The working principle of expanding machine is to have the pipe, after forming and qualified internal and external welding, set outside the expansion head of the Expander, and to expand the internal wall of the pipe section by section through the expansion of the dies, causing the material flow along the pipe wall, thus eliminating strange internal stress developped during forming and welding.

 

The strict control over expansion amount of dies can realize extremely high accuracy of diameter and roundness of the steel pipe. Moreover, in light of the principle of easy straightening during the flowing of materials, a straightening system is set up where a small straightening force can control the straightness of pipe body within the scope of 2/1000.

 

Expansion rate: 0.8%-1.5%, optimum: 1%-1.12%

Accuracy expanded steel pipes

Diameter tolerance: D-0.75 / D+2mm

Roundness: ≤±0.25D%

Straightness: ≤0.15%