To obtain high mechanical properties of sheet products, hot rolling mills are equipped with controlled water cooling units (CCU). Such units usually include a large number of sections, located above and under the stock in the direction of its movement. Laminar cooling units became especially popular on plate and strip mills.
The main task of the CCU is to ensure the stock cooling at a specified speed down to the specified temperature without its buckling. Modern requirements to the temperature control accuracy and to its stability along the stock length can be satisfied only through automatic control over the CCU operation.
RPC «DONIX» offered a conception of automatic control over the sheet products cooling and the basic mathematical software for it, which were implemented in 2001 during the upgrade of the laminar strip cooling system on the exit roller table of 1700 mill of OJSC «ISPAT-KARMET». At present this system is in permanent use and ensures the specified coiling temperature along 95% of the strip length with deviations within ± 10 ºС for the stock thickness under 4 mm and ± 15 ºС for the stock thickness over 4 mm. As a result, the mill yield which is dependent on mechanical properties increased from 97,1 to 98,9 % and the stability of the finished stock properties improved in 2002-2003 in comparison with 2000 (period of the cooling system operation before the upgrade). [Ivantsov O. V., Kaskin B. K., Vas'kin A. M., Viventsov A. S., Zimakov Y. A. Stabilization of the rolled stock mechanical properties after the laminar cooling system upgrade on the continuous wide strip rolling mill 1700 // Metallurg, 2005, №2. c. 42-44.].
The present conception of automatic control over the controlled cooling unit consists in using a special table — the so-called «basic matrix» to choose the specified values (tasks) to control the cooling section valves during the stock movement. This table contains data on the valves setup for all the combinations of three process variables — temperature at the entry into the cooling unit, metal speed and deviation of the temperature at the exit from the cooling unit from the specified value — which are possible for the given lot of the rolled stock. The basic matrix is prepared before the cooling of the stock begins. So to cool each section along the stock length the controller has just to choose the necessary cell in this table.
To setup the system before the cooling begins the cell which meets the specified variables (initial setting) is chosen in the matrix. When the cooling begins the cells which meet the actual values from the in-process measurement sensors are chosen in the matrix (correction). Thus, if the temperature at the entry into the CCU or the metal speed change, or if the temperature at the exit from the CCU deviates from the specified value, the controller program «slides» over the matrix, changing from one of its cells to another. The basic matrix itself is calculated on a separate computer and transferred to the controller before the rolling of the lot begins.
With the present conception it is not necessary to calculate the corrective actions in the controller during the stock movement. Besides, it ensures the most rapid response of the control system to any disturbances and deviations of the process variables.
In 2005 RPC «DONIX» created a program package for the automated control systems of the CCU for plate products based on the described conception. It includes five main software products:
The program package can be integrated into the control system of any laminar CCU, existent or being constructed. To ensure the compatibility with a CCU of any configuration, the mathematical model of cooling was improved significantly in comparison with the version implemented on 1700 mill of OJSC «ISPAT-KARMET». The programs for the basic matrix calculation and for the calculation model adaptation are realized in Delphi 7 environment. The visualization program was developed using the Wonderware® InTouch® program package, included into the general Wonderware FactorySuite™ package.
To check and preset the software, as well as to demonstrate its possibilities, RPC «DONIX» developed a simulation model of the CCU automated control system. It simulates the stock cooling process on a certain plate mill on the computer monitor in real-time mode. The user («mill operator») enters the rolling schedule for a certain period (i.e., for the next hour or the next shift) and observes the entire mill operation process on the monitor.
The simulation model works on any IBM-compatible personal computer with the operational system Microsoft Windows XP.
