Gear tooth failure

Machine Design

Gear Drive

Introduction:

There are different modes of failure of gear teeth and their possible remedies to avoid the failure.

Causes of Gear Tooth Failure

1. Bending failure.

• Every gear tooth acts as a cantilever.
• If the total repetitive dynamic load acting on the gear tooth is greater than the beam strength of the gear tooth, then the gear tooth will fail in bending, i.e. the gear tooth will break.
• In order to avoid such failure, the module and face width of the gear is adjusted so that the beam strength is greater than the dynamic load.

2. Pitting.

• It is the surface fatigue failure which occurs due to many repetition of Hertz contact stresses.
• The failure occurs when the surface contact stresses are higher than the endurance limit of the material.
• The failure starts with the formation of pits which continue to grow resulting in the rupture of the tooth surface. In order to avoid the pitting, the dynamic load between the gear tooth should be less than the wear strength of the gear tooth.

3. Scoring.

• The excessive heat is generated when there is an excessive surface pressure, high speed or supply of lubricant fails. It is a stick-slip phenomenon in which alternate shearing and welding takes place rapidly at high spots.
• This type of failure can be avoided by properly designing the parameters such as speed, pressure and proper flow of the lubricant, so that the temperature at the rubbing faces is within the permissible limits.

4. Abrasive wear.

• The foreign particles in the lubricants such as dirt, dust or burr enter between the tooth and damage the form of tooth.
• This type of failure can be avoided by providing filters for the lubricating oil or by using high viscosity lubricant oil which enables the formation of thicker oil film and hence permits easy passage of such particles without damaging the gear surface.

5. Corrosive wear.

• The corrosion of the tooth surfaces is mainly caused due to the presence of corrosive elements such as additives present in the lubricating oils.
• In order to avoid this type of wear, proper anti-corrosive additives should be used.