Q:Before electrogalvanizing, a pretreatment step is required, which involves degreasing. How many types of degreasing are there?
A:Chemical degreasing: Use alkaline solution (such as sodium hydroxide, sodium carbonate, surfactant mixture) to remove animal and vegetable oils through saponification reaction, or remove mineral oil through emulsification.
Electrolytic degreasing: The workpiece is used as the anode or cathode, and electricity is passed through the alkaline electrolyte to use bubbles to peel off the grease (cathode degreasing is efficient, but may cause hydrogen embrittlement; anode degreasing does not have hydrogen embrittlement, but may corrode the substrate).
Ultrasonic degreasing: Use chemical agents to accelerate the detachment of grease through high-frequency vibration.
Q:What is the chemical composition of the plating solution?
A:Main salt: Provides zinc ions, common types include:
Cyanide zinc plating: zinc cyanide + sodium cyanide, fine coating but highly toxic (gradually phased out).
Cyanide-free zinc plating: Chloride zinc plating: zinc chloride + potassium chloride / sodium chloride, simple process, fast deposition speed, suitable for bright coating.
Sulfate zinc plating: zinc sulfate + sodium sulfate, low cost, suitable for thick zinc plating or wire.
Zincate zinc plating: zinc oxide + sodium hydroxide, environmentally friendly but poor dispersion ability.
Q:Why is passivation the key process of electrogalvanizing?
A:The purpose of passivation is to form a dense passivation film on the surface of the zinc layer, which significantly improves the corrosion resistance (salt spray resistance time can be increased from a few hours to hundreds of hours).
Q:How many types of passivation are there?
A:Hexavalent chromium passivation: Traditional process, excellent corrosion resistance (such as blue-white passivation, color passivation), but hexavalent chromium is toxic and is only used in specific scenarios.
Trivalent chromium passivation: Environmentally friendly process, corrosion resistance close to hexavalent chromium, optional color (such as blue-white, black).
Chromium-free passivation: Silane treatment, titanate treatment, etc., in line with RoHS standards, suitable for high-end environmental protection needs.
Q:How to test the quality after electrogalvanizing?
A:1. Appearance inspection: The coating should be uniform, without missing plating, bubbles, burns and other defects.
2. Thickness detection: Magnetic thickness gauge: Applicable to zinc layer on steel substrate (most commonly used).
Coulometric method: Measure the thickness by electrolytic stripping of the coating, with high accuracy.
3. Adhesion test: Bending method, cross-cutting method, observe whether the coating falls off.
4. Corrosion resistance test: Salt spray test, requiring the salt spray resistance time to meet the standard (such as 72 hours without white rust).