After the structure of the ball screw nut pair of Shenyang machine tools and the ball circulation process, it leaves the screw thread raceway and returns to the screw through the spiral groove and cannula on the outer surface of the nut to re-enter the circulation.

The outer circle of the nut is equipped with a helical intubation port, and the two ends of the pipe are inserted into the holes at both ends of the ball nut to search for the multi-circle circulating chain of the balls formed by the intubation of the balls.

This type of Shenyang machine tool ball screw nut pair has a simple structure, good manufacturability, and high bearing capacity, but the radial size is large, and the wear resistance and impact resistance of both ends of the elbow are poor. It is currently the most widely used and can be used in heavy-duty transmission systems. Slotting on the surface of the nut is connected to the tangential hole, and installing two balls in the threaded raceway instead of the elbow, it is a spiral groove type external circulation.

In this way, the radial size of the nut is small, but the difference between the groove and the hole. The interface is a non-smooth connection, and it is easy to generate impact when the ball passes through.

The recirculating balls remain in contact with the screw surface during the cycle. It connects the adjacent raceways by the reverser installed on the nut, so that the balls circulate in a single circle. The number of reversers 2 is equal to the number of ball turns.

The advantages of the internal circulation method are that the loop of the ball circulation is short, the structure is compact, the rigidity is good, the ball circulation is good, and the efficiency is high, but the manufacturing precision is high and the manufacturing is difficult. It is mainly used for high-sensitivity and high-precision feed systems, and it is not suitable for heavy-duty transmission.

Pre-tightening method of ball screw nut pair of Shenyang machine tool

The transmission clearance of the ball screw is the axial clearance, and its value refers to the maximum axial movement between the screw and the nut when there is no relative rotation between the two. In addition to the clearance of the structure itself, it also includes the application of axial load. The amount of movement of the shaft caused by the elastic deformation afterward.

The existence of the axial gap causes backlash error when the lead screw rotates in the reverse direction, which affects the transmission accuracy and axial grace. In order to reduce the axial clearance caused by elastic deformation, the method of preloading (preloading) is usually used.

The basic principle of the preloading of the ball screw nut pair is to make the two nuts produce axial displacement to apply the preloading force and cut the gap between them. However, excessive preload will increase frictional resistance, reduce transmission efficiency and shorten service life. Therefore, it generally needs to be adjusted several times to ensure that the gap is eliminated and the operation is flexible. 

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