xx大学机械工程学院毕业设计
The application of Acoustic Emission for detecting
incipient cavitation and the best efficiency point of a
60KW centrifugal pump; case study
L. Alfayez, D. Mba, G. Dyson July 2005 Abstract
Pumps play a significant role in Industrial plants and need continuous monitoring to minimize loss of production. To date, there is limited published information on the application of Acoustic Emission (AE)to incipient pump cavitation. This paper presents a case study where AE has been applied for detecting incipient cavitation and determining the best efficiency point (BEP)of a 60KW centrifugal pump. Results presented are based on NPSH (Net Positive Suction Head)and performance tests. In conclusion the AE technique was shown to offer early detection of incipient cavitation, furthermore, the technique has demonstrated the ability to determine the BEP of a pump
Keywords:
Acoustic Emission; best efficiency point; cavitation; condition monitoring;
Pump performance
1.Introduction
Typically the pump manufacturer will undertake performance and NPSH(Net Positive Suction Head)tests on supplied pumps, the significance of the latter is to determine the 3%drop in head at which serious cavitations will occur. The NPSH can be expressed as the difference between the suction head and the liquids vapour head. The concept of NPSH was developed for the purpose of comparing inlet condition of the system with the inlet requirement of the pump. Cavitation causes a loss of pump efficiency and degradation of the mechanical integrity of the pump. It must be noted that cavitation starts to develop before the
3%drop in head. It is generally accepted that the critical pressure for inception of cavitation is not constant and varies with operation fluid physical properties and the surface roughness of the hydraulic equipment.
Application of the high frequency Acoustic Emission (AE)technique in condition monitoring of rotating machinery has been growing over recent years[1-9].Typical frequencies associated with AE activity range from 20 KHz to 1MHz.The most commonly used method for identifying the presence of cavitation is based on observations of the drop in head. Whilst other techniques such as vibration analysis and hydrophone observations for pump fault diagnosis are well established, the application of AE to this field is still in its infancy. In addition, there are a limited number of publications on the application of AE to pump health and cavitation monitoring. Derakhshan et al [10]investigated the cavitation bubble collapse as a source of acoustic emission and commented that the high amplitude pressure pulse associated with bubble collapse generated AE. With the AE sensor was placed on the actual specimen experiencing cavitation Derkhshan observed increasing AE r.m.s levels with increased pressure of flow and cavitation. However, with the AE sensor mounted on the tank wall the reverse was observed, decreasing AE r.m.s levels with increasing pressure and cavitation. This was attributed to a visible bubble cloud that increased with pressure. It was commented that this cloud attenuated the AE signature prior to reaching the transducer on the wall casing. Neill et al[11,12]assessed the possibility of early cavitation detection with AE and also noted that the collapse of cavitation bubbles was an impulsive event of the type that could generate AE. It was observed that when the pump was under cavitation the AE operational background levels dropped in comparison to non-cavitating conditions. In conclusion Neill stated that loss in NPSH before the 3%drop-off criterion was detectable with AE and evidence of incipient cavitation was detectable in the higher frequency band(0.5 to 1MHz).
The papers reviewed above have clearly associated AE with the collapse of cavitation bubbles. The presence of cavitation has been shown to increase or decrease operational AE noise levels[10,11,12].This paper presents a case study to ascertain the applicability of the AE technique for detecting incipient cavitation, and, to access the opportunities offered by the AE technique for determining the best efficiency point(BEP)of a pump.
2. Experimental setup
A series of performance and NPSH tests were undertaken on a two stage
‘ DavidBrown’60KW centrifugal pump(Model DB22)with a maximum capacity of 204m 3/h at an efficiency of 70.6%.These tests were undertaken using a closed loop arrangement with a vacuum facility in accordance with BS 9906.It must be noted that best endeavours were undertaken to reduce the time taken to reach the required flow rate during performance and NPSH tests.
Acoustic Emission sensors were located at a distance of 0.5 m from suction flange; at the suction flange; on the pump casing in the vicinity of impeller suction eye; on the casing in the vicinity of the impeller discharge tip;0.5m from discharge flange, see figure 1.
3. Data acquisition systems
The AE sensors used for all of the experiments were broadband type sensors with a relative flat response in the region between 100 KHz to 1MHz (Model:WD,‘Physical Acoustics Corporation’).The output signal from the AE sensors was pre-amplified at 40dB.Continuous AE r.m.s values were calculated in real time by the Analogue to Digital Converter(ADC).The sampling rate for acquisition was set at 100ms for all tests and the time constant for calculating the AE r.m.s was also set at 100 ms.
4. Experimental results and observation
4.1 Performance test
Figure 2 details the performance characteristics of the pump, highlighting the BEP at
94.5m/hr. The performance test were undertaken twice to ensure repeatability. Observations
of AE r.m.s activity during the performance test are displayed in figure 3.During the performance test, AE activity from the sensor located in the vicinity of impeller on pump casing was found to have the largest magnitude, providing the best position for correlating AE activity to pump performance. It was observed that the minimum AE r.m.s value was obtained for a flow rate of 94.5m/hr. At this flow rate the AE activity generated from the fluid flow within the pump and pipes was lowest in comparison to other flow rates. Either side of this flow rate resulted in increasing AE r.m.s activity with increased flow rates. Based 3 3
on these observations it was concluded that the BEP must occur where there was minimal flow turbulence in the system, and hence minimum AE activity. The predicted efficiency point of 94.5m/hr was checked with the manufacturer’s performance test and was found to be accurate. Interestingly this is the first known correlation between AE activity and the BEP and agrees with observations of McNulty [13], though McNulty’s investigation was centred at frequencies in the audible range; lower than the AE range. The advantage offered by the AE technique is the inherent rejection of typical mechanical and process operational background noise(less than 20 KHz)
4.2 NPSH test
A total of three NPSH tests were undertaken at flow rates of 101,141 and 180m/hr, see figure
4.As with the performance tests, the best AE signature response was located on the pump casing in the vicinity of the impeller eye
Figures 5 to 7 detail the associated AE r.m.s levels for the three flow rates considered.The following observations were noted:
At a flow rate of 101m/h an increase of 165%in AE r.m.s levels was observed from an NPSH value of 8.2m to 7m.Relatively constant levels followed until an NPSH of 5.8 m when a rapid decrease in AE r.m.s levels was noted. With further reductions in NPSH, spikes in AE r.m.s signal vels associated with cavitation was also observed by Neill[11].Observations of AE levels from the suction and discharge pipes mirrorthis observation.
a flow rate of 141m/h an increase of 43%in AE r.m.s was observed at NPSH value of 12.7m to 9.3m.A rapid decrease in level was noted at an NPSH of 9.3m.With further reductions in NPSH, spikes in AE r.m.s signal were observed as with the test a flow rate of 101m/hr. Again, observations of AE levels from the suction and discharge pipes mirrored this observation.
At a flow rate of 181m/h an increase in AE r.m.s of 223%was observed at NPSH value of 11m to 7.3m.A gradual decrease in the AE levels followed to an NPSH of 1.7 m, where an increase in the r.m.s value was observed.
5.Discussions
5.1Performance test
The observations of AE activity during the performance test were very encouraging. The ability to predict a systems BEP by observing variations in the AE r.m.s response offer process engineers a powerful tool for monitoring plant performance. Whilst further research is still required the opportunities offered by such a tool could be applied to determining system BEP irrespective of the type of medium (liquid, gases, semi-solids, etc )in the system. The observations noted in this investigation correlate with hydrophone measurements undertaken by McNulty [13],where the minimum sound intensity coincided with the pump BEP.
5.2 NPSH test
It is essential to understand the cavitation sequence if it is to be correlated to observed AE activity. Once the suction pressure starts to decrease, vortexes start to occur at the impeller blade tips. With further reduction in pressure these vortexes take the form of travelling bubbles in the liquid. These bubbles are initially created in lower pressure area on the suction surface of the blades. Eventually the bubbles move to higher-pressure areas where they collapse. With even further reduction in the suction pressure, the bubbles combine into larger cavities. These cavities are usually formed on the impeller blade suction surface.
For all NPSH tests an increase in AE r.m.s levels was noted as values of NPSH started to decrease. A maximum level of AE r.m.s was reached after which further reductions in NPSH resulted in a decrease in AE r.m.s levels. This was also observed on the sensors located on the suction and discharge flanges. It is postulated that at the start of the NPSH test the increase in AE r.m.s levels was attributed to the onset of cavitation. The drop in AE r.m.s with decreasing NPSH values was attributed to the attenuation caused by bubble clouds. Following the creation of bubbles, and the eventual formation of the bubble cloud, the AE r.m.s levels were expected to drop. The loss in AE strength due to the presence of cavitation and the bubble cloud was noted by Neill[11,12]and Derakhshan [10]respectively.
5.3 Conclusions
The results from acoustic emission analysis have shown a clear relationship between AE activity measured from the pump casing, suction and discharge pipes, and incipient cavitation. At a relatively high NPSH value, when incipient cavitation is known to occur, an increase in AE r.m.s levels was observed.
However, as cavitation developed a reduction in AE r.m.s levels due to attenuation was noted This would suggest that the AE technique is more suited to detecting incipient, and not developed, cavitation.AE was also found to have enormous potential in determining the BEP of a pump and/or process employing pumps though further research on this observation is required.
6.References
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A pplicability of Acoustic Emission to rail track fault detection. NDT&E
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声发射检测初生空化及其应用
60KW离心泵最佳效率点案例研究
L.法浦亚斯，D.姆巴，G.戴森 2005年7月
摘要
泵在工业领域发挥着显著的作用，需要持续监控，以尽量减少生产损失。到目前为止，将声发射技术（AE）应用于泵初生空化的信息依然很有限。本文介绍了一个声发射技术（AE）已应用于检测初生空化和确定60KW离心泵的最佳效率点（BEP）的研究案例。该案例的结果是基于NPSH（汽蚀余量）和性能测试得到的。总之，声发射技术被证明可以提供初生空化的检测，此外，该技术已还证明，声发射具有确定泵的最佳效率点（BEP）的能力。
关键字:声发射；最佳效率点；空化；状态监测；泵性能
1.介绍
泵广泛的应用于我们的生活和工业当中。泵的制造商会提供说明泵在给定条件下的性能特性曲线。这些曲线表明泵的放电能力，泵的扬程，功率和工作效率之间的关系。一台泵的理想工作点被称为最佳效率点（BEP）。在这一点，泵的流量和压头相结合，使泵达到最佳效率。如果泵在最佳效率点（BEP）外运行，不仅将使泵的效率受到影响，而且会加剧磨损，降低泵的使用寿命。通常情况下，泵制造商将对泵进行性能和NPSH（汽蚀余量）测试，后者的意义在于确定扬程
下降3％时将发生严重的气穴现象。汽蚀余量（NPSH）可以表示为总水头和液体汽化时的压力头之间的差。 NPSH的概念是因比较泵的入口条件与泵的入口要求而提出的。气蚀引起泵的效率和泵机械完整性降低。必须指出，空化开始发生于扬程下降3％之前。人们普遍认为初生空化的临界压力不是恒定的，而且与工作流体的物理性质及液压设备的表面粗糙度的变化有关。
声发射技术在回转机械状态监测中的应用一直在增长。声发射的范围从20 KHz到1MHz。最常用的用于识别汽蚀存在的方法是观测泵扬程的下降。虽然振动分析及泵故障诊断水听器观测等技术已经非常成熟，声发射技术在这一领域的应用尚处于起步阶段。此外，将声发射技术应用到泵的性能和空化监测的出版物的数量仍十分有限。
德拉哈思汉等人研究认为空化泡破裂是声发射的一种来源，并认为与泡沫破裂相关的高振幅压力脉冲产生了声发射。通过放置在空化实验样品中的声发射传感器，德拉哈思汉观察到AE有效值、水平流动和空化压力都增大了。然而，将AE传感器安装在实验箱箱壁上却得到了相反的结果，AE有效值、水平与空化压力都下降了。这是由一个随着压力增大的可见的气泡云造成的。这就是说，气泡云产生的AE在到达实验箱箱壁上的AE传感器之前在不断地衰减。尼尔等人评估了利用AE检测早期气蚀的可能性，并且指出，空化气泡的破裂所产生的脉冲可以产生声发射。据观察，泵在空化条件下的AE水平比在无空化条件下的要低。总之尼尔表示，比标准低3 ％的汽蚀余量是可以被声发射检测到的，并且，初生空化的证据在较高的频带（0.5至1MHz）也是可检测的。
上文已明确表明AE与空化气泡的破裂有关。汽蚀的存在已被证明增加或减少AE水平。本文介绍了一个案例研究，以确定声发射技术检测初生空化的适用性，并利用声发射技术确定泵的最佳效率点（BEP）。
2.实验装置
一系列的性能和汽蚀余量的测试将分两个阶段进行。大卫·布朗的60KW离心泵（型号DB22），最大流量为204m3/h，效率为70.6％。这些试验在BS9906标准的真空封闭设备中进行。必须指出的是，在泵的性能和汽蚀余量测试实验中，实验人员尽了最大的努力，从而降低了泵达到实验所要求的流量所需的时间。声发
射传感器分别被安装在距吸入口法兰0.5m处，叶轮入口附近的壳体上，叶轮放电尖端附近壳体上及距出口法兰0.5m处。参见图1。
3.数据采集系统
实验中的声发射传感器均是工作范围为100 kHz至1MHz的（型号：WD，物理声学公司）传感器。AE传感器的输出信号将预放大为40dB，连续的声发射有效值将会被数字转换器（ADC）实时计算。所有测试的采样率均为100毫秒，计算声发射有效值的时间也是100毫秒。
4. 实验结果
4.1性能测试
图2详细描述了泵的性能特征，表明泵的最佳效率点在流量为94.5m3/h时。泵的性能测试进行了两次，以确保其可重复性。 AE有效值测试结果如图3所示。AE活动的峰值出现在泵壳叶轮附近从设在叶轮上的泵壳体附近，AE的相关活动为泵的性能提供了最佳的位置。据观察，在流量为94.5m3/h时AE的有效值最低。相比于其他流量下流体在泵和管道内产生的声发射，在94.5m3/h的流量下所产生的声发射最低。高于或低于这个流量都将会导致AE活动的增加。基于这些观察可以得出结论，最佳效率点（BEP）一定出现在系统湍流最小点，也就是声发射活动最低点。预测的最佳效率点94.5m3/h是制造商通过性能测试的得到的，并且该点被证明是正确的。有趣的是，这第一次证明了的AE活性和最佳效率点存在相关性并且和麦克纳尔蒂的观察相符合，虽然麦克纳尔蒂的调查集中在比AE范围低的可听频率范围内。AE技术的优点是降低了传统的机械噪音（低于20千赫）。
4.2汽蚀余量测试
实验分别测试了流量分别为101、141、180m3/h时的汽蚀余量。如图4所示。由性能测试实验可知，最好的AE信号出现在叶轮入口附近的泵壳处。
图5到图7详细的表明了在三种不同流量下的声发射有效值
观察结果表明:
1）在流量为101m3/h，汽蚀余量为7m至8.2m时，AE有效值增加了165%。当汽蚀余量为5.8m时，AE有效值会急剧增大。随汽蚀余量继续降低，AE有效值会出现尖峰，此时泵的扬程下降了3%。尼尔也观察到了这种和空化有关的AE有效值的变化，泵吸入口和排出口处的AE有效值变化也印证了这种现象。2）在流量为141m3/h，汽蚀余量为9.3m至12.7m时，AE有效值增加了43%。当汽蚀余量为9.3m时，AE有效值会急剧增大。随汽蚀余量继续降低，同流量为101m3/h 时相同，AE有效值出现了尖峰。泵吸入口和排出口处的AE有效值变化又再一次印证了这一现象。
3）在流量为180m3/h，汽蚀余量为7.3m至11m时，AE有效值增加了223%。随汽蚀余量继续降低，在汽蚀余量为1.7m之前，AE有效值逐渐降低。当汽蚀余量低于1.7m时，AE有效值会增加
5.讨论
5.1 性能测试
性能测试中声发射活动的观察是非常令人鼓舞的。通过AE相应的变化预测系统的最佳效率点给工艺工程师提供了一个检测装置性能的强大的工具。虽然还需要进一步的研究，但这个工具可以确定系统的最佳效率点，而不用考虑介质类型（液体，气体，半固体，等）。将本研究的发现与水听器测量麦克纳尔蒂的实验进行比较，其中最小的声音强度符合泵的最佳效率点。
5.2 汽蚀余量测试
如果要观察到声发射活动，必需要了解空化本质。一旦吸入压力开始下降，叶轮的叶片尖端将产生漩涡。随着压力的进一步降低，这些漩涡在液体中形成气泡。这些气泡最初在低压区中的叶片的负压面上创形成。最终，气泡进入到高的压区，并最终破裂。随着吸入口压力的进一步降低，气泡的合并成较大空腔。这些空腔通产生于叶轮叶片负压面。
在所有的汽蚀余量测试中，随着汽蚀余量值的降低AE 有效值都出现上升。AE有效值达到最高值之后，进一步减少汽蚀余量会导致AE 有效值的下降。这种现象吸入口和排出口法兰处。据推测，在NPSH试验开始时AE有效值增加是因为
气蚀。AE有效值的下降与汽蚀余量值的减小是由气泡云的衰减引起的。随着气泡的生成，并且最终形成气泡云时，AE有效值将会将下降。声发射的强度由于空化和气泡云的存在而减弱是由尼尔和德拉哈思汉分别指出的。
5.3实验结果
声发射分析的结果表明，泵壳，吸入口和排出口的初生空化与AE活性之间有明确的关系。在汽蚀余量值相对高的地方，初始空化发生后，AE有效值将会增加。然而，随着空化发展的AE有效值将会降低。这表明，AE技术更适合于检测早期的并没有发展的空化现象。AE也被发现在确定泵的最佳效率点上具有巨大的潜力，虽然这一潜力尚需进一步的研究。
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附录A Lathe fixture design and analysis Ma Feiyue (School of Mechanical Engineering, Hefei, Anhui Hefei 230022, China) Abstract: From the start the main types of lathe fixture, fixture on the flower disc and angle iron clamp lathe was introduced, and on the basis of analysis of a lathe fixture design points. Keywords: lathe fixture; design; points Lathe for machining parts on the rotating surface, such as the outer cylinder, inner cylinder and so on. Parts in the processing, the fixture can be installed in the lathe with rotary machine with main primary uranium movement. However, in order to expand the use of lathe, the work piece can also be installed in the lathe of the pallet, tool mounted on the spindle. THE MAIN TYPES OF LATHE FIXTURE Installed on the lathe spindle on the lathe fixture
On the vehicle sideslip angle estimation through neural networks: Numerical and experimental results. S. Melzi,E. Sabbioni Mechanical Systems and Signal Processing 25 (2011)：14~28 电脑估计车辆侧滑角的数值和实验结果 S.梅尔兹,E.赛博毕宁 机械系统和信号处理2011年第25期：14~28
摘要 将稳定控制系统应用于差动制动内/外轮胎是现在对客车车辆的标准（电子稳定系统ESP、直接偏航力矩控制DYC）。这些系统假设将两个偏航率(通常是衡量板)和侧滑角作为控制变量。不幸的是后者的具体数值只有通过非常昂贵却不适合用于普通车辆的设备才可以实现直接被测量,因此只能估计其数值。几个州的观察家最终将适应参数的参考车辆模型作为开发的目的。然而侧滑角的估计还是一个悬而未决的问题。为了避免有关参考模型参数识别/适应的问题,本文提出了分层神经网络方法估算侧滑角。横向加速度、偏航角速率、速度和引导角,都可以作为普通传感器的输入值。人脑中的神经网络的设计和定义的策略构成训练集通过数值模拟与七分布式光纤传感器的车辆模型都已经获得了。在各种路面上神经网络性能和稳定已经通过处理实验数据获得和相应的车辆和提到几个处理演习(一步引导、电源、双车道变化等)得以证实。结果通常显示估计和测量的侧滑角之间有良好的一致性。 1 介绍 稳定控制系统可以防止车辆的旋转和漂移。实际上，在轮胎和道路之间的物理极限的附着力下驾驶汽车是一个极其困难的任务。通常大部分司机不能处理这种情况和失去控制的车辆。最近,为了提高车辆安全，稳定控制系统(ESP[1,2]; DYC[3,4])介绍了通过将差动制动/驱动扭矩应用到内/外轮胎来试图控制偏航力矩的方法。 横摆力矩控制系统（DYC）是基于偏航角速率反馈进行控制的。在这种情况下,控制系统使车辆处于由司机转向输入和车辆速度控制的期望的偏航率[3,4]。然而为了确保稳定，防止特别是在低摩擦路面上的车辆侧滑角变得太大是必要的[1,2]。事实上由于非线性回旋力和轮胎滑移角之间的关系，转向角的变化几乎不改变偏航力矩。因此两个偏航率和侧滑角的实现需要一个有效的稳定控制系统[1,2]。不幸的是,能直接测量的侧滑角只能用特殊设备(光学传感器或GPS惯性传感器的组合)，现在这种设备非常昂贵,不适合在普通汽车上实现。因此, 必须在实时测量的基础上进行侧滑角估计，具体是测量横向/纵向加速度、角速度、引导角度和车轮角速度来估计车辆速度。 在主要是基于状态观测器/卡尔曼滤波器(5、6)的文学资料里, 提出了几个侧滑角估计策略。因为国家观察员都基于一个参考车辆模型,他们只有准确已知模型参数的情况下，才可以提供一个令人满意的估计。根据这种观点,轮胎特性尤其关键取决于附着条件、温度、磨损等特点。 轮胎转弯刚度的提出就是为了克服这些困难,适应观察员能够提供一个同步估计的侧滑角和附着条件[7,8]。这种方法的弊端是一个更复杂的布局的估计量导致需要很高的计算工作量。 另一种方法可由代表神经网络由于其承受能力模型非线性系统，这样不需要一个参
毕业论文（设计） 外文翻译 题目：机械加工介绍
机械加工介绍 1.车床 车床主要是为了进行车外圆、车端面和镗孔等项工作而设计的机床。车削很少在其他种类的机床上进行，而且任何一种其他机床都不能像车床那样方便地进行车削加工。由于车床还可以用来钻孔和铰孔，车床的多功能性可以使工件在一次安装中完成几种加工。因此，在生产中使用的各种车床比任何其他种类的机床都多。 车床的基本部件有：床身、主轴箱组件、尾座组件、溜板组件、丝杠和光杠。 床身是车床的基础件。它能常是由经过充分正火或时效处理的灰铸铁或者球墨铁制成。它是一个坚固的刚性框架，所有其他基本部件都安装在床身上。通常在床身上有内外两组平行的导轨。有些制造厂对全部四条导轨都采用导轨尖朝上的三角形导轨（即山形导轨），而有的制造厂则在一组中或者两组中都采用一个三角形导轨和一个矩形导轨。导轨要经过精密加工以保证其直线度精度。为了抵抗磨损和擦伤，大多数现代机床的导轨是经过表面淬硬的，但是在操作时还应该小心，以避免损伤导轨。导轨上的任何误差，常常意味着整个机床的精度遭到破坏。 主轴箱安装在内侧导轨的固定位置上，一般在床身的左端。它提供动力，并可使工件在各种速度下回转。它基本上由一个安装在精密轴承中的空心主轴和一系列变速齿轮(类似于卡车变速箱)所组成。通过变速齿轮，主轴可以在许多种转速下旋转。大多数车床有8~12种转速，一般按等比级数排列。而且在现代机床上只需扳动2~4个手柄，就能得到全部转速。一种正在不断增长的趋势是通过电气的或者机械的装置进行无级变速。 由于机床的精度在很大程度上取决于主轴，因此，主轴的结构尺寸较大，通常安装在预紧后的重型圆锥滚子轴承或球轴承中。主轴中有一个贯穿全长的通孔，长棒料可以通过该孔送料。主轴孔的大小是车床的一个重要尺寸，因此当工件必须通过主轴孔供料时，它确定了能够加工的棒料毛坯的最大尺寸。 尾座组件主要由三部分组成。底板与床身的内侧导轨配合，并可以在导轨上作纵向移动。底板上有一个可以使整个尾座组件夹紧在任意位置上的装置。尾座体安装在底板上，可以沿某种类型的键槽在底板上横向移动，使尾座能与主轴箱中的主轴对正。尾座的第三个组成部分是尾座套筒。它是一个直径通常大约在51~76mm之间的钢制空心圆柱体。
Lathes Lathes are machine tools designed primarily to do turning, facing and boring, Very little turning is done on other types of machine tools, and none can do it with equal facility. Because lathes also can do drilling and reaming, their versatility permits several operations to be done with a single setup of the work piece. Consequently, more lathes of various types are used in manufacturing than any other machine tool. The essential components of a lathe are the bed, headstock assembly, tailstock assembly, and the leads crew and feed rod. The bed is the backbone of a lathe. It usually is made of well normalized or aged gray or nodular cast iron and provides s heavy, rigid frame on which all the other basic components are mounted. Two sets of parallel, longitudinal ways, inner and outer, are contained on the bed, usually on the upper side. Some makers use an inverted V-shape for all four ways, whereas others utilize one inverted V and one flat way in one or both sets, They are precision-machined to assure accuracy of alignment. On most modern lathes the way are surface-hardened to resist wear and abrasion, but precaution should be taken in operating a lathe to assure that the ways are not damaged. Any inaccuracy in them usually means that the accuracy of the entire lathe is destroyed. The headstock is mounted in a foxed position on the inner ways, usually at the left end of the bed. It provides a powered means of rotating the word at various speeds . Essentially, it consists of a hollow spindle, mounted in accurate bearings, and a set of transmission gears-similar to a truck transmission—through which the spindle can be rotated at a number of speeds. Most lathes provide from 8 to 18 speeds, usually in a geometric ratio, and on modern lathes all the speeds can be obtained merely by moving from two to four levers. An increasing trend is to provide a continuously variable speed range through electrical or mechanical drives. Because the accuracy of a lathe is greatly dependent on the spindle, it is of heavy construction and mounted in heavy bearings, usually preloaded tapered roller or ball types. The spindle has a hole extending through its length, through which long bar stock can be fed. The size of maximum size of bar stock that can be machined when the material must be fed through spindle. The tailsticd assembly consists, essentially, of three parts. A lower casting fits on the inner ways of the bed and can slide longitudinally thereon, with a means for clamping the entire assembly in any desired location, An upper casting fits on the lower one and can be moved transversely upon it, on some type of keyed ways, to permit aligning the assembly is the tailstock quill. This is a hollow steel cylinder, usually about 51 to 76mm(2to 3 inches) in diameter, that can be moved several inches longitudinally in and out of the upper casting by means of a hand wheel and screw. The size of a lathe is designated by two dimensions. The first is known as the swing. This is the maximum diameter of work that can be rotated on a lathe. It is approximately twice the distance between the line connecting the lathe centers and the nearest point on the ways, The second size dimension is the maximum distance between centers. The swing thus indicates the maximum work piece diameter that can be turned in the lathe, while the distance between centers indicates the maximum length of work piece that can be mounted between centers. Engine lathes are the type most frequently used in manufacturing. They are heavy-duty machine tools with all the components described previously and have power drive for all tool movements except on the compound rest. They commonly range in size from 305 to 610 mm(12 to 24 inches)swing and from 610 to 1219 mm(24 to 48 inches) center distances, but swings up to 1270 mm(50 inches) and center distances up
The development of automobile As the world energy crisis and the war and the energy consumption of oil -- and are full of energy in one day someday it will disappear without a trace. Oil is not inresources. So in oil consumption must be clean before finding a replacement. With the development of science and technology the progress of the society people invented the electric car. Electric cars will become the most ideal of transportation. In the development of world each aspect is fruitful especially with the automobile electronic technology and computer and rapid development of the information age. The electronic control technology in the car on a wide range of applications the application of the electronic device cars and electronic technology not only to improve and enhance the quality and the traditional automobile electrical performance but also improve the automobile fuel economy performance reliability and emission spurification. Widely used in automobile electronic products not only reduces the cost and reduce the complexity of the maintenance. From the fuel injection engine ignition devices air control and emission control and fault diagnosis to the body auxiliary devices are generally used in electronic control technology auto development mainly electromechanical integration. Widely used in automotive electronic control ignition system mainly electronic control fuel injection system electronic control ignition system electronic control automatic transmission electronic control ABS/ASR control system electronic control suspension system electronic control power steering system vehicle dynamic control system the airbag systems active belt system electronic control system and the automatic air-conditioning and GPS navigation system etc. With the system response the use function of quick car high reliability guarantees of engine power and reduce fuel consumption and emission regulations meet standards. The car is essential to modern traffic tools. And electric cars bring us infinite joy will give us the physical and mental relaxation. Take for example automatic transmission in road can not on the clutch can achieve automatic shift and engine flameout not so effective improve the driving convenience lighten the fatigue strength. Automatic transmission consists mainly of hydraulic torque converter gear transmission pump hydraulic control system electronic control system and oil cooling system etc. The electronic control of suspension is mainly used to cushion the impact of the body and the road to reduce vibration that car getting smooth-going and stability. When the vehicle in the car when the road uneven road can according to automatically adjust the height. When the car ratio of height low set to gas or oil cylinder filling or oil. If is opposite gas or diarrhea. To ensure and improve the level of driving cars driving stability. Variable force power steering system can significantly change the driver for the work efficiency and the state so widely used in electric cars. VDC to vehicle performance has important function it can according to the need of active braking to change the wheels of the car car motions of state and optimum control performance and increased automobile adhesion controlling and stability. Besides these appear beyond 4WS 4WD electric cars can greatly improve the performance of the value and ascending simultaneously. ABS braking distance is reduced and can keep turning skills effectively improve the stability of the directions simultaneously reduce tyre wear. The airbag appear in large programs protected the driver and passengers safety and greatly reduce automobile in collision of drivers and passengers in the buffer to protect the safety of life. Intelligent electronic technology in the bus to promote safe driving and that the other functions. The realization of automatic driving through various sensors. Except some smart cars equipped with multiple outside sensors can fully perception of information and traffic facilities
外文翻译 通常，应变计应用在两个方面：在机械和结构的实验力分析中和应用力，扭矩，压力,流量以及加速度传感器结构中。非粘贴丝式应变计通常是当作专门的转换器来使用，其结构是使用一些有预载荷的电阻丝连接成惠斯登电桥，如图4.11： 在最初的预载荷中，四根金属丝的应变和电阻在理论上是相等的，它们组成一个平衡电桥，并且e0 = 0 （参考第10章电桥电路特性）。输入端一个小的位移（满量程≈0.04 mm）将会使两根金属丝的拉力增大而使另外两根的拉力减小（假设金属丝不会变松弛），引起电阻阻值的变化，电桥失衡，输出电压与输入位移成比例。金属丝可以由砷镍、镍铬和铁镍等多种合金制造，直径约为0.03 mm，可以承受的最大应力仅为0.002 N，灵敏系数为2到4，每个桥臂的电阻为120Ω到1000Ω, 最大激励电压5到10V，满量程输出典型值为20到50mV。 粘结丝式应变计（现在主要被粘贴箔式结构的应变计取代）应用于应力分析和作为转换器。具有很细丝式敏感栅粘贴在待测试件表面，来感受应变。金属丝被埋入矩形的粘合剂中，不能弯曲从而如实地反映待测试件的压缩和拉伸应力。因为金属丝的材料和尺寸与那些非粘贴应变计相似，所以灵敏度和电阻具有了可比性。 粘贴箔式应变计采用与丝式应变计相同或类似的材料，现在主要用于多用途力分析任务及多种传感器中。 其感应元件是利用光腐蚀工艺加工成厚度小于0.0002的薄片，当其形状改变时，它具有很大的灵活性。如图4.12： 例如，这三个线形敏感栅应变计被设计成端部宽大的形状。这种局部的增大将会减小横向灵敏度，以及在测量应变沿敏感栅单元的长度方向的分量时产生的干扰输入信号。在丝式应变计中，这种端部形状也应用在纵向单元的连接处，以便增加横向抗干扰能力。并且在制造过程中也非常方便在图4.12上的全部四个应变计上焊接焊盘。
毕业设计(论文)外文资料翻译 系部： 专业： 姓名： 学号： 外文出处：English For Electromechanical (用外文写) Engineering 附件：1.外文资料翻译译文；2.外文原文。 指导教师评语： 此翻译文章简单介绍了各机床的加工原理，并详细介绍了各机床的构造，并对方各机床的加工方法法进行了详细的描述， 翻译用词比较准确，文笔也较为通顺，为在以后工作中接触英 文资料打下了基础。 签名： 年月日注：请将该封面与附件装订成册。
附件1：外文资料翻译译文 机床 机床是用于切削金属的机器。工业上使用的机床要数车床、钻床和铣床最为重要。其它类型的金属切削机床在金属切削加工方面不及这三种机床应用广泛。 车床通常被称为所有类型机床的始祖。为了进行车削，当工件旋转经过刀具时，车床用一把单刃刀具切除金属。用车削可以加工各种圆柱型的工件，如：轴、齿轮坯、皮带轮和丝杠轴。镗削加工可以用来扩大和精加工定位精度很高的孔。 钻削是由旋转的钻头完成的。大多数金属的钻削由麻花钻来完成。用来进行钻削加工的机床称为钻床。铰孔和攻螺纹也归类为钻削过程。铰孔是从已经钻好的孔上再切除少量的金属。 攻螺纹是在内孔上加工出螺纹，以使螺钉或螺栓旋进孔内。 铣削由旋转的、多切削刃的铣刀来完成。铣刀有多种类型和尺寸。有些铣刀只有两个切削刃，而有些则有多达三十或更多的切削刃。铣刀根据使用的刀具不同能加工平面、斜面、沟槽、齿轮轮齿和其它外形轮廓。 牛头刨床和龙门刨床用单刃刀具来加工平面。用牛头刨床进行加工时，刀具在机床上往复运动，而工件朝向刀具自动进给。在用龙门刨床进行加工时，工件安装在工作台上，工作台往复经过刀具而切除金属。工作台每完成一个行程刀具自动向工件进给一个小的进给量。 磨削利用磨粒来完成切削工作。根据加工要求，磨削可分为精密磨削和非精密磨削。精密磨削用于公差小和非常光洁的表面，非精密磨削用于在精度要求不高的地方切除多余的金属。 车床 车床是用来从圆形工件表面切除金属的机床，工件安装在车床的两个顶尖之间，并绕顶尖轴线旋转。车削工件时，车刀沿着工件的旋转轴线平行移动或与工件的旋转轴线成一斜角移动，将工件表面的金属切除。车刀的这种位移称为进给。车
汽车保险中英文对照外文翻译文献(文档含英文原文和中文翻译)
汽车保险 汽车保险是在事故后保证自己的财产安全合同。尽管联邦法律没有强制要求，但是在大多数州（新罕布什和威斯康星州除外）都要求必须购买汽车保险；在各个州都有最低的保险要求。在鼻腔只购买汽车保险的两个州，如果没有足够的证据表明车主财力满足财务责任法的要求，那么他就必须买一份汽车保险。就算没有法律规定，买一份合适的汽车保险对司机避免惹上官和承担过多维修费用来说都是非常实用的。 依据美国保险咨询中心的资料显示，一份基本的保险单应由6个险种组成。这其中有些是有州法律规定，有些是可以选择的，具体如下： 1.身体伤害责任险 2.财产损失责任险 3.医疗险或个人伤害保护险 4.车辆碰撞险 5.综合损失险 6.无保险驾驶人或保额不足驾驶人险 责任保险 责任险的投保险额一般用三个数字表示。不如，你的保险经纪人说你的保险单责任限额是20/40/10，这就代表每个人的人身伤害责任险赔偿限额是2万美元，每起事故的热身上海责任险赔偿限额是4万美元，每起事故的财产损失责任险的赔偿限额是1万美元。 人身伤害和财产损失责任险是大多数汽车保险单的基础。要求汽车保险的每个州都强令必须投保财产损失责任险，佛罗里达是唯一要求汽车保险但不要求投保人身伤害责任险的州。如果由于你的过错造成了事故，你的责任险会承担人身伤害、财产损失和法律规定的其他费用。人身伤害责任险将赔偿医疗费和误工工资；财产损失责任险将支付车辆的维修及零件更换费用。财产损失责任险通常承担对其他车辆的维修费用，但是也可以对你的车撞坏的灯杆、护栏、建筑物等其他物品的损坏进行赔偿。另一方当事人也可以决定起诉你赔偿精神损失。
高精度稳压直流电源 文摘:目前对于可调式直流电源的设计和应用现在有很多微妙的,多种多样的,有趣的问题。探讨这些问题(特别是和中发电机组有关),重点是在电路的经济适用性上,而不是要达到最好的性能。当然，对那些精密程度要求很高的除外。讨论的问题包括温度系数，短期漂移，热漂移，瞬态响应变性遥感和开关preregualtor型机组及和它的性能特点有关的的一些科目。 介绍 从商业的角度来看供电领域可以得到这样一个事实，在相对较低的成本下就可以可以获得标准类型的0.01%供电调节。大部分的供电用户并不需要这么高的规格，但是供应商不会为了减少客户这么一点的费用而把0.1%改成0.01%。并且电力供应的性能还包括其他一些因素，比如说线路和负载调解率。本文将讨论关于温度系数、短期漂移、热漂移,和瞬态的一些内容。 目前中等功率直流电源通常采用预稳压来提高功率/体积比和成本，但是只有某些电力供应采用这样的做法。这种技术的优缺点还有待观察。 温度系数 十年以前，大多数的商业电力供应为规定的0.25%到1%。这里将气体二极管的温度系数定位百分之0.01[1]。因此，人们往往会忽视TC（温度系数）是比规定的要小的。现在参考的TC往往比规定的要大的多。为了费用的减少，后者会有很大的提高，但是这并不是真正的TC。因此，如果成本要保持在一个低的水平，可以采用TC非常低的齐纳二极管，安装上差动放大电路，还要仔细的分析低TC绕线电阻器。 如图1所示，一个典型的放大器的第一阶段，其中CR1是参考齐纳二极管，R是输出电位调节器。
图1 电源输入级 图2 等效的齐纳参考电路 假设该阶段的输出是e3，提供额外的差分放大器，在稳定状态下e3为零，任何参数的变化都会引起输出的漂移；对于其他阶段来说也是一样的，其影响是减少了以前所有阶段的增益。因此，其他阶段的影响将被忽略。以下讨论的内容涵盖了对于TC整体的无论是主要的还是次要的影响。 R3的影响 CR1-R3分支的等效的电路如图2所示，将齐纳替换成了它的等效电压源E'和内部阻抗R2。对于高增益调节器，其中R3的变化对差分放大器的输入来说可以忽略不计，所以前后的变化由R3决定。 如果进一步假定IB << Iz;从（1）可以得到 同时，
机床加工外文翻译参考文献(文档含中英文对照即英文原文和中文翻译) 基本加工工序和切削技术 基本加工的操作 机床是从早期的埃及人的脚踏动力车和约翰·威尔金森的镗床发展而来的。它们为工件和刀具提供刚性支撑并可以精确控制它们的相对位置和相对速度。基本上讲，金属切削是指一个磨尖的锲形工具从有韧性的工件表面上去除一条很窄的金属。切屑是被废弃的产品，与其它工件相比切屑较短，但对于未切削部分的厚度有一定的增加。工件表面的几何形状取决于刀具的形状以及加工操作过程中刀具的路径。 大多数加工工序产生不同几何形状的零件。如果一个粗糙的工件在中心轴上转动并且刀具平行于旋转中心切入工件表面，一个旋转表面就产生了，这种操作称为车削。如果一个空心的管子以同样的方式在内表面加工，这种操作称为镗孔。当均匀地改变直径时便产生了一个圆锥形的外表面，这称为锥度车削。如果刀具接触点以改变半径的方式运动，那么一个外轮廓像球的工件便产生了；或者如果工件足够的短并且支撑是十分刚硬的，那么成型刀具相对于旋转轴正常进给的一个外表面便可产生，短锥形或圆柱形的表面也可形成。
平坦的表面是经常需要的，它们可以由刀具接触点相对于旋转轴的径向车削产生。在刨削时对于较大的工件更容易将刀具固定并将工件置于刀具下面。刀具可以往复地进给。成形面可以通过成型刀具加工产生。 多刃刀具也能使用。使用双刃槽钻钻深度是钻孔直径5-10倍的孔。不管是钻头旋转还是工件旋转，切削刃与工件之间的相对运动是一个重要因数。在铣削时一个带有许多切削刃的旋转刀具与工件接触，工件相对刀具慢慢运动。平的或成形面根据刀具的几何形状和进给方式可能产生。可以产生横向或纵向轴旋转并且可以在任何三个坐标方向上进给。 基本机床 机床通过从塑性材料上去除屑片来产生出具有特别几何形状和精确尺寸的零件。后者是废弃物，是由塑性材料如钢的长而不断的带状物变化而来，从处理的角度来看，那是没有用处的。很容易处理不好由铸铁产生的破裂的屑片。机床执行五种基本的去除金属的过程：车削，刨削，钻孔，铣削。所有其他的去除金属的过程都是由这五个基本程序修改而来的，举例来说，镗孔是内部车削；铰孔，攻丝和扩孔是进一步加工钻过的孔；齿轮加工是基于铣削操作的。抛光和打磨是磨削和去除磨料工序的变形。因此，只有四种基本类型的机床，使用特别可控制几何形状的切削工具1.车床，2.钻床，3.铣床，4.磨床。磨削过程形成了屑片，但磨粒的几何形状是不可控制的。 通过各种加工工序去除材料的数量和速度是巨大的，正如在大型车削加工，或者是极小的如研磨和超精密加工中只有面的高点被除掉。一台机床履行三大职能：1.它支撑工件或夹具和刀具2.它为工件和刀具提供相对运动3.在每一种情况下提供一系列的进给量和一般可达4-32种的速度选择。 加工速度和进给 速度，进给量和切削深度是经济加工的三大变量。其他的量数是攻丝和刀具材料，冷却剂和刀具的几何形状，去除金属的速度和所需要的功率依赖于这些变量。 切削深度，进给量和切削速度是任何一个金属加工工序中必须建立的机械参量。它们都影响去除金属的力，功率和速度。切削速度可以定义为在旋转一周时
汽车变速器设计 ----------外文翻译 我们知道，汽车发动机在一定的转速下能够达到最好的状态，此时发出的功率比较大，燃油经济性也比较好。因此，我们希望发动机总是在最好的状态下工作。但是，汽车在使用的时候需要有不同的速度，这样就产生了矛盾。这个矛盾要通过变速器来解决。 汽车变速器的作用用一句话概括，就叫做变速变扭，即增速减扭或减速增扭。为什么减速可以增扭，而增速又要减扭呢？设发动机输出的功率不变，功率可以表示为 N = w T，其中w是转动的角速度，T是扭距。当N固定的时候，w与T是成反比的。所以增速必减扭，减速必增扭。汽车变速器齿轮传动就根据变速变扭的原理，分成各个档位对应不同的传动比，以适应不同的运行状况。 一般的手动变速器内设置输入轴、中间轴和输出轴，又称三轴式，另外还有倒档轴。三轴式是变速器的主体结构，输入轴的转速也就是发动机的转速，输出轴转速则是中间轴与输出轴之间不同齿轮啮合所产生的转速。不同的齿轮啮合就有不同的传动比，也就有了不同的转速。例如郑州日产ZN6481W2G型SUV车手动变速器，它的传动比分别是：1档3.704:１；2档2.202:1；3档1.414:1；4档1:1；5档（超速档）0.802:1。 当汽车启动司机选择1档时，拨叉将1/2档同步器向后接合1档齿轮并将它锁定输出轴上，动力经输入轴、中间轴和输出轴上的1档齿轮，1档齿轮带动输出轴，输出轴将动力传递到传动轴上（红色箭头）。典型1档变速齿轮传动比是3:1,也就是说输入轴转3圈，输出轴转1圈。 当汽车增速司机选择2档时，拨叉将1/2档同步器与1档分离后接合2档齿轮并锁定输出轴上，动力传递路线相似，所不同的是输出轴上的1档齿轮换成2档齿轮带动输出轴。典型2档变速齿轮传动比是2.2:1，输入轴转2.2圈，输出轴转1圈，比1档转速增加，扭矩降低。
中文4285字 附录1 LATHES & MILLING A shop that is equipped with a milling machine and an engine lathe can machine almost any type of product of suitable size. The basic machines that are designed primarily to do turning，facing and boring are called lathes. Very little turning is done on other types of machine tools，and none can do it with equal facility. Because lathe can do boring，facing，drilling，and reaming in addition to turning，their versatility permits several operations to be performed with a single setup of the workpiece. This accounts for the fact that lathes of various types are more widely used in manufacturing than any other machine tool. Lathes in various forms have existed for more than two thousand years. Modern lathes date from about 1797，when Henry Maudsley developed one with a leads crew. It provided controlled，mechanical feed of the tool. This ingenious Englishman also developed a change gear system that could connect the motions of the spindle and leadscrew and thus enable threads to be cut. Lathe Construction.The essential components of a lathe are depicted in the block diagram of picture. These are the bed，headstock assembly，tailstock assembly，carriage assembly，quick-change gearbox，and the leadscrew and feed rod. The bed is the back bone of a lathe. It usually is made of well-normalized or aged gray or nodular cast iron and provides a heavy，rigid frame on which all the other basic components are mounted. Two sets of parallel，longitudinal ways，inner and outer，are contained on the bed，usually on the upper side. Some makers use an inverted V-shape for all four ways，whereas others utilize one inverted V and one flat way in one or both sets. Because several other components are mounted and/or move on the ways they must be made with precision to assure accuracy of alignment. Similarly，proper precaution should betaken in operating a lathe to assure that the ways are not damaged. Any inaccuracy in them usually means that the accuracy of the entire lathe is destroyed. The ways on most modern lathes are surface hardened to