I have a question regarding the pump shaft
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I have a self-priming pump here that uses an electric motor to directly drive the impeller. The shaft in this pump has suddenly broken; it’s a single-piece shaft, with a diameter of 100 mm in the first half and 45 mm in the second half. The break occurred at the junction between these two diameters. Judging from the fracture surface, it seems that the shaft was already partially broken before – that half had rusted away. Since this pump isn’t operated frequently, that’s why it stopped working completely this time. I would like to ask: is it reasonable for the shaft to have such a large difference in diameter between the front and back sections? Could this difference in diameter lead to the shaft breaking? This type of pump has no bearings; are there any requirements regarding its rotation speed, or is there a maximum limit?
How is the chamfering at the root? Stress concentration tends to occur in that area
What material is the pump shaft made of? The cracks are gradually growing
Stress tends to concentrate in the diameter-changing section; however, the change from 100 to 45 seems to be quite abrupt.
For a 100mm shaft, a 200KW motor is likely required. Such shafts are made from 45# steel and undergo quenching and tempering treatment to achieve the necessary hardness. However, with such large shafts, the processing method becomes particularly important – whether it is turned as a whole or after welding – as this determines the shaft’s lifespan. Additionally, it is crucial that the tempering and quenching processes are carried out properly; if there are no inherent defects, then the problem lies in the quenching and tempering process, which leads to increased brittleness of the shaft. The cooking temperature is very important; if it’s too crisp, it will break easily, and if it’s too soft, the impeller will scrape against the box.
To be honest, the shaft diameter and sudden changes in its size have no direct relation to shaft breakage; most breaks occur at the points where there are size changes, and this is due to insufficient rounding of the shaft diameter as well as unreasonable transition zones for load relief