20. A Rational Basis for Determining Vibration Signature of Shaft/Coupling Misalignment in Rotating Machinery

Shaft misalignment is the most common fault in rotating machinery besides unbalance. A poorly aligned machine can cost a factory upward of 30–40% in machine down time, replacement parts, inventory, and energy consumption. Vibration analysis is prompted as a most common methodology for determining misalignment while a machine is in operation. Considering the importance of alignment, the vibration spectrum of misalignment lacks a consensus and is elusive. This work is an evolution from the research performed on a large body of the vibration data to determine a unique vibration signature for shaft/coupling misalignment while operating under varying conditions such as speed, type and level of misalignment, coupling types and machinery dynamic stiffness. The data is analyzed from tests conducted on different machinery fault simulators operated at several shaft speeds, types of couplings, shaft diameters, structural stiffnesses, and multiple misalignment configurations. The results indicate a confusing picture of misalignment vibration signature. In this paper we present the results of vibration data analysis and outline an approach for vibration analysis of the shaft/coupling misalignment of rotating machines. This includes uses of rotor frequency response function and physics based predictive model.