The hot strip mill consists of a roughing mill and a finishing mill. The roughing mill consists of three types: semi-continuous, 3/4 continuous, and fully continuous:
①The semi-continuous type has a scale breaking (removing iron oxide scale) frame and a reversible frame with vertical rollers;
② For the 3/4 continuous type, in addition to the above racks, there are also 2 consecutive racks arranged in series;
③The full continuous type consists of 6~7 racks. The finishing mills are composed of 5 to 7 consecutively arranged stands and coilers. Hot strip mills are named according to the length of the roll body, and those with a length of more than 914mm are called wide-band steel mills. The length of the work roll of the finishing mill is 1700mm, which is called a 1700mm hot strip mill. This mill can produce strip coils with a width of 1550mm.
There are four ways of hot strip rolling according to product width and production process:
Hot continuous rolling of the wide strip, reversible hot rolling of the wide strip, hot continuous rolling of the narrow strip, and hot strip rolling with a planetary 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 its economic rationality still needs to be considered from the overall situation.
③Use the hydraulic bending roll 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 a 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%. The material of the rolls was improved, and the rolling oil was used to prolong the life of the rolls; a quick roll changing device was installed 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 increased by 90%。