Release time：2020-01-16 18:44 Browse：
To achieve eco-friendly zinc plating for long screws while meeting 72+ hours of salt spray resistance, consider the following methods:
Chloride or alkaline zinc plating: More environmentally friendly than traditional methods, with easier wastewater treatment.
Zinc diffusion (Sherardizing): A powder-based, zero-waste process offering superior corrosion resistance (500+ hours salt spray).
Dacromet (Zn-Cr coating): Highly corrosion-resistant (1000+ hours salt spray) and hydrogen embrittlement-free, but more expensive.
Trivalent chromium passivation (replacing toxic hexavalent chromium) improves corrosion resistance.
Chromium-free sealants (e.g., silane, organic coatings) can extend salt spray resistance to 200+ hours.
Combination: Zinc plating + sealant + oil coating further enhances rust prevention.
Electroplated zinc: 8–12 μm (too thin reduces protection; too thick affects thread fit).
Diffusion zinc: 10–50 μm (more uniform, ideal for long screws).
Avoid zinc plating for Grade 10.9+ screws; use phosphating or zinc diffusion instead.
If electroplating is necessary, bake at 200°C for 4 hours within 2 hours to remove hydrogen.
Use heavy metal wastewater treatment (e.g., chemical precipitation, membrane filtration).
Implement water recycling systems to reduce discharge.
| Method | Process | Salt Spray (Hours) | Eco-Friendliness | Cost |
|---|---|---|---|---|
| Zinc plating + trivalent passivation | Chloride/alkaline | 72–200 | Good | Low |
| Zinc plating + Cr-free sealant | Chloride | 200+ | Excellent | Medium-High |
| Zinc diffusion | Powder-based | 500+ | Best | Medium-High |
| Dacromet | Zn-Cr coating | 1000+ | Excellent (but contains Cr) | High |
Recommended Approach:
Basic corrosion resistance (72 hours): Zinc plating + trivalent passivation.
High corrosion resistance (200+ hours): Zinc diffusion or Cr-free sealed zinc plating.
Extreme environments (500+ hours): Dacromet or zinc diffusion.
