Pinion tip radius and pinion tip relief
Despite geometrically correct profiles and theoretically adequate gears, meshing problems may still occur in highly stressed gears, e.g. "scuffing" or "chipping" at the dedendum flank of the wheel, as shown:
This phenomenon occurs primarily in gears with hardened pinions where the tip edges of the pinion act as scrapers.
Various causes may be responsible.
Bending
Dynamic load peaks under high force applications, accelerations, braking actions or vibrations will cause elastic deformations in the meshing teeth.
Pitch errors
Manufacturing tolerances in gears cannot be prevented, especially pitch errors, which in combination with the bending effect can produce negative influences.
Drive unit
Most slewing drive units are mounted in an overhung arrangement, and deflections of the pinion shaft are unavoidable. The high forces will simultaneously produce elastic deformations at the interface of the slewing drive and mounting structure. Such deformations may also lead to meshing problems.
Lubrication
The three influential factors mentioned will result in high peak loads acting on the tip edge of the pinion, which can cause the lubricant film to break.
The direct metallic contact will increase the chipping effect.
Occasional damage which has occurred in the past, can now be prevented by providing a tip relief at the pinion and a radius at the tip edge of the pinion.
Tip relief has become a means of reducing the effects of vibration (noises) in high-speed gear mechanisms.
Investigations have led us to specify pinions with a tip edge radius of 0.1 – 0.15 times module for applications with extreme load conditions.
The radius must blend into the addendum flank without forming an edge.