Continuous reheating furnaces are used for heating of stocks at metallurgical and machine-building enterprises in rolling and forge shops before processing by pressure (rolling, forging, stamping). In the conditions of disturbances’ influence on heating process obtaining the required quality of heating is possible only at automatic control of continuous furnace operation. The block diagram of the developed automatized control system of slab heating in a continuous furnace is represented in figure 1.

Figure 1 – Block diagram of the developed automatized slab heating control system a continuous furnace

Control of heating process in the conditions of downtimes is based on comparison of each slab heating curve (HC) in a furnace with predetermined reference heating curve (RHC). Downtimes are divided into three groups: planned, emergency with the predicted duration and emergency with not predicted duration. When a downtime occurs, RHC moves on its duration. The generalized values of deviations of HC from RHC on each heated zone arrive in the local PID-regulators which outputs are temperature settings of furnace zones. Settings are set taking into account results of calculations of the block of optimization on complex criterion on the basis of a method of successive concessions.

The block of slab heating tracking provides to mathematical model not only the readings of thermocouples and/or pyrometers, but also information about change of lining emissivity factor. Also this block traces positions of slabs in a furnace using data on number of pushings made by ram. From the tracking block technological personnel receives information on current thermal state of furnace zones. Personnel has possibility of manual correction of furnace zones temperature settings.

The model for temperature field of continuous pusher furnace operating space has been created in the finite element package COMSOL Multiphysics intended for solution of heat conductivity differential equation by finite element method [1]. This model considers heat engineering and design features with assumptions on calculation of scale layer thickness, on symmetry of a furnace in the longitudinal direction, on uniformity of slab load, etc.

The complex criterion (vector) has been developed for slab heating optimization. It considers the basic parameters characterizing process of slab heating in a continuous furnace [2]:

(1)

where ΔTs – deviation of stock surface temperature at the exit from a furnace from set, °C; Δtex – difference of temperatures on stock thickness at the exit from the furnace, °C; Δtmax – maximum difference of temperatures on stock thickness during the whole time of heating, °C; δ – losses of metal at the expense of scaling processes, %.

As a result of considered optimizing task solution on a method of successive concessions optimum value of specific fuel rate for furnace has been calculated on the furnace and corresponding to it values of partial optimization criteria have been defined.

On the basis of a probabilistic method of decision-making validity determination numerical values of validity have been received at optimizing task solution.

In the block of rational batching of continuous furnace slab load the algorithm considering belonging of a slab to heating group is realized. Slab batching is combined with slab cutting and sorting of selected slabs on one of three criteria: bulk charging temperature of stocks, urgency of order implementation or slab width. Output data of this algorithm are a list of the slabs sorted by chosen criterion. The considered algorithm has been realized in the form of the computer program in the programming environment Delphi 3 [3].

The developed automatized slab heating control system in a continuous furnace ensures increase of sheet production output efficiency and rational batching of slab load in the conditions of variable booking.

2. Serdobintsev, Y. P. The choice of a complex criterion of heating process optimization in a continuous furnace / Serdobintsev Y. P., Kukhtik M. P., Kuadio K. F. // Proceedings of VSTU: Interuniversity Coll. of Scient. Art. Ser. "Progressive Technologies in Machine Building". – Vol. 9, No. 7. – pp. 111-113 .

3. Program of rational batching of a continuous reheating slab load [Electronic resource] / Y. P. Serdobintsev [et al.] // Modern problems of science and education: electronic scientific magazine. – 2013 . – No. 2. – Access mode : http://www.science-education.ru/108-9143