Sealing Performance Analysis of Flareless Tube Connection Under 35 MPa Pressure

In view of the current aircraft hydraulic system pressure grade of is developing to 35 MPa. Aming at the unclear sealing performance of many tube connection forms in the current hydraulic system of high-pressure system, the flareless tube connections with nominal diameters of 6 and 8 mm were selected for research. According to the theoretical analysis of metal-to-metal sealing, the simulation calculation using finite element software, and the prototype test according to the sealing test standard of aircraft hydraulic pipeline connectors, the results show that the sealing performance of the flareless tube connection form is reliable under the 35 MPa pressure system, which meets the leak-free performance requirements required by engineering applications. It should be noted that according to the recommended torque of aviation standards, when the minimum preload torque is applied, the nominal diameter of 6 mm flareless tube connection is reliable to seal, while the nominal diameter of 8 mm flareless tube connection is not reliable enough to seal. For the nominal diameter of 6 mm flareless tube connection, when the minimum equivalent axial force is 4410 N, the median equivalent axial force is 7410 N and the maximum equivalent axial force is 9870 N, the simulation calculation of the sealing length is 0.3 mm, 0.7 mm and 1.05 mm, respectively, which are greater than the theoretical (minimum) sealing length of 0.14 mm. For the flareless tube connection with a nominal diameter of 8mm, when the minimum equivalent axial force of 4710 N is applied, the simulation calculation seal length is 0.1 mm, which is less than the theoretical (minimum) sealing length of 0.14 mm, that is, the seal is unreliable; when the median equivalent axial force of 7600 N and the maximum equivalent axial force of 10,500 N are applied, the simulation calculation of the sealing length is 0.6 mm and 0.5 mm, respectively. Both are greater than the theoretical (minimum) seal length of 0.14 mm; it is worth noting that the sleeve and fitting have been damaged to varying degrees when the maximum equivalent axial force is applied. In the actual use process, it is recommended to use the median moment in the recommended torque of aviation standards to ensure that the sealing performance of the flareless tube connection is good while the structure is not damaged.