Optimization Of Solidification Structure And Continuous Casting Process Of SCR7000 Copper Billet

The cast wheel scaling,billet porosity defects and abnormal solidification organization of the five-wheel continuous casting machine seriously endanger the tensile properties of copper rods.In this paper,the microscopic morphology and physical characteristics of cast wheel fouling specimens were studied,the thermodynamic mechanism of cast wheel fouling was analysed,and the fouling mechanism and inhibition measures were proposed.A model of the solidification temperature field of copper liquid was established to study the influence of pouring temperature and casting speed on the solidification organization,providing a theoretical basis for the optimization of continuous casting process parameters.SEM,EDS and XRD were used to analyse the scaling layer on the surface of the SCR 7000 cast wheel crystalliser,and the interaction between the spray cooling water and the high temperature cast wheel was investigated.The results show that the internal and external surfaces of the cast wheel crystalliser are scaled with different phase compositions.The composition of the scale layer in the inner groove of the cavity consists of a mixture of carbon black,Cu,Cu₂O and Ca O,while the composition of the scale layer on the external surface of the crystalliser is mainly composed of Ca CO₃,which is due to the different temperatures and contact media on the internal and external surfaces of the cast wheel crystalliser.The inner cavity of the crystallizer is in contact with the medium of acetylene incomplete combustion into the carbon black,slag water,high temperature copper billet,copper liquid,the inner surface temperature is high,prompting the carbon black enrichment,slag water Ca CO₃concentrated precipitation and high temperature decomposition,copper crystallizer and copper billet of high temperature diffusion and other factors compound formation of the inner cavity scale layer.The lower temperature of the outer surface layer of the crystalliser,as well as the attachment of Ca CO₃particles in the spray water film at the bottom of the circumferential movement cast wheel by centrifugal force,accelerates the supersaturated precipitation of Ca CO₃crystals in the spray water.The differences in the phase,thickness and uniformity of the scaling layer on each face of the cast wheel crystalliser resulted in abnormal solidification organisation of the inverted trapezoidal copper billets.By adding scale inhibitors,purifying the concentrated drainage and making up soft water measures to stabilise the hardness of the caster water and adopting the process measures of slag flushing with net circulating water,the degree of scaling in the cast wheel and the solidification organisation of the copper billets were significantly improved.By analysing the characteristics of the location of pore capture in copper cast billets,and combining with the fluid analysis software Fluent to simulate the flow state of copper liquid in the cast wheel cavity and the behaviour of the entrained gas,the mechanism of the formation of pore defects in cast billets was analysed.The results show that the origin of the porosity defects in different locations in the cast billet is different.The porosity defects near the cast wheel side come from the entrainment of air during pouring,and with the increase of pouring speed,the vortex is formed near300mm from the pouring liquid surface,and the vortex formed is bigger when the pouring speed is 44t/h.The vortex causes the formation of porosity defects in the cast billet 5-10mm from the cast wheel side.The solidification centreline porosity mainly comes from the high content of hydrogen in the copper liquid reacting with the oxygen in the copper liquid to produce water vapour,which cannot be discharged.The solidification centreline voids are caused by the solidification end point exceeding the6 o’clock position of the casting wheel and the copper liquid not being fully solidified and flowing backwards.ProCAST software was used to simulate the effect of pouring temperature and pouring speed on the solidification behaviour of the copper liquid in the crystalliser of the casting wheel and to investigate the relationship between pouring temperature,pouring speed and cooling water flow.The billet linear cooling curve was fitted to obtain the billet temperature measurement data in the air-cooling stage,and further fitted to obtain the billet water-cooling cooling curve by combining the copper liquid pouring temperature and the copper liquid solidification temperature at the 6 o’clock position to back-calibrate the heat transfer coefficient of the cast wheel in each zone.A five-wheel continuous casting machine billet movement algorithm was developed and programmed to achieve simulative billet movement.The results of the study show that for every 10°C increase in pouring temperature,the solidification end point increases by approximately 320mm downwards,and when the pouring temperature is at 1130°C,the solidification point of the copper liquid is beyond 6 o’clock,and in order to obtain a good solidification organisation,the pouring temperature needs to be controlled within the range of 1120±5°C.For every 2t/h increase in pouring speed,the solidification end point increases about 100mm downwards.At a pouring speed of44t/h,the arc length of the solidification end point from the liquid surface is2969.34mm,which does not exceed 6 o’clock.