(1) Choose a film of moderate width and thickness; because aluminum profiles have complex cross-sectional shapes, with large differences between wide and narrow surfaces, edges are easily lifted, which reduces the film's coverage ability and affects the quality of spraying. If the film is too narrow, it obviously cannot cover the surface adequately, making spraying impossible. On the other hand, when selecting the film thickness, as long as it can provide coverage and has elasticity, it is sufficient. There is no need to choose an overly thick film, as a thicker film increases aluminum profile production costs and is unnecessary.
(2) Spray promptly after applying the film. After the profile is covered with the film, spraying should be done in a timely manner, with as short a wait time as possible. If the wait time is too long, the adhesive on the film dries and loses its stickiness. Especially with exposure to wind, the film may peel off, making spraying difficult. Therefore, to ensure the quality of both film application and spraying, the waiting time after applying the film should generally not exceed 16 hours.
(3) Choose films with moderate viscosity. In the production of bicolor aluminum profiles, selecting the appropriate film is crucial. If the film's viscosity is too low, it cannot adhere properly. The film is prone to falling off, which poses significant challenges for spraying. If the film's viscosity is too high, it indicates that there is too much adhesive on the film. When the film is removed, the adhesive may stick to the profile, affecting the surface quality of the profile. On the other hand, when selecting a film, try to choose one whose adhesive composition is the same as or close to that of the paint, which can reduce the impact on the color of the paint film.
(4) Determine the color, dividing surfaces, and dividing lines. Before spraying aluminum profiles, it is essential to distinguish the color to be sprayed on each surface, which surface is the dividing surface, and which line is the dividing line, as well as its location, based on the profile's functional use and customer requirements. Generally speaking, the inside is a light color and the outside is a dark color. Only after clarifying the requirements for dividing surfaces, dividing lines, and colors can the film be applied, and it is crucial not to misplace the film.
(5) Film application quality: Applying the film is a key process in the processing of bicolor aluminum profiles. The quality of film application directly affects the surface quality of aluminum profile processing, which mainly includes the following aspects: First, try to avoid creating excessive tension in the film during application, meaning the film should not deform; otherwise, the film may shrink after application, causing the ends of the aluminum profile to be unprotected. On the other hand, when the film at the ends of the aluminum profile is cut off, it should be sliced with a blade rather than torn, because torn film will also shrink. Second, the film width should match the width to be covered. Generally, the film should be slightly wider than the area to be covered on the aluminum profile. If the film is too wide and extends excessively beyond the edge, it can be lifted by compressed air during spraying. If the film is too narrow and does not fully cover the surface, it is obviously unacceptable. Fourth, when the edge of the coated area is at the groove, the film's excess edge must be pressed into the groove; otherwise, airflow during spraying can lift the film, affecting the coating quality. Fifth, during film application, the film must be applied flat to prevent wrinkles or curling. Sixth, for profiles with complex cross-sections, if applying the film in one go is difficult, it can be done in two or more steps to ensure full coverage. Seventh, for aluminum profiles with thin walls or large cantilevers, the film should not be applied too tightly, and care must be taken to avoid deforming the profile. Eighth, after the first spray coat, the aluminum profile should not be left standing for too long, as dust will settle on the profile surface, making the film application difficult and thus affecting its quality.
(6) Strictly follow the film application process. Aluminum profiles must have the film applied after the first coating, not directly after chromating. This is because the film has adhesive; if it is applied directly onto the chromate layer, the adhesive will stick to the chromate layer or, when removing the film, it may peel off the chromate layer. This would significantly reduce the adhesion of the paint film, ultimately affecting the spraying quality of the aluminum profile processing and leading to paint peeling, with consequences that are unimaginable.
(7) Film removal timing. After aluminum profiles have undergone film application and spraying, the film needs to be removed. However, it should not be removed immediately after spraying; the timing must be controlled. Generally, after spraying, allowing the paint to level, the film should solidify for no less than 10 minutes before it can be removed. Otherwise, if the paint film has not set, during the removal process, pieces of the film may remain on the aluminum profile, affecting paint film quality. Additionally, the removal process should be done quickly to avoid compromising the quality of the film removal.
(8) Avoid multiple reworks. In the production process of two-color aluminum profiles, rework is inevitable due to various factors. However, each rework requires an additional curing. For the paint film, multiple coatings continuously increase the film thickness, and after multiple curing processes, the adhesion of the paint film is reduced, making it prone to peeling. Therefore, in the production of two-color aluminum profiles, multiple reworks should be avoided as much as possible.
9) Reasonable control of film thickness: The production of two-color aluminum profiles requires more than two rounds of spraying. If we operate as if it were a single spray, it will result in some surfaces having a thicker topcoat and others having a thinner topcoat, causing serious unevenness in film thickness. Therefore, reasonable control must be applied during spraying. During the first spray, focus only on the key surfaces, while the other surface can be left unsprayed or lightly sprayed. The second spray should focus as much as possible on the surfaces that need attention, while other surfaces are not sprayed or lightly sprayed. At the same time, the thickness of the second spray must be reasonably controlled according to the first spray and the chosen paint color, ensuring that the second spray properly covers the first spray.
(10) For the spraying sequence in processing two-color aluminum profiles, two colors need to be applied, which inevitably include a dark color and a light color. Spraying must be done in a certain order, so before spraying, it is necessary to consider which color should be sprayed first and which should be sprayed later, depending on the specific situation. If the light color is sprayed first and the dark color later, the initially sprayed light color will go through two cures, that is, two baking processes, which can easily cause the light color to change. If the dark color is sprayed first and the light color later, the coverage of the light color over the previously sprayed dark color will be affected to some extent. To cover the dark color, the coating thickness must be increased, but if the coating becomes too thick, it can easily lead to peeling. Therefore, in actual production, using the process of spraying light color first and dark color later is more feasible.
