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1、0 / 11 毕业论文 设计）外 文 翻 译题目：如何延长轴承寿命系部名称：专业班级：学生姓名：学号：指导教师：教师职称：如何延长轴承寿命摘要：自然界苛刻的工作条件会导致轴承的失效，但是如果遵循一些简单的规则，轴承正常运转的机会是能够被提高的。在轴承的使用过程当中，过分的忽视会导致轴承的过热现象，也可能使轴承不能够再被使用，甚至完全的破坏。但是一个被损精选学习资料 - - - - - - - - - 名师归纳总结 - - - - - - -第 1 页，共 11 页1 / 11 坏的轴承，会留下它为什么被损坏的线索。通过一些细致的侦察工作，我们可以采取行动来避免轴承的再次失效。关键词：轴承 失效
2、 寿命导致轴承失效的原因很多，但常见的是不正确的使用、污染、润滑剂使用不当、装卸或搬运时的损伤及安装误差等。诊断失效的原因并不困难，因为根据轴承上留下的痕迹可以确定轴承失效的原因。然而，当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。1 轴承失效的原因在球轴承的失效中约有40% 是由灰尘、脏物、碎屑的污染以及腐蚀造成的。污染通常是由不正确的使用和不良的使用环境造成的，它还会引起扭矩和噪声的问题。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
3、效的原因。通过失效后的分析可以得知对已经失效的或将要失效的轴承应该在哪些方面进行查看。弄清诸如剥蚀和疲劳破坏一类失效的机理，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
4、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。消除振动源并保持良好的轴承润滑可以防止低荷振蚀。给设备加隔离垫或对底座进行隔离可以减轻环境的振动。另外在轴承上加一个较小的预载荷不仅有助于滚珠和轴承圈保持紧密的接触，并且对防止在设备运输中产生的低荷振蚀也有帮助。造成轴承卡住的原因是缺少内隙、润滑不当和载荷过大。在卡住之前，过大的摩擦和热量使轴承钢软化。过热的轴承通常会改变颜色，一般会变成蓝黑色或淡黄色。精选学习资料 - - - - - - - - - 名师归纳总结 - - - - - - -第 2 页，共 11 页2 / 11 摩擦还会使保持架受力，这会破坏支承架，
5、并加速轴承的失效。材料过早出现疲劳破坏是由重载后过大的预载引起的。如果这些条件不可避免，就应仔细计算轴承寿命，以制定一个维护计划。另一个解决办法是更换材料。若标准的轴承材料不能保证足够的轴承寿命，就应当采用特殊的材料。另外，如果这个问题是由于载荷过大造成的，就应该采用抗载能力更强或其他结构的轴承。蠕动不象过早疲劳那样普遍。轴承的蠕动是由于轴和内圈之间的间隙过大造成的。蠕动的害处很大，它不仅损害轴承，也破坏其他零件。蠕动的明显特征是划痕、擦痕或轴与内圈的颜色变化。为了防止蠕动，应该先用肉眼检查一下轴承箱件和轴的配件。蠕动与安装不正有关。如果轴承圈不正或翘起，滚珠将沿着一个非圆周轨道运动。这个问题
6、是由于安装不正确或公差不正确或轴承安装现场的垂直度不够造成的。如果偏斜超过 0.25 ，轴承就会过早地失效。检查润滑剂的污染比检查装配不正或蠕动要困难得多。污染的特征是使轴承过早的出现磨损。润滑剂中的固体杂质就象磨粒一样。如果滚珠和保持架之间润滑不良也会磨损并削弱保持架。在这种情况下，润滑对于完全加工形式的保持架来说是至关重要的。相比之下，带状或冠状保持架能较容易地使润滑剂到达全部表面。锈是湿气污染的一种形式，它的出现常常表明材料选择不当。如果某一材料经检验适合工作要求，那么防止生锈的最简单的方法是给轴承包装起来，直到安装使用时才打开包装。2 避免失效的方法解决轴承失效问题的最好办法就是避免失
7、效发生。这可以在选用过程中通过考虑关键性能特征来实现。这些特征包括噪声、起动和运转扭矩、刚性、非重复性振摆以及径向和轴向间隙。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。精选学习资料 - - - - - - - - - 名师归纳总结 - - - - - - -第 3 页，共 11 页3 / 11 在轴承转动过程中，如果内圈和外圈之间存
8、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 M 。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
9、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
10、；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。轴承缺陷可以通过其频率特性进一步加以鉴定。通常轴承缺陷被分为低、中、高三个波段。缺陷还可以根据轴承每转动一周出现的不规则变化的次数加以鉴定。低频噪声是长波段不规则变化的结果。轴承每转一周这种不规则变化可出现1.610 次，它们是由各种干涉 例如 轴承圈滚道上的凹坑）引起的。可察觉的凹坑是一种制造缺陷，它是在制造过程中由于多爪卡盘夹的太紧而形成的。中频噪声的特征是轴承每旋转一周不规则变化出现1060次。这种缺陷是由在轴承圈和滚珠的磨削加工中出现的振动引起的。轴承每旋转一周高频不规则
11、变化出现60300次，它表明轴承上存在着密集的振痕或大面积的粗糙不平。利用轴承的噪声特性对轴承进行分类，用户除了可以确定大多数厂商所使用的ABEC 标准外，还可确定轴承的噪声等级。ABEC 标准只定义了诸如孔、外径、振摆等尺寸公精选学习资料 - - - - - - - - - 名师归纳总结 - - - - - - -第 4 页，共 11 页4 / 11 差。随着 ABEC 级别的增加 从3增到9），公差逐渐变小。但 ABEC 等级并不能反映其他轴承特性，如轴承圈质量、粗糙度、噪声等。因此，噪声等级的划分有助于工业标准的改进。 It may also be caused by improper
12、assembly, Which places a load across 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
13、 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. False brinelling is prevent
14、ed 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 preven
15、t false brinelling 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 colored Friction also
16、causes stress in the retainer，which can break and hasten bearing failure 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 outAnother solution for figh
17、ting 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
18、be used Creep is less common than premature fatigue In bearingsit 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精选学习资料 - - - - - - - - - 名师归纳总结 - - - -
19、- - -第 6 页，共 11 页6 / 11 0ther more likely creep indicators are scratches ，scuff marks，or discoloration 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 related If races are misaligned o
20、r cocked The balls track in a noncircumferencial path The problem is incorrect mounting or tolerancing ， or insufficient squareness of the bearing mounting siteMisalignment of more than 1/4can cause an early failure Contaminated lubricant is often more difficult to detect than misalignment or creep
21、Contamination shows as premature wearSolid contaminants become an abrasive in the lubricant In addition。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 con
22、trast，allow lubricants to more easily reach all surfaces Rust is a form of moisture contamination and often 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 A
23、voiding failures The best way to handle bearing failures is to avoid themThis 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 playIn some applications, these
24、 items are so critical that specifying an ABEC level alone is not sufficientTorque 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 inap
25、propriate 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 Nonrepetitive runout(NRRoccurs during rotation as a random eccentricity
26、 between the inner and outer races ，much like a cam actionNRR can be caused by retainer tolerance or 精选学习资料 - - - - - - - - - 名师归纳总结 - - - - - - -第 7 页，共 11 页7 / 11 eccentricities of the raceways and ballsUnlike repetitive runout, no compensation can be made for NRR. NRR is reflected in the cost of
27、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 0.3um is used when minimal runout is needed ，such as in diskdrive spindle motorsSimilarly ，machinetool spindles tolerate only minimal deflecti
28、ons to maintain precision cutsConsequently, 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 dirtHowever，a perfect bearing seal is not possible
29、because of the movement between inner and outer racesConsequently，lubrication migration and contamination are always problems Once a bearing is contaminated, its lubricant deteriorates and operation becomes noisierIf it overheats ，the bearing can seize At the very least，contamination causes wear as
30、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 illustrates some methods for controlling contamination Noise is as an indicator of bearing qualityVarious noise grades have been developed to
31、classify 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 spindl
32、e. 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 example, makes an irregular crackling. Ball scratches make a consistent popping and are the most difficult to identify. Inner-race damag
33、e 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 irregu
34、larities per revolution. Low-band noise is the effect of long-wavelength irregularities that occur about 1.6 to 10 精选学习资料 - - - - - - - - - 名师归纳总结 - - - - - - -第 8 页，共 11 页8 / 11 times per revolution. These are caused by a variety of inconsistencies, such as pockets in the race. Detectable pockets a
35、re manufacturing flaws and result when the race is mounted too tightly in multiplejaw chucks. 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 irregularities
36、occur at 60 to 300 times per revolution and indicate closely spaced chatter marks or widely spaced, rough irregularities. 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 tole
37、rances 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.精选学习资料 - - - - - - - - - 名师归纳总结 - - - - - - -第 9 页，共 11 页0 / 11 教师评语教师签名：2018 年 03 月 12日精选学习资料 - - - - - - - - - 名师归纳总结 - - - - - - -第 10 页，共 11 页1 / 11 精选学习资料 - - - - - - - - - 名师归纳总结 - - - - - - -第 11 页，共 11 页