Product Overview
The Hot-Dip Galvanized (HDG) Nut is a heavy-duty fastener that has been immersed in molten zinc to create a thick, metallurgically bonded coating. This process provides exceptional and long-lasting protection against corrosion, making it the industry standard for applications exposed to harsh weather, moisture, chemicals, and outdoor elements. The characteristic spangled finish and robust zinc layer offer both functional durability and a distinctive appearance for structural and industrial assemblies.
Key Features & Benefits
Unmatched Corrosion Resistance: The zinc coating acts as a durable, sacrificial barrier, protecting the underlying steel from rust and oxidation for decades in most atmospheric conditions.
Robust Mechanical Protection: The thick coating (typically 45-85 μm) provides excellent resistance to abrasion and physical damage during handling and installation.
Complete Coverage: The immersion process ensures uniform coating coverage, including threads and corners, offering comprehensive protection.
Cathodic Protection: Even if the coating is scratched, zinc sacrificially corrodes to protect the exposed steel, preventing rust creep.
Cost-Effective Longevity: Offers the best lifecycle cost for applications requiring long-term reliability with minimal maintenance.
Material Specifications & Grades
HDG coating is applied to nuts manufactured from various steel grades to suit different strength requirements.
| Base Material & Grade | Standard (Before Galvanizing) | Minimum Tensile Strength | Typical Applications for HDG Version |
|---|---|---|---|
| Carbon Steel, Grade 5 | ASTM A563 Gr. C / ISO 898-2 Cl. 5 | 120 ksi / 830 MPa | General construction, utility poles, fencing, where high strength is not the primary concern. |
| Carbon Steel, Grade 8 | ASTM A563 Gr. DH / ISO 898-2 Cl. 8 | 150 ksi / 1035 MPa | Structural connections, heavy-duty outdoor equipment, and high-strength bolting in corrosive environments. |
| High-Strength Structural Steel | ASTM A325 / A490 (Type 1) | As per A325/A490 | For critical structural bolted joints (e.g., bridges, transmission towers) requiring corrosion protection. |
| Cast / Forged Steel (Heavier Shapes) | Various | – | Used with matching hot-dip galvanized bolts in custom fabrications. |
Hot-Dip Galvanizing Process & Specifications
Process Steps: Cleaning (degreasing, pickling) → Fluxing → Immersion in molten zinc (~450°C / 840°F) → Cooling → Optional quenching or passivation.
Coating Specification: Compliant with ASTM A153 (Class C for fasteners) and ISO 10684.
Coating Thickness: Typically ranges from 45 to 85 microns (1.8 to 3.5 mils), significantly thicker than electroplated zinc.
Thread Treatment: Post-galvanizing, internal threads are often retapped or treated to restore proper fit and clear excess zinc, ensuring compatibility with galvanized bolts.
Performance Data & Characteristics
Salt Spray Resistance: Can provide 500 to 1500+ hours to first red rust in neutral salt spray (ASTM B117), depending on coating thickness and environment.
Service Temperature: Suitable for continuous exposure up to 200°C (390°F). Above this, the zinc-iron alloy layers may begin to peel.
Appearance: Features the characteristic crystalline “spangle” pattern. Can be dull gray if quenched after galvanizing.
Installation Note: A small amount of white zinc oxide powder may form during storage; this is normal and does not affect performance.
Limitations & Handling Notes
Hydrogen Embrittlement Risk: High-strength steels (e.g., Grade 8 and above) require proper baking after galvanizing to remove hydrogen introduced during the acid cleaning stage.
Thread Fit: Always pair with hot-dip galvanized bolts. The thickened threads may not properly engage with standard black or electroplated bolts without causing galling or thread stripping. Use of oversize taps in the field may be necessary.
Torque & Tension: The zinc coating has a lower friction coefficient than bare steel. This must be accounted for in torque-tension calculations. Use of calibrated tools and specified installation procedures is critical, especially for structural connections.
Common Applications
Outdoor Structures: Bridges, highway guardrails, lighting poles, transmission towers, and stadiums.
Construction: Steel framework, balconies, roofing systems, and exterior facades.
Utilities & Infrastructure: Water treatment plants, power generation facilities, marine docks, and fencing.
Agriculture & Mining: Equipment and structures exposed to fertilizers, moisture, and abrasive conditions.
Transportation: Truck trailers, railcar components, and shipping containers.
Quality Assurance & Compliance
Coating Quality: Batch testing for coating thickness (magnetic gauge per ASTM E376), adherence (quench test, knife test), and appearance.
Dimensional Verification: Threads are gauged post-galvanizing to ensure they meet applicable dimensional standards (e.g., ASME B18.2.2, ISO 4032).
Material & Process Certs: Supplied with Certificates of Compliance (CoC) detailing the base material grade, galvanizing process, and test results. Mill certificates for raw material are traceable.
Standards: Manufactured and processed in accordance with ISO 1461 and ASTM A153/A123.
Manufacturing Partner
Our Hot-Dip Galvanized Nuts are supplied by Hebei Wohe Fastener Manufacturing Co., Ltd., which partners with certified, specialized galvanizing facilities that adhere to strict process controls. Our role encompasses the sourcing and pre-processing of high-quality nuts in appropriate grades, managing the logistics to and from the galvanizer, and performing final quality inspection to ensure the finished product meets both dimensional and coating specifications. This integrated approach guarantees that our HDG nuts provide the reliable, long-term corrosion protection required by the construction, infrastructure, and heavy industry sectors we serve globally.
Ordering Information:
Specification: Please specify Base Material Grade, Nut Style (e.g., Heavy Hex, Hex), Size, Thread, and any special post-galvanizing requirements (e.g., retapping, passivation).
Packaging: Typically bulk packaged in cartons or kegs to minimize coating damage. Desiccant may be included for long sea voyages.
Minimum Order Quantity (MOQ): Varies by size and grade, typically starting from 1,000 pieces for common sizes.
Lead Time: Standard items: 25-30 working days, including galvanizing process time. Project orders require advance scheduling.
Disclaimer: Hot-dip galvanizing is a batch process that can cause minor dimensional variations. The performance data provided is typical. Actual service life depends heavily on specific environmental conditions (e.g., coastal vs. industrial atmosphere). Engineers must specify compatible bolting assemblies and proper installation procedures. All specifications are subject to change.
