Screw bearing failure case analysis

As nc machine tools work precision and speed of higher requirements, such as, high precision ball screw bearing is widely used in the machine tool industry. Accuracy, installation and its temperature determines the precision of the machine tool drive unit, thereby affecting the machining accuracy of machine tools. Bearing failure after simple change doesn't rule out the risk of failure again, need to analyze the failure reason and improve it, to take the initiative to improve the bearing life cycle, to prevent the same causes failure again. 1, the working condition of screw bearing installation figure 1 as a screw for a machine tool manufacturer bearing arrangement, specific parameters is: screw phi 40 mm x 10 mm; Length is 800 mm; Vertical installation; Carrying 3000 N. In figure 1), (3) bearing are FAG ZKLF3080; (2) place for FAG bearing ZKLF2575. Temperature rise of the shafting is unknown, the pre-tension amount is unknown. 2, bearing failure situation according to the user, the machine is running after a period of time bearing failure, lead to machine can't normal operation. After dismantling found that ZKLF2575 medial raceway bearing outer ring and inner ring outer raceway are peeling, and inner ring sliding trace, details of which are shown in figure 2. 3, failure reason analysis according to the failure of screw parameters and hypothesis temperature of 5 ℃, is because of the temperature rise of screw pre-stretching force F: F = & # 8710; 莱城/ l; ∆ l =∆ Kal。 Type in the & # 8710; L for screw pre-stretching quantity; A, for the screw shaft area. E for the modulus of elasticity, 210 GPa; ∆ K for temperature variation; A for thermal expansion coefficient, 11. 7μm/（ m¹ ·℃¹ ） 。 The known data substitution ( 1) Type by the calculated temperature is 5 ℃ when the force F = 15438 n. According to the bearing capacity graph FAG bearing samples, and the ultimate bearing capacity of the screw bearing ZKLF2575 about 5500 N, and the force of 15438 N generated by the temperature rise of the shafting, far more than the limit of bearing can carry through leading to premature failure of the bearing. Through the analysis and calculation, the failure reasons for the screw in the process of operation temperature rise is too large, screw elongation, increase the bearing load, lead to failure of the bearings. 4, conclusion: the cause of screw bearing failure is: in the process of operation caused by temperature rise too high. Solution is: when screw bearing preloading is too large, in addition to by increasing the amount of pretensioning ( 0. 02 - 0. 3 mm recommended value) To compensate for outside, still can add a butterfly spring (by optimizing the structure, Similar to the elastic preloaded) To improve the temperature effect on the bearing, its structure as shown in figure 3, the structure has been used successfully in many Japanese machine tool.