1.What is the impact of pickling and rinsing water quality?
Calcium/magnesium ions (hardness ions) hazards:
React with hydrochloric acid to form CaCl₂/MgCl₂, which deposits hard scale on the surface of steel parts, hinders the uniformity of pickling, and causes plating spots after plating.
Iron ion (Fe²⁺) accumulation: When the Fe²⁺ concentration in the pickling solution is >80g/L, FeCl₂ crystals are formed and attached to the surface. The residue after rinsing causes the porosity of the coating to increase by 30%.
Control solution: Use demineralized water to dilute hydrochloric acid;
Install ion exchange resin or reverse osmosis system to remove Ca²⁺/Mg²⁺.
2.What influence does water quality have on activation effect?
Preparation of plating aid and replenishing water
Sodium/potassium ions: When the concentration is >100ppm, it destroys the stability of ZnCl₂·NH₄Cl plating aid, resulting in an increase in solution viscosity and a 50% increase in the amount of workpiece carried out.
Sulfate: It reacts with Zn²⁺ in the plating aid to form ZnSO₄ precipitation, which blocks the nozzle, and the precipitate is entrained into the zinc bath to form zinc slag.
Silicate: It comes from groundwater or poor quality industrial water, forming colloidal silicon adsorbed on the surface of steel parts, hindering the zinc-iron reaction, causing the coating adhesion to decrease by 40%.
3.What are the risks in post-plating water cooling?
Dissolved oxygen: 5ppm DO induces oxygen concentration difference corrosion on the surface of high-temperature plated parts, generating porous ZnO/Zn(OH)₂ white rust (thickness can reach 10μm).
Chloride ions: Residual Cl⁻ concentrates in cooling water, inducing pitting and perforation of the coating.
Microorganisms: Form biofilm attached to the coating, secrete acidic metabolites, and the local pH drops to 4.0, accelerating corrosion.
4.How to treat wastewater?
Fluoride: It comes from the fluorine-containing inhibitor of acid washing. When the concentration is >15ppm, it will corrode the RO membrane and require lime precipitation pretreatment.
Grease: 50mg/L of grease will clog the resin column and requires flotation separation + activated carbon adsorption.
5.What is the engineering value of water quality control?
Reduced defect rate: Controlling Cl⁻/hardness can reduce missed plating and white rust by more than 70%;
Zinc consumption saving: Optimizing the water quality of the plating aid, zinc slag generation↓25%;
Environmental compliance: Wastewater classification reuse rate>80%, achieving near-zero emissions;
Coating life guarantee: Cooling water corrosion inhibition treatment extends the corrosion life of the coating by 30%.