Study Of Dynamic Control Model For Secondary Cooling Zone Of Continuous Casting

Secondary cooling is one of the three core technics of continuous casting. It not only determines the solidification process of continuous casting, but also directly affects its quality. Due to variable practical production conditions and requirement of casting multi-grade steel, the control technic of secondary cooling tends to be more intelligent, general and complete.Since Shijiazhuang Iron and Steel Company has many problems with their secondary cooling technic, such as controlling of the total water, water allocation of different segments and method of controlling, so, the bearing steel GCr15 billet casting made there always show the deficiencies like internal crack, center porosity and component segregation, ect.Using the Gleeble-3500 thermal simulation testing machine, the high-temperature mechanical properties of GCr15 Bearing steel was tested, and studied the effect on plastic made by deformation temperature, deformation rate and cooling rate, found out the optimum target temperature in each section of secondary cooling zone. By establishing a non-steady state solidification heart transfer mathematical model and also using this model to calculate water flux and to simulate the course of billet solidification and combining with target temperature, according to certain metallurgy rule, the research finally defines the proper technological parameter of water distribution in secondary cooling zone. Using virtual casting speed as control parameter could avoid the problem brought by traditional water control method which always made the water amount rapidly change due to the fluctuation of casting speed and then lead to severe temperature change on billet surface. At the same time, it could also overcome the defect lag, inaccuracy and large investment of other controlling method, ect.The developing software of dynamic controlling system adopted language Visual Basic 6.0 could put both off-line emulation and on-line production control into effect. The main function of emulation and analogue is to calculate the surface temperature distributions in the solidified shell, the thickness of shell and the length of the liquid core by inputting steel grade, cross section , casting speed , spray water rate and some other relevant parameters; On-line production control is targeted at bearing steel and its function is to calculate the water amount of each section of secondary cooling zone based on the parameters of casting speed, casting temperature and selected cross section which are all sent back by the equipment and then record the historical water amount curve.This research shows 1) The brittle temperature area of GCr15 is between 950℃～600℃, the well-plastic temperature area is between 1250℃～950℃. 2) soft cooling could be used to reduce the crack of billet and the center segregation is minimum when spray water rate is 0.40L/Kg. 3) Casting speed makes the maximum influence on liquid core when other condition is stable. 4) Leading-in virtual casting speed could slow up the severe fluctuation of water amount.For improving the billet quality and the production capacity and designing secondary cooling water-distributing for developing new steel grade, this research would offer significant theoretical guides as well as practical value.