How is the square galvanized pipe formed

　　Solid bend

　　Solid bending, as the name implies, is the compaction of the bend. During the actual bending, the inner and outer rollers and the inner and outer walls of the square galvanized pipe blank are compacted in both directions.

　　1. The advantages of solid bending are small rebound and accurate forming, and as long as the roll shape is accurate, the R of inner angle forming is more accurate.

　　2. The disadvantage of solid bending is that it has stretching / thinning effect. The first is that the full bending will stretch the bend, and the tensile effect will shorten the longitudinal length of the bending line; the second is that the metal at the real bending will become thinner due to stretching.

　　Hollow bend

　　Empty bending is the bending moment formed by the one-way contact between the outer roller and the outer wall of the square galvanized pipe blank to make the strip material bend. The empty bending will compress the bending line, and the compression effect will make the bending line longitudinally elongate, and the metal at the bend will accumulate and thicken, which is the compression / thickening effect of the hollow bending.

　　1. The advantage of empty bending is that the side length can be bent when the actual bending cannot be carried out, such as synchronous bending and finishing of the top / side of square galvanized pipe. Hollow bending can also bend the inner angle of R < 0.2T without breaking the square galvanized pipe wall.

　　2. The disadvantage of empty bending is that when the upper and lower rollers produce pressure at the same time, the forming force is easy to exceed the critical point, resulting in the edge instability and concave, and it will also affect the stable operation of the unit and the forming quality. This is also the different characteristics of hollow bending of square galvanized pipe and round pipe.