1. Check the Environmental Corrosion Level: Is it Corrosion-Proof?
Low-Corrosion Environment (Dry Indoors): If the nut is used in water-free and salt-free environments such as furniture and office equipment, electroplating or blackening treatment is sufficient.
✅ Judgment Criteria: Salt spray test ≥72 hours, cost controllable.
Medium-High Corrosion Environment (Outdoor, Humid): For applications such as streetlights, communication towers, and agricultural machinery, Dacromet or hot-dip galvanizing should be selected.
✅ Judgment Criteria: Dacromet salt spray test ≥500 hours, hot-dip galvanizing coating thickness 55–120μm, can guarantee rust-free outdoor use for 15 years.
Strong Corrosion Environment (Marine, Chemical): For applications such as ships, offshore platforms, and acid/alkali equipment, Dacromet, Teflon coating, or stainless steel + passivation must be used.
✅ Judgment Criteria: Dacromet withstands over 1200 hours of salt spray without red rust; Teflon is resistant to strong acids and alkalis and has a low coefficient of friction.
🔍 Self-Inspection Suggestion: If white rust (zinc corrosion products) or red rust (iron substrate corrosion) is found on the nut surface, it indicates insufficient protection and requires upgrading the treatment process.
2. Check Mechanical Performance Requirements: Can it withstand the load?
High-strength Connections (≥8.8 grade bolts): Electroplating zinc may cause hydrogen embrittlement, leading to a risk of breakage.
✅ Judgment Criteria: Dacromet is the preferred choice, as its hydrogen-free characteristics make it suitable for high-strength fasteners of grade 10.9 and above.
High-Vibration Conditions (Engines, Rail Transit): Requires strong coating adhesion and good fatigue resistance.
✅ Judgment Criteria: Dacromet has excellent adhesion; its effect is even better when used with anti-loosening nuts.
High-Temperature Environments (>200℃): Ordinary zinc plating is prone to peeling and failure.
✅ Judgment Criteria: Dacromet has a heat resistance of over 300℃, making it an ideal choice.
3. Assemble and Use Experience: Can it be tightened and disassembled?
Precision assemblies or stainless steel nuts are prone to "seizing."
✅ Judgment Criteria: Uses Teflon coating or DLC diamond-like carbon coating, with a stable coefficient of friction between 0.08 and 0.12, preventing stripping and jamming^[A3]^.
Requires subsequent coating or bonding: The surface must have good adhesion.
✅ Judgment Criteria: Uses phosphating treatment as a primer to improve the adhesion strength of paint or adhesives.
Conductivity Requirements (Electronic Equipment Grounding): The coating cannot be insulating.
✅ Judgment Criteria: Nickel plating can balance conductivity and corrosion resistance.
4. Cost and Environmental Compliance: Is it worthwhile? For general projects with limited budgets: Electroplating offers the best cost-performance ratio, but wastewater treatment issues must be considered.
For projects with high environmental requirements (such as exports to Europe): Traditional electroplating contains hexavalent chromium, posing environmental risks.
✅ Judgment Criteria: Dacromet's production process is pollution-free and conforms to modern environmental trends.
For small-batch customization or special specifications: Mechanical plating or PVD vacuum ion plating can be considered to avoid heat treatment deformation and is suitable for miniature nuts (M1–M3).
