Dacromet Flange Bolts–Anti-Corrosion Flange Fasteners with Zinc-Aluminum Flake Coating 

Part 1 — Flange Bolt Overview

What Is a Flange Bolt?

A flange bolt is a hex head bolt with an integrated washer-like flange at the base of the head. The flange distributes the clamping load over a wider area, reducing surface pressure on the connected material and preventing damage to soft or painted surfaces. This eliminates the need for a separate flat washer, simplifying assembly and reducing part count.

Key Design Features

Integral flange: Distributes clamping force over a larger area than a standard hex head, reducing bearing stress and preventing surface indentation.

Serrated option: Serrated flange underside bites into the mating surface, providing built-in anti-loosening resistance without additional locking components.

Standardized dimensions: Manufactured to DIN 6921, ISO 4162, or GB/T 5787, ensuring interchangeability across global supply chains.

High-strength grades: Available in property class 8.8 and 10.9, suitable for structural and load-bearing applications.

Specifications

Part 2 — Dacromet Coating Technology

Dacromet (达克罗) is a water-based, non-electrolytic surface treatment that deposits a thin film of overlapping zinc and aluminum flakes bonded by inorganic chromium compounds. Applied via a dip-spin-cure process, it provides multiple layers of corrosion protection without introducing hydrogen into the steel — a critical advantage for high-strength fasteners.

Corrosion Protection Mechanism

Sacrificial protection: Zinc flakes corrode preferentially to protect the steel substrate, even when the coating is scratched.

Physical barrier: Overlapping zinc-aluminum flakes create a tortuous path that blocks moisture, oxygen, and corrosive ions.

Chemical passivation: Chromium compounds form a passive layer that slows zinc dissolution and provides self-healing at micro-scratches.

Key Advantages for Flange Bolts

No hydrogen embrittlement: Non-electrolytic process — safe for Grade 8.8–10.9 high-strength flange bolts where electroplating is restricted.

Thin & uniform: 4–10 µm coating preserves thread fit and flange geometry. No re-tapping of nuts required.

500–1,200 hrs salt spray: 5–10 times better than conventional zinc plating, suitable for long-term outdoor exposure.

Heat resistant: Withstands continuous service up to 250°C — ideal for engine bay and exhaust-adjacent fasteners.

Environmentally compliant: Cr⁶⁺-free, RoHS and REACH compliant.

Coating Comparison

Salt spray per ISO 9227 NSS. Hydrogen embrittlement risk applies to electroplated fasteners Grade 10.9 and above.

Summary

Dacromet flange bolts offer a compelling combination of mechanical efficiency and corrosion protection. The integral flange simplifies assembly while distributing load evenly, and 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 both reliable clamping performance and long-term durability are essential.