| Mould is the heart of continuous caster, and plays an important part in the continuous casting of steel billets. The phenomenon of solidification shrinkage in the mould is particular and complex. There are many difficulties in researching this phenomenon by using experimental method, but numerical simulation technology is a very good method to study solidification shrinkage processing of steel in continuous casting mould. At the same time, mastering the characteristic and rules of pouring steel in the mould can provide basic theory for optimizing and designing novel continuous casting mould.Based on intensive research on the continuous casting, a thermal-mechanical coupled model is employed to simulate the temperature and strain-stress fields of continuous casting steel billets with ANSYSTM software. In the model, a gap-dependent heat transfer condition is introduced to modify the function of heat flux, and the corner effect is fully considered in the square billet corner. The relations between thermal and mechanical properties of materials are considered in a temperature function. The solidification and shrinkage process of four round billets and two square billets with different working conditions provided by enterprise are simulated by indirect coupled method.The simulation results show that the models with different petals influence on the shape of billets in the mould exit obviously. The shape of billet at the mould exit as the evaluated standard, six-petal mould is better than two-petal, three-petal and four-petal. The max shrinkage valves of four round billets(12CrMoV,37Mn5, ST45EQ and X42) reach to 1.79mm,1.21mm,0.986mm and 1.75mm respectively in the center of round arcs (M point) and the others reach to 1.35mm,1.1mm,0.859mm and 1.35mm respectively in the end of arcs (N point). In the cross section of square billet, the shrinkage values in the center of billet surface and billet corner are obviously bigger than that in the off-corner. At the mould exit, the shrinkages of B72LX and ER70S6 steel reach to 1.19mm and 1.4mm in the billet surface center, and ones are 2.19mm and 3.54mm in the corner.The project of optimizing and designing moulds with different steel and working conditions is developed by feeding law. According to the comparability of calculated results for round and square billets with different steels and working conditions, the best taper of mould is determined by average shrinkage curves of billet surface. The round petal mould profile is gained by shrinkage curves in the billet cross section, but the petal geometry changes traditional round profile from meniscus to 350mm below meniscus gradually. The round mould taper is continuous parabola profile in the taper direction. For the square mould, the excessive taper is designed from meniscus to 350mm below meniscus and the great radius is applied in the mould corner. The corner radius is frozen at 5mm from 350mm below meniscus to the mould exit, and the inner cavity profile is changed into beeline frame. The taper changes with shrinkage curve of billet surface along the height of mould.The designing and optimizing novel mould is validated in the steel factory. The results show that the working lifetime of novel round mould reaches to 322 heats, higher than the factory's requirements and more than the lifetime of imported mould which reaches to 200 heats. Lack of producing task, the square mould lifetime is not tested. The tested billets qualities are equivalent or even better than that produced by the existing advanced moulds. In other words, the factory considers that the novel moulds have reached to improving the requirement in the term of billet qualities. At present, the novel moulds which are designed and optimized in this research have applied and replaced of the former advanced moulds.
|
PDF Full Text Request