Structure of a tube expander

A structure for a tube expander, comprising:

• a body with a trunk part, a neck part at the top end of the trunk part, the trunk part having a guiding groove for a pinch block that holds a tube, and a through hole inside the trunk part with the top end thereof going out of the neck part and the bottom end thereof connecting to the guiding groove;
• a ring fixed inside the neck part in the through hole and being hollow with an internal thread;
• a bearing fixed to the bottom end of the through hole and adjacent to the guiding groove;
• a driving head having an external thread to engage the internal thread of the ring as the driving head rotates forward and to leave the internal thread as the driving head rotates in reverse;
• an axle inside the body with the top end thereof going out of the neck part and connecting to the driving head and the bottom end thereof having a guiding pin positioned in the bearing, and having a tapered head disposed under the guiding pin and off the center;
• and
• a compressible elastic element disposed inside the trunk part and mounted on the axle, with the top end thereof urging against the bottom rim of the ring and the bottom end thereof pushing the guiding pin downward.