Process optimization for hot strip mill.

Abstract

SynopsisIn order to search for suitable technological schedule of hot strip mill, there is proposed an economo-mathematical model, in which production cost is a function of technological parameters such as threading speed, thickness of transfer bar and extract temperature from reheating furnace. The optimization of these parameters is performed to produce high quality strip with minimum production cost. The optimization code was applied for a hot strip mill in Bulgaria and also for one in Japan. The economical situation for production of hot strip differs much from each other in these two countries, and the type of hot strip also differs, but the code could output proper solutions. With the use of the code, a new rolling schedule, in which the transfer bar thickness decreased with length of strip, proved the possibility to reduce production cost and improve gage accuracy. I. IntroductionDuring the last 10 15 years the hot strip mill technology, automatization and the equipments have developed very remarkably in all countries especially in Japan. The main subject in the operation hot strip mill today is a production of better quality strip at higher production rate with lower operation cost.3,5) This will be achieved by an effort of energy saving,1 4> because of enormous increase in energy cost,3,5) Surely a very large number of achievements have already been made with the optimization of heating processesl) and by the applications of direct rolling porcess,1-3) of hot and reverse charge,4) and of schedule-free rolling.3) It is important to keep in mind that hot strip mill (HSM) problems are reciprocity contradictory to each other. Moreover, there are many possibilities to realise the rolling technology and to choose the HSM equipment and layout. In such situation, it is necessary to employ optimization technique in order to decide the suitable technology schedules.Some efforts have been done to formulate the approach to choose the controlling method of HSM, considering the reheating furnace, roughing and finishing groups as a united complex and to realise a HSM economo-mathematical model as an instrument to search for the proper technology version. Here, the authors could show that the proposed optimization concept was valid in both cases of Bulgarian and Japanese technological and economical situations, and moreover, they could propose a new rolling schedule where the transfer bar thickness decreases from top to tail end on the basis of the concept.

Simulation of accelerated strip cooling on the hot rolling mill run-out roller table

“…On cooling the strip to the collecting roller table mill hot rolling the metal undergoes a polymorphic transformation of γ → α, which is accompanied by significant heat release. The vast majority of mathematical models of the thermal state of the band on the collecting roller table, for example, [2][3][4][5][6], does not include a calculation of the polymorphic transformation as transportation for the band collecting roller table, which can lead to substantial error in the prediction of coiling temperature variation of process parameters in a wide range. To calculate the polymorphic transformation in the collecting roller table to know Ar3 transformation temperature of the beginning and end of the conversion of Ar1.…”