The Importance of Shaft Alignment

Proper shaft alignment is one of the most important factors influencing rotating equipment performance, including from a lubrication perspective.

Misaligned shafts can generate excessive forces during equipment operation that place significant stress on the rotating components. These same forces can also place more stress on the lubricant. If too severe, these forces can reduce the lubricant’s film thickness, which can in turn lead to accelerated wear and component degradation from sustained metal-to-metal contact.

So, it’s critical for every industrial operator to understand shaft alignment – what it is, how it can be detected and how it can be addressed.

With that in mind, here’s a quick look at shaft alignment basics.

What is shaft alignment and why is it critical to proper equipment performance?

Shaft alignment is when the rotational centers of two or more shafts are co-linear when the equipment is running under normal conditions, as is the case in the picture below:

Source: SKF

Misalignment, as the name implies, is when the rotational centers of those shafts are not in line with each other. This can come in the form of either parallel misalignment or angular misalignment, pictured below. The top image shows parallel misalignment, while the second image shows angular misalignment.

Source: SKF

You can learn more about the different types of misaligment here in an article published by SKF in Flow Control magazine here:

While shafts and couplings are designed with a tolerance to accommodate a degree of misalignment, excessive misalignment leads to the increased vibration and loads on machine components as described above.

So, how can you detect misalignment?

As many of the operators reading this article already know, misalignment is not easy to detect when equipment is in operation. The radial forces transmitted from shaft to shaft are hard to measure externally, and there are no monitoring devices that can be placed on the outside of a machine to measure the force that is being applied to the equipment components.

The best way to determine proper alignment is by inspecting the equipment when it’s not in operation. This requires trained rotating equipment technicians equipped with the proper alignment tools.

Measurement tools vary from simple tools such as a straightedge ruler to more advanced options like dial indicators and laser guides. Generally speaking, laser-guided tools are the most accurate and easy-to-use tools.

How do you correct misalignment?

When conducting an inspection, the first step is to shut down the machinery and use lock-out/ tag out safety protocols. Conduct a preliminary check of all key components, such as bearings and couplings.

Once you’ve made sure all the components are in order, perform the measurement using the tools you have available. Identify if the shaft positions are within the acceptable alignment tolerance. If not, you’ll need to identify how to re-position the equipment to ensure proper alignment. Make any necessary adjustments and then re-measure the shafts to see if you have corrected the issue.

Once you have ensured proper alignment, start your equipment using your standard start-up and safety protocols. Remember, measuring alignment should not be considered a one-off event. It’s critical to conduct regular alignment checks to help identify any alignment issues before they become a problem.