Steel plate rolling machines are widely used in industries such as pressure vessels, deep submersibles, and national defense. It is related to people’s lives and property safety. The influence of the pressure between the upper and lower rollers on the forming speed of the plate is analyzed, and the ductility (thickness) of the plate after forming is analyzed. Influence, the impact on the ductility (length) of the sheet after the sheet is formed and the effect on the quality of the sheet forming. Determine the pressure range to ensure the quality of the plate. If the thickness of the plate becomes thinner by one millimeter, people’s lives and property will be in danger.
The theoretical process of roll bending
The four-roll plate rolling machine has different roll bending processes for bending plates of different sizes, but its working principle is basically the same.
The upper and lower rollers are driving wheels, and the rollers on both sides are driven wheels. The upper and lower rollers drive the force acting on the sheet, which is the displacement force of the sheet. The side rollers generate frictional resistance to the tangential force of the sheet, and the direction is along the direction of tangential displacement. the opposite direction. During bending, the upper and lower rollers clamp the sheet to ensure continuous and stable bending deformation of the sheet driven by the friction force of the rollers. When rolling and bending, the plate undergoes elastic-plastic deformation under the action of external force in the deformation zone, and the plate rebounds after leaving the deformation zone. However, due to the plastic deformation, the plate can still maintain the corresponding radius of curvature after rebounding.
The influence of pressure on the quality of plate forming
The forming equipment of this test uses a four-roller steel plate rolling machine, and a 31mm thick Q235 plate is used in the test to analyze the influence of different pressures on the forming quality of the plate.
Figure 1: Formed shapes of plates tested under pressure of 2 MPa, 4MPa, and 6MPa
The position of the side rolls is set to 580, and the pressure of the upper and lower rolls is respectively set to three different pressure values of 2MPa, 4MPa, and 6MPa. According to the forming ability of the steel plate rolling machine, test forming a plate with a radius of 1650mm, form a plate with the same material and the same radius (bending radius), observe and measure the bending and forming of the plate under different pressures.
Effect of pressure on sheet elongation
Before processing, measure the thickness of the plate and mark 10 points A, B, C, D, E, and F on the plate. Use the pressure values of 2MPa, 4MPa and 6MPa on the upper and lower rolls to process the plate respectively. After the process is completed, measure the marked points twice and record and analyze the influence of the pressure value on the ductility (thickness) of the plate. When the pressure of the upper and lower rollers is 2MPa, the average thickness difference before and after processing is 0.03mm, and when the pressure of the upper and lower rollers is 4MPa, the average thickness difference between before and after processing is 0.11mm. When the pressure of the upper and lower rollers is 6MPa, the average thickness difference between before and after processing is 0.26mm.
Before processing, measure the length of the plate. Upper A, middle B, and lower C. Use the upper and lower rollers to process the plate with pressure values of 2MPa, 4MPa, and 6MPa respectively. After processing, take 2 measurements and record and analyze the impact of the pressure value on the ductility of the plate ( length).
The neutral layer of the plate after processing is defined as a rational neutral layer, the length tolerance of the upper, middle and lower sides of the plate before processing is defined as 0~2 mm, and the theoretical tolerance after processing is 0~10 mm.
The upper and lower roller pressure is 2MPa
When the pressure of the upper and lower rolls is 2MPa, the length of the plate before and after processing changes: before processing, the length of the plate is 12564mm, 12566mm, and 12565mm, and the actual length after processing is 12659mm, 12660mm, and 12658mm. The theoretical length after processing is 12657.34 mm. When the pressure of the upper and lower rollers is 2MPa, the average actual length of the plate after processing is 12659 mm, and the theoretical length after processing is 12657.34 mm. The sheet length is extended by 1.66 mm.
The upper and lower roller pressure is 4MPa
When the pressure of the upper and lower rollers is 4MPa, the length of the plate before and after processing changes: before processing, the length of the plate is 12565 mm at the top, 12566 mm at the center and 12565 mm at the bottom. The actual length after processing is 12666mm at the top, 12668mm at the middle and 126675mm at the bottom. The theoretical length after processing is 12657.34mm. When the pressure of the upper and lower rollers is 4 MPa, the average actual length of the plate after processing is 12659 mm, and the theoretical length after processing is 12657.34 mm. The sheet length is extended by 1.66 mm. When the pressure of the upper and lower rollers is 4MPa, the average actual length of the plate after processing is 12667.1 mm, and the theoretical length after processing is 12657.34 mm. Sheet length extended by 10.1 mm.
The upper and lower roller pressure is 6MPa
When the pressure of the upper and lower rollers is 6MPa, the length of the plate before and after processing changes: before processing, the length of the plate is 12566mm, 12565mm, and 12565mm; after processing, the actual length is 12683mm, 12682mm, and 12683mm, and the theoretical length after processing is 12657.34mm.
When the pressure of the upper and lower rollers is 6MPa, the average actual length of the plate after processing is 12682.6 mm, and the theoretical length after processing is 12657.34 mm. The sheet length is extended by 25.3 mm.
Test Analysis and Results
In order to study the forming shape and forming quality of the plate under different pressures of the upper and lower rollers, the test analyzes the bending and forming shape of the plate when the pressure values of the upper and lower rollers are 2, 4, and 6MPa respectively. The results are as above, and the forming conditions of the plate under different pressure values can be seen from the data. It is different. When the pressure value is 2MPa, the forming radius is significantly smaller than the forming radius when the pressure is 4MPa and 6MPa.
Data analysis
From the data analysis, it can be known that the changing trend of the plate under different pressure values is the same, that is, the radius of the plate forming is related to the pressure. When the pressure is 2MPa, the forming of the plate is relatively small. When the pressure gradually increases, the forming radius of the plate Gets smaller and smaller. When the pressure is 6MPa, it can be seen that the radius of the plate forming is relatively small, and the plate has completely undergone plastic deformation. Roll forming is a continuous loading process. It can be seen from Figure 1 that when the pressure increases from 2MPa to 6MPa, the plate undergoes a large deformation. Because the increase of pressure also increases the rolling force when the plate is rolled and bent, the increased rolling force on the plate makes the fluidity between the metals worse, the load on the plate is uneven, and the deformation is not sufficient. Therefore, changes in the size of the pressure affect the forming quality of the sheet.
Result
In order to study the change of the ductility of the sheet under different pressures of the upper and lower rollers, the test analyzes the ductility (length) and ductility (thickness) of the sheet before and after processing when the pressure values of the upper and lower rollers are 2, 4, and 6MPa respectively. It can be seen from the data that the sheets under different pressure values The ductility is different. When the pressure value is 2MPa, the elongation of the plate is significantly smaller than that of the pressure 4MPa and 6MPa. It can be seen from the above that the change trend of the sheet under different pressure values is the same, that is, the elongation of the sheet after forming is related to the pressure. When the pressure is 2MPa, the elongation of the sheet after forming is relatively small. When the pressure gradually increases, The amount of elongation after forming the sheet is increasing. When the pressure is 6MPa, it can be seen that the elongation of the plate after forming is greater, which has exceeded the tolerance range and affects the quality of the processed plate. At the same time, the part with a length exceeding the tolerance needs to be cut off. During the cutting process, due to high temperature, the processed plate will be damaged. The smoothness of the arc affects the product quality.
Epilogue
The forming radius of the plate decreases with the increase of the pressure of the upper and lower rolls. When the pressure of the upper and lower rolls is small, the change of the forming radius of the plate is small. When the pressure of the upper and lower rolls gradually increases, the change of the forming radius of the plate is larger. The molding quality is reduced.
The amount of change in ductility of the sheet is proportional to the pressure of the upper and lower rolls. The greater the pressure of the upper and lower rolls, the greater the elongation of the sheet after processing. Excessive pressure of the upper and lower rollers will affect the forming quality of the sheet, make the processed sheet thinner and longer, and affect the smoothness of the processed arc.
Determine the influence of the pressure of the upper and lower rollers on the elongation of the sheet, and lay the foundation for the realization of zero margin processing in the future.
Determine the correct pressure of the upper and lower rollers according to different plates, which can ensure the forming quality of the plates after processing. In the case of ensuring that the sheet is clamped during the processing, the pressure of the upper and lower rollers during the processing of the Q235 sheet with a thickness below 30mm can be less than 2MPa, which can ensure that the sheet has a small amount of elongation during the processing, and the thickness of the sheet will not occur. Big changes that can make pressure vessels safer.
Works Cited: The influence of the pressure of the four-roll plate rolling machine on the quality of the plate forming – Zhu Lianhai, Wang Qiushi, Zang Yongxin, Du Qiuyang, Xu Jin