4 Ways to Diagnose and Correct Shaft Misalignment

Technology and advanced tools are enabling maintenance teams to address shaft misalignment faster and easier.

Shaft misalignment happens when two rotating shafts are not parallel to one another, or are parallel but offset in different planes. This kind of machinery misalignment is extremely common in rotating equipment and is often the root cause of failure.

The good news is that today’s shaft alignment tools make it faster and easier to identify misalignment in motors, pumps, blowers, and fans. Once shaft misalignment is diagnosed, these same shaft alignment tools also make it easier than ever to fix the problem and complete a precise machinery alignment.

What Does Misalignment Mean?

Rotating equipment like fans and pumps require the use of shafts to transfer mechanical power from the motor to the attached equipment. The motor generates torque and speed at its output shaft. The motor shaft is connected to the shaft of another piece of equipment, like a fan or pump, through a coupling, which allows the transfer of torque between the shafts. This allows the fan or pump to receive the mechanical power needed to perform its intended operation. 

For the most effective transfer of power, the two shafts must be perfectly aligned. Shaft misalignment means that the shafts are not properly aligned on the same axis and don’t share the same center line. 

While the power may still transfer from the motor to the connected equipment, misalignment is detrimental to both pieces of equipment. Shaft misalignment can cause problems like vibration or excessive wear and tear on the equipment. And if the misalignment isn’t corrected, it can reduce equipment lifespan, increase wear and tear on parts, or cause maintenance costs to spike. If left unchecked, misalignment can ultimately cause failure of the motor, the attached equipment, or both.

5 Types of Machine Misalignment

Experts generally agree that there are five types of machine shaft misalignment. However, alignment issues are often a combination of multiple types of misalignment. This is also called a compound misalignment. 

Here are the five types:

1. Parallel misalignment: Parallel misalignment happens when two shafts have centerlines parallel to each other, but the centerlines are offset. The shafts may be misaligned on either the vertical or the horizontal planes. 
2. Vertical angle misalignment: Vertical angle misalignment is a misalignment of two shafts in the vertical plane. The shafts intersect at an angle on the vertical plane instead of being co-linear and form an angle when viewed from the side.
3. Horizontal angle misalignment: Horizontal angle misalignment is a misalignment of two shafts in the horizontal plane. The shafts intersect at an angle on the horizontal plane instead of being co-linear and form an angle when viewed from above.
4. Combined vertical angle and offset misalignment: The combined vertical angle and offset misalignment occurs when one shaft is at an angle with another shaft, but both shafts still operate in the same vertical plane.
5. Combined horizontal angle and offset misalignment: Combined horizontal angle and offset misalignment occurs when one shaft is at an angle with another shaft, but both shafts still operate in the same horizontal plane.

Under normal conditions, shaft alignment is achieved when the positioning of the rotational centers of two or more shafts are arranged in a single straight line, both horizontally and vertically. But even if shafts were properly aligned during installation, misalignment can occur over time as different forces work on the shafts and motors, eventually leading to misalignment.

Causes and Effects of Misalignment

There are several main causes of machine shaft misalignment:

• Settling of a base plate, resulting in soft foot: If the rotating machinery is set on its base or frame and one foot fails to make full contact, it can lead to misalignment issues.
• Shaft deformation caused by torsion during startup: When a shaft experiences torsion during startup, the twisting motion can cause a deformation, which changes the shape of the shaft itself and results in misalignment.
• Insufficient or poor-quality alignment measurements due to human error: While tools like a straight edge may be used to improve alignment, they aren’t sufficient to provide a precise and accurate alignment long term.
• Pipe strain that leads to parallel and angular misalignment: Improper installation, thermal pressure, or process changes can all lead to unwanted pipe movement, which can then cause misalignment.
• Thermal expansion: Temperature increases that occur while machines are working can cause thermal expansion which can ultimately move the rotational center into misalignment. 
• Vibrations or shocks: External forces, such as vibrations from other equipment or mechanical shock from something knocking into the shaft, motor, or attached equipment, can shift the shafts into misalignment.

While there are many causes of misalignment, the effects of misalignment are the same. 

Misalignment of shaft centerlines can give rise to shaft wobbling and significant vibration. This may lead to noise, reduced efficiency, and damage to surrounding components like seals, bearings, and couplings. 

It can also lead components to overheat due to the increased friction occurring between parts. The friction causes increased temperatures, reducing the effectiveness of lubrication and degrading components. 

Shaft misalignment can also lead to damage and warping of the shaft itself, resulting in shortened equipment lifespan or a sudden costly failure requiring the entire unit to be replaced.

All of these effects result in increased maintenance costs for both labor and parts since damaged parts will need to be replaced more frequently than they would otherwise. Misalignment can also lead to costly unplanned downtime, reduced production, and energy inefficiency.

Misalignment detection and identification of the underlying causes are imperative to ensuring that a machine can reach its expected lifespan. Not only does proper alignment reduce maintenance costs and improve the overall efficiency of the plant, but it also reduces costs for equipment replacement and improves asset lifespan.

4 Ways to Detect Shaft Misalignment Issues

Checking for shaft misalignment is often the first course of action when a machine starts having a problem. Sometimes, misalignment is clearly visible by watching the machine as it works. Traditional tools like a straight edge may also provide some information to help you identify major misalignments. However, these tools are time-consuming to use and can be inaccurate.

Using modern diagnostic tools can help provide more precise information about how the shafts are misaligned. They can also reveal how much damage the misalignment is causing to other components. Some of these tools can also help determine the best way to correct the misalignment.

1. Diagnosis Via Laser Shaft Alignment System
   A laser shaft alignment system determines misalignment at the coupling and calculates the appropriate machine movement to be performed at its base. Laser shaft alignment systems provide real-time, accurate, and precise measurements that tell you exactly when alignment is achieved.
   
   Laser shaft alignment tools can be either dual or single-laser types. However, a dual-laser alignment system is not as capable as a single-laser system. Often, technicians find it hard to maintain the line to the detector when trying to correct an angular misalignment.
   
   Unfortunately, as the measurement distance increases, so does the difficulty. As a result, technicians must restart measurements that require them to stop, loosen the feet, move the machine, and re-tighten the feet — all with no guarantee that the detector will then be in range. With every repeat, process time increases, and the potential for error grows.
   
   A single-laser alignment system removes all the problems of the dual-laser system. It addresses almost any shaft alignment challenge, whether it’s straightforward or complex, such as a vertical flanged machine with right-angle gearboxes. A single-laser system leverages two optical detector planes in a single sensor, eliminating the technician’s need to stop, loosen, and re-tighten feet, or repeat measurements. Single-laser technology enables precise, swift completion of alignment tasks.
   
2. Vibration Analysis
   Vibration monitoring and vibration analysis have become more commonplace in recent years because of the speed at which modern data collectors can process triaxial sensor signals. Every machine has its level of normal vibration, but there are instances when machine vibration increases or exceeds acceptable parameters.
   
   Some of the reasons for vibration increases include looseness, resonance, unbalance, and of course, misalignment. Vibration is most often measured by using accelerometers, followed by proximity sensors or velocity transducers. Once these signals are acquired with a data collector and sensors, a vibration analyst can further diagnose the machine faults.
   
   Since the monitors are often left on assets for a period of time, the data collector captures both the real-time data and the historical data. New data can be compared against historical data to identify when vibrations began increasing. One of the main benefits of vibration analysis is that it can be paired with a system that notifies team members when vibration exceeds the normal parameters, giving technicians the ability to identify and correct the problem before it results in machine failure or unplanned downtime.
   
3. Thermography
   Thermography can provide early detection of misalignment issues by identifying abnormal hot spots. Misalignment can cause an increase in friction within a machine and, therefore, an increase in temperature. A thermal imaging camera detects and measures an object’s infrared energy and turns the infrared data into an electronic image showing the object’s apparent surface temperature.
   
   Areas can be scanned with thermography tools periodically so that technicians can note temperature increases. They may also be mounted to focus on one problem area to provide constant monitoring. With the use of thermography, technicians can pinpoint the source of the temperature increase and use that information to identify and correct misalignment issues. 
   
4. Oil Analysis
   Oil analysis can help detect misalignment by providing the general condition of an asset, oil, and contaminants. When condition monitoring detects an abnormality through oil analysis, immediate actions can be taken to identify the root cause or to act on the emerging failure.
   
   Increased contaminants can be a sign of the increased friction caused by shaft misalignment. Ball bearings, seals, and couplings may break apart and contaminate the oil. Oil analysis can be complicated; as a result, many organizations contract specialty companies to do the work.

Shaft misalignment causes a variety of symptoms and severe machinery issues. Implementing a preventive maintenance routine to verify precise machinery alignment will save money and time. By keeping shafts aligned, you also improve energy efficiency, increase uptime, and maximize production output.

Learn more about misalignment and how to correct it by reading this white paper.