Does aluminum plate spraying undergo pre-treatment such as degreasing, alkali cleaning, and pickling before spraying?
Publish Time: 2025-09-02
Aluminum plate spraying is a widely used surface treatment process in modern architectural curtain walls, interior decoration, and industrial manufacturing. Its ultimate effectiveness depends not only on the quality of the coating itself and the spraying technique, but also on the surface pre-treatment before spraying. While not visible in the final appearance, this step is the cornerstone of the coating's adhesion, durability, and overall quality. In actual production, pre-treatment steps such as degreasing, alkali cleaning, and pickling are not optional extras but essential to ensuring the ideal aluminum surface condition. Only through systematic cleaning and activation can the sprayed coating form a strong bond with the aluminum substrate, resist environmental corrosion, and achieve long-term stability.
During processing, transportation, and storage, aluminum surfaces inevitably become contaminated with grease, dust, fingerprints, oxides, and other contaminants. If these substances are not thoroughly removed, they form an invisible barrier, preventing direct contact between the paint and the metal. Even the most precise spraying process can still cause blistering, flaking, or premature failure of the coating due to adhesion to loose impurities. Therefore, the primary task of pretreatment is to thoroughly clean the surface and restore the aluminum to its "pure" state.
Degreasing is the first step in pretreatment, aiming to remove organic contaminants from the aluminum sheet's surface, such as stamping oil, anti-rust oil, and fingerprints left during handling. These oils are generally insoluble in water and require emulsification and decomposition with specialized degreasing agents or alkaline cleaning solutions. Through immersion, spraying, or ultrasonic cleaning, the oil is effectively removed, laying the foundation for subsequent treatment. Incomplete degreasing can lead to a decrease in localized adhesion of the coating, especially in high-temperature and high-humidity environments, where moisture can easily penetrate along the interface, causing bulging and rust.
Alkaline cleaning goes a step further, primarily removing the natural oxide film and minor mechanical damage layers on the aluminum surface. Aluminum rapidly forms a thin, loose oxide layer in air. This film has an uneven structure and weak adhesion to subsequent coatings. Alkaline cleaning, through a controlled reaction between a strong alkaline solution and aluminum, evenly etches the surface, exposing a fresh, active metal layer. It also removes fine particles and residual impurities, leaving the surface cleaner. This process not only cleans but also micro-activates it, creating a roughness that enhances the coating's adhesion.
Acid washing is typically performed as a neutralization and polishing step after alkaline washing, neutralizing any residual alkaline solution and preventing further corrosion of the aluminum. Certain acidic solutions can also further remove the "gray film" or micro-precipitates that may form after alkaline washing, resulting in a uniform metallic luster. Acid washing also subtly adjusts the surface microstructure, improving the coating's wettability and adhesion. The acid-washed aluminum sheet's surface is denser and more uniform, facilitating even coating application and curing.
These pretreatment steps are typically performed on a continuous processing line, with extensive water washes between each process to ensure thorough removal of chemicals from previous stages and prevent cross-contamination. The entire process requires strict control of temperature, concentration, and treatment time to ensure consistent treatment for each aluminum sheet, ensuring stability in mass production.
Notably, with increasing environmental protection requirements, traditional chroming is being replaced by chromium-free passivation technologies. This new type of conversion coating effectively improves coating adhesion and corrosion resistance without the use of heavy metals, demonstrating the sustainable development of pretreatment processes.
In summary, pretreatment processes such as degreasing, alkaline cleaning, and acid cleaning before spraying aluminum plates are crucial for ensuring coating quality. It's more than just a simple "cleaning" process; it's a scientific surface engineering system that uses physical and chemical methods to create an ideal substrate for spraying. Neglecting pretreatment is like building a tall building on an unstable foundation. Even if the appearance is temporarily perfect, it will struggle to withstand the test of time and the environment. Only by paying attention to every detail can aluminum plate spraying achieve comprehensive excellence in aesthetics, functionality, and longevity.
