Theoretic Study And Practical Application On New Type High Speed Continuous Casting Mold

The key technology of the high speed continuous casting is that the uniform solidified shell with enough thickness and intensity was formed to support the ferrous pressure and prevent breakthrough, during the elevated-temperature melting steel passing through the cavity of mold in a very short time. The vital part of the mold design is the mold taper curve design. The substantial characteristic of the high speed continuous casting mold is its optimized continuous taper curve. However, the design and calculation formula for the mold taper curve design, involving the various influencing factors, has not been established quantificationally, because of the unfavorable working conditions and the various influencing factors. The design of the mold taper curve has been limited to the experiment-design-improvement process. Therefore, the investigation on the forming mechanism of the taper curve for the high speed continuous casting mold is very important in theory and practicality.In the paper, the control difference equations of the solidification heat transfer process in continuous casting mold were differentiated into two types, one is the three-dimensional heat transfer difference equation, and the other is a set of conversation equations. The characteristics and their applications of these two types of control difference equations were discussed in detail. Both the temperature control difference equation of the solidification heat transfer process in continuous casting mold written with enthalpy form and the finite difference equations for alterable grid spaces were built. The thermal boundary conditions on the interface between the billet and the mold were differentiated into two types, one is the form of mold heat transfer flow on the interface, and the other is the form of mold heat transfer coefficients on the interface. The characteristics of the two types of thermal boundary conditions and the simplification calculation correlating the two types of thermal boundary conditions were studied in detail. The creep mechanical model of the solidified shell deformation in mold and the heat elastic mechanical model of the mold cupper tube deformation were built too.The forming mechanisms of the optimal longitudinal profile curves on the inside wall and the optimal taper curves for inside cavity of the square billet mold, the round billet mold and rectangular billet mold were studied thoroughly. The design and the calculation formula of the optimal longitudinal profile curves on the inside wall and the optimal taper curves for inside cavity of the square billet mold, the round billet mold and rectangular billet mold for high speed continuous casting were obtained. The formula with the performance of simpleness and convenience, show quantificationally the effects of composition of steel, casting speed and cooling condition etc. on the design of the mold taper curve. The optimal design of the inside corner configuration of the high speed continuous casting mold was studied in detail too. The design and the calculation formula of the inside corner configuration for the mold whose corner taper is smaller than middle taper were obtained.The square billet mold for casting Q195 steel with the dimension of 154.5 mm×152.5 mm was illustrated. Using of the model developed in this paper and the finite element method, the temperature fields and deformation fields of the billet and the mold cupper tube were calculated. By means of translating the thermal boundary condition on the interface between the billet and the mold from the form of heat transfer coefficient into the form of heat transfer flow, coupling calculation between the temperature field and stress field was avoided. Using of the design and calculation formula for the optimal longitudinal profile curve and the optimal taper curve of the high speed continuous casting mold, the longitudinal profile curve and the taper curve of the mold copper tube were designed.The new type square billet mold for casting 154.5 mm×152.5 mm square billet has being used since April 2005 on continuous caster 3 in Tangshan Iron and Steel Co. Ltd.. The steels poured involved plain carbon steel, hard string steel and steel holding little alloy. The casting speed was v =2.2~2.6m/min. The maximal casting speed was up to v =3.3m/minaccidentally when the molten steel temperature was very low. There was no obvious oscillation mark on the billet surface. The average steel production of a copper tube was 3700 ton.