180T吨六梁桥式铸造起重机结构毕业论文.doc

毕 业 设 计（论 文）设计(论文)题目：180T六梁桥式铸造起重机结构设计大学毕业设计(任务)说明书学院（直属系）：机械电子工程学院 时间： 2009 年6月13 日学 生 姓 名指 导 教 师设计（论文）题目180吨六梁桥式铸造起重机结构设计主要研究内容载荷分析及其组合；内力计算，按照不同的载荷组合计算各危险面的内力，简化计算模型是必须考虑主、端梁之间相互约束的影响；在此基础上进行各截面的静强度、静刚度、动刚度、疲劳强度、局部稳定性和整体稳定性的验算，以及主、端梁的连接计算，最后确定结构的截面工程尺寸。研究方法在满足结构的强度，刚度，稳定性以及疲劳强度的情况下，减小结构的尺寸，做到经济性安全性最优组合。主要技术指标(或研究目标)工作级别为A8级，且为六梁结构。副主梁与副端梁的连接可采用焊接。主要参考文献1 徐克晋主编 金属结构 北京：机械工业出版社 1982.2 徐格宁主编 起重运输机金属结构设计 北京：机械工业出版社 1995.3 大连起重机器厂编 起重机设计手册 沈阳：辽宁人民出版社 1979.4 徐格宁主编 机械装备金属结构设计 普通高等教育十一五国家级规划教材 2008.95 起重机设计手册编写组 起重机设计手册 北京：机械工业出版社 1977.6 倪庆兴、王殿臣主编 起重输送机械图册 北京:机械工业出版社 1992.7 张质文、王金诺主编 起重机设计手册 北京：中国铁道出版社 1997.8 陈道楠、盛汉中主编 起重机课程设计 冶金工业出版社 1982.目录摘要IIAbstractIII前言IV第一章 总体方案设计- 1 -1.1 原始参数- 1 -1.2总体结构及设计- 1 -1.3 材料选择及许用应力- 1 -1.4各部件尺寸及截面性质- 2 -第二章 桥架分析- 10 -2.1 载荷组合的确定- 10 -2.2 桥架假定- 10 -2.3 载荷计算- 10 -2.4简化模型- 18 -2.5 垂直载荷- 19 -2.6 水平载荷- 22 -第三章 主主梁计算- 27 -3.1 强度校核- 27 -3.2 主主梁疲劳强度校核- 28 -3.3 主梁的稳定性- 30 -3.4 刚度计算- 35 -第四章 副主梁校核- 38 -4.1 强度校核- 38 -4.2 副主梁疲劳强度校核- 39 -4.3 副主梁的稳定性- 41 -4.4 刚度计算- 44 -4.5 桥架拱度- 46 -第五章 端梁校核- 48 -5.1 主主梁端部耳板设计- 48 -5.2 副主梁一侧端梁的校核- 51 -致谢- 57 -参考文献- 58 -附录A- 59 -附录B- 65 -摘要六梁铸造起重机是桥式起重机的重要组成部分，是中大型起重设备，由四根主梁和两根端梁组成。本设计采用偏轨箱型主梁，设计过程中从强度、刚度、稳定性三个方面来计算，对于A7工作级别的起重机来说还要进行疲劳强度校核，这就和A6以下工作级别的起重机的设计有了很大的区别，在设计时会出现静强度有很大的富余，在计算局部稳定性的时候还要注意局部轮压的作用，这时候需要验算加劲肋的区格验算，很有可能需要再次验算。设计中在满足刚度、强度、稳定性的前提下，探讨了该机型金属结构受力的空间传递分配规律，推导出内力计算公式。本文针对空间桥架内力的传递进行探讨，在一定假定条件下，得出主、副梁及主、端梁间的传递规律。关键词：铸造起重机,应力, 疲劳强度, 稳定性AbstractCasting six beams overhead cranes are an important component part of the medium and large lifting equipment, by the four main girder beams and two-component, the design based on the partial tracks box girder, the design process from the strength, stiffness, Stability three aspects, for the working-level A7 crane will run for calibration. This and the following working-level A6 crane design with vastly different, in the design when there are large static strength of the surplus in the calculation of regional stability but also to the partial pressure of the round, This needs time checking STIFFENER checking the grid, is likely to be checked again. The structure of the crane is composed of the primary centrol girder, the assistant centrol girder, the primary dead-end girder and the assistant dead-end girder according to the trait of the crane. On the advance of the intensity, rigidity and structure supporting the load is studied mainly. At the same time we also include the formulate which is used to calculate the internal force. Some kinds of conditions are assured in order to hold the internal relation between them.Key words: rigidity, intensity, fatigue strength, stability前言本设计为180/50t桥式铸造起重机金属结构设计，由于此桥式铸造起重机的起重量大、跨度大、工作级别高，在设计计算时疲劳强度为其首要约束条件。因此在选材时选用稳定性好，对应力集中情况不敏感的Q235-A，降低材料的成本。为减少结构的超静定次数，改善受力，同时又方便运输，桥架采用六梁铰接式结构。主、副小车的起重量均偏大，故采用偏轨箱型梁桥架。偏轨箱型梁桥架不仅可减小小车的外形尺寸，同时也增大了起升空间，有利于铸造厂间的应用。在设计时，本着满足疲劳强度、刚度、稳定性的前提下，尽可能节约材料。考虑铸造起重机主、副小车之间有一定得高度差，使副小车能自如地从主小车下面通过，故在设计主主梁时采用大截面、薄钢板，从而达到节省材料、重量轻的要求。同时采用大截面又提高了梁的刚度和稳定性。根据梁的受力特点，偏轨箱型梁主腹板上侧受局部压应力，将主腹板上侧的板加厚。而其它受力较小的地方则采用较薄的板，以节约材料。在设计过程中，全部采用国家标准，并借鉴了在实习时所参观的太原重工、大连重工起重同类产品的设计。在结构上进行改进，对桥架的受力进行了较详尽的分析。整个设计安全、可靠、节材、耐用，满足了设计要求。第一章 总体方案设计1.1 原始参数起重量Q(主/副) 180/50t跨度S 22m工作级别Ai A8起升高度H(主/副) 20/22m起升速度V(主/副) 4.5/11.4 m/min运行速度(主/副/大车) 36/33.7/73.5 m/min轮距(主/副/大车) 4080/1850/9800 mm轨距(主/副/大车) 8700/3000/22000 mm轮压(主/副/大车) 34500/19640/87600 kg起重机重量 220t1.2总体结构及设计根据已给参数，此桥式铸造起重机吨位、跨度较大，为减少结构的超静定次数，改善受力，方便运输，选用六梁铰接式结构。结构框架如图(1)图(1)1.3 材料选择及许用应力根据总体结构，铸造起重机工作级别A8为重级，工作环境温度较高，设计计算时疲劳强度为其首要约束条件，选用Q235-A，考虑起重量较大，主/副梁均采用偏轨箱型梁。材料的许用应力及性能常数见表1、表2。表1.1 材料许用应力板厚正应力剪应力mm16370152.0167.9184.487.7696.94106.5370158.8175.4192.691.7101.3111.2表1.2 材料性能常数表弹性模量E剪切弹性模量G密度1.4各部件尺寸及截面性质1. 主主梁尺寸初选高度=12941571mm考虑大车运行机构安装在主梁内，且主主梁与副主梁的高度差必须满足一定得要求，故将主主梁取为大截面薄钢板的形式，以达到节省材料、重量轻的要求。因此取腹板高度mm。为了省去走台，对宽型偏轨箱型梁，主主梁腹板内侧间距取mm=440mm。上下翼缘板厚度mm，上翼缘板长2530mm，下翼缘板长2326mm，主腹板厚度 mm，副腹板厚度 mm。上下翼缘板外伸部分长不相同。有轨道一侧上翼缘板外伸长度mm，取250mm。其它翼缘外伸部分长度 mm。mm (焊缝厚度) 取=50mm。轨道侧主腹板受局部压应力，应将板加厚，由局部压应力的分布长度，设计离上翼缘板350mm的一段腹板板厚取为18mm。主主梁跨中截面尺寸如图(2)图(2)2主主梁跨端截面尺寸高度mm要确定主主梁跨端截面尺寸，只需确定其高度，取=1300mm，跨端下翼缘板厚度为18mm。主主梁跨端截面尺寸如图(3)3截面性质(1) 主主梁跨中 建立如图示的坐标系，计算形心位置 =1256.851257mm。 =1238.881239mm 计算弯心位置mm弯心近似地在截面对称形心轴上，其至主腹板中线的距离为1021mm。净截面面积 毛截面面积 计算惯性矩 对形心轴的惯性矩对形心轴的惯性矩(2) 主主梁跨端截面性质净截面面积 毛截面面积 建立图示的坐标系，计算形心位置计算惯性矩，对形心轴的惯性矩对形心轴的惯性矩二、副主梁尺寸1. 初选梁高 =12941571mm，取腹板高度 ，上下翼缘板厚度 ，腹板厚度：主腹板 ，副腹板厚度 ，副主梁总高 副主梁宽度 ，取腹板内侧间距 且 1100，主腹板一侧上翼缘板外伸长度 ，取外伸长 ，其余悬伸长大于1.5倍的焊缝厚度，取。其尺寸如下图图(4)2. 副主梁跨端截面尺寸的确定 确定其高度 ，取腹板高度为800 副主梁跨端截面尺寸如图(5)图(5)3. 截面性质( 1) 跨中 建立图示的直角坐标系，求形心位置净截面面积 毛截面面积 计算弯心位置A 弯心距主腹板板厚中线的距离为 计算惯性矩 对形心轴的惯性矩：对形心轴的惯性矩： 副主梁跨端截面性质 建立图示的坐标系，求截面形心位置净截面面积 毛截面面积 对形心轴的惯性矩：对形心轴的惯性矩：三、端梁截面尺寸考虑大车车轮的安装及台车的形状尺寸，端梁内宽取为600。初设截面尺寸如下图 图(6)形心即对称中心 对形心轴的惯性矩：净截面面积 毛截面面积 四、各截面尺寸及性质汇总表图(7)尺寸汇总表 1.3 单位：mm主主梁跨中181814122530232622002400跨端181814122530232622001264副主梁跨中16161081270118011001500跨端1616108127011801100800端梁12121010660660600776截面性质汇总表1.4净面积毛面积主主梁跨中123912571512085351034跨端12376751216722837066副主梁跨中629782662001681244跨端62442753600904944端梁33040031360480680第二章 桥架分析2.1 载荷组合的确定一、动力效应系数的计算1起升冲击系数 0.9 对桥式铸造起重机 2起升动载系数 主主梁 副主梁 3运行冲击系数 为大车运行速度 =73.5，为轨道街头处两轨面得高度差 ，根据工作级别，动载荷用载荷组合 进行计算，应用运行冲击系数。2.2 桥架假定 为了简化六梁铰结桥架的计算，特作如下假定：1 根据起重机的实际工作情况，以主、副小车一起工作为最不利载荷工况。2 主主梁、副主梁的端部与端梁在同一水平面内。3 由于端梁用铰接分成5段，故副主梁的垂直载荷对相互间受力分析互不影响。4 将端梁结构看作多跨静定梁，主主梁受力作为基本结构对副主梁无影响；副主梁受力作为附属部分对主主梁有影响。5 计算副主梁水平载荷时，将铰接点看成刚性连接。 2.3 载荷计算1主主梁自重 由设计给出的主小车轮压34500kg，选用车轮材料ZG35CrMnSi，车轮直径，轨道型号QU120，许用值38700kg。由轨道型号QU120查得轨道理论重量，主小车轨道重量 栏杆等重量 主梁的均布载荷 2主小车布置，两侧起升机构对称布置，重心位于对称中心。吊具质量 起升载荷 小车重量 因主小车吨位较大，采用台车形式八个车轮，可求实际主小车满载时的静轮压一根主主梁上空载小车轮压 3惯性载荷一根主主梁上小车惯性力主小车上主动轮占一半，按主动车轮打滑条件确定主小车的惯性力 大车起、制动产生的惯性力4偏斜运行侧向力一根主主梁的重量为 主主梁跨端焊接上两块耳板，与副主梁端梁连接，在计算时，按假想端梁截面进行计算。图(8)与主主梁连接的端梁部分（将超出轨距的一部分所假想而成的端梁截面尺寸） 其截面尺寸如下形心 对形心轴 的惯性矩：对形心轴的惯性矩：端梁净截面积 端梁毛截面积 一根端梁单位长度重量一组大车运行机构重量 司机室及其电气设备的重量 主主梁侧假想端梁重 (1) 满载小车在主主梁跨中左侧端梁总静轮压由下图(12)计算 由 查图3-8得，侧向力为 满载小车在主主梁左端极限位置左侧端梁总静轮压为 此处省略NNNNNNNNNNNNNNNNNNNNN字起升质量 起升载荷 起升钢丝绳滑轮组的最大下放长度为 取，为吊具最小下放距离桥架跨中静位移为查选用倍率 ，由钢丝绳静拉力 选用型钢丝绳 起升钢丝绳滑轮组的静伸长 结构质量影响系数 桥式起重机的垂直自振频率4水平动刚度起重机水平动刚度以物品高位悬挂，满载小车位于桥架跨中的水平自振频率来表征。半桥架中点的换算质量为半刚架跨中在单位水平力作用下产生的水平位移为桥式起重机的水平自振频率为4.5 桥架拱度桥架跨度中央的标准拱度值考虑制造因素，实取跨度中央两边按抛物曲线 设置拱度，如下图(34)距跨中为 的点，距跨中为 的点，距跨中为 的点，第五章 端梁校核5.1 主主梁端部耳板设计计算主主梁跨端结构受力，工况：满载小车位于主梁跨端，大小车同时运行起制动及桥架偏斜。1垂直载荷主梁最大支承力 因作用点的变动引起的附加力矩为按假想端梁计算自重 计算简图(35)端梁支座反力如图，截面1-1 弯矩 剪力 截面2-2 弯矩 剪力 2水平载荷端梁的水平载荷有，亦按简支梁计算，见图(36)因作用点外移引起的附加水平弯矩为弯矩 截面1-1 剪切力 截面2-2在，水平力作用下，2-2处水平反力3主梁端部耳板设计截面性质：建立如图示坐标系校核截面2-2处腹板中轴处切应力 合格1 截面1-1处销轴所受剪应力在验算端梁完计算，见后面。5.2 副主梁一侧端梁的校核1.端梁校核载荷计算：副主梁与端梁看作是多跨静定梁的附属部分；主主梁对附属部分无影响。工况：取满载小车位于主梁跨端，大小车同时起、制动及桥架偏斜。(1) 垂直载荷主梁最大支承力 因作用点的变动引起的附加力矩为端梁自重 端梁在垂直载荷作用下按简支梁计算端梁支反力 截面1-1 截面2-2 (2) 水平载荷端梁的水平载荷有，按简支梁计算。因作用点外移引起的附加水平弯矩为先求支反力：端梁的水平反力 水平剪切力 弯矩 截面1-1剪切力 轴向力 2强度校核只需校核2-2截面截面角点处应力腹板边缘的应力翼缘板对中轴的静矩为折算应力为 3疲劳强度只考虑垂直载荷，工况：满载小车位于跨中及跨端截面2-2。满载小车在副主梁跨端时，端梁截面2-2的最大弯矩和剪切力为空载小车位于跨中时，端梁支反力下翼缘板焊缝应力根据A8及Q235，下翼缘板采用双面贴角焊缝，应力集中等级，查得 焊缝拉伸疲劳许用应力 合格按查得取拉伸疲劳许用应力 合格4稳定性整体稳定性 （稳定）局部稳定性 翼缘板 （稳定）腹板 不需设置横隔板。5校核销轴所受的力如图(40),耳板与端梁连接处销轴1、4，所受垂直方向的剪力较大，而2、3受水平方向拉力，其在垂直方向几乎不受力。只需校核受力较大的1、4销轴。设计销轴直径为对销轴 合格对支撑板的挤压应力，设支撑板厚20mm。支撑板的挤压力 合格6副主梁与端梁的连接副主梁与端梁采用连接板贴角焊缝连接，主梁两侧各用一块连接板与端梁的腹板焊接，连接板厚 ，高度 ，取主梁腹板与端梁腹板之间留有的间隙，在组装桥架时用来调整跨度。主梁翼缘板伸出梁端套装在端梁翼缘板外侧。用贴角焊缝，周边焊住，必要时在主梁端部内侧，主、端梁的上下翼缘板处焊上三角板，以增强连接的水平刚度，承受水平剪力。副主梁最大支承力 连接处需要的焊缝长度为： （合格）至此桥架设计全部合格，桥架结构施工图见附图。致谢经过近三个月的设计，我对桥式铸造起重机的设计步骤、内容和方法有了更深入的了解，同时巩固了已学的金属结构的相关知识，为以后的工作学习打下了坚实的基础。这次设计桥式铸造起重机的突出特点是工作级别高、起重量大。在设计计算时高工作级别的结构所允许的疲劳强度许用值很低，疲劳强度成为设计计算的首要约束条件，因此要重点校核疲劳强度。另一个收获就是要学会根据结构受力的特点应用材料，将材料用到该用的地方。而受力小的地方就尽可能少用材料。比如主腹板上侧受局部压应力较大，则局部加厚主腹板上侧部分，使其能够承担更大的应力。这种有针对性的设计能最大限度地节省材料，更加合理。在设计过程中，得到了学院有关领导的关心和支持，尤其是指导老师给了我们很大的帮助，在此对他们认真负责的精神和付出的辛苦表示衷心的感谢。由于时间较紧，而且我也是第一次完成这样完整的设计，由于实践经验的欠缺，在设计中一定有许多考虑不周的地方。需要在今后的学习和工作中总结提高。希望各位老师和同学批评指正。参考文献1 徐克晋主编 金属结构 北京：机械工业出版社 1982.2 徐格宁主编 起重运输机金属结构设计 北京：机械工业出版社 1995.3 大连起重机器厂编 起重机设计手册 沈阳：辽宁人民出版社 1979.4 徐格宁主编 机械装备金属结构设计 普通高等教育十一五国家级规划教材 2008.95 起重机设计手册编写组 起重机设计手册 北京：机械工业出版社 1977.6 倪庆兴、王殿臣主编 起重输送机械图册 北京:机械工业出版社 1992.7 张质文、王金诺主编 起重机设计手册 北京：中国铁道出版社 1997.8 陈道楠、盛汉中主编 起重机课程设计 冶金工业出版社 1982.9 徐格宁、智浩编 太原重型机械学院学报 1993年第4期第14卷铸造起重机桥架空间结构分析与疲劳计算 1993.10 刘鸿文主编 材料力学 高等教育出版社 2003.附录APortal powerChinas rapid economic growth in the past decade has resulted in a big increase in freight traffic through the countrys seaports . Old ports are being expanded and new ports built to handle the large growth in container and bulk cargo traffic all along the Chinese coastline.Chinas port expansion programme has provided a strong boost to the domestic port equipment industry, which has enjoyed a strong increase in demand for port cranes of various types, including container cranes and portal cranes along with bulk cargo handling equipment.State-run China Harbour Engineering (group) Corporation Ltd, established under the ruling State Council, is Chinas largest supplier of port cranes and bulk cargo handling equipment. The organization controls both Shanghai Zhenhua Port Machinery Co Ltd (ZPMC),the worlds largest manufacturer of quayside container cranes, and Shanghai Port Machinery Plant (SPMP), which specializes in the manufacturer of portal cranes and other cranes used in ports along with dry bulk cargo handling equipment.SPMPs main market is China, although the company is looking to expand its overseas sales. Although less well known than its associate ZPMC, SPMP also operates large manufacturing facilities, and is due to move part of its production shortly to Changxing Island near Shanghai where ZPMC already operates a large container crane fabrication plant.Portal and other harbour cranes are SPMPs major production item. During the past two years, the corporation has won contracts for 145 portal cranes from port authorities throughout China, both from new ports under construction and ports undergoing expansion.In recent years, SPMP has also supplied portal cranes to the United States, Iraq,and Myanmar.The port Rangoon of Myanmar in has purchased a 47m,40t portal crane while BIW of the United States has purchased three cranes-15t,150t, and 300t portal cranes. Elsewhere, SPMP has supplied 12 portal cranes to several ports in Iraq since the end of the Saddam regime. In China, SPMPs recent major orders for portal cranes include eight 40t, 45m radius cranes for Tianjin Overseas Mineral Terminal, while Yan Tai Port Bureau in Guangdong in southern China has purchased six 40t, 45m radius cranes. Other large orders include seven 10t, 25m radius cranes for Zhenjiang Port Group and an order of 1025t, 33m radius cranes from Fangcheng Port Bureau, while the Yingkou Port Group has ordered 1325t,35m radius cranes along with two 40t, 44m radius port cranes.MANY CRANES BUILT TO ORDERSPMP also supplies other cranes used in ports and harbours, many of which are built to order for clients. Quayside container cranes have been supplied to a number of foreign clients including Bangkok Port in Thailand, Kaohsiung Port in Taiwan, and Port of Vancouver in Canada. In China, SPMP has supplied quayside container cranes to Shanghai Port, Tianjin Port, Yin Kou Port, Yan Tai Port and others. The company also supplies rubber-tyred container gantry cranes to domestic and overseas clients.Customers for other cranes used in ports include Guangzhou Port in Guangdong, which purchased a 25t floating crane while Zhonggang Port has bought two double trolley 125/63t gantry cranes, along with a700t overhead crane, In 2003 Zhonggang Port awarded a contract to SPMP for a 2,600t floating crane, whichi is the largest crane the company has made in recent years.Other customers include Zhongyuan Nanytong Shipyard of Jiangsu Province has purchased two 300t goliath cranes for use in its shipyard, while Shanghai Waigaoqiao Shipyard uses two of SPMPs 600t goliath cranes for its shipbuilding operations. SPMP has two factories. The Shanghai plant employs 2,000 workers while a factory in Jiangsu Province employs 1,500 workers. The combined total of 3,500 workers includes 800 technical and management staff involved in designing, developing, and building portal and other cranes along with dry bulk cargo loading and unloading equipment.Currently, SPMP is preparing to vacate its Shanghai factory site as the companys existing plot of land is part of a riverside area earmarked by the Shanghai Expo in 2010. SPMPs Shanghai factory will close at the end of 2006, and move to a new site on nearby Changxing Island.“The new factory will be much bigger than the present plant,” Li said. “Phase 1 will be ready for us when we move at the end of 2006.”In addition to moving the Shanghai factory to a new site, SPMP expects future business operation with ZPMC.Officials at China Harbour Engineering (Group) Corporation are understood to have told SPMP of plants for SPMP and ZPMC to co-operate more in bidding for projects in future. Both companies are expected to retain their individual manufacturing capability, however, with precise details of future co-operation still some way from being finalised.Meanwhile, SPMP associate company ZPMC is strengthening its position as the worlds largest manufacturer of ship-to-shore container cranes, supplying slightly more than half the annual international container crane market. In addition to operating four crane production complexes for its crane manufacturing and other businesses.ZPMCs full range of products includes quayside container cranes, rubber-tyred gantry cranes, bulk material ship loaders and unloaders, bucket-wheel stackers and reclaimers, portal cranes, floating cranes, and engineering vessels. The company has also diversified into manufacturing other large steel structures including large steel bridges.ZPMC EXPANDING PRODUCTIONZPMCs cranes and other products are in use at over 150 shipping terminals in 37 countries and regions worldwide. By the end of December 2005, ZPMC had supplied 705 quayside container cranes, and had orders in hand to deliver another 128 quayside container cranes in 2006. In addition, at the end of 2005 ZPMC had delivered 1,148 rubber-tyred gantry cranes to customers worldwide and had orders in hand to deliver 308 rubber-tyred gantry cranes to customers in 2006.ZPMC is expanding production facilities in expectation that the volume of orders will grow in future. The company owns four crane production complexes in Shanghai and the surrounding area at Jiangyin, Changzhou, Zhangjiang and Changxing Island.The Changxing production site, which was completed in 2001, covers one million sq m, and has a 3.5km coastline. The facility is capable of manufacturing 160 quayside ship-to-shore container cranes each year along with 300 rubber-tyred gantry cranes and 200,000 metric tons of large steel bridge structures.Plans call for a futher 3 million sq m of land to be reclaimed at Changxing, which ZPMC will develop to become its largest production centre.Korea looks inward In a fragmented global port crane industry, Korean manufacturers are being forced to look for more business in their domestic markets South Koreas container crane and port crane equipment manufacturing industry has become more focused on the domestic market in recent years as manufacturers have faced tough price competition from ZPMC of China in major foreign markets. The problem is the same as that faced by other port crane manufacturers around the world, none of which account for more than about an 8% share of the world container crane market. As well as ZPMC, competition from European and Japanese equipment suppliers is also strong, both for quayside container cranes and for rubber-tyred gantry crane contracts. While South Korean firms-including Hyundai Heavy Industries, Samsung Heavy Industries, Doosan Heavy Industries, and Hanjin Heavy Industries continue to bid for international contracts, winning large orders has become increasingly rare. Doosan Heavy Industries & Construction Co Ltd is believed to be the only South Korean port crane maker to have won a large container crane contract during the past few years, with most orders booker by Korean manufacturers being for less than 10 crane units. Doosan recently completed delivery of a 42-unit rubber-tyred gantry crane (RTGC) order to the Port of Singapore Authority PSN that was awarded in 2004