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Thursday, 10 December 2015

GEAR NOISE AND VIBRATION

We were discussing in our previous posts about Gear terminology, Gear Classification, Gear box inspection procedure and how to inspect gear box, now we will come to see in this post about the various causes of noise in gearbox and the respective remedies in order to reduce the noise during operation of gears.

I have studied one note of KHK stock gears and I have noted and want to share here one very important data about the contributions of various causes of vibration and noise in gears, So let us see the below graph to secure the overview of the contributions of various causes of vibration and noise in gears.


We can see in above graph about the various contributions of various causes of vibration and noise in gears.

Let us see the various causes of noise

  1. Poor tooth contact
  2. Larger tooth profile error
  3. Bad tooth surface finishing
  4. Play between gear and shaft
  5. Larger pitch error
  6. Rotation might be fast
  7. Bearing might be damage and producing noise
  8. Center distance might be too small
  9. Gear tooth might be damage slightly or more
  10. Backlash might be increased
  11. Wear and tear between gear teeth

Let us see the various points that must be considered to avoid the creation of abnormal sound during operation of gearbox

  1. Inspect the runout and avoid runout in gear
  2. Minimize the pitch error
  3. Minimize the tooth profile error
  4. Minimize the backlash within optimum limit to avoid noise level during operation
  5. Implementation of crowning of surface
  6. Remove sharp corners over gear tooth by chamfering
  7. Make smooth the tooth surface by removing the roughness
  8. Enhance the contact ratio as larger contact ratio will reduce the noise level during operation of gearbox.
  9. Before selecting of gearbox or gears, we must be sure about the material of casting of gears as the quality of material of gear will define the quality of gearbox. Gear material must be heat treated to secure the desired mechanical and physical properties.
  10. Bearing must be fixed with optimum tolerances; there must not be any axial or radial movement between inner ring of bearing and bearing sheet of shaft. Before fixing of bearing with shaft we need to check the bearing and bearing must be in healthy condition. However if we are considering that bearing may work properly but we are not sure , in that situation we need to make it in our record and simultaneously we need to inform to our superior to secure the decision whether to use existing bearing or new bearing.
  11. Before fixing of gears or pinions with shaft, we need to make sure about all the dimensions to secure the desired tolerances to avoid any play.
  12. Gearbox casing must be designed to suitable installation of bearings, shaft to avoid any clearance or play.
  13. Cover fasteners hole must be drilled precisely to secure air tight sealing between gearbox covers.
  14. Before covering the gearbox, we must use sealing agent secure air tight sealing between gearbox covers.
  15. During assembly of gears with gearbox, we need to take care closely so that each gear may secure the respective position as if each gear will be fixed to its position then there will be least chances of creation of noise in gearbox during operation.
  16. During operation, we must be sure about the quality of lubrication as poor quality of lubrication will contribute in the creation of noise during operation of gearbox.
  17. Once gearbox will be installed, we need to secure the alignment of shaft within optimum limit to avoid creation of noise during operation of gearbox.

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