Technical Essentials for Hot-Dip Galvanizing of Steel Grating

Steel grating is a structural flooring and load-bearing system made by combining steel bearing bars with cross bars, forming an open-grid pattern.

Unlike solid steel plates, steel grating allows:

• Light and air to pass through
• Water and debris to drain easily
• Strong load support with less material

Because of this unique structure, steel grating offers an excellent balance of strength, safety, and efficiency.

In simple terms, steel grating is designed to carry heavy loads while remaining lightweight and open.

A common question is why engineers choose steel grating instead of solid steel plate.

For most industrial flooring and access applications, steel grating offers superior performance.

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I. Base Material Control

Material: Q235 low-carbon steel. High-carbon steel or steel with excessive manganese content is strictly prohibited.

Welding Points: Spot welds must be full and firm. No cold welds, false welds, or open welds. Welding slag must be ground clean.

Gaps: Gaps between bearing bars and cross bars must be clear and unobstructed. No closed sections or trapped air pockets; no dead zones or blind cavities.

Flatness: Grating must be free of deformation or warping to ensure it does not tilt or get stuck during the dipping process.

II. Degreasing and Oil Removal

Alkaline Degreasing: Temperature 50 ~ 65°C.

Thoroughly remove rolling oil, welding grease, and dust.

Verification: After water rinsing, the entire surface should be hydrophilic (no water beads). Residual alkalinity must meet standards.

III. Acid Pickling and Rust Removal (Critical Step)

Hydrochloric Acid Pickling: Temperature 40 ~ 55°C.

Strict Time Control: Prevent over-pickling to avoid thinning of bearing bars and loss of structural strength.

Thoroughly remove all oxide scales from both sides and inside the gaps.

Replace acid promptly if ferrous iron levels are too high to prevent surface blackening or bare spots.

IV. Rinsing + Fluxing

Double-stage fresh water rinsing to ensure no residual acid.

Fluxing Agent: Ammonium chloride + zinc chloride composite solution.

Concentration: 180 ~ 260g/L; Temperature 60 ~ 75°C.

Ensure uniform immersion and complete wetting of all grating gaps.

Low-Temperature Drying: 100 ~ 160°C. Must be bone-dry without dampness; avoid scorching. Dampness entering the zinc pot will cause bubbling, bare spots, or peeling.

V. Core Galvanizing Process (Specific Parameters)

Zinc Ingot: 0# Zinc ≥ 99.99%.

Zinc Bath Temperature: 440 ~ 448°C.

Aluminum Content: 0.015 ~ 0.025% to reduce zinc dross and ensure a bright, fine finish.

Immersion Time: 40 ~ 90 seconds (Short for thin grating, long for thick grating; ensure full coverage).

Operational Key: Enter the bath horizontally and slowly; shake up and down to exhaust air.

Ensure smooth air discharge from gaps (no air pockets/trapped gas).

Withdraw at a uniform speed with sufficient drainage to reduce edge zinc nodules.

Promptly remove zinc dross, as it easily clogs the grating gaps.

VI. Cooling, Leveling, and Passivation

Warm water cooling for rapid setting and prevention of warping.

Correct flatness and alignment immediately after cooling.

Chromium-Free Passivation: Room temperature for 15 ~ 25s. Significantly prevents white rust and improves outdoor salt spray resistance.

VII. Galvanized Coating Thickness Standards

Bearing Bar Thickness ≤ 3mm: Average ≥ 65μm.

Bearing Bar 3 ~ 6mm: Average ≥ 70 ~ 80μm.

Stair Treads / Heavy-Duty Platforms: ≥ 80μm.

VIII. Common Defects and Causes

Bare Spots at Corners: Poor air exhaust, inadequate pickling, or uneven fluxing.

Zinc Clogging/Lumps: Zinc temperature too low, slow drainage, or insufficient shaking.

Rough Surface/Excess Dross: Excessive zinc dross or bath temperature too high.

Warping/Deformation: Bath entry too fast, uneven cooling, or improper stacking.

Coating Peeling: Over-pickling corrosion, residual oil on base material, or fluxing failure.

IX. Finished Product Inspection Points

Appearance: Uniform and bright; no bare spots, pitting, or large zinc nodules.

Grid Clarity: Gaps must be clear and unclogged for seamless installation.

Integrity: No detached or cracked welding points.

Flatness: Must meet standards; no warping or twisting.

Compliance: Thickness must meet specifications for long-term outdoor, marine, or municipal corrosion protection.

Q1: How long does hot-dip galvanized steel grating last in outdoor environments?

A: In standard rural or residential areas, it can last 40-50 years. In industrial or coastal areas with higher salt spray, it typically lasts 20-30 years before maintenance is required, depending on the coating thickness.

Q2: Can hot-dip galvanized steel grating be painted?

A: Yes, this is known as a "Duplex System." However, the galvanized surface must be properly cleaned and often "etched" or primed with a specific wash primer to ensure the paint adheres correctly to the zinc layer.

Q3: What is "White Rust" and is it a sign of product failure?

A: White rust (zinc storage stain) is a powdery deposit formed when new galvanized grating is exposed to moisture with restricted air circulation. It is usually superficial and does not mean the corrosion protection has failed, but it should be cleaned if aesthetics are important.

Q4: Why is my steel grating warped after galvanizing?

A: Warping is usually caused by internal stress relief during the high-temperature (450°C) zinc bath. This is more common in gratings with thin bearing bars or asymmetric designs. Professional manufacturers use leveling machines post-galvanizing to correct this.

Q5: How do I calculate the weight of hot-dip galvanized steel grating?

A: The weight is calculated based on the total surface area of the steel. After hot-dip galvanizing, the weight typically increases by approximately 5% to 9% due to the added zinc coating.