How to distinguish the quality of aluminum foil?

n the process of buying aluminum foil, it is necessary to have a discerning eye. Whether the quality of the aluminum foil is good or bad can be purchased, how can the quality of the aluminum foil be distinguished?

 

In the production process of aluminum foil, it is necessary to go through a number of processes, such as rolling, finishing, annealing, packaging, etc., and any one of the problems may cause problems in the quality of the aluminum foil. The quality of many aluminum foils can sometimes be seen by the naked eye. Let us introduce how the quality of aluminum foil is distinguished.

 

1.Pinhole

 

The main drawback of aluminum foil is the pinhole problem. In the raw materials, on the rolls, in the rolling oil, even if the dust in the air reaches about 6 μm and enters the roll gap, pinholes are caused. Therefore, it is impossible to have pinholes in the 6 μm aluminum foil, and it can only be evaluated by how much and size. Of course, the use of alloying and other means 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 product is cleaned well, the 6 μm aluminum foil pinhole is 200/m2 or less.

 

2.Dark lines

 

Most of the dark-faced stripes appear on the double-jointed product, and the dark surface has a distinct light-dark strip pattern along the rolling direction, which affects the appearance.

 

3. Dark surface color difference

 

The surface of the aluminum foil has a strip-like protrusion in the longitudinal direction, and the hand touches with a convex and concave feeling, sometimes disappears after removing the outer aluminum foil, and sometimes runs through the entire roll of aluminum foil.

 

4. Surface bubbles

 

The aluminum foil with surface bubble defects has irregular circular or strip-shaped cavity protrusions on the surface of the foil; the edges of the protrusion are round, the two sides are asymmetrical, the distribution is irregular, and the surface bubbles cause the aluminum foil to be stressed at various points. Unbalanced, it is likely to cause a break.

 

5. Aluminum foil bruises, scratches, scratches

 

Aluminum foil bump refers to damage caused by the foil on the surface or end face after collision with other objects during handling or storage. Most of the bruises are caused by inadvertent attention when packaging aluminum foil. Scratch: A bundle (or group) distribution of scratches on the surface of the foil due to the relative sliding of the edges and faces between the materials, or the contact between the faces and the faces. Scratch: Intermittent or continuous groove-like scars on the surface of the foil. Typically produced when the sharp object slides in contact with the surface of the foil.

 

6. Imprint

 

There are a variety of conditions that can cause impressions on the surface of the aluminum foil, such as defects in the surface of the roll or guide roll or dirt such as metal chips. The surface of the sleeve or the die is not clean or there are smooth protrusions locally, or the surface of the foil is taken up. Sticking to foreign objects and so on. The surface of the foil on which the impression appears is generally free of individual or periodic depressions or projections that are easily discernible.

 

7. Oil spots

 

Common aluminum foil oil stains are formed after annealing, generally pale yellow, brown, yellowish brown spots. In addition, the degreasing is not clean, and the detection of degreasing is clean. Generally, after annealing, the degreasing grade is detected by brushing method. If the level specified by the brushing test is not reached, the aluminum foil may have oil.

 

8. Corrosion

 

The surface of the aluminum foil is in contact with the surrounding medium. After a chemical reaction or an electrochemical reaction, defects on the surface of the aluminum foil may be lost on the surface of the corroded aluminum foil, and gray corrosion products may be generated in severe cases. The corroded aluminum foil has a great influence on the aesthetics of the products produced at the terminal.

 

9. Wrinkle

 

Due to the severely bad shape of the plate, wrinkles are formed when the aluminum foil is taken up or unfolded, and the essence is that the tension is insufficient to flatten the foil surface.

 

10. Cracked edge

 

The phenomenon that the longitudinal edge of the surface of the aluminum foil is broken is called a split edge. In severe cases, obvious gaps can be seen at the edges.

 

11. Water spots

 

Water spot refers to the white spot on the foil surface before rolling, which is formed after rolling. When it is light, it will affect the surface condition of the foil surface. In severe cases, it will cause the broken tape. Water spots are formed by the presence of water droplets in the oil or the presence of water droplets on the foil surface. Controlling the moisture and water in the oil is the only measure to avoid water spots.

 

12. Adhesion

 

The aluminum foil roll is not easy to open, and the multiple sheets are plate-shaped when opened. The free fall length of the product cannot meet the standard requirements. In severe cases, the single sheet cannot be opened, and the adhesion of the aluminum foil will seriously affect the production of the product.

 

13. Poor plate type

 

Due to uneven deformation, the surface of the foil is locally undulated, which is called poor plate shape. According to the location of the defect, it is divided into intermediate waves, side waves, two-ribbed waves and composite waves.

 

14. Rolling, roll, uneven gloss

 

It is mainly caused by aluminum foil defects caused by rolls, which are divided into three types: point, line and surface. The most notable feature appears in three cycles. The main causes of such defects are: improper grinding of the rolls; foreign objects damage rolls: incoming defects, impression rolls; roll fatigue; roll impact, slip, etc. All factors that can cause damage to the surface of the roll can be a hazard to aluminum foil rolling. Because the aluminum foil rolling roll surface finish is high, slight uneven gloss will also affect its surface state.

 

15. Loose roll

 

Since the coiling is not tight when slitting, when the foil is taken up in the direction of the core, the foil is displaced between layers; when the foil is pressed with a finger, a partial depression may occur.

 

16. slitting

 

Slotting is a peculiar defect in foil rolling, which is split flat in the longitudinal direction during rolling, often accompanied by a metal wire. The root cause of the slit is the discount on the inlet side, which often occurs in the middle, mainly due to the looseness of the incoming material or the poor roll. Severe slits cannot be rolled, and slight slits crack at the subsequent slitting, which often results in a large amount of waste.

 

17. Thickness difference

 

Thickness is difficult to control is a feature of aluminum foil rolling, 3% thickness difference may not be difficult in sheet metal production, but it is very difficult to produce aluminum foil. The reason is that the thickness is thin, and other trace conditions can affect, 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 about 10 hours. 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 all contribute to the difficulty of thick control of aluminum foil rolling. Therefore, the true control of the thickness difference within 3% requires many conditions to ensure that the difficulty is considerable.

 

18. Burr, curled edge

 

After shearing, there are thorns of varying sizes at the edges of the foil. Warping: The phenomenon that the ends of the aluminum foil roll are lifted up at one end or one end, which is called the warping edge. The feature is that the aluminum foil curled up in the upper part and can be touched by hand, which will have obvious concave and convex feeling.

 

19. Highlights, bright marks, bright spots

 

The double point is bright, bright and bright because of the improper use of the double oil. It is mainly because the strength of the double oil film is insufficient, 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 keep the incoming material clean and the roll surface uniform is an effective measure to solve such defects.

 

20. Staggered layer

 

The irregularity of the end face layer and the layer of the aluminum foil roll causes the end face to be uneven.

 

21. Wrinkles, wrinkles

 

Wrinkles: Small, longitudinal or obliquely convex, one or several smooth grooves on the surface of an aluminum foil. Wrinkling: The longitudinal or transverse wrinkles of the aluminum foil roll surface that cannot be flattened.

 

22. Tower shape

 

The misalignment between the end face layer of the aluminum foil and the layer causes a tower-like offset, which is called a tower shape. The tower shape is a special case of a split layer, and the side looks like a spire.

 

23. Black lines, bright lines, white bars

 

Black line: A longitudinally continuous dark line on the surface of the aluminum foil. The resulting part has a distinct color difference from other parts. Bright line: Similar to the dark line, the bright line is a vertical continuous bright strip on the surface of the aluminum foil, and the resulting part has obvious color difference with other parts. White strip: White streaks of aluminum foil surface that vary in rolling direction, width or spacing. Generally, the lower surface of the casting strip appears, and the stripes are concentrated in the middle of the aluminum foil and at the two rib positions. As the aluminum foil is rolled and thinned, the stripes are obviously aggravated.

 

24. End pattern

 

When the end of the aluminum foil is partially or completely rolled, the core has a radial pattern along the wall thickness; after the unwinding, there is a slight wave at the edge of the aluminum foil.

 

25. Arrow

 

A certain number of layers on the end face of the aluminum foil roll are convex from the inside to the outside at the same place, and the degree of protrusion gradually decreases from the inside to the outside or from the outside to the inside.

 

26. Horizontal stripes, herringbone lines

 

Horizontal stripes: The surface of the aluminum foil has regular fine stripes on the surface. It is generally white and has no unevenness. Sometimes it is partially on the coil, sometimes covering the entire surface, which also affects the appearance. Herringbone pattern: The regular herringbone pattern on the surface of the foil is generally white with a noticeable chromatic aberration on the surface, but it is very smooth.

 

27. Starting the drum

 

The surface of the aluminum foil has a strip-like protrusion in the longitudinal direction, and the hand touches with a convex and concave feeling, sometimes disappears after removing the outer aluminum foil, and sometimes runs through the entire roll of aluminum foil.

 

28. Airway

 

Due to the high hydrogen content of the melt, the aluminum foil is crushed in the strip direction in the rolling direction during the rolling process, and has a certain width.

 

29. Non-metallic press-in

 

The non-metallic inclusions are pressed into the surface of the foil, and the surface has obvious dot-like or long strips of yellow-black defects, which can be clearly seen.

 

The above is the common quality defect of aluminum foil. Everyone should pay attention to the screening when buying aluminum foil.