機(jī)械設(shè)計(jì)與制造畢業(yè)設(shè)計(jì)論文中英文翻譯外文翻譯

1、<p>　　畢業(yè)設(shè)計(jì)（論文）外文翻譯</p><p><b>　　如何延長(zhǎng)軸承壽命</b></p><p>　　摘要： 自然界苛刻的工作條件會(huì)導(dǎo)致軸承的失效，但是如果遵循一些簡(jiǎn)單的規(guī)則，軸承正常運(yùn)轉(zhuǎn)的機(jī)會(huì)是能夠被提高的。在軸承的使用過(guò)程當(dāng)中，過(guò)分的忽視會(huì)導(dǎo)致軸承的過(guò)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(gè)被損壞的軸承，會(huì)留下它為什么被損壞

2、的線索。通過(guò)一些細(xì)致的偵察工作，我們可以采取行動(dòng)來(lái)避免軸承的再次失效。</p><p>　　關(guān)鍵詞： 軸承 失效 壽命</p><p>　　軸承（“Bearing”，日本人稱“軸受”）是在機(jī)械傳動(dòng)過(guò)程中起固定和減小載荷摩擦系數(shù)的部件。也可以說(shuō)，當(dāng)其它機(jī)件在軸上彼此產(chǎn)生相對(duì)運(yùn)動(dòng)時(shí)，用來(lái)降低動(dòng)力傳遞過(guò)程中的摩擦系數(shù)和保持軸中心位置固定的機(jī)件。軸承是當(dāng)代機(jī)械設(shè)備中一種舉足輕重的零部件。它的主要功

3、能是支撐機(jī)械旋轉(zhuǎn)體，用以降低設(shè)備在傳動(dòng)過(guò)程中的機(jī)械載荷摩擦系數(shù)。按運(yùn)動(dòng)元件摩擦性質(zhì)的不同，軸承可分為滾動(dòng)軸承和滑動(dòng)軸承兩類。</p><p>　　1.軸承壽命的基本概念</p><p>　　根據(jù)最新的軸承疲勞壽命理論，一只設(shè)計(jì)優(yōu)秀、材質(zhì)卓越、制造精良而且安裝正確的軸承，只要其承受的負(fù)荷足夠輕松（不大于該軸承相應(yīng)的某個(gè)持久性極限負(fù)荷值），則這個(gè)軸承的材料將永遠(yuǎn)不會(huì)產(chǎn)生疲勞損壞。因此，只要軸承

4、的工作環(huán)境溫度適宜而且變化幅度不大，絕對(duì)無(wú)固體塵埃、有害氣體和水分侵入軸承，軸承的潤(rùn)滑充分而又恰到好處，潤(rùn)滑劑絕對(duì)純正而無(wú)雜質(zhì)，并且不會(huì)老化變質(zhì)，則這個(gè)軸承將會(huì)無(wú)限期地運(yùn)轉(zhuǎn)下去。</p><p>　　這個(gè)理論的重大意義不僅在于它提供了一個(gè)比ISO壽命方程更為可靠的預(yù)測(cè)現(xiàn)代軸承壽命的工具，而且在于它展示了所有軸承的疲勞壽命都有著可觀的開(kāi)發(fā)潛力，并展示了開(kāi)發(fā)這種潛力的途徑，因而對(duì)軸承產(chǎn)品的開(kāi)發(fā)、質(zhì)量管理和應(yīng)用技術(shù)有著

5、深遠(yuǎn)的影響。</p><p>　　但是，軸承的無(wú)限只有在實(shí)驗(yàn)室的條件下才有可能“實(shí)現(xiàn)”，而這樣的條件對(duì)于在一定工況下現(xiàn)場(chǎng)使用的軸承來(lái)說(shuō)，既難辦到也太昂貴。</p><p>　　現(xiàn)場(chǎng)使用軸承，其工作負(fù)荷往往大于其相應(yīng)的疲勞持久性極限負(fù)荷，在工作到一定的期限后，或晚或早總會(huì)由于本身材料達(dá)致電疲勞極限，產(chǎn)生疲勞剝落而無(wú)法繼續(xù)使用。即使某些軸承的工作負(fù)荷低于其相應(yīng)的持久性極限負(fù)荷，也會(huì)由于難以根絕

6、的軸承污染問(wèn)題而發(fā)生磨損失效。總之，現(xiàn)場(chǎng)使用中的軸承或多或少總不能充分具備上述實(shí)驗(yàn)室所具備的那些條件，而其中任一條件稍有不足，都會(huì)縮短軸承的可用期限，這就產(chǎn)生了軸承壽命的問(wèn)題。</p><p><b>　　2.軸承壽命類別</b></p><p>　　軸承的失效形式多種多樣，但其中多數(shù)失效形式迄今尚無(wú)可用的壽命計(jì)算方法，只有疲勞壽命、磨損壽命、潤(rùn)滑壽命和微動(dòng)壽命可以通

7、過(guò)計(jì)算的方法定量地加以評(píng)估。</p><p><b>　?。?）疲勞壽命</b></p><p>　　在潤(rùn)滑充分而其他使用條件正常的情況下，軸承常因疲勞剝落而失效，其期限疲勞壽命可以樣本查得有關(guān)數(shù)據(jù)，按規(guī)定的公式和計(jì)算程序以一定的可靠性計(jì)算出來(lái)。</p><p><b>　?。?）磨損壽命</b></p>&

8、lt;p>　　機(jī)床主軸承取大直徑以保證其高剛度，所配軸承的尺寸相應(yīng)也大，在其遠(yuǎn)末達(dá)到疲勞極限之前，常因磨損而喪失要精度以致無(wú)法繼續(xù)使用，對(duì)這類軸承必須用磨損壽命來(lái)徇其可能性的服務(wù)期限。實(shí)際上，現(xiàn)場(chǎng)使用的軸承大多因過(guò)度磨損而失效，所以也必須考慮磨損壽命問(wèn)題。</p><p><b>　?。?）潤(rùn)滑壽命</b></p><p>　　主要對(duì)于雙面帶密封的脂潤(rùn)滑軸承，一

9、次填脂以后不再補(bǔ)充加脂，此時(shí)軸承有壽命便取決于滾脂的使用壽命。</p><p><b>　?。?）微動(dòng)磨蝕壽命</b></p><p>　　絞車、懸臂式起微型重機(jī)和齒輪變速箱以及汽車離合器等機(jī)構(gòu)中的軸承，在其非運(yùn)轉(zhuǎn)狀態(tài)下受到振動(dòng)負(fù)荷所產(chǎn)生的微動(dòng)磨蝕損傷。往往會(huì)發(fā)展成軸承失效的主導(dǎo)原因，對(duì)這類機(jī)構(gòu)中的軸承，有時(shí)需要計(jì)算其微動(dòng)磨蝕壽命。</p><p&

10、gt;　　導(dǎo)致軸承失效的原因很多，但常見(jiàn)的是不正確的使用、污染、潤(rùn)滑劑使用不當(dāng)、裝卸或搬運(yùn)時(shí)的損傷及安裝誤差等。診斷失效的原因并不困難，因?yàn)楦鶕?jù)軸承上留下的痕跡可以確定軸承失效的原因。</p><p>　　然而，當(dāng)事后的調(diào)查分析提供出寶貴的信息時(shí)，最好首先通過(guò)正確地選定軸承來(lái)完全避免失效的發(fā)生。為了做到這一點(diǎn)，再考察一下制造廠商的尺寸定位指南和所選軸承的使用特點(diǎn)是非常重要的。</p><p&g

11、t;<b>　　1 軸承失效的原因</b></p><p>　　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(huì)引起扭矩和噪聲的問(wèn)題。由環(huán)境和污染所產(chǎn)生的軸承失效是可以預(yù)防的，而且通過(guò)簡(jiǎn)單的肉眼觀察是可以確定產(chǎn)生這類失效的原因。</p><p>　　通過(guò)失效后的分析可以得知對(duì)已經(jīng)失效的或?qū)⒁?/p>

12、的軸承應(yīng)該在哪些方面進(jìn)行查看。弄清諸如剝蝕和疲勞破壞一類失效的機(jī)理，有助于消除問(wèn)題的根源。</p><p>　　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(guò)材料屈服極限時(shí)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(huì)產(chǎn)生剝蝕。軸承圈上的壓坑還會(huì)產(chǎn)生噪聲、振動(dòng)和附加扭矩。</p><p>　　類似的一種

13、缺陷是當(dāng)軸承不旋轉(zhuǎn)時(shí)由于滾珠在軸承圈間振動(dòng)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(yùn)輸中的設(shè)備和不工作時(shí)仍振動(dòng)的設(shè)備中都會(huì)產(chǎn)生。此外，低荷振蝕產(chǎn)生的碎屑的作用就象磨粒一樣，會(huì)進(jìn)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(rùn)滑劑中會(huì)產(chǎn)生淡紅色。</p><p>　　消除振動(dòng)源并保持良好的軸承潤(rùn)滑可以防止低荷振蝕。給設(shè)備加隔離墊或?qū)Φ鬃M(jìn)行隔離可以減輕環(huán)境的振動(dòng)。另外在軸承上加一個(gè)較小

14、的預(yù)載荷不僅有助于滾珠和軸承圈保持緊密的接觸，并且對(duì)防止在設(shè)備運(yùn)輸中產(chǎn)生的低荷振蝕也有幫助。</p><p>　　造成軸承卡住的原因是缺少內(nèi)隙、潤(rùn)滑不當(dāng)和載荷過(guò)大。在卡住之前，過(guò)大的摩擦和熱量使軸承鋼軟化。過(guò)熱的軸承通常會(huì)改變顏色，一般會(huì)變成藍(lán)黑色或淡黃色。摩擦還會(huì)使保持架受力，這會(huì)破壞支承架，并加速軸承的失效。</p><p>　　材料過(guò)早出現(xiàn)疲勞破壞是由重載后過(guò)大的預(yù)載引起的。如果這些

15、條件不可避免，就應(yīng)仔細(xì)計(jì)算軸承壽命，以制定一個(gè)維護(hù)計(jì)劃。</p><p>　　另一個(gè)解決辦法是更換材料。若標(biāo)準(zhǔn)的軸承材料不能保證足夠的軸承壽命，就應(yīng)當(dāng)采用特殊的材料。另外，如果這個(gè)問(wèn)題是由于載荷過(guò)大造成的，就應(yīng)該采用抗載能力更強(qiáng)或其他結(jié)構(gòu)的軸承。</p><p>　　蠕動(dòng)不象過(guò)早疲勞那樣普遍。軸承的蠕動(dòng)是由于軸和內(nèi)圈之間的間隙過(guò)大造成的。蠕動(dòng)的害處很大，它不僅損害軸承，也破壞其他零件。&l

16、t;/p><p>　　蠕動(dòng)的明顯特征是劃痕、擦痕或軸與內(nèi)圈的顏色變化。為了防止蠕動(dòng)，應(yīng)該先用肉眼檢查一下軸承箱件和軸的配件。</p><p>　　蠕動(dòng)與安裝不正有關(guān)。如果軸承圈不正或翹起，滾珠將沿著一個(gè)非圓周軌道運(yùn)動(dòng)。這個(gè)問(wèn)題是由于安裝不正確或公差不正確或軸承安裝現(xiàn)場(chǎng)的垂直度不夠造成的。如果偏斜超過(guò)0.25°，軸承就會(huì)過(guò)早地失效。</p><p>　　檢查潤(rùn)滑

17、劑的污染比檢查裝配不正或蠕動(dòng)要困難得多。污染的特征是使軸承過(guò)早的出現(xiàn)磨損。潤(rùn)滑劑中的固體雜質(zhì)就象磨粒一樣。如果滾珠和保持架之間潤(rùn)滑不良也會(huì)磨損并削弱保持架。在這種情況下，潤(rùn)滑對(duì)于完全加工形式的保持架來(lái)說(shuō)是至關(guān)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_(dá)全部表面。</p><p>　　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(dāng)。如果某一材料經(jīng)檢驗(yàn)適合工作要求，那么防止生銹的最簡(jiǎn)單的方法是給軸承

18、包裝起來(lái)，直到安裝使用時(shí)才打開(kāi)包裝。</p><p><b>　　2 避免失效的方法</b></p><p>　　解決軸承失效問(wèn)題的最好辦法就是避免失效發(fā)生。這可以在選用過(guò)程中通過(guò)考慮關(guān)鍵性能特征來(lái)實(shí)現(xiàn)。這些特征包括噪聲、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。</p><p>　　扭矩要求是由潤(rùn)滑劑、保持架、軸承圈質(zhì)量（彎曲部分

19、的圓度和表面加工質(zhì)量）以及是否使用密封或遮護(hù)裝置來(lái)決定。潤(rùn)滑劑的粘度必須認(rèn)真加以選擇，因?yàn)椴贿m宜的潤(rùn)滑劑會(huì)產(chǎn)生過(guò)大的扭矩，這在小型軸承中尤其如此。另外，不同的潤(rùn)滑劑的噪聲特性也不一樣。舉例來(lái)說(shuō)，潤(rùn)滑脂產(chǎn)生的噪聲比潤(rùn)滑油大一些。因此，要根據(jù)不同的用途來(lái)選用潤(rùn)滑劑。</p><p>　　在軸承轉(zhuǎn)動(dòng)過(guò)程中，如果內(nèi)圈和外圈之間存在一個(gè)隨機(jī)的偏心距，就會(huì)產(chǎn)生與凸輪運(yùn)動(dòng)非常相似的非重復(fù)性振擺（NRR）。保持架的尺寸誤差和軸承

20、圈與滾珠的偏心都會(huì)引起NRR。和重復(fù)性振擺不同的是，NRR是沒(méi)有辦法進(jìn)行補(bǔ)償?shù)摹?lt;/p><p>　　在工業(yè)中一般是根據(jù)具體的應(yīng)用來(lái)選擇不同類型和精度等級(jí)的軸承。例如，當(dāng)要求振擺最小時(shí)，軸承的非重復(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的振擺，以保證切削精度。因此在機(jī)床的應(yīng)用中應(yīng)該使用非重復(fù)性振擺較小的軸承。</p><p>　　在許多工業(yè)產(chǎn)品中，污染是不可避免的，因此常用密

21、封或遮護(hù)裝置來(lái)保護(hù)軸承，使其免受灰塵或臟物的侵蝕。但是，由于軸承內(nèi)外圈的運(yùn)動(dòng)，使軸承的密封不可能達(dá)到完美的程度，因此潤(rùn)滑油的泄漏和污染始終是一個(gè)未能解決的問(wèn)題。</p><p>　　一旦軸承受到污染，潤(rùn)滑劑就要變質(zhì)，運(yùn)行噪聲也隨之變大。如果軸承過(guò)熱，它將會(huì)卡住。當(dāng)污染物處于滾珠和軸承圈之間時(shí)，其作用和金屬表面之間的磨粒一樣，會(huì)使軸承磨損。采用密封和遮護(hù)裝置來(lái)?yè)蹰_(kāi)臟物是控制污染的一種方法。</p>&

22、lt;p>　　噪聲是反映軸承質(zhì)量的一個(gè)指標(biāo)。軸承的性能可以用不同的噪聲等級(jí)來(lái)表示。</p><p>　　噪聲的分析是用安德遜計(jì)進(jìn)行的，該儀器在軸承生產(chǎn)中可用來(lái)控制質(zhì)量，也可對(duì)失效的軸承進(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的轉(zhuǎn)速旋轉(zhuǎn)。測(cè)量噪聲的單位為anderon。即用um/rad表示的軸承位移。</p><p>　　根據(jù)經(jīng)驗(yàn)，觀察者可以根據(jù)聲音辨別出

23、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(nèi)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。</p><p>　　軸承缺陷可以通過(guò)其頻率特性進(jìn)一步加以鑒定。通常軸承缺陷被分為低、中、高三個(gè)波段。缺陷還可以根據(jù)軸承每轉(zhuǎn)動(dòng)一周出現(xiàn)的不規(guī)則變化的次數(shù)加以鑒定。</p><p>　　低頻噪聲是長(zhǎng)波段不規(guī)則變化的結(jié)果。軸承每轉(zhuǎn)一周這

24、種不規(guī)則變化可出現(xiàn)1.6~10次，它們是由各種干涉（例如 軸承圈滾道上的凹坑）引起的。可察覺(jué)的凹坑是一種制造缺陷，它是在制造過(guò)程中由于多爪卡盤(pán)夾的太緊而形成的。</p><p>　　中頻噪聲的特征是軸承每旋轉(zhuǎn)一周不規(guī)則變化出現(xiàn)10~60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(dòng)引起的。軸承每旋轉(zhuǎn)一周高頻不規(guī)則變化出現(xiàn)60~300次，它表明軸承上存在著密集的振痕或大面積的粗糙不平。</p>

25、<p>　　利用軸承的噪聲特性對(duì)軸承進(jìn)行分類，用戶除了可以確定大多數(shù)廠商所使用的ABEC標(biāo)準(zhǔn)外，還可確定軸承的噪聲等級(jí)。ABEC標(biāo)準(zhǔn)只定義了諸如孔、外徑、振擺等尺寸公差。隨著ABEC級(jí)別的增加（從3增到9），公差逐漸變小。但ABEC等級(jí)并不能反映其他軸承特性，如軸承圈質(zhì)量、粗糙度、噪聲等。因此，噪聲等級(jí)的劃分有助于工業(yè)標(biāo)準(zhǔn)的改進(jìn)。</p><p>　　為了延長(zhǎng)軸承的使用壽命，要注重工業(yè)軸承的保養(yǎng)、檢修、

26、以求防事故于未然，確保運(yùn)轉(zhuǎn)的可靠性，提高生產(chǎn)性、經(jīng)濟(jì)性。保養(yǎng)最好相應(yīng)機(jī)械運(yùn)轉(zhuǎn)條件的作業(yè)標(biāo)準(zhǔn)，定期進(jìn)行。內(nèi)容包括監(jiān)視運(yùn)轉(zhuǎn)狀態(tài)、補(bǔ)充或更換潤(rùn)滑劑、定期拆卸的檢查。作為運(yùn)轉(zhuǎn)中的檢修事項(xiàng)，有軸承的旋轉(zhuǎn)音、振動(dòng)、溫度、潤(rùn)滑劑的狀態(tài)等等。</p><p>　　1、軸承的清洗：拆卸下軸承檢修時(shí)，首先記錄軸承的外觀，確認(rèn)潤(rùn)滑劑的殘存量，取樣檢查用的潤(rùn)滑劑之后，洗軸承。作為清洗劑，普通使用汽油、煤油。拆下來(lái)的軸承的清洗，分粗清洗和

27、細(xì)清洗，分別放在容器中，先放上金屬的網(wǎng)墊底，使軸承不直接接觸容器的臟物。粗清洗時(shí)，如果使軸承帶著臟物旋轉(zhuǎn)，會(huì)損傷軸承的滾動(dòng)面，應(yīng)該加以注意。在粗清洗油中，使用刷子清除去潤(rùn)滑脂、粘著物，大致干凈后，轉(zhuǎn)入精洗。精洗，是將軸承在清洗油中一邊旋轉(zhuǎn)，一邊仔細(xì)的清洗。另外，清洗油也要經(jīng)常保持清潔。</p><p>　　2、軸承的檢修和判斷：為了判斷拆卸下來(lái)的軸承是否可以使用，要在軸承洗干凈后檢查。檢查滾道面、滾動(dòng)面、配合面的

28、狀態(tài)、保持架的磨損情況、軸承游隙的增加及有無(wú)關(guān)尺寸精度下降的損傷，異常。非分離型小型球軸承，則用一只手將內(nèi)圈支持水平，旋轉(zhuǎn)外圈確認(rèn)是否流暢。圓錐滾子軸承等分離形軸承，可以對(duì)滾動(dòng)體、外圈的滾道面分別檢查。大型軸承因不能用手旋轉(zhuǎn)，注意檢查滾動(dòng)體、滾道面、保持架、擋邊面等外觀，軸承的重要性愈高愈須慎重檢查。</p><p>　　3、軸承潤(rùn)滑的目的：滾動(dòng)軸承的潤(rùn)滑目的是減少軸承內(nèi)部摩擦及摩損，防止燒粘、其潤(rùn)滑效用如下。進(jìn)

29、口泵 閥門(mén)</p><p>　?。?）、減少摩擦及摩損。在構(gòu)成軸承的套圈、滾動(dòng)體及保持器的相互接觸部分，防止金屬接觸，減少摩擦、磨損。</p><p>　?。?）、延長(zhǎng)疲勞壽命。 軸承的滾動(dòng)疲勞壽命，在旋轉(zhuǎn)中，滾動(dòng)接觸面潤(rùn)滑良好，則延長(zhǎng)。相反地，油粘度低，潤(rùn)滑油膜厚度不好，則縮短。</p><p>　?。?）、排出摩擦熱、冷卻。循環(huán)給油法等可以用油排出由摩擦發(fā)生的熱

30、，或由外部傳來(lái)的熱，冷卻。防止軸承過(guò)熱，防止?jié)櫥妥陨砝匣?lt;/p><p>　?。?）、其他：也有防止異物侵入軸承內(nèi)部，或防止生銹、腐蝕之效果。 潤(rùn)滑方法：軸承的潤(rùn)滑方法，分為脂潤(rùn)滑和油潤(rùn)滑。為了使軸承很好地發(fā)揮機(jī)能，首先，要選擇適合使用條件、使用目的的潤(rùn)滑方法。若只考慮潤(rùn)滑，油潤(rùn)滑的潤(rùn)滑性占優(yōu)勢(shì)。但是，脂潤(rùn)滑有可以簡(jiǎn)化軸承周圍結(jié)構(gòu)的特長(zhǎng)，將脂潤(rùn)滑和油潤(rùn)滑的利弊比較。</p><p>　

31、　4、軸承的安裝：軸承的安裝是否正確，影響著精度、壽命、性能。因此，設(shè)計(jì)及組裝部門(mén)對(duì)于軸承的安裝要充分研究。希望要按照作業(yè)標(biāo)準(zhǔn)進(jìn)行安裝。作業(yè)標(biāo)準(zhǔn)的項(xiàng)目通常如下：（1）、清洗軸承及軸承關(guān)連部件；（2）、檢查關(guān)連部件的尺寸及精加工情況；（3）、安裝；（4）、安裝好軸承后的檢查；（5）、供給潤(rùn)滑劑。</p><p>　　5、希望在即將安裝前，方才打開(kāi)軸承包裝。一般潤(rùn)滑脂潤(rùn)滑，不清洗，直接填充潤(rùn)滑脂。潤(rùn)滑油潤(rùn)滑，普通也不

32、必清洗，但是，儀器用或高速用軸承等，要用潔凈的油洗凈，除去涂在軸承上的防銹劑。除去了防銹劑的軸承，易生銹，所以不能放置不顧。 再者，已封入潤(rùn)滑脂的軸承，不清洗直接使用。</p><p>　　6、軸承的安裝方法，因軸承結(jié)構(gòu)、配合、條件而異，一般，由于多為軸旋轉(zhuǎn)，所以內(nèi)圈需要過(guò)盈配合。圓柱孔軸承，多用壓力機(jī)壓入，或多用熱裝方法。錐孔的場(chǎng)合，直接安裝在錐度軸上，或用套筒安裝。</p><p>　

33、　7、安裝到外殼時(shí)，一般游隙配合多，外圈有過(guò)盈量，通常用壓力機(jī)壓入，或也有冷卻后安裝的冷縮配合方法。用干冰作冷卻劑，冷縮配合安裝的場(chǎng)合，空氣中的水分會(huì)凝結(jié)在軸承的表面。所以，需要適當(dāng)?shù)姆冷P措施。</p><p>　　畢業(yè)設(shè)計(jì)（論文）外文翻譯原文</p><p>　　EXTENDING BEARING LIFE</p><p>　　Abstract：Nature wo

34、rks 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 possibly seizure or, at worst, an explosion. But eve

35、n a failed bearing leaves clues as to what went wrong. After a little detective work, action can be taken to avoid a repeat performance.</p><p>　　Keywords: bearings failures life</p><p>　　Be

36、arings fail 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 be

37、aring usually leaves telltale signs about what went wrong．</p><p>　　However，while a postmortem yields good information，it is better to avoid the process altogether by specifying the bearing correctly in The

38、first place．To do this，it is useful to review the manufacturers sizing guidelines and operating characteristics for the selected bearing.</p><p>　　Equally critical is a study of requirements for noise, torqu

39、e, 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.</p><p>　　1 Why bearings fail

40、</p><p>　　About 40% of ball bearing failures are caused by contamination from dust, dirt, shavings, and corrosion. Contamination also causes torque and noise problems, and is often the result of improper han

41、dling or the application environment．Fortunately, a bearing failure caused by environment or handling contamination is preventable，and a simple visual examination can easily identify the cause．</p><p>　　Cond

42、ucting a postmortem il1ustrates what to look for on a failed or failing bearing．Then，understanding the mechanism behind the failure, such as brinelling or fatigue, helps eliminate the source of the problem.</p>&l

43、t;p>　　Brinelling is one type of bearing failure easily avoided by proper handing and assembly. It is characterized by indentations in the bearing raceway caused by shock loading－such as when a bearing is dropped-or in

44、correct 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 across the races．Raceway dents

45、 also produce noise，vibration，and increased torque.</p><p>　　A similar defect is a pattern of elliptical dents caused by balls vibrating between raceways while the bearing is not turning．This problem is call

46、ed false brinelling. It occurs on equipment in transit or that vibrates when not in operation. In addition, debris created by false brinelling acts like an abrasive, further contaminating the bearing. Unlike brinelling,

47、false binelling is often indicated by a reddish color from fretting corrosion in the lubricant.</p><p>　　False brinelling is prevented by eliminating vibration sources and keeping the bearing well lubricated

48、. Isolation pads on the equipment or a separate foundation may be required to reduce environmental vibration. Also a light preload on the bearing helps keep the balls and raceway in tight contact. Preloading also helps p

49、revent false brinelling during transit.</p><p>　　Seizures can be caused by a lack of internal clearance, improper lubrication, or excessive loading. Before seizing, excessive, friction and heat softens the b

50、earing steel. Overheated bearings often change color，usually to blue-black or straw colored．Friction also causes stress in the retainer，which can break and hasten bearing failure．</p><p>　　Premature material

51、 fatigue is caused by a high load or excessive preload．When these conditions are unavoidable，bearing life should be carefully calculated so that a maintenance scheme can be worked out．</p><p>　　Another solut

52、ion 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 t

53、raced back to excessive loading，a higher capacity bearing or different configuration may be used．</p><p>　　Creep is less common than premature fatigue．In bearings．it is caused by excessive clearance between

54、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．</p><p>　　0ther more likely creep indicators are scra

55、tches，scuff marks，or discoloration to shaft and bore．To prevent creep damage，the bearing housing and shaft fittings should be visually checked．</p><p>　　Misalignment is related to creep in that it is mountin

56、g related．If races are misaligned or cocked．The balls track in a noncircumferencial path．The problem is incorrect mounting or tolerancing，or insufficient squareness of the bearing mounting site．Misalignment of more than

57、1/4·can cause an early failure．</p><p>　　Contaminated lubricant is often more difficult to detect than misalignment or creep．Contamination shows as premature wear．Solid contaminants become an abrasive i

58、n the lubricant．In addition。insufficient lubrication between ball and retainer wears and weakens the retainer．In this situation，lubrication is critical if the retainer is a fully machined type．Ribbon or crown retainers，i

59、n contrast，allow lubricants to more easily reach all surfaces． </p><p>　　Rust is a form of moisture contamination and often indicates the wrong material for the application．If the material checks out for the

60、 job，the easiest way to prevent rust is to keep bearings in their packaging，until just before installation．</p><p>　　2 Avoiding failures</p><p>　　The best way to handle bearing failures is to av

61、oid them．This can be done in the selection process by recognizing critical performance characteristics．These include noise，starting and running torque，stiffness，nonrepetitive runout，and radial and axial play．In some appl

62、ications, these items are so critical that specifying an ABEC level alone is not sufficient．</p><p>　　Torque requirements are determined by the lubricant，retainer，raceway quality(roundness cross curvature an

63、d surface finish)，and whether seals or shields are used．Lubricant viscosity must be selected carefully because inappropriate lubricant，especially in miniature bearings，causes excessive torque．Also，different lubricants ha

64、ve varying noise characteristics that should be matched to the application. For example，greases produce more noise than oil．</p><p>　　Nonrepetitive runout(NRR)occurs during rotation as a random eccentricity

65、between the inner and outer races，much like a cam action．NRR can be caused by retainer tolerance or eccentricities of the raceways and balls．Unlike repetitive runout, no compensation can be made for NRR.</p><p

66、>　　NRR is reflected in the cost of the bearing．It is common in the industry to provide different bearing types and grades for specific applications．For example，a bearing with an NRR of less than 0.3um is used when min

67、imal runout is needed，such as in disk—drive spindle motors．Similarly，machine—tool spindles tolerate only minimal deflections to maintain precision cuts．Consequently, bearings are manufactured with low NRR just for machin

68、e-tool applications．</p><p>　　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 pos

69、sible because of the movement between inner and outer races．Consequently，lubrication migration and contamination are always problems．</p><p>　　Once a bearing is contaminated, its lubricant deteriorates and o

70、peration 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

71、surfaces．Fending off dirt with seals and shields illustrates some methods for controlling contamination．</p><p>　　Noise is as an indicator of bearing quality．Various noise grades have been developed to class

72、ify bearing performance capabilities．</p><p>　　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

73、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.</p><p>　　With experience, insp

74、ectors 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 co

75、nstant high-pitched noise, while a damaged outer race makes an intermittent sound as it rotates.</p><p>　　Bearing defects are further identified by their frequencies. Generally, defects are separated into lo

76、w, medium, and high wavelengths. Defects are also referenced to the number of irregularities per revolution.</p><p>　　Low-band noise is the effect of long-wavelength irregularities that occur about 1.6 to 10

77、 times per revolution. These are caused by a variety of inconsistencies, such as pockets in the race. Detectable pockets are manufacturing flaws and result when the race is mounted too tightly in multiplejaw chucks.</

78、p><p>　　Medium-hand noise is characterized by irregularities that occur 10 to 60 times per revolution. It is caused by vibration in the grinding operation that produces balls and raceways. High-hand irregularit

79、ies occur at 60 to 300 times per revolution and indicate closely spaced chatter marks or widely spaced, rough irregularities.</p><p>　　Classifying bearings by their noise characteristics allows users to spec

80、ify a noise grade in addition to the ABEC standards used by most manufacturers. ABEC defines physical tolerances such as bore, outer diameter, and runout. As the ABEC class number increase (from 3 to 9), tolerances are t