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徐州工程学院毕业设计（论文）任务书 机电工程 学院 机械设计制造及自动化 专业设计（论文）题目 随车起重机下车设计 学 生 姓 名 陆卫杰 班 级 04机本4班 起 止 日 期 2008.2.252008.6.2 指 导 教 师 李清伟 教研室主任 李志 发任务书日期 2008 年 2 月 25 日1.毕业设计的背景： 本课题来源于模拟生产实际,属于工程应用。起重机是当代最为得力的起重设备之一。随着国民经济的不断发展,多种类型的起重机广泛的运用于冶金、矿山、水泥、码头、化工、粮食等行业的各种场合。同时在各种场合对不同的工况所使用的起重机也不尽相同，近年来由于起重机的应用范围的扩大，品种的增多以及质量的不断提高， 对加工设计起重机提出了更高的要求。2.毕业设计(论文)的内容和要求：根据随车起重机的结构和特点，重点对随车起重机下车各部分进行了设计和计算；回转部分采用液压马达驱动回转支撑实现，回转机构的液压控制系统设置了双向液压锁，支腿机构通过水平液压缸和垂直液压缸实现各支腿的收缩动作，采用并联控制系统实现各支腿的同时动作。3.主要参考文献：1 朱文坚，黄平，吴昌林.机械设计M.北京：高等教育出版社，2005.2谢开泉.前置式随车起重运输汽车的总体设计J.广西机械，2000，(3):33-36.3徐斌.QY25型随车起重机设计D.大连理工大学，2004.4 哈尔滨建筑学院.工程起重机M.哈尔滨：中国建筑工业出版社，1981.5徐新才.机械设计手册M.北京：机械工业出版社，1992.4.毕业设计(论文)进度计划(以周为单位)：起 止 日 期工 作 内 容备 注第一周第二周第三周第四周第五周第六周第七周第八周第九周第十周第十一周第十二周第十三周第十四周第十五周第十六周调研、查阅相关文献，收集资料。调研、查阅相关文献，收集资料。综合分析文献资料，提出并论证下车整体设计方案计算并确定支腿的跨距和支撑形式。设计起重臂的回转方式。设计回转台结构并绘制其结构图。设计回转台结构并绘制其结构图。设计支腿结构并绘制其结构图。设计支腿结构并绘制其结构图。确定下车液压系统整体结构，绘制下车液压系统原理图。根据下车液压系统与原理图，计算选择液压原件。根据下车液压系统与原理图，计算选择液压原件。绘制下车装配图，并根据装配图修改完善回转台和支腿的结构图绘制下车装配图，并根据装配图修改完善回转台和支腿的结构图整理图纸资料，撰写毕业论文。整理图纸资料，撰写毕业论文。教研室审查意见： 室主任 年 月 日学院审查意见： 教学院长 年 月 日徐州工程学院毕业设计（论文）开题报告课 题 名 称： 随车起重机下车设计 学 生 姓 名： 陆卫杰 学号： 20040601418指 导 教 师： 李清伟 职称： 讲师 所 在 学 院： 机电工程学院 专 业 名 称： 机械设计制造及自动化 徐州工程学院2008 年 3月 4 日说 明1根据徐州工程学院毕业设计(论文)管理规定，学生必须撰写毕业设计（论文）开题报告，由指导教师签署意见、教研室审查，学院教学院长批准后实施。2开题报告是毕业设计（论文）答辩委员会对学生答辩资格审查的依据材料之一。学生应当在毕业设计（论文）工作前期内完成，开题报告不合格者不得参加答辩。3毕业设计开题报告各项内容要实事求是，逐条认真填写。其中的文字表达要明确、严谨，语言通顺，外来语要同时用原文和中文表达。第一次出现缩写词，须注出全称。4本报告中，由学生本人撰写的对课题和研究工作的分析及描述，没有经过整理归纳，缺乏个人见解仅仅从网上下载材料拼凑而成的开题报告按不合格论。5. 课题类型填：工程设计类；理论研究类；应用（实验）研究类；软件设计类；其它。6、课题来源填：教师科研；社会生产实践；教学；其它课题名称随车起重机上车设计课题来源模拟生产实际课题课题类型工程应用选题的背景及意义本课题来源于模拟生产实际,属于工程应用。起重机是当代最为得力的起重设备之一。随着国民经济的不断发展,多种类型的起重机广泛的运用于冶金、矿山、水泥、码头、化工、粮食等行业的各种场合。同时在各种场合对不同的工况所使用的起重机也不尽相同，近年来由于起重机的应用范围的扩大，品种的增多以及质量的不断提高，对加工设计起重机提出了更高的要求。研究内容拟解决的主要问题通过分析和计算确定随车起重机下车支腿的支撑形式及其跨距，设计起重臂的回转形式，设计支腿的结构以及回转部分的结构。设计随车起重机下车支腿水平伸缩、起重臂回转所需的下车液压系统。并且根据下车液压系统需要，计算选择合适的泵、油缸及阀等液压元件。研究方法技术路线研究了随车起重机的结构和特点，重点对随车起重机下车的各部分进行了设计与计算；回转部分采用液压马达驱动回转支承实现，回转机构的液压控制系统设置了双向液压锁，支腿机构通过水平液压缸和垂直液压缸实现各支腿的收缩动作，采用并联控制系统实现各支腿的同时动作。研究的总体安排和进度计划第一周：调研、查阅相关文献，收集资料。第二周；调研、查阅相关文献，收集资料。第三周：综合分析文献资料，提出并论证下车整体设计方案第四周：计算并确定支腿的跨距和支撑形式。第五周：设计起重臂的回转方式。第六周：设计回转台结构并绘制其结构图。第七周：设计回转台结构并绘制其结构图。第八周：设计支腿结构并绘制其结构图。第九周：设计支腿结构并绘制其结构图。第十周：确定下车液压系统整体结构，绘制下车液压系统原理图。第十一周：根据下车液压系统与原理图，计算选择液压原件。第十二周：根据下车液压系统与原理图，计算选择液压原件。第十三周：绘制下车装配图，并根据装配图修改完善回转台和支腿的结构图第十四周：绘制下车装配图，并根据装配图修改完善回转台和支腿的结构图第十五周：整理图纸资料，撰写毕业论文。第十六周：整理图纸资料，撰写毕业论文。主要参考文献湖北汽车学院.随车起重机新机型D.湖北：中国汽车工业出版社，2003.谢开泉.前置式随车起重运输汽车的总体设计J.广西机械，2000，(3):33-36.徐斌.QY25型随车起重机设计D.大连理工大学，2004.徐新才.机械设计手册M.北京：机械工业出版社，1992.朱宏涛.液压与气压传动M.北京：清华大学出版社，2005.杜国森.液压元件产品样本M.北京：机械工业出版社，2000.顾迪民.工程起重机M.北京：中国建筑工业出版社，1981.Charles.Wilson.Kinematics and Dynamics of MachineryJ.New York,2000， (6):120-132.指导教师意 见 指导教师签名： 年 月 日 教研室意见学院意见教研室主任签名：年 月 日 教学院长签名： 年 月 日徐州工程学院毕业设计摘 要随着现代科学技术的迅速发展，起重机在现代化生产过程中应用越来越广。本文首先介绍了随车起重机的结构和特点，重点对随车起重机下车的各部分进行了设计；回转机构采用液压马达驱动回转支承实现，回转机构的液压控制系统设置了缓冲阀，可以实现自由滑转和平稳微动；支腿机构通过水平液压缸和垂直液压缸实现各支腿的收缩动作，采用并联控制系统实现各支腿的同时动作。具体内容主要包括：1支腿的选型与跨距的确定,稳定性的校核与验算。2回转机构的设计,支承装置的选型与计算.3液压系统的设计以及液压元件的选择。本设计的主要特点是：机构简单,节省投资，控制方便。对确定中、小随车起重机设计具有一定的参考价值。关键词：随车起重机；回转机构；支腿 ；液压系统AbstractWith the rapid development of the science and technology, the truck crane is widely used in the modernization production process.In the article, the structure of the truck crane is briefly introduced, The second part is designed:The pump is used to drive the rotation structure and the dead value is used in the hydraulic system in order to rotate steadily;The level and vertical hydraulic cylinder are used to drive the support legs.This design main content includes:1.The design of the type and span of the legs and the checkout of the stability;2.The design of rotation structure and its type;3.The design of hydraulic system and the choice of the hydraulicunits.The advantage of the design is simple structure and operation. It can help to design truck crane.Keywords： truck crane ; rotation fulcrum arrangement ; Leg；Hydraulic system目 录1 绪论11.1概论11.2随车起重机市场的发展水平和趋势11.3随车起重机的数字化简介22 随车起重机的技术参数42.1主要性能参数42.2参数确定53 支腿型式选择与计算63.1支腿型式分类及选择63.2 支腿跨距确定63.3支腿受力分析73.4活动支腿危险截面计算84 底盘类型与选择94.1汽车起重机底盘分类94.2底盘选择和承载力计算104.2.1底盘选择104.2.2起重车轴载质量分配105 起重车稳定性计算135.1起重车最不利工况135.2起运车最不利工况位置的整车质量145.3动稳定性校核计算145.4静稳定性校核计算176 回转机构设计196.1工况及载荷196. 2 回转支承选型及强度验算196.2.1回转支承选型196.2.2回转支撑强度验算216.2.3回转支撑联接螺栓计算216.3回转机构的设计226.3.1回转机构的类型226.3.2回转机构的布置型式选择226.3.3回转机构驱动装置设计227 液压系统原理设计及液压原件选择287. 1液压系统型式287.1.1开式和闭式系统287.1.2单泵和多泵系统287. 2液压系统的控制297.2.1定量节流控制系统297.2.2变量系统307.3下车液压系统设计307.4液压缸的选择337.4.1缸体与缸盖连接结构337.4.2活塞与活塞杆连接结构337.4.3活塞杆头部结构：337.4.4导向套结构337.4.5密封与防尘结构337.4.6缓冲结构337.4.7垂直液压缸的选择347.4.8水平液压缸的选择357.4.9液压缸主要零部件材料及技术要求367.5其他液压元件的选择367.6液压系统性能验算37结论40致谢41参考文献42附录43附录一43英文原文43中文翻译59 4 徐州工程学院毕业设计附录附录一英文原文Hydraulic Conductors and FittingsEric Sandgren *, T.M. Cameronto account for uncertainty aMechanical Engineering, Virginia Commonwealth University, 601 West Main Street, P .O. Box843015, Richmond, VA 23284-3015, USA Received 19 October 2001;accepted 5 June 20021.1 INTRODUCTIONIn a hydraulic system, the fluid flows through a distribution system consisting of conductors and fittings, which carry the fluid from the reservoir through operating components and back to the reservoir. Since power is transmitted throughout the system by means of these conducting lines (conductors and fittings used to connect system components), it follows that they must be properly designed in order for the total system to function properly.Hydraulic systems use primarily four types of conductors:1.Steel pipes2.Steel tubing3.Plastic tubing4.Flexible hosesThe choice of which type of conductor to use depends primarily on the systems operating pressures and flow rates. In addition, the selection depends on environmental conditions such as the type of fluid, operating temperatures, vibration, and whether or not there is relative motion between connected components.Conducting lines are available for handling work pressures up to 10,000 Pa or greater. In general, steel tubing provides greater plumbing flexibility and neater appearance and requires fewer fittings than piping. However, piping is less expensive than steel tubing. Plastic tubing is finding increased industrial usage because it is not costly and circuits can be very easily hooked up due to its flexibility. Flexible hoses are used primarily to connect components that experience relative motion. They are made from a large number of elastomeric (rubberlike) compounds and are capable of handling pressures exceeding 10,000 Pa.Stainless steel conductors and fittings are used if extremely corrosive environments are expected. However, they are very expensive and should be used only if necessary. Copper conductors should not be used in hydraulic systems because the copper promotes the oxidation of petroleum oils. Zinc, magnesium, and cadmium conductors should not be used either because they are rapidly corroded by water-glycol fluids. Galvanized conductors should also be avoided because the galvanized surface has a tendency to flake off into the hydraulic fluid. When using steel pipe or steel tubing, hydraulic fittings should be made of steel except for inlet, return, and drain lines, where malleable iron may be used.Conductors and fittings must be designed with human safety in mind. They must be strong enough not only to withstand the steady-state system pressures but also the instantaneous pressure spikes resulting from hydraulic shock. Whenever control valves are closed suddenly, this stops the fluid, which possesses large amounts of kinetic energy. This produces shock waves whose pressure levels can be two or four times the steady-state system design values. Pressure spikes can also be caused by sudden stopping or starting of heavy loads. These high-pressure pulses are taken into account by the application of an appropriate factor of safety.1.2 CONDUCTOR SIZING FOR FLOW-RATE REQUIREMENTSA conductor must have a large enough cross-sectional area to handle the flow-rate requirements without producing excessive fluid velocity. Whenever we speak of fluid velocity in a conductor such as a pipe, we are referring to the average velocity. The concept of average velocity is important since we know that the velocity profile is not constant. As shown in Chapter 5 the velocity is zero at the pipe wall and reaches a maximum value at the centerline of the pipe. The average velocity is defined as the volume flow rate divided by the pipe cross-sectional area: In other words, the average velocity is that velocity which when multiplied by the pipe area equals the volume flow rate. It is also understood that the term diameter by itself always means inside diameter and that the pipe area is that area that corresponds to the pipe inside diameter. The maximum recommended velocity for pump suction lines is 4 ft/s (1.2 m/s) in order to prevent excessively low suction pressures and resulting pump cavitation. The maximum recommended velocity for pressure lines is 20 ft/s (6.1 m/s) in order to prevent turbulent flow and the corresponding excessive head losses and elevated fluid temperatures. Note that these maximum recommended values are average velocities.EXAMPLE 1-1A pipe handles a flow rate of 30 gprn. Find the minimum inside diameter that will provide an average fluid velocity not to exceed 20 ft/s.Solution Rewrite Eq. (3-26), solving for D:EXAMPLE 1-2A pipe handles a flow rate of 0.002. Find the minimum inside diameter that will provide an average fluid velocity not to exceed 6.1 m/s.Solution Per Eq. 3-35) we solve for the minimum required pipe flow area:The minimum inside diameter can now be found, becauseSolving for D we have1.3 PRESSURE RATING OF CONDUCTORS Tensile StressA conductor must be strong enough to prevent bursting due to excessive tensile stress (called hoop stress) in the wall of the conductor under operating fluid pressure. The magnitude of this tensile stress, which must be sustained by the conductor material, can be determined by referring to Figure 4-1. In Fig. 4-1(a), we see the fluid pressure ( P ) acting normal to the inside surface of a circular pipe having a length (L). The pipe has outside diameter D0 , inside diameter Di, and wall thickness t. Because the fluid pressure acts normal to the pipes inside surface, a pressure force is created that attempts to separate one half of the pipe from the other half.Figure 4-1(b) shows this pressure forcepushing downward on the bottom half of the pipe. To prevent the bottom half of the pipe from separating from the upper half, the upper half pulls upward with a total tensile force F. One-half of this force ( or F/2 ) acts on the cross-sectional area (tL) of each wall, as shown.Since the pressure force and the total tensile force must be equal in magnitude, we havewhere A is the projected area of the lower half-pipe curved-wall surface onto a horizontal plane. Thus, A equals the area of a rectangle of width Di and length L, as shown in Figure 4-1(b). Hence,The tensile stress in the pipe material equals the tensile force divided by the wall cross-sectional area withstanding the tensile force. This stress is called a tensile stress because the force (F) is a tensile force (pulls on the area over which it acts).Substituting variables we have where = Greek symbol (sigma) = tensile stress.As can be seen from Eq. (4-2), the tensile stress increases as the fluid pressure increases and also as the pipe inside diameter increases. In addition, as expected, the tensile stress increases as the wall thickness decreases, and the length of the pipe does not have any effect on the tensile stress.Burst Pressure and Working PressureThe burst pressure (BP) is the fluid pressure that will cause the pipe to burst. This happens when the tensile stress () equals the tensile strength ( S ) of the pipe material. The tensile strength of a material equals the tensile stress at which the material ruptures. Notice that an axial scribe line is shown on the pipe outer wall surface in Fig. 4-1(a). This scribe line shows where the pipe would start to crack and thus rupture if the tensile stress reached the tensile strength of the pipe material. This rupture will occur when the fluid pressure (P) reaches BR Thus, from Eq. (4-2) the burst pressure is The working pressure (WP) is the maximum safe operating fluid pressure and is defined as the burst pressure divided by an appropriate factor of safety (FS). A factor of safety ensures the integrity of the conductor by determining the maximum safe level of working pressure. Industry standards recommend the following factors of safety based on corresponding operating pressures:FS = 8 for pressures from 0 to 1000 PaFS = 6 for pressures from 1000 to 2500 PaFS = 4 for pressures above 2500 PaFor systems where severe pressure shocks are expected, a factor of safety of 10 is recommended.Conductor Sizing Based on Flow Rate and Pressure ConsiderationsThe proper size conductor for a given application is determined as follows:1. Calculate the minimum acceptable inside diameter (Di) based on flow-rate requirements.2. Select a standard-size conductor with an inside diameter equal to or greater than the value calculated based on flow-rate requirements.3. Determine the wall thickness (t) of the selected standard-size conductor using the following equation: 4. Based on the conductor material and system operating pressure (P), determine the tensile strength (S) and factor of safety (FS).5. Calculate the burst pressure (BP) and working pressure (WP) using Eqs. (1.3) and (1.4).6. If the calculated working pressure is greater than the operating fluid pressure, the selected conductor is acceptable. If not, a different standard-size conductor with a greater wall thickness must be selected and evaluated. An acceptable conductor is one that meets the flow-rate requirement and has a working pressure equal to or greater than the system operating fluid pressure.The nomenclature and units for the parameters of Eqs. (1.2), (1.3), (1.4), and （1.5) are as follows:BP = burst pressure (Pa, MPa)Di = conductor inside diameter (in., m)D0 = conductor outside diameter (in., m)FS = factor of safety (dimensionless)P = system operating fluid pressure (Pa, MPa)S = tensile strength of conductor material (Pa, MPa)t = conductor wall thickness (in., m)WP = working pressure (Pa, MPa)= tensile stress (Pa, MPa)EXAMPLE 1-3A steel tubing has a 1.250-in, outside diameter and a 1.060-in, inside diameter. It is made of SAE 1010 dead soft cold-drawn steel having a tensile strength of 55.000 Pa. What would he the safe working pressure for this tube assuming a factor of safety of 8?Solution First, calculate the wall thickness of the tubing:Next, find the burst pressure for the tubing:Finally, calculate the working pressure at which the tube can safely operate:Use of Thick-Walled ConductorsEquations (1.2) and (1.3) apply only for thin-walled cylinders where the ratio Di / t is greater than 10. This is because in thick-walled cylinders (Di / t 10), the tensile stress is not uniform across the wall thickness of the tube as assumed in the derivation of Eq. (1.2). For thick-walled cylinders Eq. (1.6) must be used to take into account the nonuniform tensile stress, 式（1.6）Thus, if a conductor being considered is not a thin-walled cylinder, the calculations must be done using Eq. (1.6). As would be expected, the use of Eq. (1.6) results in a smaller value of burst pressure and hence a smaller value of working pressure than that obtained from Eq. (1.3). This can be seen by comparing the two equations and noting the addition of the 1.2t term in the denominator of Eq. (1.6).Note that the steel tubing of Example 1.3 is a thin-walled cylinder because = 1.060 in./0.095 in. =11.2 10. Thus, the steel tubing of Example 1.3 can operate safely with a working pressure of 1230 Pa as calculated using a factor of safety of 8. Using Eq. (1.6) for this same tubing and factor of safety yieldsAs expected the working pressure of 1110 Pa calcu1ated using Eq. (1.6) is less than the 1230 Pa value calculated in Example 4-3 using Eq. (1.3).1.4 STEEL PIPESSize DesignationPipes and pipe fittings are classified by nominal size and schedule number, as illustrated in Fig. 4-2. The schedules provided are 40, 80, and 160, which are the ones most commonly used for hydraulic systems. Note that for each nominal size the outside diameter does not change. To increase wall thickness the next larger schedule number is used. Also observe that the nominal size is neither the outside nor the inside diameter. Instead, the nominal pipe size indicates the thread size for the mating connections. The pipe sizes given in Fig. 4-2 are in units of inches.Figure 4-3 shows the relative size of the cross sections for schedules 40, 80, and 160 pipes. As shown for a given nominal pipe size, the wall thickness increases as the schedule number increases.Thread Design Pipes have tapered threads, as opposed to tube and hose fittings, which have straight threads. As shown in Fig. 4-4, the joints are sealed by an interference fit between the male and female threads as the pipes are tightened. This causes one of the major problems in using pipe. When a joint is taken apart, the pipe must be tightened farther to reseal. This frequently requires replacing some of the pipe with slightly longer sections, although this problem has been overcome somewhat by using Teflon tape to reseal the pipe joins. Hydraulic pipe threads are the dry-seal type. They differ from standard pipe threads because they engage the roots and crests before the flanks. In this way, spiral clearance is avoided.Pipes can have only male threads, and they cannot be bent around obstacles. There are, of course, various required types of fittings to make end connections and change direction, as shown in Fig. 4-5. The large number of pipe fittings required in a hydraulic circuit presents many opportunities for leakage, especially as pressure increases. Threaded-type fittings are used in sizes up to in. in diameter. Where larger pipes are required, flanges are welded to the pipe, as illustrated in Fig. 4-6. As shown, flat gaskets or 0-rings are used to seal the flanged fittings.1.5 STEEL TUBINGSize DesignationSeamless steel tubing is the most widely used type of conductor for hydraulic systems as it provides significant advantages over pipes. The tubing can be bent into almost any shape, thereby reducing the number of required fittings. Tubing is easier to handle and can be reused without any sealing problems. For low-volume systems, tubing can handle the pressure and flow requirements with less bulk and weight. However, tubing and its fittings are more expensive. A tubing size designation always refers to the outside diameter. Available sizes include-in. increments from -in. outside diameter up to -in. outside diameter. For sizes from-in. to 1 in. the increments are -in. For sizes beyond 1 in., the increments are-in. Figure 4-7 shows some of the more common tube sizes (in units of inches) used in fluid power systems.SAE 1010 dead soft cold-drawn steel is the most widely used material for tubing. This material is easy to work with and has a tensile strength of 55,000 Pa. If greater strength is required, the tube can be made of AISI 4130 steel, which has a tensile strength of 75,000 Pa.Tube FittingsTubing is not sealed by threads but by special kinds of fittings, as illustrated in Fig. 4-8. Some of these fittings are known as compression fittings. They seal by metal-to-metal contact and may be either the flared or flareless type. Other fittings may use 0-rings for sealing purposes. The 370 flare fitting is the most widely used fitting for tubing that can be flared. The fittings shown in Fig. 4-8(a) and (b) seal by squeezing the flared end of the tube against a seal as the compression nut is tightened. A sleeve inside the nut supports the tube to dampen vibrations. The standard 450 flare fitting is used for very high pressures. It is also made in an inverted design with male threads on the compression nut. When the hydraulic component has straight thread ports, straight thread 0-ring fittings can be used, as shown in Fig. 4-8(c). This type is ideal for high pressures since the seal gets tighter as pressure increases.Two assembly precautions when using flared fittings are:1.The compression nut needs to be placed on the tubing before flaring the tube.2. These fittings should not be over-tightened. Too great a torque damages the sealing surface and thus may cause leaks.For tubing that cant be flared, or if flaring is to be avoided, ferrule, 0-ring, or sleeve compression fittings can be used see Fig. 4-8(d), (e), (f). The O-ring fitting permits considerable variations in the length and squareness of the tube cut.Figure 4-9 shows a Swagelok tube fitting, which can contain any pressure up to the bursting strength of the tubing without leakage. This type of fitting can be repeatedly taken apart and reassembled and remain perfectly sealed against leakage. Assembly and disassembly can be done easily and quickly using standard tools. In the illustration, note that the tubing is supported ahead of the ferrules by the fitting body. Two ferrules grasp tightly around the tube with no damage to the tube wall. There is virtually no constriction of the inner wall, ensuring minimum flow restriction. Exhaustive tests have proven that the tubing will yield before a Swagelok tube fitting will leak. The secret of the Swagelok fitting is that all the action in the fitting moves along the tube axially instead of with a rotary motion. Since no torque is transmitted from the fitting to the tubing, there is no initial strain that might weaken the tubing. The double ferrule interaction overcomes variation in tube materials, wall thickness, and hardness.In Fig. 4-10 we see the 450 flare fitting. The flared-type fitting was developed before the compression type and for some time was the only type that could successfully seal against high pressures.Four additional types of tube fittings are depicted in Fig. 4-11: (a) union elbow, (b) union tee, (c) union, and (d) 45 male elbow. With fittings such as these, it is easy to install steel tubing as well as remove it for maintenance purposes.EXAMPLE 1-4Select the proper size steel tube for a flow rate of 30 gpm and an operating pressure of 1000 Pa. The maximum recommended velocity is 20 ft/s, and the tube material is SAE 1010 dead soft cold-drawn steel having a tensile strength of 55,000 Pa,Solution The minimum inside diameter based on the fluid velocity limitation of 20 ft/s is the same as that found in Example 4-1 (0.782 in.).From Fig. 4-7, the two smallest acceptable tube sizes based on flow-rate requirements are1-in. od , 0.049-in, wall thickness, 0.902-in. ID1-in. od , 0.065-in, wall thickness, 0,870-in. IDLets check the 0.049-in, wall thickness tube first since it provides the smaller velocity:This working pressure is not adequate, so lets next examine the 0.065-in, wall thickness tube:This result is acceptable, because the working pressure of 1030 Pa is greater than the system-operating pressure of 1000 Pa and10.1.6 PLASTIC TUBINGPlastic tubing has gained rapid acceptance in the fluid power industry because it is relatively inexpensive. Also, it can be readily bent to fit around obstacles, it is easy to handle, and it can be stored on reels. Another advantage is that it can be color-coded to represent different parts of the circuit because it is available in many colors. Since plastic tubing is flexible, it is less susceptible to vibration damage than steel tubing.Fittings for plastic tubing are almost identical to those designed for steel tubing. In fact many steel tube fittings can be used on plastic tubing, as is the case for the Swagelok fitting of Fig. 4-9. In another design, a sleeve is placed inside the tubing to give it resistance to crushing at the area of compression, as illustrated in Fig. 4-12. In this particular design (called the Poly-Flo Flareless Tube Fitting), the sleeve is fabricated onto the fitting so it cannot be accidentally left off.Plastic tubing is used universally in pneumatic systems because air pressures are low, normally less than 100 Pa. Of course, plastic tubing is compatible with most hydraulic fluids and hence is used in low-pressure hydraulic applications.Materials for plastic tubing include polyethylene, polyvinyl chloride, polypropylene, and nylon. Each material has special properties that are desirable for specific applications. Manufacturers catalogs should be consulted to determine which material should be used for a particular application.1.7 FLEXIBLE HOSESDesign and Size DesignationThe fourth major type of hydraulic conductor is the flexible hose, which is used when hydraulic components such as actuators are subjected to movement. Examples of this are found in portable power units, mobile equipment, and hydraulically powered machine tools. Hose is fabricated in layers of elastomer (synthetic rubber) and braided fabric or braided wire, which permits operation at higher pressures.As illustrated in Fig. 4-13, the outer layer is normally synthetic rubber and serves to protect the braid layer. The hose can have as few as three layers (one being braid) or can have multiple layers to handle elevated pressures. When multiple wire layers are used, they may alternate with synthetic rubber layers, or the wire layers may be placed directly over one another.Figure 4-14 gives some typical hose sizes and dimensions for single-wire braid and double-wire braid designs. Size specifications for a single-wire braid hose represent the outside diameter in sixteenths of an inch of standard tubing, and the hose will have about the same inside diameter as the tubing. For example, a size 8 single-wire braid hose will have an inside diameter very close to a-in. standard tubing. For double-braided hose, the size specification equals the actual inside diameter in sixteenths of an inch. For example, a size 8 double-wire braid hose will have a-in. inside diameter. The minimum bend radii values provide the smallest values for various hose sizes to prevent undue strain or flow interference.Figure 4-15 illustrates five different flexible hose designs whose constructions are described as follows:a. FC 194: Elastomer inner tube, single-wire braid reinforcement, and elastomer cover Working pressures vary from 375 to 2750 Pa depending on the size.b.FC195: Elastomer inner tube, double-wire braid reinforcement, and elastomer cover. Working pressures vary from 1125 to 5000 Pa depending on the size.c.FC 300: Elastomer inner tube, polyester inner braid, single-wire braid reinforcement, and polyester braid cover. Working pressures vary from 350 to 3000 Pa depending on the size.d.1525: Elastomer inner tube, textile braid reinforcement, oil and mildew resistant, and textile braid cover. Working pressure is 250 Pa for all sizes.e.2791: Elastomer inner tube, partial textile braid, four heavy spiral wire reinforcements, and elastomer cover. Working pressure is 2500 Pa for all sizes.Hose FittingsHose assemblies of virtually any length and with various end fittings are available from manufacturers. See Fig. 4-16 for examples of hoses with the following permanently attached end fittings: (a) straight fitting, (b) 45 elbow fitting, and (c) 90 elbow fitting.The elbow-type fittings allow access to hard-to-get-at connections. They also permit better flexing and improve the appearance of the system.Figure 4-17 shows the three corresponding reusable-type end fittings. These types can be detached from a damaged hose and reused on a replacement hose. The renewable fittings idea had its beginning in 1941. With the advent of World War II, it was necessary to get aircraft with failed hydraulic lines back into operation as quickly as possible.Hose Routing and InstallationCare should be taken in changing fluid in hoses since the hose and fluid materials must be compatible. Flexible hose should be installed so there is no kinking during operation of the system. There should always be some slack to relieve any strain and allow for the absorption of pressure surges. It is poor practice to twist the hose and use long loops in the plumbing operation. It may be necessary to use clamps to prevent chafing or tangling of the hose with moving parts. If the hose is subject to rubbing, it should be encased in a protective sleeve. Figure 4-18 gives basic information on hose routing and installation procedures.1.8 QUICK DISCONNECT COUPLINGSOne additional type of fitting is the quick disconnect coupling used for both plastic tubing and flexible hose. It is used mainly where a conductor must be disconnected frequently from a component. This type of fitting permits assembly and disassembly in a matter of a second or two. The three basic designs are:1. Straight through: This design offers minimum restriction to flow but does not prevent fluid loss from the system when the coupling is disconnected.2.One-way shutoff: This design locates the shutoff at the fluid source connection but leaves the actuator component unblocked. Leakage from the system is not excessive in short runs, but system contamination due to the entrance of dirt in the open end of the fitting can be a problem, especially with mobile equipment located at the work site.3.Two-way shutoff: This design provides positive shutoff of both ends of pressurized lines when disconnected. See Fig. 4-19 for a cutaway of this type of quick disconnect coupling. Figure 4-20 shows an external view of the same coupling. Such a coupling puts an end to the loss of fluids. As soon as you release the locking sleeve, valves in both the socket and plug close, shutting off flow. When connecting, the plug contacts an 0-ring in the socket, creating a positive seal. There is no chance of premature flow or waste due to a partial connection. The plug must be fully seated in the socket before the valves will open.1.9 METRIC STEEL TUBINGIn this section we examine common metric tube sizes and show how to select the proper size tube based on flow-rate requirements and strength considerations.Figure 4-21 shows the common tube sizes used in fluid power systems. Note that the smallest od size is 4 mm (0.158 in.), whereas the largest od size is 42 mm (1.663 in.). These values compare to 0.125 in. and 1.500 in., respectively, from Fig. 4-7 for common English units tube sizes. It should be noted that since 1 m = 39.6 in. then 1 mm = 0.0396 in.Factors of safety based on corresponding operating pressures becomeFS = 8 for pressures from 0 to 1000 Pa (0 to 7 MPa or 0 to 70 bars)FS = 6 for pressures from 1000 to 2500 Pa (7 to 17.5 MPa or 70 to 175 bars)FS = 4 for pressures above 2500 Pa (17.5 MPa or 175 bars)The corresponding tensile strengths for SAE 1010 dead soft cold-drawn steel and AISI 4130 steel are:SAE 101055,000 Pa or 379 MPaAISI 413075,000 Pa or 517 MPaEXAMPLE 1-5Select the proper metric size steel tube for a flow rate of 0.00190m3/s and an operating pressure of 70 bars. The maximum recommended velocity is 6.1 m/s and the tube material is SAE 1010 dead soft cold-drawn steel having a tensile strength of 379 MPa.Solution The minimum inside diameter based on the fluid velocity limitation of 6.1 rn/s is found using Eq. (3-18):Solving for A we have:Since we have the final resulting equation: 式(1.7)Substituting values we have:From Fig. 4-21, the smallest acceptable od tube size is:22-mm od, 1.0-mm wall thickness, 20-mm IDFrom Eq. (4-3) we obtain the burst pressure.Then we calculate the working pressure using Eq. (1.4).This pressure is not adequate (less than operating pressure of 70 bars), so lets examine the next larger size od tube having the necessary ID.28-mm od, 2.0-mm wall thickness, 24-mm IDThis result is acceptable.1.10 KEY EQUATIONSFluid velocity: Pipe tensile stress: Pipe burst pressure: Pipe working pressure: 附录二 中文翻译液压管路和管接头Eric Sandgren *, T.M. Cameron弗吉尼亚联邦大学机械工程系, Richmond西部大街601号, 邮编843015, VA23284-3015收稿2001 年10月19 日; 修回2002 年6月5 日。1.1 介绍在液压系统中, 液压油经过的系统包括管路和管接头, 这些液压油从油箱经过各机构的组成部分又回到油箱。因为在这过程中能量是通过这些管路传送到液压系统的各个部分(用来连接系统组分的管路和管接头), 所以为了总系统能够很好的发挥效率，必须进行恰当地设计。液压系统主要使用四种管路:1.钢管2.无缝钢管3.塑料管4.软管选用管路类型主要取决于系统的工作压力和流量。另外, 它的选择还取决于环境条件譬如油液的类型, 操作温度, 振动, 而且和连接部分之间是否有相对行动也有关系。管路可以通过的工作压力可以达到1000 Pa或者更大。一般情况下, 钢管材与管道相比，配管的灵活性更好、更加洁净而且管接头也比较少，更加的方便。但是, 用管道输送比钢管材较便宜。塑料管材因为它资源利用率高并且由于它的灵活性连接比较方便，增加了它的工业用途。软管主要用来连接相对行动组分的部分。它们由大量的弹性化合物组成，能处理超出10,000 Pa的压力 。在腐蚀性比较强的条件下一般使用不锈钢管路和管接头。但是, 它们比较昂贵, 只有在需要的情况下才可使用。铜管路不应该用在液压机构中，因为铜具有促进石油氧化作用。锌, 镁, 和钙管路也不应该被使用，因为由于水甘醇它们会迅速地被腐蚀掉。应该避免使用镀锌的管路，因为它的表面很容易剥落并且会融入液压液体。当使用钢管或钢管材, 液压管接头应该由钢制成除了一些回路等地方，这些地方可以使用铸铁。在设计管路和管接头时必须慎重地考虑它的安全性。它们必须具有足够的强度，不仅能够承受稳定系统压力而且还要承受由于液压震动而产生的瞬间压力。当控制阀突然被关闭时, 停止液压,这需要很多的动能。稳定系统设计时，应该考虑到这一过程可能需要二倍或四倍的冲击力。并且考虑由于突然停止或重载初可能造成的压力冲击。在设计时应该考虑到这些高压冲击的安全因素。1.2管路尺寸管路必须有一个足够大的面积，用来处理变速的要求。在一个管路中当我们谈到可变的速度譬如管子, 我们提到平均速度。因为速率是变化的所以平均速度的概念非常重要。依照章节5 里速度是在管壁和在管子的中心线上达到一个最大值。由管子断面划分平均速度被定义为容量流速: 换句话说, 平均速度是以管子合计容量流速的速度。一般被理解为流经管子最大内径的那个区积的速度。泵吸油管路的最大被允许速度为4ft/s (1.2 m/s)，是为了防止压力太低同时引起泵的运转。规定可通过的最大流速是20 ft/s (6.1 m/s)，这样是为了防止冲击、损失和油液的升温过大。规定这些最大值就是平均速度。例子1-1管子通过的流速是30gprn 。最小内径允许液压通过的平均速度不超出20 ft/ s 。解答 由式(3-26),求D:例子1-2通过管子的流量为0.002。求出可以通过平均速度低于6.1 m/ s的最小内径。解答 我们求得最小需要的管子截面积为:现在可以求出最小内径, 因为，可以求D为：1.3 管路压力规定值拉伸力由于在液压运动下管路壁上会产生的强大压力(叫做强压)，所以管路必须具有足够强度用来防止爆裂。这巨大的压力, 必须由管路材料承受, 由图4-1可确定。在图 4-1(a), 我们变化的压力(p) 相对一个圆管子的长度(l)。管子外径D0, 内径Di,并且壁厚为t。由于液压的压力一般在管子的内表面上,它试图把有压力的一半从管子的另外一半分离出来。图4-1(b) 显示这压力作用在管子的底下一半。为了防止管子的底下一半从上半方分离, 上半方总的向上的拉伸量为F。二分之一力(或F/2 )作用在各壁的断面(tL), 如显示。重要的是压力大小和总拉力必须是相等,可以有：A是管子曲壁表面区积平分线以下的一半。因而,均等宽度Di和长度L长方形的区积, 如上图4-1(b)。因此,作用在管子上的压力由壁断面划分承受的总力。这压力称压强，因为力(f) 是拉伸力(作用在它)的区积。替代变换我们可以求得： 这里= 希腊标志(斯格码)= 压强由式 (4-2)我们可以求得,当液压的压力增加，压强随着增加，当管子内径并且增加。 另外, 当管厚减小压强增加，并且管子的长度对压强没有任何影响。爆裂压力和工作压力爆裂压力(BP)是可以导致管子裂裂的液压的压力。当压强 ()大于抗拉强度(s)是 管子发生爆裂。材料爆裂的压强取决于材料的抗拉强度。注意,一个轴向划线被显示在管子外壁表面如图4-1(a)。这个划线行显示何处管子会发生崩裂和如果压强达到了管子的抗拉强度时材料因而爆裂。当液压压力(p)达到BR 时，这爆裂将发生。因而,由式(1.2) 爆裂压力是 工作压力(WP) 是安全工作的最大液压压力并且被定义为划分了由爆裂压力安全(FS) 一个适当的因素。 安全因素是保证管路的坚固用来确定工作压力的最高安全水平。根据对应的工作压力标准推荐下面的安全因素:FS=8 为压力从0 到1000 PaFS=6 为压力从1000 年到2500 PaFS=4 为压力在2500 Pa之上为了达到期望压力的系统, 规定10种安全因素。管路尺寸根据流速和压力考虑通过给定条件确定管路尺寸如下:1.根据流速要求计算最小内径(Di)。2.根据流速要求选择管路的标准内径大于或等于计算出来的值。3.由选出的标准使用以下等式确定壁厚(t): 4.根据管路材料和系统工作压力(p), 确定抗拉强度(s)和安全因素(FS)。5. 由式(1.3)和(1.4)计算爆裂压力(BP) 和工作压力(WP) 。6. 如果计算的工作压力大于液压的工作压力, 选择的管路是可接受的。如果不是,必须重新选择管路的标准尺寸以及壁厚。一个可用的管路必须是一个符合流速要求和等于或大于系统的工作压力。命名原则和参量单位 式s(1.2), (1.3), (1.4),和(1.5)如下:BP=裂裂了压力(Pa, MPa)Di=管路内径(in., m)D0=管路外部直径(in., m)FS=安全因素(dimensionless)P=系统工作的可变压力(Pa, MPa)S=管路材料抗拉强度(Pa, MPa)t=管路壁厚(in., m)WP=工作压力(Pa, MPa)=压强(Pa, MPa)例子1-3钢管材有外部直径a 1.250m,和内径a 1.060m。它由SAE 1010 冷制钢制成，抗拉强度有55.000 Pa。这支管会它安全工作压力为承担安全因素.首先解答,计算管材的壁厚:其次,管材爆裂压力为:最后,计算管安全工作压力:厚壁管管路的用途等式(1.2)和(1.3)只能允许厚壁圆筒比率Di/t大于10。这是因为在厚壁圆筒里(Di /t10), 依照式(1.2)假设拉力管的壁厚和管径不是一致的。式(1.6)为厚壁圆筒，使用时必须考虑到不均匀的拉力, 因而,如果考虑管路不是一个薄壁圆筒, 计算时必须使用式(1.6)。如被期望的那样，由式(1.6)计算比由式(1.3)计算，可以获得更小的爆裂压力和工作压力。这能比较二个等式并且注意发现在式(1.6)分母上加1.2t。注意钢管材例子4-3 是一个薄壁圆筒，因为=1.060/0.095=11.210。因而, 依照计算，钢管材例子4-3可以1230 Pa安全地工作，使用工作压力安全因素8。用式(4-6) 为这个同样管材和安全因素 例子用式(1.6)计算出来的工作压力为1110 Pa要比用式(1.3)计算出的1230 Pa更小。1.4 钢管指定尺寸管子和管子管接头划分不同的大小和数字,在图4-2上说明。表提供有40,80,和160, 这些在液压机构中是最常用的几种。注意各个不同的大小它的外径是不改变的。为了增加壁厚，用下个更大的表中的数字。并且观察,外部和内径都是尺寸不想同的。同时,不同管子大小表明联接的螺纹尺寸。管子大小显示在图4-2 ，单位是英寸。图4-3 显示横剖面的相对大小为安排40, 80, 和160个管子。依照显示指定的管子大小,当表数字增加时壁厚度增加。螺纹设计 管子逐渐变细螺纹,与管和管接头相对,有平直的螺纹。依照图4-4显示,当管子被拉紧，在两螺纹之间的接点由干涉被密封。这造成的最大问题是其中一个在使用管子。 当联接分开, 管子必须被拉紧重新密封。在细长的部分要求频繁地替换一些管子, 虽然这个问题由使用加入聚四氟乙烯磁带重新密封管子克服了一部分。液压管子螺纹是干燥密封类型。 它们从标准管子分出，因为在这之前它们参与了处理。这样,螺旋清除被避免了。管子可能有唯一主螺纹, 并且它们不能在障碍附近弯曲。当然也有各种各样的必需的管接头类型做终端连接和用来改变方向, 依照图4-5显示大量的管子管接头需要液压油路提供机会用来泄漏,特别是当压力增量时。穿线类型管接头被使用在尺寸达到直径的。耳轮缘焊接到管子上，这里是大管子必需的,在图4-6说明。根据显示 平的垫圈或0 圆环被使用密封被安装边缘的管接头。1.5 钢管材指定尺寸无缝的钢管材是广泛被应用的管路类型因为它为液压机构在管子上提供了非常大的好处。管材可以弯曲成任一形状,因此减少了一些必需的管接头的数量。管材更加容易处理并且可以被重复利用而且没有任何质量问题。为低流量系统, 管材可能要求以少量轻质来处理压力和流量。但是,管材和它的管接头是相对昂贵的。管材尺寸设计总提到外部直径。可利用的大小包括从1/8增加1/16。外部直径增加到3/8。外部直径从3/8增加到1寸。增加是1/8大小在1in.之外,增加是1/4。 图4-7显示一些相同尺