Tianjin Yuantaiderun Group operates a total of 10 hot-dip galvanizing production
lines. Among these, Yuantai Gongmao has 6 blow galvanizing lines, while Yuantai
Jianfeng has 4 lines (2 rack plating lines and 2 blow plating lines).
The hot-dip galvanizing processes at Tianjin Yuantaiderun Group are divided into two
types are blow plating and rack plating.
Blow Plating Details:
Standard zinc coating: Average of 200g (approximately 30μm).Note: 1μm ≈ 7g.
Maximum zinc coating: Up to 320g (approximately 45μm).
Minimum tube dimensions:Rectangular tubes: 20mm × 30mm. Square tubes: 20mm × 20mm.
Minimum wall thickness: 1.5mm.Risks for thinner walls (<1.5mm): Higher defect
rates due to weld seam cracking under strong airflow.
Limitation for thicker walls (>2.0mm): Inner diameter becomes too small for blow rods to enter, preventing internal coating.
Maximum tube dimensions:Rectangular tubes: 150mm × 200mm.Square tubes:
200mm × 200mm.
Maximum wall thickness: 5.75mm.Beyond 5.75mm: Tubes become too heavy for
magnetic rollers to lift, leading to inefficiency. Rack platzing is recommended.
Length range: 4m to 8m.（Because acid tanks and zinc pots are 1.5m deep × 1.5m wide × 9m long. Tubes exceeding 8m should use rack plating.）
Cost adjustments for low-tonnage orders: Small-volume orders incur additional fees due to setup requirements (e.g., configuring machines, dedicated blow heads, air rings, and rods).
Compatibility: Blow plating also applies to round pipes, ranging from 3/4 inches to 6 inches.
Rack Plating Details:
Standard zinc coating: Average of 60μm (approximately 400g).Note: 1μm ≈ 7g.
Maximum zinc coating: Up to 85μm (approximately 600g).
Maximum tube dimensions:Cross-section: 900mm × 900mm. Length: Up to 12m.
Applicability:
Required for tubes with side lengths exceeding 200mm or wall thickness over 5.75mm (excluding 5.75mm).
Compatible with diverse materials such as angle steel, channel steel, flat steel, steel plates, solar brackets, straight-seam round tubes, seamless square&rectangular tubes, seamless round tubes, and various profiles.
Limitations:Welded components and small parts are excluded.Beacause acid tanks
and zinc pots are large (13m long × 1.5m deep × 1.5m wide). Processing small items
is inefficient, resulting in low output and profitability risks for the production line.
Next, we will provide a detailed introduction to the process flow.
1. Welded Tube Inspection
Purpose: Check raw tubes for bending/deformation and burrs at pipe ends.
Bending/deformation: Affects smooth operation in production lines, increasing defect risks.
Burrs: Prevent tubes from entering the equipment.
2. Acid Pickling
Procedure:Qualified tubes are immersed in acid tanks via overhead crane for 3–5
minutes.The crane lifts and lowers the tubes 3–5 times to ensure even pickling.
Total pickling time: 5–10 minutes. Inspect tubes to confirm complete rust removal.
Post-pickling handling:Lift tubes at a 15-de gree angle to drain residual acid.Allow
residual liquid to drain for 5–10 minutes before proceeding.
Common defects:
Under-pickling:
Causes: Insufficient removal of iron oxide scale, rust, or contaminants.
Result: Residual rust or debris on the tube surface.
Over-pickling:
Causes: Excessive pickling time, corroding the base metal.
Result: Rough/pitted surfaces, blackened appearance, or coarse black textures.
3. Rinsing
Purpose: Remove residual acid and iron salts from the tube surface. Residual
contaminants from the acid pickling tank can adversely affect galvanizing quality.
4. Flux Treatment
Remove residual moisture, iron salts, oxides, and other impurities from the
tube surface after rinsing.Prevent oxidation of the metal substrate (iron salts and
oxides can re-oxidize within seconds upon exposure to air and moisture).
Create a protective barrier to isolate the metal substrate from air, inhibiting
oxidation.Poor flux treatment can directly lead to uncoated areas.
Ensure the iron substrate reacts properly with molten zinc during immersion, forming
a continuous iron-zinc (Fe-Zn) alloy layer.This alloy layer is essential for adhesion
and corrosion resistance of the zinc coating.
5. Alignment
Inspect welded tubes and solvent-coated tubes to ensure smooth entry into the drying oven and subsequent galvanizing process.
6. Drying
Remove residual acid, water, and solvent from the tube surface.Inadequate drying can
cause explosions or violent splashing when tubes enter the zinc pot.
7. Galvanizing
Extend the service life of steel tubes by providing anti-corrosion and anti-rust
properties.
Mechanism:Galvanized tubes remain stable in dry air but form a protective oxide film
in humid environments (e.g., greenhouses), preventing oxidation.For exampl
galvanized tubes used in humid greenhouse conditions outlast untreated black steel
tubes.
8. External Blowing
Remove excess zinc nodules, zinc ash, flux residues, and other surface contaminants.
Enhance the gloss and uniformity of the zinc coating on both inner and outer surfaces,
improving durability.Optimize zinc layer thickness for material efficiency and cost
reduction.
9. Internal Blowing
Replace internal blowing nozzles according to tube specifications.Align the internal
blowing unit with the centerline of the galvanized tube.Regularly clean zinc nodules
adhering to the internal blowing equipment.If use hooks to reposition tubes if they fail
to align properly during the process.
10. Water Cooling
Submerge galvanized tubes in a water pool to cool them.Without cooling, the high
temperature of the tubes makes it impossible to handle or inspect the galvanizing
quality.
11. Inspection
Tubes are unloaded from the water pool via chains.Check for bending and uncoated
areas.If there are minor bare spots,repair using specialized zinc-rich paint.If
there are large uncoated areas,should set aside for re-galvanizing.When all the steps
passing inspection going to the next step.
12. Passivation Spraying
Prevent alkali efflorescence, moss-like growth, and corrosion.Ensure uniform
passivation layer via airflow to spread the solution evenly.Poor handling can lead to
zinc layer corrosion or white rust.
13. Marking
Use automated marking machines to print labels directly on tubes after passivation.
14. Bundling
Tubes are transported via rollers to automatic bundling machines.It is high efficiency
and reduced labor costs.
15. Affixing Certificates
Attach quality inspection certificates to approved products.
16. Warehousing
Rack Plating vs. Blow Plating
The processes for rack plating and blow plating are fundamentally similar. In
rack plating, after immersion in flux, steel tubes are secured with iron wire or
custom fixtures for hoisting. They are then galvanized, water-cooled, and passivated
directly using an overhead crane, eliminating the need for the tubes to pass through
production line machinery.
