A billet rolling mill is a rolling mill that rolls small ingots or large billets into small billets, such as three roll billet mill and a billet continuous mill, with a roll diameter of 450~750mm. The working principle and main structure of all kinds of rolling mills are basically the same, but the rolling temperature, pressure, and speed are different. The rolling mill can also be divided into a semi-finished rolling mill and a finished rolling mill. Semi-finished rolling mill is mainly a blooming mill, including a blooming mill, slab mill, and billet mill. The process of pressing steel billets with a rolling mill to obtain the required shape, specification, and performance. The rolling mill is mainly composed of several groups of rolls. The roll is a pair of rolls with opposite rotation directions. A gap or hole of a certain shape is formed between the two rolls, and the billet becomes steel of a certain shape through the roll. Rolling above the recrystallization temperature is called hot rolling; Rolling below the recrystallization temperature is called cold rolling.
The billet rolling mill is mainly used to supply square billet (50 × 50~240 × 240 mm), flat stock of strip mill, and tube stock of tube mill（ Φ 70~270 mm).
There are basically two types of billet mills: horizontal and continuous. In some metallurgical plants with small production scales, there is generally no special billet rolling mill. The billet is only a product of a rail beam mill and large section mill, so the horizontal rolling mill generally produces not only billets, but a variety of finished products. The continuous billet rolling mill is specially used to produce steel billets, as the continuation of the large blooming mill, which is on the same rolling line as the blooming mill. It is directly installed behind the blooming mill, so that the output of the blooming mill can be increased.
Commonly Used Billet Rolling Mills
Commonly used bloom rolling mills include blooming mills, three-roll bloom mills and continuous billet rolling mills.
Blooming Mill
The blooming mill is widely used in large and medium-sized steel rolling production systems.
The main features of the blooming mill are: a two-roll reversible single stand mill with a roll diameter of 750~1500mm; Drive with high power (up to 14000kW), low speed, wide speed regulation range (0~30~120 rpm), and good acceleration and braking performance; The upper roll has a large rise (up to 2700 mm for slab blooming mill) and a fast reduction speed (up to 300 mm/s); The pass reduction can reach 80~150 mm, the rolling pressure can reach 2000~4000 tons, and the maximum rolling torque can reach 650~910 tons/m.
The blooming mill can be divided into square bloom mill, square bloom slab bloom mill, and slab bloom mill. The elevation of the upper roll of the slab blooming sail is greater than that of the first two, and there is also an opposite roll to process the side of the slab.
Three-roll Bloom Machine
The three high bloomers are generally arranged by several three high mills in one or two rows, with a roll diameter of 500~750 mm. This mill can roll small ingots weighing less than 1.5 tons into billets, and can also directly roll a part of finished steel products, so it has great production flexibility and is suitable for local small and medium-sized steel rolling production systems.
The three high-rolling mills can cross rolling up and down at the same time. The lifting platform is set in front of the rolling mill, and the steel upender is set behind the rolling mill, which is easy to realize mechanization. The 650mm three-high rolling mill is a typical representative of this kind of rolling mill, with an annual output of more than 300000 tons.
The three-roll bloomer can also be set behind the blooming mill below 850mm to further roll the blooms with a section of 120X120~200X200mm into 38X38mm billets.
Continuous Billet Mill
The continuous billet rolling mill is generally divided into two groups, each group consisting of 6~8 rolling mills. It is generally installed at the back of the blooming mill, and the billet with a larger section rolled by the blooming mill is hot rolled into the billet with a smaller section. In this way, the product section of the blooming mill can be increased, the rolling passes can be reduced, and the capacity of the blooming mill can be brought into play.
Baosteel blooming plant adopts two 1350mm blooming mills arranged in series, and a group of six stand billet continuous mills arranged alternately by vertical roll stands and horizontal roll stands is equipped behind it, which can handle 3.44 million tons of steel ingots annually.
Billet Rolling Process
The modern blooming workshop is composed of a soaking pit section, the rolling mill itself, the shear, the main power room, the scrap bay, the billet warehouse, etc.
After demolding, the steel ingots are transported to the blooming soaking bay by ingot car, loaded into the soaking pit furnace by clamp crane for heating, and the steel ingots are placed vertically. Cold ingots weighing less than 3 tons can be heated in a continuous heating furnace. When the supply of hot ingots is interrupted, cold ingots can be sent to the soaking pit from the ingot warehouse. After the steel ingot is heated to the specified temperature in the soaking pit, the tong crane is used to take the heated steel ingot out of the furnace and place it in the skip of the ingot car, or directly place it on the fixed skip of the receiving roller table.
The steel ingot car sends the steel ingot to the receiving roller table, turns the steel ingot onto the receiving roller table, or turns the steel ingot from the fixed steel tipping bucket onto the receiving roller table. The steel ingot passes through the extension roller table along the input roller table to the working roller table. There is a rotary table on the input roller table. At the beginning of rolling, the end with small section faces the rolling mill.
After the steel ingot is rolled to the specified size on the rolling mill according to the rolling procedure, the large billet is sent to the hot shear along the working roller table, extension roller table, and output roller table behind the rolling mill. The shears cut off the head of the large billet from the blooming mill, and then cut it into the specified lengths and tails. The returned steel for cutting head and printing tail is sent to the scrap bay by a special conveyor as the returned scrap raw materials for the steelmaking workshop. After shearing, the large billet will continue to be rolled while hot when the blooming mill is followed by the continuous billet mill. Otherwise, after the steel billet is sheared, it will be sent to the steel billet warehouse by the output roller table and some horizontal moving equipment.
In the billet warehouse, flame cleaning and air shovel cleaning of surface defects are carried out respectively according to the steel type. Some steel grades are subject to slow cooling. At this point, the billet rolling is completed and ready to be sent to the finished product rolling workshop.
Utilization of Billet Rolling Mill
Our common automobile plates, bridge steel, boiler steel, pipeline steel, rebar, electrical silicon steel, galvanized plates, and tinned plates, including train wheels, are all processed through the steel rolling process. China’s large steel plants have used advanced continuous rolling mills since the 1970s. The continuous rolling mills have adopted a complete set of advanced automatic control systems. The production process and operation monitoring of the whole line is controlled by computers. The rolled pieces are rolled on several rolling mills at the same time, greatly improving production efficiency and quality. China’s crude steel output ranks first in the world. The annual crude steel output of the top ten domestic iron and steel enterprises is more than 10 million tons.
