Rotating Machinery Vibration Analysis: A Deep Dive

Introduction

In the world of mechanical engineering, the analysis of vibrations in rotating machinery plays a crucial role in maintaining the health and efficiency of equipment. This is vital in areas like refinement/NVH (Noise, Vibration & Harshness), where vibration from rotating parts dictates the vibration profile of vehicles and other products. In industries relying heavily on turbines, engines, and pumps, such as power generation, automotive, and aerospace. Understanding the vibration patterns of these machines helps in proactive maintenance and enhancing their operational lifespan and efficiency.

Prosig and CMTG brands Beran Instruments Ltd Ltd and Helitune are all experts in this field. This article takes a high-level view of the entire topic. You will find many case studies and other explainers on this subject on the Prosig Noise & VIbration Blog. A more comprehensive version of this article will appear on the blog soon.

Understanding Vibrations in Rotating Machinery

The Basics of Vibration

Vibration in machinery is the oscillatory motion around an equilibrium point. It can be periodic (regular and repeating) or random. In rotating machinery, vibrations are typically a response to internal forces (like misalignment) or external forces (like uneven loading).

Measuring Vibration

Key metrics in vibration analysis include amplitude (the magnitude of vibration), frequency (how fast the machine components vibrate), and phase (the time shift between the vibration and a reference point). These metrics provide insights into the health and performance of the machinery.

Characterizing Vibrations in Specific Machinery

Engines

In engines, vibration analysis is crucial for the automotive and aerospace sectors. This involves checking for misfires, imbalances, and bearing failures. The goal is to ensure maximum performance with minimal wear and tear.

Turbines

Turbines, especially in power plants, are high-speed machines whose efficiency directly impacts energy production. Vibration analysis in turbines often involves monitoring blade health, bearing conditions, and overall turbine alignment.

Pumps

In industrial settings, pumps are essential for the movement of fluids. Vibration analysis in pumps can help detect cavitation (formation of vapor cavities in a liquid), impeller damage, and alignment issues.

Identifying Common Faults

Imbalance

One of the most common issues in rotating machinery is imbalance. It occurs when the machine's centre of mass does not align with its axis of rotation, causing the machine to experience centrifugal forces. Symptoms include increased vibration amplitude proportional to the speed.

Misalignment

Misalignment happens when the machine's shafts are not correctly aligned. It can be parallel or angular misalignment or a combination of both. Misalignment leads to uneven load distribution and can significantly increase vibrations.

Bearing Defects

Bearings are critical in managing the load and reducing friction in rotating machines. Over time, bearings can wear out or get damaged, leading to increased vibration and noise. Monitoring bearing health is, therefore, integral to vibration analysis.

Advanced Techniques in Vibration Analysis

Spectral Analysis

Spectral analysis involves breaking down the vibration signal into its constituent frequencies using a Fast Fourier Transform (FFT). This helps in identifying specific vibration signatures associated with certain defects.

Time-Frequency Analysis

In some cases, the frequency of vibration may change over time. Time-frequency analysis, through methods like Wavelet Transform, provides a more dynamic view of the vibration characteristics.

Envelope Analysis

Envelope analysis is particularly useful for bearing fault detection. It involves demodulating the high-frequency components of the vibration signal to detect bearing faults.

Operational Deflection Shape (ODS) Analysis

ODS analysis visualizes the vibration pattern of the entire machine or structure under operational conditions. It helps in identifying the deformation patterns that occur during operation.

Case Studies and Applications

Case Study 1: Automotive Engine

An automotive company used vibration analysis to diagnose an issue in one of their engine models. The analysis revealed an imbalance at the crankshaft, which was causing excessive vibration and reduced engine efficiency. Balancing the crankshaft resolved the issue.

Case Study 2: Power Plant Turbine

Engineers detected an unusual vibration in a power plant in one of the turbines. Spectral analysis identified a blade passing frequency issue, indicating a potential problem with the turbine blades. Subsequent inspection revealed minor blade damage, which was rectified before it could lead to a significant failure.

Case Study 3: Industrial Pump

An industrial facility noticed a decrease in pump efficiency. Vibration analysis indicated cavitation within the pump. Adjustments were made to the operation parameters, reducing the cavitation and restoring efficiency.

You can find many more real-world examples of vibration measurement and analysis on the Prosig website.

Conclusion

Vibration analysis in rotating machinery is vital for predictive maintenance and fault diagnosis. It helps identify issues like imbalance, misalignment, and bearing defects, thus preventing costly downtimes and ensuring efficient operation. As technology advances, so do the methods and techniques for effective vibration analysis, making it an ever-evolving field within mechanical engineering.