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Abstract: Aiming at the early failure problems such as fracture of cages and separate rings for insert deep groove ball bearings 607 used in multi － propose tool under the operating condition，the reasons for early failure are analyzed combining with the actual operating condition of bearings，and the main parameters and cages of bearings are improved.
Key words: insert deep groove ball bearing; structural improvement; nylon cage
1. Service conditions and problems of bearings
The 607 outer spherical deep groove ball bearing is applied to a multifunctional tool, and the working principle of the multifunctional tool (Figure 1) is as follows: when the electric motor rotates at high speed, due to the eccentricity between the axis of the rotor and the outer spherical bearing mating part and the rotation axis of the electric motor, the outer spherical bearing drives the shift fork to swing high-frequency with the output shaft as the rotation center, thereby causing the saw blade, polishing head, etc. fixed on the output shaft to swing high-frequency, Realize functions such as cutting and polishing.
1- Output shaft; 2- Output shaft rear bearing; 3- Shift fork; 4-607 outer spherical bearing; 5- Front bearing of rotor; 6- rotor; 7- Rear bearing of rotor; 8- Front bearing of output shaft; 9- Screw; 10- Saw blade
Figure 1 Working principle diagram of multifunctional tool
During the relevant life test, the bearing experienced polyamide cage fracture and bearing loose sleeve failure after only running for 15-30 hours, as shown in Figure 2.
Figure 2 Image of Early Failure of Bearings
2. Failure Cause Analysis
Based on the actual application conditions and failure forms of bearings, it is analyzed that the main reasons for early failure of bearings are as follows: (1) During bearing operation, there is strong impact and friction between the outer ring and the shift fork, which generates more heat and increases the bearing temperature. PA66 reinforced polyamide cages age at high temperatures and their strength decreases; (2) There is a significant impact force between the outer ring of the bearing and the shift fork, causing rigid deformation of the outer ring and a certain impact force on the polyamide cage.
3. Improvement measures
For the above two reasons, on the one hand, improve the surface roughness of the relevant contact surfaces and reduce frictional heating; On the other hand, adjusting the structural parameters of the bearings to increase their rigidity, reduce the impact force on the cage, and improve the strength of the cage.
3.1 Improvement of Cage
The original cage adopts a reinforced polyamide cage structure with 607 sealed deep groove ball bearings, and the bottom diameter thickness of the pocket hole S=0.35 mm, as shown in Figure 3. Due to the open structure of the 607 outer spherical deep groove ball bearing designed in the article, S can be increased to around 1.1 mm without changing the outer dimensions of the bearing to enhance the strength of the cage. Using the newly improved cage for installation testing, the bearing life has been increased from 15-30 hours to 40-80 hours.
3.2 Improvement of Main Parameters of Bearings
The number of improved bearing steel balls remains unchanged (7 pieces), the diameter of the steel balls is adjusted from 3.5 mm to 3.175 mm, the pitch diameter of the ball group is adjusted from 13 mm to 12.5 mm, and the filling angle is reduced from 187 ° to 176 °. In Figure 4, B=(D-Dpw-Dw)/2, where D is the outer diameter of the bearing and D=19 mm. By substituting relevant parameters, it was calculated that B increased from 1.25 mm before improvement to 1.66 mm. This change greatly enhances the rigidity of the outer ring, making it less prone to deformation when colliding with the shift fork, thereby eliminating the impact on the cage caused by outer ring deformation and avoiding damage to the cage.
Figure 3 Cage Structure
Figure 4 Outer Ring Structure Diagram
4. Conclusion
After the redesign of the bearing structure, the rigidity of the outer ring has been strengthened, which greatly helps to improve the service life of the bearing. In theory, a decrease in the diameter of the steel ball will reduce the rated load and service life of the bearing. However, in practical applications, this bearing is prone to early abnormal failure. The reduction in the diameter of the steel ball improves this situation and is actually beneficial for improving the actual working life of the bearing. The improved bearings were used for installation testing, and the service life reached 80-120 hours, basically meeting the working requirements.
2024 January 4th Week KYOCM Product Recommendation:
A spherical plain bearing is a bearing that permits angular rotation about a central point in two orthogonal directions (usually within a specified angular limit based on the bearing geometry). Typically these bearings support a rotating shaft in the bore of the inner ring that must move not only rotationally, but also at an angle.
KYOCM The Spherical Bearing is a heavy-duty self-aligning sliding bearing. Highly resistant to impact loads, this product is most fitted to the oscillating section under slow, heavy loads.
https://www.kyocm.com/products/Spherical-Plain-Bearing/742.html
2024-01-31