The Importance of Motor Shaft Alignment
Laser Shaft Alignment is one of the many onsite services that Kurz Industrial Solutions offers. The objective of optimized shaft alignment is to increase the operating life span of rotating machinery. To achieve this goal, components that are most likely to fail must be made to operate within their acceptable design limits.
While misalignment has no measurable effect on motor efficiency, correct shaft alignment ensures the smooth, efficient transmission of power from the motor to the driven equipment. Incorrect alignment occurs when the centerlines of the motor and the driven equipment shafts are not in line with each other. Misalignment produces excessive vibration, noise, coupling and bearing temperature increases, and premature bearing, coupling or shaft failure.
How Motor Shaft Alignment Helps
- Avoid unscheduled downtime
- Energy savings
- Reduced wear and tear on bearings, seals, and couplings
- Improved production quality on manufacturing processes that produce delicate products such as films, optics and certain types of paper.
Motor Shaft Alignment Tips & Tricks
- Check newly installed equipment for alignment changes due to foundation settling after 3 to 6 months of operation
- Check shaft alignment of all production-critical equipment annually
- Monitor for vibrations and for increasing vibration trends as an indication of misalignment. Misalignment might be caused by foundation settling, insufficient bolt tightening, or output shaft faults
- Apply predictive maintenance techniques, including vibration tests and frequency spectrum analysis, to distinguish between bearing wear, shaft misalignment, or electrically caused vibrations.
The Three Types of Motor Misalignment:
- Angular misalignment occurs when the motor is set at an angle to the driven equipment. If the centerlines of the motor and the driven equipment shafts were to be extended, they’d cross each other rather than run along a common centerline. The difference in slope of the motor shaft when compared with the slope of the stationary machine shaft can have horizontal misalignment, vertical misalignment, or both. Angular misalignment, in particular, can cause severe damage to the driven equipment and the motor.
- Parallel misalignment occurs when the two shaft centerlines are parallel, but not in the same line. There are two planes of parallel misalignment as shafts may be offset horizontally, vertically or both.
- Combination misalignment occurs when the motor shaft suffers from angular misalignment in addition to parallel misalignment.
Larger motors are usually directly coupled to their loads with rigid or flexible couplings. Rigid couplings do not compensate for any motor-to-driven-equipment misalignment, while flexible couplings tolerate small amounts of misalignment. Flexible couplings also can reduce vibration transmitted from one piece of equipment to another. Some can even insulate the driven equipment shaft against stray electrical currents. Even flexible couplings have alignment requirements, defined in the instruction sheet for the coupling. However, it’s a mistake to rely on coupling flexibility for excessive misalignment. Flexing of the coupling and of the shaft will exert forces on the motor and driven-equipment bearings. These forces may result in premature bearing, seal, or coupling failures, shaft breaking or cracking, and excessive radial and axial vibrations. Secondary effects include loosening of foundation bolts and loose or broken coupling bolts. Operating life is shortened when shafts are misaligned.
No industry standard on alignment exists. Proper shaft alignment is especially critical when the motor is operated at high speeds. Standard industry norms for alignment tolerances are shown below:
In practice, proper alignment is difficult to achieve without using alignment equipment such as dial indicators or laser alignment tools. The proper shaft alignment procedure is to secure the driven equipment first because moving a pump, for example, would stress the connecting piping. Next, install the coupling to the driven equipment. The motor should then be moved into proper alignment and joined to the coupling.
After the equipment has operated long enough to become temperature stabilized, shut it down and immediately recheck alignment. Due to thermal growth, machines that are aligned in the “cold” pre-operating condition are almost always out of alignment when operating temperatures are attained. Many equipment manufacturers publish thermal offset values so the alignment technician can correct for thermal growth during the initial alignment process.