Precision Seamless Steel Tube

Excellent Internal & External Surface Uniformity
The advanced cold rolling technology guarantees consistent geometric precision, uniform wall thickness, and superior inner surface smoothness — essential for shock absorber inner/outer tubes, hydraulic cylinder barrels, pneumatic components, and high-pressure fluid systems.

Enhanced Mechanical Properties & High Strength
Cold working delivers improved tensile strength, higher hardness, greater durability, and excellent toughness. Tubes withstand rigorous tests including high pressure resistance, cold bending, flaring, flattening, and expansion without cracking, making them ideal for fatigue-resistant, load-bearing parts in automotive and engineering applications.

Superior Wall Thickness Uniformity & Consistency
Multi-roll cold rolling ensures minimal variation along the tube length, outperforming traditional cold drawing methods and providing reliable performance in precision-fit assemblies.

Lightweight yet High-Strength Design
Offers exceptional bending strength, torsional rigidity, and impact resistance relative to low weight — perfect for weight-sensitive precision machine elements, structural components, automotive suspension systems, and lightweight engineering solutions.

Material Versatility, Wide Grade Options & Full Customization
Available in premium carbon steels (e.g., 10#, 20#, 45#, ST35, ST37, ASTM 1020, C22), alloy steels, and stainless grades (304, 316, 316L). Supports extensive customization: non-standard sizes, special deep processing (cutting, chamfering, expanding, necking, threading), surface treatments, and even H8/H9 tolerance honed versions for ready-to-use hydraulic applications.

Typical Size Range & Application-Focused Specifications
Specializes in small to medium diameters (e.g., OD 15–90 mm ), thin to medium wall thicknesses (commonly 1–5 mm or custom). Ideal for high-precision, high-pressure uses in motorcycle front fork tubes, automotive shock absorber cylinders, hydraulic/pneumatic systems, auto parts, construction machinery, and fluid power components.

1. Raw Material and Hot Forming Phase (Hot Processing to Produce the Hollow Shell)

• Steel bar from steel plant → High-quality round steel billet (solid bar) arrives from the mill.
• Physical & chemical inspection → Strict checks on composition, mechanical properties, and internal defects to ensure material suitability.
• Surface treatment → Descaling, grinding, or shot blasting to remove surface oxides and defects.
• Cutting → Cutting the billet to precise lengths suitable for piercing.
• Heating → Billet is heated in a rotary hearth or walking beam furnace to ~1100–1300°C to make it malleable.
• Hot piercing → Using the Mannesmann piercing mill, the heated billet is pierced with a plug/mandrel to form a thick-walled hollow tube (mother shell or capillary tube).

→ At this point, a hot-rolled hollow shell is obtained (thicker walls, lower precision).

2. Intermediate Processing of the Shell (Preparation for Cold Working)

• Cooling and initial trimming → Shell cools, heads/tails are cut off to remove uneven ends.
• Pickling and lubrication → Acid pickling removes scale/oxides, followed by lubrication (often phosphating + soap coating) to prepare for cold deformation.
• Annealing treatment → Full annealing or spheroidizing to relieve stresses, soften the material, and improve ductility for cold working.
• Shell storage → Temporary storage of prepared shells before entering the cold line.

3. Cold Working / Precision Reduction Phase (Core Multi-Pass Deformation)

This is the most intensive part, involving repeated cycles to achieve high precision:

• Cold rolling or Cold drawn → Primary reduction: tube is passed through dies/rolls to reduce diameter and wall thickness while improving surface finish and dimensional accuracy.
• Punching → End preparation or hole processing if needed.
• Cutting → Intermediate cutting to manageable lengths.
• Pickling and lubrication (repeated) → After each pass, re-pickling to remove any new scale and re-lubricating for the next deformation.
• Annealing treatment (repeated) → Intermediate annealing (e.g., after 1–3 passes) to prevent excessive work hardening and cracking.
• Multiple loops of cold drawing/rolling + annealing + pickling until target dimensions (OD, wall thickness, ovality, etc.) are reached.

→ This results in high-precision tubes with tolerances as tight as ±0.05 mm, excellent surface finish, and improved mechanical properties.

4. Final Finishing and Quality Control Phase

• Black phosphated heat treatment → Phosphating (for corrosion resistance and lubrication) combined with specific heat treatments like NBK (normalized + bright annealed) or GBK (annealed in controlled atmosphere) to achieve desired microstructure and properties.
• Cleaning → Removal of residues after heat treatment.
• High pressure oil blowing → Internal high-pressure oil flushing to clean the bore thoroughly.
• Eddy current testing → Non-destructive eddy current inspection for surface and near-surface defects.
• Antirust oil painting → Application of anti-rust oil inside and outside.
• Straightening → Multi-roll straightening to eliminate any bending or curvature.
• Trim → Final cutting to exact lengths, chamfering ends if required.
• Size inspection → Measurement of outer diameter, wall thickness, length, ovality, etc.
• Out and inner surface cleaning / Polishing → Mechanical cleaning, shot blasting, or polishing for superior finish.
• Mechanics inspection → Tensile, hardness, flattening, flaring, bending, and impact tests.
• Chemical inspection → Re-verification of composition if necessary.

5. Packaging and Delivery Phase

• Print → Marking with product details (grade, size, batch number, date, etc.) via inkjet or stamping.
• Packing → Bundling, protective wrapping, and crating.
• Finished storage → Warehousing of approved tubes.
• Delivery with quality certificate → Shipment accompanied by mill test certificates (MTC), inspection reports, etc.