Study On The Surface Maintenance Process Of Landing Gear Inner Cylinder Of Civil Aircraft

The surface treatment process such as cadmium plating and chrome plating technologies performed during the overhaul with landing gear of the AIRBUS A320 commercial airplane were studied.The structure and the function,composition and working principle of A320landing gear system were introduced.The overhaul procedure,the process specification applies and the quality control of the sliding tube of A320 main landing gear was researched.The surface treatment process is the key work step in overhaul of landing gear.If all the surface treatment lines which relate to overhaul were build up,it means that there is the fundamental capacity to the overhaul landing gear.There are hundreds of parts when one main landing gear was disassembled.Every part was needed to apply one or several surface treatments according to their defect and damage.The application of hard chrome plating,the electronic cadmium plating and the nickel plating were studied during the overhaul the sliding tube of A320 main landing gear.The implementation of hard chrome plating and cadimium plating technologies in A320main landing gear inner cylinder overhaul was studied.Firstly,the reason of and control method to the hydrogen embrittlement occurred during high strength steel plating are analyzed.The impact on safety of important force bearing components such as landing gear inner cylinder,etc.from hydrogen embrittlement will be eliminated using the dehydrogenation technology method of implementation of pre-plating treatment,low hydrogen embrittlement plating technology and post-plating curing.Secondly,the effect of hard chrome plating on fatigue performance of landing gear using a sample of 300M steel which is the same material as main landing gear inner cylinder was studied.The test result indicates that fatigue intensity and fatigue life at same stress condition of plated sample reduces for 60%compared to sample not plated,the thicker the plating layer is,the lower the life will be,and fatigue perforation is not apparently related to number of times of plating.All fatigue cracks on plated 300M start from the plating layer.Fatigue crack source can be formed due to high brittleness,net shaped crack and cracks generated and extended fuel to force bearing of chrome plating layer.Many times of plating and striping increases the risk of hydrogen embrittlement generation,but dehydrogenation can avoid fatigue cracks generation due to hydrogen embrittlement effectively.The test result shows that neither content of hydrogen is obviously increased,nor any trend of hydrogen embrittlement of 300M steel after many times of plating as long as dehydrogenation as per current specification PCS2110 is carried out.Additionally,the reason of cracks generated on chrome layer surface after chrome plating and grinding during landing gear inner cylinder overhaul is also was analyzed and studied,and respective improvement suggestions are raised.Chrome plating improvement suggestions to landing gear inner cylinder chrome layer cracks are:controlling strictly concentration of CrO₃ at 240-260g/L,and SO4^2-at 2.4-2.6g/L;temperature of main tanker of chrome plating at53-57?;and current density at 35-40A/dm².These suggestions have been found effective in production activities where chrome plating quality was improved outstandingly and opportunity of crack generation and rework times were reduced significantly.Grinding improvement suggestions to landing gear inner cylinder chrome layer cracks are:to improve piece parts grinding quality and avoid cracks due to improper grinding by increasing linear speed,grinding in rows,controlling feed at 0.005mm per circle at radial direction,using proper sand wheel,reducing sand wheel grinding material granularity at d=250-350um,more frequently trimming of sand wheel,etc.Surface quality of A320 main landing gear was improved greatly;reworks due to cracks on chrome layer decreased dramatically,and efficiency and reliability of landing gear overhaul were increased.