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Correct selection of rolls to meet production requirements

Article tags:Correct selection of rolls to meet production requirements

Residual stress and thermal stress will occur in the roll preparation process before operation and operation. The effect of various periodic stresses, including tortuosity, change, shear, contact stress and thermal stress, is further subjected to the application. The distribution of these stresses along the roll body is uneven and constantly changing. The reasons are not only the planning elements, but also the wear, temperature and roll shape of the roll in operation. In addition, the rolling conditions are often abnormal. If the roll is not properly cooled after operation, it will also be harmed by thermal stress. Therefore, besides wear, rolls often suffer from crack, fracture, spalling, indentation and other parts of damage and surface damage. A good roll should have a better match among its strength, wear resistance and other performance indicators. In this way, it is not only durable under normal rolling conditions, but also less harmful when some abnormal rolling conditions occur. Therefore, it is necessary to strictly control the metallurgical quality of rolls or supplement external measures in order to enhance the bearing capacity of rolls.

There are many kinds of rolling mills to produce long products. Therefore, the selection and layout of rolling mill types, the selection of roll materials and the determination of roll size are very wide. At the same time, the rolls selected by different rolling mills are also different. It is necessary to select the rolls according to the production requirements.

Long Product Mill

Before choosing suitable rolls to increase productivity and improve product quality, it is necessary to fully understand the types and configurations of various rolling mills.

1. Bar and Small Profile Mill

Generally speaking, bar and small section mills can use ingots with sizes ranging from 80 mm to 150 mm, or continuous casting billets with the same sizes to produce small and small bars. The initial feeding temperature of bars and small section mills is 1200 C. The mill can be produced either semi-continuous or fully continuous. Continuous rolling mill is the current trend of development, among which there are rough rolling, medium rolling and finishing mill stands. Rough mill stands are arranged in horizontal/vertical order, which mainly depends on product composition. The intermediate stand and finishing stand can be either vertical or horizontal. For bars, the rolling mechanism is more vertical stand, while for other small profiles, the horizontal stand is often used.

In the small section mill, according to the difference of feeding material and final product size, the selected roll diameter is 300-600 mm and the length of roll body is 700 mm. For product tolerance, users generally require one third of the international tolerance standards, and the product should have a good surface finish. For small steel, the rolling speed of the mill is from 12 m/s to 20 m/s, while for bar mill, the rolling speed has been increased to 36 m/s.

2. Wire Rolling Mill

Wire mill has roughing mill stand and intermediate stand similar to small section mill. Compared with the two-wire rolling mills, these mills are generally designed to perform slitting rolling up to four lines simultaneously. However, the current development trend is to adopt single-wire high-speed rolling. Modern wire mills generally have 8 to 10 torsionless stands, which are arranged at 90 degrees in each other in finishing mills.

At present, the diameter of rolls used in wire mills is limited to 200 mm. The rolling speed can reach 140 m/s.

3. Medium Profile Mill and Large Profile Mill

After the rough mill stand, there are two sets of continuous stands for the medium section mill. Continuous rolling mill can be arranged horizontally or vertically according to pass design. For section steel and channel steel with parallel edges, it is also equipped with universal rack. When rolling other profiles, the universal stand can be replaced by the horizontal stand. The rolls of the horizontal stand have deep passes, but the universal stand does not.

Horizontal rolls with larger diameters determine the shape of the section steel, while opposite rolls with smaller diameters are used to roll the edges. Good surface finish and dimension tolerance can be obtained when the billet passes through the finishing rolls of traditional stand and universal stand.

Selection of Roll Parameters

- Rolled steel grades

Rolled steel is the key factor in selecting rolls. Its anti-deformation ability varies with the chemical composition of the billet, mainly in the magnitude and variation of the deformation load at each stage of rolling. Rolls must be selected according to the strength and hardness determined.

- Rolling Mill Layout and Pass Design

The position of the stand in the production line and the design of the pass have a great influence on the selection of rolls. According to the position of the stand, the force mode and performance of the roll can be greatly changed. This is because the rolls used in roughing and finishing mills have very different force modes, which results in expected changes in roll performance. In addition, the time interval between one billet passing through the stand and the next billet passing through the mill and the productivity of the mill also have a great influence on the selection of rolls. It can be observed from the test that the bending of rolls and the torsional stress combined with high rolling pressure are the factors determining the selection of rolls for rough steel stand. However, in finishing mill stand, hardness, wear resistance and surface quality are the key factors for roll selection.

- Friction between roll and blank

Because of the difference between the circumferential speed of rolls and the billet speed, friction plays a very important role, especially at low speed, it can have a good occlusion, such as the blooming mill and roughing mill stand. Therefore, the relevant data create conditions for proper selection of rolls to be suitable for a particular stand.

- Thermal state

The hot state of roll and billet is also very important. The main reason is the temperature of the roll.


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