In recent decades, with the advancement of continuous casting technology and the improvement of online computer-controlled rolling automation, the H-beam production process has become increasingly mature. The rolling process from special-shaped billets to finished products is limited by conditions such as relatively low temperature of the rolled piece and poor plasticity of the metal. The first thing is to prevent lateral metal flow during the rolling process. The method is to ensure that the diameter ratio of the drive horizontal roller and the driven vertical roller of the frame is controlled at 3:1. At the same time, when designing the hole type and adjusting the rolling mill, it is necessary to ensure that the extension of the legs and waist of the rolled piece is consistent, otherwise it will affect the accuracy of the finished product size and the integrity of the appearance.
1. Rolling marks
Rolling marks are generally divided into two types, namely periodic rolling marks and non-periodic rolling marks.
Periodic rolling marks are regularly distributed on H-beams. The front and rear rolling marks appear in the same part of the rolled piece and the same depth. The distance between the two is exactly equal to the circumference of the roller where they are located. Periodic rolling marks are bulges or pits on the surface of the rolled piece caused by the loss of meat from the roll or the presence of iron oxide in the hole type.
Non-periodic rolling marks are caused by the serious wear of the guide device or the collision of mechanical equipment such as the roller, which causes the steel to be scratched and then rolled, and then the steel surface is formed with grooves or missing meat. Most of them are distributed along the rolling direction.
2. Folding
Folding is a common defect similar to cracks. After pickling, it can be clearly seen that there is a crack in the cross section of the folding part that is connected to the outside world. Folding is caused by improper hole design or improper adjustment of the rolling mill. The ears are formed at the hole opening due to overfilling. After rolling, the ears are pressed into the body of the rolled piece, but they cannot be welded with the body. The depth depends on the height of the ears. In addition, improper design or severe wear of the arc between the waist and the legs will cause grooves and edges on the surface of the rolled piece, and then rolling will also form folds.
3. Waves
H-shaped steel waves can be divided into two types: one is the waist wave with a washboard shape at the waist; the other is the leg wave with crests and troughs at the leg ends. Both types of waves cause damage to the appearance of H-shaped steel. Waves are caused by the inconsistent elongation of various parts of the rolled piece during the hot rolling process. When the waist is pressed down too much, the waist extends too much, while the leg extends little, thus forming waist waves, and in severe cases, the waist can be torn. When the leg extends too much and the waist extends little, leg waves are generated. There is another reason that can also form waves. That is, when the design ratio of the steel section, especially the waist thickness and leg thickness, is unreasonable, during the cooling process of the steel, the thinner part cools first and the thicker part cools later. Under the action of the temperature difference, a large thermal stress is formed inside the steel, which will also cause waves. The solution to this problem is: first, the hole type should be reasonably designed to try to complete the uneven deformation in the first few passes; in the finishing pass, strive to make the waist and leg extensions of each part of the H-shaped section consistent; to reduce the temperature difference between the waist and the leg, the leg of the rolled piece can be sprayed after the finished hole to accelerate the cooling of the waist, or vertical cooling operation can be adopted.
4. Rounded corners at the leg ends
The rounded corners at the leg ends of H-shaped steel refer to the unevenness between the leg ends and the two sides of the leg, and the contour is less meaty than the standard section, failing to fill the entire leg end. There are several reasons for the rounded corners at the leg ends: one is that the cutting hole of the blanking machine is worn, and the leg parts rolled out become thicker. When entering the next hole, the leg ends cannot be processed well due to the wedge effect; the second is that during the rolling of the unit, due to the mismatch between the frame and the edge rolling machine speed, the steel pulling phenomenon caused by excessive tension occurs, so that the leg parts of the rolled pieces cannot reach the required height, so that the leg ends cannot be processed vertically in the edge rolling hole, and the rounded corners at the leg ends will also be formed; the third is that the web plate on the side of the population is offset during the entire rolling process, causing the rolled pieces to deviate from the symmetric axis of the hole when biting A, and the above defects will also occur at this time.
5. Asymmetric leg length
There are two types of asymmetric leg lengths of H-shaped steel: one is that the upper leg is longer than the lower leg; the other is that one leg is longer on the upper leg and the other leg is longer on the lower leg. Generally, leg length asymmetry is often accompanied by uneven leg thickness, with the longer leg being slightly thinner and the shorter leg being thicker. There are several reasons for leg length asymmetry: one is that during the billet opening process, the billet is not aligned with the hole type when cutting deep, resulting in a cut deviation, making one leg of the shaped billet thicker and the other thinner. Although the reduction is reasonably distributed in the subsequent rolling process, it is difficult to correct, and eventually the leg length asymmetry is formed; the other is the horizontal roll bundle alignment of the rolling mill. Axial misalignment causes serious uneven lateral pressure of the vertical roll on the leg, resulting in diagonally distributed leg length asymmetry.
1. Rolling marks
Rolling marks are generally divided into two types, namely periodic rolling marks and non-periodic rolling marks.
Periodic rolling marks are regularly distributed on H-beams. The front and rear rolling marks appear in the same part of the rolled piece and the same depth. The distance between the two is exactly equal to the circumference of the roller where they are located. Periodic rolling marks are bulges or pits on the surface of the rolled piece caused by the loss of meat from the roll or the presence of iron oxide in the hole type.
Non-periodic rolling marks are caused by the serious wear of the guide device or the collision of mechanical equipment such as the roller, which causes the steel to be scratched and then rolled, and then the steel surface is formed with grooves or missing meat. Most of them are distributed along the rolling direction.
2. Folding
Folding is a common defect similar to cracks. After pickling, it can be clearly seen that there is a crack in the cross section of the folding part that is connected to the outside world. Folding is caused by improper hole design or improper adjustment of the rolling mill. The ears are formed at the hole opening due to overfilling. After rolling, the ears are pressed into the body of the rolled piece, but they cannot be welded with the body. The depth depends on the height of the ears. In addition, improper design or severe wear of the arc between the waist and the legs will cause grooves and edges on the surface of the rolled piece, and then rolling will also form folds.
3. Waves
H-shaped steel waves can be divided into two types: one is the waist wave with a washboard shape at the waist; the other is the leg wave with crests and troughs at the leg ends. Both types of waves cause damage to the appearance of H-shaped steel. Waves are caused by the inconsistent elongation of various parts of the rolled piece during the hot rolling process. When the waist is pressed down too much, the waist extends too much, while the leg extends little, thus forming waist waves, and in severe cases, the waist can be torn. When the leg extends too much and the waist extends little, leg waves are generated. There is another reason that can also form waves. That is, when the design ratio of the steel section, especially the waist thickness and leg thickness, is unreasonable, during the cooling process of the steel, the thinner part cools first and the thicker part cools later. Under the action of the temperature difference, a large thermal stress is formed inside the steel, which will also cause waves. The solution to this problem is: first, the hole type should be reasonably designed to try to complete the uneven deformation in the first few passes; in the finishing pass, strive to make the waist and leg extensions of each part of the H-shaped section consistent; to reduce the temperature difference between the waist and the leg, the leg of the rolled piece can be sprayed after the finished hole to accelerate the cooling of the waist, or vertical cooling operation can be adopted.
4. Rounded corners at the leg ends
The rounded corners at the leg ends of H-shaped steel refer to the unevenness between the leg ends and the two sides of the leg, and the contour is less meaty than the standard section, failing to fill the entire leg end. There are several reasons for the rounded corners at the leg ends: one is that the cutting hole of the blanking machine is worn, and the leg parts rolled out become thicker. When entering the next hole, the leg ends cannot be processed well due to the wedge effect; the second is that during the rolling of the unit, due to the mismatch between the frame and the edge rolling machine speed, the steel pulling phenomenon caused by excessive tension occurs, so that the leg parts of the rolled pieces cannot reach the required height, so that the leg ends cannot be processed vertically in the edge rolling hole, and the rounded corners at the leg ends will also be formed; the third is that the web plate on the side of the population is offset during the entire rolling process, causing the rolled pieces to deviate from the symmetric axis of the hole when biting A, and the above defects will also occur at this time.
5. Asymmetric leg length
There are two types of asymmetric leg lengths of H-shaped steel: one is that the upper leg is longer than the lower leg; the other is that one leg is longer on the upper leg and the other leg is longer on the lower leg. Generally, leg length asymmetry is often accompanied by uneven leg thickness, with the longer leg being slightly thinner and the shorter leg being thicker. There are several reasons for leg length asymmetry: one is that during the billet opening process, the billet is not aligned with the hole type when cutting deep, resulting in a cut deviation, making one leg of the shaped billet thicker and the other thinner. Although the reduction is reasonably distributed in the subsequent rolling process, it is difficult to correct, and eventually the leg length asymmetry is formed; the other is the horizontal roll bundle alignment of the rolling mill. Axial misalignment causes serious uneven lateral pressure of the vertical roll on the leg, resulting in diagonally distributed leg length asymmetry.
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