Analysis of the causes of spiral shaft fracture
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Recently, one of our company’s screw shafts, which had been in use for four or five years, broke. The fracture location is at the seal between the reducer and the screw intermediate filler; the screw shaft is a hollow shaft, and the fractured shaft is the output shaft of the reducer. I’m hoping everyone can help me out. I checked the current trend graph in DCS; the 5.5-kilowatt motor did not show any signs of overcurrent, and the waveform at this point also appears to be smooth, which makes me suspect a brittle fracture.
Have there been any changes in the viscosity and density of the material?
There isn’t one; all the materials are the same
The last edit to this post was made by my_love_jh on 2021-11-27 at 20:14. As can be seen from the images, it is a simple fatigue fracture, with a smooth fracture surface; it should be a fatigue fracture due to rotational bending； The fracture surface runs across the entire axis, indicating that high stress was applied here (due to high operating loads on the equipment). The fractured area accounts for roughly half of the entire shaft cross-section, suggesting high stress concentration in this region. The shaft’s fractured cross-section has multiple steps, which also indicates high stress concentration in that area
Thank you. Does annealing during the shaft processing ensure the strength of this shaft?
We have encountered this issue at this port as well; it is likely due to fatigue fracture at stress concentration points, related to vibration or frequency shocks
Is alignment okay? Is fatigue fracture caused by alternating loads on the rotating shaft?
For the cause analysis, I agree with the opinion from the 4th floor: since the motor is connected to the screw through a reducer, an overload generally does not result in an overcurrent.
The white area represents brittle fracture, while the blackened areas around it are likely the regions where fatigue cracks have formed; these fatigue cracks have caused a reduction in strength at the shaft end step, leading to brittle fracture. It’s likely not caused by overload; rather, it results from long-term operation, affected by equipment vibration, leading to fatigue stress in this area.