High production rate and feed powder efficiency are critical in the HVOF hardfacing of aircraft landing gear, turbine, and actuator components traditionally electroplated with carcinogenic hard chromium. Desired improvements are hindered by rapid heat build-up in substrate component and thermal expansion mismatch between the carbide coating and steel, titanium or aluminum substrate. A new, cryogenic nitrogen gas (-195°C) cooling system has been developed which limits the thermal expansion and substrate softening problems, and enables a non-stop, gun-on-target spraying. Fully automated, the operation of the new AP LIN-Cooling System is based on thermal imaging of the entire substrate and multi-zone cooling with novel, cryofluidic nozzles. Thermal logs and images of components processed are saved by the system for quality auditing purposes. This paper presents results of industrial tests of the system during WC-10Co4Cr coating of Boeing 737 landing gear, demonstrating a 50% reduction in spraying time, corresponding reductions in the consumption of powder and HVOF gases, and additional labor savings due to the use of flexible masking, unfeasible with the traditional cooling methods. Analysis of residual stresses, structures and properties of the coating and AISI 4340 steel substrate shows that the cryogenic nitrogen cooling results in high-quality products.

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