The outer circulation means that the ball screw returns to the screw nut through the spiral groove or the intubation on the outer surface of the nut after the circulation process is over. The return methods of the outer circulation ball screw nut pair according to the ball circulation mainly include end cap type, intubation type and spiral groove type. Commonly used outer circulation method: end cap type; intubation type; spiral groove type. In the end cap type, a longitudinal hole is machined on the nut to serve as the return passage of the balls. The cover plates at both ends of the nut have return ports for the balls, and the balls enter the return pipe to form a cycle.
Intubation type, it uses the elbow as the return pipe. This structure has good manufacturability, but because the pipe protrudes outside the nut, the radial dimension is larger. Spiral groove type, it is a spiral groove milled on the outer circle of the nut, and through holes are drilled at both ends of the groove and tangent to the threaded raceway to form a return channel. This structure has a smaller radial size than the cannula structure, but Manufacturing is more complicated. The outer circulation ball screw has a simple outer circulation structure and manufacturing process and is widely used. The disadvantage is that it is difficult to smooth the joints of the raceways, which affects the stability of the ball raceways.
