Wide Steel Strip Improves Surface Quality And Thickness Accuracy

The first generation of hot strip rolling mill The earliest hot strip rolling mill was put into operation in the United States in 1926. A four-high mill is used to increase rigidity and produce wide and thin products. The main motor of the finishing mill is a DC motor, which is powered by a motor-generator set. The slab used in this generation of rolling mills is 150-200mm thick, 1200-1550mm wide and 2.5-5m long. The thickness of the rolling stock from the roughing mill is generally 20 to 30 mm, and the maximum speed of the finishing mill is 8 to 10 meters per second. The maximum coil weight is less than 10 tons, and the coil weight per unit width is about 8kg/mm. The annual production capacity is about 600,000 to 2,000,000 tons. The 1700mm semi-continuous rolling mill put into operation by China Anshan Iron and Steel Company in 1959 belongs to this type.

The second-generation hot strip hot rolling mill was put into operation in the United States in 1961, and is characterized by the adoption of a speed-increasing rolling process on the rolling mill. When the strip comes out of the finishing mill and the front end is fed into the coiler, the finishing mill, roller table and coiler are accelerated at the same time, so that the speed of the finishing mill is increased to 15-20m per second, and the coil weight per unit width is 18-20kg/ mm, the roll weight is 30 tons, and the annual production capacity is 4 million tons. Automatic thickness control, thickness and width measuring instruments, perfect descaling and strip cooling control system, good speed control system and micro tension looper device are adopted in this type of rolling mill. At the same time, the rigidity of the rolling mill and the power of the main motor have been increased, a rapid roll changing device has been added, and a computer control system has been adopted to improve the surface quality and thickness accuracy.

The third-generation wide band hot continuous rolling mill With the maturity and application of the second-generation rolling mill technology, combined with the development of continuous casting machines and walking furnaces, the third-generation rolling mill was developed from 1970 to 1978. The furnace with this type of rolling mill can heat slabs weighing up to 45 tons and up to 15 meters long. It can also reduce the black marks produced during heating and reduce the scratches on the surface of the slab. The heating capacity of each furnace is 300 tons. The coil weight per unit width is 36kg/mm, and the maximum rolling speed is 28.5m per second. The annual production capacity is 6 million tons. The third-generation rolling mill has the following characteristics: ①Reduce the length of the roughing mill, save equipment and plant investment, and most use 3/4 continuous rolling mills. The finishing mill train consists of 7 stands, and the thickness of the rolling stock entering the finishing mill train is 30-50mm. ② The size of rolled products ranges from 0.8 to 25 mm, but their economic rationality still needs to be considered from the overall perspective. ③Use the hydraulic bending device to control the shape of the plate and use the laminar flow cooling of the strip to improve the quality of the steel plate. And try to install the shape detector closed-loop control shape. ④ The production process of the whole workshop (from slab warehouse to finished product warehouse) is managed and controlled by computer. ⑤ Achievements have been made in reducing energy consumption, improving operation rate, improving product quality, and improving yield, such as the width tolerance of strip steel reaches ±1mm, the thickness tolerance reaches 0.05mm, the rejection rate is reduced to 0.02%, and the loss of iron oxide scale is reduced. It is 0.7%, the cutting amount is 0.05-0.1%, and the finished product rate reaches 99%. Improve the material of the rolls, use rolling lubricants to prolong the life of the rolls; and install a quick roll changing device to reduce the total roll changing time from 10 to 15% of the total operating time to 4%, and the rolling mill operation rate in some workshops has increased to 90%.