Heat Transfer Effect Of Grooved-type Mold And Its Influence On Solidification Behavior Of Metal

Solidification and heat transfer in continuous casting mold are critical for the process operation and billet quality.The interfacial heat transfer of the mold wall is the key factor affecting the solidification and heat transfer of molten steel and it also has an important effect on the homogeneity of the primary solidified shells and the surface quality of the cast slabs.In this paper,the effect of groove on the heat transfer of the mold was investigated to explore a new way to improve the heat transfer of the primary solidification shell by the method of set grooves on the wall of the mold,which has important theoretical significance and practical value.A self-designed grooved-type mold,which is assembled with copper plates of longitudinal tiny grooves of different sizes,was used to carried out the casting experiment of Sn-Pb-Bi alloy.We have systematically studied the influence of different groove size on the solidification heat transfer and the uniformity of the shell by the detection of copper wall temperature during solidification and the analysis of primary solidified shell,and also analyzed its mechanism in order to provide the theoretical basis and technical basis for the development and application of grooved-type mold technology.First of all,the casting experiments with Sn-Pb-Bi alloy were carried out using a combination mold with different groove depth of 2mm,4mm,6mm and without grooves respectively under the same groove width of 6mm.The experimental results show that,when the mold without grooves,the temperature gradient of copper is largest and the maximum average heat flux reached up to 459.6kW/m2.The primary solidified shells are rugged in the transverse and longitudinal directions with a low average unevenness of 0.18055.However,after the groove is set in the mold,the temperature gradient of the copper plate significantly decreased and the average heat flux of the copper plate also decreased and became stable.The inner surface of the primary solidified shell is smooth and flat and the thickness became thin.Furthermore,the uniformity in the transverse and longitudinal directions is remarkably improved.It showed that the grooved-type mold could effectively control the heat transfer on the mold wall and the growth of the shell tended to be uniform.When the groove width is 6mm and the groove depth is 2mm,4mm and 6mm respectively,the maximum heat fluxes of mold copper wall is 268.1kW/m,277.7kW/m2 and 373.4kW/m2 respectively,which decreased by 41.7%,39.6%and 18.8%comparing with that without grooves.In these cases,the heat flow distribution at the depth of 4 mm is most stable and gentle.The average unevenness of primary solidified shell is 0.03542,0.06181 and 0.08819 respectively.The results showed that the uniformity of the shell is highest when the depth is 2mm,and the uniformity of the shell is second highest when the depth is 4mm.Secondly,The casting experiments of Sn-Pb-Bi alloy were carried out using a combination mold with different groove depth of 1mm and 3mm respectively under the same groove width of 6mm.The experiment results show that both the heat flow of mold copper wall and he heat flow gradient are larger when the groove depth is 1mm.The average unevenness of primary solidified shell is 0.07883 and there is a slight uneven area on the inner surface of the shell.When the groove depth is 3mm,the heat flow of the copper wall of the mold obviously reduced and the heat flow gradient reduced remarkably.The average unevenness of primary solidified shell is 0.06197,and uniformity is significantly improved.The numerical simulation results show that when the groove depth is 2mm and 4mm respectively,the temperature difference on transverse solidifying shell is less than that of the groove depth of 6mm and that without groove.This result is consistence to the experimental results,that is the influence of groove depth on the average heat flux of the mold wall and the thickness distribution of casting shell.The above research results of numerical and casting experiments show that,when the groove width is 6mm and the groove depth was 2mm,3mm and 4mm respectively,which meant that the ratio of groove width to groove depth is between 1.5 to 3,the groove mold could effectively control the mold wall heat transfer and achieve uniformly slow cooling to made the shell evenly slow growth.