Research Of Low Pressure Casting Technology And Properties Of Aluminum Alloy Ratchet For High-Speed Railway

Ratchet compensator is one of the most important parts in the high-speed railway contact net. Low pressure permanent mold casting process is used to produce the castings in order to meet the high dynamic fatigue and mechanical performance demand. However due to the complex shape and thickness of ratchet compensator structure, casting defects usually appear, which harm for the safty of railway. Based on low pressure casting ratchet compensator as the research object, the low pressure casting technology and hot treatment were optimazed. And the castings with high mechanical properties were obtained.3-d drawing software was used for the three dimensional entity modelling of casting model, and Pro CAST software was employed for numerical simulation of temperature field and flow field in the process of casting, which can get metal flow pattern of different casting time and temperature distribution in the solidification process, predicting the position and mechanism of casting defects, such as shrinkage porosity and oxide defects. The numerical simulation results show that the whole filling process is smooth, without impact and other unstable phenomenon. And the filling process can satisfy the requirment of high quality casting production. But due to the complex structure and inhomogeneous wall thickness, unreasonable distribution of temperature field in solidification process generates. And shrinkage defects formed in the thickness parts, which were predicted in the simulation result and confirmed by X-ray radiographic inspection. The reason for formation of these defects is insufficient feeding.Based on the simulation results, a serial of methods were taken to control the solidification order of the castings, which were including gas cooling of upper-mold, water cooling of the center tap cone, gas cooling for lower die overall to get temperature equilibrium. And the shrinkage defects were disappeared, qualified castings were obtained.Optimized heat treatment processes were taken for the low pressure casting ratchet compensation device. Solid solution temperature is 535±?, time of 8 h; Quenching temperature was 60?, 2 h; Aging temperature for 160±5?, time of 3 h. The ultimate tensile strength of the casting is 320 MPa, and ductility is 5.4%, which can satisfy the requirement of mechanics performance standards of ZL114 A ratchet compensation device at present. Fatigue test was carried on homemade and imported castings, and the tests result indicating that the casting is operating normally, without any crack and deformation within the standard requirement of 2×104 times.