Research And Application On Cooling Characterizes And Control Strategy Of LP Plates

Being a kind of reducing and saving steel product with the optimization design of longitudinally section, longitudinally profiled(LP) plates have been applied overseas. But there are few studies on the rolling theory of LP plates in domestic. As the important production chain of LP plates, control cooling process is an important part to get products with qualified microstructure and mechanical property. The cooling process of LP plates was studied in this dissertation. The temperature and cooling rates distribution of LP plates during control cooling process were analyzed by numerical analysis method and control strategy was then established. Temperature and cooling rates distribution along length direction of LP plates were studied through control cooling experiment, and application of the control model in controlled cooling of plates indicated the feasibility of the control model. The main works were as follows:(1) According to the characteristic of thickness variation in the length direction of LP plates, two-dimensional FEM temperature field calculation model was established. The cooling process of LP plates that slowly moving into cooling zone can be simulated with the temperature field model. The effect of temperature on the material physical property was analyzed to decide the parameters value, and the calculation accuracy for the temperature field during cooling process was improved.(2) Variation law of cooling rates was analyzed based on the calculation of the temperature field during cooling process. Average cooling rate was calculated by the average temperature calculation model. Effect of plate thickness, water flow density, start and finish cooling temperature, together with header arrangement on average cooling rates were studied. According to the temperature distribution, cooling rates distribution in thickness direction was analyzed. Effect of cooling time, water flow density, start cooling temperature and water temperature on the cooling distribution were also studied. Experiment indicated that the microstructure were different because of the cooling rates distribution in thickness direction.(3) The relationship between cooling rates and heat transfer coefficient was analyzed by numerical simulation. The results showed that the existence of the ultimate cooling rate under special cooling condition and the change of cooling rates with increased heat transfer coefficient present an S-like curve, and then the cooling rates gradually tended to be stable, and that was the ultimate cooling rate. With the increasing heat transfer coefficient, the temperature of plate surface approximated to that of cooling water at finish cooling and the ultimate cooling rate comes true. The effect of plate thickness, start cooling temperature, finish cooling temperature and water temperature on the ultimate cooling rate was analyzed.(4) The temperature field during cooling process of LP plates was calculated by FEM, and the temperature and cooling rates distribution characterizes along the length direction of LP plates was analyzed. The effect of control cooling type, thickness and slope of LP plates, water flow density and cooling time on the temperature and cooling rates distribution along the length direction of LP plates was also analyzed under the same cooling condition.(5) According to the temperature and cooling rates distribution characteristic of LP plates, control strategy of the finish cooling temperature and cooling rates was studied. By optimizing the plate transferred speed or controlling cooling zone length by opening or closing the header during cooling process to adjust cooling time, the temperature of each sample can be controlled. The cooling rates can be controlled by water flow density and headers arrangement adjustment.(6) The cooling process of different thickness position along the length direction of LP plates was simulated through cooling experiment of different thickness plates. The temperature and cooling rates distribution along the length direction of LP plates were analyzed. The results indicated that the numerical analysis results were reasonable. The application of the control model in plate cooling indicated the feasibility of the model, and got well results.