Fretting corrosion on tapered roller bearing outer race. Photo courtesy GEARTECH © 2013.
Definition: Fretting is a surface wear phenomenon that is created when two contacting surfaces have oscillating relative motion of small amplitude. A special type of fretting in which chemical reaction predominates in known as fretting corrosion. A milder form of fretting that is confined to the oxide layer is called false brinelling.
Identification: Fretting can be identified by the presence of ruts along the line of contact, along with the presence of reddish brown or black wear debris.
Discussion: Fretting corrosion generates wear particles in the form of oxides such as hematite (red in color) and false brinelling generates magnetitie (black in color). Fretting corrosion is very damaging to gears and bearings. The wear scars created by fretting corrosion act as stress risers. The wear debris is very abrasive, and can result in large amounts of abrasive wear. Generally, false brinelling can be tolerated, as long as it does not escalate into fretting corrosion.
Prevention: Avoid extended parking of rotating equipment. Minimize vibration levels.