Two forming methods for industrial seamless square steel pipes

1. Solid bending: Solid bending, as the name implies, is for compression bending. During the overall bending process, the inner and outer walls of the inner and outer rollers and the blank are compacted in two directions.

1) The advantages of solid bending are small rebound and accurate forming. As long as the roller type is accurate, the R of the inner angle forming is more accurate.

2) The disadvantage of solid bending is the effect of stretching/thinning. First, solid bending will stretch the bend, and the stretching effect will shorten the longitudinal length of the bending line; second, the metal at the solid bend will be thinned by stretching.

2. Empty bending: Empty bending is a bending moment formed by the unidirectional contact between the outer roller and the outer wall of the tube blank to bend the strip. Empty bending will cause the bending line to be compressed, and the compression effect will cause the bending line to be longitudinally elongated, and the metal at the bending point will accumulate and thicken. This is the compression/thickening effect of empty bending.

1) The advantage of empty bending is that it can bend the side length when bending is not possible, such as when the upper/side of the rectangular tube is bent and completed at the same time. Empty bending can also bend the inner angle of R<0.2t without causing the tube wall to rupture.

2) The disadvantage of empty bending is that when the rectangular tube is synchronously bent/sided at the upstream end, due to the pressure of the upper roller and the lower roller, the forming force is easy to exceeds the critical point, causing instability and concave edges, which also affects the stable operation of the device and the forming quality. This is also the different characteristics of rectangular tubes and circular tubes formed by hollow bending.

In practical applications, these two basic methods should be configured to a reasonable process position according to product needs in the forming of rectangular tubes. Attention should be paid to the influence of the stretching/dilution effect of solid empty bending and the compression/thickening effect on the quality of the product, otherwise, it will cause the concave formation of one side of the rectangular tube, and the longitudinal bending of the finished tube will be difficult to be straight.