Patent ID: 7854156

Claim:
A closing device which presses a die against a rotating pipe body such that an open end portion of the pipe body is plastically closed by the die, comprising: a cored bar inserted into the pipe body to close the open end portion of the pipe body on an opposite side to the die; and a reactive force applying mechanism which allows the cored bar to retreat and applies a reactive force to the retreating cored bar when the cored bar receives a predetermined load or more during processing of the pipe body by the die, the reactive force applying mechanism comprising: a hydraulic cylinder divided into a rod side oil chamber and a bottom side oil chamber by a piston to which a rod supporting the cored bar is connected, which performs an expanding/contracting operation by supplying and discharging a working fluid to and from the two oil chambers; and a second cylinder divided into an air chamber sealed with air, and an oil chamber filled with a working fluid and connected to the bottom side oil chamber of the hydraulic cylinder via a flow passage, wherein the supply and discharge of the working fluid to and from the bottom side oil chamber of the hydraulic cylinder is shut off during processing of the pipe body, and when the cored bar receives a load during processing of the pipe body by the die, the air chamber of the second cylinder is compressed via the bottom side oil chamber and the oil chamber of the second cylinder, whereby the cored bar retreats and receives the reactive force.