Reasons for the fracture of the main shaft in liquid ring vacuum pumps
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The unit is equipped with a liquid ring vacuum pump. During its operation, the radial vibration of the bearings increased gradually; after about over a year, the main shaft broke, with the break occurring in the middle of the keyway, that is, at the midpoint where the bearings are supported. The material of the shaft is DIN1.4122. Let’s discuss the reasons for this issue; I hope experts can offer some advice :)
1. The reason for the shaft bending in water ring vacuum pumps is insufficient shaft stiffness, coupled with significant imbalance in the impeller, which leads to deformation during operation. Axial cracks and fractures usually occur at locations where stress is concentrated, such as at the edges of keyways or where the diameter changes abruptly; the cause of such damage is often fatigue resulting from vibration. 2. The working fluid corrodes the shaft and impeller, reducing their fatigue resistance; corrosion and wear increase the clearance between these components, which not only affects performance but also exacerbates vibration and leads to fatigue fracture. (Generally, the shafts of water ring vacuum pumps are not heat-treated, resulting in low fatigue strength.) 3. During operation, gas is present inside the pump chamber, and the force exerted on the pump shaft due to this gas is known as a radial force; this force is the main cause of fatigue failure. An unreasonable structure is also a cause of fatigue failure in the shaft of water ring vacuum pumps.