About the rebound when the welded pipe is formed

During the forming of low carbon steel welded pipe, the spring back is generally not a very prominent problem. With the application of various new materials in the welded pipe industry, the addition of various metal elements such as low alloy and alloy steel welded pipe, and the development and production of alloy welded pipe, their spring back in the forming process has become a more prominent problem.

Forming spring back is mainly shown as follows:

1.The forming roll is designed according to the pass design method. Due to rebound, the actual final forming is not the required shape, especially the edge forming of strip steel is insufficient.

2.During high-speed production of alloy welded pipe, large rebound will cause cracks at the weld that has not fully solidified when leaving the extrusion roll, and cracks will appear on the inner surface of the weld of welded pipe.

3.In order to improve the welding speed of alloy welded pipe, the two edges of the pipe blank need to be in close contact. If the rebound is large, the pipe blank will open at the front and rear edges of the extrusion roll, making the welding impossible.

The forming of welded pipe is a plastic deformation process, which includes part of elastic deformation, and it is elastic deformation that causes spring back. Metal is not an ideal plastic deformation material. The work hardening phenomenon of metal materials and the complexity of deformation conditions in the forming process of welded pipe make it difficult to accurately solve the spring back problem.

As far as iron and steel materials are concerned, their elastic modulus is not very sensitive to small changes in chemical composition and micro structure, and there is little difference in their elastic modulus. Therefore, their resilience mainly depends on the yield strength. Therefore, as a low-carbon steel, cold-rolled strip has higher strength and greater resilience than hot-rolled strip, and the strength of low-alloy steel and alloy steel is higher than that of low-carbon steel, Therefore, the rebound is large.

Several methods to overcome rebound:

1.Properly increase the deformation of forming roll

For some materials with large spring back or large welded pipe, when designing the forming roll, the factor of large spring back should be considered, and the deformation of each forming roll should be appropriately increased to make the shape of the pipe blank after spring back reach the required shape, especially the edge part of the metal belt. This method is conducive to preventing the occurrence of peach shaped pipe.

2.Heating forming method is adopted

Because the yield strength and elastic modulus of metal materials will decrease with the increase of temperature, heating forming can reduce the amount of spring back in the forming process.

3.Adopt asymmetric forming method

Asymmetric forming method refers to the use of two groups of asymmetric forming rollers before the extrusion roller, so that the pipe blank has two asymmetric deformation before entering the extrusion roller. As long as the asymmetric roller is reasonably designed, under the action of the two groups of extrusion rollers, the two edges of the pipe blank can maintain close contact within a certain distance, so as to meet the welding requirements.