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 with a size of about 6 μm entering the roll gap will cause pinholes, so it is impossible for the 6 μm aluminum foil to have no pinholes, and it can only be evaluated by how much and the size. Due to the improvement of aluminum foil rolling conditions, especially the effective filtration of dust prevention and rolling oil and the convenient roll change system, the number of pinholes in aluminum foil is increasingly 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 component segregation. Effective aluminum liquid purification, filtration, and grain refinement all help to 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 by 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 less than 200/㎡. In the aluminum foil rolling process, other factors that cause pinholes are many, even catastrophic, and thousands of pinholes per square meter are not uncommon. Effective filtering 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 low tension rolling will also help to reduce pinholes.
2. Roller printing, roller eyes, and 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 is the emergence of three cycles. The main reasons for this defect are: incorrect grinding of the roll; damage to the roll by foreign objects; damage to the roll by incoming material defects; fatigue of the roll; impact and slipping between the rolls, etc. All factors that can cause damage to the roll surface can cause harm to aluminum foil rolling. Because the surface finish of the aluminum foil rolling roll is very high, slight uneven gloss will also affect its surface state. Regularly cleaning the rolling mill, keeping the rolling mill clean, ensuring the normal operation of the roller cleaner, changing the rollers regularly, and grinding reasonably are the basic conditions to ensure the uniformity of the aluminum foil surface after rolling.
3. Wrinkle. Due to the serious bad shape of the plate, wrinkles will be formed when the aluminum foil is rolled up or unrolled, the essence of which is that the tension is not enough to flatten the foil surface. For a device with a tension dimension of 20MPa, the shape of the foil surface must not be greater than 30I, and when it is greater than 30I, it will inevitably wrinkle. Because the aluminum foil is often subjected to greater tension during rolling than subsequent processing, some of them only show poor shape during rolling, including incorrect roll grinding, incorrect roll shape, poor incoming material shape and incorrect shape adjustment.
4. Highlights, bright marks, bright spots. The bright spots, bright marks, and bright spots on the double-joint surface caused by improper use of double-joint oil are mainly due to insufficient strength of the double-joint oil film, or uneven rolling deformation caused by uneven roll surface, and the appearance is hemp or foreign matter pressed into it. . It is an effective measure to solve this kind of defects to choose a reasonable duplex oil, keep the incoming material clean and the roll surface of the roll uniform. Of course, it is also necessary to change the reduction and select a good aluminum plate.
5. Thickness difference. Difficulty in controlling the thickness difference is a characteristic of aluminum foil rolling. A thickness difference of 3% may not be difficult in plate production, but it is very difficult in aluminum foil production. The reason is that the thickness is thin, and other micro-conditions can affect it, such as temperature, oil film, oil and gas concentration, etc. Aluminum foil rolling can reach hundreds of thousands of meters per roll, and the rolling time is about 10 hours. With the extension of time, the thickness difference is easy to form, and the only means of adjusting the thickness is the tension speed. These factors have made it difficult to control the thickness of aluminum foil rolling. Therefore, the real control of the thickness difference within 3% requires many conditions to ensure that it is quite difficult.
6. Oil pollution. Oil stain 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 complex in composition. The oil stain on the surface of aluminum foil is more harmful than that of other rolled materials. First, because most of the finished 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 here, which affects the use. The number of oil stain defects is a very important indicator for evaluating the quality of aluminum foil.
7. Water spots. Water spot refers to the white spots formed after water drop on the foil surface before rolling, which will affect the surface condition of the foil surface if it is slight, and cause strip breakage if it is serious. Water spots are caused by water droplets in the oil or water droplets falling on the foil surface in the rolling mill. Controlling the moisture in the oil and the water source is the only measure to avoid water spots.
8. Vibration marks. Vibration marks refer to periodic transverse waves on the surface of aluminum foil. There are two reasons for vibration marks: one is formed during roll grinding, with a period of about 10-20 mm; the other is vibration due to discontinuity of the oil film during rolling, which often occurs in a speed range with a period of 5 ~10mm. The root cause of vibration marks is insufficient oil film strength, which can usually be eliminated by improving the lubrication state.
9. Tension line. When the thickness reaches 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 of single sheets. Increasing tension and roll roughness is an effective measure to reduce and eliminate tension lines, and high tension must be based on good shape.
10. Slit. Slit is a defect unique to foil rolling. It is split longitudinally and straightly during rolling, often accompanied by metal wires. The root cause of the slit is that the entrance side is folded, which often occurs in the middle, mainly due to the loose middle of the incoming material or poor rolls. Severe slits cannot be rolled, while slight slits will be split during subsequent slitting, which often results in a large amount of scrap.
11. Airway. Strip crushing occurs during rolling, and the edge is a drop-shaped curve with a certain width. The slight airway is not crushed, and it is white strip with dense pinholes. The presence of dense pinholes on the front and rear ends of the crushed aluminum foil is a major indicator of airways and other defects. The air passage comes from the raw material, and it is very important to choose a material with low gas content as the aluminum blank.
12. Coiling defects. Coiling defects mainly refer to loose coils or loose inside and tight outside. Due to the limited tension on the aluminum foil, it is very difficult to take up a hard roll. 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 quality of coiling ultimately depends on the shape of the plate. A coil that is loose on the inside and tight on the outside will form a horizontal edge, while a loose coil will form an ellipse, which will affect subsequent processing.
Although there are many types of aluminum foil rolling defects, the final main manifestations are: pinholes, roll eyes, slits, and air passages characterized by holes; oil stains, uneven gloss, vibration marks, tension lines, and water Spots, bright spots; plate shape, wrinkling, discounting, and poor coiling that affect post-process processing; thickness differences characterized by size, etc. In essence, the only defects unique to aluminum foil are pinholes, and other types of defect plates also have them, but the severity of the performance is different or the requirements are different.