Introduction
This paper relates specifically to gears that are finish ground and considered high speed per ANSI/AGMA 6011; meshing elements with PLVs (pitch line velocities) in excess of 35 m/s or rotational speeds greater than 4,500 rpm (Ref. 1). Current application standards by AGMA & ISO both provide methods for rating gears for macropitting and bending fatigue. However, neither have a standard to calculate scuffing risk. Both have provided documents; AGMA 925-A03 and ISO/TS 6336-20 (formally ISO/TR 13989-1) as informative suggestions to consider scuffing risk in gear design. Nevertheless, scuffing requires the same consideration as macropitting and bending in rating gears — especially in high-speed applications with high sliding velocities. Scuffing is not a fatigue phenomenon and may occur instantly, often during early stages of operation. This failure is directly related to the lubricant oil film, which does not adequately separate the surfaces. Figure 1 is a classic example of gear tooth scuffing. One or more of the following are typical root causes for scuffing:
- The threshold for scuffing resistance may not have been considered when designing the geometry of the gearset. For example, excessive sliding velocities occurring between the meshing elements.
- The lubricant selected was not in accordance with the original lubricant intended for the application.
- The load distribution along the tooth flanks did not consider mechanical (elastic) deflection and thermal deformation resulting in either non-uniform load or less than full face width loading along the entire flank at full load
- The surface roughness of the gearset was excessive
Read the of the technical document beinning on page 50 of Gear Technology April 2020