(1) Wave bend

It is the phenomenon that the edge part of the strip is repeatedly bent along the longitudinal direction, which is caused by the uneven deformation of the center and edge along the width direction during strip rolling. Wavy bends will cause serious lap welding during the forming and welding of square and rectangular tubes, making production impossible, so they are not allowed.

(2) Scar indentation

Scarring and indentation are caused by foreign matter sticking to the roll during rolling. Scratches are caused by the strip being scratched by foreign objects on the roller table or on the floor during the running process, especially when the cold-rolled strip is not oiled, it is easier to scratch. The unevenness of the head and tail is caused by direct coiling without cutting the head and tail after rolling. These defects eventually lead to the unqualified appearance quality of square rectangular tubes and reduce the qualified rate of tubes.

(3) Loose rolls

 Because the steel belt packaging is not firm, the operation is improper during the loading and unloading process, or the raw material management is not good, the coils are scattered due to pressing the warehouse and hoisting back and forth. Slight loose rolls can still be used after sorting, but severe loose rolls cannot be sorted so the scattered parts must be cut before use, which increases metal consumption and reduces the yield.

(4) Sickle bend

Sickle bend is a phenomenon that the strip bends to one side on the horizontal plane along the length direction of the strip, which is caused by uneven deformation along the width direction of both sides during strip rolling. Sickle bends are likely to cause lap welding during production, and deviation or even overturning during molding.

(5) Oxidized skin

The entry of scale into the weld zone between the edges of the strip will cause welding defects. In addition, the iron oxide sheets on the surface of the strip enter the forming machine to accelerate the wear of the forming roll. Descaling of hot-rolled strip steel with serious scale should be carried out.

(6) Gnaw the edge

Edge gnawing is the phenomenon that the edge of the strip steel is jagged and uneven, and it generally occurs on the slitting strip steel. The reason is that the disc scissors of the slitting machine are blunt or have gaps. The quality and stability of the weld seam will be affected when the strip steel with serious edge gnawing is welded, and the square tube will have cracks and cracks due to the local lack of meat.

(7) Tower rolls

The tower-shaped coil is a square-rectangular tube strip steel coil that is tower-shaped from the inner ring to the outer ring and is generally not allowed to be larger than 50mm.