Four-roll steel plate rolling machines find widespread applications in various industries, including pressure vessels, deep submersibles, wind power, and defense. The working principle of these machines involves a three-point forming process to achieve circular bends. During the three-roll plate rolling process, frequent switching of the elevation of the front and rear rolls is required, making the process complex. Additionally, the influence of the sheet metal’s gravity during the switch can cause deformation in the curved arc. In contrast, four-roll steel plate rolling machines utilize four rolls, eliminating the need for front and rear roll switching and reducing bending moment effects, resulting in improved efficiency and better forming quality.

## Theoretical Process of Four-Roll Plate Bending Machines

Four-roll plate rolling machines have different rolling processes for varying sizes of sheet metal, but their working principles remain similar. The upper and lower rolls act as driving wheels, while the side rolls serve as driven wheels. The forces exerted by the upper and lower rolls drive the sheet metal, while the friction between the side rolls and the sheet metal creates opposing forces along the tangential direction. During bending, the upper and lower rolls clamp the sheet metal to ensure continuous and stable bending deformation under the influence of roll frictional forces.

## Force Analysis of Three-roller Work Roll-bending Forming Process of Four-roller Plate Rolling Machine

The working principle of the four-roller plate rolling machine is to make the plate form a circle under force at three points.

The left roller rises and contacts the pre-bent rolled sheet, and the pre-bent rolled sheet has a certain curvature, so the displacement of the left roller is different from the displacement of the right roller during pre-bending. In Figure 1, A is The contact point between the upper roller and the plate, and B is the contact point between the lower roller and the plate. The mechanical form of the four-roll plate rolling machine during work is similar to that of the asymmetrical three-roll steel plate rolling machine. When the right end of the plate is driven by the upper and lower rollers to move to After approaching point A, it is necessary to lower the left roller and raise the right roller, and repeatedly lift the left and right rollers until the arc meets the process requirements.

As shown in Figure 2, because the upper and lower rollers clamp the plate with its own gravity factor, when the left roller is completely unloaded, the center of gravity of the plate and the upper and lower rollers form a lever phenomenon, and the bending moment formed at the same time causes bending deformation. main factor. Because the external force is greater than the yield strength of the plate, plastic deformation will occur near the B end, which will affect the forming quality of the arc.

## Force Analysis of Four-roller Working Roll-bending Forming Process of Four-roller Plate Rolling Machine

The four-roller steel plate rolling machine works with four rolls. Its working principle is to make the plate be rounded by two three-point forces. The left roller rises and contacts the pre-bent rolled sheet, and the pre-bent rolled sheet has a certain curvature, so the displacement of the left roller is different from that of the right roller during pre-bending, and the right roller also Rise to the same height as the left roller.

In Fig. 3, A is the contact point between the left roller and the sheet, B and C are the contact points between the lower roller and the sheet, and point D is the contact point between the right roller and the sheet. The mechanical form of the four-roller bending process of the four-roller steel plate rolling machine is similar to that of two asymmetrical three-roller plate bending machines. When the plate moves to the vicinity of point B or C under the drive of the upper and lower rollers, the left side does not need to be lowered. The roller and the right roller can directly raise the height of the left and right rollers until the arc of the sheet meets the process requirements.

### Conclusion

As shown in Figure 3, because the upper and lower rollers clamp the plate, the plate has its own gravity factor, the center of gravity of the plate, and the lever phenomenon formed by the upper and lower rollers, because the left and right rollers are not completely unloaded, and the A and D points of the left and right rollers play a supporting role. The bending moment of the self-weight of the plate is reduced, and the influence of the self-weight of the plate on the bending deformation of the plate is eliminated. Because the bending moment of self-weight is less than the yield strength of the plate, the plate will not undergo plastic deformation near the A and D ends, and the forming quality of the plate is guaranteed at the same time.

## The difference between the two bending methods of the four-roll plate rolling machine

The difference between the three rollers of the four-roller plate bending machine and the force of the four-roller plate is different. From Figure 1, it can be seen that when the three rollers of the four-roller plate bending machine are working, the upper work roll, the lower work roll, and one side work roll form a force. In the system, the plate undergoes plastic deformation under the action of an external force in the deformation zone.

It can be seen from Figure 3 that when the four work rolls of the four-roll steel plate rolling machine are working, two force systems are formed by the upper work roll, the lower work roll, and the two side work rolls. The plate is subjected to two external forces in the deformation zone. Under plastic deformation.

The processing curvature of the sheet is fixed, and when the three rollers are working, the external force on the sheet is F1 to achieve the required processing curvature.

When the four rollers are working, the external forces on the plate are respectively F_{2 }and F_{3} to achieve the required processing curvature.

It can be assumed that F_{1} ×L_{1}=F_{2} ×L_{2}+F_{3} ×L_{3} is deduced, because the position of the upper and lower rollers of the four-roller plate bending machine is fixed, so the distance L_{2} from the left roller to the center of the lower roller and the distance from the right roller to The distance L_{3} of the center of the lower roller is equal to L_{2}=L_{3}, F_{1}L_{1}=(F_{2}+F_{3})L_{2}, so the force system of F_{1} is equal to the force system of F_{2} and F_{3}.

### Conclusion

Four-roll plate bending machines offer distinct advantages over their three-roll counterparts in terms of efficiency and forming quality. The force analysis during bending reveals that the four-roll machines utilize two force systems to achieve the desired curvature, reducing the influence of the sheet metal’s weight on deformation. This ensures precise and high-quality bending processes, making four-roll steel plate rolling machines a preferred choice for various industries.

## Test Analysis and Results

During the test, a Q235 plate with a thickness of 33 mm and a length of 7000 mm was used to set the radius of the arc to R4000 for the test, and the pressure of the upper and lower rollers was set to be fixed at 2.5 MPa.

### Three work rolls roll bending the sheet metal

The four-roller plate rolling machine has three working rollers to process the plate. The centered plate is pre-bent from left to right, and the height of the plate is 380 when the left roller is raised until it is just in contact with no deformation. The plate moves to the left until it is close to up and down. Roller and observe the forming size of the arc of the plate with the sample plate. The height of the left roller is 400 when the left roller is raised, and the height of the right roller is 400. The plate moves to the right until it is close to the upper and lower rollers. Move to the left, repeat the above operation process repeatedly until the side roller height value is 530 and the plate arc meets the process requirements. The processing time is 3 hours.

### Four work rolls roll bending the sheet metal

Four-roller steel plate rolling machine with four working rollers process the plate, pre-bend the centered plate left and right, then raise the left and right side rolls to a value of 380 when the plate is just in contact without any deformation, and move the plate to the left to fast Close to the position of the upper and lower rollers, use the arc template to observe the arc of the deformed sheet, and then raise the height of the left and right side rollers at the same time to a value of 390, and then move the sheet to the right to the position close to the upper and lower rollers, and continue to use the sample to adjust the arc of the sheet Observe that the height of the left and right side rollers is 400 at the same time, and the plate moves to the left. Repeat the above operation process until the height of the left and right side rollers is 460. The arc of the plate meets the process requirements. The processing time is 1.5h.

### Test Results

Through the actual operation process, it can be determined that the four-roller plate rolling machine cylinder plate processing, the work efficiency of the four-work roll processing method is significantly higher than the three-work-roll processing method, and the processing steps of the four-work roll are simpler and do not need to be repeated Lifting side rollers.

When the three rollers of the four-roller plate bending machine are working, as shown in Figure 2, when the plate is close to the upper and lower rollers, it is necessary to lower the left roller and raise the right roller. When the left roller falls to the point that it cannot provide any supporting force to the plate, the plate will exert a downward force FG on the plate that has undergone plastic deformation due to its own gravity, and at the same time, there will be no support force increase because the left roller has completely descended The bending moment of the gravity FG makes the original bending moment L1 become L. When the gravity FG bending moment of the sheet becomes larger than the yield strength of the sheet itself, the sheet will undergo plastic deformation near point B near the upper and lower rollers, forming a bending deformation opposite to the original.

When the four rolls of the four-roll plate bending machine are working, as shown in Figure 4, when the plate is close to the upper and lower rolls, there is no need to lower the two side rolls. The sheet bending moments L4 and L5 are smaller than the bending moment L in Fig. 2, because there are front and rear rollers as support points to make the bending moment smaller, which reduces the opposite bending deformation of the sheet due to excessive bending moments.

## Conclusion

- The four-roller plate rolling machine adopts four work rolls to process the cylindrical plate, and the test proves that the method is feasible.
- The four-roll plate rolling machine rolls cylindrical plates and the four-work-roll processing method is significantly more efficient than the three-work-roll processing method, and the steps are simple while reducing the use time of the equipment and increasing the service life of the equipment.
- The four-roller steel plate rolling machine adopts four working rolls for processing cylindrical plates. Because the front and rear rolls are used as support points, the bending moment becomes smaller, which reduces the influence of excessive bending moments on the plate and improves work efficiency and plate quality. molding quality.

**Works Cited:** Processing method of cylindrical plate with four-roller plate rolling machine. Wang Qiushi, Zhang Qiurui, Zhang Xin, Lian Jun, Zhang Zhiming – 2021