Problems with Hefei Xinhu shielded pumps
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The shielded pumps produced by our factory in Hefei Xinhu are used to transport semi-saturated liquid; the density of this medium is 1049 KG/M3, its viscosity is 3.53, and the temperature is 49.3 degrees. The outer diameter of the impeller is 252 mm, and the motor required for operation is 75 KW, 50HZ. After 3 years of operation, a rotor fracture occurred; the rotor broke off at the front of the sliding bearing at the impeller end. Upon disassembly, it was checked that neither the front nor rear thrust discs nor the sliding bearings showed any signs of wear. However, there seemed to be welding marks at the site of the rotor fracture. Please help analyze the cause of the pump shaft fracture. The image is as follows:
There can be various reasons for a pump shaft to break. Firstly, based on the welding marks you mentioned, it is possible that there was a welding defect in the rotor during its manufacturing or repair process; this results in the strength of the material in that area being lower than in other parts. Over time, fatigue accumulation in the material can lead to fracture. Furthermore, mechanical vibration, shaft imbalance, or mechanical stress concentration during prolonged operation can also lead to fracture. It is also possible that the presence of foreign objects inside the pump, or hard particles in the semi-liquid phase, causes prolonged wear that damages the shaft material until it eventually breaks. Finally, the absence of wear marks on the bearings does not mean that there are no hidden problems in other parts; slight displacement or failure of the bearings and thrust plates can also lead to abnormal loads on the shaft, thereby causing it to break. It is necessary to conduct a thorough review of the pump’s usage and maintenance records, as well as to carefully analyze the processes involved in its design, manufacturing, and repair. .
The fracture occurred due to stress concentration caused by welding, resulting from prolonged operation; ultimately, it was due to the repair of the welded shaft – there are no other causes. As for bearings and such, they can be one of the factors that lead to fracture under operating conditions. The same issue has occurred multiple times in our company due to fractures resulting from welding repairs
Since leaving the manufacturer’s factory, this shaft has not undergone any maintenance; it has been in use continuously since it was installed there. Are the rotor of this shielded pump and the rotor of the motor welded together?
Also, are the pump rotor and the motor rotor of the shielded pump welded together? Are the motor stator and shielding sleeve also welded together?
This post was last edited by Siege Lion_peyWD on 2024-4-12 at 14:57 ……
The shaft of the shielded pump from Hefei Xinhu cannot be repaired. A few days ago I did some research; in a canned motor pump, the motor rotor and the pump rotor are integrated. To isolate the medium, a rotor shield is welded around the rotor assembly to achieve isolation from the medium. The fluid circulates in the narrow gap between the rotor shield and the stator shield, serving to lubricate and cool the sliding bearings. It broke at the weld site; it seems that the weld was not properly handled after welding. The semi-liquid medium contains hydrogen sulfide, and during operation, corrosion of the weld site progressed from pitting to intergranular corrosion, eventually leading to breakage.
Isn’t the shaft portion manufactured as a single piece?
I’ve learned about it – how stable is the operation of the shielded pumps in Xinhu? Do you carry out the repairs yourselves?