August 6, 2014
How to Perform a Precision Alignment When Nearby Machines Are Vibrating.
By Stan Riddle
Equipment rooms can sometimes have numerous machines running all at once-side by side. Often, technicians are required to perform a precision alignment next to a machine which is running. The technicians are right to be concerned about vibration from nearby machines, but the concern can be greatly reduced if certain procedures are followed.
The first is to conduct a repeatability test. Here are a couple of methods to do this:
- take several sets of alignment readings, and see how much (or little) the numbers change. If the coupling values change by less than one-half of your alignment tolerance, it is safe to assume the machine can be aligned successfully even though the adjacent machine is vibrating.
- use the Repeatability Test function of your laser alignment tool, if it has it. The Fixturlaser NXA has a Repeatability Test, which takes five consecutive measurements of the laser transmitter/detectors, and compares the relative positional changes in both target movement and angular position. Again, if the measured movement is less than one-half of your alignment tolerance, alignment can be completed successfully. Pay attention to the angular movement of your laser tool as well. Excessive angular changes could mean the transmitter/detectors are moving, or that coupling backlash is playing a role in the changes.
Even though you may detect vibration, it could be that the two machine components being aligned are moving in phase-that is, moving up and down at the same time, and by similar amounts. Think of it like performing alignment in a moving vehicle. The vehicle may be moving, but the machine components are not moving relative to each other.
If you perform a repeatability test, and the movement is greater than your tolerance:
1. Inspect for how the vibration is being transmitted to the machine:
- Are pipe hangers and vibration isolators working properly?
- Is bolting tight, including both machines, and their bases and support structures?
2. Can the vibrating machine be shut down while the other machine is aligned? This eliminates the concern about vibration from nearly machines, but may often not be possible. However, with modern laser alignment tools, the measurements can be taken quickly. It may be that the offending machine could be shut down for a couple of minutes without interrupting operations.
3. Can it be done during a changeover, an off-shift, or during a break?
4. Can it be scheduled during a down day?
Lastly, if you have a nearby machine that vibrating so much you can’t perform an alignment, you might want to investigate why THAT machine is vibrating so much!