外文翻译
How to extend the service life of bearing Nature\'s harsh working conditions can lead to the failure of bearing, but if you follow some simple rules, opportunities for normal operation of the bearing can be improved.In the using proce of bearing,extreme neglect in a bearing leads to overheating and poibly 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.Some of the reasons for bearing failure, but common is incorrect use of improper use, pollution, lubricants, loading and unloading or handling damage and installation error, etc.The problem is often not difficult to diagnose, because of a failed bearing usually leaving the slightest trace what went wrong.However，while a postmortem yields good information，it is better to avoid the proce 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 important is the research requirement of noise, torque, beating, and poible exposure to pollutants, hostile liquid, and extreme temperatures.Whether can provide further clues bearing is suitable for this work.
1 bearing failure reason
- 1
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 exceive loading.Before seizing, exceive, friction and heat softens the bearing steel.Overheated bearings often change color，usually to blue-black or straw colored．Friction also causes stre in the retainer，which can break and hasten bearing failure．
Premature material fatigue is caused by a high load or exceive 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 exceive loading，a higher capacity bearing or different configuration may be used．
Creep is le common than premature fatigue．In bearings．it is caused by exceive 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 squarene 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。
- 3
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 poible 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 claify 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.
- 5
事后的调查分析提供出宝贵的信息时，最好首先通过正确地选定轴承来完全避免失效的发生。为了做到这一点，再考察一下制造厂商的尺寸定位指南和所选轴承的使用特点是非常重要的。同样重要的是噪声的研究要求,转矩,跳动,以及可能的暴露于污染物,敌对的液体,和极端温度。这可以提供进一步的线索轴承是否适合工作。
1 轴承失效的原因
大约40%的球轴承故障是由污染引起的灰尘、污垢,刨花和腐蚀。污染也导致转矩和噪声问题,往往是由于操作不当或应用程序。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。进行后期给出了寻找失败或失败的轴承,然后理解失败背后的机制,如渗碳硬化或疲劳,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。
- 7
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。
噪声是反映轴承质量的一个指标。轴承的性能可以用不同的噪声等级来表示。
噪声的分析是用安德逊计进行的，该仪器在轴承生产中可用来控制质量，也可对失效的轴承进行分析。将一传感器连接在轴承外圈上，而内圈在心轴以1800r/min的转速旋转。测量噪声的单位为anderon。即用um/rad表示的轴承位移。
根据经验，观察者可以根据声音辨别出微小的缺陷。例如，灰尘产生的是不规则的劈啪声；滚珠划痕产生一种连续的爆破声，确定这种划痕最困难；内圈损伤通常产生连续的高频噪声，而外圈损伤则产生一种间歇的声音。
- 9
