How does misalignment occur?
Common misalignments are usual and can happen to machines in a variety of ways. Left alone misalignment can reduce the longevity of bearings, shafts, seals, and even couplings. Misalignment is the root cause of most machine breakdowns: bearing failures, and damaged seals, shafts, and couplings. In fact, it is widely believed that 50% of machine failures are due to misalignment. Treating the misalignment early on, whether by a soft-foot correction, dial indicator alterations or a full-fledged laser alignment, will help to prevent total machine failure and save a lot of money. The basic rule of thumb is machines that are precision aligned will function for a longer period and costs less to run.
Common misalignments are the result of two rotating shafts not parallel to one another, either by a slightly offset or angled gap at the coupling. However, sometimes in most real-life situations it is both, which is called a compound misalignment. There are several causes for misalignment:
- Pipe strain
- Thermal expansion
- Human error
- Wear causing sheave to deform
- Baseplate settles irregular to form a ‘soft-footing’
- Inaccurate assembly of components, such as motors and pumps.
The primary point to remember is that any unsteady motion or movement to shaft centrelines that goes against the intended motion of the machine can cause bearing or couplings to be stressed, and the seals to undergo damage in need of immediate repair.
Five types of common misalignment
1. Parallel misalignment
This occurs when two shafts (or sheaves) do not exist on a parallel plane—while their centrelines may be parallel to one another, the actual centreline is offset.
2. Horizontal angle misalignment
This occurs when the angle of one shaft is different to the angle of the other on a horizontal plane.
3. Vertical angle misalignment
This occurs when the angle of one shaft is different to the angle of the other on a vertical plane.
4. Horizontal angled and offset misalignment
This is a compound misalignment that occurs when one shaft is both offset and angled differently than the other shaft along a horizontal plane.
5. Vertical angled and offset misalignment
This is a compound misalignment that occurs when one shaft is both offset and angled differently than the other shaft along a vertical plane.
How best to recognise and detect common misalignment?
While it is important to understand the root causes of misalignment and the most basic forms in which it occurs, the most important thing to know is how to recognize misalignment before it reduces the life of bearings, seals, shafts and couplings. As mentioned, a properly precision aligned machine will run more effectively and last longer, therefore the detection of misalignment is often best ascribed as a form of preventative maintenance, rather than a reactive resolution.
How to detect shaft speed using a SpeedVue laser
With that in mind, there are five primary methods used to detect common misalignment:
Becoming increasingly popular for its ability to recognise misalignment easily in machines, especially in belt drive applications. A clear indication of misalignment is an increase in friction as the offset or angular shafts are likely pulling against one another ever so slightly more. This, in turn, increases the temperature of the machine at the problem area.
The job of thermal-imagery, then, is to measure these hot-spots and determine exactly where the problem is occurring or beginning to occur. Thermography is a secondary indicator as when there is an increase in temperature damage is being caused mechanically.
2. Vibration analysis
Vibration analysis is effective at assessing the micro-vibrations of a machine and noting when it approaches or exceeds acceptable parameters. This minuet observations can be used proactively, just as thermography, to recognise an issue with misalignment and stop it before the bearings or belts wear down to catastrophic levels. As the variables of those micro-vibration increases can vary by degree and complexity, often a result of some things more than only misalignment, imbalance or looseness overtime, the analysis is conducted using Accelerometers and correct sampling for the expected failure mode predictor. An important aspect of vibration analysis is phase analysis used to diagnose and pinpoint the type of misalignment early on. All these tools of measure help the analyst to determine exactly what is causing the disruption or how to prevent it escalating.
3. Oil analysis
One of the more complicated measures to determine common misalignment, oil analysis is a process by which an analyst can measure misalignment through the general wear-and-tear on contaminants in oil of the machine. While specialists are often required to conduct a proper oil analysis, its results often are not as effective for preventative maintenance with misalignment.
4. Laser shaft analysis
Likely the most common of all forms of misalignment checks, laser shaft alignment systems can accurately calculate the degree to which a coupling may be offset and allows for an accurate measure of remedy to get it along an even plane. Precision Laser alignment results can be greatly affected by operator experience and training.
5. Motion Amplification
This is the easiest of user’s interfaces to visually diagnose misalignment and also to visually see the rout cause of the misalignment. You do not need to be experienced or an engineer to view a motion amplification video so see there is misalignment.
How to correct common misalignments?
The good news is that the hardest part of misalignment is determining where it exists for how long it has existed. The solutions to misalignment vary from simple to complex. Often it can be replacing bearings, belts, or couplings and other times those pieces are in good enough shape that all that is needed is a ‘soft-footed’ correction or slight alignment correction. If a misalignment has gone on for too long unnoticed, it might be the reason that the machine is beyond repair. On the other hand, preventative maintenance and scheduled misalignment analysis can help to ensure machine’s longevity, improve energy efficiency, maximize output, and overall save money by mitigating problems before they move beyond repair.
If you have any questions about common misalignment in maintenance and how Reliability Maintenance Solutions can help you, please feel free to contact us, or leave a comment below.
FAQs on common misalignments
What is the best method for precise shaft alignment?
Of the different methods available, Laser alignment is the most accurate method. Laser alignment uses lasers to determine the exact shaft position but is very dependent on user experience in the process of precision alignment.
How is shaft misalignment best checked?
Measuring different sections along the horizontal and vertical planes will help determine shaft misalignment and whether the misalignment is angular, parallel, or often both. Phase analysis offers the most precises diagnose of misalignment.
In what ways can shaft misalignment be prevented?
When installing bearings be aware that common misalignment can often occur. Ensure that the housing is rigid to best ensure support for the bearing.