Dacromet Flange Bolts: Superior Anti-Corrosion and Anti-Rust Performance for Demanding Applications 

Dacromet is a non-electrolytic, water-based inorganic coating system composed primarily of overlapping zinc and aluminum flakes dispersed in a chromium-containing or chromium-free inorganic binder. Applied by dip-spin, spray, or dip-drain methods and subsequently heat-cured, the coating forms a thin (typically 5–15 μm), uniform, silver-gray protective film that adheres tightly to the steel substrate.

The anti-corrosion mechanism of Dacromet operates through four complementary actions:

1.Barrier protection: Overlapping zinc and aluminum flakes create multiple layers that impede the penetration of moisture, oxygen, and corrosive ions.

2.Sacrificial (galvanic) protection: Zinc acts as a sacrificial anode, preferentially corroding to shield the underlying steel from rust.

3.Self-healing / self-repairing: Oxidation products of zinc and aluminum fill micro-damage in the coating, maintaining continuous anti-rust integrity.

4.Passivation: The inorganic binder and passivating compounds slow the sacrificial consumption of zinc, prolonging overall corrosion resistance.

Because the process involves no acid pickling or electrolysis, Dacromet coating completely eliminates the risk of hydrogen embrittlement—a critical advantage for high-strength bolts (Grades 10.9, 12.9, and ASTM A490 / F3125). This makes Dacromet flange bolts both mechanically reliable and highly resistant to rust and environmental degradation.

3. Key Advantages of Dacromet Flange Bolts

3.1 Exceptional Corrosion and Rust Resistance

Dacromet-coated flange bolts routinely achieve 1,000 hours or more of neutral salt spray testing (ASTM B117 / ISO 9227) without the appearance of red rust. In many specifications, white rust is delayed beyond 240–500 hours, and overall anti-corrosion performance is 7–10 times superior to conventional electrogalvanizing. This outstanding rust-inhibiting capability ensures long service life in coastal, marine, industrial, and de-icing-salt environments.

3.2 No Hydrogen Embrittlement Risk

Unlike electroplating processes that introduce hydrogen into high-tensile steel, the Dacromet dip-spin or spray process is entirely non-electrolytic. Consequently, high-strength flange bolts retain their full mechanical properties and are free from delayed brittle fracture caused by hydrogen embrittlement—providing both anti-rust protection and structural safety.

3.3 Thin, Uniform Coating with Excellent Dimensional Control

Typical coating thickness ranges from 5 to 15 μm. This thin film does not significantly alter thread dimensions, allowing standard nuts to be used without overtapping. The coating penetrates complex geometries, threads, and recesses uniformly, ensuring complete anti-corrosion coverage even on intricate flange bolt profiles.

3.4 High-Temperature Stability and Additional Benefits

Dacromet coatings remain effective at continuous temperatures up to approximately 250–300 °C, far exceeding the thermal limits of conventional zinc plating. Additional advantages include good paintability, controlled friction coefficients (especially with lubricated topcoats), bimetallic compatibility with aluminum, and compliance with many automotive and environmental standards.