722 雙鉸接剪叉式液壓升降臺的設計

722 雙鉸接剪叉式液壓升降臺的設計,鉸接,剪叉式,液壓,升降臺,設計 外文資料翻譯1EXTENDING BEARING LIFE如何延長軸承壽命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 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.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。Keywords: bearings failures life關鍵詞： 軸承 失效 壽命Bearings 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 bearing usually leaves telltale signs about what went wrong．導致軸承失效的原因很多，但常見的是不正確的使用、污染、潤滑劑使用不當、裝卸或搬運時的損傷及安裝誤差等。診斷失效的原因并不困難，因為根據(jù)軸承上留下的痕跡可以確定軸承失效的原因。However，while a postmortem yields good information，it is better to avoid the process 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.然而，當事后的調查分析提供出寶貴的信息時，最好首先通過正確地選定軸承來完全避免失效的發(fā)生。為了做到這一點，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是非常重要的。Equally critical is a study of requirements for noise, torque, 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.外文資料翻譯對軸承的噪聲、扭矩、偏差、可暴露于污物和有害液體的程度以及溫度極限的要求進行研究同樣是至關重要的。研究上述要求可以為確定軸承是否用于某種工作提供進一步的線索。1 Why bearings fail1 軸承失效的原因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 handling 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．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)境和污染所產生的軸承失效是可以預防的，而且通過簡單的肉眼觀察是可以確定產生這類失效的原因。Conducting 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.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。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 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 across the races．Raceway dents also produce noise，vibration，and increased torque.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生剝蝕。軸承圈上的壓坑還會產生噪聲、振動和附加扭矩。A similar defect is a pattern of elliptical dents caused by balls vibrating between raceways while the bearing is not turning．This problem is called 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, false binelling is often indicated by a reddish color from fretting corrosion in the lubricant.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生的橢圓形壓痕。這種外文資料翻譯破壞稱為低荷振蝕。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生。此外，低荷振蝕產生的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生淡紅色。False brinelling is prevented by eliminating vibration sources and keeping the bearing well lubricated. 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 prevent false brinelling during transit.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生的低荷振蝕也有幫助。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 colored．Friction also causes stress in the retainer，which can break and hasten bearing failure．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。Premature material 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．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，就應仔細計算軸承壽命，以制定一個維護計劃。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 excessive loading，a higher capacity bearing or different configuration may be used．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。Creep is less common than premature fatigue．In bearings．it is caused by excessive 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．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。0ther more likely creep indicators are scratches，scuff marks，or discoloration to shaft and 外文資料翻譯bore．To prevent creep damage，the bearing housing and shaft fittings should be visually checked．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。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 squareness of the bearing mounting site．Misalignment of more than 1/4·can cause an early failure．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。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。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，in contrast ，allow lubricants to more easily reach all surfaces． 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。Rust is a form of moisture contamination and often indicates the wrong material for the application． If the material checks out for the job，the easiest way to prevent rust is to keep bearings in their packaging，until just before installation．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 Avoiding failures2 避免失效的方法The best way to handle bearing failures is to avoid 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 applications, these items are so critical that specifying an ABEC level alone is not sufficient．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。外文資料翻譯Torque requirements are determined by the lubricant，retainer，raceway quality(roundness cross curvature and 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 have varying noise characteristics that should be matched to the application. For example，greases produce more noise than oil．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。Nonrepetitive runout(NRR)occurs during rotation as a random eccentricity 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.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 是沒有辦法進行補償?shù)摹RR 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 minimal 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 machine-tool applications．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。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 possible because of the movement between inner and outer races．Consequently，lubrication migration and contamination are always problems．在許多工業(yè)產品中，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。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 外文資料翻譯metal surfaces．Fending off dirt with seals and shields illustrates some methods for controlling contamination．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。采用密封和遮護裝置來擋開臟物是控制污染的一種方法。Noise is as an indicator of bearing quality．Various noise grades have been developed to classify bearing performance capabilities．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。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.噪聲的分析是用安德遜計進行的，該儀器在軸承生產中可用來控制質量，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。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.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，灰塵產生的是不規(guī)則的劈啪聲；滾珠劃痕產生一種連續(xù)的爆破聲，確定這種劃痕最困難；內圈損傷通常產生連續(xù)的高頻噪聲，而外圈損傷則產生一種間歇的聲音。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.軸承缺陷可以通過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。Low-band noise is the effect of long-wavelength irregularities that occur about 1.6 to 10 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.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) 1.6~10 次，它們是由各種干涉（例如 軸承圈滾道上的凹坑）引起的?？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。Medium-hand noise is characterized by irregularities that occur 10 to 60 times per revolution. 外文資料翻譯It is caused by vibration in the grinding operation that produces balls and raceways. High-hand irregularities occur at 60 to 300 times per revolution and indicate closely spaced chatter marks or widely spaced, rough irregularities.中頻噪聲的特征是軸承每旋轉一周不規(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)的振動引起的。軸承每旋轉一周高頻不規(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。Classifying bearings by their noise characteristics allows users to specify 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 tightened. ABEC class, however, does not specify other bearing characteristics such as raceway quality, finish, or noise. Hence, a noise classification helps improve on the industry standard.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。外文翻譯資料8