Abrasion between Rotary Shaft/Seal Pairs under Extremes of Lunar Highland Regolith Exposure

This study investigates the abrasive effects of Lunar Highland regolith simulant (TH100) and the particle size effect on stainless steel/PTFE rotary shaft–lip seal assemblies. A custom-built sand-pot testing rig filled with Nitrogen gas was used to expose EN-1.4404 stainless steel shafts paired with spring-loaded natural PTFE seals to fine (≤0.125 mm) and coarse (1.400–2.000 mm) Lunar Highland regolith particles. Each rotating pair was operated for 0.25, 0.5, and 24 hours at sequential shaft positions. Wear progression was assessed through shaft surface roughness measurements and scanning electron microscopy of the seals before and after testing. All tests under fine particles were completed without failure, whereas the sealing system exposed to coarse particles failed during the final shaft position and test was stopped. Fine particles primarily induced micro-cutting on the shaft surface, while coarse particles produced a combination of micro-cutting and micro-ploughing. These findings reveal the pronounced influence of particle size on wear mechanisms in lunar dust-exposed rotary sealing systems, with implications for the durability of moving components in extraterrestrial environments.