The production process for color-coated aluminum coil is relatively complex, primarily involving a series of processing steps from plain aluminum coil to produce color-coated aluminum coil with a variety of colors and properties. The following details each step of the production process.
Bare aluminum coils undergo cleaning, chromizing, roller coating, and baking to become color-coated aluminum coils.
Bare aluminum coils are first cleaned to remove surface impurities and dirt. Next, chromizing forms a chromate film on the surface, improving corrosion resistance and adhesion to the paint. The paint is then evenly applied to the surface of the coil using roller coating. Finally, baking cures the paint, forming a durable coating. After these processing steps, the plain aluminum coils are transformed into color-coated aluminum coils with a variety of colors and decorative effects.
Cleaning and pretreatment, including water jet cleaning and chemical conversion coating treatment, enhance corrosion resistance and paint adhesion.
Cleaning and pretreatment are crucial steps in the production of color-coated aluminum coils. Pre-treated aluminum coils undergo repeated water jet cleaning, a more efficient method than traditional cleaning methods. Water can be reused, reducing energy consumption. After water jet cleaning, the aluminum coil surface is cleaner, paving the way for subsequent processing.
Chemical conversion coating treatment forms a chemical conversion film on the aluminum surface, further enhancing the product's corrosion resistance and paint adhesion. This process begins with hot alkaline degreasing. Due to the high speeds of pre-coating lines, the degreasers used are typically highly concentrated, typically containing sodium hydroxide, sodium carbonate, water glass, and phosphates. Hot alkaline degreasing is typically a two-step process, often using spray and brush cleaning to ensure a thorough cleaning of the substrate surface.
Next, hot water cleaning is performed, primarily to remove any residual degreaser from the substrate surface and prevent secondary contamination. Immersion and spray and brush cleaning are commonly used. The water used should be of a low hardness to prevent mineral deposits from forming on the substrate surface. Finally, passivation treatment is performed. Passivation involves applying a passivating agent to form a conversion coating on the substrate surface through pressurized spraying, dipping, or roller coating. Pressurized spraying is generally used, but the sludge generated during the use of the passivating solution often clogs the spray holes, affecting spray efficiency. While dipping solves this problem, it consumes a large amount of passivating solution. Roller coating is the most effective passivation application method, offering uniform coating, economical application, and the elimination of rinsing. Aluminum sheets are typically treated with a chromate/oxide-based treatment agent, which contains chromates, chromic acid, phosphoric acid, fluorides, and molybdates. For aluminum sheets intended for food and beverage use, phosphoric acid must be added.
The coil coating process consists of two main stages: primer and topcoat.
In the first stage, the aluminum coil passes through a roller coater, where a primer is applied to one or both sides. The primer protects the aluminum coil. After the primer is roller-coated, the coating needs to be cured to prevent damage during transport.
After drying, the aluminum coil passes through a second roller coater, where it is coated on one or both sides. Topcoat roller coating is a critical step, applying a tinted finish to the surface of the pre-coated aluminum coil according to customer specifications. Similar to primer roller coating, curing is also required after the topcoat is applied.
Curing and subsequent processing require setting the appropriate temperature to ensure the coating cures. The cured aluminum coil can then be further processed into other designs.
The aluminum strip passes through a curing oven, set at a controlled temperature to ensure that all volatiles on the strip are removed and the coating is fully cured. Depending on the coating system, the curing temperature is set between 200 and 300 degrees Celsius, a critical technical requirement for ensuring product quality.
Regarding processing, the painted aluminum coil can be further processed into other designs, such as roller shutters, strips, or embossed patterns. When using color-coated aluminum coils in different fields, different coatings and types of products can be selected according to different requirements, so that they can play a better role in the field.
