Common defects in aluminum foil rolling

- Dec 11, 2018-

First, the pinhole

Pinholes are the primary disadvantage of aluminum foil. In the original guess, on the rolls, in the rolling oil, and even in the air, the size of the dust reaching 6μm into the roll gap will cause pinholes, so it is impossible to have pinholes in the 6μm aluminum foil, and it can only be evaluated by how much and how large. Because of the improvement of aluminum foil rolling conditions, especially the dust filtration and rolling oil useful filtration and the convenient roll change system setting, the number of aluminum foil pinholes is increasingly dependent on the metallurgical quality and processing disadvantages of the material, because the pinhole is usually It is difficult to find a corresponding link with the original shortcomings.

It is generally believed that pinholes are primarily associated with gas content, doping, segregation of compounds and components. Adopting useful aluminum cleaning, filtration, and grain refinement all help to reduce pinholes. Of course, the use of alloying and other techniques to improve the hardening properties of the material also helps to reduce pinholes. The pinholes of 6μm aluminum foil rolled by high-quality hot rolled products can be less than 100/m2. When the cast-rolled material is better cleaned, the pinhole of the 6 μm aluminum foil is below 200/m2. During the aluminum foil rolling process, other elements that make up the pinholes, or many, even catastrophic, are not rare for thousands of pinholes per square meter. The useful filtration of the rolling oil, the short-term replacement of the rolls and the dust-proof method are all necessary conditions for reducing the pinhole of the aluminum foil, and the use of large rolling force, the small tension rolling will also help to reduce the pinhole.

Second, roll printing, roll eyes, uneven gloss

It is mainly the shortcomings of aluminum foil caused by rolls, which are divided into three types: point, line and surface. The most obvious feature is the three-cycle presentation. The primary reasons for this shortcoming are: improper grinding of the rolls; damage to the rolls by foreign objects: defects in the printing rolls; fatigue of the rolls; impact between rolls, slipping, etc. All the elements that can constitute the damage to the surface of the roll can damage the aluminum foil rolling. Because the aluminum foil rolling roll surface is very smooth, the uneven gloss unevenness will also affect its appearance. Timing finishing of the rolling mill, keeping the rolling mill clean, ensuring the normal operation of the roller cleaner, timing the roll change, and reasonable grinding are the basic conditions for ensuring uniform appearance of the aluminum foil after rolling.

Third, wrinkle

Because the shape of the plate is severe, the wrinkles are formed when the aluminum foil is taken up or opened, and the essence is that the tension is lacking to flatten the foil surface. Regarding the equipment with tension dimension of 20 MPa, the shape of the foil surface shall not be greater than 30I, and when it is greater than 30I, it will inevitably wrinkle. Since the aluminum foil generally receives a larger tension than the subsequent processing during rolling, some of them are only in the form of poor sheet shape during rolling, including incorrect roll grinding, incorrect roll type, poor shape of the incoming sheet, and incorrect adjustment of the shape of the sheet.

Fourth, bright spots, bright marks, bright spots

The double point is bright, bright, and bright because of the improper use of double oil. The first reason is that the strength of the double oil film is lacking, or the uneven surface of the roll causes uneven rolling deformation, and the appearance is hemp or foreign matter. . The use of reasonable double oil to maintain the cleaning of the incoming material and the uniform roll surface of the rolls is a useful solution to these shortcomings. Of course, it is also necessary to change the amount of pressing and to select an excellent aluminum plate.

Five, thickness difference

Thickness is difficult to control is a feature of aluminum foil rolling, 3% thickness difference may not be difficult when the sheet is produced, but it is very difficult when the aluminum foil is produced. The reason is that the thickness is thin, and other trace conditions can affect the composition, such as temperature, oil film, oil and gas concentration. A roll of aluminum foil can reach several hundred thousand meters, and the rolling time can be as long as 10h. With the extension of time, the thickness difference is easy to form, and the method of thickness adjustment only has the tension speed. These factors constitute the difficulty of thick control of aluminum foil rolling. Therefore, the true control thickness difference is less than 3%, and many conditions are required to ensure that the difficulty is considerable.

Six, oil pollution

Oil stain refers to the remaining oil on the outer surface of the aluminum foil after rolling, that is, oil other than the rolled oil film. These oils are usually smashed, splashed, and dropped on the foil surface at the roll neck or at the exit of the mill, and are dirty and have a messy composition. The oil on the outer surface of the aluminum foil is more damaging than the oil on the other rolled materials. First, because the finished aluminum foil is mostly used as a decoration or packaging material, it must have a clean appearance. Second, its thickness is thin, and it tends to form a bubble when it is annealed in the back. And because the amount of oil is too large, it constitutes too much residue and affects the application. The shortcomings of oil pollution are a very important indicator for assessing the quality of aluminum foil.

Seven, water spots

Water spot refers to the white spot on the foil surface before rolling, which is formed after rolling. When it is fine, it will affect the appearance of the foil surface. When it is severe, it will lead to broken tape. Water spots are caused by water droplets in the oil or water droplets on the foil surface. Controlling the moisture and water in the oil is a special way to prevent water spots.

Eight, vibration marks

The vibration mark refers to the periodic transverse wave of the aluminum foil. There are two kinds of vibration marks: one is because the roll is formed, the cycle is 10~20mm; the other is because the oil film discontinuously oscillates during rolling, often occurs in a speed range, the period is 5 ~10mm. The base of the occurrence of the vibration marks is due to the lack of strength of the oil film, which can usually be eliminated by using an improved smooth condition.

Nine, tension line

When the thickness reaches 0.015 mm or less, parallel stripes are formed in the longitudinal direction of the aluminum foil, which is commonly called a tension line. The tension line distance is 5~20 mm, the smaller the tension, the wider the tension line and the more obvious the stripe. When the tension reaches a certain value, the tension line is very small or even missing. The smaller the thickness, the greater the possibility of tension lines, and the possibility of tension lines occurring in double-rolling is larger than that of a single sheet. Increasing tension and roll roughness are useful ways to reduce and eliminate tension lines, while large tensions must be based on an outstanding plate shape.

Ten, slit

Slotting is a peculiar disadvantage of foil rolling, which splits straight in the longitudinal direction during rolling, often accompanied by a metal wire. The bottom edge of the slit is the discount on the inlet side, which often occurs in the center, mainly because it is difficult to guess the center loose or the roll. Severe slits cannot be rolled, and fine slits crack in the future slitting, which usually constitutes a lot of waste.

Eleven, airway

In the rolling moment, the strip is crushed, the margin is a droplet-shaped curve, and the width is a certain width. The light air passage is not crushed, and it has a white strip shape and dense pinholes. The presence of dense pinholes at the front and rear ends of the crushed aluminum foil is the primary symbol for determining airway and other shortcomings. The airway is derived from the material, and it is very important to select a material with a low gas content as the aluminum blank.