Characteristics of High Frequency Longitudinal Welded Pipe Sizing

High-frequency straight seam welded pipe sizing refers to rolling welded pipes with special pass rollers, adjusting round or special-shaped pipes with irregular sizes and shapes into finished pipes with regular shapes and sizes that meet the requirements of the standard. The welded pipe sizing process has six characteristics: fasting rolling, micro tension rolling, active rolling and passive rolling, large rolling force and large line speed are not at the same point, small pass type accepts large pipes and micro-reducing rolling.

1. Slight reducing rolling, whether it is round-to-round sizing rolling, or circular variation, different-to-different shaping rolling, the reduction ratio is generally very small. For welded pipes with an outer diameter of φ15~200mm, the total diameter reduction usually only accounts for 1.2%~0.65% of the outer diameter D of the finished pipe. This feature has guiding significance for sizing roll pass design, sizing allowance setting and actual operation, and provides a basis for formulating sizing process parameters.
2. Empty rolling, welded pipe sizing belongs to the category of open-web cold rolling. The empty-web welded pipe is rolled with sizing rollers. As long as a small rolling force is applied, the shape and size of the welded pipe can be changed. In the process, the circumference of the welded pipe becomes shorter, the cross-section becomes thicker, and the longitudinal direction becomes longer. This feature requires that the rolling force applied by the sizing pass should not be too large, otherwise the cross-sectional size of the welded pipe will suddenly shrink and the shape will be deformed, and the process purpose cannot be achieved.

3. Slight tension rolling. The whole process of welded pipe rolling is inseparable from the longitudinal tension. The longitudinal tension of the sizing section is closely related to the forming section and the welding section. After the specification and variety of the welded pipe are determined, the main factors affecting the sizing tension are the line speed and rolling force of the sizing flat roll pass. Slightly faster than the line speed of the forming flat rolls to obtain the greater friction required for the sizing process.
4. Active rolling and passive rolling coexist. In addition to reducing the diameter deformation, another important function of the sizing flat roll is to provide driving force for the operation of the welded pipe, while the force exerted by the sizing vertical roll hinders the operation of the welded pipe. This feature requires that we not only care about the size adjustment when adjusting the sizing flat and vertical rolls, but also consider the adjustment of the rolling force of the flat roll and the vertical roll to ensure that the rolling force of the flat roll is greater than the rolling force of the vertical roll. This is the basic principle that needs to be followed when adjusting the sizing flat and vertical rolls.

5. The larger rolling force of the sizing flat roll pass is contrary to the larger line speed. Taking the sizing round pass as an example, in the normal production process, care should be taken to prevent the size of the round tube from being higher than the upper and lower and the upper difference in the horizontal direction.
6. The small pass adopts the large welded pipe. According to the sizing process and principle, the geometric size of the welded pipe before entering the next sizing roller pass is always larger than the pass. In fact, in order to avoid friction between the welded pipe entering the pass and the larger linear velocity A and B of the pass, the size of the corresponding welded pipe is always adjusted to be slightly smaller than the pass. The contradiction between the theoretical design of the round pass and the actual adjustment of the welded pipe to an ellipse directly leads to two bad consequences: one is to increase the friction between the edge of the pass and the welded pipe, and accelerate the wear of the edge of the pass; The second is that the parts on the surface of the welded pipe corresponding to the edge of the pass are vulnerable to extrusion damage. Although this wear and extrusion is sometimes slight, it can be avoided. This inspires people to improve the design ideas of the existing round (including some special-shaped pipes) pass, so that the theory is close to reality, so as to prevent the adverse effects of the pass on the welded pipe and the pass itself, and prolong the use of the roll pass.