Factors Affecting the Surface Quality of Aluminum Foil for Cables

Aluminum foil for cables is a composite product of aluminum foil and also an aluminum foil composite strip. It can protect the cable from corrosion, and it can also shield the signal from leakage.

Because aluminum foil has high airtightness and shielding properties, the aluminum-plastic composite foil formed by coating a layer of plastic film on one or both sides, that is, cable protection foil, is an ideal cable protection layer. The quality requirements of the aluminum box for cables are mainly that the surface has less oil, no holes on the surface, and has high mechanical properties.

The surface of the communication wire needs to be covered with a layer of aluminum foil to play a protective and barrier role, so it can also be called cable shielding foil.

The surface quality of the cable foil

The cable foil is made by attaching a special plastic film (0.058mm thick) on the upper and lower surfaces of the 0.15-0.20mm thick aluminum foil. There are two methods of attaching: dry attaching and wet attaching. The dry method uses a high temperature (200℃) roll pressing method to attach the film; the wet method uses glue. Most of them currently use dry methods. After attaching the plastic film, use a special instrument to tear off the film from the aluminum foil to determine the degree of adhesion of the plastic film. This measurement data is very important and is called peel strength. According to the communication cable industry-standard (code YD/T 723.2-94), the strength should not be less than 6.13N/cm; in addition, the heat sealing strength should not be less than 17.5N/cm. The surface quality of aluminum foil is the most important factor affecting the peel strength. The main surface quality problems are oil spots, corrosion, and over-oxidation.

1.Greasy spots

Oil spots are the most common quality problem on the surface of aluminum foil. The main reason is that the rolling oil is mixed with oil or the rolling oil has a high kinematic viscosity. In addition, the angle of the air nozzle at the exit of the rolling mill is not correct, the air pressure is too small, and the oil on the foil is not blown clean. The solution is: ①Prevent the oil from being mixed into the rolling oil; ②Control the kinematic viscosity of the rolling oil, not to exceed 2.34×10-6m2/s; ③The rolling oil should be heated in cold weather; ④Control the addition of additives, 5%-7%; ⑤Add two rows of upper and lower nozzles at the exit of the rolling mill, with 2 rows of nozzles on the upper row and 4 nozzles on the lower row, blowing from the middle to both sides; ⑥ Manually wipe off the aluminum foil in the last rolling pass Oil stains on the surface; ⑦When the aluminum foil is annealed, stay at 200°C for a period of time to allow the rolling oil to fully evaporate.

2. Corrosion

Many people confuse the corrosion and oxidation of aluminum foil. In fact, the two are completely different. Corrosion is when aluminum atoms lose electrons to form a white powder, and the product has no protective effect on the substrate. Oxidation is the synthesis of oxides by aluminum atoms and oxidation, and the products have protective effects on the aluminum matrix. In nature, aluminum itself forms an oxide film of about 1/500μm, which plays a role of self-protection. The white ash formed on the surface of the aluminum foil after corrosion will seriously reduce the peel strength of the plastic-coated foil. The corrosion of aluminum foil is caused by contact with water or lye. Aluminum foil getting wet by rain during the transportation is a common cause of corrosion. Another thing that is overlooked is caused by fog. When the aluminum coil foil is transported for a long distance at night under high temperature, one side of the aluminum coil is cooled quickly, and the other side is at a high temperature. The mist in the cooling area condenses on the aluminum coil and penetrates into the aluminum foil. After being delivered to the customer's warehouse, the low temperature side is heated by the high temperature, which causes the corrosion of the aluminum coil. The solution is: ①The aluminum coil is tightly packed and protected from rain; ②The aluminum coil in the high-temperature state is not packaged and transported.

3. Peroxidation

An oxide film formed naturally on the surface of aluminum has a protective effect, but if it is cooled by strong wind at a high temperatures, it will inevitably cause over-oxidation and surface discoloration like a rainbow. Peroxidized aluminum foil also reduces the peel strength of the plastic-coated foil. The prevention method is to not use the strong wind to cool the aluminum foil after annealing and let it cool slowly.

The above information is provided by an aluminum plastic film factory.