EXTENDING BEARING LIFE
Bearings fail for a number of reasons，but the most common are misapplication，contamination，improper lubricant，shipping or handling damage，and misalignment. The problem is often not difficult to diagnose because a failed bearing usually leaves telltale signs about what went wrong．However，while a postmortem yields good information，it is better to avoid the process altogether by specifying the bearing correctly in The first place．To do this，it is useful to review the manufacturers sizing guidelines and operating characteristics for the selected bearing.
Equally critical is a study of requirements for noise, torque, and runout, as well as possible exposure to contaminants, hostile liquids, and temperature extremes. This can provide further clues as to whether a bearing is right for a job.
1 Why bearings fail
About 40% of ball bearing failures are caused by contamination from dust, dirt, shavings, and corrosion. Contamination also causes torque and noise problems, and is often the result of improper handling or the application environment．Fortunately, a bearing failure caused by environment or handling contamination is preventable，and a simple visual examination can easily identify the cause．
Conducting a postmortem il1ustrates what to look for on a failed or failing bearing．Then，understanding the mechanism behind the failure, such as brinelling or fatigue, helps eliminate the source of the problem.
Brinelling is one type of bearing failure easily avoided by proper handing and assembly. It is characterized by indentations in the bearing raceway caused by shock loading－such as when a bearing is dropped-or incorrect assembly. Brinelling usually occurs when loads exceed the material yield point(350,000 psi in SAE 52100 chrome steel)．It may also be caused by improper assembly, Which places a load across the races．Raceway dents also produce noise，vibration，and increased torque.
A similar defect is a pattern of elliptical dents caused by balls vibrating between raceways while the bearing is not turning．This problem is called false brinelling. It occurs on equipment in transit or that vibrates when not in
operation. In addition, debris created by false brinelling acts like an abrasive, further contaminating the bearing. Unlike brinelling, false binelling is often indicated by a reddish color from fretting corrosion in the lubricant.
False brinelling is prevented by eliminating vibration sources and keeping the bearing well lubricated. Isolation pads on the equipment or a separate foundation may be required to reduce environmental vibration. Also a light preload on the bearing helps keep the balls and raceway in tight contact. Preloading also helps prevent false brinelling during transit.
Seizures can be caused by a lack of internal clearance, improper lubrication, or excessive loading. Before seizing, excessive, friction and heat softens the bearing steel. Overheated bearings often change color，usually to blue-black or straw colored．Friction also causes stress in the retainer，which can break and hasten bearing failure．
Premature material fatigue is caused by a high load or excessive preload．When these conditions are unavoidable，bearing life should be carefully calculated so that a maintenance scheme can be worked out．Another solution for fighting premature fatigue is changing material．When standard bearing materials，such as 440C or SAE 52100，do not guarantee sufficient life，specialty materials can be recommended. In addition，when the problem is traced back to excessive loading，a higher capacity bearing or different configuration may be used．
Creep is less common than premature fatigue．In bearings．it is caused by excessive clearance between bore and shaft that allows the bore to rotate on the shaft．Creep can be expensive because it causes damage to other components in addition to the bearing．
0ther more likely creep indicators are scratches，scuff marks，or discoloration to shaft and bore．To prevent creep damage，the bearing housing and shaft fittings should be visually checked．
Misalignment is related to creep in that it is mounting related．If races are misaligned or cocked．The balls track in a noncircumferencial path．The problem is incorrect mounting or tolerancing，or insufficient squareness of the bearing mounting site．Misalignment of more than 1/4·can cause an early failure．
Contaminated lubricant is often more difficult to detect than misalignment or creep．Contamination shows as premature wear．Solid
contaminants become an abrasive in the lubricant．In addition。insufficient lubrication between ball and retainer wears and weakens the retainer．In this situation，lubrication is critical if the retainer is a fully machined type．Ribbon or crown retainers，in contrast，allow lubricants to more easily reach all surfaces．
Rust is a form of moisture contamination and often indicates the wrong material for the application．If the material checks out for the job，the easiest way to prevent rust is to keep bearings in their packaging，until just before installation．
2 Avoiding failures
The best way to handle bearing failures is to avoid them．This can be done in the selection process by recognizing critical performance characteristics．These include noise，starting and running torque，stiffness，nonrepetitive runout，and radial and axial play．In some applications, these items are so critical that specifying an ABEC level alone is not sufficient．Torque requirements are determined by the lubricant，retainer，raceway quality(roundness cross curvature and surface finish)，and whether seals or shields are used．Lubricant viscosity must be selected carefully because inappropriate lubricant，especially in miniature bearings，causes excessive torque．Also，different lubricants have varying noise characteristics that should be matched to the application. For example，greases produce more noise than oil．
Nonrepetitive runout(NRR)occurs during rotation as a random eccentricity between the inner and outer races，much like a cam action．NRR can be caused by retainer tolerance or eccentricities of the raceways and balls．Unlike repetitive runout, no compensation can be made for NRR.
NRR is reflected in the cost of the bearing．It is common in the industry to provide different bearing types and grades for specific applications．For example，a bearing with an NRR of less than 0.3um is used when minimal runout is needed，such as in disk—drive spindle motors．Similarly，machine—tool spindles tolerate only minimal deflections to maintain precision cuts．Consequently, bearings are manufactured with low NRR just for machine-tool applications．
Contamination is unavoidable in many industrial products，and shields and seals are commonly used to protect bearings from dust and dirt．However，a perfect bearing seal is not possible because of the movement between inner and outer races．Consequently，lubrication migration and contamination are always problems．
Once a bearing is contaminated, its lubricant deteriorates and operation becomes noisier．If it overheats，the bearing can seize．At the very least，contamination causes wear as it works between balls and the raceway，becoming imbedded in the races and acting as an abrasive between metal surfaces．Fending off dirt with seals and shields illustrates some methods for controlling contamination．
Noise is as an indicator of bearing quality．Various noise grades have been developed to classify bearing performance capabilities．
Noise analysis is done with an Anderonmeter, which is used for quality control in bearing production and also when failed bearings are returned for analysis. A transducer is attached to the outer ring and the inner race is turned at 1,800rpm on an air spindle. Noise is measured in andirons, which represent ball displacement in μm/rad.
With experience, inspectors can identify the smallest flaw from their sound. Dust, for example, makes an irregular crackling. Ball scratches make a consistent popping and are the most difficult to identify. Inner-race damage is normally a constant high-pitched noise, while a damaged outer race makes an intermittent sound as it rotates.
Bearing defects are further identified by their frequencies. Generally, defects are separated into low, medium, and high wavelengths. Defects are also referenced to the number of irregularities per revolution.
Low-band noise is the effect of long-wavelength irregularities that occur about 1.6 to 10 times per revolution. These are caused by a variety of inconsistencies, such as pockets in the race. Detectable pockets are manufacturing flaws and result when the race is mounted too tightly in multiplejaw chucks.
Medium-hand noise is characterized by irregularities that occur 10 to 60 times per revolution. It is caused by vibration in the grinding operation that produces balls and raceways. High-hand irregularities occur at 60 to 300 times
per revolution and indicate closely spaced chatter marks or widely spaced, rough irregularities.
Classifying bearings by their noise characteristics allows users to specify a noise grade in addition to the ABEC standards used by most manufacturers. ABEC defines physical tolerances such as bore, outer diameter, and runout. As the ABEC class number increase (from 3 to 9), tolerances are tightened. ABEC class, however, does not specify other bearing characteristics such as raceway quality, finish, or noise. Hence, a noise classification helps improve on the industry standard.
Flexible and Smart Online Monitoring and Fault Diagnosis
System for Rotating Machinery
Abstract
Monitoring the vibration signals of rotating machinery, ulteriorly, assessing the safety of equipment plays a significant role in ensuring the security of equipment and in saving maintenance fee. This paper integrated the idea of “configuration” in the industry control software, developed the“flexible” network-based online monitoring and fault diagnosis system. The network topology, configuration module, database, data acquisition workstation and monitoring components were presented. With the smart data acquisition strategy and strong adaptive monitoring tools, the system can be applied on kinds of rotating machinery, and the practical application of the system was introduced.
Keywords – online monitor, flexible system, smart system, configuration, rotating machinery
CONCLUSION
Based on the development trend of the network-based online monitoring and diagnosis system, this paper introduced the idea of “flexible” of ICS and the smart data acquisition strategy, developed the configurable and smart online monitor and diagnosis system with strong flexibility. The system can be applied on kinds of rotating machinery. The smart signal analysis tools can provide the appropriate diagnosis method kinds of equipment, hence can level up the accuracy of fault diagnosis and condition evaluation.
I. INTRODUCTION
With the development of the modern technology, a variety of rotating machinery (such as steam turbine, fan,wind turbine, etc.) raises the level of automatic operation.Due to the significant roles of the rotating machinery in the modern production process, to ensure the safety, reliability,economical and optimized operation, and to evaluation of the
condition of the current equipment have become very important research fields. Thereinto, condition monitoring and fault diagnosis have been put more attention [1].
The database technology and network technology were introduced in the current online monitor and fault diagnosis system for rotating machinery. It not only enhanced the technology of online condition monitor and provided more sufficient and reliable data for the fault diagnosis, but also
made it possible to share the machinery information,ulteriorly to establish the fault analysis and diagnosis center in the special institute and provide the remote technique support for factory [2, 3, 4].
However, for the requirements of equipment management nowadays, the current network-based online monitoring system remains some defects as follows: (a) the measure point (MP), the interfaces of the software and the hardware had been fixed before developing of the monitoring system, therefore it was difficult to adapt the modern plant with numerous and various equipment; (b) the object of the current system was always the machinery or equipment, and it was difficult to achieve the goal of centralized management to the modern plant; (c) the data acquisition strategy was simple and cannot be changed with the change of the equipment state, and it was easily lead to the miss of the critical fault data and effected the accuracy of the fault diagnosis;
(d) the tools and methods for signal analysis and fault diagnosis were simple and could not meet
the demand of information fusion[5, 6].
Therefore, developing the system efficiently and reliably become a key problem in the development of modern monitoring system. The successful application of Industrial Control Software (ICS) provides a good idea for the
development of network-based Online Monitoring and Diagnosis System (OMDS). Although the ICS emphasize on control function while the OMDS put more attention on the data acquisition, signal analysis and save of long-running data, the “configurable” approach during the development of ICS can make the OMDS well adapt to various machinery and become “flexible”. Additionally, the OMDS become more smarted by integrating the information fusion methods and neutral network with normal frequency-spectrum analysis methods, and enhance the capability of fault diagnosis and safety assessment for rotating machinery [7].
The direction of dissertation in the future
Professional introduction
My major is mechanical manufacturing and automation, it is to combine the mechanical equipment and automation by the way of computer, forming a series of advanced manufacturing technology, including CAD (Computer Aided Design), CAM (Computer Aided Manufacturing), FMC (Flexible Manufacturing System) and so on, and finally forms the large-scale computer integrated manufacturing system (CIMS) which make the traditional mechanical process get a qualitative leap. This professional directly reflect the modernization and industrialization level of a country, it relates to the design of mechanical industry of manufacturing, technology development, application study, operation management and sales management and so on , it is a large business of social demand .
The ability of the machinery manufacturing, directly affect the development of the whole society of industry. Recently the level of mechanical engineering and automation between China and the developed countries has been gradually reduced. With the demands of our country modernization, development in the aerospace, shipbuilding, mining industry, machinery manufacturing and automation needs more rapid development, and has great development space. At school we must learn PLC (programmable logic controller), grasp the weak electrical appliance control, the use of servo system and AC servo motor, the general design of electric circuit, and be
familiar with the metal material, metal heat treatment and manufacturing technology, mechanical design and other professional knowledge.
The professional employment situation is very good, many enterprises relate to machinery we can participate in , and even management can also do. Graduate students can engage in industrial production department of mechanical product design and development, manufacturing, tooling design, production process management, application of numerical control technology, industrial automation production management, computer software application, marketing and other aspects of the work, also can take part in teaching and research work in Colleges and universities or scientific research departments.
My research is superhard nano-micron PVD films applied research , PVD is the abbreviation of physical vapor deposition , it is a physical method used in the condition of vacuum , the surface of the solid or liquid material vaporized into gas atoms, molecules or parts of ionized into a plasma , and through the low pressure gas ( or plasma ) process , depositing on the substrate surface with a thin film for special functions . Physical vapor deposition methods include vacuum deposition , sputtering , arc plasma plating, ion plating, electron beam evaporation and molecular epitaxy . Not only can the metal or alloy film be deposited, many materials like compounds, ceramics, semiconductor, polymer film can also be deposited,it is a new material with wide application prospect in manufacturing technology. The superhard film made by this technology not only has high hardness, and ultrathin, high temperature resistance, no pollution, almost zero emissions, it is suitable for tools, spare parts and abrasion resistance, anti-oxidation, anti-corrosion, self lubrication of the surface of friction and wear and other special properties, it is a technology of the most promising and valuable application in the modern surface engineering technology.
the simplest and most effective way to go into a field is to find a discussion of this field monographs or textbooks, when the basic concepts in this field as well as the correlation between the meaning is clear, just go to read the papers in this field, we will know the score and grasp them. Therefore, before the thesis proposal in October of next year , I will seriously learning materials, and finally understand and master the papers of instructors and the various papers about PVD coating technology at home and abroad , step by step and in good order to learn everything, in the the thesis proposal of the day can not panic disorder and keep calm .
如何延长轴承寿命
1 轴承失效的原因
在球轴承的失效中约有40%是由灰尘、脏物、碎屑的污染以及腐蚀造成的。污染通常是由不正确的使用和不良的使用环境造成的，它还会引起扭矩和噪声的问题。由环境和污染所产生的轴承失效是可以预防的，而且通过简单的肉眼观察是可以确定产生这类失效的原因。
通过失效后的分析可以得知对已经失效的或将要失效的轴承应该在哪些方面进行查看。弄清诸如剥蚀和疲劳破坏一类失效的机理，有助于消除问题的根源。
只要使用和安装合理，轴承的剥蚀是容易避免的。剥蚀的特征是在轴承圈滚道上留有由冲击载荷或不正确的安装产生的压痕。剥蚀通常是在载荷超过材料屈服极限时发生的。如果安装不正确从而使某一载荷横穿轴承圈也会产生剥蚀。轴承圈上的压坑还会产生噪声、振动和附加扭矩。
类似的一种缺陷是当轴承不旋转时由于滚珠在轴承圈间振动而产生的椭圆形压痕。这种破坏称为低荷振蚀。这种破坏在运输中的设备和不工作时仍振动的设备中都会产生。此外，低荷振蚀产生的碎屑的作用就象磨粒一样，会进一步损害轴承。与剥蚀不同，低荷振蚀的特征通常是由于微振磨损腐蚀在润滑剂中会产生淡红色。
消除振动源并保持良好的轴承润滑可以防止低荷振蚀。给设备加隔离垫或对底座进行隔离可以减轻环境的振动。另外在轴承上加一个较小的预载荷不仅有助于滚珠和轴承圈保持紧密的接触，并且对防止在设备运输中产生的低荷振蚀也有帮助。
造成轴承卡住的原因是缺少内隙、润滑不当和载荷过大。在卡住之前，过大的摩擦和热量使轴承钢软化。过热的轴承通常会改变颜色，一般会变成蓝黑色或淡黄色。摩擦还会使保持架受力，这会破坏支承架，并加速轴承的失效。
材料过早出现疲劳破坏是由重载后过大的预载引起的。如果这些条件不可避免，就应仔细计算轴承寿命，以制定一个维护计划。
另一个解决办法是更换材料。若标准的轴承材料不能保证足够的轴承寿命，就应当采用特殊的材料。另外，如果这个问题是由于载荷过大造成的，就应该采用抗载能力更强或其他结构的轴承。
蠕动不象过早疲劳那样普遍。轴承的蠕动是由于轴和内圈之间的间隙过大造成的。蠕动的害处很大，它不仅损害轴承，也破坏其他零件。
蠕动的明显特征是划痕、擦痕或轴与内圈的颜色变化。为了防止蠕动，应该先用肉眼检查一下轴承箱件和轴的配件。
2 避免失效的方法
解决轴承失效问题的最好办法就是避免失效发生。这可以在选用过程中通过考虑关键性能特征来实现。这些特征包括噪声、起动和运转扭矩、刚性、非重复性振摆以及径向和轴向间隙。
扭矩要求是由润滑剂、保持架、轴承圈质量（弯曲部分的圆度和表面加工质量）以及是否使用密封或遮护装置来决定。润滑剂的粘度必须认真加以选择，因为不适宜的润滑剂会产生过大的扭矩，这在小型轴承中尤其如此。另外，不同的润滑剂的噪声特性也不一样。举例来说，润滑脂产生的噪声比润滑油大一些。因此，要根据不同的用途来选用润滑剂。
在轴承转动过程中，如果内圈和外圈之间存在一个随机的偏心距，就会产生与凸轮运动非常相似的非重复性振摆（NRR）。保持架的尺寸误差和轴承圈与滚珠的偏心都会引起NRR。和重复性振摆不同的是，NRR是没有办法进行补偿的。
在工业中一般是根据具体的应用来选择不同类型和精度等级的轴承。例如，当要求振摆最小时，轴承的非重复性振摆不能超过0.3微米。同样，机床主轴只能容许最小的振摆，以保证切削精度。因此在机床的应用中应该使用非重复性振摆较小的轴承。
在许多工业产品中，污染是不可避免的，因此常用密封或遮护装置来保护轴承，使其免受灰尘或脏物的侵蚀。但是，由于轴承内外圈的运动，使轴承的密封不可能达到完美的程度，因此润滑油的泄漏和污染始终是一个未能解决的问题。
一旦轴承受到污染，润滑剂就要变质，运行噪声也随之变大。如果轴承过热，它将会卡住。当污染物处于滚珠和轴承圈之间时，其作用和金属表面之间的磨粒一样，会使轴承磨损。采用密封和遮护装置来挡开脏物是控制污染的一种方法。
柔性的和智能的在线监测与故障诊断的旋转机械系统
旋转机械振动信号的监测，进一步地说，在确保设备的安全性和节省维修费用上设备安全性的评估起到非常重要的角色。本文整合了工业控制软件中的“配置”理念，开发出“柔性的”基于网络的在线监测和故障诊断的系统。该网络的拓扑结构、配置模块、数据库、数据采集工作站和监视组件已得到介绍。随着智能数据采集策略和强大的适应监测工具的开发应用，该系统可以应用于各种旋转机械，而且该系统的实际应用也以得到介绍。
关键词：在线监测，柔性系统，智能系统，结构配置，旋转机械
基于以网络为基础的在线监测和故障诊断系统的发展趋势，本文介绍了因特网连接共享和智能的数据采集策略“柔性”的思想，开发出具有很强的灵活性的结构配置和智能的在线监测与诊断系统。该系统可以用于各种旋转机械。智能信号分析工具能为各种设备提供适当的诊断方法，因此能够提高故障诊断和工况评估的准确性。
引言
随着现代科技的发展，各种各样的旋转机械（如蒸汽机，风扇，风力发电机组等等）提升了自动控制的层次。由于旋转机械在现代生产过程中的重要作用，以确保安全性，可靠性，经济性和优化操作，并评价当前设备的状态已成为非常重要的研究领域。其中，状态监测和故障诊断已投入更多的关注。
数据库技术和网络技术已经在旋转机械当前的在线监测和故障诊断系统中介绍过，它不仅提高了在线状态监测技术和为故障诊断提供更充分更可靠的数据，而且使得机械信息共享成为可能，进而在专门研究机构建立故障分析和诊断中心，为制造厂提供远程技术支持。
然而，对于当前的设备管理要求，目前的这种基于网络在线监测系统仍然存在一些缺陷，如下：（a)测量点（MP),在监测系统研发之前，系统的软件和硬件的接口已经被固定了，因此该系统很难适应现代工厂众多和各种各样的设备；（b)当前系统的对象仍然是机械装置或者设备，现代工厂很难实现集中管理的目标；（c)数据采集策略很简单，也不能随着设备状态的变化而变化，而且很容易导致决定性错误数据的缺失和影响故障诊断的准确性；（d)信号分析和故障诊断的工具和方法简单而且不能满足信息融合的需求。
因此，有效地和可靠地开发系统已成为现代监测系统发展的关键问题。工业控制软件（ICS)的成功应用为基于网络在线监测和故障诊断系统（OMDS)提供了一个好的思想。尽管工业控制软件强调控制功能而在线监测和故障诊断系统专注于数据采集，信号分析和长期数据的保存，在工业控制软件的发展过程中“结构配置”的方法能使得在线监测和故障诊断系统很好的适应各种机械装置和成为“柔性化”。此外，在线监测和故障诊断系统通过集成的信息融合法和带有正常频谱的神经网络分析法而变得更加智能，它提高了故障诊断和旋转机械的安全评估能力。
专业介绍：
我的专业是机械制造及其自动化，它是将机械设备与自动化通过计算机的方式结合起来，形成一系列先进的制造技术，包括CAD（计算机辅助设计）、CAM（计算机辅助制造）、FMC（柔性制造系统）等等，最终形成大规模计算机集成制造系统（CIMS），使传统的机械加工得到质的飞跃。此专业直接反映一个国家的现代化和工业化水平，它涉及到机械行业中的设计制造、科技开发、应用研究、运行管理和经营销售等诸多的方向，是社会需求很
大的一个行业。
机械制造的能力，直接影响整个社会工业产业的发展。我国现在机械设计制造及其自动化水平与发达国家已经在逐步缩小。随着我国现代化建设的需要，在航天、造船、采矿等工业领域的发展，机械制造和自动化更加需要长足的发展，并且存在极大的发展空间。我们在学校期间须多学习PLC(可编程控制器)，掌握弱电电器控制，伺服系统及交流伺服电机的使用，普通强电电路的设计，而且要熟悉金属材料，金属热处理及制造工艺，机械设计基础等专业知识。
本专业就业形势很好，与机械有关的很多企业都可以去，甚至管理的也可以。学生毕业后可从事工业生产部门的机械产品设计开发、加工制造、工装模具设计、生产过程管理、数控技术应用、工业自动生产维护管理、计算机软件应用、产品营销等方面的工作，也可在高等院校、科研部门从事教学和科研工作。
今后的学位论文方向：
我的研究方向是超硬纳微米PVD薄膜的应用研究，PVD是物理气相沉积（Physical Vapor Deposition)的英文缩写，它是一种在真空条件下采用物理方法，将固体或液体材料表面气化成气态原子、分子或部分电离成离子，并通过低压气体（或等离子体)过程，在基体表面沉积具有某种特殊功能薄膜的技术。物理气相沉积的方法包括真空蒸镀、溅射镀膜、电弧等离子体镀、离子镀、电子束蒸镀及分子外延等。物理气相沉积的不仅可以沉积金属膜、合金膜，还可以沉积化合物、陶瓷、半导体、聚合物膜等，是具有广泛应用前景的新材料制造技术。采用此技术制备的超硬薄膜不仅具有超高硬度，且超薄、耐高温、无污染、几乎零排放，适合于工具、零件和摩擦磨损件表面的耐磨损、抗氧化、防腐蚀、自润滑等特殊性能要求，是现代表面工程技术中最具有发展前途和应用价值的一种技术。
进入一个领域最简单也是最有效的办法就是找一本这个领域的论述专著或者教材，当把这个领域的基本概念的内涵以及相互之间的关系搞清楚了之后，再去读这个领域的论文，就会因为心中有数而能够很好地把握了。因此在明年十月份开题之前，我会认真学习教材，最后理解和掌握导师的论文和国内外有关PVD涂层技术的各项论文资料，循序渐进有条不紊地学习，在开题的那天能不慌不乱，从容面对。
电气工程及其自动化专业英语 考试题型：选择10*2 单词翻译10*2 短句翻译5*4 长句翻译4*10 Exercise All the simple circuit elements that will be 在下面进行的工作中我们要研究的简单电路元件,可以根据流过元件的电流与元件两端的电压的关系进行分类。例如，如果元件两端的电压正比于流过元件的电流，即u＝ki，我们就把元件称为电阻器。其他的类型的简单电路元件的端电压正比于电流对时间的导数或正比于电流关于时间的积分。还有一些元件的电压完全独立于电流或电流完全独立于电压，这些是独立源。此外，我们还要定义一些特殊类型的电源，这些电源的电压或电流取决于电路中其他的电流或电压，这样的电源将被称为非独立源或受控源。 It must be emphasized that the linear 必须强调的是线性电阻器是一个理想的电路元件；它是物理元件的数学模型。我们可以很容易地买到或制造电阻器，但很快我们发现这种物理元件只有当电流、电压或者功率处于特定范围时其电压——电流之比才是恒定的，并且这个比值也取决于温度以及其它环境因素。我们通常应当把线性电阻器仅仅称为电阻器。只有当需要强调元件性质的时候才使用更长的形式称呼它。而对于任何非线性电阻器我们应当始终这么称呼它，非线性电阻器不应当必然地被视为不需要的元件。 If a circuit has two or more independent 如果一个电路有两个或多个独立源，求出具体变量值（电流或电压）的一种方法是使用节点分析法或网孔分析法。另一种方法是求出每个独立源对变量的作用然后把它们进行叠加。而这种方法被称为叠加法。叠加法原理表明线性电路某个元件两端的电压（或流过元件的电流）等于每个独立源单独作用时该元件两端的电压（或流过元件的电流）的代数和。 The ratio of the phase voltage to the 相电压与相电流之比等于电路的阻抗，符号为字母Z，阻抗是一个具有量纲为欧姆的复数量。阻抗不是一个相量，因此不能通过把它乘以e jωt,并取其实部把它转换成时域形式。但是，我们把电感器看作是通过其电感量L表现为时域形式而通过其阻抗jωL表现为频域形式，电容在时域里为电容量C而在频域里为1/jωc，阻抗是某种程度 上的频域变量而非时域变量。 Both wye and delta source connections 无论是星型连接的电源还是三角形连接的电源都有重要的实际应用意义。星型连接的电源用于长距离电力传输，此时电阻损耗(I2R)将达到最小。这是由于星型连接的线电压是三角形连接的线电压的√3倍，于是,对于相同的功率来说，三角型连接的线电流是星形连接的线电流的√3倍。三角形连接的电源使用在根据三相电源而需要的三个单相电路中。这种从三相到单相的转变用在住宅布线中因为家用照明和设备使用单相电源。三相电源用在需要大功率的工业布线中。在某些应用场合，无论负载是星形连接还是三角形连接并不重要。
01.THE ELEMENTS AND THE PERIODIC TABLE 01元素和元素周期 表。 The number of protons in the nucleus of an atom is referred to as the atomic number, or proton number, Z. The number of electrons in an electrically neutral atom is also equal to the atomic number, Z. The total mass of an atom is determined very nearly by the total number of protons and neutrons in its nucleus. This total is called the mass number, A. The number of neutrons in an atom, the neutron number, is given by the quantity A-Z. 原子核中的质子数的原子称为原子序数，或质子数，卓电子数的电中性的原子也等于原子序数Z，总质量的原子是非常接近的总数量的质子和中子在原子核。这被称为质量数，这个数的原子中的中子，中子数，给出了所有的数量 The term element refers to, a pure substance with atoms all of a single kind. To the chemist the "kind" of atom is specified by its atomic number, since this is the property that determines its chemical behavior. At present all the atoms from Z = 1 to Z = 107 are known; there are 107 chemical elements. Each chemical element has been given a name and a distinctive symbol. For most elements the symbol is simply the abbreviated form of
Lesson 1 力学的基本概念 1、词汇： statics [st?tiks] 静力学；dynamics动力学；constraint约束；magnetic [m?ɡ＇netik]有磁性的；external [eks＇t?:nl] 外面的, 外部的；meshing啮合；follower从动件；magnitude [＇m?ɡnitju:d] 大小；intensity强度，应力；non-coincident [k?u＇insid?nt]不重合；parallel [＇p?r?lel]平行；intuitive 直观的；substance物质；proportional [pr?＇p?:??n?l]比例的；resist抵抗，对抗；celestial [si＇lestj?l]天空的；product乘积；particle质点；elastic [i＇l?stik]弹性；deformed变形的；strain拉力；uniform全都相同的；velocity[vi＇l?siti]速度；scalar[＇skeil?]标量；vector[＇vekt?]矢量；displacement代替；momentum [m?u＇ment?m]动量； 2、词组 make up of由……组成；if not要不，不然；even through即使，纵然； Lesson 2 力和力的作用效果 1、词汇： machine 机器；mechanism机构；movable活动的；given 规定的，给定的，已知的；perform执行；application 施用；produce引起，导致；stress压力；applied施加的；individual单独的；muscular [＇m?skjul?]]力臂；gravity[ɡr?vti]重力；stretch伸展，拉紧，延伸；tensile[tensail]拉力；tension张力，拉力；squeeze挤；compressive 有压力的，压缩的；torsional扭转的；torque转矩；twist扭，转动；molecule [m likju:l]分子的；slide滑动; 滑行；slip滑，溜；one another 互相；shear剪切；independently独立地，自立地；beam梁；compress压；revolve (使)旋转；exert [iɡ＇z?:t]用力，尽力，运用，发挥，施加；principle原则, 原理，准则，规范；spin使…旋转；screw螺丝钉；thread螺纹； 2、词组 a number of 许多；deal with 涉及，处理；result from由什么引起；prevent from阻止，防止；tends to 朝某个方向；in combination结合；fly apart飞散； 3、译文： 任何机器或机构的研究表明每一种机构都是由许多可动的零件组成。这些零件从规定的运动转变到期望的运动。另一方面，这些机器完成工作。当由施力引起的运动时，机器就开始工作了。所以，力和机器的研究涉及在一个物体上的力和力的作用效果。 力是推力或者拉力。力的作用效果要么是改变物体的形状或者运动，要么阻止其他的力发生改变。每一种
当一个命题函数的所有变量都赋上了值，所得到的语句就有了真假值。然而,还有另一个重要的方法,称为量词化,为了从一个命题函数中生成一个命题，两种形式的量词化将在本节中被讨论，即全称量词和存在量词。 许多数学家陈述断言，对于所有在特定的定义域内的变量，它的取值是真的，其中特定的定义域称为论域，像这样的量词化例子我们通常用全称量词化。全称量词化是一个命题函数对于在论域内的所有x的取值，P(x)都是真的，论域指的是对于x可能取的值。 定义1：P(x)的全称量词化是这样一个命题：对论域中的所有x,P(x)都是真的。把P(x)的全称量词化记作?xP(x)。这里?是被叫做全称量词。 命题xP(X)也可以表达成“对于所有的xP(x)”或者对于“每一个 xP(x)” 注意：最好不用any这个词，因为它可能意指“每一个”或“某一个”，经常导致意义含糊不清。而在某些情况下，例如用于否定句中，如在句子“there is not any reason not to study hard.”（没有任何不努力学习的理由）中，any的含义却是清楚的。 例题5. 用全称量词化表达一个句子“对于班上的每一个学生都学习了微积分。” 方法：设P(x)为语句“x 学习了微积分。” 然后语句“对于班上每一个学生都学习了微积分”可以被写成?xP(x)的形式，然而学生都包含在班上这个论域里。
这个语句也能被表达成 ?x(s(x)→P(x)), 然而S(x)语句是“x在班上”。 P(x)同前者一样，论域是所有学生的集合。 例题5说明，对于一个定理，可采用不止一种的好办法来证明。 许多数学家陈述断言，对于一个有特定取值的元素，像这样的语句通常用存在量词化，对于存在量词化，我们形成一个命题是正确的，当且仅当P(x)是真的至少对于一个在论域内的x。 定义2.P(x)的存在量词化是这样一个命题：在论域中存在一个元素x 使得P(x)都是真的，把P(x)的存在量词化记作?xP(x)。这里?是存在量词。 存在量词化?xP(x)也可以表达为“对于P(x)存在一个x”,“对于P(x)至少有一个x”,或者对于一些xP(x)”。 例题6.设P(x)为语句“x>3”.对于存在量词化?xP(x)在那些情况下是真的，然而论域是真值的集合。 方法：因为“x>3”是真的，例如，当x=4则对于存在量词化P(x)，即?xP(x)是真的。
After winning the important game they hoisted their captain to their shoulders in shouting triumph. 赢得那场重要的比赛之后，他们把队长抬到肩膀上欢呼着胜利。 Anyone who picks up this novel and reads the first paragraph will be hard pressed to put it down. 任何人只要拿起这本小说读了第一段，就会发现很难把它放下。 A true hero possesses has courage, a noble purpose and a willingness to make sacrifices. 一个真正的英雄有勇气，有高尚的目标，而且乐于奉献。 For now, it remains to me to thank you once more for joining us and wish you good luck in your work. 且让我再次感谢大家的参与，祝你们工作顺利。 He took a gamble on starting a factory with all the money his parents had left him. 他孤注一郑，用父母留给他的所有钱来开一家工厂。 He decided to channel his energies into something useful, instead of being glued to sitting in front of the TV set all day long. 他决定把自己的精力用到有益的事上，而不是整天守在电视机前。 He teaches in a middle school, but he does some translation work on the side to bring in extra cash money. 他在中学教书，但也兼职做些翻译来赚取外快。 He travelled from one village to another, dropping in on families and listening to their complaints and problems. 他从一个村子来到另一个村子，走家串户，听他们诉苦。 His words were drowned out by loud cheers from the crowd. 他的话被群众的大声欢呼所淹没。 He may promise to change, but it’s the same old story of saying one thing and doing another.他也许会答应改变，但无非又是说一套做一套罢了。 I racked my brains about how to break the terrible news to him. 我苦苦思索该怎样把这可怕的消息告诉他。 It will be impossible for me to repay my parents for everything they have done for me. 我将永远无法报答父母为我所做的一切。 I said right from the beginning that he would cause us trouble. 我一开始就说过，他会给我们惹麻烦的 In a sense, life is like swimming; if you keep holding on to the sides of the pool, you (will) never learn. 从某种意义上说，生活就像游泳。如果你总是扶住池边，就永远也学不会。 I just can’t figure her out, she’s a mystery to me. 我简直摸不透他，他对我是个迷 I looked at the printed page but the words made no sense. 我看着那印满字的书页，但不知上面写些什么 In the rush to go for globalization, we should watch out for collision of cultures. 在全球化热潮中，我们要堤防不同文化的冲突 In the circumstances it was not surprising that there was trouble. 在这种情况下，出现麻烦是不足为奇的 It’s good to be confident (about yourself), but there’s a difference betwe en (self-)confidence and conceit. 自信是件好事，但自信与自负是有区别的。 Jim always sides with John in an arg ument. 在答辩中吉姆总是站在约翰那一边。 Only those who have lived through a similar experience can fully appreciate this. 只有那些有过类似经历的人，才能够完全理解这一点。 Only those who stick it out can achieve success. Those who give up halfway will never realize their dreams. 只有坚持到底的人才会成功。半途而废的人永远也无法实现梦想。
外文翻译 英文原文 Belt Conveying Systems Development of driving system Among the methods of material conveying employed，belt conveyors play a very important part in the reliable carrying of material over long distances at competitive cost．Conveyor systems have become larger and more complex and drive systems have also been going through a process of evolution and will continue to do so．Nowadays，bigger belts require more power and have brought the need for larger individual drives as well as multiple drives such as 3 drives of 750 kW for one belt(this is the case for the conveyor drives in Chengzhuang Mine)．The ability to control drive acceleration torque is critical to belt conveyors’performance．An efficient drive system should be able to provide smooth，soft starts while maintaining belt tensions within the specified safe limits．For load sharing on multiple drives．torque and speed control are also important considerations in the drive system’s design. Due to the advances in conveyor drive control technology，at present many more reliable．Cost-effective and performance-driven conveyor drive systems covering a wide range of power are available for customers’ choices[1]. 1 Analysis on conveyor drive technologies 1．1 Direct drives Full-voltage starters．With a full-voltage starter design，the conveyor head shaft is direct-coupled to the motor through the gear drive．Direct full-voltage starters are adequate for relatively low-power, simple-profile conveyors．With direct fu11-voltage starters．no control is provided for various conveyor loads and．depending on the ratio between fu11-and no-1oad power requirements，empty starting times can be three or four times faster than full load．The maintenance-free starting system is simple，low-cost and very reliable．However, they cannot control starting torque and maximum stall torque；therefore．they are
专业英语翻译1
Basic Chemistry 1. Atomic Structure Matter has mass and takes up space. Atoms are basic building blocks of matter, and cannot be chemically subdivided by ordinary means. Both the protons and neutrons reside in the nucleus. Protons have a positive (+) charge, neutrons have no charge --they are neutral. Electrons reside in orbitals around the nucleus. They have a negative charge (-). It is the number of protons that determines the atomic number. The number of protons in an element is constant but neutron number may vary, so mass number (protons + neutrons) may vary. 1。原子结构 物质有质量，占空间。原子是物质的基本组成物，不能用普通的方法进行化学细分。 质子和中子都驻留在原子核中。质子有一个正电荷，中子是不带电的，它们是中性的。电子在原子核周围的轨道上。他们有一个负电荷（-）。 它是确定原子序数的质子数。在一个元素中的质子的数量是恒定的，但中子数可能会有所不同，所以质量数（质子+中子）可能会有所不同。 The same element may contain varying numbers of neutrons; these forms of an element are called isotopes. The chemical properties of isotopes are the same, although the physical properties of some isotopes may be different. Some isotopes are radioactive-meaning they "radiate" energy as they decay to a more stable form, perhaps another element half-life: time required for half of the atoms of an element to decay into stable form. Another example is oxygen, with atomic number of 8 can have 8, 9, or 10 neutrons. 相同的元素可能含有不同数量的中子，这些元素
第一章：应力与应变 1.That branch of scientific analysis which motions, times and forces is called mechanics and is made up of two parts, statics and dynamics. 研究位移、时间和力运动乘力是科学分析法的一个分歧，被称作力学，力学由两大部分组成，静力学和动力学。 2.For example, if the force operating on a sleeve bearing becomes too high, it will squeeze out the oil film and cause metal-to-metal contact, overheating and rapid failure of the bearing. 例如：如果止推轴承上的作用力过大的话，会挤出油膜，引起金属和金属之间的相互接触，轴承将过热而迅速失效。 3.Our intuitive concept of force includes such ideas as place of application, direction, and magnitude, and these are called the characteristics of a force. 力的直观概念包括力的作用点、大小、方向，这些被称为力的三要素。 4.All bodies are either elastic or plastic and will be deformed if acted upon by forces. When the deformation of such bodies is small, they are frequently assumed to be rigid, i.e., incapable of deformation, in order to simplify the analysis. 所有的物体既可以是弹性的也可以是塑性的，如果受到力的作用就产生变形。当变形很小的时候它们被假设成刚体，也就是不产生变形。 5.The rigid-body assumption cannot be used in internal stresses and strains due to the applied forces to be analyzed. Thus we consider the
一．电气名词Electric items 二．线路（母线、回路）Lines (Bus , circuits) 三．设备Equipments 四．保护、继电器Protection , relays 五．电气仪表Electric instruments 六．防雷Lightning protection 七．接地Grounding , earthing 八．室、所Room , Substation 九．电修车间设备Equipments of electric repair 十．材料Material 十一．图名Drawings , diagrams 十二．表头Tables 十三．标准图词汇Terms from standard DWG 一．电气名词Electric items 交（直）流Alternating (direct) current 短路电流Short-circuit current 起始次暂态短路电流Initial subtransient short-circuit current 冲击电流Impulse current 稳态短路电流Steady state short-circuit current 临界电流Critical current 切断电流Rupturing current 熔断电流Blow-out current 故障电流Fault current 计算电流Calculating current 极限有限电流Limit effective current 过电流Over current 逆电流Inverse current 整定电流Setting current 额定电流Rated current 电流密度Current density 短路电流最大有效值Maximum effective value of short-circuit current 高压High-voltage , High-tension 低压Low-voltage , Low-tension 计算电压Calculating voltage 激磁电压Exciting voltage 冲击电压Impulse voltage 临界电压Critical voltage
United 1 材料科学与工程 材料在我们的文化中比我们认识到的还要根深蒂固。如交通、房子、衣物，通讯、娱乐和食物的生产，实际上，我们日常生活中的每一部分都或多或少地受到材料的影响。历史上社会的发展、先进与那些能满足社会需要的材料的生产及操作能力密切相关。实际上，早期的文明就以材料的发展程度来命名，如石器时代，铜器时代。早期人们能得到的只有一些很有限的天然材料，如石头、木材、粘土等。渐渐地，他们通过技术来生产优于自然材料的新材料，这些新材料包括陶器和金属。进一步地，人们发现材料的性质可以通过加热或加入其他物质来改变。在这点上，材料的应用完全是一个选择的过程。也就是说，在一系列非常有限的材料中，根据材料的优点选择一种最适合某种应用的材料。直到最近，科学家才终于了解材料的结构要素与其特性之间的关系。这个大约是过去的 60 年中获得的认识使得材料的性质研究成为时髦。因此，成千上万的材料通过其特殊的性质得以发展来满足我们现代及复杂的社会需要。很多使我们生活舒适的技术的发展与适宜材料的获得密切相关。一种材料的先进程度通常是一种技术进步的先兆。比如，没有便宜的钢制品或其他替代品就没有汽车。在现代，复杂的电子器件取决于所谓的半导体零件. 材料科学与工程有时把材料科学与工程细分成材料科学和材料工程学科是有用的。严格地说，材料科学涉及材料到研究材料的结构和性质的关系。相反，材料工程是根据材料的结构和性质的关系来设计或操纵材料的结构以求制造出一系列可预定的性质。从功能方面来说，材料科学家的作用是发展或合成新的材料，而材料工程师是利用已有的材料创造新的产品或体系，和/或发展材料加工新技术。多数材料专业的本科毕业生被同时训练成材料科学家和材料工程师。“structure”一词是个模糊的术语值得解释。简单地说，材料的结构通常与其内在成分的排列有关。原子内的结构包括介于单个原子间的电子和原子核的相互作用。在原子水平上，结构包括原子或分子与其他相关的原子或分子的组织。在更大的结构领域上，其包括大的原子团，这些原子团通常聚集在一起，称为“微观”结构，意思是可以使用某种显微镜直接观察得到的结构。最后，结构单元可以通过肉眼看到的称为宏观结构。 “Property”一词的概念值得详细阐述。在使用中，所有材料对外部的刺激都表现出某种反应。比如，材料受到力作用会引起形变，或者抛光金属表面会反射光。材料的特征取决于其对外部刺激的反应程度。通常，材料的性质与其形状及大小无关。实际上，所有固体材料的重要性质可以概括分为六类：机械、电学、热学、磁学、光学和腐蚀性。对于每一种性质，其都有一种对特定刺激引起反应的能 力。如机械性能与施加压力引起的形变有关，包括弹性和强度。对于电性能，如电导性和介电系数，特定的刺激物是电场。固体的热学行为则可用热容和热导率来表示。磁学性质
1.我们可以把钢再次加热到临界温度以下的某一温度，然后在慢慢让其冷却。We can heat the steel again to a temperature below the critical temperature, then cool it slowly. 2.无论任何简单的机床，都是由单一元件即通称为机械零件或部件组成的。However simple, any machine is a combination of individual components generally referred to as machine elements or parts. 3.这些金属不都是好的导体。 All these metals are not good conductors. 4. 在做带电实验的时候，再怎么小心都不为过。 You can't be too careful in performing an experiment. 5.利用发电机可以把机械能转变成电能。 The mechanical energy can be changed back into electrical energy by means of a generator or dynamo. 6.假定电源输入的电压保持不变。 Assume that the voltage input of the power supply remains the same. 7.化石燃料是发电过程中最为频繁使用的能源。 Fossil fuels are most frequently used source daring the power generation process. 8单个机械零件的可靠性成为评估整台机器使用寿命的基本因素。 The individual reliability of machine elements becomes the basis for estimating the overall life 9.说我们生活在一个电子时代，这一点都不夸张。 It's no exaggeration to say that we live in an electronic age. 10.发动机的转速不应超过最大允许值。 Engine revolution should not exceed the maximum permissible. 11.如能从大型核电站获得成本极低的电力，电解氢的竞争能力就会增强。（Electrolytic hydrogen）。 If extremely low-cost power were ever to become available from large nuclear power plants, electrolytic hydrogen would become competitive. 12.电子技术提供了一种新的显示时间的方法。 A new way of displaying time has been given by electronics. 13.远距离输电需要高压，安全用电需要低压。 High voltage is necessary for long transmission line while low voltage for safe use. 14.铝的电阻大约是同等尺寸的铜的1.5倍。 The resistance of aluminum is approximately half again as great as that of copper for the same dimensions = size 15.In fact,it is impossible for no force to be exerted on a body,since in this world everything is subject to the for ce of gravity. 事实上，物体不受外力作用是不可能的，因为在这个世界上任何物体都要受到重力的作用。 16.In a thermal power plant,all the chemical energy is not
实用资料：电气工程专业课(电力类)翻译参考 专业外语：Professional English 电路（上） electrical circuit (I) 电路（下） electrical circuit (II) 金工实习 machinery practice 电机（上） electrical machinery (I) 电工实验与测试 electrical experiment & test 电子综合实践 integrated electronic practice 信号与系统 signal & system 电子技术基础（模拟） fundamentals of electronic (analog) 电磁场electromagnetic field 电子技术实验 electronic experiment(I) 电子辅助设计EDA Electronic Design Automatic(I) 发电厂动力工程基础 Heat power engineering in generating plant 企业管理 enterprise management 电气主系统electrical system principle 电力系统稳态/暂态分析 Steady-State/ Transient-State Analysis of Power System 电力系统继电保护 Power System Relaying Protection 电力系统潮流计算机分析：Computer Analysis of Power Flow 数字电子技术 Digital Electrical Technique 微机原理 microcomputer principle 电子技术基础（数字） fundamentals of electronic (digital) 自动控制 automatic control theory 电力系统分析 electric power system analysis 电子技术基础实验electronic experiment(II) 电气主系统课程设计 electrical system principle-course design 电子辅助设计EDA Electronic Design Automatic(II) 通信与计算机网络 communication & computer networks 电力系统继电保护 electric power system relaying 电力系统继电保护 Power System Protective Relaying 电力系统远动技术electric power system remote protocol 生产实习productive practice Technology 继电保护课程设计 electric power system relaying-course design 电力电子技术 power electronics 电力电子技术基础：Fundamentals of Electronics Power Technology 电力电子课程设计 Power electronics course design 电力系统自动控制 electric power system control & automation 高电压技术 High voltage engineering Technology 变电站自动化 substation automation 电力经济 electric power system economics 电能质量控制 electric power quality control 配电网自动化 distribution system automation 电力系统新技术 new techniques on electric power system
Uint1 1这一切不是一朝一夕可以实现的（achieve实现） All this can’t be chieved overnight 2下午6点种左右体育馆通常很忙（tend to 通常、易于） The gum tend to be busy at around 6 o’clock in the ofrrrnoon 3这个地区现在不安全，还是远离它为好（take away from 远离） The area is not safe at the moment,so it’sbetter to stay away from it 4就销售而言，他们是4该地区五大超市之一（in terms of 在。。。方面、就。。。而言） In terms of sales, they are one of top five supermarket in the area 5这间房既要作卧室又要作客房（severs as 作为） The room serve as not only bedrome but also livingroom 6生产部负责监督这个项目的进展（monitor 监督） The product department is responsible for monitoring the progress 7上个月经理忙于一项对营销活动的研究工作（be involved in 参与卷入） The product was involved in a research on marking activities last month 8现在许多大公司都利用网站来推销他们的产品和服务（promote 推销） Uany big companies use websites to promote their products and seroices Uint2 1在这所新医院上面已经花费了大笔资金（a great deal of 大量） A great deal of mony has been spent on the new hospital 2成功与否取决于你的努力和能力（depend on 取决于） Success depends on your efforts ands ability 3很难时刻掌握科技方面的新发展(keep track of记录了解动态) It is difficult to keep track of new development in science and technology 4所有投诉都将由经理来处理（deal with 处理） All complains will be deal with by the managers 5不要试着自己去做，这需要专业知识（specialized 专业的） Don’t try doing it yourself, it requires specialized know ledge 6他作为最佳运动员获得了一个金牌（award 获得） He was awarded a goldcup for being the best athlete 7为什么不关掉电视区锻炼一下身体（turn off 关闭）