Sumitomo Metal Industries, Ltd. (SMI) has developed a new temperature measurement method (Fountain pyrometer) and an associated control system, for hot strip cooled by water in cooling banks.High tensile steel is seeing increasing use in lightweight cars to improve fuel economy and reduce CO2 emissions. Reliable material quality of hot strip products, including high tensile steel, requires good temperature control on the run-out table. The conventional control method is not good enough because the temperature of a hot strip cannot be accurately measured in the cooling banks, where the cooling water interferes with thermal radiation from the hot strip surface.SMI has developed the Fountain pyrometer, which uses a water purge to stabilize the passage of thermal radiation from the hot strip surface. Experiment confirms that Fountain pyrometers can reliably measure hot strip temperatures above 360 degrees Centigrade even in cooling banks with a great deal of cooling water. The response time of Fountain pyrometers is 10 or 20 ms. SMI has also developed a new control system using Fountain pyrometers, a combination that allows very precise temperature control of hot strip on the run-out table.

Synopsis : This paper describes walking control suppressing the lateral unstable movement of the strip in a hot strip finishing mill. The conventional method for controlling walking is well known as "load difference method", in which the measured load difference between the drive and operator sides of the rolling stand is fed back to the roll gap slant reference. However, analyzing the relationship between the feedback control gains of load difference and control effects, we found that the conventional method had a defect that the control effect extremely decreased, as the strip width became wide. Therefore, we developed a new control method that the manipulated value of the roll gap slant was determined based on the strip position measured by a newly developed measuring instrument. In this method, because the strip position sensor is equipped at the entry side of the controlled rolling stand with some distance, the measured strip position is not equal to that at the rolling stand, which is the controlled variable. We overcome the difficulty by applying the model predictive control having the function to predict a future value of the controlled variable and optimizing the manipulated value of the roll gap slant. The effectiveness of the new control method has been demonstrated in an actual plant.

No abstract

Synopsis :High accuracy online strip profile prediction model has been developed for realize mixed scheduled rolling of high tensile strength and mild steel in hot strip finishing mill. New method is based on matrix model. The force and tension distribution is considered by experiment and FEM analysis. First the force and tension distribution when there is no change in strip profile is calculated as the specified value, second the distribution when there is an actual change in strip profile is calculated as the variation from the specified value. Then the profile prediction accuracy of high tensile strength steel, whose rolling force is higher than that of mild steel, was improved. The model was applied to online crown, flatness, and walking control in hot strip finishing mill. As the result, mixed scheduled rolling of high tensile strength and mild steel was commercially promoted.

Synopsis: To measure strip velocity accurately between the stands of the hot strip finishing mill is effective in keeping the stable production and improving the strip dimension control accuracy. Two laser doppler velocimeters has been installed at F4 stand exit and F5 stand exit for evaluating their durability and measurement accuracy. These velocimeters have achieved accurate and stable measurement in bad environment with water splash and high temperature at interstand of hot strip finishing mill by implementing the effective countermeasures to environment and improving the digital signal processing. F5 stand mass flow gage is calculated by using the F4 stand exit gage and the strip velocities measured by these velocimeters. The F4 stand exit gage is measured by existing interstand X-ray thickness gage. The evaluation results indicate that the mass flow thickness has been measured within 0.46% accuracy and will be able to apply to the mass flow AGC (Automatic Gage Control) at the hot strip finishing mill.