders

摘要 1

Abstract 2

前言 1

第1章桥式起重机的概述 2

1.1 桥式起重机的特点 2

1.2 桥式起重机的用途 5

1.3 桥式起重机的基本参数 5

1.4 桥式起重机主要零部件 9

1.4.1吊钩 9

1.4.2钢丝绳 11

1.4.3 滑轮和滑轮组 13

1.4.4 滑轮组类型及选配原则 14

1.5滑轮组及其滑轮组的倍率 15

1.6 卷筒 16

1.7 位置限位器 17

1.8 缓冲器 18

1.9桥式起重机发展概述 18

1.9.1 国内桥式起重机发展动向 18

1.9.2 国外桥式起重机的发展动向 19

第2章大车运行机构的设计 21

2.1大车运行结构设计的基本思路及要求 21

2.2 大车运行机构传动方案的确定 21

2.3 大车运行机构具体布置时要注意的问题 22

2.4 大车运行机构的设计计算 23

2.4.1 大车运行结构的传动方案 23

2.5轮压计算及强度验算 24

2.5.1计算大车的最大轮压和最小轮压 24

2.5.2 强度计算及校核 25

2.6 运行阻力计算 27

2.7 选择电动机 28

2.8 减速器的选择 30

2.9 验算运行速度及实际功率 30

2.10 验算启动时间 31

2.11 起动工况下校核减速器功率 33

2.12 验算起动不打滑条件 33

2.13 选择制动器 36

2.14 选择联轴器 37

2.15 低速浮动轴的验算 38

2.16 缓冲器的选择 40

第3章起升小车的计算 43

3.1 确定机构的传动方案 43

3.2小车运行机构的计算 44

3.3选择车轮与轨道并验算起强度 44

3.4运行阻力计算 46

3.5 选电动机 48

3.6 验算电动机发热条件 49

3.7 选择减速器 49

3.8 验算运行速度和实际所需功率 49

3.9验算起动时间 50

3.10 按起动工况校核减速器功率 51

3.11 验算起动不打滑条件 52

3.12 选择制动器 53

3.13 选择高速轴联轴器及制动轮 54

3.14 验算低速浮动轴强度 56

3.15 起升机构的设计参数 57

3.16 钢丝绳的选择 58

3.17 滑轮、卷筒的计算 59

3.18 根据静功率初选电动机 61

3.19 减速器的选择 61

3.20 制动器的选择 63

3.21 启动时间及启动平均加速度的验算 63

3.22 联轴器的选择 65

第4章桥架结构的设计 66

4.1 桥架的结构形式 66

4.1.1 箱形双梁桥架的构成 66

4.1.2 箱形双梁桥架的选材 66

4.2 桥架结构的设计计算 67

4.2.1 主要尺寸的确定 67

4.2.2 主梁的计算 69

4.3 端梁的计算 76

4.4 端梁的尺寸的确定 82

4.4.1 端梁总体的尺寸 82

4.4.2端梁的截面尺寸 82

第5章端梁接头的设计 83

5.1 端梁接头的确定及计算 83

5.1.1 腹板和下盖板螺栓受力计算 84

5.1.2 上盖板和腹板角钢的连接焊缝受力计算 85

5.2 计算螺栓和焊缝的强度 86

5.2.1 螺栓的强度校核 86

5.2.2 焊缝的强度校核 87

总结 91

致谢 93

参考文献 94

前言

　　　桥式起重机是横架于车间和料场上空进行物料调运的起重设备。由于它两端坐落在高大的水泥柱或金属架上，形状似桥，所以俗称“天车”。桥式起重机是现代工业和起重运输中实现生产过程机械化、自动化的重要工具与设备，可减轻操作者的劳动强度，可大大提高生产率。桥式起重机在工矿企业、钢铁化工、铁路交通、港口码头以及物流周转等部门和场所应用的最为广泛，是人们生产生活不可或缺的一种设备。

　　　随着工业的迅速发展和科学技术的不断进步，桥式起重机在结构设计及自动化程度上相继出现了一些新的变化和新的特点，在结构上，国内起重设备已采用计算机优化设计，以提高起重机的机械性能，在起重质量方面逐步向大型化发展，大型桥式起重机正在钢铁、水利、发电等行业不断出现，令人世人瞩目的三峡发电厂安装了两台1200T/125T的桥式起重机，2007年9月，起重量达2万吨的桥式起重机在山东烟台佛士船厂投入使用，它标志这我国起重机行业以达到世界先进水平。

　　　总之，随着科技的迅速发展，国内各种先进的电气控制和机械技术正逐步应用到起重机上，起重机的自动化程度越来越高，结构日趋简单，性能愈加可靠，起重量越来越大，品种也越来越全。

　　　对于起重量大、跨距大的起重设备多采用箱型双梁式，箱型双梁桥式起重机有一个由两根箱型主梁和两根横向端梁构成的双梁桥架，在桥架上运行小车，可起吊和水平搬运各类物件。它适用于机械加工和装配车间、仓库和料场等场所。箱型双梁结构具有加工零件少、工艺性好、通用性好及安装检修方便等优点，因而在生产中广泛使用。

　　　　第1章桥式起重机的概述

　　　桥式起重机是桥架型起重机的一种，主要依靠起升机构和在水平面内的两个相互垂直方向移动的运行机构，能在矩形场地及其上空作业，是工矿企业广泛使用的一种其中运输机械。它具有承载能力大、工作可靠性高、制造工艺相对简单的优点。

　　　桥式起重机一般有大车运行机构的桥架、起升机构和小车运行机构的起重小车、电气设备、司机室等机构组成，外形像一个两端支撑在平行的两条架空轨道上平移运行的单跨平板桥。起升机构用来垂直升降物品，起重小车用来带着载荷作横向移动，以达到在跨度内和规定高度内组成三维空间里做搬运和装卸货物用。

　　　桥式起重机是使用最广泛、拥有量最大的一种轨道运行式起重机，其额定起重量从及吨到几百吨。最基本的形式是通用吊钩桥式起重机，其他形式的桥式起重机都是在通用吊钩桥式起重机的基础上派生发展出来的。

1.1 桥式起重机的特点

　　　桥式起重机是横架于车间、仓库和料场上空进行物料吊运的起重设备。由于它两端坐落在高大的水泥柱上或金属支架上，形状似桥，所以俗称“天车”和“行车”。它是使用、范围最广、数量最多的一种起重机械。

桥式起重机是现代工业生产和起重运输中实现生产过程机械化、自动化的重要工具和设备，可减轻操作者的劳动强度，提高生常率。桥式起重机在工矿企业、钢铁化工、铁路交通、港口码头以及物流周转等部门

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内容简介：: 河南理工大学万方科技学院本科毕业设计（论文）中期检查表指导教师：罗静职称：副教授所在院（系）：机械与动力工程学院教研室（研究室）：题目 10t桥式起重机总体设计学生姓名牛翔专业班级08机设三班学号0828070073一、选题质量：（主要从以下四个方面填写：1、选题是否符合专业培养目标，能否体现综合训练要求；2、题目难易程度；3、题目工作量；4、题目与生产、科研、经济、社会、文化及实验室建设等实际的结合程度）1、本题目符合机械设计专业的培养目标，能够充分锻炼和培养分析问题和实际操作能力，能够体现综合训练的要求；2、本题目难易适中，符合本科毕业设计要求；3、本题目工作量适中，能在规定的时间内完成； 4、所选题目10t桥式起重机总体的设计与实际贴合比较紧密，在实际的应用中比较广泛。在设计过程中，对机器的零件的设计和计算对我来说是以往所学知识的总结和应用，所以能够满足综合训练的要求二、开题报告完成情况：根据自己在各方面资料的收集和整理，通过对可行性的分析，结合实际因素，我完成了这次设计的选题。在选题结束之后，通过自己认真查阅相关的资料，最后结合本身的实际情况和设计的时间任务完成了开题报告。三、阶段性成果：1、通过对10t桥式起重机的了解，再加上有关书籍的介绍，算是对10t桥式起重机有了一个大概的了解。前期阶段主要是对有关于10t桥式起重机的各方面的文献和资料进行搜集，为设计以后的设计做了必要的准备。 2、中期阶段主要是依据参考资料，从上面找到一些关于关于10t桥式起重机的信息，首先对其零部件有了大致的了解，其次是已有了大概的设计方法，并开始了一些基本的结构设计。3、正在进行装配图的CAD画图和设计说明书。四、存在主要问题：由于这是我第一次单独进行10t桥式起重机总体设计，所以刚开始进展的并不是很顺利。而我对这方面的知识掌握比较少，所以需要在图书馆和网上查找更多的相关资料，对有关起重机的知识进行更深入的了解。不过我坚信，只要自己努力和在指导老师的指引下，我能把各方面的问题逐个击破，最终顺利完成毕业设计。五、指导教师对学生在毕业实习中，劳动、学习纪律及毕业设计（论文）进展等方面的评语指导教师：（签名）年月日2河南理工大学万方科技学院本科毕业论文The Use and History of CraneEvery 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 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 create 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 normal 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. OverviewThe first construction cranes 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 Ages, 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 centuries, power was supplied by the physical exertion of men or animals, although hoists in watermills and windmills could be driven by the harnessed natural power. The first mechanical power was provided by steam engines, the earliest 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 manual 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 while, 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 the above definition of a crane, but are generally known as cranes, such as stacker cranes and loader cranes.2. HistoryAncient GreeceThe 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 distinctive 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 gravity, 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 a sharp drop in the weights 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 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 the 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 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 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 RomeThe heyday of the crane in ancient times came during 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 Architectura 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.The simplest Roman crane, the 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 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 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 that, 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 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 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 (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 siege tower, but with the column 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 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 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 capstans.Middle AgesDuring 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 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 before 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 cathedrals. Nevertheless, both archival and pictorial sources of the time suggest that newly introduced machines like treadwheels or wheelbarrows did not completely replace more labor-intensive methods like ladders, hods and handbarrows. Rather, 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 smooth 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 connection 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 reinvention 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.Structure and placementThe 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 arms 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 thin walls of the Gothic churches which were incapable of 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 floor 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 grew and wandered with the building with the result that today all extant construction 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 secured to putlogs.Mechanics and operationIn 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 was 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 working 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 suited 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 ratchets or brakes to forestall the load from running backward. This curious absence is explained by the high friction force exercised by medieval treadwheels which normally prevented the wheel from accelerating beyond control. Harbor usageAccording 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 structure equipped with double treadwheels. These cranes were placed docksides for the loading and unloading of cargo where they replaced or complemented older lifting methods like see-saws, winches and yards. Two different types of harbor cranes can be identified with a varying geographical distribution: While gantry cranes which pivoted on a central vertical axle were commonly found at the Flemish and Dutch coastside, German sea and inland harbors typically featured tower cranes where the windlass and treadwheels were situated in a solid tower with only jib arm and roof rotating. Interestingly, dockside cranes were not adopted in the Mediterranean region and the highly developed Italian ports where authorities continued to rely on the more labor-intensive method of unloading goods by ramps beyond the Middle Ages.Unlike construction cranes where the work speed was determined by the relatively slow progress of the masons, harbor cranes usually featured double treadwheels to speed up loading. The two treadwheels whose diameter is estimated to be 4 m or larger were attached to each side of the axle and rotated together. Today, according to one survey, fifteen treadwheel harbor cranes from pre-industrial times are still extant throughout Europe.28 Beside these stationary cranes, floating cranes which could be flexibly deployed in the whole port basin came into use by the 14th century. RenaissanceA lifting tower similar to that of the ancient Romans was used to great effect by the Renaissance architect Domenico Fontana in 1586 to relocate the 361 t heavy Vatican obelisk in Rome. From his report, it becomes obvious that the coordination of the lift between the various pulling teams required a considerable amount of concentration and discipline, since, if the force was not applied evenly, the excessive stress on the ropes would make them rupture. Early modern ageCranes were used domestically in the 17th and 18th century. The chimney or fireplace crane was used to swing pots and kettles over the fire and the height was adjusted by a trammel. 3. Mechanical principlesThere are two major considerations in the design of cranes. The first is that the crane must be able to lift a load of a specified weight and the second is that the crane must remain stable and not topple over when the load is lifted and moved to another location.Lifting capacityCranes illustrate the use of one or more simple machines to create mechanical advantage.The lever. A balance crane contains a horizontal beam (the lever) pivoted about a point called the fulcrum. The principle of the lever allows a heavy load attached to the shorter end of the beam to be lifted by a smaller force applied in the opposite direction to the longer end of the beam. The ratio of the loads weight to the applied force is equal to the ratio of the lengths of the longer arm and the shorter arm, and is called the mechanical advantage. The pulley. A jib crane contains a tilted strut (the jib) that supports a fixed pulley block. Cables are wrapped multiple times round the fixed block and round another block attached to the load. When the free end of the cable is pulled by hand or by a winding machine, the pulley system delivers a force to the load that is equal to the applied force multiplied by the number of lengths of cable passing between the two blocks. This number is the mechanical advantage. The hydraulic cylinder. This can be used directly to lift the load or indirectly to move the jib or beam that carries another lifting device. Cranes, like all machines, obey the principle of conservation of energy. This means that the energy delivered to the load cannot exceed the energy put into the machine. For example, if a pulley system multiplies the applied force by ten, then the load moves only one tenth as far as the applied force. Since energy is proportional to force multiplied by distance, the output energy is kept roughly equal to the input energy (in practice slightly less, because some energy is lost to friction and other inefficiencies).StabilityFor stability, the sum of all moments about any point such as the base of the crane must equate to zero. In practice, the magnitude of load that is permitted to be lifted (called the rated load in the US) is some value less than the load that will cause the crane to tip (providing a safety margin).Under US standards for mobile cranes, the stability-limited rated load for a crawler crane is 75% of the tipping load. The stability-limited rated load for a mobile crane supported on outriggers is 85% of the tipping load. These requirements, along with additional safety-related aspects of crane design, are established by the American Society of Mechanical Engineers in the volume ASME B30.5-2007 Mobile and Locomotive Cranes.Standards for cranes mounted on ships or offshore platforms are somewhat stricter because of the dynamic load on the crane due to vessel motion. Additionally, the stability of the vessel or platform must be considered.For stationary pedestal or kingpost mounted cranes, the moment created by the boom, jib, and load is resisted by the pedestal base or kingpost. Stress within the base must be less than the yield stress of the material or the crane will fail.4. Types of the cranesMobileMain article: Mobile craneThe most basic type of mobile crane consists of a truss or telescopic boom mounted on a mobile platform - be it on road, rail or water.FixedExchanging mobility for the ability to carry greater loads and reach greater heights due to increased stability, these types of cranes are characterized that they, or at least their main structure does not move during the period of use. However, many can still be assembled and disassembled.5. Overhead CranesUseThe most common overhead crane use is in the steel industry. Every step of steel, until it leaves a factory as a finished product, the steel is handled by an overhead crane. Raw materials are poured into a furnace by crane, hot steel is stored for cooling by an overhead crane, the finished coils are lifted and loaded onto trucks and trains by overhead crane, and the fabricator or stamper uses an overhead crane to handle the steel in his factory. The automobile industry uses overhead cranes for handling of raw materials. Smaller workstation cranes handle lighter loads in a work-area, such as CNC mill or saw.HistoryAlton Shaw, of the Shaw Crane Company, is credited with the first overhead crane, in 1874. Alliance Machine, now defunct, holds an AISE citation for one of the earliest cranes as well. This crane was in service until approximately 1980, and is now in a museum in Birmingham, Alabama. Over the years important innovations, such as the Weston load brake (which is now rare) and the wire rope hoist (which is still popular), have come and gone. The original hoist contained components mated together in what is now called the built-up style hoist. These built up hoists are used for heavy-duty applications such as steel coil handling and for users desiring long life and better durability. They also provide for easier maintenance. Now many hoists are package hoists, built as one unit in a single housing, generally designed for ten-year life or less.Notable cranes and dates1874: Alton Shaw develops the first overhead crane. 1938: Yale introduces the Cable-King hoist. 1944: Shepard-Niles supplies a hoist for lifting atomic bombs for testing in New Mexico. 1969: Power Electronics International, Inc. developed the overhead hoist variable speed drive. 1983: The worlds biggest overhead crane from Bardella Company starts its operation at Itaipu dam Hydro Power Plant Brazil. 1997: Industry giant P&H files for chapter eleven bankruptcy. Later renamed Morris Material Handling but still using the P&H tradename, they again went bankrupt. 1998: Dearborn Crane supplies two 500-ton capacity overhead cranes to Verson Press of Chicago. The cranes were never used due to Versons bankruptcy. 起重机的用途与历史每当我们看到一台正在运作的起重机，我们都会惊讶不已，这些机器有时硕大无比，能把成吨的货物提升到半空中。看到这些庞然大物的时候我们心理都带着一种惊愕，有时甚至是有一点恐惧的心情，我们会去想如果吊着着的东西掉下来了或者是起重机吊错了位置会发生什么样恐怖的事情。起重机的确是一种令人着迷的机械系统，无论是成人或者是孩子无不为止惊叹。起重机的种类五花八门，并且历史悠久。起重机是用一个或者几个简单的机器来组成一个机械结构并用于运送那些人无法搬动的物品。一般来说，起重机由一个卷筒、一束金属绳或者是一条金属链组成用来同时提升、放置或者是水平移动货物。起重机的工作领域一般是在需要装卸货物的运输业、需要搬运建材的建筑业和需要组装重型设备的制造业。1. 概况第一台具有机械结构的起重机是由古希腊人发明的，并且由人或者是牲畜比如驴，作为动力源。这种起重机被用于大型建筑的建造。这种起重机后来发展成了采用人力踏板驱动的更大型的起重机，用于提升更重的物料。中世纪时港口起重机被用来装卸船上的货物，有的港口起重机为求更大的起重重量和更好的稳定性被造在了石塔里。最早的起重机是用木头制造的，但是工业革命之后，铸铁和钢材就代替了木头用于制造起重机。尽管水磨机和风车都可以利用自然的能源来驱动，但是几个世纪以来，起重机的动力源一直是人力或者是畜力。第一台真正采用机械能量的起重机用的是蒸汽机，最早的蒸汽起重机出现于18到19世纪，有一些甚至到了20世纪末仍能很好地使用。虽然由于能源的供应仍不可及，到现在有一些人力起重机还在使用，但是现代的起重机一般采用的内燃机、电动马达、液压系统能为起重机提供比之前大得多的提升力。起重机的类型多种多样每一种都是量身定做。尺寸由最小的在车间里使用的臂式起重机到用于建造高楼的最高的塔式起重机应有尽有。然而，小型的起重机也被用来建造摩天大楼，目的是为了在高楼中狭小的空间内使用使建造更加方便。最后，我们来看看更加巨型的浮船式起重机，一般用来建造石油钻探平台和打捞沉没的船只。这篇文章也会涉及到之前没有提到，但是也非常常见的的起重机械，比如说堆垛起重机和装卸起重机。2. 历史古希腊时期用来提升重型货物的其中节是古希腊人在公元前六世纪晚期发明的。考古记录显示最早在公元前515年提升夹具和铁制的吊楔开始出现在古希腊人石块结构的神殿里。由于这些是起重设备的核心装置、也由于他们是在石块的重心的中央或者是在离重心上一点距离相等的两头被发现，他们被考古学家认为是起重机当时就存在的确凿证据。绞盘与滑轮的的引入导致了人类之前用斜坡来向高处运送货物的方法被广泛替代。在接下来的两百年中，希腊的建筑都采用了这样新型的提升物料的技术，它利用了一些小型的石块来来代替大块的石头，这样更具实用性。与更早先的古希腊人神殿的建筑材料的尺寸不断变得越来越大趋势相比较，希腊古典庙宇比如帕台农神庙的石块重量都小于1520吨。而且，要把巨型的石柱竖立起来的作业古希腊人实际上更喜欢用好几块像鼓一样的圆柱石块堆叠而成。尽管确切是何时从斜坡运输进入起重机提升技术时代的时间还不是很清楚。但是当时古希腊不稳定的社会局势、和政治情况使得建造神殿更适合雇佣小型的、更加专业的建筑团队而不是像埃及和亚述那样大量使用的没有技术的劳动力。这样的情况使得起重机更像是希腊城邦发明的而非是采用纯劳动力斜坡运送货物的埃及或是亚述那样的独裁国家。文学上第一次的明确的记载滑轮组的复合系统是出现在亚里士多德的机械难题中，但是组成文字可能还要稍晚一些。与此同时，用于建造希腊神庙的石块尺寸再一次开始赶上他们的古代前辈了，这标志着当时更多的久经考验的的滑轮组一定在希腊建筑史上找到了它们的一席之地。古罗马时期起重机械在古代的全盛时期却是在古罗马帝国展开的。当时建筑物的数量激增，而且这些建筑都达到了巨型的尺寸。罗马人采用了希腊人的起重机并将其发扬光大。多亏了那些维特鲁威工程师们撰写的相当冗长的文献和亚历山大大帝的苍鹭的巢，我们才得以如此详细地了解到了它们的其中技术。目前与Haterii的墓碑一起现存于世还有两座公元一世纪晚期、雕刻精细的古罗马脚踏式起重机的浮雕作品。三饼滑车是古罗马最简单的一种起重机，它是由一个单梁吊臂、一个绞盘、一条绳子和一个三个滑轮组成的滑轮组组成的。这样就有能够省下3倍的力。经计算，假设一个人用尽力气能够长时间地提起相当于重50千克的物体那么通过这样的起重机械他可以提升约150千克的物体（3个滑轮X50千克150千克）。更加重型的起重机就拥有五个滑轮（五饼滑车），最大型的起重机会在两根、三根甚至是四根桅杆上面装上三饼和五饼的复合滑轮组（复滑车），这是由最大的负载载荷决定的。复滑车工作的时候两边需要4个人：两边各站两个已经可以提起重约3000千克的物体（3条绳子X5个滑轮X4个人X50千克3000千克）。如果用踏车来代替绞盘的话，最大的起重载荷可以在人工减半的情况下达到两倍6000千克，因为踏车有更大的直径能够提供一个大得多的力矩。这意味着，和建造埃及金字塔时50个人才能通过斜坡搬动2.5吨的石块（50千克每人）的情况相比，罗马的复滑车的提升能力把工作的效率提高60倍（3000千克每人）。然而，大量现存的古罗马建筑中那些石块的重量比复滑车所能操作的负载要重得多。这表明古罗马人全面的起重的能力要远远任何简单的起重机。以Baalbek的Jupiter神庙为例，那些楣梁的石块每块都重达60吨以上，每个檐口的石块甚至达到了100吨以上，所有这些石料都被提升到了19m的半空中。在罗马Trajan之柱的主要石块重达53.3吨，而这些石块必须被提升到34m的高度。（见Trajian之柱）假定古罗马的建筑师们是用两种方法把这么巨型石块提起来的：第一种方法是由苍鹭之巢的暗示得来，首先一座起重塔矗立了起来，它四个桅杆以两条平行的边各一个的方式形成了一个方形的形状，不像一个围起来的塔，而是塔的中间有圆柱体。然后，大量的绞盘被放置在塔周围的地面上，因为虽然绞盘的杠杆比比踏车要低，但是绞盘可以安装在更高的地方由更多的人来驱动（此外还可以用牲畜）。这种大量绞盘的使用也被Ammianus Marcellinus记录和在Circus Maximus起升的Lateranense 方尖塔联系了起来。单个绞盘的最大起重量由在那些大石块上钻的抓取孔的数量决定。就拿Baalbek楣梁上那些重量在55到60吨的石块来说，八个明显的抓取孔表明了每个吊爪允许承受7.5吨的重量，这也是每一个绞盘所要承受的重量。以既定的动作来提升如此重量的物体需要各个施力于绞盘上的各个工作组之间有大力的协调和配合。中世纪时期在中世纪时，随着西罗马帝国的灭亡，西欧洲的科技技术水平一落千丈。这时踏车式的起重机再次被大范围地使用。最早的提到踏车式是大约1225年法国的一部档案文学作品，它在一份手稿上也说明叙述了直到1240年法国人的血统起源。在航海方面，最早使用港口起重机是在1244年的Utrecht、1263年的Antwerp、1288年的Brugge和1291年的Hamburg，而在英格兰踏车式的起重机直到1331年才有所记录。一般来说，采用起重机来垂直运输比传统的方法更加的安全和经济。典型的应用领域就包括港口、矿井。值得一提的是在哥特式大教堂的建造过程中，踏车式的起重机起到了一个不可或缺的重要作用。但是，档案和图画都显示了当时新引进的机械系统如踏车、独轮手推车等却没有完全替代那些楼梯、木桶、手推车等依赖劳动力的生产方法。这样，旧式的和新式的机械在继续在中世纪的建筑和港口共存。除了踏车，中世纪的文献中也记载了由手动驱动带幅轮和曲柄的绞盘的起重机，在15世纪时也是由卷扬机发展成为了类似船轮的系统。为了缓冲这些不规则的冲击力和解决提升过程中的死点问题，调速轮最早于1123年开始投入使用。踏车式起重机具体以何种方式再次被采用的已经无从考证，尽管它再次被使用在建筑领域是被毋庸置疑地认为和哥特式建筑的崛起有相当密切的关系。踏车式起重机的再次出现可能导致了卷扬机的技术发展，因为卷扬机在踏车式起重机的结构和机械方面都有所发展。中世纪的踏车可以看作是罗马Vitruvius De工程师设计品的一个精心改造品，它们可以在很多寺庙馆藏中看到。结构与使用地点中世纪的踏车结构是由一个木轮围绕在一根中心轴上，中心轴的两旁有足够宽的踏板以供两旁的工人踩踏。虽然以前的圆盘臂有轮辐可以直接用来驱动中心轴，但是更为先进的钩状臂更适合作为轮子边缘的弦来使用，这样可以用一个更细的轴来以供一个更大的机械利益。与常理相悖的是，中世纪建筑使用的起重机既不是安装在当时相当不可靠的脚手架上，也不是安装在哥特式教堂那纤细的墙上，那种墙不足以支撑起重机械和载荷的重量。当时的起重机是被安装在建筑物最初的底台上的，经常是在建筑物的内部。每当新的一层建成后，屋顶厚重的横梁和墙连在了一起，起重机被拆卸然后在那些在拱顶建造期间一根一根被搬运上来的顶梁上。这样，起重机就跟着建筑物一起升高和移动，这也是英格兰现存的建筑用起重机都是在保存在教堂的圆顶之上屋顶之下的原因，因为它们是建造完工后保留下来用来起吊屋顶维修的材料的。技巧与操作与现代的起重机相比，中世纪的起重机更像它们在希腊和罗马的祖先，它们主要的用途仅是用于垂直地起吊物体而不同时用于水

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