Gear Scuffing Wear

General. The terms scuffing and scoring are frequently interchanged. The following definitions are provided to assist in correctly ascertaining the type of damage observed. The ASM Handbook Vol 18 defines scuffing as localized damage caused by the occurrence of solid-phase welding between sliding surfaces. It defines scoring as the formation of severe scratches in the direction of sliding. The handbook also stipulates that scoring may be caused by local solid-phase welding or abrasion, but suggests that minor scoring be considered as scratching. Gear scuffing is characterized by material transfer between sliding tooth surfaces. Generally this condition occurs when inadequate lubrication film thickness permits metal to- metal contact between gear teeth. Without lubrication, direct metal contact removes the protective oxide layer on the gear metal, and the excessive heat generated by friction welds the surfaces at the contact points. As the gears separate, metal is torn and transferred between the teeth. Scuffing is most likely to occur in new gear sets during the running-in period because the gear teeth have not sufficient operating time to develop smooth surfaces.