In the field of hot-rolled sheet steel production, a common and thorny problem is that hot-rolled sheet is prone to upwarping or downbending. If this kind of situation is not dealt with in time, the plate will accumulate in large quantities inside the mill, and then cause the stacking accident. Especially when the hot rolled plate presents a downbend defect, the plate is likely to be twisted under the roll under the action of the roll table thrust, resulting in the mill being forced to stop running. This will not only shorten the service life of the mill, but also bring huge economic losses to the steel production enterprises. Therefore, iron and steel enterprises must deeply explore the main causes of these quality defects, and actively take a combination of prevention and treatment in advance to eliminate the quality of the plate hidden dangers.
This paper analyzes the important points of hot-rolled sheet steel rolling process.
First, the main factors affecting the quality of hot rolled plate steel products
(1) Uneven surface temperature of slab
After the hot rolled slab enters the heating furnace, there is a great difference in the upper and lower surface temperatures, which seriously affects the ductility of the slab itself. The extension rate of some slabs will be limited, so that its extension length is different from other slabs, when the same batch of slab length is not different, the production of finished steel products will be prone to upwarping or downbending phenomenon.
(2) The residence time of slab is too long
Affected by production scheduling and other factors, hot-rolled slab often stays too long in the rolling line. This causes a large temperature difference between the lower surface and the upper surface of the slab in contact with the roll, resulting in an easy upwarping or downbending of the slab head.
(3) the height adjustment of the rolling line is unbalanced
The height of the rolling line is often uneven in the production of hot rolling slab, which has a serious influence on the shape and quality of slab. The high or low position of the rolling line will increase the risk of downbending of the slab head.
(4) The friction coefficient of the roll surface is inconsistent
As a key component of continuous plastic deformation of metal, roll is in contact with slab for a long time in hot rolled plate rolling. When the surface roughness of the roll is not uniform, the friction coefficient between the upper and lower rolls and the slab will change, resulting in a significant difference in the extension interval of the upper and lower rolls, which increases the probability of slab deformation.Measures to improve the quality of hot-rolled plate steel products.
1.Improvement measures for the uneven temperature of the upper and lower surface of the slab
The speed of the upper work roller can be increased and the speed of the lower work roller can be reduced when the slab is warped in the field. When the slab bends down, the speed of the upper and lower work rolls is reversed. In this way, the ductility of the same batch of slab can be kept consistent, and the probability of upwarping or downbending of slab can be effectively reduced. At the same time, the technical personnel should also adjust the temperature difference between the upper and lower surfaces of the slab in time to achieve temperature equilibrium.
2.Improvement measures for excessively long residence time of slab
Technicians can eliminate the temperature difference between the upper and lower surfaces of the slab by reducing the supply of roll cooling water and phosphorus removal water, and can also improve the heat dissipation performance of the upper and lower surfaces of the slab by moving the slab to roll the pieces, thus greatly reducing the probability of upwarping and downbending defects of the slab.
3.Improvement measures for the unbalance of rolling line height adjustment
Before the slab enters the rolling process, the technician should minimize the height error of the rolling line and ensure that the position of the rolling line is neither too high nor too low to prevent the risk of downbending of the slab head.
4.Improvement measures for inconsistent friction coefficient of roll surface
Technicians can adjust the friction coefficient between the roll and the slab by increasing the rolling pass, or directly replace the roll to minimize the friction force between the roll and the slab.
To sum up, only by deeply understanding and effectively solving these key factors affecting the quality of hot-rolled steel products can iron and steel enterprises continuously improve the production quality and efficiency of hot-rolled plate, reduce the occurrence of production accidents, and create greater economic benefits for enterprises.