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The operational workflow of an ERW tube mill dedicated to carbon steel production is a coordinated sequence of events, transforming a raw steel coil into finished pipes. At Shijiazhuang Faith Machinery Co., Ltd, the design of this workflow emphasizes precision, stability, and efficiency.
Stage 1: Payoff and Entry Section
The process initiates with the loading of a carbon steel coil onto a mandrel-type decoiler. A hydraulic or motorized mechanism expands the mandrel to grip the coil from the inside. The leading end of the coil is fed through a pinch roll unit and into a cropping shear, which makes a square cut to ensure proper entry into the subsequent stages. An accumulator loop, often consisting of multiple rollers forming a pit, allows for continuous feeding of the strip while a new coil is prepared and the ends are welded together.
Stage 2: Strip Preparation and Forming
The strip passes through a multi-roll leveler, which removes any curvature or irregularities. It then enters the forming section. This section is a series of tandem-mounted stands, each containing a set of precision-machined rolls. The first set of rolls, or breakdown passes, begin to curl the edges of the flat strip upward. Subsequent stands progressively form the strip into an open-seam circular profile. The final forming stand, the closing stand, brings the two edges together perfectly aligned and ready for welding. The geometry of each roll pass is calculated to ensure the material flows smoothly without stretching or compressing the edges.
Stage 3: Welding and Sizing
As the open-seam tube exits the closing stand, it enters the welding unit. For carbon steel, a high-frequency contact or induction welder is used. The edges are heated to a plastic state by the HF current, and immediate pressure from the squeeze rolls forges them into a homogeneous weld. The newly welded pipe then enters the sizing section. Here, several stands of rolls, arranged in a two-high or three-high configuration, cold-work the tube to achieve its final exact diameter and geometry (round, square, or rectangular). This process also strengthens the pipe and improves its dimensional consistency.
Stage 4: Cooling, Cutting, and Handling
After sizing, the pipe travels through a cooling table, where water sprays or air jets reduce its temperature. Once cooled, it reaches the flying cut-off unit. A length measurement system, such as an encoder wheel, signals the saw to synchronize its speed with the moving pipe. The saw then makes a clean, perpendicular cut. The saw head returns to its start position after each cut. The finished pipes are conveyed away from the main line, where they may be straightened, inspected, tested, and bundled for shipment. Throughout this workflow, sensors and the central PLC monitor speed, alignment, temperature, and other critical parameters to ensure stable, uninterrupted production.
