1、 北方民族大学毕业设计 外文翻译 翻译题目： 轴承失效分析 姓 名 向 延 标 学 号 20091210 专 业 过程装备与控制工程 指导教师 沙 卫 群 北方民族大学教务处制 1 BEARING LIFE ANALYSIS ABSTRACT Nature works hard to destroy bearings, but their chances of survival can be improved by following a few simple guidelines. Extreme neglect in a bearing leads to overheating and p
2、ossibly seizure or, at worst, an explosion. But even a failed bearing leaves clues as to what went wrong. After a little detective work, action can be taken to avoid a repeat performance. KEY WORDS: bearings, failures , life 1 .WHY BEARINGS FAIL An individual bearing may fail for several reasons； ho
3、wever, the results of an endurance test series are only meaningful when the test bearings fail by fatigue-related mechanisms. The experimenter must control the test process to ensure that this occurs. The following paragraphs deal with a few specific failure types that can affect the conduct of a li
4、fe test sequence. the influence of lubrication on contact fatigue life is discussed from the standpoint of EHL film generation. There are also other lubrication-related effects that can affect the outcome of the test series. The first is particulate contaminants in the lubricant. Depending on bearin
5、g size, operating speed, and lubricant rheology, the overall thickness of the lubricant film developed at the rolling element-raceway contacts may fall between 0.05 and 0.5 m . Solid particles and damage the raceway and rolling element surfaces, leading to substantially shortened endurances. Therefo
6、re, filtration of the lubricant to the desired level is necessary to ensure meaningful test result. The desired level is determined by the application which the testing purports to approximate. If this degree of filtration is not provided, effects of contamination must be considered when evaluating
7、test results. The moisture content in the lubricant is another important consideration. It has long been apparent that quantities of free water in the oil cause corrosion of the rolling contact surfaces and thus have a detrimental effect on bearing life. However, that water levels as low as 50-100 p
8、arts per million(ppm) may also have a detrimental effect, even with no evidence of corrosion. This is due to hydrogen embrittlement of the rolling element and raceway material. A maximum of 40 ppm is considered necessary to minimize life reduction effects. The chemical composition of the test lubric
9、ant also requires consideration. Most commercial lubricants contain a number of proprietary additives developed for specific purposes； for example, to provide antiwear properties, to achieve extreme pressure and/or thermal stability, and to provide boundary lubrication in case of marginal lubricant
10、films. These additives can also affect the endurance of rolling bearings, either immediately or after experiencing time-related degradation. Care must be taken to ensure that the additives included in the test lubricant will not suffer excessive deterioration as a result of accelerated life test con
11、ditions. Also for consistency of results and comparing life test groups, it is good practice to utilize one standard test lubricant from a particular producer for the conduct of all general life tests. The statistical nature of rolling contact fatigue requires many test samples to obtain a reasonabl
12、e estimate of life. A bearing life test sequence thus needs a long time. A major job of the experimentalist is to ensure the consistency of the applied test conditions throughout the entire test period. This process is not simple because subtle changes can occur during the test period. Such changes
13、might be overlooked until their effects become major. At that time it is often too late to salvage the collected data, and the test must be redone under better controls.For example, the stability of the additive packages in a test lubricant can be a source of changing test conditions. Some lubricant
14、s have been known to suffer additive depletion after an extended period of operation. The degradation of the additive package can alter the EHL conditions in the rolling content, altering 2 bearing life. Generally, the normal chemical tests used to evaluate lubricants do not determine the conditions
15、 of the additive content. Therefore if a lubricant is used for endurance testing over a long time, a sample of the fluid should be returned to the producer at regular intervals, say annually, for a detailed evaluation of its condition. Adequate temperature controls must also be employed during the t
16、est. The thickness of the EHL film is sensitive to the contact temperature. Most test machines are located in standard industrial environments where rather wide fluctuations in ambient temperature are experienced over a period of a year. In addition, the heat generation rates of individual bearings
17、can vary as a result of the combined effects of normal manufacturing tolerances. Both of these conditions produce variations in operating temperature levels in a lot of bearings and affect the validity of the life data. A means must be provided to monitor and control the operating temperature level
18、of each bearing to achieve a degree of consistency. A tolerance level of 3C is normally considered adequate for the endurance test process. The deterioration of the condition of the mounting hardware used with the bearings is another area requiring constant monitoring. The heavy loads used for life
19、testing require heavy interference fits between the bearing inner rings and shafts. Repeated mounting and dismounting of bearings can produce damage to the shaft surface, which in turn can alter the geometry of a mounted ring. The shaft surface and the bore of the housing are also subject to deterio
20、ration from fretting corrosion. Fretting corrosion results from the oxidation of the fine wear particles generated by the vibratory abrasion of the surface, which is accelerated by the heavy endurance test loading. This mechanism can also produce significant variations in the geometry of the mountin
21、g surfaces, which can alter the internal bearing geometry. Such changes can have a major effect in reducing bearing test life. The detection of bearing failure is also a major consideration in a life test series. The fatigue theory considers failure as the initiation of the first crack in the bulk m
22、aterial. Obviously there is no way to detect this occurrence in practice. To be detectable the crack must propagate to the surface and produce a spall of sufficient magnitude to produce a marked effect on an operating parameter of the bearing: for example, noise, vibration, and/or temperature. Techn
23、iques exit for detecting failures in application systems. The ability of these systems to detect early signs of failure varies with the complexity of the test system, the type of bearing under evaluation, and other test conditions. Currently no single system exists that can consistently provide the
24、failure discrimination necessary for all types of bearing life tests. It is then necessary to select a system that will repeatedly terminate machine operation with a consistent minimal degree of damage. The rate of failure propagation is therefore important. If the degree of damage at test terminati
25、on is consistent among test elements, the only variation between the experimental and theoretical lives is the lag in failure detection. In standard through-hardened bearing steels the failure propagation rate is quite rapid under endurance test conditions, and this is not a major factor, considerin
26、g the typical dispersion of endurance test data and the degree of confidence obtained from statistical analysis. This may not, however, be the case with other experimental materials or with surface-hardened steels or steels produced by experimental techniques. Care must be used when evaluating these
27、 latter results and particularly when comparing the experimental lives with those obtained from standard steel lots. The ultimate means of ensuring that an endurance test series was adequately controlled is the conduct of a post-test analysis. This detailed examination of all the tested bearings use
28、s high-magnification optical inspection, higher-magnification scanning electron microscopy, metallurgical and dimensional examinations, and chemical evaluations as required. The characteristics of the failures are examined to establish their origins and the residual surface conditions are evaluated
29、for indications of extraneous effects that may have influenced the bearing life. This technique allows the experimenter to ensure that the data are indeed valid. The post-test analysis is, by definition, after the fact. To provide control throughout the test series and to eliminate all questionable
30、areas, the experimenter should conduct a preliminary study whenever a bearing is removed from the test machine. In this portion of the investigation each bearing is examined optically at magnifications up to 30 for indications of improper or out-of-control test parameters. Examples of the types of indications that can be observed are given
