Under what circumstances will the main shaft of a chemical centrifugal pump break ？

Based on years of analysis of customer usage by ATACH Industrial Pump Factory and research on on-site feedback from customers, the following analysis and elaboration are mainly made regarding the situation of main shaft breakage in chemical centrifugal pumps:

The breakage of the main shaft of a chemical centrifugal pump is usually caused by fatigue failure, design flaws, abnormal operating conditions or installation issues. The following are the specific reasons and solutions:

Fatigue failure

The most common cause of spindle fracture is rotational reverse bending fatigue. Long-term exposure to alternating loads (such as unbalanced, misaligned or vibrating impellers) can lead to stress concentration and eventually cause crack propagation. 

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Design and manufacturing defects

Excessive L-D ratio: In a cantilever pump, if the L3/D4 value of the shaft (where L is the distance from the impeller to the bearing and D is the shaft diameter) exceeds the design range, it will intensify the bending stress. ‌

Material or process issues: Metallurgical defects (such as porosity, improper annealing) or insufficient machining accuracy (such as keyway, fillet radius not meeting standards) may reduce the strength of the shaft. 

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Abnormal operating conditions

Fluid properties: High viscosity, high specific gravity or corrosive media will increase the frictional resistance and corrosion rate of the shaft, accelerating fatigue. ‌

Variable speed operation: Torque doubles at low speeds (for example, the torque at 875 rpm is twice that at 1750 rpm), exceeding the design of the shaft

Carrying capacity. ‌

Misalignment or vibration: Slight deviation or cavitation between the drive equipment and the pump can cause bending moment, resulting in additional stress on the bearings. 

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Installation and maintenance issues

Impeller imbalance: Static balance test errors or wear of the sealing ring can cause rotor eccentricity, generating axial force. ‌

Improper installation of components: Poor fit of couplings and impellers or wear of keyways may cause fretting wear. ‌

Typical cases

Grey water medium: The inlet filter screen is clogged, causing the friction pair to dry grind, and eventually the shaft is twisted off. ‌

Wear of the friction pair: Excessive clearance of the mouth ring (such as 0.77mm) intensifies vibration and accelerates shaft fatigue. ‌

preventive measure

Optimization design: Control the L-D ratio to ensure that the shaft diameter matches the cantilever length. ‌

Material selection: Use high fatigue strength alloys to avoid corrosive environments. ‌

Operation monitoring: Regularly check the alignment, vibration value and impeller balance. ‌

Maintenance specifications: Avoid belt drive or operation at non-optimal efficiency points, and replace worn parts regularly. ‌