Indentations and dark lines are actually the products of pressure damage, the formation mechanism is similar, but the performance is relatively hidden, not carefully observed, the feel is not obvious, but their impact on the surface quality of the welded pipe is there. Indentations are usually reflective bands of 5-10 mm, especially light sources. The refractive index of light at the indentation is different from other parts. The essence of the dark line metal trim manufacturers is that the line marks that occur before the line are not found in time and are "flattened" by the subsequent rolling. Rough, and no problem can be seen; But double-check, wipe with sandpaper, and tap with nails around the surface of the pipe, otherwise the presence of dark lines can be seen or felt. Dark lines are more insidious than indentations and are more difficult to find.

Scratching: Mainly refers to the failure of the roller not moving during operation or the relative speed difference with the pipe blank, and its characteristics are related to the speed difference. For example, the vertical roller bearing is damaged, the vertical roller rotation is blocked, and the pipe surface is scratched; The linear velocity of the rolling diameter position on the hole is different from the linear velocity of other parts. Compared with the moving tube blank, there is a certain relative movement between the positions with a large speed difference, and when the friction reaches a certain level, the surface of the pipe blank will be scratched. The former is characterized by a vertical line on the surface of the pipe; The latter is characterized by an irregular curved surface of the tube, similar to "nail marks" "nail marks usually appear on the sides, bottoms and middle of the tube blank. The edge and bottom of the tube blank correspond to the position of the speed difference of the forming vertical roller, and the middle corresponds to the position of the speed difference of the forming flat roller hole.

Removing the "nail seal" can be handled from two aspects: from the perspective of hole design, without affecting the overall deformation effect, the hole type can be boldly removed, which is not only harmless to molding, but also never scratches the back cover. From the adjustment point of view, if there is an indentation under the vertical roller tube blank, the vertical roller is lowered; If there are indentations on both sides of the flat roller tube blank, tighten the vertical roller or loosen the flat roller appropriately before the flat roller. If there is an indentation on one side of the tube blank after the flat roller is unloaded, the rolling line of the vertical roll before the flat roll should be corrected.

The surface of the pipe is a aluminium tile trim profiles common defect of welded pipe, which is specifically manifested as compression, indentation and scratches. Bruising: Bruising refers to the damage of the roller hole to the surface of the tube blank, there are many types of bruising, but the causes of bruising are not only the following aspects:
(1) Adjust the bottom line of a pair of roller tables to be higher than the rolling bottom line; The rolling line produces uneven fluctuations;
(2) The vertical roller is too tight;
(3) Vertical roller elevation;
(4) The new hole may be that the chamfer of the hole edge is too small or the chamfer does not meet the requirements;
(5) The high-strength pipe blank has greater rebound and deformation resistance, and the hole edge is easy to bite into the pipe blank;
(6) The vertical roller in front of the flat roller is not enough to apply force to the pipe blank, so that the wider pipe blank enters the fixed width of the flat roller hole, and the pipe blank is "cut" by the hole type;
(7) The flat roller is low, and the lower edge of the vertical roller hole damages the pipe blank.