Aligning A Vibrating Machine
It’s a well-known fact that improper alignment of shafts is one of the most common causes of vibration problems in rotating machines. Less known however, is the fact that vibration from external sources, such as neighbouring machinery, can negatively impact the alignment of equipment, resulting in costly downtime or worse still, serious damage.
When a machine isn’t running and is subjected to excessive vibration, it can result in false brinelling of the bearings. (The appearance of false brinelling is similar to that of true brinelling but it is characterized by attrition of the steel and occurs through vibration and not necessarily excessive loading). Over a period of time, this ‘third party’ vibration will damage the bearing races.
So, what should you do when you want to align machinery that isn’t running but which is experiencing vibration from a nearby machine?
Let’s take an example of an equipment room which has numerous machines operating at once, side-by-side. Sometimes, technicians need to do a precision alignment on a machine which isn’t running next to one which is. The technicians need to be aware of vibration from nearby machines, and by following certain procedures, it is possible to isolate the machine under test from the one which is running.
If a machine is misaligned, the first priority of the maintenance technician should be to ascertain the reasons behind the vibration of the nearby machine and of course, to correct the problem. The best way of doing this is to use a modern laser device which enables fast and highly accurate precision alignment of rotating shafts.
Another complication is when the machine that needs to be aligned is shut down for extended periods of time and is still subjected to vibration from external sources. Surprisingly, this can cause more damage to the bearings than if the machine was running.
In many instances, it isn’t possible to shut down the ‘offending’ vibrating machine in order to conduct the alignment test on the adjacent machines. It is vital therefore, to perform a number of tests to determine the cause and source of the vibration and to correct any misalignment.
These tests include:
- Checking for any loose bolting connections
- Checking for signs of pipe strain
- Checking for soft foot
However, if these tests don’t reduce the vibration from the adjacent machines, you will need to then conduct a repeatability test. Do this by firstly tightening any mechanical connections such as laser brackets, chains, magnets and rods and then repeating your alignment measurements. This will enable you to work out whether the machine can be aligned successfully even though the adjacent machine is vibrating.
If your numbers repeat within prescribed tolerances, then you can continue with your alignment procedure. However, if they don’t repeat, persist by doubling the sampling time and performing the same tests again. If you’re using an alignment tool that has a filtering process, make sure you use it to minimise the effect of the vibration. Remember, ‘repeatabilty’ of the alignment data in this particular circumstance is relative and if the data repeats within acceptable tolerances for the misalignment, you can aim for an alignment result as close to zero as possible.
However, if this still doesn’t work, you will need to ascertain if the vibrating machine can be shut down so that you can measure the misalignment on your machine. Modern laser alignment tools can take measurements in minutes so the whole process could possibly be done during a changeover, an off-shift or a break and shouldn’t interrupt operations too much or affect production.
But if the offending vibrating machine can’t be shut down quickly while the other machine is aligned, you will need to wait for a scheduled shutdown to do a perfect job.
For more practical advice on machinery alignment, talk to the experts in advanced inspection and non destructive testing equipment in Australia, Nexxis. We have a wealth of industry experience and work with customers to develop cost-effective and flexible technical equipment solutions that meet the challenge, on time and on budget.
