Advantages of mechanical expanding 
(1) by expanding the pipe can fully eliminate stress due to the forming, welding and other processes caused; 
(2) Pipe through plastic deformation to produce a certain amount of work hardening, thereby improving the yield limit of the material; 
(3) by expanding the steel pipe diameter size, roundness and straightness can get long to meet and improve.

Principle of mechanical expanding
Mechanical expanding is by a power source (cylinder) is moved axially to pull the cone, the tapered surface so as to promote the distribution of the die holder in a die driven by a radial expansion of the opening to the tube wall in the circumferential direction along the pipe, a force wall of the steel pipe a certain amount of plastic deformation in the circumference.