Numerical Simulation Of The Effect Of Gas Boundary Layer On The Behavior Of The Puddle In Planar Flow Casting Process For Amorphous Ribbon

In the process of planar flow casting(PFC),the gas boundary layer forms near the roller surface during the high-speed rotation of the cooling roller.The gas boundary layer will affect the behavior of fluid flow,heat transfer and rapid solidification in the puddle(the behavior of the puddle for short),which affects the thickness,edge quality,surface quality and final service performance of the amorphous ribbon.Based on the computational fluid mechanics,the influence of the behavior of the puddle affected by the gas boundary layer in the process of planar flow casting process was studied in this project.the influence of the gas physical parameters,environmental pressure and process parameters on the gas boundary layer and the behavior of the puddle was investigated,in order to explain the mechanism of the gas boundary layer affect the quality of amorphous ribbon.The results are as follows:(1)During the process of the puddle formation,the gas boundary layer affects the behavior of the puddle.When the puddle has not been formed,the gas boundary layer takes away the heat of the amorphous melt from the amorphous melt-gas interface.After the formation of the puddle,the gas boundary layer crushes the upstream meniscus of the puddle,which causes the gas entrapment in the puddle and affects the temperature distribution of the amorphous melt.The airflow will form the gas boundary layer around the puddle in the edge,which may decrease the edge quality of the amorphous ribbon.(2)The position and the pressure of the negative suction is very important.There is little damage to the gas boundary layer when the negative pressure at the side of the upstream meniscus is low(5000Pa and 8000Pa,5mm from the center of the nozzle).The negative pressure suction(5000 Pa)near the nozzle wall decrease the gas boundary layer around the puddle,which is benefit to the quality of amorphous ribbon edge.When the negative pressure is increased to 80000Pa,the opposing gas boundary layer around the puddle with high velocity may decrease the edge quality of amorphous ribbon.(3)The speed and the direction of injecting different gas have a significant effect on the result.When Ar.He and CO2 is injected in the opposing direction,the increase of the injecting speed helps to destroy the gas boundary layer.When injecting low density gas(high temperature CO2)in the casting direction,the phenomenon of air entrainment will be reduced.(4)The adjustment of process parameters(the injection rate of the amorphous melt,the speed of the rotating cooling roll and the distance between the nozzle and the cooling roll)will affect the behavior of the puddle.The injection rate of the melt mainly affects the angle between the puddle and the cooling roller surface.Adjusting the speed of the rotating cooling roller affect the temperature distribution in the puddle.The distance between the nozzle and the cooling roll affect the velocity distribution of the gas boundary layer near the upstream meniscus,which affects the gas entrapment.When increasing the width of the ribbon,the maximum velocity of the gas around the puddle will be increased,which will affect the edge quality of the amorphous ribbon.