Coalescence And Removal Of Inclusions In Split-Type Tundish With Swirling Ladle Shroud

This paper takes the split-type tundish as the research object to simulate the coalescence and removal of inclusions.The swirling chamber was matched with the ladle shroud which equipped with spiral guide rails to form a swirling structure to promote the coalescence of inclusions.The main body of the tundish promotes the removal of inclusions by optimizing the flow control device.Based on the discrete phase model to study the trajectory and removal rate of inclusions,the L9(34)orthogonal test was designed and combined with the CFD-PBM coupling model to study the influence of different swirling structure parameters on the collision and coalescence of inclusions in tundish,the effect of different diversion structure parameters on the flow state of liquid steel was studied by using tracer species transport model.The results of the discrete phase model shows that the residence time of small size inclusions in the liquid steel is longer but the removal rate is lower.With the increases of the inclusions size,the residence time of inclusions decreases but the removal rate increases gradually.Therefore,increasing the size of inclusions is beneficial to improve the removal rate of inclusions.Firstly,the collision and coalescence of inclusions in swirling structure was separate studied and the growth rate of inclusions average diameter was taken as the judgment condition of orthogonal test.The analysis results shows that the rotating circles number of swirling guide rail had the greatest effect on the collision and coalescence of inclusions,while the height of swirling chamber had the least effect on it.By calculating the comprehensive average value between each factor and each level in the orthogonal test and taking the level corresponding to the maximum value as the swirling structure parameters that is most conducive to the collision and coalescence of inclusions,that is,the height and diameter of swirling chamber is 700 mm and 600 mm respectively,2 swirling guide rails and rotated 6 circles respectively.Applying this swirling structure to the original split-type tundish to study the coalescence and removal of inclusions and compared it with the traditional shroud.The average diameter of inclusions increased by 16.67%and the total removal rate is 19.73%when the traditional ladle shroud was applied and the collision and coalescence was considered.The average diameter of inclusions increased by 19.74%and the total removal rate is 21.86%when the swirling ladle shroud was applied and considering the collision and coalescence.Based on the above-mentioned optimal swirling structure combined with the orthogonal test,considing the influence of different diversion structure parameters on the flow state of liquid steel in tundish.The diversion structure parameters with optimum flow state of liquid steel was obtained by solving the comprehensive average value between each factor and each level,that is,the distance of the diversion partition is 300 mm,the height of the diversion hole is 400 mm,the inner diameter of diversion hole is 120 mm and the angle of inclination is 35°.At this time,the plug flow volume fraction of the liquid steel is 50.30%,and the dead zone volume fraction is 6.64%.Optimizing the flow pipeline of liquid steel between the swirling chamber and the main body of the tundish on the basis of the optimum swirling structure and diversion structure.When the height and width of flow pipeline of liquid steel is 150 mm and 200 mm respectively,the plug flow volume fraction of the liquid steel is the largest,which is 53.65%.Compared with the before optimization of tundish,it improved by 34.66%.The dead zone volume fraction is the smallest,which is 5.69%.Compared with the before optimization of tundish,it reduced by 38.75%.Comparing the coalescence and removal of inclusions before and after optimization of the split-type tundish.The average diameter of the inclusions before optimization of tundish increased by 16.67%and the average diameter after optimization of the tundish increased by 20.77%.The total removal rate of inclusions before optimization of the tundish is 18.29%and the total removal rate after optimization is 22.54%when the collision and coalescence of inclusions was not considered.The total removal rate of inclusions before optimization of the tundish is 19.73%and the total removal rate after optimization is 26.75%when the collision and coalescence of inclusions was considered.