The purpose of the steel drum rolling process is to take well-cut and deburred drum body material and use rolling equipment to continuously roll the sheet metal in a three-point bending process, processing the sheet metal into cylindrical components, preparing for the subsequent process of longitudinal seam welding of the drum body. The rolling process is indispensable in the production of steel drums. However, in production lines using fully automatic seam welding machines for longitudinal seam welding of drum bodies, the rolling process is carried out as a machining process of the fully automatic seam welding machine. Most domestic steel drum manufacturing companies use semi-automatic seam welding machines to weld the drum bodies, treating the rolling process as a separate process and using independent rolling equipment for production.
Key Points of the Rolling Process
Process Operation Requirements
(1) Adjust the gap of the rolling mill rollers to make it uniform and reasonable to meet the process requirements.
(2) Clean the sand and oil stains on the surface of the sheet metal.
(3) Feed the sheet metal into the feed rollers to enter the rollers for rolling.
Process Technology Requirements
(1) The curvature of the roll must be uniform and consistent, and there should be no defects of inconsistent diameters at both ends. The difference in diameter at both ends should not exceed 50mm.
(2) After rolling, the two ends should be aligned without misalignment, and the alignment error should not exceed 5mm.
(3) After rolling, there should be a certain amount of overlap for the longitudinal seam of the drum body, but it should not be too large or too small. The overlap width should be controlled between 100-150mm.
Plate Rolling Machine and Its Operating Procedures
Structural Principle of the Rolling Machine
Plate rolling machines used for making drums generally adopt a three-roller symmetrical structure. Figure 3-3 shows a schematic diagram of the rolling machine structure.
Figure 3-3 Schematic diagram of the three-roller rolling machine structure
The rolling machine consists of a frame, upper roller, lower roller, transmission device, and adjustment device. The upper roller is located in the middle symmetrical position of the two lower rollers, and the upper roller is passive and can be adjusted vertically to obtain different bending radii for rolling. The lower roller is active, installed in fixed bearings, and driven in the same direction and at the same speed by an electric motor through a transmission mechanism.
During operation, the sheet metal is fed between the upper and lower rollers. When the two lower rollers rotate, the sheet metal moves due to the action of friction, so that the entire sheet metal passes through the upper and lower rollers. Because the parts of the upper and lower rollers that contact the steel plate are on different planes, the steel plate is uniformly bent while passing through the three rollers.
Safety Operating Procedures for Plate Rolling Machines
Operators should be familiar with the structure and performance of the three-roller rolling machine, and it is prohibited to use the rolling machine beyond its performance.
Before starting the machine, operators should wear protective equipment correctly. Check whether the fasteners and transmission parts of the rolling machine are normal, and whether the safety protection devices are intact. After everything is normal, lubricate the rolling machine comprehensively according to regulations.
Adjust the gap between the upper and lower rollers according to the thickness, material, and product process requirements of the rolled material. Do not adjust too much at one time to avoid damaging the equipment. Adjust and try gradually, fix the adjustment device after reaching the requirements.
When encountering sheet metal that cannot be rolled in, it is forbidden to use hands to force feed the material to avoid personal injury. When the pressure roller is contaminated with dirt, stop the machine for cleaning. Stop the machine for inspection and repair in case of malfunction or abnormality.
After work is completed, the power should be cut off, and the three-roller rolling machine should be wiped clean, and the equipment and site should be cleaned.
Maintenance and Maintenance of Plate Rolling Machines
- When adjusting the gap between the upper and lower rollers, it should be adjusted on both sides of the roller simultaneously, from large to small, to keep the axis of the upper and lower rollers parallel. Avoid excessive adjustment to prevent damage to the rolling machine. After adjusting properly, the adjustment device should be locked in time to prevent changes in the gap.
- Before starting the machine every day, sufficient lubrication should be performed on various transmission parts of the machine, especially bearings and gears. During operation, if abnormal noises are heard from the equipment, stop the machine immediately for inspection and troubleshooting.
- If the radius of curvature of the produced product suddenly becomes large or small, stop the machine for inspection. If it is caused by uneven material thickness, adjust the distance between the upper and lower rollers according to the requirements of thicker plates to avoid damage to the machine due to too small gaps.
- Keep the surfaces of the three rollers clean and free of stains. Oil stains can cause the sheet metal to slip, affecting production efficiency; solid foreign objects can damage the surface quality of the sheet metal and may cause damage to the surface of the rollers. If stains are found, stop the machine immediately and wipe them clean.
- During work, check the surface condition of the sheet metal to prevent foreign objects from being brought into the machine and damaging the equipment. If damage to the roller surface is found, stop the machine for repair in time to keep the roller surface clean.
- After work is completed, the equipment surface and rollers should be wiped clean in time. When not in use for a long time, anti-rust oil should be applied to the rollers to prevent rust.
Quality Control of the Rolling Process
Common quality problems in the rolling process include external defects, surface pressure marks, and rolling cracks.
When rolling cylindrical drum bodies, common external defects include excessive bending, tapered shape, bulging, waist constriction, edge misalignment, and angular defects, as shown in Table 3-5.
|The adjustment distance of the upper roll is too large, causing excessive overlap of the two edges.
|After adjusting the rollers, use a template to check their curvature.
|The adjustment amount at the ends of the upper roll or side rolls is inconsistent, causing the centerlines of the upper and lower rolls to be non-parallel.
|Increase the feed rate of the rollers on the end with a larger curvature radius.
|During the rolling process, the rollers bend due to insufficient rigidity.
|Add support rollers in the middle section of the rollers.
|Excessive pressure from the upper roll or excessive force from the lower roll causes reverse bending of the rollers.
|Adjust the spacing between roller shafts.
|Misalignment during feeding of the blank, or the blank is not rectangular.
|Feed straight and aligned.
|Defects in the previous process lead to bending of the flange.
|Check the shape and size of the blank.
Surface pressure marks
During rolling, the oxide scale and adhering impurities on the surface of the steel plate or roller can cause surface pressure marks on the sheet metal. To reduce the harm of oxide scale, the following measures can be taken:
- Before rolling, remove the oxide scale from the surface of the sheet metal.
- The roller of the plate bending machine must be kept clean, and the surface of the roller should be free of rust, burrs, edges, or other hard particles.
- During plate rolling, attention should be paid to timely blowing off rust, dust, and other substances on the inner and outer sides.
Due to excessive deformation during bending, material cold work hardening, and stress concentration, material plasticity may deteriorate, causing cracks. To prevent rolling cracks, for materials prone to cracking, measures such as limiting deformation, annealing of steel plates, and preheating can be taken.
Scratches produced on the surface of the rolled drum body may be straight or curved. The reason for this may be the poor condition of the roller surface of the rolling mill or unreasonable speed.