The shaft is broken
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The shaft broke for the second time in a month. Please help me analyze it.
Can you explain the situation in detail? The type of pump, pump parameters, working conditions, medium conditions, and broken shaft are just a photo. There is too little information to judge. It seems that your shaft was welded and repaired, and the keyway was also repaired.
Indeed, please add information such as the environment and working conditions of the specific application.
It’s really hard to judge from just a picture. Please post the nameplate and the turning video.
No need to look, the shaft stiffness is not enough； Shaft strength was not checked during model selection
This post was last posted by 3983596_FPPZ edited on 2018-10-29 12:36 The selection should only be based on the process parameters to select the appropriate pump model. As for the power that each pump model can be used for, the flow and lift range, and whether the shaft is calibrated or not, it should be done in the early stages of pump design. There is no need to do these things in later model selection. It must be that when encountering high specific gravity media, such as concentrated sulfuric acid, you directly choose a pump or a new design pump over the limit. It is strange that no problems occur.
This shaft is welded from the fracture point and the keyway, which is very unreliable. If the fracture occurs again at the welding point, it may be very large. The shaft needs to be replaced. If the shaft diameter cannot be thickened due to structural limitations, then the shaft hollow slot at the welding point must be reasonably designed to reduce stress concentration. Otherwise, the shaft material must be replaced with a stronger one. If the working conditions permit, it is recommended to close the outlet valve and control the lower shaft power. It would be best if a reduced pressure start or soft start can be used during startup.
You can also take more photos, but it is really inconvenient for analysis.
There are generally many reasons for broken shafts, such as: 1. The material of the selected shaft itself has defects. ； It may be that the pump shaft was not produced according to the requirements, such as heat treatment, etc. ； 2. The design of the transition fillet of the undercut groove and the keyway on the shaft is unreasonable. This is generally a stress concentration point and is prone to fatigue fracture. ； 3. Whether the process operation is operated under the design conditions. Overload operation will also lead to fatigue fracture. ； 4. Whether the pump shaft passes the factory inspection. Also, what was the specific situation when the pump shaft broke for the first time? Do you have any photos? Is the second broken shaft the same as the first? Are there any abnormalities during the operation of the pump?
Judging from the angle of the roller key, it should be caused by foreign matter getting stuck in the impeller.