Here are some common surface treatment methods that can improve the cleanliness of substrate surfaces:
1、 Mechanical processing method
Sandblasting treatment:
Principle: By using high-speed sand particles to impact the surface of the substrate, impurities such as oxide scale, rust, old coatings, and dirt are removed from the surface. At the same time, a certain roughness is formed on the substrate surface, which is conducive to the adhesion of subsequent coatings. Under the driving force of high-pressure gas or water flow, sand particles collide with the substrate with high kinetic energy, and physically break the connection between impurities and the substrate, causing them to detach from the substrate surface.
Application example: Sandblasting treatment is often used before painting or applying other protective coatings on metal structural components such as bridge steel beams, ship hulls, etc. For example, for the steel beams of a steel bridge, using quartz sand through sandblasting equipment at an appropriate pressure (usually determined by factors such as the material and thickness of the steel beam, generally between 0.2-0.6MPa) can effectively remove impurities such as rust and oil stains formed by long-term exposure on its surface, and achieve a surface roughness of about 30-80 μ m, providing a good adhesion foundation for subsequent coatings.
Polishing treatment:
Principle: Friction between grinding tools such as sandpaper and grinding wheels and the substrate surface is used to remove surface irregularities, oxide layers, and impurities, making the surface smooth and clean. Manual polishing or mechanical polishing can be used. Manual polishing is suitable for small areas and complex shaped substrates, while mechanical polishing is more efficient and suitable for large-area substrate treatment.
Application example: Before painting the surface of automotive components such as engine cylinder blocks and body shells, sandpaper is commonly used to polish their surfaces. For example, first use coarse sandpaper (such as 80-120 mesh) to remove burrs, old paint layers, etc. on the surface, and then use fine sandpaper (such as 240-320 mesh) to further refine and polish, making the surface flat, smooth, and clean, and improving the adhesion between the subsequent paint coating and the substrate.
2、 Chemical treatment method
Acid washing treatment:
Principle: Soak the substrate in a solution containing acid (such as hydrochloric acid, sulfuric acid, phosphoric acid, etc.), and use the acid to react chemically with impurities such as oxides and rust on the surface of the substrate, causing them to dissolve in the acid, thereby achieving the goal of removing impurities and cleaning the surface. Different base materials and impurity types can be selected with different acid solutions and corresponding process parameters.
Application example: For stainless steel products (such as stainless steel pipes, stainless steel kitchenware, etc.), acid washing process is commonly used before surface coating or other protective treatment. For example, immersing stainless steel pipes in a mixed acid solution of nitric acid and hydrofluoric acid containing a certain concentration (usually 10% -20%), under appropriate temperature (generally controlled at 40-60 ℃) and soaking time (mostly 15-30 minutes depending on the degree of dirt and other factors of the pipeline) conditions, can effectively remove the oxide film and some slight oil stains on the surface of the pipeline, making the pipeline surface clean and bright, and facilitating subsequent coating application.
Alkali washing treatment:
Principle: By using alkaline solutions (such as sodium hydroxide, sodium carbonate, etc.) to undergo saponification or emulsification reactions with organic matter such as oil and grease on the substrate surface, these impurities are removed from the substrate surface. Alkali washing is usually combined with heating, stirring, and other operations to improve the cleaning effect.
Application example: In the mechanical processing industry, some aluminum alloy parts often require alkaline washing before surface treatment such as anodizing. For example, placing aluminum alloy parts in an alkaline washing tank containing a certain concentration (about 5% -10%) of sodium hydroxide solution, heating to 60-80 ℃, and stirring appropriately for 10-20 minutes can effectively remove cutting oil, oil stains, etc. on the surface of the parts, creating good surface conditions for subsequent oxidation treatment and coating.
3、 Physical and chemical processing methods
Ultrasonic cleaning:
Principle: Place the substrate in an ultrasonic cleaning tank containing cleaning solution, and use the high-frequency vibration generated by ultrasonic waves in the cleaning solution to form tiny cavitation bubbles in the cleaning solution. These bubbles will generate strong impact force during the growth and rupture process, acting on the impurities on the surface of the substrate and peeling them off, achieving the purpose of cleaning the surface. At the same time, the vibration of ultrasound can accelerate the chemical reaction between the cleaning solution and impurities, enhancing the cleaning effect.
Application example: Ultrasonic cleaning is often used on the surface of electronic components (such as circuit boards, chips, etc.) before applying coatings such as three proof paint. For example, placing the circuit board in an ultrasonic cleaning tank containing a specialized electronic cleaning agent, setting the appropriate ultrasonic frequency (usually between 20-80kHz) and cleaning time (5-15 minutes), can effectively remove impurities such as dust, flux residue, and oil stains on the surface of the circuit board, ensure surface cleanliness, and improve the adhesion between the three proof paint coating and the circuit board.
Plasma cleaning:
Principle: In a vacuum or low-pressure environment, plasma is formed by exciting gas. The active particles (such as ions, electrons, free radicals, etc.) in the plasma undergo physical and chemical reactions with impurities on the substrate surface, removing or converting the impurities into easily volatile small molecule substances, which are then discharged through an exhaust system to achieve cleaning of the substrate surface. This method can process substrates of various shapes and materials, and can precisely control the depth and range of cleaning.
Application example: Before coating high-precision and high demand products such as optical lenses and semiconductor chips, plasma cleaning is commonly used. For example, for optical lenses, argon gas or other gases are introduced into a vacuum environment to form plasma. The active particles in the plasma react with organic matter, water vapor and other impurities on the surface of the lens to remove impurities. After removing the impurities, the cleanliness of the lens surface is greatly improved, which is conducive to the adhesion of subsequent optical coatings and improves the coating quality.

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