The Causes of Piling and Drawing during Rebar Rolling
Reinforcing steel, also known as rebar, is an important element in steel-concrete composite construction materials and is widely used in bridge engineering and large-scale construction projects. During the rolling of reinforcing steel, piling and drawing, as two main defects of reinforcing steel, occur when adverse rolling parameters, rolling defects or adjustments in machine conditions are used.
Reinforcing steel piling can be defined as the phenomenon of non-uniform deformation or wrinkle shape or the increase of the width when the steel in the roll passes through roll-holes. The piling can cause inaccurate or incomplete realignment of the center lines of the strand and uneven rolling force happen during rolling. The result is that the steel has a clear piling shape and marks. Drawing refers to the phenomenon in which the steel in the roll is pulled out of the roll-hole, resulting in narrow and small protrusions being formed on the outer surface of the steel profile.
In the rolling process of reinforcing steel, the performance of the rolling passes is very sensitive to the material, equipment and rolling parameters. When the material property and shape of the steel change, or when the rolling parameters and equipment conditions are different, the size and shape of the deformation during rolling will be affected.
In terms of material factors, drawing can be caused by high toughness, poorly heated steel and inconsistent chemical composition. During the rolling process, if the tension is too large, the rolling parameters are too low, or the temperature of the heated material is too low, the internal stress of the material will be higher. Under high internal tension, the elongated prefabricated materials are easily drawn out when passing through the roll-hole, leading to uneven or narrow strip shape.
In terms of equipment and rolling parameters, piling can be caused by roll pass design error or roll pass sequencing error. When the roll pass section is unreasonable, the inside of the roll is easily formed into an inward rotation or backward arching shape when it is rolled through the roll-hole.
The situation of piling and drawing can also be caused by the uneven running speed or roll gap of the roll. When the rolling speed of the two rolls is not uniform, the material will be piled up in the roller gap, causing the steel material to be thickened, and the strip material is shifted to one side. If the rolling gap is not uniform, it is easy to cause the cross-section shape of the steel to change, which leads to the phenomenon of drawing.
The phenomenon of piling and drawing during rebar rolling is often accompanied by more serious problems, such as bite and scrap. Rebar rolling with piles and drawings requires strict control of the entire production process, from raw materials to equipment and personnel operation. The appropriate choice of rolling parameters and improvement of rolling technology are the key measures to reduce the occurrence of piles and drawings.
