Gear Noise Reduction

Gear Noise is a serious impediment to an optimum gear performance. Actually gear noise is the result of some process errors. Research done on the source of gear noise has come to a definitive conclusion that one of the causes of Gear Noise is the presence of plus material on its active profile in one or more teeth. This gives the impression that the gear is not of the desired quality.


Mechanism of Gear Noise ReductionThree primary causes of plus material on gear teeth are nicks, burrs and lastly heat treat scale.

• Nicks
  Nicks are caused by part handling and not because of gear manufacturing machines. Nick can be any plus material found anywhere on a part. The cause of Nick is gouging. This creates plus material which remains on the surface that needs to be hardened into a part. The noise is the result of the Nicks' action with other teeth. A gear teeth that has nicks on their active profiles, causes noise. Transmission manufacturers would know that nicks that are more than 0.002 can be a cause of transmission noise.
  
  
• Burrs
  Burrs are essentially raised material. They are generally found in places where there is meeting of involute profile with the face. Large burrs can be found on the face of gears after hobbing or shaping. These burrs are taken care of by face deburring and chamfering. As the face deburring works only on the face of gear, a natural tendency is the rolling of small burrs back on to the involute profile. Now after the heat treatment is over, this burr becomes hardened and a potential cause for gear noise as soon as it is put to use.
  
  
• Heat Treat Scale
  Heat treat scale is primarily the oxidized material found left after the end of heat treating process. If left as it is on the gear, this scale can be a potential source for noise.
  
  

Factors Influencing Noise Level in Gears
Here are listed a few of the most crucial design factors that has an impact on the noise level of gears:

• Type of gears
• Quality Level
• Profile of Tooth
• Surface Finish
• Pitch
• Gear Runout
• Pressure Angle
• Gear Ratio
• Recess Action
• Resonance
• Modification of Profile
• Lubricant Viscosity
• Overlap Ratio
• Type of Bearings
• Backlash
• Gear Material
• Tooth Loading
• Housing

Reducing Gear Noise
The following table highlights some of the effective trouble shooting techniques for gear noise reduction.

Solutions	Features
Use of High Precision Gears	Minimizes errors of pitch, tooth profile, runout and lead error. Grind teeth for improving the accuracy and the surface finish.
Better Surface Finish on Gears	Methods of lapping, grinding and honing of the tooth surface improves the overall smoothness of tooth surface and can reduce effectively the noise.
Use of Suitable Lubrication	Sufficient lubrication of gears. A high-viscosity lubricant will certainly have an effect in reducing gear noise.
Apply High Rigidity Gears	A face width increase can give a higher rigidity that checks gear noise. Reinforcing of housing and shafts increases rigidity.
Applying Sufficient Backlash	A smaller backlash helps by reducing pulsating transmission.
Proper Tooth Contact	End contact prevented by Crowning and relieving. A proper tooth profile modification also proves effective. Eliminates tooth surface impact.

Improving Gear Performance Through Noise Reduction
Materials do play a vital role in gear noise. Other things being equal a gear set made from material with good damping characteristics will be reasonably quieter than a set made with materials that lack good damping characteristics. It has been seen that graphite flakes found in gray cast iron will result in better damping properties in comparison to other ferrous metal. In case of ductile iron also, the nodules behave in an identical fashion to the graphite flakes of gray iron, giving cushioning vibrations on transmission through a part. The following figure shows the relative damping capacity of few of the metals.