Tham khảo tài liệu 'intro predictive maintenance 2e episode 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Failure-Mode Analysis 307 FREQUENCY p s or o FREQUENCY Figure 14-17 Sidebands are paired and equal. Defective Gear Profiles If the gear set develops problems the amplitude of the gear-mesh frequency increases and the symmetry of the sidebands changes. The pattern illustrated in Figure 14-18 is typical of a defective gear set where overall energy is the broadband or total energy. Note the asymmetrical relationship of the sidebands. Excessive Wear. Figure 14-19 is the vibration profile of a worn gear set. Note that the spacing between the sidebands is erratic and is no longer evenly spaced by the input shaft speed frequency. The sidebands for a worn gear set tend to occur between the input and output speeds and are not evenly spaced. Cracked or Broken Teeth. Figure 14-20 illustrates the profile of a gear set with a broken tooth. As the gear rotates the space left by the chipped or broken tooth increases the mechanical clearance between the pinion and bullgear. The result is a low-amplitude sideband to the left of the actual gear-mesh frequency. When the next . undamaged teeth mesh the added clearance results in a higher-energy impact. The sideband to the right of the mesh frequency has much higher amplitude. As a result the paired sidebands have nonsymmetrical amplitude which is caused by the disproportional clearance and impact energy. 308 An Introduction to Predictive Maintenance Moy 1 1997 12 00 01 . OAL .15 IPS-PK 0 5 10 20 0 B0 160 320 6 0 FREQUENCY IN CPM Figure 14-18 Typical defective gear-mesh signature. Figure 14-19 Wear or excessive clearance changes the sideband spacing. Improper Shaft Spacing In addition to gear-tooth wear variations in the center-to-center distance between shafts create erratic spacing and amplitude in a vibration signature. If the shafts are too close together the sideband spacing tends to be at input shaft speed but the amplitude is significantly reduced. This condition causes the gears to be deeply meshed . below the normal .
