In order to conduct an in-depth analysis of the load distribution between rows of support roller rolling bearings in a four-high plate and strip rolling mill, the changing rules of plate crown and the relationship between the two, the radial load distribution of the cylindrical roller bearings in each row of the support rolls of a laboratory four-high plate and strip rolling mill was analyzed. , the transverse thickness distribution and plate crown of the rolled piece were detected and analyzed. The research results can provide useful reference for the use of rolling bearings in plate and strip rolling mills and the establishment of plate shape analysis models.
Keywords: rolling bearing; load test; plate shape; strip rolling mill
With the advancement of plate and strip rolling technology, the rolling process is developing in the direction of large-scale, continuous and high-speed, and the production efficiency and product quality of rolling mills are constantly improving. As the main model of the four-high rolling mill for plate, strip and foil production, the work roll bearings are rolling bearings, and the back-up roll bearings are rolling bearings or oil film bearings. Due to the influence of factors such as technology and equipment, the stress on the roll bearings during the rolling process is affected. quite complicated. Literature research shows that uneven load distribution and serious eccentric load among multi-row rolling bearing rows are important factors affecting bearing life. Most finite element simulations and simplified calculation methods treat bearing loads as concentrated loads or simple uniform loads, making the rolling stock The prediction accuracy of the plate shape deviates from the actual situation. This study used a self-designed four-row experimental rolling mill support roll four-row cylindrical roller bearing force and temperature comprehensive testing device to test the load distribution of each row of cylindrical roller bearings during the rolling process, and analyzed the reduction rate, thickness The research results can provide useful reference for the use of rolling bearings and the establishment of plate shape analysis models.
Experimental research
Theoretical and experimental research on the radial load distribution of roll bearings shows that during the rolling process, the radial load of the bearing is distributed in a cosine law within an arc range corresponding to the bearing central angle of approximately 120°. In order to measure the actual distribution of bearing load between rows, a comprehensive test device for bearing force and temperature of the support roll under the four-high plate and strip mill was designed. A groove with a width of 148mm was processed along the axial direction of the roll in the load-bearing area corresponding to the bearing seat. In the groove Four pressure blocks that can move up and down are installed at positions corresponding to each row of cylindrical roller bearings. The upper arc part of each pressure block is in contact with the outer ring of the corresponding row of bearings (as shown in Figure 1(a)). The boring holes of the bearing box together form the inner hole of the bearing seat with a diameter of 170mm. Two symmetrically arranged counterbores are processed at the bottom of the pressure block for installing two radial pressure sensors. During the rolling process, the bearing is stressed and transmits the pressure to the outer ring of the bearing. The outer ring of the bearing transmits the pressure to the pressure block. The pressure block deforms the radial pressure sensor after being compressed. The radial force endured by the two pressure sensors and That is the actual radial force on the bearings in this row.
In order to facilitate the recording and analysis of the bearing load distribution, each row of cylindrical roller bearings or pressure blocks is numbered. The bearing with the driving side farthest from the roller body is the first row, and the bearings with the driving side farthest from the roller body are in sequence. Second, third, and fourth rows, the bearing closest to the roller body on the operating side is the fifth row, and as the distance from the roller body increases, it is the sixth, seventh, and eighth rows. The specific numbers of the bearings or pressure blocks in each row are as shown in the figure. As shown in 1(b).
Figure 1 Combined rolling bearing force and temperature testing device
The rolling experiment was conducted on a laboratory four-roller reversible cold rolling mill (as shown in Figure 2). The main equipment parameters are as follows: the work roll size is φ100×320mm, the support roll size is φ220×320mm; the main motor power is 90kW, and the rotation speed is 1500~2800r/min; hydraulic cylinder pressing speed 5mm/s; coiling/uncoiling tension 0.5~20kN; maximum rolling force 1200kN; rolling speed 0~60 m/min; raw material thickness ≤6mm; finished product thickness ≥0.2mm.
The experimental material is: H24 pure aluminum plate with a thickness of 2mm and a uniform thickness distribution. The experimental plan is as follows: the specimens with a length of 250mm and widths of 80mm, 120mm, 160mm, 200mm, 240mm and 300mm are rolled for experiments, and the set reduction rates are all 40%; specimens with a length of 250mm and a width of 240mm are used for rolling experiments. Rolling experiments were carried out and the reduction rates were set to 10%, 20%, 30%, 40% and 50% respectively. The rolling speeds are all 0.2m/s. Process the radial pressure sensor output data collected by the data acquisition instrument during the rolling process to obtain the radial load distribution of each row of bearings, and measure the thickness distribution of the aluminum plate along the plate width after rolling, and then obtain the plate crown of the aluminum plate.
Figure 2 Four-high plate and strip experimental rolling mill
Analysis of radial load distribution between bearing rows
In order to analyze the uneven degree of radial load distribution among the bearings in each row, the bearing load percentage α(i) is defined as the proportion of the radial load of the i-th row bearing to the total radial load, that is: α(i)=F(i) /F×100%.
In the formula, α(i) is the bearing load percentage of the i-th row bearing, F(i) is the radial load of the i-th row bearing, and F is the total radial load.
Effect of reduction rate on radial load distribution
When the widths are the same, the changes and distribution of the radial load of each row of bearings with the reduction rate are shown in Figure 3. It can be seen from Figure 3(a) that as the reduction rate increases, the radial load of each row of bearings basically increases linearly. This is the result of the increase in the reduction rate leading to an increase in the total rolling force. It can be seen from Figure 3(b) that the bearing percentage of the radial load between the bearing rows is generally distributed in an “M” shape. The second and seventh rows of bearings where the bearing seat fulcrum is located have the largest bearing percentage, exceeding 25%, close to the fulcrum. The bearings in the first, third, sixth and eighth rows have a larger load-bearing percentage, while the bearings in the fourth and fifth rows away from the fulcrum have the smallest load-bearing percentage, less than 5%; when the reduction rate is less than 43%, As the reduction rate increases, the bearing load percentages of the second and seventh rows gradually decrease. When the reduction rate is greater than 43%, as the reduction rate increases, the bearing load percentages of the second and seventh rows increase. Large; as the reduction rate increases, the bearing load percentage of the first, second, seventh, and eighth rows changes significantly, that is, the radial load distribution of the bearings mainly occurs at the fulcrum position and away from the rolling center line Between the two rows of bearings, the bearing load percentage of the other rows of bearings changes slightly. This is because the deflection and flattening deformation of the support roller are the main reasons for the uneven load distribution of the bearings in each row. When the reduction rate is less than 43%, the deflection of the support roller becomes larger as the reduction rate increases. Due to the Due to the self-positioning adjustment effect of the cylindrical pads in the second and seventh rows, the bearing load percentage of the second and seventh rows gradually decreases, while the bearing load percentage of the first and eighth rows gradually increases. When the reduction rate is greater than 43 %, the total rolling force is basically close to the maximum rolling force of the rolling mill, and the self-positioning adjustment effect of the cylindrical pad is reduced, causing the load-bearing percentage of the second and seventh rows of bearings to increase.
Figure 3 Changes and distribution patterns of radial load with reduction rate during rolling process
Effect of plate width on radial load distribution
When the incoming material thickness and reduction rate are the same, the variation and distribution of the radial load of each row of bearings with the plate width are shown in Figure 4. It can be seen from Figure 4(a) that the radial load of the bearings in each row increases with the increase in the width of the rolled piece. The growth rate of the radial load of the second and seventh row bearings slows down as the plate width increases. The radial load of the first and eighth row bearings basically increases linearly, while the radial load of the third, fourth, fifth and sixth row bearings does not change much. It can be seen from Figure 4(b) that the bearing percentage of the radial load between the bearing rows is generally distributed in an “M” shape. As the width of the rolled piece increases, the bearing percentages of the first and eighth rows gradually increase, and the bearing percentages of the remaining rows gradually increase. The bearing load percentage gradually decreases, but the change in the fourth and fifth row bearings is small, that is, the load unevenness between rows is decreasing. This is because the degree of deflection and flattening deformation of the support roll is the main reason for the uneven distribution of the bearing load. When the thickness of the incoming material and the reduction rate are the same, the rolling force increases in proportion to the width of the rolled piece, making the support The deflection deformation of the roller becomes larger, but at this time the action range of the rolling force also becomes wider, which in turn makes the deflection of the support roller smaller. The above phenomenon is the result of the combined effect of the two.
Figure 4 Changes and distribution patterns of radial load with plate width during rolling
Analysis of influencing factors of plate convexity
Effect of reduction rate on plate crown
When the width is the same, the changes in transverse thickness distribution and plate crown of the rolled piece with reduction rate are shown in Figure 5. It can be seen from Figure 5(a) that the rolled piece after rolling has relatively obvious uneven deformation along the width direction, and the rolled piece changes from the rectangular cross-section before rolling to a convex cross-section. It can be seen from Figure 5(b) that as the reduction rate increases, the plate crown first increases and then decreases. When the reduction rate is 30%, the plate crown reaches the maximum value. The deflection deformation of the work roll is the main factor affecting the shape of the roll gap and the crown of the rolled piece, and the factors affecting the deflection deformation of the work roll are mainly the rolling force and the pressure between the rolls. For aluminum plates of the same original thickness, when the width of the rolled piece is the same , the rolling force is proportional to the reduction rate, and the pressure between the rolls mainly depends on the coordinated deformation between the work roll and the support roll. In the experimental rolling mill studied in this article, the roll diameter ratio of the backup roll to the work roll is 2.2, which reaches the upper limit of the roll diameter ratio of the plate and strip mill. That is, the stiffness of the backup roll is large. When the reduction rate is less than 30%, the rolling force Small, the deflection deformation of the support roll is small, and the pressure range between the rolls is mainly concentrated in the middle area of the roll; at this time, as the reduction rate increases, the deflection of the work roll caused by the increase in rolling force increases It plays a major role, so the plate convexity increases; it can be seen from Figure 3(a) that the difference in load between the first row and the third row of bearings near the fulcrum in the bearing seat does not change much, which also indicates that the support roller is deflected and deformed. smaller. When the reduction rate is greater than 30%, the rolling force is large, and the support roller undergoes obvious deflection deformation. As the reduction rate continues to increase, the deflection of the support roller becomes larger. As the rolling force increases, the roller The range of pressure between the two becomes wider. Under the combined effect of the two, the deflection deformation of the work roll becomes smaller, resulting in a reduction in the plate convexity. As can be seen from Figure 3(a), the first part of the bearing seat close to the fulcrum The difference in load load between the bearings in the row and the third row becomes larger, indicating that the support roller has undergone greater deflection deformation.
Figure 5 Changes in transverse thickness distribution and plate crown with reduction rate after rolling
Effect of plate width on plate crown
When the reduction rate is the same, the changes in the transverse thickness distribution of the rolled piece and the plate crown with the plate width after rolling are shown in Figure 6. It can be seen from Figure 6(a) that the rolled piece after rolling has relatively obvious uneven deformation along the width direction, and the rolled piece changes from the rectangular cross-section before rolling to a convex cross-section. It can be seen from Figure 6(b) that as the plate width increases, the plate convexity first decreases, then increases and decreases again. The minimum value appears at the plate width of 120mm, and the maximum value appears at the plate width of 240mm. at. The crown of the rolled piece is mainly determined by the deflection deformation of the work roll caused by the rolling force and the pressure between the rollers. For the same original thickness of the aluminum plate, when the reduction rate is the same, the rolling force is proportional to the width of the rolled piece. When the width of the rolled piece is small and the reduction rate is large, the rolling force is small. As the width of the rolled piece increases, the rolling force increases, causing the deflection deformation of the work roll to increase, but at the same time the rolling force decreases. The scope of action is also widened, which reduces the elastic deformation of the work roll, and the deflection deformation of the support roll is also small at this time. The pressure between the rolls is also mainly concentrated in the middle area of the rolls, resulting in a convex plate when the width of the rolled piece is 120mm. degree reaches the minimum value; as the width of the rolled piece continues to increase, the rolling force continues to increase, causing a certain degree of deflection deformation of the support roll, but at this time the impact of the rolling force on the deflection deformation of the work roll increases. Still plays a major role, so the plate crown increases again. When the width of the rolled piece is 240 mm, the plate crown reaches the maximum value; when the width of the rolled piece further increases, the rolling force continues to increase, but at this time the rolling force The range of action becomes wider, and the support roller also undergoes obvious deflection deformation, and the plate convexity begins to decrease again. As can be seen from Figure 4(a), the first and third rows in the bearing seat close to the fulcrum The difference in bearing load load becomes larger, indicating that the support roller has undergone greater deflection deformation.
Figure 6 Transverse thickness distribution and plate crown changes with plate width after rolling
Effect of plate thickness on plate crown
In order to analyze the influence of plate thickness on plate crown, H24 pure aluminum plates with a width of 240mm, thicknesses of 2mm, 3mm and 5mm and uniform thickness distribution were tested at a set reduction rate of 30%. Rolling experiment (actual reduction rates are 30%, 32%, and 30% respectively). The transverse thickness distribution of the rolled piece after rolling and the change of plate crown with plate thickness are shown in Figure 7. It can be seen from Figure 7(a) that the rolled piece after rolling has relatively obvious uneven deformation along the width direction, and the rolled piece changes from the rectangular cross-section before rolling to a convex cross-section. It can be seen from Figure 7(b) that the plate crown increases as the original thickness of the rolled piece increases.
Figure 7 Transverse thickness distribution and plate crown changes with plate thickness after rolling
This is because the width of the rolled piece and the reduction rate are basically the same. As the original thickness of the rolled piece increases, the reduction increases. Although the rolling force per unit width increases, resulting in a smaller impact on the plate crown, the rolling force The increase in the deflection of the work roll plays a leading role in the influence of the plate crown, so the plate crown continues to increase, but the increasing trend gradually slows down.
Conclusion
(1) The original thickness of the rolled piece is the same. When the reduction rate or the width of the rolled piece increases, the load between the bearing rows generally shows an increasing trend, and the load-bearing percentage between the bearing rows shows an “M”-shaped distribution. The bearings in the seventh row have the largest load-bearing percentage, the bearings in the first, third, sixth and eighth rows close to the fulcrum have a larger load-bearing percentage, and the bearings in the fourth and fifth rows far away from the fulcrum have the smallest load-bearing percentage.
(2) As the reduction rate increases, the bearing load distribution mainly occurs between the second and seventh row bearings at the fulcrum position and the first and eighth row bearings away from the rolling center line. The load percentage of the remaining rows of bearings changes slightly. ; As the width of the rolling stock increases, the bearing load percentages of the first and eighth rows gradually increase, and the bearing load percentages of the remaining rows gradually decrease, but the bearing load percentages of the fourth and fifth rows change slightly.
(3) Due to the large stiffness of the support roller, when the reduction rate is small, the deflection deformation of the support roller is small. As the reduction rate increases, the deflection deformation of the support roller gradually becomes larger, and the pressure distribution between the rollers changes significantly. , under the combined effect of rolling force and pressure between rollers, the crown of the rolled plate first increases and then decreases.
(4) When the width of the rolled piece is small, the rolling force distribution has a greater impact on the deflection of the work roll. When the width of the rolled piece is larger, the impact of the rolling force on the deflection of the work roll becomes greater. As the width of the rolled piece increases, increases, and after the support roller deflects significantly, the pressure distribution between the rollers also changes significantly. Under the combined effect of the above factors, the plate crown first decreases, then increases and then decreases; when the reduction rate and When the width of the rolled piece is basically the same, the plate crown shows an increasing trend as the thickness of the rolled piece increases.
