軸承機(jī)械類畢業(yè)設(shè)計(jì)外文翻譯樣本

軸承壽命分析摘要自然界苛刻工作條件會(huì)導(dǎo)致軸承失效，但是如果遵循某些簡(jiǎn)樸規(guī)則，軸承正常運(yùn)轉(zhuǎn)機(jī)會(huì)是可以被提高。在軸承使用過(guò)程當(dāng)中，過(guò)度忽視會(huì)導(dǎo)致軸承過(guò)熱現(xiàn)象，也也許使軸承不可以再被使用，甚至完全破壞。但是一種被損壞軸承，會(huì)留下它為什么被損壞線索。通過(guò)某些細(xì)致觀測(cè)工作，咱們可以采用行動(dòng)來(lái)避免軸承再次失效。核心詞：軸承失效壽命1.軸承失效因素軸承失效有如下各種因素，然而軸承壽命實(shí)驗(yàn)卻是所有機(jī)械實(shí)驗(yàn)中最故意義。實(shí)驗(yàn)者必要控制實(shí)驗(yàn)過(guò)程以保證成果。其她失效模式在Tallian[19.2]中有詳細(xì)闡述。下邊幾段就詳細(xì)闡述了可以影響壽命實(shí)驗(yàn)成果幾種失效模式。23章中，從EHL觀點(diǎn)討論了潤(rùn)滑條件對(duì)壽命實(shí)驗(yàn)成果影響，同步尚有其她潤(rùn)滑條件會(huì)影響實(shí)驗(yàn)結(jié)論，一方面是潤(rùn)滑劑接觸面積，受到軸承尺寸，轉(zhuǎn)速，潤(rùn)滑劑流動(dòng)性等因素影響，潤(rùn)滑劑在軸承表面形成潤(rùn)滑層厚度普通不大于0.05~0.5um，不不大于這個(gè)薄層厚度固體微粒會(huì)殘留在接觸面上，從而劃傷潤(rùn)滑溝道和軸承滾動(dòng)面。從而大大縮短軸承耐用性。關(guān)于這點(diǎn)Sayles和MacPherson以及其她人均有詳細(xì)論證。因而，為了保證明驗(yàn)成果咱們必要選用適當(dāng)級(jí)別潤(rùn)滑劑。潤(rùn)滑劑選取由工況決定，實(shí)驗(yàn)時(shí)也如此。如果工況選取范疇不擬定，就必要考慮到接觸面積對(duì)實(shí)驗(yàn)成果影響。23章中討論了不同接觸面積對(duì)軸承失效壽命實(shí)驗(yàn)成果影響。潮氣是影響潤(rùn)滑成果另一種重要因素，長(zhǎng)時(shí)間在水中和油中被腐蝕不但對(duì)外觀質(zhì)量有影響，還會(huì)影響到滾動(dòng)表面軸承壽命。關(guān)于這點(diǎn)Fitch等人[19.7]有過(guò)論證。并且，雖然是僅有50~100PPM（百萬(wàn)分之一）水汽含量也會(huì)產(chǎn)生有害影響，甚至產(chǎn)生表面看不出痕跡腐蝕。這是由于軸承溝道和滾動(dòng)面之間會(huì)產(chǎn)生氫脆現(xiàn)象，從23章中也可以看出在潤(rùn)滑實(shí)驗(yàn)中濕氣是如此重要一種因素。因而在軸承壽命實(shí)驗(yàn)成果中必要考慮到潮氣影響。為了減少對(duì)壽命減少影響，潮氣含量最多不能超過(guò)40PPM。潤(rùn)滑劑化學(xué)成分也是需要考慮。大多數(shù)商業(yè)潤(rùn)滑油包括許多為特定目而開發(fā)專有添加劑。例如，為了提高抗磨損性能，為了能達(dá)到極限壓力，或者耐熱性，還可以在邊際潤(rùn)滑油膜狀況下提供邊界潤(rùn)滑還能為邊界潤(rùn)滑提供一種邊界潤(rùn)滑層。這些添加劑同步也能即時(shí)或者逐漸地影響滾動(dòng)軸承耐用性。為了避免添加劑成為加速壽命實(shí)驗(yàn)條件，咱們必要小心以保證測(cè)試潤(rùn)滑劑添加劑不會(huì)受到惡化。為了保證同組產(chǎn)品壽命實(shí)驗(yàn)成果有連貫性，最佳在整個(gè)壽命實(shí)驗(yàn)中都用同一供應(yīng)商原則潤(rùn)滑劑。為了得到一種合理成果，記錄學(xué)規(guī)定做諸多組壽命實(shí)驗(yàn)。因而一種軸承壽命實(shí)驗(yàn)需很長(zhǎng)時(shí)間。實(shí)驗(yàn)人員必要保證整個(gè)實(shí)驗(yàn)過(guò)程持續(xù)性，由于任何微小變化都會(huì)影響實(shí)驗(yàn)成果，因而這個(gè)過(guò)程是很復(fù)雜。甚至這些微小變化在導(dǎo)致重大變化之前都不會(huì)被注意到。一旦發(fā)生這樣狀況，就沒(méi)機(jī)會(huì)補(bǔ)救了。只能在更好控制條件下重新做實(shí)驗(yàn)。例如說(shuō)：添加劑穩(wěn)定性會(huì)影響到整個(gè)實(shí)驗(yàn)條件。當(dāng)前已經(jīng)懂得了某些添加劑在長(zhǎng)期使用時(shí)會(huì)導(dǎo)致大量額外損耗。這些易退化添加劑會(huì)影響軸承表面潤(rùn)滑條件，從而影響軸承壽命。普通對(duì)潤(rùn)滑劑做化學(xué)檢測(cè)時(shí)是不會(huì)檢測(cè)添加劑成分。因而，如果一種潤(rùn)滑劑用于長(zhǎng)時(shí)間軸承壽命實(shí)驗(yàn)話，生產(chǎn)者應(yīng)當(dāng)定期更換實(shí)驗(yàn)樣品，例如一年一次。用來(lái)詳細(xì)評(píng)估潤(rùn)滑劑使用規(guī)定。實(shí)驗(yàn)時(shí)還要控制是恰當(dāng)溫度。潤(rùn)滑層（油膜）厚度對(duì)溫度影響是相稱敏感，大多數(shù)裝機(jī)實(shí)驗(yàn)是在原則工業(yè)環(huán)境下進(jìn)行，在這一年實(shí)驗(yàn)時(shí)間中環(huán)境溫度變化是非常大。同步，個(gè)別軸承受溫度變化影響是會(huì)影響到整個(gè)系統(tǒng)常規(guī)制造公差。因而，所有軸承受溫度變化影響會(huì)直接影響到壽命實(shí)驗(yàn)數(shù)據(jù)精確性。因而為了保證明驗(yàn)數(shù)據(jù)連貫性，必要監(jiān)控并實(shí)時(shí)調(diào)節(jié)每個(gè)軸承使用溫度。因而對(duì)于軸承壽命實(shí)驗(yàn)時(shí)±3oC溫度公差被以為是可接受。用于軸承壽命實(shí)驗(yàn)硬件裝備磨損是另一種需要監(jiān)控恒量。用于重載實(shí)驗(yàn)軸和軸承內(nèi)圈都會(huì)受到很大載荷。重復(fù)拆裝軸承會(huì)對(duì)軸表面產(chǎn)生損害。這樣變化會(huì)影響幾何形狀。軸外徑和軸承內(nèi)徑都會(huì)受腐蝕影響。腐蝕是由于震動(dòng)產(chǎn)生微粒被氧化而產(chǎn)生。這樣也會(huì)減少軸承壽命實(shí)驗(yàn)時(shí)間。同步這樣機(jī)構(gòu)也會(huì)在裝配面上產(chǎn)生重大幾何形變，從而影響軸承內(nèi)徑，最后成為減少壽命重要因素。軸承缺陷檢測(cè)也是壽命實(shí)驗(yàn)重要考察因素。軸承缺陷最早是由原材料上微小裂紋引起。這樣缺陷在實(shí)驗(yàn)中是沒(méi)法檢測(cè)。為了檢測(cè)這個(gè)缺陷就需要使這個(gè)缺陷遞增到能影響軸承參數(shù)數(shù)量級(jí)別。例如說(shuō)噪音，溫度，震動(dòng)等缺陷?？梢栽谙到y(tǒng)中應(yīng)用這些技術(shù)辦法來(lái)檢查缺陷。而具備這樣能力系統(tǒng)可以從初期就檢測(cè)出在多樣化工作條件復(fù)雜系統(tǒng)中用來(lái)測(cè)試用缺陷軸承。而當(dāng)前還沒(méi)有一種單一系統(tǒng)能檢測(cè)出所有軸承缺陷。因而將來(lái)有必要選取一種能在軸承受到微小傷害之前就停下機(jī)器監(jiān)控系統(tǒng)。缺陷遞增速率是相稱重要。如果在實(shí)驗(yàn)結(jié)束時(shí)缺陷限度和理論計(jì)算出是一致，唯一區(qū)別就是實(shí)驗(yàn)中對(duì)缺陷檢測(cè)總是落后于理論計(jì)算。原則軸承鋼在耐久性實(shí)驗(yàn)中缺陷遞增速度是相稱快。并且這個(gè)遞增還不是重要因素，考慮到有代表性耐久性實(shí)驗(yàn)數(shù)據(jù)都是經(jīng)記錄學(xué)分析后得到。有也不一定，例如某些表面硬度不同鋼材或是專為實(shí)驗(yàn)用生產(chǎn)鋼材。因而在分析成果時(shí)候就必要考慮是原則軸承鋼還是專門實(shí)驗(yàn)用鋼材。耐久性實(shí)驗(yàn)最后成果有效性是由元素-金相分析驗(yàn)證。軸承會(huì)通過(guò)高倍光學(xué)顯微鏡，高倍電子掃描顯微鏡，高倍電子顯微鏡，化學(xué)元素分析等各種辦法來(lái)分析。生產(chǎn)時(shí)浮現(xiàn)會(huì)導(dǎo)致缺陷元素以及殘留在表面發(fā)生化學(xué)變化后來(lái)會(huì)導(dǎo)致缺陷元素（如S，P等有害元素）等都會(huì)影響軸承壽命。這些檢查辦法都是用來(lái)保證明驗(yàn)得出數(shù)據(jù)是真實(shí)有效。Tallian將所有軸承失效黑白圖片匯編起來(lái)【19.8】，可覺得判斷各種類型失效提供根據(jù)。當(dāng)前Tallian已經(jīng)將其更新為【19.9】，其中加入了彩色圖片。元素-金相實(shí)驗(yàn)可以提供一種精準(zhǔn)證據(jù)，使實(shí)驗(yàn)成果處在可控制狀況下，同步檢測(cè)有疑點(diǎn)和爭(zhēng)議地方。當(dāng)軸承從實(shí)驗(yàn)機(jī)上取下來(lái)時(shí)候可以現(xiàn)做一種初步研究，將會(huì)在30倍顯微鏡下觀測(cè)失效某些。而正常顯微圖片請(qǐng)看19.2~19.6中圖片。、圖19.2是球軸承溝道表面失效圖片。圖19.3是滾子軸承溝道由于未校準(zhǔn)而導(dǎo)致表面開裂圖片。圖19.4是一種球軸承由于外圈表面銹蝕而導(dǎo)致外圈開裂圖片。圖19.5是表面凹陷殘骸詳細(xì)圖片。圖19.6是一種由于熱變形導(dǎo)致內(nèi)圈游隙變化圖片。最后4張圖片不是用正的確驗(yàn)辦法得到有效失效模式。然而，這些錯(cuò)誤數(shù)據(jù)需要從有效失效數(shù)據(jù)中剔除掉，從而得到能對(duì)的評(píng)估壽命實(shí)驗(yàn)有效數(shù)據(jù)。2.避免失效辦法解決軸承失效問(wèn)題最佳辦法就是避免失效發(fā)生。這可以在選用過(guò)程中通過(guò)考慮核心性能特性來(lái)實(shí)現(xiàn)。這些特性涉及噪聲、起動(dòng)和運(yùn)轉(zhuǎn)扭矩、剛性、非重復(fù)性振擺以及徑向和軸向間隙。扭矩規(guī)定是由潤(rùn)滑劑、保持架、軸承圈質(zhì)量（彎曲某些圓度和表面加工質(zhì)量）以及與否使用密封或遮護(hù)裝置來(lái)決定。潤(rùn)滑劑粘度必要認(rèn)真加以選取，由于不適當(dāng)潤(rùn)滑劑會(huì)產(chǎn)生過(guò)大扭矩，這在小型軸承中特別如此。此外，不同潤(rùn)滑劑噪聲特性也不同樣。舉例來(lái)說(shuō)，潤(rùn)滑脂產(chǎn)生噪聲比潤(rùn)滑油大某些。因而，要依照不同用途來(lái)選用潤(rùn)滑劑。在軸承轉(zhuǎn)動(dòng)過(guò)程中，如果內(nèi)圈和外圈之間存在一種隨機(jī)偏心距，就會(huì)產(chǎn)生與凸輪運(yùn)動(dòng)非常相似非重復(fù)性振擺（NRR）。保持架尺寸誤差和軸承圈與滾珠偏心都會(huì)引起NRR。和重復(fù)性振擺不同是，NRR是沒(méi)有辦法進(jìn)行補(bǔ)償。在工業(yè)中普通是依照詳細(xì)應(yīng)用來(lái)選取不同類型和精度級(jí)別軸承。例如，當(dāng)規(guī)定振擺最小時(shí)，軸承非重復(fù)性振擺不能超過(guò)0.3微米。同樣，機(jī)床主軸只能容許最小振擺，以保證切削精度。因而在機(jī)床應(yīng)用中應(yīng)當(dāng)使用非重復(fù)性振擺較小軸承。在許多工業(yè)產(chǎn)品中，污染是不可避免，因而慣用密封或遮護(hù)裝置來(lái)保護(hù)軸承，使其免受灰塵或臟物侵蝕。但是，由于軸承內(nèi)外圈運(yùn)動(dòng)，使軸承密封不也許達(dá)到完美限度，因而潤(rùn)滑油泄漏和污染始終是一種未能解決問(wèn)題。一旦軸承受到污染，潤(rùn)滑劑就要變質(zhì)，運(yùn)營(yíng)噪聲也隨之變大。如果軸承過(guò)熱，它將會(huì)卡住。當(dāng)污染物處在滾珠和軸承圈之間時(shí)，其作用和金屬表面之間磨粒同樣，會(huì)使軸承磨損。采用密封和遮護(hù)裝置來(lái)?yè)蹰_臟物是控制污染一種辦法。噪聲是反映軸承質(zhì)量一種指標(biāo)。軸承性能可以用不同噪聲級(jí)別來(lái)表達(dá)。噪聲分析是用安德遜計(jì)進(jìn)行，該儀器在軸承生產(chǎn)中可用來(lái)控制質(zhì)量，也可對(duì)失效軸承進(jìn)行分析。將一傳感器連接在軸承外圈上，而內(nèi)圈在心軸以1800r/min轉(zhuǎn)速旋轉(zhuǎn)。測(cè)量噪聲單位為anderons。即用um/rad表達(dá)軸承位移。依照經(jīng)驗(yàn)，觀測(cè)者可以依照聲音辨別出微小缺陷。例如，灰塵產(chǎn)生是不規(guī)則噼啪聲；滾珠劃痕產(chǎn)生一種持續(xù)爆破聲，擬定這種劃痕最困難；內(nèi)圈損傷普通產(chǎn)生持續(xù)高頻噪聲，而外圈損傷則產(chǎn)生一種間歇聲音。軸承缺陷可以通過(guò)其頻率特性進(jìn)一步加以鑒定。普通軸承缺陷被分為低、中、高三個(gè)波段。缺陷還可以依照軸承每轉(zhuǎn)動(dòng)一周浮現(xiàn)不規(guī)則變化次數(shù)加以鑒定。低頻噪聲是長(zhǎng)波段不規(guī)則變化成果。軸承每轉(zhuǎn)一周這種不規(guī)則變化可浮現(xiàn)1.6~10次，它們是由各種干涉（例如軸承圈滾道上凹坑）引起?？刹煊X凹坑是一種制造缺陷，它是在制造過(guò)程中由于多爪卡盤夾太緊而形成。中頻噪聲特性是軸承每旋轉(zhuǎn)一周不規(guī)則變化浮現(xiàn)10~60次。這種缺陷是由在軸承圈和滾珠磨削加工中浮現(xiàn)振動(dòng)引起。軸承每旋轉(zhuǎn)一周高頻不規(guī)則變化浮現(xiàn)60~300次，它表白軸承上存在著密集振痕或大面積粗糙不平。運(yùn)用軸承噪聲特性對(duì)軸承進(jìn)行分類，顧客除了可以擬定大多數(shù)廠商所使用ABEC原則外，還可擬定軸承噪聲級(jí)別。ABEC原則只定義了諸如孔、外徑、振擺等尺寸公差。隨著ABEC級(jí)別增長(zhǎng)（從3增到9），公差逐漸變小。但ABEC級(jí)別并不能反映其她軸承特性，如軸承圈質(zhì)量、粗糙度、噪聲等。因而，噪聲級(jí)別劃分有助于工業(yè)原則改進(jìn)。BEARINGLIFEANALYSISProceedingsoftheNinthInternationalSymposiumonMagneticBearings.Kentucky.USA.,(August):3-61.WHYBEARINGSFAILAnindividualbearingmayfailforseveralreasons；however，theresultsofanendurancetestseriesareonlymeaningfulwhenthetestbearingsfailbyfatigue-relatedmechanisms.Theexperimentermustcontrolthetestprocesstoensurethatthisoccurs.SomeoftheotherfailuremodesthatcanbeexperiencedarediscussedindetailbyTallian[19.2].Thefollowingparagraphsdealwithafewspecificfailuretypesthatcanaffecttheconductofalifetestsequence.InChapter23，theinfluenceoflubricationoncontactfatiguelifeisdiscussedfromthestandpointofEHLfilmgeneration.Therearealsootherlubrication-relatedeffectsthatcanaffecttheoutcomeofthetestseries.Thefirstisparticulatecontaminantsinthelubricant.Dependingonbearingsize，operatingspeed，andlubricantrheology，theoverallthicknessofthelubricantfilmdevelopedattherollingelement-racewaycontactsmayfallbetween0.05and0.5m.Solidparticlesanddamagetheracewayandrollingelementsurfaces，leadingtosubstantiallyshortenedendurances.Thishasbeenamplydemonstratedbyandandothers.Therefore，filtrationofthelubricanttothedesiredlevelisnecessarytoensuremeaningfultestresult.Thedesiredlevelisdeterminedbytheapplicationwhichthetestingpurportstoapproximate.Ifthisdegreeoffiltrationisnotprovided，effectsofcontaminationmustbeconsideredwhenevaluatingtestresults.Chapter23discussestheeffectofvariousdegreesofparticulatecontamination，andhencefiltration，onbearingfatiguelife.Themoisturecontentinthelubricantisanotherimportantconsideration.Ithaslongbeenapparentthatquantitiesoffreewaterintheoilcausecorrosionoftherollingcontactsurfacesandthushaveadetrimentaleffectonbearinglife.IthasbeenfurthershownbyFitch[19.7]andothers，however，thatwaterlevelsaslowas50-100partspermillion(ppm)mayalsohaveadetrimentaleffect，evenwithnoevidenceofcorrosion.Thisisduetohydrogenembrittlementoftherollingelementandracewaymaterial.SeealsoChapter23.Moisturecontrolintestlubricationsystemsisthusamajorconcern，andtheeffectofmoistureneedstobeconsideredduringtheevaluationoflifetestresults.Amaximumof40ppmisconsiderednecessarytominimizelifereductioneffects.Thechemicalcompositionofthetestlubricantalsorequiresconsideration.Mostcommerciallubricantscontainanumberofproprietaryadditivesdevelopedforspecificpurposes；forexample，toprovideantiwearproperties，toachieveextremepressureand/orthermalstability，andtoprovideboundarylubricationincaseofmarginallubricantfilms.Theseadditivescanalsoaffecttheenduranceofrollingbearings，eitherimmediatelyorafterexperiencingtime-relateddegradation.Caremustbetakentoensurethattheadditivesincludedinthetestlubricantwillnotsufferexcessivedeteriorationasaresultofacceleratedlifetestconditions.Alsoforconsistencyofresultsandcomparinglifetestgroups，itisgoodpracticetoutilizeonestandardtestlubricantfromaparticularproducerfortheconductofallgenerallifetests.Thestatisticalnatureofrollingcontactfatiguerequiresmanytestsamplestoobtainareasonableestimateoflife.Abearinglifetestsequencethusneedsalongtime.Amajorjoboftheexperimentalististoensuretheconsistencyoftheappliedtestconditionsthroughouttheentiretestperiod.Thisprocessisnotsimplebecausesubtlechangescanoccurduringthetestperiod.Suchchangesmightbeoverlookeduntiltheireffectsbecomemajor.Atthattimeitisoftentoolatetosalvagethecollecteddata，andthetestmustberedoneunderbettercontrols.Forexample，thestabilityoftheadditivepackagesinatestlubricantcanbeasourceofchangingtestconditions.Somelubricantshavebeenknowntosufferadditivedepletionafteranextendedperiodofoperation.ThedegradationoftheadditivepackagecanaltertheEHLconditionsintherollingcontent，alteringbearinglife.Generally，thenormalchemicaltestsusedtoevaluatelubricantsdonotdeterminetheconditionsoftheadditivecontent.Thereforeifalubricantisusedforendurancetestingoveralongtime，asampleofthefluidshouldbereturnedtotheproduceratregularintervals，sayannually，foradetailedevaluationofitscondition.Adequatetemperaturecontrolsmustalsobeemployedduringthetest.ThethicknessoftheEHLfilmissensitivetothecontacttemperature.Mosttestmachinesarelocatedinstandardindustrialenvironmentswhereratherwidefluctuationsinambienttemperatureareexperiencedoveraperiodofayear.Inaddition，theheatgenerationratesofindividualbearingscanvaryasaresultofthecombinedeffectsofnormalmanufacturingtolerances.Bothoftheseconditionsproducevariationsinoperatingtemperaturelevelsinalotofbearingsandaffectthevalidityofthelifedata.Ameansmustbeprovidedtomonitorandcontroltheoperatingtemperaturelevelofeachbearingtoachieveadegreeofconsistency.Atolerancelevelof3Cisnormallyconsideredadequatefortheendurancetestprocess.Thedeteriorationoftheconditionofthemountinghardwareusedwiththebearingsisanotherarearequiringconstantmonitoring.Theheavyloadsusedforlifetestingrequireheavyinterferencefitsbetweenthebearinginnerringsandshafts.Repeatedmountinganddismountingofbearingscanproducedamagetotheshaftsurface，whichinturncanalterthegeometryofamountedring.Theshaftsurfaceandtheboreofthehousingarealsosubjecttodeteriorationfromfrettingcorrosion.Frettingcorrosionresultsfromtheoxidationofthefinewearparticlesgeneratedbythevibratoryabrasionofthesurface，whichisacceleratedbytheheavyendurancetestloading.Thismechanismcanalsoproducesignificantvariationsinthegeometryofthemountingsurfaces，whichcanaltertheinternalbearinggeometry.Suchchangescanhaveamajoreffectinreducingbearingtestlife.Thedetectionofbearingfailureisalsoamajorconsiderationinalifetestseries.Thefatiguetheoryconsidersfailureastheinitiationofthefirstcrackinthebulkmaterial.Obviouslythereisnowaytodetectthisoccurrenceinpractice.Tobedetectablethecrackmustpropagatetothesurfaceandproduceaspallofsufficientmagnitudetoproduceamarkedeffectonanoperatingparameterofthebearing：forexample，noise，vibration，and/ortemperature.Techniquesexitfordetectingfailuresinapplicationsystems.Theabilityofthesesystemstodetectearlysignsoffailurevarieswiththecomplexityofthetestsystem，thetypeofbearingunderevaluation，andothertestconditions.Currentlynosinglesystemexiststhatcanconsistentlyprovidethefailurediscriminationnecessaryforalltypesofbearinglifetests.Itisthennecessarytoselectasystemthatwillrepeatedlyterminatemachineoperationwithaconsistentminimaldegreeofdamage.Therateoffailurepropagationisthereforeimportant.Ifthedegreeofdamageattestterminationisconsistentamongtestelements，theonlyvariationbetweentheexperimentalandtheoreticallivesisthelaginfailuredetection.Instandardthrough-hardenedbearingsteelsthefailurepropagationrateisquiterapidunderendurancetestconditions，andthisisnotamajorfactor，consideringthetypicaldispersionofendurancetestdataandthedegreeofconfidenceobtainedfromstatisticalanalysis.Thismaynot，however，bethecasewithotherexperimentalmaterialsorwithsurface-hardenedsteelsorsteelsproducedbyexperimentaltechniques.Caremustbeusedwhenevaluatingtheselatterresultsandparticularlywhencomparingtheexperimentalliveswiththoseobtainedfromstandardsteellots.Theultimatemeansofensuringthatanendurancetestserieswasadequatelycontrolledistheconductofapost-testanalysis.Thisdetailedexaminationofallthetestedbearingsuseshigh-magnificationopticalinspection，higher-magnificationscanningelectronmicroscopy，metallurgicalanddimensionalexaminations，andchemical evaluationsasrequired.Thecharacteristicsofthefailuresareexaminedtoestablishtheiroriginsandtheresidualsurfaceconditionsareevaluatedforindicationsofextraneouseffectsthatmayhaveinfluencedthebearinglife.Thistechniqueallowstheexperimentertoensurethatthedataareindeedvalid.The“DamageAtlas”compiledbyTallianetal.[19.8]containingnumerousblackandwhitephotographsofthevariousbearingfailuremodescanprovideguidanceforthesetypesofdeterminations.ThisworkwassubsequentlyupdatedbyTallian[19.9]，nowincludingcolorphotographsaswell.Thepost-testanalysisis，bydefinition，afterthefact.Toprovidecontrolthroughoutthetestseriesandtoeliminateallquestionableareas，theexperimentershouldconductapreliminarystudywheneverabearingisremovedfromthetestmachine.Inthisportionoftheinvestigationeachbearingisexaminedopticallyatmagnificationsupto30forindicationsofimproperorout-of-controltestparameters.ExamplesofthetypesofindicationsthatcanbeobservedaregiveninFigs.19.2-19.6.Figure19.2illustratestheappearanceofatypicalfatigue-originatedspallonaballbearingraceway.Figure19.3containsaspallingfailureontheracewayofarollerbearingthatresultedfrombearingmisalignment，andFig.19.4containsaspallingfailureontheouterringofaballbearingproducedbyfrettingcorrosionontheouterdiameter.Figure19.5illustratesamoresubtleformoftestalteration，`wherethespallingfailureoriginatedfromthepresenceofadebrisdentonthesurface.Figure19.6givesanexampleofatotallydifferentfailuremodeproducedbythelossofinternalbearingclearanceduetothermalunbalanceofthesystem.Thelastfourfailuresarenotvalidfatiguespallsandindicatetheneedtocorrectthetestmethods.Furthermore，thesedatapointswouldneedtobeeliminatedfromthefailuredatatoobtainavalidestimateoftheexperimentalbearinglife.2.AVOIDINGFAILURESThebestwaytohandlebearingfailuresistoavoidthem．Thiscanbedoneintheselectionprocessbyrecognizingcriticalperformancecharacteristics．Theseincludenoise，startingandrunningtorque，stiffness，non-repetitiverunout，andradialandaxialplay．Insomeapplications，theseitemsaresocriticalthatspecifyinganABEClevelaloneisnotsufficient．Torquerequirementsaredeterminedbythelubricant，retainer，racewayquality(roundnesscrosscurvatureandsurfacefinish)，andwhethersealsorshieldsareused．Lubricantviscositymustbeselectedcarefullybecauseinappropriatelubricant，especiallyinminiaturebearings，causesexcessivetorque．Also，differentlubricantshavevaryingnoisecharacteristicsthatshouldbematchedtotheapplication.Forexample，greasesproducemorenoisethanoil．Non-repetitiverunout(NRR)occursduringrotationasarandomeccentricitybetweentheinnerandouterraces，muchlikeacamaction．NRRcanbecausedbyretainertoleranceoreccentricitiesoftheracewaysandballs．Unlikerepetitiverunout，nocompensationcanbemadeforNRR.NRRisreflectedinthecostofthebearing．Itiscommonintheindustrytoprovidedifferentbearingtypesandgradesforspecificapplications．Forexample，abearingwithanNRRoflessthan0.3umisusedwhenminimalrunoutisneeded，suchasindisk—drivespindlemotors．Similarly，machine—toolspindlestolerateonlyminimaldeflectionstomaintainprecisioncuts．Consequently，bearingsaremanufacturedwithlowNRRjustformachine-toolapplications．Contaminationisunavoidableinmanyindustrialproducts，andshieldsandsealsarecommonlyusedtoprotectbearingsfromdustanddirt．However，aperfectbearingsealisnotpossiblebecauseofthemovementbetweeninnerandouterraces．Consequently，lubricationmigrationandcontaminationarealwaysproblems．Onceabearingiscontaminated，itslubricantdeterioratesandoperationbecomesnoisier．Ifitoverheats，thebearingcanseize．Attheveryleast，contaminationcauseswearasitworksbetweenballsandtheraceway，becomingintheracesandactingasanabrasivebetweenmetalsurfaces．Fendingoffdirtwithsealsandshieldsillustratessomemethodsforcontrollingcontamination．Noiseisasanindicatorofbearingquality．Variousnoisegradeshavebeendevelopedtoclassifybearingperformancecapabilities．Whichisusedforqualitycontrolinbearingproductionandalsowhenfailedbeari