The heavy-duty four roll plate rolling machine consists of an upper active roller, two lower clamping rollers, and two side arc adjustment rollers. It can complete centering → clamping → pre bending at both ends → rolling → rounding → unloading in one clamping operation, without excess straight edges. It is suitable for processing thick plates and pressure vessel cylinders. The operation includes eight core points: pre start inspection, clamping centering, pre bending process, rolling forming, rounding correction, shutdown unloading, safety standards, and fault prevention and control.
1、 Key points for pre startup inspection (mandatory for heavy-duty thick plates)
1. Equipment structure and lubrication
-Apply lubricating grease to the roller bearings, side roller guide rails, flip supports, and gearbox according to the lubrication table, without any oil shortage or dry grinding phenomenon;
-Check that there is no welding slag, burrs, or pits on the surface of the four work rolls. Clean the roll surface before processing thick plates to prevent pressure damage to the plates;
-Check that the rack, hydraulic cylinder, and connecting bolts are not loose, and that the locking buckle of the flip unloading support is intact.
2. Hydraulic system inspection
-The hydraulic oil level is within the standard range, and the oil temperature is at room temperature of 20-45 ℃. If it is below 10 ℃, preheat it without load for 10 minutes;
-Lift and lower the upper and lower rollers, lift and lower the rollers on both sides, and rotate forward and backward without crawling, abnormal noise, or leakage;
-The rated pressure of the system is set according to the nameplate, and heavy-duty machines are typically 20-25MPa. Overpressure operation is strictly prohibited.
3. Electrical and safety devices
-The emergency stop button, safety light barrier, limit switch, and overload alarm are all valid;
-Reset the buttons, encoder, and CNC screen to zero, and reset the travel of the rollers on both sides to zero;
-Multiple people cooperate to determine the commanding personnel in advance and unify the gesture signals.
4. Plate and load verification
-The thickness, width, and material of the board shall not exceed the rated processing parameters of the equipment, and overloading is strictly prohibited;
-High strength steel and stainless steel shall be used at 80% of the rated load, and thick plates shall not be subjected to a single large downward pressure;
-Clean up the debris around the workbench, inspect the lifting equipment and crane to ensure they are in good condition, and avoid hitting the rollers when lifting steel plates.
2、 Key points for board clamping and alignment operation (preventing wrong edges, conical shapes)
1. Placement of boards
The steel plate should be smoothly fed between the upper and lower rollers, with a clamping allowance of ≥ 30mm reserved at both ends of the plate. It is prohibited to feed the material in a suspended manner on one side.
2. Precise alignment (core)
-By relying on the side material blocking ruler and laser alignment, ensure that the centerline of the board is completely perpendicular to the axis of the roller, with a left-right deviation of ≤ 2mm;
-Slowly move the upper roller to drive the board to feed slightly, observe the synchronous feeding of the edges on both sides, and immediately stop the machine and re center if there is deviation;
-Thick sheet metal is supported by side pallets to prevent sagging and displacement.
3. Clamping control
The lower roller hydraulic lift clamps the steel plate, and the clamping force is based on the absence of slippage of the plate; Lightly press the thin plate and increase the clamping pressure for the thick plate, and do not loosen the clamping during the pre bending stage.
3、 Key points of end pre bending process (unique to four rollers, eliminating straight edges)
Heavy thick plates must be pre bent at both ends, with a pre bending length of ≥ 2 times the thickness of the plate, to avoid the two ends of the cylinder being straight and unable to close.
1. Front end pre bending
Clamp the sheet without moving, slowly lift the single-sided side roller, and cooperate with the rotation of the upper roller to press the sheet head to the target curvature; Gradually apply pressure in 2-3 stages, and do not apply pressure all at once.
2. Rear pre bending
The upper roller rotates in the opposite direction, sending the tail of the sheet to the cutting point between the rollers, and lifting the other roller to complete the pre bending of the tail end; The entire process of the board does not loosen or require flipping.
3. Pre bending control standards
-Carbon steel Q235/Q355: pre bent in 2 stages; High strength steel Q690 and stainless steel are divided into 3 passes;
-Compare with a curved template after pre bending, and control the allowance for straight edges;
-Observe that there are no cracks or wrinkles on the surface of the board. If there is any surface strain, immediately apply special lubricating medium to the roller surface.
4、 Key points of rolling forming operation (gradual pressure in different stages, anti rebound, elliptical)
1. Synchronous adjustment of side rollers
After the pre bending is completed, the left and right rollers are synchronously lifted to the same set height, and the CNC machine directly inputs the cylinder diameter and plate thickness to automatically calculate the stroke of the side rollers; The scale values on both sides of the manual model must be consistent.
2. Gradual Rolling with Divided Layers (Thick Plate Core)
Prohibit one-time downward molding and gradually reduce the bending radius through multiple passes:
-Step 1: Apply light pressure to form a gentle arc on the board, releasing the internal stress of the board;
-Steps 2-3: Increase the pressure of the side rollers to 60% of the rated load and reduce the radius of the cylinder;
-Final stage: 90% to 95% rated pressure, approaching the target diameter, with reserved rebound compensation.
3. Feed rate control
Run at a low speed of 5-10 r/min throughout the entire process, with thick plates and stainless steel running at a low speed throughout the entire process; High speed is strictly prohibited in the later stage of molding to prevent the cylinder from losing its roundness and the roller from being deformed by impact.
4. Real time measurement of the process
Stop the machine 1-2 times per cycle and measure the diameter of the cylinder using a radius template and tape measure; If the diameter is too large, lift the side roller slightly, and if it is too small, decrease it slightly. Adjust it before feeding again.
5. Material differentiation operation
-Ordinary carbon steel: mainly cold rolled, with small rebound;
-Stainless steel: Apply lubrication to the roller surface, increase rebound compensation, and avoid surface indentation;
-High strength alloy steel: reduce the amount of single compression, slow roll multiple times, and preheat if necessary to reduce the risk of stress cracking.
5、 Key points for circle correction operation (eliminating ellipses and misalignment)
Before the cylinder is close, release a small amount of clamping pressure and adjust the height difference between the two rollers to correct the ellipticity;
After the cylinder is closed and docked, clamp the plate back and forth 2-3 times to make it round, ensuring that the diameter of the cylinder is uniform throughout its entire length;
3. Misalignment on both sides: Stop the machine and realign the board, correct the feeding reference, and do not rely on the side rollers to forcefully pull and correct;
4. Cylinder taper deviation: The tapered workpiece adopts asynchronous lifting and lowering of the rollers on both sides, with differential feed rates on both sides and multiple fine adjustments on the test paper.
6、 Key points for unloading and finishing operations
After reaching the standard for roundness calibration, first fully lower and reset the rollers on both sides, and then lower the lower roller to release the sheet;
2. After the main drive roller has completely stopped, operate the flipping unloading support again and prohibit flipping with material;
3. Use a crane to lift the cylinder smoothly, and do not drag the cylinder to scratch the friction roller surface;
4. After processing, clean the roller surface of oxide skin and oil stains, and remove burrs on the edges and corners of the board.
7、 Strict safety operation standards (of utmost importance for heavy equipment)
1. When the equipment is running, it is strictly prohibited to insert hands, bodies, or tools into the roller gap or transmission area, and it is forbidden to stand directly in front of the board feeding and discharging;
2. When adjusting the roller lifting, flipping the support, and repairing the hydraulic system, it is necessary to completely stop the machine and cut off the power;
3. The lifting and relocation of the board shall be directed by a dedicated person, and the lifting of the cylinder shall be smooth to prevent collision with the frame and rollers;
4. If there is abnormal equipment noise, board jamming, hydraulic oil leakage, or sudden pressure rise, immediately press the emergency stop button and troubleshoot before restarting;
5. Wear a safety helmet with long hair, non slip safety shoes, protective gloves, and prohibit loose clothing or scarves from operating on the machine;
6. If leaving the post midway, the machine must be stopped, depressurized, and the control power supply of the control panel must be cut off;
7. Off duty process: reset the side roll and lower roll to zero → clean the equipment → add lubricating oil → shut down the hydraulic station → cut off the main power supply and lock the distribution box Tiktok.
8、 Key points for preventing and controlling common defects
1. Ellipse of the roll: asynchronous lifting of the rollers on both sides, deviation in the parallelism of the rollers; Calibrate the scale of the rollers on both sides and regularly check the parallelism of the rollers;
2. The straight edges at both ends are too long: insufficient pre bending clamping force and too few pre bending cycles; Increase the clamping force of the lower roller and increase the number of pre bending cycles;
3. Misalignment of the board and conical cylinder: the feeding is not aligned, and the height of the feeding rack is inconsistent; Re calibrate the center of the board;
4. Surface indentation and scratches: There are welding slag burrs and no lubrication on the roller surface; Polish the roller surface and lubricate it specifically for stainless steel;
5. Plate cracking: excessive single compression, stress concentration in high-strength steel cold coils; Increase the number of passes and reduce the amount of deformation per pass;
6. Abnormal noise caused by roller overload: excessive plate thickness, excessive pressure; Reduce load and roll in multiple passes.
9、 Key points for daily maintenance assistance
1. Clean the roller surface, guide rail oxide skin, and metal debris after each shift's homework;
2. Check the oil quality of the hydraulic station every week and replace the hydraulic oil every 3000 hours;
3. Monthly inspection of roller parallelism, zero stroke of side rollers, and limit switches;
Before long-term shutdown, apply rust proof oil to the roller and cover it for protection.
