(1) Pinhole. Pinholes are the main defect of aluminum foil. In the raw material, on the roll, in the rolling oil, and even the dust in the air reaches about 6μm and enters the roll gap, it will cause pinholes. Therefore, it is impossible for 6μm aluminum foil to have no pinholes. It can only be evaluated by how much and its size. Due to the improvement of aluminum foil rolling conditions, especially the effective filtration of dust and rolling oil and the setting of convenient roll changing system, the number of pinholes in aluminum foil is more and more dependent on the metallurgical quality of raw materials and processing defects, because pinholes are often It is difficult to find the corresponding relationship with the original defect when the defect of the raw material falls off. It is generally believed that pinholes are mainly related to gas content, inclusions, compounds and composition segregation. Effective aluminum liquid purification, filtration, and grain refinement can help reduce pinholes. Of course, the use of alloying and other means to improve the hardening characteristics of the material also helps to reduce pinholes. The pinholes of 6μm aluminum foil rolled from high-quality hot-rolled materials can be less than 100/㎡. When the casting and rolling materials are well purified, the pinholes of 6μm aluminum foil are below 200/㎡. In the aluminum foil rolling process, there are many other factors that cause pinholes, even catastrophic, and thousands of pinholes per square meter are not uncommon. Effective filtration of rolling oil, short-term replacement of rolls and dust-proof measures are all necessary conditions to reduce pinholes in aluminum foil, and the use of large rolling force and small tension rolling will also help to reduce pinholes.
(2) Roll mark, roll eye, uneven gloss. It is mainly the aluminum foil defect caused by the roll, which is divided into three types: point, line and surface. The most notable feature appears in three cycles. The main reasons for this defect are: incorrect grinding of the rolls; damage to the rolls by foreign objects: incoming defects imprinting the rolls; roll fatigue; impact between rolls, slippage, etc. All factors that can cause damage to the surface of the roll can cause harm to the rolling of aluminum foil. Because the surface finish of the aluminum foil rolling roll is very high, slight uneven gloss will also affect its surface condition. Regular cleaning of the rolling mill, keeping the rolling mill clean, ensuring the normal operation of the roll cleaner, regular roll change, and reasonable grinding are the basic conditions to ensure the uniform surface of the aluminum foil after rolling.
(3) Wrinkling. Due to the serious bad shape of the plate, wrinkles will be formed when the aluminum foil is coiled or unrolled, and its essence is that the tension is not enough to flatten the foil surface. For the device with a tension dimension of 20MPa, the shape of the foil surface shall not be greater than 30I, and when it is greater than 30I, it must be wrinkled. Because the aluminum foil often bears more tension than the subsequent processing during rolling, some only show poor shape during rolling, including incorrect roll grinding, incorrect roll shape, poor incoming shape and incorrect adjustment of the shape.
(4) Bright spots, bright marks, bright spots. The bright spots, bright marks and bright spots on the double-helix surface caused by improper use of the double-helix oil are mainly due to the insufficient strength of the double-helix oil film, or the uneven rolling deformation caused by the uneven roll surface, and the appearance is hemp skin or foreign matter pressed in. . It is an effective measure to solve such defects to choose reasonable double oil, keep the incoming material clean and the roll surface uniform. Of course, it is also necessary to change the reduction amount and choose a good aluminum plate.
(5) Thickness difference. It is a feature of aluminum foil rolling that thickness difference is difficult to control. A thickness difference of 3% may not be difficult in sheet production, but it is very difficult in aluminum foil production. The reason is that the thickness is thin, and other trace conditions can affect it, such as temperature, oil film, oil and gas concentration, etc. A roll of aluminum foil can be rolled up to hundreds of thousands of meters, and the rolling time is about 10 hours. With the extension of time, the thickness difference is easy to form, and the only way to adjust the thickness is the tension speed. These factors all cause the difficulty of thickness control of aluminum foil rolling. Therefore, to really control the thickness difference within 3%, many conditions are required to ensure that it is quite difficult.
(6) Oil stains. Oil pollution refers to the excess oil on the surface of the aluminum foil after rolling, that is, oil other than the rolling oil film. These oils are often thrown, splashed, and dripped on the foil surface from the roll neck or the outlet of the rolling mill, and are dirty and have complex compositions. The oil stain on the surface of aluminum foil is more harmful than that of other rolled materials. First, because most of the aluminum foil products are used as decoration or packaging materials, they must have a clean surface; Moreover, due to the large amount of oil, too much residue is formed there, which affects the use. The number of oil defects is a very important indicator to evaluate the quality of aluminum foil.
(7) Water spots. Water spots refer to the white spots formed by water droplets on the foil surface before rolling, which will affect the surface condition of the foil surface when it is mild, and cause strip breakage when it is serious. Water spots are formed due to water droplets in the oil or water droplets falling on the foil surface in the rolling mill. Controlling the moisture and water sources in the oil is the only measure to avoid water spots.
(8) Vibration marks. Vibration marks refer to the periodic transverse waves on the surface of aluminum foil. There are two reasons for vibration marks: one is due to roll grinding, and the cycle is about 10~20mm; the other is due to the discontinuous vibration of the oil film during rolling, which often occurs in a speed range with a cycle of 5 ~10mm. The root cause of vibration marks is the insufficient strength of the oil film, which can usually be eliminated by improving the lubrication state.
(9) Tension line. When the thickness is below 0.015mm, parallel stripes are formed in the longitudinal direction of the aluminum foil, commonly known as tension lines. The tension line spacing is about 5~20 mm, the smaller the tension, the wider the tension line, and the more obvious the stripes. When the tension reaches a certain value, the tension line is very slight or even disappears. The smaller the thickness, the greater the possibility of producing tension lines, and the possibility of producing tension lines in double rolling is greater than that in single sheets. Increasing the tension and roll roughness is an effective measure to reduce and eliminate the tension line, and the large tension must be based on a good shape.
(10) Slitting. Slitting is a peculiar defect of foil rolling, and it splits straight in the longitudinal direction during rolling, often accompanied by metal wires. The root cause of slitting is the inlet side discount, which often occurs in the middle, mainly due to loose material in the middle or poor rolls. Severe slits cannot be rolled, while minor slits are split during subsequent slitting, which often results in a large amount of scrap.
(11) Airway. During the rolling time, strip-shaped crushing appeared, and the edge was a droplet-shaped curve with a certain width. The mild airway was not crushed, and it appeared as a white strip with dense pinholes. The presence of dense pinholes at the front and back ends of the crushed aluminum foil is the main indicator for judging airways and other defects. Air channels are derived from raw materials, and it is very important to select materials with low gas content as aluminum blanks.
(12) Coiling defects. Coiling defects mainly refer to loose coils or internal looseness and external tightness. Coiling of hard coils is difficult due to the limited tension that the foil can withstand. It is ideal to obtain a roll that is tight on the inside and loose on the outside, and sufficient tension is the condition for forming a certain tension gradient. Therefore, the coiling quality ultimately depends on the shape of the plate. The inner loose coil will form a transverse edge, while the loose coil will form an ellipse, which will affect the subsequent processing.
Although there are many types of aluminum foil rolling defects, the final main manifestations are: pinholes, roll holes, slits, and air passages characterized by holes; oil stains, uneven gloss, vibration marks, tension lines, water marks characterized by surface conditions Spots, bright spots and bright spots; plate shape, wrinkling, discounting, and poor coiling that affect subsequent processing; thickness differences characterized by size, etc. In essence, the unique defect of aluminum foil is only one type of pinhole, and there are also several other defective sheets, but the severity of the performance is different or the requirements are different.