Shaft alignment is the process of aligning two or more axes with each other into the tolerance limit. This is an absolute requirement for machinery before the machine is operated.
When a driver such as an electric motor or turbine is paired with a pump, generator, or other equipment of any kind, it is important that the axes of both sections are aligned. Any misalignment between the two increases the pressure on the shaft and will almost certainly lead to excessive wear and premature equipment damage. This can be very expensive. When equipment is down, production may go down. Also bearing or mechanical seals may be damaged and need to be replaced. The flexible coupling is designed to allow the driver (electric motor, engine, turbine, hydraulic motor) to be connected to the driven equipment. Flexible couplings use elastomer inserts to allow slight degree of misalignment. Flexible couplings can also use shim packages. This coupling is called the clutch disk. The tools used to achieve alignment may be mechanical or optical, such as Laser shaft alignment methods, or they are gyroscope based. Gyroscope-based systems can be operated very efficiently of time and can even be used if the shaft has large distances (eg on ships).
Before such a pivot alignment can be performed, it is also important that the foundations for drivers and driven parts are designed and installed properly. If that's the case, then shaft alignment can begin.
The error generated if the alignment is not achieved in the requested specification is a shaft misalignment, which may be parallel, angle, or both. Misalignment can cause increased vibrations and loads on engine parts that have not been designed (eg incorrect operation).
Video Shaft alignment
Type misalignment
There are two types of misalignment: parallel misalignment and angle. With parallel misalignment, the centerlines of both shafts are parallel but they are offset. With angle misalignment, the axis facing each other.
Parallel misalignment can be further divided in horizontal and vertical misalignment. Horizontal misalignment is misalignment of the shaft in the horizontal plane and vertical misalignment is misalignment of the shaft in the vertical plane:
- Horizontal horizontal misalignment is where the motor shaft is moved horizontally away from the pump shaft, but both shafts are still in the same horizontal and parallel planes.
- Parallel vertical alignment is where the motor shaft is moved vertically away from the pump shaft, but both axes are still in the same vertical and parallel planes.
Similarly, angular misalignment can be divided in horizontal and vertical misalignment:
- Horizontal corner angle is where the motor shaft is under an angle with the pump shaft but both axes are still in the same horizontal plane.
- Angular vertical angle is where the motor shaft is under the angle with the pump shaft but both axes are still in the same vertical plane.
Misalignment errors can be caused by parallel misalignment, angular misalignment or a combination of both.
Maps Shaft alignment
Detection misalignment
Incorrect rotary engines cause high costs for industries because they cause premature damage to the engine, loss in production and excessive energy consumption. Misalignment is the most common cause of engine malfunction. Incompatible machines can spend 20% to 30% of machine downtime, replacement parts, inventory, and energy costs. Large returns are usually seen by aligning the engine regularly. The total operating period is extended and the process conditions are optimized for efficiency. It is therefore very important for maintenance and engineering professionals to understand machine malfunctions caused by misalignment.
The vibration marks are widely promoted for studying machine malfunctions. However, most literature will not be able to provide a clear picture of signature characteristics that are uniquely and directly caused by misalignment. Each author will report a different signature. There is still no systematic and controlled trial report with various parameters. But we can do various experiments to explain each feature of a consistent vibratory signature for a non-aligned machine.
To start with let's consider the error-free simulator and able to generate controlled error, it must have three engine operation parameters, clutch type, misalignment number and motor speed which will vary systematically while all other parameters will remain constant. The machine must be error free with the deliberate systematic misalignment exclusions that vary systematically. Therefore, the initial vibration data is recorded for each test condition. Vibrations should be monitored through sensors that should be placed in strategic locations to obtain accurate data. Coordinate system X, Y, Z are used to indicate direction. For this experiment we can use three different stiffness couplings, four offset levels must be used on the left bearing housing to simulate a combination of angular and parallel misalignment. Equivalent offset on the proper bearing housing to obtain parallel misalignment. The experiment should contain four rotational velocities and the goal here should determine the effect of clutch stiffness, the level and type of misalignment and ultimately the rotational velocity on the vibration spectrum.
Data can be obtained from hardware and software designed specifically for the simulator. The purpose of this experiment should be to examine the spectrum due to misalignment between the motor and the rotor shaft. Spectrum comparison should be performed at the point of measurement of incorporation in the left bearing housing and motor. Data must be compared in a vertical and axial direction. If the results at 960 and 2100 RPM do not show significant vibrations, research may be limited to higher speeds of 2900 and 3800 RPM. Correlation between misalignment and vibration signatures can not be seen. The data for all cases contain multiple harmonics. Both axial and lateral vibrations are present in all cases. The dominant harmonics vary from one condition to another. As a general rule, as expected, an increase in misalignment results in an increase in vibration peak. As another general rule, the peak vibration on the uneven machine is in the axial direction. For a predictive maintenance application whose purpose is monitoring machine health, it is enough to realize that the problem is complex. One can routinely trend the vibration spectrum until it becomes severe. But for root cause analysis, one should be careful and do a detailed analysis. Obviously, the rules given in training courses and wall charts are undoubtedly the best. The observed changes occurring with speed shifts and misalignment do not show a distinctive mark for the vibration spectrum of misalignment. Therefore, it can be concluded that vibration misalignment is a powerful function of engine speed and clutch stiffness. A single point of vibration spectrum does not provide an indication of good machine alignment and reliable. Spectrum observations in the axial and radial directions at various speeds and at some point are needed to diagnose the effect of misalignment. Orbital vertical and horizontal measurements in the time domain may also be required. Non-linear dynamic modeling should be done to gain a full understanding of the effects of misalignment. Finally, more work in this field is only necessary to develop simple rules to diagnose machine shaft misalignment.
External links
Common Related External Links Shaft Alignment:
- parallel offset alignment diagrams, angular offset alignment and parallel and offset alignment combinations
- parallel parallel alignment, straightening angle offset and parallel flattening and offset alignment
- Misalignment Detection Using Operational Forms Deflection
- Observation of the Misalignment Vibration Signature
Source of the article : Wikipedia
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