Calculated Scuffing Risk: Correlating AGMA 925-A03, AGMA 6011-J14 and Original MAAG Gear Predictions

John Amendola, John Amendola III, and Robert Errichello

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

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