Gear FAQ: Bending Strength vs. Surface Durability
Bending strength and surface durability are two factors in gear strength. They describe different types of stress and potential failure modes for gears, but what is the difference?
Bending Strength
Bending strength denotes the strength against breakage at tooth root, when force is produced as a gear transmits power. Put simply, it is the ability of a gear tooth to withstand forces that cause it to bend or fracture at its root.
It is possible to encourage bending strength by:
- Using durable materials
- Enlarging gear size
- Strengthening tooth profile
- Increasing the contact ratio
- Improving accuracy
Surface Durability
Surface durability is the gear’s surface-endurance capabilities against wear on its tooth surface, when mating teeth contact each other repeatedly during meshing. Pitting is a form of surface fatigue where small pits or craters develop on the tooth surface due to repeated contact stresses.
Surface durability can be increased by:
- Using hard material treated by quenching to increase allowable hertz stress
- Enlarging gear size
- Increasing the contact ratio
- Consider lubrication
- Improving accuracy
Overall, bending strength is related to the structural integrity of the gear tooth itself, whilst surface durability refers to the resistance of the tooth surfaces to wear and damage from repeated contact.
Engineers must consider both bending strength and surface durability to ensure that the gear can withstand the required loads in order to operate reliably during its intended lifespan.
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