| Hydrogen energy is an important part of the national energy system.Its production,storage,transportation and use constitute the entire hydrogen energy industry chain.As one of the core equipment of high-pressure gaseous hydrogen storage method,tube bundle container type Ⅳ hydrogen storage cylinder has a wide range of application prospects.However,there are still a series of technical difficulties in the manufacture and application of type Ⅳ hydrogen storage cylinders.Since the type Ⅳ hydrogen storage cylinder is a carbon fiber fully-wound bottle with plastic liner,the heterogeneous interface between the plastic liner and the metal valve seat is very likely to cause interface peeling and even hydrogen leakage due to insufficient bonding strength under complex service conditions such as high hydrogen storage pressure and repeated hydrogen charging and discharging.Therefore,in view of the service conditions and structural characteristics of type Ⅳ hydrogen storage cylinders,this study focuses on the mechanism of the bonding strength of the heterogeneous interface between plastic liner and metal valve seat,which studies and proposes a split precision manufacturing method for plastic liner.It provides theoretical support for the manufacturing and safe service of the high-pressure and large-capacity type Ⅳ hydrogen storage cylinders in tube bundle containers from the aspects of enhancing the bonding strength between the liner and metal valve seat,optimizing the structural design of the liner and adjusting its forming process.The interfacial bonding strength between the metal valve seat and the plastic liner mainly depends on the mechanical interlock and intermolecular force brought by the melt filling into the microstructure of the metal surface.Therefore,this research innovatively proposes the multi-stage microporous undercut structure of metal surface and its preparation process,and reveals the structure-activity relationship between preparation process,microstructure morphology and interface binding performance by constructing and regulating the microstructure morphology of metal surface.On this basis,the filling behavior of melt in multi-stage microporous undercut structure is studied in-depth,and the molding process parameters related to the melt viscosity are optimized.As a result,the interface bonding strength between the metal valve seat and the plastic liner is significantly improved.In order to solve the problem of low heterogeneous interface bonding strength and the weld mark defect of head caused by the temperature difference between the metal valve seat and the mold in the liner split manufacturing process,this paper adopted the method of preparing thermal barrier coating on the surface of mold cavity to regulate the heat transfer characteristics of liner forming process.The delayed heat transfer effect of thermal barrier coating on valve seat,melt and mold core and the mechanism of its action on the bonding strength of heterogeneous interface are studied,which significantly improves the mechanical properties of weld marks and finally realizes the precision manufacturing of plastic liner.The main research results obtained are as follows:(1)In this study,aiming at the service condition of tube bundle container type Ⅳ hydrogen storage bottle,the service performance of the metal valve seat is analyzed by finite element simulation method,and the temperature gradient change of the liner and the evolution law of the resulting thermal mismatch stress at heterogeneous interface in the process of hydrogen charging and discharging were clarified.The results show that the allowable stress of Al 6061 meets the static strength requirements of the metal valve seat,and the maximum thermal stress of the heterointerface between the metal valve seat and the plastic liner is 7.1 MPa in the process of charging and discharging.Through molecular dynamics simulation,the influence of different molding methods on the bonding strength of metal-plastic heterointerfaces was revealed.The results show that injection molding can provide sufficient melt pressure to fully fill the micro-nano structure on the metal surface,which is conducive to improving the heterogeneous interfacial bonding strength.Therefore,the combination method of metal valve seat and the liner through direct injection and the split liner manufacturing method of "injection extrusion welding" were adopted in this study.(2)A multi-stage microporous undercut structure and its preparation process are innovatively proposed to improve the heterogeneous interfacial bonding strength.The study revealed the mechanism of metal surface structure on the bonding strength of heterogeneous interfaces.The new microstructure is composed of multi-stage micropores and undercut structures,which improves the interfacial bonding strength by increasing the surface area and the anchor structure with small inlet and large interior.The preparation process proposed in this paper uses a material reduction process to prepare vertical pits on metal surfaces,and then,by additive process,alumina is deposited on the wall of the vertical pit to construct a bottom-cut structure.In this study,the micro-nano structure of metal surface and its influence on the bonding strength of heterogeneous interfaces are explored by chemical corrosion and plasma treatment,and the structure-activity relationship between the preparation process,microstructure morphology and interfacial bonding performance are established.Through microporous scale control and undercut structure construction,the interfacial bonding strength between aluminum alloy and polyphenylene sulfide reached 17.58 MPa,which provides an important theoretical and application basis for improving the heterogeneous interface strength of type Ⅳ hydrogen storage bottle.(3)According to the mechanism of metal surface microstructure and heterogeneous interface bonding strength,it is found that the heterogeneous interface bonding strength is positively correlated with the filling rate of melt in the microstructure of metal surface,and the filling rate of melt is affected by the molding parameters.The influence of liner molding parameters on interfacial bonding strength was investigated.The results show that the valve seat temperature is the key parameter affecting the filling of the microstructure,followed by the injection speed and holding pressure.The parametric optimization results show that bonding strength of the heterogeneous interface reaches 8.7 MPa,which meets the application requirements of the heterogeneous interface of type Ⅳ inner liner.At the same time,the mechanism of action in which organic montmorillonite barrier modified material system on the bonding strength of metal-plastic heterointerface was studied.The results show that when the amount of montmorillonite is 2 wt.%,the barrier performance is the best,and the corresponding interfacial bonding strength is 7.98 MPa,which also meets the application requirements.(4)In order to solve the problem of temperature difference between valve seat and mold and improve the mechanical properties of the weld mark of the plastic inner liner head,the atmospheric plasma spraying technology is used to prepare zirconia coating with low thermal conductivity,and the low thermal conductivity thermal barrier coating is used to delay the heat transfer process between the valve seat and the mold core,and between the melt and mold core during the mold filling process,and at the same time ensure the temperature of the valve seat and melt convergence.The mold flow simulation and experimental results show that the cavity surface coating can significantly improve the fusion temperature of the head and the temperature of the valve seat.Taking the zirconia thermal barrier coating with a thickness of 290 μm as an example,the tensile strength of the weld joint increased by 14.09%.In view of the split molding method of plastic liner,a set of head injection mold was developed in this study,and a complete set of equipment for cylinder extrusion and head cylinder welding was built.Through mold flow analysis and process control,the head injection molding parameters and the welding parameters of the head cylinder are optimized,and the precision manufacturing of the liner of the Ⅳ hydrogen storage cylinder was realized. |
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