Definition and Explanation of Steel Plate Bow in Spiral Welded Pipe Mills

2022-05-07

Definition and Explanation of Steel Plate Crown in Spiral Steel Pipe Factories: Acn — thickness measured by the center‑line thickness gauge; hm — thickness measured by the gauge located 40 mm from the edge on the drive side; hos — thickness measured by the gauge located 40 mm from the edge on the operating side. In actual rolling processes, plate crown may develop a wedge‑shaped profile. Generally, when the crown exceeds 40 µm, Wq should be less than; when the crown is less than 20 µm, Wq should be less than 27 µm. What is the mechanism behind the formation of steel plate crown? During rolling, the crown of the strip depends on the roll crown under load, the initial crown of the metal sheet, and the shape of the mill’s roll gap, which ultimately determines the strip’s final profile. The factors involved include: - Roll crown under no load; - Original roll geometry; - Roll crown in the hot state; - Roll wear; - Load‑induced roll crown. These elements collectively determine the roll gap configuration and constitute the primary control variables in the mathematical model. By specifying the original roll setting and adjusting bending rolls and tandem rolls, it is possible to modify both crown and flatness, ensuring that the elongation at the edges and in the center of the strip remains consistent, thereby achieving an ideal profile. For hot‑rolled sheets, there are generally no explicit tolerance specifications for crown control; the main objective is to meet the requirements of subsequent cold‑rolling operations. Cold‑rolling imposes a stricter tolerance on the crown of the incoming hot‑rolled sheet, typically requiring it to be less than 0.007 mm. In spiral steel pipe factories, “plate shape” refers to the uniformity of thickness distribution across the transverse cross‑section of the steel plate and the overall flatness of its surface. It is commonly believed that poor plate shape arises from uneven longitudinal elongation along the width direction. More precisely, plate shape is caused by residual stresses remaining in the strip after rolling. Specifically, the workpiece emerging from the roll gap may still retain relatively free ends, allowing variations in width‑wise deformation to manifest visibly at the leading edge. However, as the material continues to pass through the mill, these non‑uniform elongations become constrained, and their effects no longer appear clearly at the front end. Consequently, residual stresses—primarily tensile stresses acting longitudinally across the width—develop during the rolling process. When these residual stresses reach a sufficient magnitude, they give rise to defects such as waviness or warping.
Definition and Explanation of Steel Plate Bow in Spiral Welded Pipe Mills
Acn — the thickness measured by the strip‑center thickness gauge;
hm——the thickness measured by the thickness gauge at a location 40 mm from the edge of the strip steel on the drive side;
hos——the thickness measured by a thickness gauge located 40 mm from the edge of the strip on the operating side. In actual rolling, the plate shape may develop a wedge‑shaped crown; generally, when the crown exceeds 40 µm, Wq should be less than ; and when the crown is less than 27 µm, Wq should be less than 27 µm. What is the mechanism behind the formation of steel‑plate crown? During rolling, the crown of the strip depends on the roll crown under load, the initial crown of the metal’s original slab, and the roll gap geometry established by the mill, which in turn determines the final profile of the strip. The roll crown comprises: the unloaded roll crown, the original roll profile, the hot‑state roll crown, and the loaded roll crown—calculated as: unloaded roll crown + roll deflection + elastic deformation. These factors collectively determine the roll gap geometry and constitute the primary control variables in the mathematical model. By specifying the initial roll profile and adjusting the bending rolls and roll gap, the crown and flatness can be modified so that the elongation at the strip edges and mid‑width remains consistent, thereby achieving the desired profile. For hot‑rolled sheet, there are generally no explicit tolerance specifications for crown control; the primary concern is to meet the requirements of subsequent cold rolling. Cold‑rolling imposes a stricter tolerance on the crown of the incoming hot‑rolled sheet, typically requiring it to be less than 0.007 mm.
The flatness of steel plates produced by spiral welded pipe mills refers to the uniformity of thickness distribution across the plate’s transverse cross-section and the degree of surface flatness. It is generally believed that poor flatness arises from uneven longitudinal elongation at different points along the plate width. Strictly speaking, flatness is a consequence of residual stresses remaining in the strip after rolling. For example, a workpiece rolled through the roll gap may still exhibit variations in shape at its leading edge because that portion remains relatively free; however, as the strip continues to be rolled, the resistance to further non-uniform elongation at the leading edge is no longer apparent in the final profile, resulting in longitudinal tensile stresses along the width direction. These residual stresses, once the strip has been deformed, can become evident as defects such as waviness or warping when they reach sufficiently high magnitudes.

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Traditional industries such as spiral steel pipes have come to be viewed by the public as sunset industries.