The kelly is located at the top of the drill string. Its main function is to transmit the rotary motion and torque of the turntable to the drill string, so that the drill string rotates to drive the drill bit to break the rock. Because it is at the top of the drill string, it is subjected to the drill string. The full weight.
The kelly is divided into the following two forms according to its shape:
Square square drill pipe: the pipe body is circular in cross section, and the outer square square drill pipe is coded as FZGS. Hexagonal drill pipe: a square drill pipe in the cross section of the pipe, coded as FZGL.
The kelly is composed of a driving part, an upper joint and a lower joint. The upper joint is internally threaded and connected to the faucet. Since the turntable rotates clockwise during the drilling process, the upper joint is machined into a left-hand thread and the lower joint is machined into a right-handed external thread to connect the drill pipe.