How do THK ball screws achieve ball recirculation? Generally, there are four types of recirculation components: return bends, ball returners, end plate recirculation, and return plates. Return bends are commonly used, where the steel balls are guided into the bends and returned to the previous running position via the bends for recirculation. The return-type nut of the THK ball screw is compact. The ball returner changes the travel route, returning to the previous travel position via the top of the screw shaft channel. End plate recirculation is suitable for high-speed THK screws. The steel balls on the THK ball screw shaft are guided onto the end plate and returned to the previous position through the recirculation holes in the nut. In addition, there is also a cover recirculation where the steel balls recirculate through the grooves of the spiral passage. Because the structure of this plate recirculation is much more compact than the return bend recirculation, it is used for micro ball screws.

　　What is preload? How to preload THK ball screws?

　　Preload refers to pre-applying pressure to the interior to create a negative clearance between the rolling element and the raceway. By using slightly larger steel balls, the gap between the nut and the groove of the THK ball screw shaft is eliminated. The purpose of preload is to eliminate backlash in the screw and reduce errors caused by axial elastic deformation of the rolling element under external loads.

　　THK ball screws can be preloaded using the following methods.

　　1. Within a single cycle:

　　Internal circulation uses reverse gear for ball recirculation. There are two types of reverse gear. The cylindrical part of the cylindrical cam is embedded in the nut, and a reverse groove is provided at the end. The reverse groove is positioned by the cylindrical outer periphery and the circular key at its upper end, allowing reliable alignment with the direction of the screw thread. The flat elliptical block and the hairpin are typical round-head flat keys. The block is embedded in the groove of the nut, and a reverse groove is provided at its end, which is positioned by the outer contour of the block. Compared with the two types of reversing gears, the latter has smaller dimensions, thus reducing the radial dimensions and shortening the axial dimensions of the nut. However, this reverse gear's shape and the accuracy of the nut groove dimensions are very demanding.

　　2. External circulation:

　　External circulation refers to the balls returning to the space between the nuts to enter the circulation after the circulation process is completed through the spiral groove or insert tube on the outer surface of the nut. The return methods mainly include end cap type, insert tube type, and spiral groove type when the outer circulation THK ball screw nut and the ball recirculate together.

　　THK ball screw external circulation methods:

　　a) End cap type

　　b) Insert tube type

　　c) Spiral groove type. For the end cap type, longitudinal holes are provided on the nut as return channels for the balls, and return ports for the balls are provided on the caps at both ends of the nut. The balls enter the return tube and recirculate. The insert tube type uses a return bend as the bent tube. This structure has good technology, but due to the tube protruding to the outside of the nut, the radial dimension is larger. The spiral groove type cuts spiral grooves on the outer periphery of the nut, and through-holes are provided at both ends of the grooves, which contact the screw threads to form return channels. The radial dimension is smaller than that of the insert tube type, but the manufacturing is more complex. The external circulation THK ball screw external circulation structure and manufacturing technology are simple and widely used. The disadvantage is that the seams of the ball return tube are difficult to smooth, which will affect the smoothness of the ball return.

　　The above is an introduction to how THK ball screws achieve ball recirculation. If you need to know more, please feel free to contact us!