延长轴承寿命
摘： 然界苛刻工作条件会导致轴承失效果遵循简单规轴承正常运转机会够提高轴承程中分忽视会导致轴承热现象轴承够甚完全破坏损坏轴承会留什损坏线索通细致侦察工作采取行动避免轴承次失效
关键词： 轴承 失效 寿命
导致轴承失效原常见正确污染润滑剂装卸搬运时损伤安装误差等诊断失效原困难根轴承留痕迹确定轴承失效原
然事调查分析提供出宝贵信息时首先通正确选定轴承完全避免失效发生做点考察制造厂商尺寸定位指南选轴承特点非常重
1 轴承失效原
球轴承失效中约40灰尘脏物碎屑污染腐蚀造成污染通常正确良环境造成会引起扭矩噪声问题环境污染产生轴承失效预防通简单肉眼观察确定产生类失效原
通失效分析知已失效失效轴承应该方面进行查弄清诸剥蚀疲劳破坏类失效机理助消问题根源
安装合理轴承剥蚀容易避免剥蚀特征轴承圈滚道留击载荷正确安装产生压痕剥蚀通常载荷超材料屈服极限时发生果安装正确某载荷横穿轴承圈会产生剥蚀轴承圈压坑会产生噪声振动附加扭矩
类似种缺陷轴承旋转时滚珠轴承圈间振动产生椭圆形压痕种破坏称低荷振蚀种破坏运输中设备工作时振动设备中会产生外低荷振蚀产生碎屑作象磨粒样会进步损害轴承剥蚀低荷振蚀特征通常微振磨损腐蚀润滑剂中会产生淡红色
消振动源保持良轴承润滑防止低荷振蚀设备加隔离垫底座进行隔离减轻环境振动外轴承加较预载荷仅助滚珠轴承圈保持紧密接触防止设备运输中产生低荷振蚀帮助
造成轴承卡住原缺少隙润滑载荷卡住前摩擦热量轴承钢软化热轴承通常会改变颜色般会变成蓝黑色淡黄色摩擦会保持架受力会破坏支承架加速轴承失效
材料早出现疲劳破坏重载预载引起果条件避免应仔细计算轴承寿命制定维护计划
解决办法更换材料标准轴承材料保证足够轴承寿命应采特殊材料外果问题载荷造成应该采抗载力更强结构轴承
蠕动象早疲劳样普遍轴承蠕动轴圈间间隙造成蠕动害处仅损害轴承破坏零件
蠕动明显特征划痕擦痕轴圈颜色变化防止蠕动应该先肉眼检查轴承箱件轴配件
蠕动安装正关果轴承圈正翘起滚珠着非圆周轨道运动问题安装正确公差正确轴承安装现场垂直度够造成果偏斜超025°轴承会早失效
检查润滑剂污染检查装配正蠕动困难污染特征轴承早出现磨损润滑剂中固体杂质象磨粒样果滚珠保持架间润滑良会磨损削弱保持架种情况润滑完全加工形式保持架说关重相带状冠状保持架较容易润滑剂达全部表面
锈湿气污染种形式出现常常表明材料选择果某材料检验适合工作求防止生锈简单方法轴承包装起直安装时开包装
2 避免失效方法
解决轴承失效问题办法避免失效发生选程中通考虑关键性特征实现特征包括噪声起动运转扭矩刚性非重复性振摆径轴间隙
扭矩求润滑剂保持架轴承圈质量（弯曲部分圆度表面加工质量）否密封遮护装置决定润滑剂粘度必须认真加选择适宜润滑剂会产生扭矩型轴承中尤外润滑剂噪声特性样举例说润滑脂产生噪声润滑油根途选润滑剂
轴承转动程中果圈外圈间存机偏心距会产生凸轮运动非常相似非重复性振摆（NRR）保持架尺寸误差轴承圈滚珠偏心会引起NRR重复性振摆NRR没办法进行补偿
工业中般根具体应选择类型精度等级轴承例求振摆时轴承非重复性振摆超03微米样机床轴容许振摆保证切削精度机床应中应该非重复性振摆较轴承
许工业产品中污染避免常密封遮护装置保护轴承免受灰尘脏物侵蚀轴承外圈运动轴承密封达完美程度润滑油泄漏污染始终未解决问题
旦轴承受污染润滑剂变质运行噪声变果轴承热会卡住污染物处滚珠轴承圈间时作金属表面间磨粒样会轴承磨损采密封遮护装置挡开脏物控制污染种方法
噪声反映轴承质量指标轴承性噪声等级表示
噪声分析安德逊计进行该仪器轴承生产中控制质量失效轴承进行分析传感器连接轴承外圈圈心轴1800rmin转速旋转测量噪声单位anderonumrad表示轴承位移
根验观察者根声音辨出微缺陷例灰尘产生规劈啪声滚珠划痕产生种连续爆破声确定种划痕困难圈损伤通常产生连续高频噪声外圈损伤产生种间歇声音
轴承缺陷通频率特性进步加鉴定通常轴承缺陷分低中高三波段缺陷根轴承转动周出现规变化次数加鉴定
低频噪声长波段规变化结果轴承转周种规变化出现16~10次种干涉（例 轴承圈滚道凹坑）引起察觉凹坑种制造缺陷制造程中爪卡盘夹太紧形成
中频噪声特征轴承旋转周规变化出现10~60次种缺陷轴承圈滚珠磨削加工中出现振动引起轴承旋转周高频规变化出现60~300次表明轴承存着密集振痕面积粗糙
利轴承噪声特性轴承进行分类户确定数厂商ABEC标准外确定轴承噪声等级ABEC标准定义诸孔外径振摆等尺寸公差着ABEC级增加（3增9）公差逐渐变ABEC等级反映轴承特性轴承圈质量粗糙度噪声等噪声等级划分助工业标准改进
毕业设计（文）外文翻译原文
EXTENDING BEARING LIFE
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
Keywords bearings failures life
Bearings fail for a number of reasonsbut the most common are misapplicationcontaminationimproper lubricantshipping or handling damageand misalignment The problem is often not difficult to diagnose because a failed bearing usually leaves telltale signs about what went wrong．
Howeverwhile a postmortem yields good informationit is better to avoid the process altogether by specifying the bearing correctly in The first place．To do thisit is useful to review the manufacturers sizing guidelines and operating characteristics for the selected bearing
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
1 Why bearings fail
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 preventableand a simple visual examination can easily identify the cause．
Conducting a postmortem il1ustrates what to look for on a failed or failing bearing．Thenunderstanding 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 characterized by indentations in the bearing raceway caused by shock loading－such as when a bearing is droppedor incorrect assembly Brinelling usually occurs when loads exceed the material yield point(350000 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 noisevibrationand increased torque
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
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
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 colorusually to blueblack or straw colored．Friction also causes stress in the retainerwhich can break and hasten bearing failure．
Premature material fatigue is caused by a high load or excessive preload．When these conditions are unavoidablebearing life should be carefully calculated so that a maintenance scheme can be worked out．
Another solution for fighting premature fatigue is changing material．When standard bearing materialssuch as 440C or SAE 52100do not guarantee sufficient lifespecialty materials can be recommended In additionwhen the problem is traced back to excessive loadinga higher capacity bearing or different configuration may be used．
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．
0ther more likely creep indicators are scratchesscuff marksor discoloration to shaft and bore．To prevent creep damagethe bearing housing and shaft fittings should be visually checked．
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 tolerancingor insufficient squareness of the bearing mounting site．Misalignment of more than 14·can cause an early failure．
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 additioninsufficient lubrication between ball and retainer wears and weakens the retainer．In this situationlubrication is critical if the retainer is a fully machined type．Ribbon or crown retainersin contrastallow lubricants to more easily reach all surfaces．
Rust is a form of moisture contamination and often indicates the wrong material for the application．If the material checks out for the jobthe easiest way to prevent rust is to keep bearings in their packaginguntil just before installation．
2 Avoiding failures
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 noisestarting and running torquestiffnessnonrepetitive runoutand radial and axial play．In some applications these items are so critical that specifying an ABEC level alone is not sufficient．
Torque requirements are determined by the lubricantretainerraceway quality(roundness cross curvature and surface finish)and whether seals or shields are used．Lubricant viscosity must be selected carefully because inappropriate lubricantespecially in miniature bearingscauses excessive torque．Alsodifferent lubricants have varying noise characteristics that should be matched to the application For examplegreases produce more noise than oil．
Nonrepetitive runout(NRR)occurs during rotation as a random eccentricity between the inner and outer racesmuch 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
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 examplea bearing with an NRR of less than 03um is used when minimal runout is neededsuch as in disk—drive spindle motors．Similarlymachine—tool spindles tolerate only minimal deflections to maintain precision cuts．Consequently bearings are manufactured with low NRR just for machinetool applications．
Contamination is unavoidable in many industrial productsand shields and seals are commonly used to protect bearings from dust and dirt．Howevera perfect bearing seal is not possible because of the movement between inner and outer races．Consequentlylubrication migration and contamination are always problems．
Once a bearing is contaminated its lubricant deteriorates and operation becomes noisier．If it overheatsthe bearing can seize．At the very leastcontamination causes wear as it works between balls and the racewaybecoming imbedded in the races and acting as an abrasive between metal surfaces．Fending off dirt with seals and shields illustrates some methods for controlling contamination．
Noise is as an indicator of bearing quality．Various noise grades have been developed to 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 1800rpm on an air spindle Noise is measured in andirons which represent ball displacement in μmrad
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 Innerrace damage is normally a constant highpitched 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 irregularities per revolution
Lowband noise is the effect of longwavelength irregularities that occur about 16 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
Mediumhand 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 Highhand irregularities 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 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
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摘： 然界苛刻工作条件会导致轴承失效果遵循简单规轴承正常运转机会够提高轴承程中分忽视会导致轴承热现象轴承够甚完全破坏损坏轴承会留什损坏线索通细致侦察工作采取行动避免轴承次失效
关键词： 轴承 失效 寿命
导致轴承失效原常见正确污染润滑剂装卸搬运时损伤安装误差等诊断失效原困难根轴承留痕迹确定轴承失效原
然事调查分析提供出宝贵信息时首先通正确选定轴承完全避免失效发生做点考察制造厂商尺寸定位指南选轴承特点非常重
1 轴承失效原
球轴承失效中约40灰尘脏物碎屑污染腐蚀造成污染通常正确良环境造成会引起扭矩噪声问题环境污染产生轴承失效预防通简单肉眼观察确定产生类失效原
通失效分析知已失效失效轴承应该方面进行查弄清诸剥蚀疲劳破坏类失效机理助消问题根源
安装合理轴承剥蚀容易避免剥蚀特征轴承圈滚道留击载荷正确安装产生压痕剥蚀通常载荷超材料屈服极限时发生果安装正确某载荷横穿轴承圈会产生剥蚀轴承圈压坑会产生噪声振动附加扭矩
类似种缺陷轴承旋转时滚珠轴承圈间振动产生椭圆形压痕种破坏称低荷振蚀种破坏运输中设备工作时振动设备中会产生外低荷振蚀产生碎屑作象磨粒样会进步损害轴承剥蚀低荷振蚀特征通常微振磨损腐蚀润滑剂中会产生淡红色
消振动源保持良轴承润滑防止低荷振蚀设备加隔离垫底座进行隔离减轻环境振动外轴承加较预载荷仅助滚珠轴承圈保持紧密接触防止设备运输中产生低荷振蚀帮助
造成轴承卡住原缺少隙润滑载荷卡住前摩擦热量轴承钢软化热轴承通常会改变颜色般会变成蓝黑色淡黄色摩擦会保持架受力会破坏支承架加速轴承失效
材料早出现疲劳破坏重载预载引起果条件避免应仔细计算轴承寿命制定维护计划
解决办法更换材料标准轴承材料保证足够轴承寿命应采特殊材料外果问题载荷造成应该采抗载力更强结构轴承
蠕动象早疲劳样普遍轴承蠕动轴圈间间隙造成蠕动害处仅损害轴承破坏零件
蠕动明显特征划痕擦痕轴圈颜色变化防止蠕动应该先肉眼检查轴承箱件轴配件
蠕动安装正关果轴承圈正翘起滚珠着非圆周轨道运动问题安装正确公差正确轴承安装现场垂直度够造成果偏斜超025°轴承会早失效
检查润滑剂污染检查装配正蠕动困难污染特征轴承早出现磨损润滑剂中固体杂质象磨粒样果滚珠保持架间润滑良会磨损削弱保持架种情况润滑完全加工形式保持架说关重相带状冠状保持架较容易润滑剂达全部表面
锈湿气污染种形式出现常常表明材料选择果某材料检验适合工作求防止生锈简单方法轴承包装起直安装时开包装
2 避免失效方法
解决轴承失效问题办法避免失效发生选程中通考虑关键性特征实现特征包括噪声起动运转扭矩刚性非重复性振摆径轴间隙
扭矩求润滑剂保持架轴承圈质量（弯曲部分圆度表面加工质量）否密封遮护装置决定润滑剂粘度必须认真加选择适宜润滑剂会产生扭矩型轴承中尤外润滑剂噪声特性样举例说润滑脂产生噪声润滑油根途选润滑剂
轴承转动程中果圈外圈间存机偏心距会产生凸轮运动非常相似非重复性振摆（NRR）保持架尺寸误差轴承圈滚珠偏心会引起NRR重复性振摆NRR没办法进行补偿
工业中般根具体应选择类型精度等级轴承例求振摆时轴承非重复性振摆超03微米样机床轴容许振摆保证切削精度机床应中应该非重复性振摆较轴承
许工业产品中污染避免常密封遮护装置保护轴承免受灰尘脏物侵蚀轴承外圈运动轴承密封达完美程度润滑油泄漏污染始终未解决问题
旦轴承受污染润滑剂变质运行噪声变果轴承热会卡住污染物处滚珠轴承圈间时作金属表面间磨粒样会轴承磨损采密封遮护装置挡开脏物控制污染种方法
噪声反映轴承质量指标轴承性噪声等级表示
噪声分析安德逊计进行该仪器轴承生产中控制质量失效轴承进行分析传感器连接轴承外圈圈心轴1800rmin转速旋转测量噪声单位anderonumrad表示轴承位移
根验观察者根声音辨出微缺陷例灰尘产生规劈啪声滚珠划痕产生种连续爆破声确定种划痕困难圈损伤通常产生连续高频噪声外圈损伤产生种间歇声音
轴承缺陷通频率特性进步加鉴定通常轴承缺陷分低中高三波段缺陷根轴承转动周出现规变化次数加鉴定
低频噪声长波段规变化结果轴承转周种规变化出现16~10次种干涉（例 轴承圈滚道凹坑）引起察觉凹坑种制造缺陷制造程中爪卡盘夹太紧形成
中频噪声特征轴承旋转周规变化出现10~60次种缺陷轴承圈滚珠磨削加工中出现振动引起轴承旋转周高频规变化出现60~300次表明轴承存着密集振痕面积粗糙
利轴承噪声特性轴承进行分类户确定数厂商ABEC标准外确定轴承噪声等级ABEC标准定义诸孔外径振摆等尺寸公差着ABEC级增加（3增9）公差逐渐变ABEC等级反映轴承特性轴承圈质量粗糙度噪声等噪声等级划分助工业标准改进
毕业设计（文）外文翻译原文
EXTENDING BEARING LIFE
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
Keywords bearings failures life
Bearings fail for a number of reasonsbut the most common are misapplicationcontaminationimproper lubricantshipping or handling damageand misalignment The problem is often not difficult to diagnose because a failed bearing usually leaves telltale signs about what went wrong．
Howeverwhile a postmortem yields good informationit is better to avoid the process altogether by specifying the bearing correctly in The first place．To do thisit is useful to review the manufacturers sizing guidelines and operating characteristics for the selected bearing
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
1 Why bearings fail
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 preventableand a simple visual examination can easily identify the cause．
Conducting a postmortem il1ustrates what to look for on a failed or failing bearing．Thenunderstanding 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 characterized by indentations in the bearing raceway caused by shock loading－such as when a bearing is droppedor incorrect assembly Brinelling usually occurs when loads exceed the material yield point(350000 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 noisevibrationand increased torque
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
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
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 colorusually to blueblack or straw colored．Friction also causes stress in the retainerwhich can break and hasten bearing failure．
Premature material fatigue is caused by a high load or excessive preload．When these conditions are unavoidablebearing life should be carefully calculated so that a maintenance scheme can be worked out．
Another solution for fighting premature fatigue is changing material．When standard bearing materialssuch as 440C or SAE 52100do not guarantee sufficient lifespecialty materials can be recommended In additionwhen the problem is traced back to excessive loadinga higher capacity bearing or different configuration may be used．
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．
0ther more likely creep indicators are scratchesscuff marksor discoloration to shaft and bore．To prevent creep damagethe bearing housing and shaft fittings should be visually checked．
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 tolerancingor insufficient squareness of the bearing mounting site．Misalignment of more than 14·can cause an early failure．
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 additioninsufficient lubrication between ball and retainer wears and weakens the retainer．In this situationlubrication is critical if the retainer is a fully machined type．Ribbon or crown retainersin contrastallow lubricants to more easily reach all surfaces．
Rust is a form of moisture contamination and often indicates the wrong material for the application．If the material checks out for the jobthe easiest way to prevent rust is to keep bearings in their packaginguntil just before installation．
2 Avoiding failures
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 noisestarting and running torquestiffnessnonrepetitive runoutand radial and axial play．In some applications these items are so critical that specifying an ABEC level alone is not sufficient．
Torque requirements are determined by the lubricantretainerraceway quality(roundness cross curvature and surface finish)and whether seals or shields are used．Lubricant viscosity must be selected carefully because inappropriate lubricantespecially in miniature bearingscauses excessive torque．Alsodifferent lubricants have varying noise characteristics that should be matched to the application For examplegreases produce more noise than oil．
Nonrepetitive runout(NRR)occurs during rotation as a random eccentricity between the inner and outer racesmuch 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
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 examplea bearing with an NRR of less than 03um is used when minimal runout is neededsuch as in disk—drive spindle motors．Similarlymachine—tool spindles tolerate only minimal deflections to maintain precision cuts．Consequently bearings are manufactured with low NRR just for machinetool applications．
Contamination is unavoidable in many industrial productsand shields and seals are commonly used to protect bearings from dust and dirt．Howevera perfect bearing seal is not possible because of the movement between inner and outer races．Consequentlylubrication migration and contamination are always problems．
Once a bearing is contaminated its lubricant deteriorates and operation becomes noisier．If it overheatsthe bearing can seize．At the very leastcontamination causes wear as it works between balls and the racewaybecoming imbedded in the races and acting as an abrasive between metal surfaces．Fending off dirt with seals and shields illustrates some methods for controlling contamination．
Noise is as an indicator of bearing quality．Various noise grades have been developed to 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 1800rpm on an air spindle Noise is measured in andirons which represent ball displacement in μmrad
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 Innerrace damage is normally a constant highpitched 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 irregularities per revolution
Lowband noise is the effect of longwavelength irregularities that occur about 16 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
Mediumhand 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 Highhand irregularities 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 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
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