Product Overview
The Hot-Dip Galvanized (HDG) Bolt is a heavy-duty structural fastener that has undergone immersion in molten zinc, resulting in a thick, metallurgically bonded alloy coating. This process provides unmatched, long-term protection against corrosion, making it the preferred choice for critical connections exposed to severe atmospheric conditions, moisture, chemicals, and outdoor weathering. Its characteristic spangled appearance signifies robust, sacrificial protection for applications where structural integrity and longevity are paramount.
Key Features & Benefits
Superior Long-Term Corrosion Resistance: The zinc coating acts as a durable barrier and sacrificially protects the underlying steel, significantly extending service life in harsh environments.
Excellent Abrasion Resistance: The thick, alloy-bonded coating (typically 55-85 µm) withstands handling, transportation, and installation damage better than electroplated finishes.
Complete Coverage: The immersion process ensures uniform coating over all surfaces, including thread roots and under the head, providing comprehensive protection.
Cathodic Protection: If the coating is damaged, zinc preferentially corrodes to protect the exposed steel, preventing underlying rust.
Proven Performance: The industry standard for corrosion protection in infrastructure, utilities, and marine applications.
Material Specifications & Property Classes
HDG coating is applied to high-strength bolts manufactured to international standards. Post-galvanizing, high-strength bolts must be baked to mitigate hydrogen embrittlement.
| Base Material & Standard | Property Class / Grade | Minimum Tensile Strength | Core Hardness | Key Application Note |
|---|---|---|---|---|
| Carbon / Alloy Steel | ASTM A325 / ISO 898-1 Cl. 8.8 | 120 ksi / 830 MPa | HRC 24-32 | Common for structural steelwork. Requires proper hydrogen embrittlement relief. |
| Alloy Steel | ASTM A490 / ISO 898-1 Cl. 10.9 | 150 ksi / 1040 MPa | HRC 33-39 | For highest strength structural connections in corrosive environments. |
| Heavy Hex Bolts | ASME B18.2.1 (HDG) | Varies by grade | Varies by grade | General construction, utility, and fabrication. |
Hot-Dip Galvanizing Process & Specifications
Process: Cleaning (alkaline, acid pickling) → Fluxing → Immersion in molten zinc bath (~449°C / 840°F) → Controlled withdrawal and cooling.
Coating Standards: Compliant with ASTM A153 (Class C for fasteners) and ISO 10684. Coating thickness typically ranges from 55 to 85 microns.
Thread Compatibility: Internal threads of mating nuts are often oversize-tapped post-galvanizing. Always use hot-dip galvanized nuts to ensure proper fit and avoid thread galling.
Appearance: Characteristic zinc spangle (crystalline pattern). Can be quenched to produce a dull gray finish.
Performance & Installation Data
Corrosion Protection: Can provide 500 to 2,000+ hours to first red rust in neutral salt spray (ASTM B117), depending on environment (rural, industrial, marine).
Friction Coefficient: The zinc coating has a lower and more variable friction coefficient than bare steel. This critically impacts the relationship between applied torque and achieved bolt tension (clamp force).
Installation Torque: Torque values must be adjusted from those used for plain or electroplated bolts. Always refer to specifications (e.g., AISC, RCSC) that account for the lubricity of the HDG coating. Use of calibrated torque wrenches or direct tension indicators (DTIs) is strongly recommended for structural joints.
Temperature Limit: Suitable for continuous service up to 200°C (390°F).
Applications courantes
Infrastructure: Bridges, highway guardrails, light poles, transmission towers, and sound barriers.
Industrial Construction: Water and wastewater treatment plants, power generation facilities, chemical plant structures.
Marine & Coastal: Dock and pier constructions, boat lifts, seawall tie-backs.
Agricultural & Mining: Exposed equipment frameworks, processing facilities.
Quality Assurance & Traceability
Process Control: Our sourced bolts are galvanized by certified partners with strict bath chemistry and temperature controls.
Testing: Coating thickness is verified per ASTM E376. Adherence is tested via hammer or quench test. High-strength bolts undergo hydrogen embrittlement relief (baking).
Certification: Bolts are supplied with Mill Test Certificates (MTCs) for the base material and Galvanizing Certificates of Compliance (CoC), ensuring full traceability.
Marking: Grade/class identification markings remain legible post-galvanizing.
Manufacturing & Supply
Hebei Wohe Fastener Manufacturing Co. Ltd. manages the integrated supply chain for hot-dip galvanized fasteners. We source high-quality bolts from trusted manufacturers, coordinate the specialized galvanizing process with certified facilities that perform mandatory hydrogen embrittlement relief for high-strength grades, and conduct final inspection to ensure dimensional and coating quality meets project specifications. We supply these critical components to engineering firms and fabricators working on global infrastructure and heavy industrial projects.
Ordering & Specification:
Specify: Standard (ASTM/ISO), Grade/Class, Diameter, Length, Thread, and any special post-galvanizing requirements.
Kitting: Available as individual bolts or in matched assemblies with HDG nuts and hardened washers.
MOQ: Project-based, typically starting from 2,000 pieces per size/grade.
Lead Time: 30-40 working days for standard specifications, including galvanizing cycle time.
Critical Installation Note: Hot-dip galvanized bolts require specific installation procedures. The lubricity of the zinc coating means that a given torque will produce a higher bolt tension than on an uncoated bolt. Overtorquing and bolt failure are risks if standard torque tables are used. Always follow the bolt manufacturer’s or project engineer’s specified torque/tension values for HDG fasteners.
