A brief analysis of solutions to vibrations in serpentine spring couplings

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Based on the on-site measurement data, the vibration at the non-drive end of the fan (the impeller side) is lower than that at the drive end; the vibrations in these fans are not caused by an imbalance in the mass of the serpentine spring coupling of the impeller itself or by an imbalance in the mass of the fan rotor after installation. The vibrations in each bearing and in all directions are primarily at the power frequency, with a relatively distinct 2nd harmonic component. A close examination of the spectrum diagram revealed no distinct bearing failure frequencies, indicating that none of the bearings are faulty and that they are properly installed and lubricated. No distinct blade passage frequency was detected in the spectrum, and field tests confirmed that fan vibration is unrelated to the damper opening, indicating that the flow-through section of the fan is functioning properly. http://www.btlzq.com/UploadFiles/200991162927145.jpg Based on the above analysis, fault causes such as uneven mass of the fan impeller, imbalance of the fan rotor, damaged bearings, poor installation lubrication, and damage to the fan’s flow-through components were ruled out. The fact that the vibration of the bearings at the drive end of the fan is greater than that of the bearings at the non-drive end, that the vibration of the bearings at the fan’s drive end is similar in magnitude to but opposite in phase to that of the bearings at the motor’s drive end, along with high levels of horizontal, vertical, and axial vibration in all bearings, and the presence of significant 2nd harmonic components in the spectra, indicate that both fans may have an issue with misalignment between their rotor and the motor rotor. Fault confirmation and handling process: After investigation, it was decided to recheck the alignment between the fan rotor and the motor rotor. First, measure the runout of the shaft journals on the fan and motor sides without removing the cover of the helical spring coupling; then remove that cover to assess the alignment of the two rotors; finally, remove the helical springs as well to check the alignment of the two rotors. 12. The teeth of the helical spring coupling are curved in shape: when the load is low, the straight sections of the helical springs are essentially parallel to the axis of rotation of the connected components ； As the load increases, the deformation of the helical spring increases, as does the contact arc area with the teeth; meanwhile, the distance between the contact points with the teeth becomes shorter, resulting in increased stiffness. The relative rotation angle of the two half-couplings and the torque transmitted exhibit a nonlinear relationship, classifying it as a coupling with variable stiffness helical springs. Straight tooth profiles are easy to manufacture and have low costs, but they are only suitable for applications where the torque variation is small. Curved tooth couplings are suitable for applications with large torque variations and bidirectional rotation, and they provide good shock absorption; however, the manufacturing process for curved teeth is complex, resulting in higher production costs.