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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.
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.
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.
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 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.
机械设计基础
1、车床
车床主要是用来车削外圆、车削端面和钻孔的机械工具。车削很少用其他形式的机械工具,而且没有一个同等的机械设备能像车床那样完成车削加工。因为车床还可以完成钻孔和铰孔，车床的多功能性允许工件的一次安装能完成多次加工。因此，在制造业中各种机床的使用比其他机械工具都多。
车床的基本部件有床身、主轴箱总成、尾座总成、溜板组件、丝杠和光杠。
床身是车床的主干。床身通常是由充分正火或者时效处理的灰铸铁或球墨铁制成。车床是刚性构架，所以其他基础部件都安装在上面。通常在车床床身上有内外两个平行、纵向的导轨一些制造厂采用四个导轨都是三角形导轨，而有的制造厂则在一组或两组中采用一个三角形导轨和一个矩形导轨。导轨要经过精密加工来保证对齐精度。大多数现代机床的导轨都是采用表面硬化来抗磨损和擦伤，但是在操作机床时为确保导轨不被磨损应采取预防措施。导轨上的任何错误都以为着整个机床的精度被破坏。源'自^751;文,论`文'网]www.751com.cn
主轴箱安装在内侧轨道的一个固定位置，通常在左侧的床尾。它提供一个动力使工件以不同的速度旋转。它基本上由一个安装在精密轴承上的空心主轴和一系列类似卡车变速器的变速齿轮——通过这些变速齿轮，主轴可以以许多不同的速度旋转。大多数车床有8~12种转速，通常以几何比例排列，而且在现代车床上只要扳动2~4个手柄就可获得所有的速度。一个正在不停增长的趋势是通过电气或机械设备驱动来提供一个持续不断的变速范围。