The surface of bubble cover aluminum foil we see is smooth and bright, but some surfaces may have a lot of bright spots, which are mostly caused by some inappropriate operations in the production process. These bright spots, also known as sparkles, are often uneven spots that appear on the dark surface of aluminum foil during tandem rolling.

This kind of bright spot is not conducive to the subsequent processing of aluminum foil, which will lead to the overall performance of foam cover aluminum foil, and the appearance is not good. The sparry crystals are found on the dark side of the foil, which is usually oval, but occasionally rectangular. They’ll be scattered on one side of the foil. The color of this bright spot is darker and brighter than the basic color of aluminum. It will be out of place on the surface of aluminum foil. Some bright spots will form pinholes when they are serious, affecting the insulation tightness of aluminum foil.

To eliminate this bright spot, we need to understand exactly how it comes about and eliminate the cause at the source of production. Aluminum foil in the normal rolling process, the roll surface is not in direct contact with the surface of aluminum foil, the middle of the rolling force is transmitted by rolling oil film. From the perspective of metal forming tribology, the separation between the two contact surfaces of roller and aluminum foil is completely separated by the liquid lubricant. The aluminum foil surface attached to a lubricating liquid, during the forming process of friction is fluid friction, this friction is very small. But if in the rolling process, the oil film formed between the two surfaces is destroyed, or partially destroyed, the original fluid friction will form mixed friction. This situation can easily lead to the abnormal forming of the rolled workpieces. At this time the forming pressure will not pass through the oil film, but through the local point direct contact to the rolled workpiece, this time will form a local “bright spot”, which is the specific reason for the source of the bright spot in the aluminum foil production process.

Huawei Aluminum standardized aluminum foil production

Knowing the causes of bright spots, how to eliminate this situation? We can start from the following aspects.

(1) Reasonable control of coiling machine oiling. Too little or uneven oiling in the process of coiling will affect the rolling of aluminum foil, which is easy to lead to the formation of dry friction or boundary friction between the two layers of aluminum foil, and destroy the subsequent process of aluminum foil. Therefore, in the process of coiling, the amount of oiling should be appropriately increased, the speed of coiling should be reduced, and the oil should be evenly coated to avoid dry friction.
(2) the production of low flash point double oil. In conventional production, the rolling base oil with a flashpoint of 82 ℃ was first used, and then the double oil with a flashpoint of 70 ℃ was changed. Compared with 82 ℃ oil, 70 ℃ oil will be lower in viscosity, the oil film formed is thinner, and evenly distributed, so that the friction between the two aluminum foil increases, so that there is no relative sliding between the two layers of aluminum foil.
(3) Roll roughness mismatch is also a cause of sparry. If the roughness of the upper and lower roller is uneven in the production process, it will lead to different friction factors, and the speed of the roller is synchronous in this case, it will lead to dislocation of the aluminum foil layer, sliding.
(4) Aluminum foil thickness control before double-bonding. Double when the thickness difference between the two pieces of aluminum foil must meet the requirements, if the thickness difference between the two pieces of aluminum foil is large because the metal has certain liquidity, there will be two pieces of aluminum foil processing rate is inconsistent, flow is not synchronized, so that the aluminum foil dislocation, produce bright spots.