Misalignment

Misalignment is a condition where the centerlines of coupled shafts do not coincide. If the misaligned shaft centerlines are parallel but not coincident, then the misalignment is said to be parallel misalignment. If the misaligned shafts meet at a point but are not parallel, then the misalignment is called angular misalignment. Almost all misalignment conditions of machines seen in practice are a combination of these two basic types.

Type of misalignment :

1. Parallel Misalignment : condition where the misaligned shaft centerlines are parallel but not coincident. This type of misalignment produce shear forces and bending moment on the coupled end of each shaft. Vibration are dominated at 1x and 2x running speed at radial direction and most often spectrum at 2x lf are higher. Axial vibration at 1x and 2x running speed will be low.

Figure 1. Parallel misalignment

2. Angular Misalignment : condition where the misaligned shaft meet at a point but not parallel to each other. This misalignment produces a bending moment on each shaft. And generate high vibration at 1x and some vibration at 2x and 3x in the axial direction at both bearings. The vibration will be 180 degree out of phase across the coupling in the axial direction, and in phase in the radial direction.

Figure 2. Angular misalignment