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CHAPTER FIVE:
Accurate Diagnosis of Antifriction Bearings
章节5
滚动轴承的精确诊断
INTRODUCTION 简介
This chapter describes procedures for identifying defects in antifriction bearings by analyzing frequencies generated by the moving parts. Defects on bearing raceways, rolling elements, and the cage generate different frequencies. The spectrum shape, amplitude, frequency, sum and difference frequencies, and the time domain signal are useful in identifying the nature, location, combination, and size of defects.
本章节描述了如何通过分析运动部件产生的频率来识别滚动轴承的缺陷。轴承滚道，滚动元
件和保持架上的缺陷会产生不同的频率。频谱形状，振幅，频率，和差频率，以及时域信号都有助于辨认缺陷的性质，位置，组合和大小。
Methods are presented to calculate the bearing frequencies; identify if the bearing is in a thrust or radial load; calculate the length of inner race defects with the time domain signal; and measure the length of a defect on the outer race in the frequency domain spectra. The nature of the defect, such as shallow flaking, deep fatigue spalls, corrosion, acid etching, fluting, and inadequate lubrication can be determined by analyzing the frequency and time domain data. These techniques can also identify bearings with excessive clearance and bearings that are not properly installed, such as those turning on the shaft or loose in the housing. Techniques used to predict the life span of a defective bearing are discussed.
提出计算轴承频率的方法；确定轴承是否承受轴向或径向负荷；通过时域信号计算内圈缺陷长度；通过频域谱估算外圈上某个缺陷的长度。缺陷的性质，如浅层剥落，深层疲劳碎裂，腐蚀，酸蚀，电蚀和润滑不足等都可以通过分析频域和时域数据确定。这些技术也可
以用于识别轴承游隙过量以及轴承安装不当，例如跑内圈或跑外圈。对预测有缺陷轴承寿命的技术进行了讨论。
DATA COLLECTION 数据采集
Data collection is the most important step in evaluation of bearing condition. Data should be collected by placing the transducer in the bearing load zone with due respect to flexibility. If this is not done, the best signal definition may not be obtained. For example, with a radial bearing in a radial load, the best signal is obtained in the radial position. For an angular contact bearing or a radial bearing in a thrust load, the best signal definition is obtained in the axial direction. The machine internal geometry, as well as which problems generate radial or thrust loads, must be determined in order to properly place the transducer. Data should be taken where the transfer function is best; for example, put the transducer on a bolt head, not the cover. For pillow-block, tending side dryer, and similar bearings, the transducer should be placed near the top of the bearing. For bearings in gear housings, the transducer should be placed on a bolt head in the load zone.
数据采集是评估轴承状况最重要的一步。采集数据时应该把传感器布置在轴承的承载区同时兼并灵活性。不这样做就无法获得最好的清晰信号。举例，在一个承受径向载荷的径向轴承，径向承载区可以采集到最好的信号。对于角接触轴承和径向轴承承受轴向载荷时，最佳的信号的采集位置是在轴向。为了合理安装传感器，必须确认设备内部构造，以及哪些故障会产生径向或轴向载荷。数据应当在信号传递路径最好的位置采集；例如，把传感器放在螺栓头上，而不是轴承座端盖上。针对枕式轴承,操作侧吹风机，和类似的轴承，传感器应当被放在接近轴承顶部的位置。齿轮箱里的轴承，传感器应该放在承载区的螺栓头部上。
TRANSDUCER SELECTION 传感器的选择
Success or failure in diagnosing bearing defects often depends on the selection of the proper transducer. The discussions of transducer selection in other chapters apply. However, a few words should be added here. Spherical roller bearings rotating at 1200 RPM can generate harmonics of BPFO in the 3,000 Hz range when fluting occurs. An accelerometer must be used in such cases.
诊断轴承缺陷成功或失败通常取决于是否选择了适当的传感器。关于传感器的选择其他章节已经讨论过。但是，这里需要做一些简单说明。转速1200RPM的球面滚子轴承，当出现电蚀的时候能在3000HZ范围内产生外圈缺陷频率的谐波。其他类似情况必须使用加速度传感器
Low speed machines rotating as low as 2 or 3 RPM, other machines when bearing frequencies are below 10 Hz, and lightweight shafts installed in heavy housings all require either contacting or non-contacting displacement transducers for accurate diagnostics.
低速设备的转速可能只有2或3RPM，其他设备如当轴承频率低于10HZ时以及重量轻的轴安装在较重的轴承座中时都需要接触式或非接触位移传感器才可以准确诊断
The velocity transducer is still the best choice for frequencies between 10 and 2,000 Hz.
针对频率处在10-2000Hz内的设备，速度传感器依然是最好的选择。
GENERATED FREQUENCIES 产生的频率
In order to understand the relationships between the different rotating elements of a bearing, the equations describing the relative speeds must first be developed. These equations define the frequencies generated by antifriction bearings. angular安装A machine with a defective bearing can generate at least five frequencies. These frequencies are:
为了理解一个轴承不同旋转部件之间的关系，必须先建立一个描述其相对速度关系的公式。这些公式定义滚动轴承产生的频率。这些频率分别为：
1. Rotating unit frequency or speed (S)
2. Fundamental train frequency (FTF)
3. Ball pass frequency of the outer race (BPFO)
4. Ball pass frequency of the inner race (BPFI)
5. Two times ball spin frequency (2 X BSF)
1 旋转部件的频率或速度(S)
2 轴承保持架故障频率 (FTF)
3 外圈通过频率(BPFO)
4 内圈通过频率(BPFI)
5 2倍的滚珠滚动频率 (2 X BSF)
Figs. 5-1 and 5-2 show the axial and cross-sectional views of the geometry for a ball bearing, where vo, vc and vi are the linear velocities of the outer race, ball center, and inner race, respectively. Bd is the ball diameter, Pd is the pitch diameter of the bearing and is measured from ball center to ball center, andΦis the contact angle. If a vertical line is drawn through the bearing and another line is drawn where the ball contacts the inner and outer races, the angle between the two lines is the contact angle. See Fig. 5-2.

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