1.Pre-treatment cleanliness and activation
- Key point: Ensuring that the surface of the brass substrate is absolutely clean, free of oxidation, and fully activated is the basis for successful electroplating.
- Why is it important?
o Oil stains, fingerprints, polishing paste residues, and slight oxide films will hinder the bonding of the coating to the substrate, causing blistering, peeling, pitting, or flowery coating.
o Brass contains zinc, and the surface state is more sensitive. Insufficient activation will lead to uneven coating coverage or poor bonding.
- Core measures:
o Multi-stage cleaning: Degreasing (alkaline/ultrasonic) → pickling (remove the oxide layer, control the acid concentration and time to prevent over-corrosion) → activation (weak acid etching, such as dilute sulfuric acid) → pure water rinsing (prevent impurities from entering the plating tank).
o Strict water washing: Rinse thoroughly with flowing pure water between each process to prevent cross contamination.
o Instant electroplating: Put the plating into the tank as soon as possible after activation to avoid re-oxidation of the surface.
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- Precise control of plating solution composition, temperature and pH value
- Key points: Maintain stable concentration of plating solution composition, constant temperature and pH value in the optimal process window.
- Why is it important?
o Imbalance of composition: Low concentration of main salt leads to loose coating; consumption of additives affects brightness and leveling; accumulation of impurities causes fogging, brittleness, pinholes or streaks in the coating.
o Temperature fluctuation: Affects deposition rate, internal stress of coating, current efficiency and additive efficiency. Too high temperature may accelerate the decomposition of additives, while too low temperature reduces conductivity.
o pH value deviation: Affects coating composition, dispersion ability, anode dissolution and additive effect. Too high pH is prone to hydroxide inclusions; too low pH may corrode the substrate or coating.
- Core measures:
o Regular analysis and testing: Detect the concentration of main salt, additives and impurity ions according to the frequency required by the process.
o Automatic replenishment system: Use Hall cell test or automatic controller to accurately add additives.
o Constant temperature control: Equipped with heating/cooling system and temperature sensor.
o Automatic pH monitoring: Use online pH meter and equipped with automatic acid/alkali adding device.
o Continuous filtration: Keep the plating solution clean and remove particulate impurities.
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- Current density and distribution uniformity
- Key point: Accurately control the applied current density and ensure that it is evenly distributed on the surface of the workpiece.
- Why is it important?
o Too high current density: Causes the coating to be charred, rough, dendritic or cracked due to excessive internal stress.
o Too low current density: Slow deposition speed, dark and dull coating, and poor coverage.
o Uneven distribution: Causes inconsistent coating thickness, brightness and even color at different positions on the same hanger, seriously affecting the uniformity of appearance.
- Core measures:
o Calculation and setting: Accurately calculate the total current based on the total area of the workpiece and set it within the recommended range of the process.
o Optimize the design of the hanger: Use appropriate hanging points/hooks, arrange the workpieces reasonably, add auxiliary anodes or shielded cathodes when necessary, and ensure uniform distribution of power lines.
o Cathode movement/air stirring: Enhance the convection of the plating solution, reduce concentration polarization, and improve the dispersion ability and deep plating ability.
o Check the anode regularly: Ensure that the anode dissolves evenly and conducts well, and clean or replace it when necessary.
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- Plating thickness and bonding strength
- Key points: Ensure that the plating reaches the specified minimum thickness and is firmly bonded to the brass substrate.
- Why is it important?
o Insufficient thickness: Corrosion resistance and wear resistance do not meet the requirements, and it is easy to expose the bottom, discolor, and wear.
o Poor bonding strength: The plating is easy to peel and peel, and completely loses its protective and decorative properties.
- Core measures:
o Thickness control: Accurately control the thickness through current density, time, and temperature. Use an X-ray fluorescence thickness gauge (XRF) or a metallographic microscope to spot check the thickness of key parts.
o Adhesion test: Strictly implement destructive tests for verification.
o Strictly control pretreatment and activation: The root cause of adhesion problems is often in pretreatment.
o Avoid power failure during the process: Power failure during electroplating can easily lead to delamination.
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- Post-treatment and sealing protection
- Key points: Thorough cleaning, passivation/sealing treatment should be performed immediately after electroplating to prevent degradation of the coating.
- Why is it important?
o Residual plating solution: Acid/alkali solution in the gaps or blind holes will slowly corrode the coating, causing spots and discoloration.
o Porosity in the coating: Even bright coatings have micropores, and corrosive media in the environment will corrode the underlying metal through the micropores.
o Fingerprints and water stains: Contact or incomplete drying during operation will leave traces, affecting the appearance.
- Core measures:
o Multi-stage countercurrent rinsing: Use pure water to thoroughly clean the surface of the workpiece and the residual plating solution in the gaps.
o Passivation/sealing treatment: Chromate passivation or special sealer is used to fill the pores of the coating, significantly improving corrosion resistance.
o Anti-fingerprint treatment: AF coating is applied to high-end accessories to improve touch and easy cleaning.
o Hot pure water scalding/drying: Ensure complete drying to prevent water stains.
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Summary: The electroplating of brass bag accessories is a precise and interlocking process. From the “clean” of pre-treatment, to the “stable” of plating solution parameters, to the “accurate” current control, the “thick” and “firm” of the coating are finally ensured, and the “protection” of post-treatment is achieved to achieve long-term beauty and durability. Any loss of control in any link may lead to batch quality problems, so a strict process specification and process monitoring system must be established.
