COMMON SLEEVE FAILURE MODES

Fatigue Fracture. 

A common failure mode for coated shaft sleeves is Fatigue Fracturing. Fatigue fracturing occurs when a material is put under a repeat load cycle such as rotary movement with a high radial load creating a flexing effect and or torsional load.

In most weld coatings parent material of the sleeve is undercut to facilitate the weld / thermal inlay. This results in a metallurgical bond of a harder, high carbide matrix to a ductile substrate. In service torsional and radial loads are applied to the sleeve, the substrate with lower hardness and higher toughness can generally withstand these forces. The harder weld inlay however always has a lower fracture toughness along with inherent stress causing fatiguing and fractures in a spiral type tortoise shell pattern that depicts the loads being applied in service.

Traditional spray coatings such as HVOF suffers a similar fate as the harder coating is fractured and compromised.

The image below shows a typical failure mode for PTA shaft sleeve that is becoming more prevalent within the industry.