Skewing

Skewing, also known as belt flipping, is a phenomenon that can occur at any time during the rolling process in the steel pipe making machine, due to various reasons. It is manifested when the pipe blank exits the horizontal or vertical rolls, and its edges are uneven in height. In severe cases, the pipe blank flips over, preventing it from smoothly entering the next pass, forcing a shutdown for adjustment. This directly impacts production efficiency.

Chapter 1 discussed three reasons for skewing in the horizontal rolls of the pipe mill. In addition, three more reasons are explained in this chapter.

4. Insufficient Pressure

Insufficient pressure refers to a situation where, after the upper roll is pressed down, there is still a large gap between the pipe blank and the roll pass, preventing the roll pass from effectively controlling the pipe blank, leading to skewing. This results in the pipe blank swaying back and forth during operation, moving laterally and vertically. If this occurs during the lead-in, the head of the pipe blank will tilt upwards. This can be resolved by appropriately increasing the reduction.

5. Misalignment of Multiple Passes

Misalignment of multiple passes refers to the situation where the centers of two or more roll passes are not aligned with the rolling centerline. When the pipe blank skews, an abnormal phenomenon often occurs during adjustment. For example, when the pipe blank flips outward, we typically adjust it inward to correct the outward skew. However, after adjustment, the pipe blank may suddenly flip inward, and in some cases, the rear part of the pipe blank may also exhibit the same inward flip. This issue cannot be resolved with conventional adjustment methods. The root cause is the misalignment of multiple roll passes. In such cases, the pipe blank exhibits a twisting motion in the mill (as shown in Figure 11). To resolve this skewing, the cause should be traced to the rear part of the pipe blank and adjustments should be made pass by pass from the front of the mill to ensure that the centers of all roll passes align with the rolling center. This is the basis for the adjustment saying “adjust the front to correct the rear skew.”

6. Misalignment of Vertical Rolls

Misalignment of the vertical rolls is also an important factor causing skewing after the pipe blank exits the horizontal rolls. This issue is often overlooked because the pipe blank appears to operate normally in the vertical roll section. Therefore, in production, particular attention should be paid to whether the pipe blank enters the horizontal rolls properly after exiting the vertical rolls. If the vertical roll center is misaligned, a small adjustment to the vertical roll position can ensure that the pipe blank enters the horizontal rolls in the optimal direction, resolving the skewing issue.