【机械类毕业论文中英文对照文献翻译】轴承的振动分析
【机械类毕业论文中英文对照文献翻译】轴承的振动分析,机械类毕业论文中英文对照文献翻译,机械类,毕业论文,中英文,对照,对比,比照,文献,翻译,轴承,振动,分析
中文翻译:轴承的振动分析Dr. S. J. Lacey舍夫勒(英国)有限公司工程经理摘要:在生产过程中,滚动轴承振动产生的复杂几何缺陷可能会导致滚动表面上的缺陷或相关组件的几何误差。噪音和振动在所有类型的设备中正变得越来越关键,因为它常常被认为是质量的代名词并常被用于预测和维护。这篇文章是关于一些轴承振动的不同来源是如何随着缺陷的频率特征而展现出来的。文中给出了一些例子来说明了如何利用振动来进一步分析探测机器状态的恶化。关键词:轴承振动,维修工程,可靠性工程,振动探测。介绍:几乎所有类型的旋转机械都要用到滚动接触轴承,他们的可靠性依赖于轴承选定的类型以及所有相关组件的精度,即轴、垫片、螺帽等。在假定轴承正确安装、操作和维护时,轴承工程师一般使用疲劳和正常的失效模式。今天,由于制造工艺和材料的改进,一般情况下轴承疲劳寿命(与表面应力相关)并不是限制因素而且不必考虑那些不足3%的误差。不过,尽管许多轴承因为污染、润滑不良、极端温度、恶劣的装修、不平衡和不合理的维修而过早失效,所有这些因素导致轴承振动的增加,而且在使用了多年之后的状态监测仍然会对轴承造成灾难性失效(与停工期的相关费用或身体机器其他部位的重大损害)。滚动轴承通常被用于噪声敏感的电器中,如家电用电动机往往使用中小型轴承。因此轴承振动不论是从它对机器质量的重要性方面,还是从环境方面考虑,它都变得越来越重要。现在人们普遍认为安静的运行形式是滚动接触表面光洁度的代名词。因此,轴承制造商已经开发它们作为衡量质量和振动试验的有效方法。一个常用的方法是把它安装在一个安静运行的主轴轴承上和对轴承的外圈点和三个频段,分别是径向速度。 50-300,300-1800和1800-10000赫兹。轴承必须符合三个频段的均方根速度的限制。由于轴承振动信号是由机械结构修改的,所以在大多数情况下轴承振动不能被直接测量。这种情况下因为其它设备(如电动马达,齿轮,皮带)的振动进一步复杂化,会使那些未受过训练的专家很难对振动数据做出解释,在某些情况下会导致误诊断,造成不必要的停机时间和成本增加。振动源: 滚动轴承振动是一个复杂的系统,其组成部分包括:滚动体,内滚道,外圈滚道和笼,相互作用产生复杂的振动。虽然滚动轴承是采用高精密机床加工,进行严格的质量控制和清洁,像其他制成品一样,通过互动的滚动和滑动组合,他们有缺陷且表面产生震动。如今,虽然表面缺陷的幅度在纳米级别,仍然可以在整个可听频率范围(20赫兹- 20千赫)内产生显着的振动。该振动水平将取决于许多因素,包括冲击能量,在哪个振动测量点和轴承的结构。变量合规: 即使轴承有非常完美的几何外形,在承受径向载荷下,轴承振动也是滚动轴承的固有特点,而非质量差的原因。这样的振动类型通常被称为变量合规,而且外部负载发生的原因是其位置由一个方面的负荷随时间不断变化造成的。(见图1) 图1变刚度振动严重依赖于配套的滚动体外所加的负载数目,滚动体的数量越多,它的振动就越小。由于径向加载或错位轴承的游隙决定了外部负载区域,因此,一般情况下随着间隙变合规,运行间隙不应与径向内部游隙(里克)相混淆,由于过盈配合运行中的内、外圈热膨胀的原因,前者通常是低于里克。变刚度振动水平可以比粗糙度和表面波纹度的滚动产生的更高。然而,在应用中至关重要的是振动可以通过使用正确的水平轴向预紧力来减少到一个可以忽略的水平。几何缺陷: 由于生产过程中使用的性质,生产轴承零件的几何缺陷将始终存在,其不同程度根据轴承精度等级而定。对于受压球轴承在中等速度运行下的临界轧制表面形式和表面光洁度是轴承的噪音和振动的最大来源。因此控制部件波纹和在生产过程中的表面光洁度是至关重要的,因为它可能不仅有显著影响,而且振动可能会影响轴承的使用寿命。为方便起见,考虑到滚动体,滚道的接触宽度不完善之处几何缺陷的波长 被称为粗糙表面特征,而波长较长的特点被称为波纹(见图2)。 图2 表面粗糙度: 表面粗糙度是振动的一个重要的来源,当其表面粗糙度高时,在滚动体与滚道的接触处(见图2)产生较厚的润滑油膜。在此条件下表面粗糙可以突破润滑膜,并与对方互动的表面,造成金属与金属的接触。由此产生的振动,组成了一个激发所有的轴承和支撑结构的自然模式随机序列。 表面粗糙度产生的振动主要发生在六十次频率轴承转速上。因此频谱的高频部分通常显示为一个系列的共振。用于估计相互作用的粗程度一个常见的参数是lambda比()。这是复合润滑膜厚度,表面粗 糙度糙度比率,由表达式给出 = h (2 + r2)0.5 其中 =粗糙程度的相互作用 h=油膜厚度 =粗糙度球 r=滚道表面粗糙度 图3如果我们假定滚道表面光洁度是滚动体的两倍,那么对于一个典型的润滑油膜厚度为0.3m的表面饰面比0.06微米更加需要实现三值和较低的相互作用发生率。如需0.1_m表面润滑油膜厚度比0.025_m完成须达到= 3。 对轴承的寿命的影响见图3。如果小于1,轴承将因破损而不可能达到估计的设计使用年限,这可能迅速导致滚动表面疲劳破坏。一般来说,比值大于三显示完整的表面分离。从全弹流(弹流润滑)过渡到混合润滑(有些粗糙接触弹流润滑膜部分)发生在1至3范围。 波纹: 对于更长波长的表面特征,与赫兹触点相比峰值是低的,滚动运动是随着表面轮廓与滚动体相连续的。表面间的几何形状和振动水平的关系是复杂的,视轴承和接触几何以及载荷和速度情况而定。波纹能够产生振动频率高达约三百次的旋转速度,但通常是低于六十次的频率转速为主。上限是由于滚动体的滚道接触的有限区域最终得到更短特点的平均波长。在滚动方向上,接触时弹性变形减轻对简单的谐波波形接触宽度见图4。 图4在极限情况下,波长随衰减水平的减小而提高,直到一个波长等于接触宽度,波纹幅度在理论上是零。接触长度也是短波长的衰减表面特征。通常较差的相关性可能存在于平行面之间高度的轨道,在不同的点抽取不同的配置文件,并全波纹度测量幅值平均值低一级。对于典型的轴承表面的平行面只有在更短的波长存在较差的相关性。即使是现代精密加工技术波纹也不能被完全消除,尽管在相对较低的水平,但波纹元素将始终存在。对于轴承本身,相关的零部件的质量也会影响轴承的振动而且任何轴的几何外径的误差,可能在振动轴承的滚道中反映出来。因此,需要特别注意形式和所有相关的轴承零件的精度。离散缺陷: 而表面粗糙度和波纹度的结果直接从轴承零部件生产制造工艺,离散的缺陷是指表面的滚动由于污染,操作,安装,保养不善等而造成的过大的损害。这些缺陷可能会非常小,难以察觉,但可能对振动的关键设备产生重大影响或可能导致轴承寿命降低。此类缺陷可能有很多种类的形式。压痕,划痕和整个沿轧制表面,坑,碎片及润滑油中的颗粒。轴承制造商对成品缺陷的检测都采用简单的振动测量,但这些往往受到轴承的类型和大小的限制。这方面的一个类型的测量例子如图5(a)和5(b)所示,与一个良好的轴承相比,在轴承外圈滚道离散损害产生了典型的脉冲振动,具有较高的峰值/有效值比。图5(a)图5(b)在大量的缺陷发生个别峰值处不具有很明确的定义,但在RMS振动水平数倍于通常与轴承相关的良好条件的总和。参考文献1.Harris T A, Rolling Bearing Analysis (4th Ed), Wiley, New York, 2001.2.Lacey S J, Vibration monitoring of the internal centreless grinding process, Part 1: mathematical models. Proc Instn Mech Engrs. Vol 24. 1990.3.Lacey S J, Vibration monitoring of the internal centreless grinding process, Part 2: experimental results. Proc Instn Mech Engrs. Vol 24. 1990.4.Wardle F P and Lacey S J, Vibration Research in RHP. Acoustics Bulletin.外文资料:An Overview of Bearing Vibration AnalysisDr. S. J. LaceyEngineering Manager, Schaeffler (UK) Ltd AbstractVibration produced by rolling bearings can be complex and can result from geometrical imperfections during the manufacturing process, defects on the rolling surfaces or geometrical errors in associated components. Noise and vibration is becoming more critical in all types of equipment since it is often perceived to be synonymous with quality and often used for predictive maintenance. In this article the different sources of bearing vibration are considered along with some of the characteristic defect frequencies that may be present. Some examples of how vibration analysis can be used to detect deterioration in machine condition are also given.Keywords: Bearing Vibration, maintenance engineering, reliability engineering, Vibration detectionINTRODUCTIONRolling contact bearings are used in almost every type of rotating machinery whose successful and reliable operation is very dependent on the type of bearing selected as well as the precision of all associated components, i.e. shaft, housing, spacers, nuts etc. Bearing engineers generally use fatigue as the normal failure mode, on the assumption that the bearings are properly installed, operated and maintained. Today, because of improvements in manufacturing technology and materials, it is generally the case that bearing fatigue life, which is related to sub-surface stresses, is not the limiting factor and probably accounts for less than 3% of failures in service. Unfortunately though, many bearings fail prematurely in service because of contamination, poor lubrication, temperature extremes, poor fitting/fits, unbalance and misalignment. All these factors lead to an increase in bearing vibration and condition monitoring has been used for many years to detect degrading bearings before they catastrophically fail (with the associated costs of downtime or significant damage to other parts of the machine). Rolling element bearings are often used in noise sensitive applications, e.g. household appliance electric motors which often use small to medium size bearings. Bearing vibration is therefore becoming increasingly important from both an environmental consideration and because it is synonymous with quality. It is now generally accepted that quiet running is synonymous with the form and finish of the rolling contact surfaces. As a result, bearing manufacturers have developed vibration tests as an effective method for measuring quality. A common approach is to mount the bearing on a quiet running spindle and measure the radial velocity at a point on the bearings outer ring and in three frequency bands, viz. 50-300, 300-1800 and1800-10000 Hz. The bearing must meet RMS velocity limits in all three frequency bands. in most situations bearing vibration cannot be measured directly and so the bearing vibration signature is modified by the machine structure, this situation being further complicated by vibration from other equipment on the machine, i.e. electric motors, gears, belts, hydraulics, structural resonances etc. This often makes the interpretation of vibration data difficult other than by a trained specialist and can in some situations lead to a mis-diagnosis, resulting in unnecessary machine downtime and costs. In this paper the sources of bearing vibration are discussed along with the characteristic vibration frequencies that are likely to be generated.SOURCES OF VIBRATION Rolling contact bearings represents a complex vibration system whose components i.e. rolling elements, inner raceway, outer raceway and cage interact to generate complex vibration signatures. Although rolling bearings are manufactured using high precision machine tools and under strict cleanliness and quality controls, like any other manufactured part they will have degrees of imperfection and generate vibration as the surfaces interact through a combination of rolling and sliding. Nowadays, although the amplitudes of surface imperfections are in the order of nanometres, significant vibrations can still be produced in the entire audible frequency range (20 Hz 20 kHz). The level of the vibration will depend upon many factors, including the energy of the impact, the point at which the vibration is measured and the construction of the bearing.Variable compliance Under radial and misaligning loads bearing vibration is an inherent feature of rolling bearings even if the bearing is geometrically perfect and is not therefore indicative of poor quality. This type of vibration is often referred to as variable compliance and occurs because the external load is supported by a discrete number of rolling elements whose position with respect to the line of action of the load continually changes with time (see Figure 1).图1 Variable compliance vibration is heavily dependent on the number of rolling elements supporting the externally applied load; the greater the number of loaded rolling elements, the less the vibration. For radially loaded or misaligned bearings running clearance determines the extent of the load region, and hence, in general, variable compliance increases with clearance. Running clearance should not be confused with radial internal clearance (RIC), the former normally being lower than the RIC due to interference fit of the rings and differential thermal expansion of the inner and outer rings during operation. Variable compliance vibration levels can be higher than those produced by roughness and waviness of the rolling surfaces. However, in applications where vibration is critical it can be reduced to a negligible level by using ball bearings with the correct level of axial pre-load.Geometrical imperfectionsBecause of the very nature of the manufacturing processes used to produce bearing components geometrical imperfections will always be present to varying degrees depending on the accuracy class of the bearing. For axially loaded ball bearings operating under moderate speeds the form and surface finish of the critical rolling surfaces are generally the largest source of noise and vibration. Controlling component waviness and surface finish during the manufacturing process is therefore critical since it may not only have a significant effect on vibration but also may affect bearing life. It is convenient to consider geometrical imperfections in terms of wavelength compared with the width of the rolling element-raceway contacts. Surface features of wavelength of the order of the contact width or less are termed roughness, whereas longer wavelength features are termed waviness (see Figure 2). 图2SURFACE ROUGHNESS Surface roughness is a significant source of vibration when its level is high compared with the lubricant film thickness generated between the rolling element-raceway contacts (see Figure 2). Under this condition surface asperities can break through the lubricant film and interact with the opposing surface, resulting in metal-to-metal contact. The resulting vibration consists of a random sequence of small impulses which excite all the natural modes of the bearing and supporting structure. Surface roughness produces vibration predominantly at frequencies above sixty times the rotational speed of the bearing. Thus the high frequency part of the spectrum usually appears as a series of resonances. A common parameter used to estimate the degree of asperity interaction is the lambda ratio (). This is the ratio of lubricant film thickness to composite surface roughness and is given by the expression = h (2 + r2)0.5 where =degree of asperity interaction h =the lubricant film thickness =RMS roughness of the ball r =RMS roughness of the racewayIf we assume that the surface finish of the raceway is twice that of rolling element, then for a typical lubricant film thickness of 0.3m surface finishes better than 0.06 m are required to achieve avalue of three and a low incidence of asperity interaction. For a lubricant film thickness of 0.1_m surface finishes better than 0.025 _m are required to achieve =3. The effect of on bearing life is shown in Figure 3.图3If is less than unity it is unlikely that the bearing will attain its estimated design life because of surface distress, which can lead to a rapid fatigue failure of the rolling surfaces. In general, ratios greater than three indicate complete surface separation. A transition from full EHL (elastohydrodynamic lubrication) to mixed lubrication (partial EHL film with some asperity contact) occurs in the range .Waviness For longer wavelength surface features, peak curvatures are low compared with that of the Hertzian contacts and rolling motion is continuous with the rolling elements following the surface contours. The relationship between surface geometry and vibration level is complex, being dependent upon the bearing and contact geometry as well as conditions of load and speed. Waviness can produce vibration at frequencies up to approximately three hundred times rotational speed but is usually predominant at frequencies below sixty times rotational speed. The upper limit is attributed to the finite area of the rolling element raceway contacts which average out the shorter wavelength features.In the direction of rolling, elastic deformation at the contact attenuates simple harmonic waveforms over the contact width (see Figure 4).图4 The level of attenuation increases as wavelength decreases until, in the limit, for a wavelength equal to the contact width, waviness amplitude is theoretically zero. The contact length also attenuates short wavelength surface features. Generally poor correlation can exist between parallel surface height profiles taken at different points across the tracks and this averages measured waviness amplitudes to a low level. For typical bearing surfaces poor correlation of parallel surface heights profiles only exists at shorter wavelengths.Even with modern precision machining technology waviness cannot be eliminated completely and an element of waviness will always exist albeit at relatively low levels. As well as the bearing itself, the quality of the associated components can also affect bearing vibration and any geometrical errors on the outside diameter of the shaft or bore of the housing can be reflected on the bearing raceways with the associated increase in vibration. Therefore, careful attention is required to the form and precision of all associated bearing components. Discrete defectsWhereas surface roughness and waviness result directly from the bearing component manufacturing processes, discrete defects refer to damage of the rolling surfaces due to assembly, contamination, operation, mounting, poor maintenance etc. These defects can be extremely small and difficult to detect and yet can have a significant impact on vibration-critical equipment or can result in reduced bearing life. This type of defect can take a variety of forms, viz. indentations, scratches along and across the rolling surfaces, pits, debris and particles in the lubricant. Bearing manufacturers have adopted simple vibration measurements on the finished product to detect such defects but these tend to be limited by the type and size of bearing. An example of this type of measurement is shown in Figures 5(a) and 5(b) where, compared to a good bearing, the discrete damage on a bearing outer ring raceway has produced a characteristically impulsive vibration which has a high peak/RMS ratio. Where a large number of defects occurs individual peaks are not so clearly defined but the RMS vibration level is several times greater than that normally associated with a bearing in good conditio图5(a)图5(b)Bearing characteristic frequenciesAlthough the fundamental frequencies generated by rolling bearings are expressed by relatively simple formulas they cover a wide frequency range and can interact to give very complex signals. This is often further complicated by the presence on the equipment of other sources of mechanical, structural or electro-mechanical .REFERENCES1.Harris T A, Rolling Bearing Analysis (4th Ed), Wiley, New York, 2001.2.Lacey S J, Vibration monitoring of the internal centreless grinding process, Part 1: mathematical models. Proc Instn Mech Engrs. Vol 24. 1990.3.Lacey S J, Vibration monitoring of the internal centreless grinding process, Part 2: experimental results. Proc Instn Mech Engrs. Vol 24. 1990.4.Wardle F P and Lacey S J, Vibration Research in RHP. Acoustics Bulletin.
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