What is the hot dip galvanizing process?

Hot dip galvanizing process involves cleaning steel fasteners, fluxing, and immersing them in a molten zinc bath (around elevated temperature). The zinc reacts with the steel to form metallurgically bonded zinc-iron alloy layers, providing a thick, durable coating. For fasteners, the coating thickness is specified by ISO 10684, with a minimum local thickness of per standard class and batch average of per standard class.

What is the difference between hot dip galvanizing vs electro galvanizing?

Hot dip galvanizing produces a much thicker coating (local 35–per standard class per ISO 1461 for general steel, ≥per standard class for fasteners) compared to electro-galvanizing (5–per standard class per ISO 2081). This makes HDG more suitable for outdoor and corrosive environments, while electro-galvanizing is preferred for indoor applications requiring tighter tolerances. The hot dip galvanizing cost is higher per part, but the longer service life often justifies it.

What is the hot dip galvanizing thickness requirement for fasteners?

Per ISO 10684:2004 (and GB/T 5267.3-2008), the minimum local coating thickness is per standard class, and the minimum batch average is per standard class. For general steel articles, ISO 1461/GB/T 13912 specifies tiers based on steel thickness, ranging from per standard class local for steel <per specification to per standard class local for steel ≥per specification.

Which hot dip galvanizing standard applies to fasteners?

The primary hot dip galvanizing standard for fasteners is ISO 10684:2004, which is identically adopted as GB/T 5267.3-2008 in China. For general steel articles, ISO 1461:2022 and GB/T 13912-2020 apply. ASTM A123/A153 are also relevant for North American projects.

Can you provide hot dip galvanized bolts and fasteners?

Yes, as a hot dip galvanized fasteners manufacturer, we offer a catalog of 381 active SKUs of hot dip galvanized fasteners, including bolts, nuts, and washers. We work with partner hot dip galvanizing plants and station our resident QC on site for every batch to ensure compliance with ISO 10684 and GB/T 13912.

Hot Dip Galvanizing Process & HDG Fastener Manufacturer

Q: Which hot dip galvanizing standard applies to fasteners?

The primary hot dip galvanizing standard for fasteners is ISO 10684:2004, which is identically adopted as GB/T 5267.3-2008 in China. For general steel articles, ISO 1461:2022 and GB/T 13912-2020 apply. ASTM A123/A153 are also relevant for North American projects.

Q: Can you provide hot dip galvanized bolts and fasteners?

Yes, as a hot dip galvanized fasteners manufacturer, we offer a catalog of 381 active SKUs of hot dip galvanized fasteners, including bolts, nuts, and washers. We work with partner hot dip galvanizing plants and station our resident QC on site for every batch to ensure compliance with ISO 10684 and GB/T 13912.

Process Overview

How It Works

Hot dip galvanizing is a process where steel fasteners are immersed in a bath of molten zinc, forming a metallurgically bonded zinc-iron alloy coating. The sequence includes surface cleaning, fluxing, immersion, withdrawal, quenching, and inspection. This coating provides sacrificial protection, making it ideal for long-term outdoor service. For fasteners, the coating thickness always exceeds per standard class, so threads require special manufacturing limits to ensure fit (ISO 10684:2004 clause 6.2).

Key Advantages

✓Thick, durable zinc coating: local minimum 40 µm, batch average 50 µm per ISO 10684 for fasteners
✓Sacrificial protection: zinc corrodes preferentially, protecting steel even at scratches and cut edges
✓Metallurgical bond: zinc-iron alloy layers formed by diffusion, not just a surface deposit
✓Proven in harsh environments: suitable for C2 to C5 corrosivity categories per ISO 9223
✓Cost-effective long-term protection: lower maintenance compared to paint systems

Typical Applications

Hot dip galvanized fasteners are used in outdoor structures, power transmission, substations, solar mounting, agriculture, marine environments, and infrastructure projects where long-term corrosion resistance is critical.

Capability Envelope

Applicable standards	ISO 10684:2004, GB/T 13912-2020, GB/T 5267.3-2008, ASTM A123/A153
Thread size range	M8 to M64 (coarse thread)
Property class	Up to 10.9 for bolts/screws/studs; up to 12 for nuts
Coating thickness (fasteners)	Local ≥per standard class, batch average ≥per standard class (ISO 10684)
Coating thickness (general steel)	Per ISO 1461 / GB/T 13912 tiers (local 35–per standard class, average 45–per standard class by steel thickness)
Production model	Partner hot-dip galvanizing plant with resident QC on site
Catalog SKUs	381 active hot-dip galvanized fastener SKUs
Quality reports	Coating thickness reports, material certificates, salt spray test reports (on request)

We operate a partner hot-dip galvanizing plant model: for every batch, our resident QC is stationed at the external galvanizer to verify coating thickness, thread fit, and surface quality. This ensures compliance with ISO 10684 and GB/T 13912 without maintaining our own plant. For hot dip galvanizing services, hot dip galvanizing companies, or hot dip galvanizing machine inquiries, we focus on fasteners—contact us for hot dip galvanized bolts and fasteners.

Per ISO 10684:2004 / ISO 1461:2022 / GB/T 13912-2020 / GB/T 5267.3-2008 / ASTM A123/A123M-24 / ASTM A153/A153M-23 / ISO 9223:2012 / ISO 14713-1:2017 / ISO 14713-2:2019 / ISO 14713-3:2017 (drawing callouts take precedence)

Design & Cost Tips (DFM)

Leave tool radius on inside corners

Sharp internal corners are not machinable: R ≥ tool radius (R1.5–R3 typical). Smaller radii mean more tool changes and higher cost.

Thin walls and deep cavities

Wall thickness ≥per specification for aluminum and ≥per specification for steel is recommended. Cavities deeper than ~5× tool diameter need a drawing review first.

Tolerate only critical features

Tight tolerances everywhere means expensive everywhere. Put per drawing on mating features and leave the rest to ISO 2768-mK.

Rethink small threads

Deep blind tapped holes need runout allowance. Below M2, evaluate rivet nuts or wire thread inserts for better cost and consistency.

Finishing changes dimensions

Anodizing and plating add microns to surfaces. Mask precision fits or leave allowance — and state it on the drawing.

Cost structure and volume breaks

Material, machine time, finishing and inspection are quoted separately. Unit price breaks clearly at batch-dependent — tell us the target volume.

Selection Boundaries: When to Use, When Not

Good fit

✓Outdoor structures and infrastructure: bridges, guardrails, transmission towers, substations
✓Coastal and industrial atmospheres with corrosivity categories C3 to C5 (ISO 9223)
✓Fasteners requiring thick, durable zinc coating: bolts, nuts, washers, studs
✓Applications where long-term maintenance is costly or difficult

Not recommended

✗Indoor, dry environments where thinner electro-galvanizing is sufficient and more cost-effective
✗High-strength fasteners above property class 10.9 (risk of hydrogen embrittlement)
✗Parts with fine threads below M8 (coating thickness may affect fit)
✗Applications requiring precise dimensional tolerances that thick coating would compromise

Choosing between adjacent processes

Electro-galvanizing

Thinner zinc coating (5–per standard class) applied electrolytically. Suitable for indoor use and where dimensional precision is critical. See our electro-galvanizing process page.

Process Flow

1

Surface cleaning: degreasing and acid pickling to remove oil, rust, and mill scale

2

Fluxing: application of flux solution to prevent oxidation before immersion

3

Drying: preheating to remove moisture and activate the flux

4

Immersion in molten zinc bath: zinc-iron alloy layers form by diffusion

5

Withdrawal and draining: excess zinc is removed, coating solidifies

6

Quenching and passivation: cooling and optional chromate treatment

7

Inspection: coating thickness measurement, thread fit check, visual inspection

Quality & Inspection

Inspection Capability

•Quality & Inspection equipment per standard requirements
•Coating thickness gauge (magnetic method, per ISO 1461 / ISO 10684)
•Visual inspection of coating continuity and surface condition
•Salt spray chamber (ISO 9227, project-case validation)

Available Reports

•Coating thickness measurement report (per ISO 1461 / ISO 10684)
•Material test certificate (MTC, lot traceable)
•Resident QC batch inspection records (partner plant)
•Third-party testing (SGS/BV on request)

Industries & Typical Parts

Power & Energy

-Substation structures and busbar supports
-Solar mounting systems
-Wind turbine tower bolts

Agriculture

-Greenhouse frames and fasteners
-Fencing and livestock equipment
-Irrigation systems

Industrial

-Conveyor systems and supports
-Storage racks and platforms
-Chemical plant structures

Municipal & Infrastructure

-Highway guardrails and signage
-Bridges and walkways
-Water treatment facilities

Mining

-Conveyor structures
-Screening equipment
-Ventilation systems

FAQ

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Hot Dip Galvanizing: Durable Zinc Coating for Fasteners