| Due to its advantages of high maneuverability and high efficiency,adjustable propeller propeller has become a future development trendsency of marine propeller. And hub as the core component connected the adjustable pitch propeller and the tail shaft of engine,bearing the weight of the huge torque of gear and internal pressure.Its working conditions is very bad.hub is the key to realize the sailing of the ship under different conditions.Due to the characteristics of the large hub complex shape and structure,thick wall, being oxidized easily in pouring process, product had more defects in actual production,which impacts safety of ship navigation. So this artical makes one large hub as the research object.First,analyse the defects of the hub,using numerical simulation to determine the causes of the defects.and then optimize casting process of the hub. At the same time, in order to obtain high performance of the hub,the heat treatment of ZCu Al9Fe4Ni4Mn2 nickel aluminum bronze materials was explored.Penetrant inspection, microstructure analysis and fracture analysis were done,so that find out the defects existing in the hub. It was found in penetrant inspection that there were larger tubular shrinkage at the bottom of the hub window,and there were shrinkage porosity defect in the upper surface.Tensile fracture observation was done in the key part of the hub, a lot of oxide films and micro shrinkage defects were found at the bottom of the hub window,and there were lots of micro shrinkage porosity defect in the upper surface of the hub. The analysis found that the grain structure of the hub was large.In order to determine the causes of hub defect, using finite element simulation software Pro CAST to simulate casting filling and solidification process, simulation results show that the liquid metal filling process in the turbulent flow phenomenon is serious, resulting in the film heavily involved in.Solidification process, for the premature solidification of the supplementary metal liquid filling channel under the window, leading to the emergence of tubular shrinkage. Liquid metal in the upper surface of the hub has begun to solidify during the spreading process, resulted in same time solidification state of this region and a large amount of shrinkage porosity in this region.By changing the hub casting structure, optimizing the gating system, setting pad and adopting feed head technology, the original casting process is optimized and improved. By setting the blind riser in the top of the hub window, the defects beneath the window are eliminated.numerical simulation is done to determinethe appropriate time of filling the riser, it is found that the riser’s concentrating shrinkage hole close to the upper surface of the hub if filling the riser immediately after bottom filling.The effect is the best when standing for 1.5min after bottom pouring. By useing the feed head technology, not only eliminates the shrinkage porosity defect on the upper surface of the hub, but also greatly improves the casting process yield. Based on original casting process using circular riser the yield was 49%, By useing the feed head the casting process yield increased to 61%, saving approximately liquid metal 4 tons.The heat treatment of the ZCu Al9Fe4Ni4Mn2 nickel aluminum bronze alloy has been explored.The results show that the annealing process of heat preservation in 980℃ for 2 hours then cooling to 570℃ in the furnace,and then cooling out of the air achieves perfect effect.The as casting microstructure of coarse k II phase has been refined, and greatly improve the mechanical properties of the hub. After heat treatment the material tensile strength increased from the original 488 MPa to 610 MPa, elongation by the original 16.98% up to 17.85%. At the same time, The average rate of 60 days corrosion of the material is also reduced from 0.0082g·m-2·h-1to 0.0056g·m-2·h-1... |
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