Vibration analysis for preventive maintenance

IN ANY machine, the amount of vibration depends on several factors — the exciting force, the closeness of frequency of these exciting forces to structural resonances or their multiples (harmonics), and the restraints the machine structure imposes to vibration. Vibration analysis is a non-intrusive, fast response, preventive maintenance solution that measures vibration characteristics in rotating equipment based on three main parameters — velocity, displacement and acceleration. 

It can detect changes in machinery caused by imbalance, misalignment or mechanical looseness.  As part of a predictive maintenance strategy, vibration analysis can prove crucial to predicting breakage, planning appropriate repair and substituting damaged parts before disaster strikes. 

How does it work?
An accelerometer, which proportionally converts mechanical energy to electrical energy, is used to collect vibration readings which are analysed by software systems to detect anomalies. Its sensors are connected to a vibrating structure and read the incoming electrical voltage generated by the piezoelectric crystal. The analysis can be conducted on either the time waveforms (amplitude versus time) or on the frequency spectrum (amplitude versus frequency) by applying a Fourier transform on the time waveforms or on both.

The time waveforms analysis is efficient for understanding when and how often severe abnormal vibration happens. It works by measuring the number of times a complete motion cycle occurs during a period of one second, but it does not take into account the time duration and the energy in the event. Thus, it is limited to generating insights into the overall condition of a machine.

However, a complex machine has many components, each generating its own vibration. Critical components like bearings, impellers and shafts in large rotating equipment require a more in-depth evaluation. In this case, a spectrum analysis is better to get a clearer picture of the vibration frequency.

The data collected using either method is recorded using a vibration transducer at various points around an electric motor, pump or generator. A qualified engineer will analyse the findings, flag issues and recommend actions to prevent breakdown. 

Why is it needed?
Vibration analysis helps equipment owners spot issues early on and plan repairs, while minimising costs and reducing downtime. Acceptable operational vibration is pre-defined through long-term use, maintenance history or through standards established by the OEM. If this limit is breached, it indicates a potential defect or health problem. 

In the case of a roller bearing outer race, if a crack develops, it would cause constant collision with the bearing rollers. By analysing the vibration frequency using the spectrum method, engineers can inspect the periodicity of the collisions and detect the presence of bearing faults. Thus, they can take appropriate action and replace the bearing before the issue compromises the functionality of the whole machine. 

Furthermore, vibration analysis supports remote condition monitoring, as it can be performed while the system is running. If a fault is observed on one of the components, repairs can be scheduled in advance during non-productive times to avoid costly downtime. As part of a robust predictive maintenance strategy, vibration analysis can also increase operational safety.

New developments in automated accelerators and artificial intelligence-equipped sensors allow even non-specialist users to work with vibration analysis. When the vibration level of an equipment is exceeded, the owner receives message alerts. 

However, an experienced analyst or technician is still needed. While most vibration analysis systems can provide a good level of data analysis, an experienced engineer can provide a more informed interpretation of the readings and advise machine owners on the necessary steps. 

At Houghton International, we plan a suitable analysis schedule, depending on the criticality of the application. Following vibration analysis, we suggest the best course of action, which could range from balancing equipment on site, replacing bearings, or the complete removal of the unit from site for repair and overhaul in our workshop. 

As vibration analysis brings a great deal of benefits to engineers, from real-time reaction to reduced downtime and increased operational safety, it is important that they make the most of it by working with a specialised technician. 

Chris Robson is sales director at Houghton International,
www.houghton-international.com 
0191 234 3000