1.What is the core process of SECC's electrogalvanizing process?
Substrate preparation and pretreatment
Electrogalvanizing core process (electrolytic deposition)
Post-coating treatment (passivation, fingerprint resistance, etc.)
Finished product drying, slitting, and inspection
2.What are the purpose and key operating details of the degreasing (oil removal) process?
Remove residual rolling oil, lubricating oil, and other organic contaminants from the substrate rolling process.
Use an alkaline degreaser (such as sodium hydroxide or sodium carbonate solution) or a solvent (such as gasoline or trichloroethylene) for degreasing.
Control the temperature at 40-60°C and use a spray or immersion method combined with ultrasonic cleaning to ensure thorough removal of any contaminants. Rinse with clean water to remove any remaining degreaser residue.
3.What is the core process principle of electrogalvanizing?
Electrolytic Zinc Deposition
This step involves an electrolytic cell reaction, reducing zinc ions to metallic zinc on the substrate surface, forming a uniform, dense zinc coating. SECC typically utilizes either "acid galvanizing" or "alkaline galvanizing" processes. Acid galvanizing is more widely used due to its excellent coating uniformity and suitability for thin coatings (5-20μm per side is common in SECC).
Core Principle
Electrolytic Cell Composition:
Anode: Soluble zinc plate (pure zinc with a purity of ≥99.95% to ensure stable dissolution of zinc ions);
Cathode: Pre-treated cold-rolled steel sheet (substrate, workpiece to be plated);
Plating Solution: Acidic zinc salt solution (primarily zinc chloride (ZnCl₂) or zinc sulfate (ZnSO₄), with boric acid (H₃BO₃) as a pH buffer and organic additives to improve coating gloss and smoothness).
4.How to control key process parameters?
Current Density: 10-30 A/dm² (A current density that is too low results in a thin and uneven coating; a current density that is too high results in a rough coating with pinholes).
Bath Temperature: 15-40°C (Acid zinc plating is temperature-sensitive; high temperatures can cause additive decomposition and reduce the coating's gloss).
Bath pH: 3.5-5.0 (Borate buffering is used; a pH that is too low can accelerate substrate corrosion, while a pH that is too high can cause zinc ions to form zinc hydroxide precipitates, contaminating the bath).
Plating Time: Adjust according to the target coating thickness (e.g., a 10μm coating on one side requires 2-5 minutes of plating).
Bath Circulation and Filtration: Pump circulation combined with continuous filtration (5-10μm filter element) ensures uniform bath composition, removes impurities, and prevents "granular defects" in the coating.
5.What are the core features of the SECC electrogalvanizing process?
Good coating uniformity: Electrolytic deposition can achieve micron-level uniform coatings, making it suitable for workpieces with complex shapes (however, SECC is primarily flat and requires subsequent stamping).
Flexible process: The coating thickness (5-20μm) can be precisely controlled by adjusting the current and time to meet different corrosion protection requirements.
Environmental performance needs improvement: Traditional chromate passivation contains hexavalent chromium (which is toxic). Currently, "chromium-free passivation" (such as titanate and zirconate passivation) is being gradually promoted and complies with environmental standards such as RoHS.