畢業(yè)設計機械外文翻譯

1、精選優(yōu)質文檔-傾情為你奉上專心-專注-專業(yè)如如何何延延長長軸軸承承壽壽命命摘要：自然界苛刻的工作條件會導致軸承的失效，但是如果遵循一些簡單的規(guī)則，軸承正常運轉的機會是能夠被提高的。在軸承的使用過程當中，過分的忽視會導致軸承的過熱現(xiàn)象，也可能使軸承不能夠再被使用，甚至完全的破壞。但是一個被損壞的軸承，會留下它為什么被損壞的線索。通過一些細致的偵察工作，我們可以采取行動來避免軸承的再次失效。1 軸承失效的原因在球軸承的失效中約有40%是由灰塵、臟物、碎屑的污染以及腐蝕造成的。污染通常是由不正確的使用和不良的使用環(huán)境造成的，它還會引起扭矩和噪聲的問題。由環(huán)境和污染所產(chǎn)生的軸承失效是可以預防的，而且通

2、過簡單的肉眼觀察是可以確定產(chǎn)生這類失效的原因。通過失效后的分析可以得知對已經(jīng)失效的或將要失效的軸承應該在哪些方面進行查看。弄清諸如剝蝕和疲勞破壞一類失效的機理，有助于消除問題的根源。只要使用和安裝合理，軸承的剝蝕是容易避免的。剝蝕的特征是在軸承圈滾道上留有由沖擊載荷或不正確的安裝產(chǎn)生的壓痕。剝蝕通常是在載荷超過材料屈服極限時發(fā)生的。如果安裝不正確從而使某一載荷橫穿軸承圈也會產(chǎn)生剝蝕。軸承圈上的壓坑還會產(chǎn)生噪聲、振動和附加扭矩。類似的一種缺陷是當軸承不旋轉時由于滾珠在軸承圈間振動而產(chǎn)生的橢圓形壓痕。這種破壞稱為低荷振蝕。這種破壞在運輸中的設備和不工作時仍振動的設備中都會產(chǎn)生。此外，低荷振蝕產(chǎn)生的

3、碎屑的作用就象磨粒一樣，會進一步損害軸承。與剝蝕不同，低荷振蝕的特征通常是由于微振磨損腐蝕在潤滑劑中會產(chǎn)生淡紅色。消除振動源并保持良好的軸承潤滑可以防止低荷振蝕。給設備加隔離墊或對底座進行隔離可以減輕環(huán)境的振動。另外在軸承上加一個較小的預載荷不僅有助于滾珠和軸承圈保持緊密的接觸，并且對防止在設備運輸中產(chǎn)生的低荷振蝕也有幫助。造成軸承卡住的原因是缺少內隙、潤滑不當和載荷過大。在卡住之前， 過大的摩擦和熱量使軸承鋼軟化。 過熱的軸承通常會改變顏色，一般會變成藍黑色或淡黃色。摩擦還會使保持架受力，這會破 壞支承架，并加速軸承的失效。材料過早出現(xiàn)疲勞破壞是由重載后過大的預載引起的。如果這些條件不可避免

4、，就應仔細計算軸承壽命，以制定一個維護計劃。另一個解決辦法是更換材料。若標準的軸承材料不能保證足夠的軸承壽命，就應當采用特殊的材料。另外，如果這個問題是由于載荷過大造成的，就應該采用抗載能力更強或其他結構的軸承。蠕動不象過早疲勞那樣普遍。軸承的蠕動是由于軸和內圈之間的間隙過大造成的。蠕動的害處很大，它不僅損害軸承，也破壞其他零件。蠕動的明顯特征是劃痕、擦痕或軸與內圈的顏色變化。為了防止蠕動，應該先用肉眼檢查一下軸承箱件和軸的配件。精選優(yōu)質文檔-傾情為你奉上專心-專注-專業(yè)蠕動與安裝不正有關。如果軸承圈不正或翹起，滾珠將沿著一個非圓周軌道運動。 這個問題是由于安裝不正確或公差不正確或軸承安裝現(xiàn)場

5、的垂直度不夠造成的。如果偏 斜超過0.25，軸承就會過早地失效。檢查潤滑劑的污染比檢查裝配不正或蠕動要困難得多。污染的特征是使軸承過早的出現(xiàn)磨損。潤滑劑中的固體雜質就象磨粒一樣。如果滾珠和保持架之間潤滑不良也會磨損并削弱保持架。在這種情況下，潤滑對于完全加工形式的保持架來說是至關重要的。相比之下，帶狀或冠狀保持架能較容易地使?jié)櫥瑒┑竭_全部表面。銹是濕氣污染的一種形式，它的出現(xiàn)常常表明材料選擇不當。如果某一材料經(jīng)檢驗適合工作要求，那么防止生銹的最簡單的方法是給軸承包裝起來，直到安裝使用時才打開包裝。2 避免失效的方法解決軸承失效問題的最好辦法就是避免失效發(fā)生。這可以在選用過程中通過考慮關鍵性能特

6、征來實現(xiàn)。這些特征包括噪聲、起動和運轉扭矩、剛性、非重復性振擺以及徑向和軸向間隙。扭矩要求是由潤滑劑、保持架、軸承圈質量（彎曲部分的圓度和表面加工質量）以及是否使用密封或遮護裝置來決定。潤滑劑的粘度必須認真加以選擇，因為不適宜的潤滑劑會產(chǎn)生過大的扭矩，這在小型軸承中尤其如此。另外，不同的潤滑劑的噪聲特性也不一樣。舉例來說，潤滑脂產(chǎn)生的噪聲比潤滑油大一些。因此，要根據(jù)不同的用途來選用潤滑劑。在軸承轉動過程中，如果內圈和外圈之間存在一個隨機的偏心距，就會產(chǎn)生與凸輪運動非常相似的非重復性振擺（ NRR）。保持架的尺寸誤差和軸承圈與滾珠的偏心都會引起NRR。和重復性振擺不同的是， NRR 是沒有辦法進

7、行補償?shù)?。在工業(yè)中一般是根據(jù)具體的應用來選擇不同類型和精度等級的軸承。例如，當要求振擺最小時，軸承的非重復性振擺不能超過0.3 微米。同樣，機床主軸只能容許最小的振擺，以保證切削精度。因此在機床的應用中應該使用非重復性振擺較小的軸承。在許多工業(yè)產(chǎn)品中，污染是不可避免的，因此常用密封或遮護裝置來保護軸承，使其免受灰塵或臟物的侵蝕。但是，由于軸承內外圈的運動，使軸承的密封不可能達到完美的程度，因此潤滑油的泄漏和污染始終是一個未能解決的問題。一旦軸承受到污染，潤滑劑就要變質，運行噪聲也隨之變大。如果軸承過熱，它將會卡住。當污染物處于滾珠和軸承圈之間時，其作用和金屬表面之間的磨粒一樣，會使軸承磨損。采

8、用密封和遮護裝置來擋開臟物是控制污染的一種方法。噪聲是反映軸承質量的一個指標。軸承的性能可以用不同的噪聲等級來表示。噪聲的分析是用安德遜計進行的，該儀器在軸承生產(chǎn)中可用來控制質量，也可對失效的軸承進行分析。將一傳感器連接在軸承外圈上，而內圈在心軸以 1800r/min 的轉速旋轉。測量噪聲的單位為anderon。即用um/rad 表示的軸承位移。根據(jù)經(jīng)驗，觀察者可以根據(jù)聲音辨別出微小的缺陷。例如，灰塵產(chǎn)生的是不規(guī)則的劈啪聲；滾珠劃痕產(chǎn)生一種連續(xù)的爆破聲，確定這種劃痕最困難；內圈損傷通常產(chǎn)生連續(xù)的高頻噪聲，而外圈損傷則產(chǎn)生一種間歇的聲音。精選優(yōu)質文檔-傾情為你奉上專心-專注-專業(yè)軸承缺陷可以通過

9、其頻率特性進一步加以鑒定。通常軸承缺陷被分為低、中、高三 個波段。缺陷還可以根據(jù)軸承每轉動一周出現(xiàn)的不規(guī)則變化的次數(shù)加以鑒定。低頻噪聲是長波段不規(guī)則變化的結果。軸承每轉一周這種不規(guī)則變化可出現(xiàn) 1.610次，它們是由各種干涉（例如 軸承圈滾道上的凹坑）引起的?？刹煊X的凹坑是一種制造缺陷，它是在制造過程中由于多爪卡盤夾的太緊而形成的。中頻噪聲的特征是軸承每旋轉一周不規(guī)則變化出現(xiàn) 1060 次。這種缺陷是由在軸承圈和滾珠的磨削加工中出現(xiàn)的振動引起的。軸承每旋轉一周高頻不規(guī)則變化出現(xiàn) 60300 次，它表明軸承上存在著密集的振痕或大面積的粗糙不平。利用軸承的噪聲特性對軸承進行分類，用戶除了可以確定大

10、多數(shù)廠商所使用的 ABEC標準外，還可確定軸承的噪聲等級。 ABEC 標準只定義了諸如孔、外徑、振擺等尺寸公差。隨著ABEC 級別的增加（從3 增到9），公差逐漸變小。但ABEC 等級并不能反映其他軸承特性，如軸承圈質量、粗糙度、噪聲等。因此，噪聲等級的劃分有助于工業(yè)標準的改進。精選優(yōu)質文檔-傾情為你奉上專心-專注-專業(yè)EXTENDING BEARING LIFEAbstract：Nature works hard to destroy bearings, but their chances of survival can be improved by following a few simp

11、le guidelines. Extreme neglect in a bearing leads to overheating and possibly 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.Keywords: bearings failures lifeBearings fa

12、il 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 wrongHowever，while a postmortem yield

13、s good information，it is better to avoid the process altogether by specifying the bearing correctly in The first placeTo 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, to

14、rque, 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 failAbout 40% of ball bearing failures are caused by contamination from dust, dirt, shavings, and corros

15、ion. Contamination also causes torque and noise problems, and is often the result of improper handling or the application environmentFortunately, a bearing failure caused by environment or handling contamination is preventable，and a simple visual examination can easily identify the causeConducting a

16、 postmortem il1ustrates what to look for on a failed or failing bearingThen，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 characte

17、rized by indentations in the bearing raceway caused by shock loadingsuch 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 acro

18、ss the racesRaceway 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 turningThis problem is called false brinelling. It occurs on equipment in transit or that vibrates when no

19、t 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 a

20、nd keeping the bearing well lubricated. Isolation pads on the equipment or a separate foundation may be required to reduce 精選優(yōu)質文檔-傾情為你奉上專心-專注-專業(yè)environmental vibration. Also a light preload on the bearing helps keep the balls and raceway in tight contact. Preloading also helps prevent false brinelli

21、ng 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 coloredFriction also causes stress in th

22、e retainer，which can break and hasten bearing failurePremature material fatigue is caused by a high load or excessive preloadWhen these conditions are unavoidable，bearing life should be carefully calculated so that a maintenance scheme can be worked outAnother solution for fighting premature fatigue

23、 is changing materialWhen 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 usedCreep is less commo

24、n than premature fatigueIn bearingsit is caused by excessive clearance between bore and shaft that allows the bore to rotate on the shaftCreep can be expensive because it causes damage to other components in addition to the bearing0ther more likely creep indicators are scratches，scuff marks，or disco

25、loration to shaft and boreTo prevent creep damage，the bearing housing and shaft fittings should be visually checkedMisalignment is related to creep in that it is mounting relatedIf races are misaligned or cockedThe balls track in a noncircumferencial pathThe problem is incorrect mounting or toleranc

26、ing，or insufficient squareness of the bearing mounting siteMisalignment of more than 1/4can cause an early failureContaminated lubricant is often more difficult to detect than misalignment or creepContamination shows as premature wearSolid contaminants become an abrasive in the lubricantIn addition。

27、insufficient lubrication between ball and retainer wears and weakens the retainerIn this situation，lubrication is critical if the retainer is a fully machined typeRibbon or crown retainers，in contrast，allow lubricants to more easily reach all surfaces Rust is a form of moisture contamination and oft

28、en indicates the wrong material for the applicationIf the material checks out for the job，the easiest way to prevent rust is to keep bearings in their packaging，until just before installation2 Avoiding failuresThe best way to handle bearing failures is to avoid themThis can be done in the selection

29、process by recognizing critical performance characteristicsThese include noise，starting and running torque，stiffness，nonrepetitive runout，and radial and axial playIn some applications, these items are so critical that specifying an ABEC level alone is not sufficientTorque requirements are determined

30、 by the lubricant，retainer，raceway quality(roundness cross curvature and surface finish)，and whether seals or shields are usedLubricant viscosity 精選優(yōu)質文檔-傾情為你奉上專心-專注-專業(yè)must be selected carefully because inappropriate lubricant，especially in miniature bearings，causes excessive torqueAlso，different lub

31、ricants have varying noise characteristics that should be matched to the application. For example，greases produce more noise than oilNonrepetitive runout(NRR)occurs during rotation as a random eccentricity between the inner and outer races，much like a cam actionNRR can be caused by retainer toleranc

32、e or eccentricities of the raceways and ballsUnlike repetitive runout, no compensation can be made for NRR.NRR is reflected in the cost of the bearingIt is common in the industry to provide different bearing types and grades for specific applicationsFor example，a bearing with an NRR of less than 0.3

33、um is used when minimal runout is needed，such as in diskdrive spindle motorsSimilarly，machinetool spindles tolerate only minimal deflections to maintain precision cutsConsequently, bearings are manufactured with low NRR just for machine-tool applicationsContamination is unavoidable in many industria

34、l products，and shields and seals are commonly used to protect bearings from dust and dirtHowever，a perfect bearing seal is not possible because of the movement between inner and outer racesConsequently，lubrication migration and contamination are always problemsOnce a bearing is contaminated, its lub

35、ricant deteriorates and operation becomes noisierIf it overheats，the bearing can seizeAt 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 surfacesFending off dirt with seals and shields illustrat

36、es some methods for controlling contaminationNoise is as an indicator of bearing qualityVarious noise grades have been developed to classify bearing performance capabilitiesNoise analysis is done with an Anderonmeter, which is used for quality control in bearing production and also when failed beari

37、ngs 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 m/rad.With experience, inspectors can identify the smallest flaw from their sound. Dust, for examp

38、le, 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, def