Just because UNBALANCE is the most common vibration problem it isn’t always so!
It is widely recognized that Unbalance is one of the most common vibration problems affecting rotating machinery. However it appears that this fact often gets in the way of properly diagnosing vibrations that occur at 1X running speed frequency. Many times a balance effort is started after the vibration on a machine is measured at 1X Synchronous Frequency and only when this does not deliver the expected results other possibilities are considered.
Vibration Analysis work requires a good knowledge of the fundamentals of rotor behavior. Knowing what the expectations are with regards to Synchronous (1X) motion of the rotor should be the starting point of any analysis of any vibration problems. This means that as much data and information as possible should be collected and used to consider all the factors that can affect the synchronous rotor response.
This presentation is based on the author’s recent experiences where he was requested to assist with balancing work and none of these cases actually proved to be a balancing problem.
In all cases high 1X Vibration amplitude was measured and in all cases balance work had been attempted but did not produce the expected results.
Proper knowledge of Fundamental Rotor behavior coupled with collecting enough data/information to compare against “what is expected” should allow analysts to make clear distinctions between unbalance and other 1X vibration problems.
Using the simple 1X = Unbalance approach is a gamble with pretty good odds. However for high speed critical machines which are often the main ‘money makers’ in a plant, taking risks should be avoided as this approach can become VERY expensive. Proper analysis, of what appears to be a fairly simple and common problem, is required to avoid costly mistakes.
John is originally from the Netherlands but has spent more than half his age in South-East Asia. His career has revolved around the vibration business starting as a Service Engineer installing, commissioning and (in some cases) repairing machine protection system. Through company education and self-study ha has attained a Category IV Vibration Analyst Certification.