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Electric Resistance Welding (ERW) remains the dominant and highly efficient technology for manufacturing a vast range of carbon steel tubing, from structural and mechanical applications to conduit and low-pressure fluid handling. An ERW tube mill carbon steel is engineered specifically to leverage this process, offering a compelling combination of high production speeds, consistent quality, and versatility across diameters and wall thicknesses.
The core principle of ERW involves using the electrical resistance of the steel itself to generate the heat required for welding. The flat carbon steel strip is formed into a cylindrical shape with its longitudinal edges brought into close proximity. High-frequency electrical current (typically 100 kHz to 800 kHz) is then introduced:
Contact Welding (HFC): Current is transferred via sliding contacts (shoes) directly onto the strip edges.
Induction Welding (HFI): Current is induced into the strip edges using an induction coil encircling the tube, without physical contact.
Both methods effectively concentrate current along the strip edges, rapidly heating them to a forging temperature (approx. 1300-1400°C / 2372-2552°F) through resistance heating. Immediately following heating, high pressure is applied by squeeze rolls, forging the heated edges together metallurgically to form a solid-state weld. This pressure weld typically exhibits a fine-grained structure with strength characteristics often matching or exceeding the base metal.
The advantages of ERW for carbon steel are significant:
High Speed: Capable of very high production rates (often hundreds of meters per minute).
No Filler Metal: Simplifies the process and avoids introducing dissimilar materials.
Efficiency: Generally lower energy consumption compared to fusion welding processes.
Versatility: Suitable for a wide range of diameters (from small conduit to large pipe) and wall thicknesses.
Consistency: Automated control enables highly repeatable weld quality.
A modern ERW tube mill carbon steel integrates several key components beyond the welding station:
Precision Forming: A multi-stand forming section with carefully designed contour rolls progressively shapes the strip into an open oval, then a closed circular shape with precisely aligned edges. Roll design is critical for edge condition and preparation for welding.
HF Welding Power & Control: Sophisticated solid-state power supplies deliver stable high-frequency current. Control systems meticulously regulate power, frequency, V-angle (the convergence angle before welding), speed, and squeeze pressure based on real-time feedback.
Weld Bead Removal: The internal and external weld bead (flash) is typically removed immediately after welding using carbide-tipped scarfing tools or precision planing knives. This is crucial for achieving a smooth surface and preventing defects downstream.
Sizing: Multiple stands of sizing rolls cold-work the tube to achieve its final precise OD, wall thickness (within tight tolerances), and roundness. This process also improves the mechanical properties of the weld zone.
Cooling: Controlled cooling sections manage the temperature profile after welding and sizing.
NDT & Inspection: Ultrasonic Testing (UT) is standard, continuously scanning the entire weld length for volumetric defects. Eddy Current Testing (ET) might be used for surface defect detection. Laser gauging monitors OD and ovality.
Cutting: High-speed flying saws cut the tube to length without stopping production.
Mill design prioritizes robustness for continuous operation, ease of maintenance, and quick changeovers between different tube sizes and specifications. Shijiazhuang Faith Machinery Co., Ltd. specializes in designing and building reliable and efficient ERW tube mills optimized for carbon steel production, focusing on achieving high weld integrity, dimensional precision, and overall operational productivity.
