Coated aluminum coils cannot be produced with just one coil equipment. Generally, a production line for coated aluminum coils requires four major steps: pre-treatment, coating, heating, and exhaust gas recovery. Today, we will share with you Mingtan aluminum coil with manufacturers: coated aluminum coil forming four major steps:
First, the volume of aluminum pretreatment
Substrate pretreatment technology is accompanied by the production of coating technology, it is for the coating technology services, is for the preparation of excellent coating foundation. Pre-painted aluminum all the substrate in the production process of the surface will remain some grease and lubricants, of course, in the transportation process may also be adhering to other substances, if not remove these grease and adhesion, will have an impact on the volume of aluminum coating and use. In addition, the clean substrate surface needs to be chemically treated to produce a stable conversion film to improve the corrosion resistance of the substrate and the adhesion to the coating.
Due to the high speed of the pre-coating line, these process conditions require that all pretreatments must also be efficient to ensure that the substrate is clean and that the conversion film covers all substrate surfaces.
The pre-treatment section mainly includes hot alkali degreasing, hot water cleaning, chemical treatment and passivation treatment processes.
1、hot alkali degreasing because of the fast line speed of the pre-painting line, so the general concentration of the degreasing agent used is high, typical degreasing agent contains sodium hydroxide (NaOH), sodium carbonate (Na2Co3), water glass (Na2SiO3), phosphate and other components. Hot alkali degreasing process is generally divided into two steps to ensure that the surface of the substrate is clean, and most of the way to spray brush cleaning.
2、hot water cleaning hot water cleaning is mainly to clean the surface of the substrate residual degreasing agent to ensure that these residues can be dissolved in order to prevent these degreasers on the substrate to cause secondary pollution. The use of the way more for the dip and spray brushing way. The hardness of the water used had better not be too high, otherwise, the minerals in the water will create spots on the surface of the substrate.
3、passivation treatment passivation treatment is through pressure spraying, dipping or roller coating and other ways to make passivation agent in the substrate surface to form a conversion film. Generally, when using the pressure spraying method, the sludge generated by the passivation solution in the course of use will often block the spray holes, thus affecting the spraying effect. The dip coating method solves this problem, but the consumption of passivation solution is higher. Both of these methods require water to rinse the excess passivation solution in practice, which leads to the problem of recycling and purification of waste water. Aluminum panels are generally treated with chromate/oxide type agents, which contain chromate, chromic acid, phosphoric acid and accelerators fluoride and molybdate. Phosphoric acid must be added to this type of treatment, otherwise it cannot be used to treat aluminum plates for food and beverage.
Second, coating method
Coating is the core part of the production line, the main equipment includes roller coating machine and drying channel. Generally, the process of front or back side painting is adopted, and according to the different directions of coating rollers and transmission rollers, it can be divided into two kinds of process: forward coating and reverse coating.
1、 Coating equipment roller coating machine is a kind of equipment that uses the roller to coat the paint on the volume of aluminum, the most used is double-roller machine and three-roller machine. Double-roller machine is mainly composed of paint trough, lifting roller, coating roller and transmission roller. When working, the pre-adjusted paint is pumped into the paint tank, the lifting roller is responsible for sticking the paint in the paint tank and transferring it to the coating roller, the coating roller applies the paint to the coil of aluminum in transmission, and the transmission roller is mainly responsible for the transmission of the metal coil. In the actual operation, the relative rotation speed between the lifting roller, coating roller and transmission roller has a certain ratio.
Compared with the two-roller machine, the three-roller machine has one more control roller, which is used to adjust the amount of paint transferred from the lifting roller to the coating roller, and has a certain role in accurately controlling the amount of paint applied. If the speed ratio between the three rollers is not reasonable, the coated material will have surface problems such as horizontal and vertical stripes. In general, the linear speed of the three rollers is as follows:
Coating roller speed > drive roller speed > lifting roller speed
Reasonable control of three rollers rotation speed and mutual ratio is one of the key factors for coating a good appearance of the film, and the three-roller machine is mainly used in applications with high surface requirements.
2、Coating process general pre-coated aluminum coating process according to the number of coating layers can be divided into three coating process, two coating process and single coating process. According to the rotation direction of coating rollers and drive rollers, it can be divided into two kinds of processes, namely, coating and reverse coating. The coating method with the same direction of rotation of the coating rollers and the direction of the substrate is cis-coating. The opposite is reverse coating. Generally, the paralleling process can only produce a low wet film thickness and the surface appearance of the coating film is not ideal. The reverse coating process is the most used coating process, by adjusting the rotation ratio between the rollers and the speed of the substrate, you can get the required thickness and smooth appearance of the coating film. The coating is the core part of the whole production line, the main attention to several parts of this section.
（1）The relative rotation speed ratio between the rollers
（2）The thickness of the substrate and the balance between the speed and the surface temperature of the substrate
（3）The viscosity of the coating and the size of the gap between the rollers
（4）Dry film thickness of the coating film and the relationship between the coating and the roller gap
（5）Relationship of curing time, length of baking channel, substrate speed, substrate thickness and surface temperature.
3、 Post-treatment stage Post-treatment section is used to further process the produced rolled aluminum to give it better protection and decorative effect. There are mainly film, printing, embossing and embossing. Here is a brief explanation: lamination is the peelable film of polyolefin pressed onto the topcoat. Stamping is to print various patterns and designs on the painted metal roll. Embossing is the heat embossing of relief-like patterns on the surface of the lacquer film.Press type is through the Yin and Yang pattern matching steel roller, is pressed out of the three-dimensional pattern.
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