The motor shaft of the centrifuge has broken; please help with analysis
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The centrifuge was purchased last year; it has an 18.5KW motor. After about five months of use, the motor shaft broke suddenly while the machine was operating at normal speed. I would appreciate it if experts could help analyze this issue. Thank you
It is caused by issues such as shaft alignment, loose foundation bolts, installation level, dynamic balance, and bearing damage. To analyze such problems, it is not enough to just look at the damaged section; is the cracking of the bearing cover related to axial displacement? In particular, issues related to the connection between the foundation and the equipment are not easy to detect; this is provided for reference.
Without a coupling, the motor shaft and pulley are fixed together by keys.
Is it related to excessive load, especially when the load fluctuates greatly?
Inference: 1. The end face is flat with no plastic deformation; it should be fatigue fracture； 2. The final fracture area accounts for approximately 20% of the total cross-sectional area, indicating that the equipment was under light load; the fracture was not caused by overload ； 3. There are distinct radiating patterns all around the 360° circumference of the end face, indicating that the fracture of this shaft was not caused by a single crack defect. Considering that the fracture site is likely at a stepped area, it can be inferred that the fracture was not resulting from a material defect ； 4. The final fracture point was located in the lower half of the cross-section, off the axis and close to the edge; it is inferred that this area represents a region with high stress concentration. Conclusion: It is likely due to a problem with the chamfered transition at the axis (which leads to high stress concentration)
Is it a 18.5KW bag centrifuge? It could be a defect in the motor itself, or it might be that the pulley wasn’t installed properly – it was forced in using external force. I am a manufacturer specializing in centrifuges; you can add me on WeChat so we can discuss this technically
This is closely related to the machining of the motor shaft at the stepped areas; if the arc-shaped chamfer of the tool withdrawal groove is too small, micro-cracks will appear, leading to stress concentration and an increased risk of fracture
As can be seen from the image, the pulley is located near the end of the motor’s main shaft; this results in a large torque being transmitted by the belt, which in turn causes the main shaft to experience high bending moments. This is prohibited according to the motor’s operating instructions – check the manual to find out more.