Q:What is the reason for poor coating adhesion?
A:1. Incomplete pretreatment: Grease, rust, and scale are not removed completely, resulting in an isolation layer between the zinc layer and the substrate; Over-pickling or under-pickling: Over-pickling will cause the substrate surface to become too rough (forming a loose layer), while under-pickling will result in residual oxide film.
2. Poor activation: The concentration of the activation solution is too low or aged, and the thin oxide film generated after pickling is not completely removed.
3. Incomplete water washing before electroplating: Acid or other impurities are brought into the plating tank, forming a film on the surface of the workpiece to hinder bonding.
4. Problems with substrate material: High-carbon steel, cast iron and other materials have many pores on the surface, which are prone to residual acid or gas.
Q:How to deal with poor coating adhesion (falling off, peeling)?
A:Strengthen pre-treatment: After degreasing, use the water film method to test (the surface water film is continuous without breaks to be qualified), and if necessary, extend the degreasing time or increase the temperature; control the time and concentration during pickling to avoid over-corrosion; cast iron parts can be "double pickled" (first use concentrated acid to etch thick rust for a short time, and then use dilute acid to activate).
Activation liquid maintenance: Regularly replace the activation liquid to ensure the concentration (such as hydrochloric acid concentration maintained at 10%~15%), and control the activation time to 10~30 seconds.
Thoroughly wash before electroplating: Increase the number of water washing tanks (at least 2 levels of water washing), use countercurrent rinsing, and ensure that the pH value is close to neutral.
Special material pretreatment: High carbon steel parts can be pre-plated with cyanide copper or nickel before electroplating to enhance bonding strength.
Q:What is the reason for the rough surface and many particles in the coating?
A:1. Plating solution impurity contamination:
Metal impurities: originate from the dissolution of the matrix or the impurity of the anode zinc plate, which makes the coating crystal coarse.
Solid particles (such as anode mud, tank bottom sediment, pre-treatment residual sand): adsorbed on the surface of the workpiece to form bulges.
2. Improper process parameters: Too high current density: leads to "burning" phenomenon (rough and black edges or tips).
Temperature is too low: the viscosity of the plating solution is high, the ion migration is slow, and the crystal particles are coarse.
Additive imbalance: Excessive brightener will cause organic impurities to accumulate and form flocculent adsorption; insufficient leveling agent cannot cover the pits.
3. Insufficient stirring: The plating solution does not flow smoothly, the local metal ions are depleted, and dendrites are formed.
Q:How to deal with the rough surface and many particles of the coating?
A:1. Purify the plating solution:
Metal impurity treatment: Fe²+: 30% H₂O₂ can be added to chloride zinc plating to oxidize to Fe³+, adjust the pH value to 5.5~6.0, and precipitate and filter.
Cu²+, Pb²+: Use zinc powder (1~3 g/L) to stir for 30 minutes for adsorption, and filter to remove.
Solid particles: Clean the bottom of the plating tank regularly, and use acid-resistant polyester cloth or nylon cloth for the anode sleeve to prevent the anode mud from falling off.
2. Optimize process parameters: Reduce the current density to the lower limit of the process range (such as chloride zinc plating from 8 A/dm² to 5 A/dm²).
Increase the plating solution temperature (such as zincate zinc plating from 40℃ to 50℃), or add a cooling device to control the temperature (chloride zinc plating requires room temperature).
Adjust additives: Add brightener in small amounts and multiple times to avoid excessive amounts; regularly use activated carbon to treat organic impurities (such as once every 1~3 months).
3. Increase stirring: Turn on air stirring or cathode moving device to ensure uniform flow of plating solution.
Q:Ideas for troubleshooting electrogalvanizing problems?
A:1. Check the pre-treatment first: more than 80% of the coating problems are caused by incomplete degreasing and pickling. Prioritize the inspection of water film continuity, activation time, etc.
2. Check the process parameters again: whether the current density, temperature, and pH value are within the process range, which can be quickly verified by the "Hull cell test" (small cell test plating).
3. Finally, check the plating solution and equipment: analyze the composition of the plating solution, test the equipment (such as power supply stability, stirring effect), and gradually eliminate hardware failures.