Positive and negative screw screening machine

The utility model discloses a positive and negative screw screening machine. Bottom plate, a protection box and a fixing box are fixed to the upper end of the bottom plate. The protection box and thefixed box are fixed with each other; a rotating device is arranged on one side of the protection box; a rotating shaft is arranged on the rotating device, one end of the rotating shaft penetrates through the side wall of the protection box and is rotatably connected to the side wall of one end in the protection box, the rotating shaft is fixedly sleeved with a second gear, a shell is fixed to oneside of the fixing box, and two rotating rods are rotatably connected to the side wall of one end in the protection box. According to the screw screening device, the problem that forward and reverse screws are inconveniently and quickly screened by a mechanical method is solved, the problems that time is consumed and the screening efficiency is low due to multiple times of screening are also solved, the production efficien