Fastening-loosening knife device

The invention discloses a fastening-loosening knife device which comprises a knife holder. A hydraulic cylinder is fixedly installed in the knife holder. A piston rod of the hydraulic cylinder is connected with a movable rod for an upper pipe clamp. Threads are arranged on the movable rod for the upper pipe clamp, two nuts are sleeved on the threads, a resetting clamping device is arranged on the movable rod for the upper pipe clamp, the knife holder is extended from one end of the movable rod for the upper pipe clamp far away from a piston rod, a wedge-shaped block is installed at the end of the movable rod through a screw, the inclined face of the wedge-shaped block is matched with a knife seat, the other face of the wedge-shaped block is contacted with a knife body, and the knife seat is fixedly installed on the knife holder. The hydraulic cylinder is adopted to provide power for a loosening knife to facilitate centralized control. The device is convenient to operate, reliable in clamping due to the fact that the wedge-shaped block is utilized to clamp a knife, capable of adjusting tightness degree of a belleville spring by rotating the two nuts arranged on the movable rod for the upper pipe clamp and capable of adjusting clamping force intermittently.