Shock Hazard Prevention through Self-Healing Insulative Coating on SSA Metallic Bearings
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The space suit contains metallic bearings at the wrist, neck, and waist, which are exposed to the space environment but are also able to contact the skin of the astronaut inside the suit. Currently, several methods are employed that help protect against electrical hazards, which include keep out zones, de-energizing power lines, plasma mitigation systems (plasma contactor unit), anodizing exposed metallic parts, and adhesively applied Kapton® film to cover exposed metallic parts. The present paper describes the development of a more permanent insulation method that is also easy to maintain. Shock hazard prevention has been addressed by developing an insulative multi-layer polymer coating on metallic bearings. The coating is less than 25 microns thick. The relatively thin multi-layer polymer coating stack is comprised of an epoxy-based primer layer, with an overlay of a self-healing coating. Not only does the top layer heal itself when the surface is damaged, but it does so at room temperature without manual intervention and the healing process can be repeated multiple times. Under normal wear and tear usage conditions, any minor damage to the surface can be healed autonomously. Deeper damages that penetrate through the coating can be healed by a heat stimulus above 60C, which can be achieved during routine maintenance. To date, the applicability of the Self-Healing Coating (SHC) system on 17-4 PH stainless steel, titanium and anodized aluminum, has been demonstrated. Both flat and curved surfaces, resembling that of a wrist bearing, have been coated and tested for electrical insulation, as well as mechanical properties, such as impact damage at ambient and cryogenic temperatures. The self-healing response of the SHC system under use conditions, will be described.