Pipe surface scars are common defects in the production of used welded pipe machine, with specific manifestations such as crushing, indentation and scratches.

① Crush injury

It refers to the damage of the roll pass to the surface of the tube blank, and there are many types of crush injuries, but the reasons for this are nothing more than the following aspects:

(1) The bottom line of a vertical roll pass is adjusted higher than the rolling bottom line; the entire rolling line has uneven undulations;

(2) The vertical roller is too tight;

(3) The vertical roller has an elevation angle;

(4) The new hole type may be that the edge chamfering of the hole type is too small or the chamfering angle does not meet the requirements;

(5) The high-strength tube blank has large springback and large deformation resistance, and the edge of the hole shape is easy to "bite" the tube blank;

(6) The vertical roller in front of the flat roller exerts insufficient lateral force on the tube blank, causing the wider tube blank to enter the flat roll pass with a fixed width, and the tube blank is "sheared" by the pass;

(7) The flat roll is too low, causing the tube blank to be crushed by the lower edge of the vertical roll pass;

(8) The vertical roll deviates from the rolling center line, causing the tube blank to be crushed in the flat roll.

② Indentation and dark lines:

The indentation and the dark line are actually the product of pressure injury, and the formation mechanism is roughly the same, but the performance is more hidden when the used welded pipe machine is used to make pipes. all exist.

The indentation usually appears as a 5~10mm reflective strip, which is especially obvious to the light source. The refractive index of the light at the indentation is different from that of other parts.

The essence of the dark line is that the linear scars that occurred earlier were not detected in time and were "flattened" by the subsequent rolling. At first glance, no fault can be seen; but after careful inspection, wiping with sandpaper, and scribing along the circumference of the tube surface with a fingernail, you can still see or feel the existence of dark lines. Dark lines are more subtle and harder to spot than indentations.

③ Scratches:

It mainly refers to the damage to the running tube blank by the rollers that do not move or the relative moving speed difference is large, and is characterized by the speed difference. For example, the bearing of the vertical roller is damaged, causing the rotation of the vertical roller to be blocked and scratching the surface of the tube; the linear speed of the rolling diameter position on the pass is different from the linear speed of other parts, and the position with a large speed difference is compared with the moving forming tube blank. There is a certain relative movement between them, and the surface of the tube will be scratched when the frictional force reaches a certain level. The scratch feature of the former is that there are vertical straight lines on the surface of the tube; the feature of the latter is that there is an irregular arc like a "nail print" on the surface of the tube. "Nailprints" mostly occur at the two edges, bottom and middle of the forming tube blank. The edge and bottom of the tube blank correspond to the position where the speed difference between the vertical rollers is the largest, and the middle corresponds to the position where the speed difference is the largest. 

Removing "nail marks" can be handled from two aspects: hole type and adjustment:

From the point of hole design, without affecting the overall deformation effect, bold removal of the hole is not only harmless to the molding, but also can never cause scratches.

From the perspective of adjusting used welded pipe machine, if there is an indentation under the tube blank of the vertical roll, lower the vertical roll; if there are indentations on both sides of the tube blank of the flat roll, tighten the vertical roll before the flat roll or properly Loosen the flat roll, if there is an indentation on one side of the tube blank after the flat roll, the center line of the vertical roll before the flat roll should be corrected.