Tooth Root Strength
Tooth root strength is the resistance of a gear to fracture caused by bending stress at the tooth root. It is verified per DIN 3990 / ISO 6336 and depends on material, module, profile shift, and surface quality.
Basics of Tooth Root Loading
When two teeth come into mesh, the mesh force acts as a bending load on the tooth root. The most critical point lies at the Lewis 30° tangent (root fillet). The maximum bending stress σ_F results from the tangential force, the module, the form factor (tooth shape), and various correction factors for load distribution, speed, and application. The tooth root strength must exceed the permissible bending stress of the material.
Influencing Factors and Countermeasures
Tooth root strength is increased by: larger module (thicker tooth), positive profile shift (more root material), higher-grade material (case-hardening or nitriding steel instead of mild steel), surface hardening (case hardening, nitriding, induction hardening), and shot peening (compressive residual stresses in the root zone). It is reduced by undercut, too small root fillet radii, incorrect heat treatment, or notch effects from machining marks.
Thank you for your feedback.
Anonymous · without cookies