In the production of strip steel, only by ensuring its good shape can production proceed smoothly and product output and quality be continuously improved. When the residual stress inside the strip steel is large enough, it will cause the strip steel to warp, manifested as side bending, edge waves, small edge waves, and small medium waves. When the steel grade of the strip is determined, the occurrence of warping is related to the width and thickness of the strip. The thinner and wider the strip, the easier it is to warp during production. At present, the market demand for strip materials is both wide and thin, therefore, good shape control is very important.
l Main Reasons for Plate Shape Problems in Production
1. Uneven heating or cooling of strip steel
When the heating or cooling of the strip steel is uneven, internal stress will be generated, and when its value exceeds the limit, plate shape problems will occur. When uneven stress occurs in the width direction, edge waves or small edge waves may occur
2. Incompatible blank size
If the size of the billet does not meet the specifications and the thickness of the cross-section is uneven, it will cause uneven extension of the strip width direction.
3. Unreasonable roll gap setting
If the roller gap setting is uneven and the unilateral difference is large, it will lead to inconsistent strip elongation
4. Roller issues
(1) During the rolling process, the roller may experience a harmful deformation zone due to the influence of large rolling forces, thermal convexity, wear, etc.
(2) Due to issues with the material or casting of the roller, significant wear and tear may occur during use, and accidents can also cause the end of the roller to peel off, resulting in severe uneven stress on the strip and lateral bending.
(3) The loose fixation of the roller guide and the large gap between the roller bearing seat and the frame window can also cause lateral movement of the roller.
l Preventive Measures
1. Strictly implement the heating system to ensure the heating quality. During production, the heating system and the cooling system for stopping rolling must be strictly implemented. According to the rolling rhythm, the furnace temperature of each section should be reasonably controlled to ensure the rolling temperature and ensure uniform heating of the billet.
2. Ensure the surface quality and dimensional accuracy of the billet
Before loading, the surface of the billet should be inspected, surface defects should be removed in a timely manner, and dimensional accuracy should be ensured.
3. Reasonably set the roller gap
Reasonably adjust the reduction amount of each pass according to the rolling regulations, and the rolling speed must be adapted to the reduction amount. During the rolling process, the precision rolling unit maintains a small set of micro tension rolling, and the tension free micro pile rolling is maintained between the precision and rough rolling units. The single side difference of rough rolling shall not exceed 0.5mm, and the single side difference of finish rolling shall not exceed 0.03mm
4. Correct selection of roller material and reasonable design of roller shape
Calculate the bending deflection of the support roll and design the roll shape reasonably based on the size of the harmful deformation zone of the roll during the rolling process. Change to a stepped transition at both ends of the support roller. In addition, the material of the roller should be reasonably selected to reduce surface wear of the roller and minimize harmful deformation areas as much as possible. During hot rolling, the surface of the roller is subjected to both high temperature and water quenching, resulting in working stress, thermal stress, and fatigue stress that can cause cracks on the roller surface. Moreover, due to the large rolling force on the surface of the roller, it is prone to wear and tear. Therefore, the work roll adopts cast iron roll and increases the alloy content to improve the hardness of the roll. The hardness control range is HS68~80. Due to the large pressure of metal on the hot rolled work roll being transmitted to the support roll, the support roll should withstand large bending stress and have good rigidity to reduce the elastic deformation of the work roll. For this reason, forged steel rollers are generally used as support rollers, mainly by increasing the Cr content to improve their hardness value. Control the hardness between HS55~65
5. Ensure smooth equipment installation
The fixing of the guide device of the rough rolling mill is done using an inclined iron method instead of screws. During installation, first weld a skew iron on the upper surface of the rolling mill guide device. After the guide is installed into the rolling mill, determine the fixed position of another skew iron according to the position of the guide. When installing on the memorial archway, it is required to deviate from the lower skew iron by 5~10mm. In this way, the guide device is firmly fixed. To ensure the clearance between the roll bearing pedestal and the rolling mill memorial archway, the wear of the sliding plate of the memorial archway should be checked regularly to ensure that the roll is assembled in place and the roll is up and down; There is no movement left or right.
6. Reasonable roll changing system
Timely replacement of rolls is an effective means to avoid excessive wear of rolls. A reasonable number of roll changing supports should be determined based on the type and specification of steel being rolled. Ensure that the rollers are replaced in a timely manner before serious damage occurs. Pay attention to observation during the production of traditional Chinese medicine. If a large number of cracks or severe wear occur before the number of rollers is changed, it should also be replaced in a timely manner to avoid affecting the shape of the plate.
l Plate Shape Control Can be Approached from the Following Three Aspects
1. Continuously optimize the roll shape, reduce the presence of harmful materials, select appropriate roll materials, ensure roll quality, and reduce roll wear.
2. Continuously improve the operational level to ensure the accuracy of rolling mill adjustment
3. Continuously improve equipment and optimize processes to ensure a good operating environment for the board and strip.
Post time: Oct-16-2023