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Dacromet Flange Bolts
2026-07-23
Dacromet Flange Bolts
Anti-Corrosion Flange Fasteners with Zinc-Aluminum Flake Coating
Dacromet flange bolts combine the load-distributing flange head design with Dacromet zinc-aluminum flake coating. The integral flange replaces a separate washer, while the Dacromet coating delivers 500–1,200 hours of salt spray resistance without hydrogen embrittlement — ideal for automotive, construction, and marine applications.
Part 1 — Flange Bolt
A flange bolt is a hex head bolt with an integrated washer-like flange at the head base. The flange distributes clamping load over a wider area, reducing surface pressure and preventing damage to connected materials. This eliminates the need for a separate washer, simplifying assembly.
Key Features
- Load distribution: Flange spreads clamping force, reducing bearing stress by up to 50% compared to standard hex bolts.
- Anti-loosening: Serrated flange option provides built-in vibration resistance without locking washers.
- Standards: DIN 6921 / ISO 4162 / GB/T 5787; M6–M20; Grade 8.8 and 10.9 per ISO 898-1.
- Materials: Carbon steel (Grade 8.8) or low-alloy steel (Grade 10.9), quenched and tempered.
Part 2 — Dacromet Coating
Dacromet is a water-based, non-electrolytic coating of overlapping zinc and aluminum flakes bonded by chromium compounds. Applied via dip-spin-cure cycles at 280–300°C, it provides three-layer corrosion protection without hydrogen embrittlement.
Protection Mechanism
- Sacrificial protection: Zinc flakes corrode preferentially to protect steel, even when coating is scratched.
- Physical barrier: Overlapping flakes block moisture, oxygen, and corrosive ions.
- Chemical passivation: Chromium compounds slow zinc dissolution and self-heal micro-scratches.
Key Advantages
- No hydrogen embrittlement: Non-electrolytic process — safe for Grade 8.8–10.9 high-strength bolts.
- Superior corrosion resistance: 500–1,200 hrs salt spray (ISO 9227), 5–10x better than zinc plating.
- Thin & uniform: 4–10 µm preserves thread fit and flange geometry. No re-tapping needed.
- Heat resistant & eco-friendly: Withstands 250°C; Cr⁶⁺-free, RoHS/REACH compliant.
Coating Comparison
| Property | Dacromet | Zinc Plating | Hot-Dip Galv. |
| Salt Spray (hrs) | 500 – 1,200 | 96 – 240 | 300 – 1,000 |
| Hydrogen Embrittlement | None | Risk (Gr. 10.9+) | None |
| Coating Thickness | 4 – 10 µm | 5 – 25 µm | 45 – 85 µm |
| Thread Fit Impact | Minimal | Low | Significant |
| Heat Resistance | 250°C | 200°C | 250°C |
| Appearance | Silver-grey, matte | Blue-white | Bright / spangled |
Summary
Dacromet flange bolts offer an optimal combination of mechanical efficiency and corrosion protection. The integral flange distributes load and simplifies assembly, while the Dacromet zinc-aluminum flake coating delivers 500–1,200 hours of salt spray resistance without hydrogen embrittlement. These fasteners are widely used in automotive, construction, wind energy, and marine applications where reliable clamping and long-term durability are essential.
