Internal and external circulation and installation method of ball screw

The ball sometimes disengages from the screw during the circulation process, which is called external circulation; The constant contact with the screw is called internal circulation. Each closed loop of the ball is called a column, and the number of turns contained in each closed loop of the ball is called the number of turns. Each nut of the internal circulation ball screw pair has several types such as 2 columns, 3 columns, 4 columns, 5 columns, etc., with only one turn per column; There are several types of outer loops in each column, including 1.5 loops, 2.5 loops, and 3.5 loops.
1) External circulation: External circulation refers to the process where the ball passes through the spiral groove or insertion tube on the outer surface of the nut and returns to the screw nut space to re-enter the circulation after the cycle is completed. As shown in Figure 2-3, the return modes of the external circulation ball screw nut pair during ball circulation mainly include end cap type, insert tube type, and spiral groove type. Common external circulation method: end cap type; Intubation type; Spiral groove type. End cap type, a longitudinal hole is machined on the nut as a return channel for the ball. The cover plates at both ends of the nut have return ports for the ball, which allows the ball to enter the return pipe and form a loop. Intubation type, which uses a bent pipe as the return pipe, has good processability, but due to the protruding nut body of the pipe, the radial size is relatively large. Spiral groove type, which is milled on the outer circle of the nut, with through holes drilled at both ends of the groove and tangent to the threaded raceway to form a return channel. This structure has smaller radial dimensions than the insert tube type structure, but is more complex to manufacture. The external circulation ball screw has a simple structure and manufacturing process, and is widely used. Its disadvantage is that it is difficult to make the seam of the rolling track smooth, which affects the smoothness of the ball rolling track.
2) Internal circulation: The internal circulation adopts a reversing device to achieve ball circulation, and there are two types of reversing devices. Cylindrical convex key reverser, with its cylindrical part embedded in the nut and a reverse groove 2 at the end. The reverse groove is positioned by the outer circular surface of the cylinder and the circular key 1 at its upper end to ensure alignment with the direction of the threaded raceway. Flat round block reverser, which is a general round head flat key block. The block is embedded in the groove of the nut, and its end has a reverse groove 3, which is positioned by the outer contour of the block. Comparing two types of inverters, the latter has a smaller size, which reduces the radial size of the nut and shortens the axial size. But the precision requirements for the outer contour of this reverser and the groove size on the nut are relatively high.
Several installation methods of ball screw
There are only three typical applications:
1. Fixed at one end and supported at the other end, this is the most common installation method, suitable for medium speed to high-speed rotation, and the accuracy level can reach medium precision and high precision;
2. Fixed at both ends, only suitable for medium speed rotation, with high precision;
3. Fixed at one end and free at the other, suitable for low-speed rotation and medium precision.