Key Processes in Seamless Square Tube Manufacturing

Many defects in square tubes are caused during piercing, so the work transfer process during the tube blank is a critical step in square tube production. The primary difficulty in piercing high-alloy materials lies in their poor piercing performance. To ensure quality, the deformation parameters must be rationally selected.

 

 

Insufficient compression can lead to instability in the piercing process. Therefore, the critical compression of the plug should generally be set at around 7% of the initial compression. Otherwise, the plug will lose its grip, even increasing movement or causing front jamming. Increasing the compression in front of the plug can also form cavities and internal defects. To overcome this problem, the square tubes blank must be centered, and the depth of the centering cavity should be comparable to that of other steel grades.

 

Hot-rolled rectangular tubes, continuous cast billets, and blooms are used as raw materials. They then pass through a heating furnace, where high-pressure water is used to remove phosphorus from the surface. The roughing mill then cuts the head and tail of the rectangular tube. The tube is then fed to the finishing mill for computer-controlled precision rolling.

 

After laminar cooling, the square tube is rolled in a coiler and then coiled. However, when re-curling, the thickness and accuracy often show errors. This is equivalent to the edges being prone to defects. Then, the coil is re-curled and trimmed with a straightening process after the cutting head to ensure the thickness and accuracy of the rectangular tube.