Common surface treatment methods can be categorized by "metal substrate" and "non-metal substrate (plastic, wood, etc.)." The core types and characteristics are as follows:
Common Surface Treatments for Metal Substrates
1. Electroplating: A metal workpiece is placed in an electroplating solution. Electrolysis causes metal ions to adhere to the surface, forming a coating (such as zinc plating, chrome plating, and nickel plating). This primarily enhances rust resistance, wear resistance, or aesthetics (such as chrome plating for rust prevention on hardware and silver plating for decorative jewelry).
2. Anodizing: For metals such as aluminum and magnesium, an oxide film is formed on the surface of the workpiece through electrolysis (such as anodizing aluminum alloys). This film can be dyed (commonly silver and black) and enhances corrosion resistance and surface hardness. It is widely used in door and window profiles and electronic housings.
3. Spraying: A coating (liquid paint, powder coating) is applied to the workpiece surface using a spray gun or electrostatic adsorption. The coating forms after curing. These include:
Liquid spraying: Suitable for complex-shaped workpieces, such as automobile body painting.
Powder spraying: Solvent-free, produces thick coatings, and is commonly used for appliance housings and guardrails.
4. Phosphating: Plating metal (mostly steel) in a phosphating solution creates a phosphate film on the surface. This film serves primarily as a "base layer" for subsequent spraying/electroplating, enhancing coating adhesion and improving short-term rust protection (e.g., phosphating a car chassis before painting).
5. Passivation: Treating the metal surface with a chemical solution (such as chromates or chromium-free passivators) creates a passivation film that prevents further oxidation. This is commonly seen on stainless steel (improves rust resistance) and galvanized parts (extends rust protection).
Common Surface Treatments for Non-Metallic Substrates
1. Plastic Spraying/Painting: For plastic parts (such as ABS and PP), specialized plastic paints are used to enhance appearance (e.g., matte finish on mobile phone cases) and wear resistance. Some applications can also achieve a desired feel (e.g., soft-glue paint or rubberized paint).
2. Plastic Electroplating: The plastic surface is first roughened and activated, followed by electroplating with a metal layer (e.g., nickel or chrome plating on ABS plastic). This process is commonly used for decorative components (e.g., faucet handles, toy accessories).
3. Wood Finishing: This includes painting (clear varnish, color lacquer), waxing, and veneer. These processes primarily protect the wood (resisting moisture and scratches) and enhance its aesthetics. For example, furniture is varnished to preserve the wood grain, while floors are waxed to enhance wear resistance.
4. Ceramic/Glass Surface Treatment:
Glazing: Glaze is applied to the surface of ceramics before firing, resulting in a smooth, stain-resistant, and easy-to-clean surface (e.g., tiles and tableware).
Coating: Metallic films are applied to glass surfaces (e.g., silver-plated mirrors) or privacy films (e.g., mobile phone screens) to achieve specific functions.
Precautions
Common surface treatments (such as spraying, electroplating, phosphating, and anodizing) must focus on three key areas: pre-treatment cleaning, process parameter control, and post-treatment protection. Key considerations are as follows:
1. Pre-treatment: The foundation for surface treatment effectiveness
Thorough degreasing: Remove oil, cutting fluid, fingerprints, and other contaminants from the workpiece surface, as these can cause blistering and flaking of the coating/plating. Common cleaning methods include solvent cleaning, alkaline cleaning, or ultrasonic cleaning.
Complete rust/oxidation removal: For metal workpieces, remove rust and scale through methods such as pickling and sandblasting to ensure a strong bond between the treated layer and the substrate.
Clean and dry: After pre-treatment, the workpiece must be thoroughly rinsed (to avoid residual cleaning agent/acid) and then dried/air-dried to prevent moisture from affecting subsequent processes.
2. Process: Precision Control is Key
Strict Parameter Matching: Depending on the workpiece material (e.g., steel, aluminum, plastic) and treatment type, strictly control temperature (e.g., spray curing temperature, electroplating bath temperature), time (e.g., phosphating time, anodizing time), and concentration (e.g., paint viscosity, electroplating bath concentration). Parameter deviations can directly lead to quality issues (e.g., coating sagging and uneven coating thickness).
Environmental Requirements: Spraying, electroplating, and other processes must be performed in a clean, well-ventilated environment to avoid dust intrusion and surface particles. Humid environments may affect coating adhesion and paint drying.
Workpiece Placement: Ensure that workpieces are unobstructed and evenly stressed during processing. For example, avoid stacking workpieces during electroplating to prevent areas without coating. Adjust the angle during spraying to avoid missed areas.
3. Post-Processing: Ensure the performance and lifespan of the finished product.
Timely Curing/Drying: Some processes (e.g., powder coating and electrophoresis) require curing at a specified temperature after treatment to ensure coating hardness and corrosion resistance. Natural drying processes should be avoided in high-humidity and dusty environments.
Inspection and Repair: After treatment, inspect the surface for defects such as pinholes, scratches, and bubbles. Minor defects can be repaired with touch-up coating or polishing, while major defects require rework.
Protective Storage: Finished products must be properly protected based on the type of treatment. For example, electroplated parts can be coated with anti-rust oil, and spray-painted parts should be protected from contact with sharp objects. Storage should be moisture-proof, well-ventilated, and away from direct sunlight and high temperatures.
