It is generally believed that the single-sheet rolling speed of the aluminum foil should reach 80% of the rolling design speed of the rolling mill. Huawei Aluminum Company introduced a 1500 mm four-high irreversible aluminum foil roughing mill from Germany ACIIENACH. The design speed is 2 000 m/min. At present, the single-sheet aluminum foil rolling speed is basically at the level of 600m/miT, and the domestic single-sheet rolling speed is generally 60% to 70% of the setting speed.
Aluminum foil often encounters problems such as wrinkling, layering, drumming, and poor plate shape during high-speed rolling. Any defect may cause the next pass to be scrapped, and the yield rate will drop significantly. The author makes some qualitative analysis on the aluminum coil drum phenomenon encountered in high-speed rolling production.
1 Definition of drumming
Drumming means that the surface of the rolled aluminum foil is locally or continuously raised along the rolling direction. The essence is that the aluminum foil at this place is looser, and the protruding porosity after coiling is larger than that of the flat place. As the drum kicks heavier, the drum kicks up, and the drum kicks up. Gu Meng?
2 Causes of drumming
During the aluminum foil rolling process, a large amount of deformation heat and friction heat will be generated. The rolling deformation zone is always in a heated state. If the local temperature of the roll in the deformation zone is too high. If the maximum cooling capacity of the rolling cooling oil is exceeded, the thermal expansion at the place becomes larger, and the aluminum foil at the corresponding outlet becomes loose. For example, it cannot be flattened during the aluminum foil coiling process. Then the porosity of the coiled area is larger than that of the flat area. After accumulation, a drum is formed, which is called a hot drum in some materials. In actual production, the main reasons for the aluminum roll-up drum are as follows:
(1) The roll crown is large; (2) The shape parameters are unreasonable. The blank has a large convexity; (3) The coolant injection pressure is insufficient or the nozzle is blocked; (4) The process lubricating oil is unreasonably prepared (5) The support roller has scratches; (6) The flattening machine has a large pressure; (7) Road Large amount of sub-reduction
3 Cause analysis and preventive measures
(1) The crown of the roll of the high-speed aluminum foil rolling mill is different from the positive in the speed-up phase: the difference is large during normal operation, and the temperature of the roll is relatively low when the speed is increased. The crown is also small, especially for the new rolls, the crown is relatively smaller. In the process from speed increase to the thickness of the mouth mark, the material panel shaped lamp is broken and the silicon is directly planted to the base quality site of the juice roll. When the convexity is small, the speed increase process is that the two sides of the material are loose. After a certain thermal convexity is established to make the material smooth, the bottoming is too long, and the two sides of the material are too loose to form a drum; the pressure on the flattening roller Under the action of the aluminum foil, the aluminum foil that is connected to the bottom is affected by the bottom bulging material, which will also produce a large amount of bulging, which not only makes it difficult to increase the bottom speed, but also affects the rejection rate due to the large amount of bulging and unusable bottom material. When the convexity is large, the bottoming quality of the speed-up will be significantly improved, but due to the large thermal convexity of high-speed rolling, the middle drum is often formed due to the looseness of the middle plate.
Therefore, adjusting the roll crown in time according to the shape of the bottoming on the exit side to ensure the quality of the bottoming and the shape control during normal rolling is one of the measures to prevent this kind of drumming.
(2) The so-called shape parameter refers to the set target shape curve: the typical target board is a parabola, that is, the secondary curve of tightness and loose edges, which can be modified if necessary. The shape parameter value should be determined according to the online export shape and the next-order production situation. If the setting of the shape parameter of the pass causes the material to be convex, and the transition with the shape parameter of the next pass is improper. The deformation zone of the convex area is relatively long, the deformation heat in the middle of the roll is relatively large, and the heat of the roll is relatively large. The shape of the middle of the material is loose, and the phenomenon of middle bulging may occur.
Therefore, the setting of the plate shape parameters must ensure that the exit plate shape is flat and the middle part is slightly tighter than the edge part, that is, to maintain a certain middle height, and the reasonable transition of the plate shape parameters between passes must be considered.
(3) When the high-speed aluminum foil rolling mill is roughing and rolling, the deformation zone will generate large deformation heat. The cooling effect of the rolling oil is important to maintain the roll shape and stable rolling. If the injection pressure and flow rate of the cooling oil are insufficient, the cooling effect will be affected. However, in the actual production process, the pressure and flow rate of the cooling oil are monitored. Generally, there will be no problems. Many weather-resistant nozzles are plugged or the tubing connecting the nozzles falls off or ruptures mechanical failures, resulting in insufficient coolant flow and pressure in the working area, and the cooling effect is greatly reduced. Make the rolling degree of the corresponding area higher, the plate shape is loose and bulging,
Therefore, the spray effect of the nozzle should be checked regularly, once the bulging phenomenon occurs. Stop the machine in time to check the working conditions of the spraying liquid: This is one of the measures to prevent the drumming:
(4) The actual rolling deformation zone of aluminum foil is mostly in a mixed lubricating state. The boundary film ruptures due to the excessively high contact pressure of the micro convex body in the deformation zone, which leads to direct metal contact. At this time, a part of the pressure in the deformation zone is borne by the fluid. In the other part, the thickness of the oil film in the shaped area is borne by the contacting micro-protrusions and decreases with the increase of the reduction rate. at the same time. In the high-speed rolling state, a large amount of deformation heat will cause the deformation temperature to rise, the thermal movement of lubricating oil molecules increases, and the directional adsorption decreases. The strength of the oil film decreases, and even the oil film ruptures. The metal surface begins to scratch, and the absolute temperature at this time is called the rolling oil critical failure temperature Τ. If the local temperature of the deformation zone exceeds Τ, the boundary will rupture, leading to direct contact with the metal surface, which will increase the friction factor and wear, and the temperature of the deformation zone will also increase, which further promotes the rupture of the oil film. The percentage M of the area where the metal surface is in direct contact. It will increase rapidly, and the heat will accumulate rapidly in this place, causing the material surface at the outlet to become slab and bulge.