KIT-GEAR 2111331 - Caterpillar

Fretting (Corrosion) Wear
Fretting (corrosion) wear typically results from movement between two surfaces that are pressed tightly together. The type of movement that causes fretting is high frequency, low amplitude, that is, movement resulting from vibration of the parts.Note: Moving surfaces not pressed tightly together tend to polish and become smoother rather than fretting and becoming rougher.Fretting damage occurs when frictional heating causes high points (called asperities) on two surfaces to weld together and then movement rips the surfaces apart. This action roughens the surfaces, pits the surfaces, and produces fine debris particles. When the debris particles produced by the fretting action corrode and are smeared back on the moving surfaces, the damage is referred to as fretting corrosion.Tight contact between two surfaces can result from several things:
Bolted joints
Press fit parts
The weight of one part pressing against anotherFretting wear damage can be identified by the following characteristics:
The wear damage is at a tight contact area between two parts.
The contact surface area between two parts is rough and pitted.
The contact surface area is discolored in or around the rough, pitted area.
Illustration 163 g01203657
(1) The wear damage is at a tight contact area between two parts.When the load on a part exceeds the clamping force between two surfaces (such as this connecting rod and cap joint), movement can produce fretting damage.
Illustration 164 g01203663
(2) The contact surface area between two parts is rough and pitted. (3) The contact surface area is discolored in or around the rough, pitted area.Fretted surfaces are rough because tiny areas have welded and pulled pieces of metal out of the surface. Fretting debris sometimes corrodes and discolors fretted surfaces.
Illustration 165 g01203667
Sometimes fretted surfaces appear roughened by microwelding and metal pull out as on this bolt head surface.
Illustration 166 g01203668
With iron-based materials, fretting often produces a red to reddish brown surface discoloration in the damaged area as on this bolt shank.
Illustration 167 g01203672
Black colored deposits produced by frettingFretting can produce black colored deposits, too. The color of the deposits, if present, depends on the metal that is fretting and the conditions under which the fretting damage occurred. The left side of this figure shows fretting damage with a black deposit on a connecting rod bore. The right side of the figure shows bearing damage resulting from running a bearing over area built up from fretting. Significance of Fretting (Corrosion) Wear
Fretting (corrosion) wear found on parts indicates that two surfaces that were held tightly together have been forced to move, vibrate or oscillate slightly against each other at high frequency. Look for the following things:
What was the load that caused the surfaces to move?
If fretting has occurred at a bolted joint:
Were the joint surfaces clean prior to tightening?
Was the correct hardware used?
Were any of the clamped surfaces excessively rough?
Were the fasteners properly tightened?
Were instructions regarding lubrication followed?
What might have overloaded the joint in service?
Is there any evidence of overheating at the joint?
In multi-fastener joints, were the other fasteners tightened properly?Failure Analysis Training and Consulting Services
The information in this tool has dealt primarily with collecting