Shaft Alignment in Industrial Equipment: Here is What You Need to Know

If you have industrial equipment that requires the transfer of power from one shaft to another, it is important to ensure they are properly aligned for optimal performance. Properly aligned shafts help to increase the life of rotating parts, from sprockets to bearings, which are used for power transmission.  

What is Shaft Alignment?

This is the positioning of rotational centers of two or more shafts so that they are collinear when operating under normal conditions. Note that good shaft alignment is not defined by the total indicator reading (TIR) of the hubs or shafts but by the actual rotational centers of the shaft that support the members. 

It is important to appreciate the two main types of shaft misalignments, the angular and offset. Offset misalignment (parallel misalignment) is the distance between the shaft’s centers of rotation when measured at the plane of the power transmission. To put it differently, it is measured at the coupling center. Angular misalignment (gap), on the other hand, is the difference in the slope of one shaft compared to that of another machine (stationary). Misalignments are measured in mills. 

In addition to the two misalignments that should be addressed promptly, you need to appreciate two additional potential plane misalignments; vertical (up and down) and horizontal (side to side). Each misalignment plane comes with both angular and offset components, and so you should consider the misalignments that require adjusting as four instead of two. 

A Brief about Shaft Alignment Tolerances 

Traditionally, tolerances for shaft alignment were governed by design specifications provided by the bearing manufacturer. Indeed, the main function of flexible couplings was to try and accommodate some shaft misalignments using feeler gauges or a straight edge. Indeed, there are some coupling designers who manufacture couplings to withstand forces arising from as much as 75 mils of offset misalignment. 

Harmonic Forces and the Damage they can Cause Your System

If your shaft is misaligned, it generates harmonic forces. These forces can create a lot of stress on rotating components. While it is true that your couplings will not fail because of the harmonic forces, they can be a serious danger, especially for the bearings and seals.  When operating normally, seals and bearings have some internal clearances, and the harmonic forces act as a hammer, resulting in rapid wearing.  

Excessive shaft misalignment, say something such as 2 mills, under standard conditions, can create a lot of force, resulting in excess fatigue. In extreme cases, the bending stress can cause the shaft to fracture and even break. This is likely to necessitate shaft and/or motor replacement. 

Reducing and eliminating shaft misalignment is an important part of enhancing the performance of industrial equipment. If you allow the system to operate with misaligned shafts, there is a risk of damaging more parts, such as bearings, sprockets, and seals. In extreme cases, you are likely to face regular downtimes from equipment failure. Therefore, make sure your shafts, and indeed, the entire facility's equipment, from motors to pump, are in top condition all the time.