Study On Heat Transfer Mechanism Of Hollow Insulation Board And Improving Feeding Effect During Ingot Casting

For the ingot casting process,the riser is the key part,especially for large ingots,and its thermal insulation performance directly affects the solidification process of liquid steel inside the riser,and then it affects the feeding effect of this part.In the process of ingot casting,the effect of riser on the shrinkage and solidification structure of ingot is very important.In order to improve the thermal insulation of the riser,for many years,researchers have been looking for and developing insulation boards with lower thermal conductivity and high temperature resistance.However,generally speaking,high temperature resistant materials usually have large volume density and high thermal conductivity,on the country the materials with low thermal conductivity are usually not resistant to high temperature.Therefore,the performance improvement range of currently applied thermal insulation materials is limited.In this paper,the insulation boards with hollow and inserted plate were proposed to improve its insulation performance by taking advantage of the low thermal conductivity of air,and its heat transfer mechanism and process were studied.Under the condition that the improvement of the thermal insulation performance of the existing ingot thermal insulation board is limited,by using the hollow insert plate structure,the thermal insulation performance of the ingot riser was greatly improved,the feeding effect of the riser was improved,and then the ingot quality and yield also was improved.The heat transfer mathematical model of hollow structure has been constructed,and the heat transfer law of hollow structure was studied by using the thermal resistance theory.The heat transfer experiment of the hollow structure in the laboratory was carried out.Based on the coincidence between the calculation results of the mathematical model and the experimental results,the effects of hollow structure parameters,material thermophysical properties,inner surface blackness and total material thickness on the heat transfer of the hollow structure were studied by using ANSYS fluent software.The heat transfer mechanism of hollow structure under high temperature was clarified,the influence of various parameters on the heat transfer characteristics of materials is analyzed,and the variation law of equivalent thermal conductivity of hollow structure was obtained.The experimental and simulation results showed that the smaller the thickness of the air interlayer,the more the number of layers,the lower the blackness of the inner surface of the air interlayer,the closer the air interlayer structure was to the low temperature side,and the lower the equivalent thermal conductivity of the hollow structure.The mathematical model of heat transfer,solidification and shrinkage cavity coupling of14.5 ton ingot was established,and the temperature field of ingot solidification process was calculated by Pro CAST software.On the basis that the calculated results were consistent with the measured temperature on the surface of the ingot,the influence of the hollow structure riser insulation plate on the heat transfer,solidification and feeding process of the liquid steel at the head of the ingot was studied.The orthogonal analysis method is introduced to study the influence of the riser parameters on the heat transfer of the liquid steel at the head of the ingot.It is clear that the thermal insulation at the side of the riser is the primary factor affecting the feeding effect;The parameters such as the thickness,position,number of layers and the blackness of the inner surface of the interlayer of the insulating board with hollow structure were optimized.The calculation results show that the insulating board riser with hollow insert plate structure can significantly improve the thermal insulation performance of the riser and the feeding effect of the ingot.The insulation board with 55 mm thick hollow insert plate structure was used for 14.5 ton ingot.When the time when the ingot temperature reaches the solidus,the maximum concave depth of primary shrinkage cavity,shrinkage cavity volume and average shrinkage cavity rate were better than the traditional solid 55 mm thick insulation board,the original riser volume were reduced from 13% to 12% of the liquid steel body.