HEJ, HU ISSN 1418-7108 Manuscript no.: MET-000123-A

Motion of the balls from the end of the thread to the start of the thread

The motion of the balls in the thread was discussed earlier. It was stated there that in case of improper profile shape the balls could come to the edge of the nut or pin thread. So for larger loads the deformation of the balls increases significantly. Because of the increase of the element's deformation the axial play of the thread (the longitudinal displacement of the pin and the nut compared to each other) will be larger as well than that of belonging to the normal thread. Because of the axial "shearing" of the thread profile the unloaded balls are able to enter the thread only under the effect of a large force. This force effect closes on the balls in the thread through the balls blocking in the ball returning tubes and if a ball is just at the leaving ear for blocking the ear is loaded by a significant component of the blocking force. If the ball returning tubes are able to go up as well the blocking force lifts the tubes and leaving and entering the thread will occur really at the same time as it can be seen on the figure and then the larger force acts on the ear. The blocking force is increased on by the displacement of the bores of the ball returning tube from the thread profile.

The blocking position of the balls can be determined on the basis of the wear scheme of the examined used returning tube.

 

Figure 3: Change in the action angle in the function of load in case of totally symmetric thread profile

 

Figure 4: Change in the action angle for a nut thread profile having decreased connecting angle

 

Figure 5: Position of the balls in the ball returning tube in case of blocking

Figure 5 shows the lying of the balls and leave and enter of the balls. The ball laying shown by the picture is the same as the wear scheme taken for some shelly worn ball returning tubes. It can be concluded that the shelly- wear form formed in the ball returning tubes due to the improper thread machining.

Since for large loads or improper profile shapes the balls run on the edge of the thread profile, also the entering ball contacts the edge of the thread first. The effect of this sharp corner - because of the penetration of the bore and the thread - can cause a cut-like stress on the balls, which can be observed very well in these used gears.

HEJ, HU ISSN 1418-7108 Manuscript no.: MET-000123-A