Speed Disturbance Compenation in the Secondary Cooling Zone in Continuous Casting.

Abstract

The continuous casting process is used for the solidification of molten steel into semi-finished shapes. Several factors influence the quality of cast steel, including mould level oscillation and cooling patterns in the secondary cooling zone. This article presents a dynamic model that can be used to study heat transfer in the continuous casting process. Temperature measurements in the secondary cooling zone are infeasible due to the effects of scale and steam on the measurement equipment. Two different feedforward controllers are proposed and compared to eliminate the effects of varying casting speed on the strand temperature; thus reducing the defects in the finished product. The first controller is based on typical controllers found in practice and a design methodology is proposed for the design of this controller. The second controller has dynamic properties and makes full use of the plant and disturbance transfer functions in its design. It is shown that disturbance rejection of the second controller is better than that of the first controller.KEY WORDS: continuous casting; secondary cooling zone; feedforward control; dynamic modelling. plants in the world is of the bow caster type (see Fig. 1).The ladle arrives at the caster containing liquid steel at a temperature well above the liquidus temperature. The ladle feeds the tundish which acts as a reservoir of molten steel. The tundish controls the flow of steel into the mould through some mechanism such as a stopper rod. The primary extraction of heat from the strand takes place in the mould. Below the mould, the secondary cooling zone removes most of the heat from the strand through water sprays. The water sprays are grouped into 3 to 6 zones, with each zone independently controlled through valves to regulate the flow of water to the sprays. The secondary cooling zone is typically 6 metres long for billet casters. The strand is supported by rollers and movement of the strand is effected by extraction rollers. Below the secondary cooling zone, the strand cools off naturally in the radiation zone. After the radiation zone, the strand is cut into specified lengths and sent for further processing. ApproachThe approach taken is to first of all derive a dynamic model describing heat transfer in the continuous casting process. The model is dynamic in the sense that it calculates changes in strand temperatures with time, in response to changes in casting speed and spray water flow rate. The dynamic model can be simplified to obtain a steady state model.Since temperature is generally not measured along the secondary cooling zone, plant input/output data is not available to 1. validate the dynamic model accurately, 2. apply system identification* to obtain a model from plant experiments, 3. apply direct output feedback control. For these reasons, the dynamic model is used to represent the actual plant for controller design purposes, and input/output (I/O) data is generated from the dynamic model for system identification.In this model, the inputs are the heat transfe...

A dynamic simulation system for secondary cooling process in continuous slab casting

“…Moreover, the heat transfer in the width direction is negligible in the case of slab casting, where the width is many times of thickness. [2,[4][5][6][7] E. Dynamic simulation model To solve the equation (1) when the casting speed, the casting temperature, the boundary conditions, the steel 3-547 grade and the geometric will not change with time, the steady-state temperature field in the strand can be obtained, i.e. the temperature distribution will not change with the time.…”

“…The product quality and casters' productivity can be improved by the application of advanced control to the spray zones in the secondary cooling process of continuous casting. To improve the basic understanding and caster design, a large amount of mathematical models and simulation program concerning the thermal-transfer and solidification of steel in secondary cooling area have been developed [1][2][3][4][5][6][7] . However, most of them are concerned about the off-line simulation of the steady-state casting process, failing to reflect the dynamic (time-varying) casting process with frequent changes of working conditions, let alone to let users change the disturbance parameters or operate the process during the progress of simulation.…”

Design and implementation of an automated secondary cooling system for the continuous casting of billets

“…Depending on the grade of steel and the caster characteristics, a different target temperature profile of the strand is defined. Various optimization routines such as multi-objective optimization [13], minimization of cost function [14][15][16][17]5], neural networks [18], knowledge based heuristic search [19], genetic algorithms [20], etc., are used to generate the heat flux values for each block of the secondary cooling zone. Using correlations between the heat flux and the water flow rate, the water distribution of the secondary cooling zones for different grades of steel is optimized for some key casting speeds as well as for superheat.…”

“…Thus, controlling the water flow in the secondary cooling zones can minimize the variation in surface temperature of the strand and improve the steel quality. Numerous schemes for controlling the water flow rate of secondary cooling zones have been developed over the years and implemented in billet casters operating across the world [10][11][12][13][14][15][16][17][18][19][20][21].…”

Dynamic 3D heat transfer simulation of continuous casting

“…Many authors have dealt with this problem, which is basically solving the heat transfer equation. [1][2][3][4] All these approaches have in common that they either assume constant density or are not enthalpy and mass conserving in case of temperature dependent density. A prototype of the package has been installed at voestalpine Stahl Linz, casting machine No.…”