Let’s say we have a motor, a fan, and a bearing. What do they have in common? Well, aside from each being an asset, they’re linked by the fact that they all generate mechanical vibrations.
As many maintenance workers know, many industrial assets emit a spectrum of vibrations – it identifies and distinguishes them from each other. Known as the original spectral signature, it’s generated by different asset components.
Because each machine produces this particular signature identifying it, mechanical vibrations are considered a key indicator of an asset’s performance and health. This is where condition monitoring and predictive maintenance come into play, to help combat these harmful mechanical vibrations.
There are several vibration analysis techniques and sensors in the industry that measure mechanical vibration with different variables. It’s all about choosing the most reliable and efficient solution.
To fully understand its benefits, we first must learn what mechanical vibrations are and why they’re so crucial for asset monitoring.
What Are Mechanical Vibrations?
In general, mechanical vibration is the swaying motion of a body or structure around a reference or equilibrium point. In the maintenance industry, it’s the vibration that occurs when an asset (usually rotating equipment) is affected by external factors.
The main variables measured by mechanical vibration analysis are amplitude, frequency, and direction. Measuring these indicators is essential – it determines the root cause of a problem and takes the necessary measures to solve it.
For example, let’s consider an electric motor. Mechanical vibration can have adverse effects on the alignment of its components, causing misalignment. This often leads to premature wear on bearings and seals, limiting the performance and life of the asset.
Similarly, excessive mechanical vibration can create unbalance in the motor rotor. This can generate even more vibration and noise, resulting in an increase in the operating temperature. An unexpected stall will likely occur if this issue isn’t corrected in time.
Mechanical vibration can wreak havoc on critical assets, like described above. They can also cause fluctuations in the motor load that flexes its shaft, increasing its power consumption and decreasing its efficiency. Any motor operating like this will most likely show a performance deficit.
There are multiple different types of mechanical vibrations that affect asset performance. Before analyzing the most common ones, it’s important to know the principle used for their analysis.
Hooke’s Law
Hooke’s Law is used to calculate the restoring force acting on an object displaced away from the equilibrium point. This force causes the disturbed object to return to its position.
In other words, Hooke’s Law calculates the natural frequency of vibration of an object. This is the frequency at which the object will vibrate freely after it has been disturbed, and subsequently released.
The natural frequency can be calculated using the following formula:
f = 1/(2π) √(k/m)
f is the natural frequency
k is the constant force of the object
m is the mass of the object
Once the natural frequency of vibration of an object is known, this formula can be used to predict the response to different external forces.
For example, if the excitation frequency matches the natural frequency of the object, a resonance occurs and the object vibrates with a very high amplitude. This can be detrimental to the object, and its environment.
Now that we’ve established the principle governing the behavior of mechanical vibrations, let’s look at the different types.
Types of Mechanical Vibrations
Just like with the types of maintenance, to best learn how to combat unnecessary mechanical vibration we have to go through its types and benefits. There are two categories of vibrations that act as an umbrella over the rest:
- Damped vibrations have resistive forces that eventually cause them to stop moving.
- Undamped vibrations have no resistive forces or energy losses, and will vibrate forever if not acted against.
Within these two categories, there are various types of mechanical vibrations, and each affects assets in different ways. Following are a few of these types.
Free Vibration
Free vibration occurs when a force is applied once and the object is allowed to vibrate at its natural frequency – there is no externally applied force. The object oscillates back and forth at a specific natural frequency known as the resonant frequency.
Industrial fans are a great example; they can experience excessive mechanical vibration when the rotor deviates slightly from its equilibrium position. This is due to a disturbance, like a draft or rotor unbalance.
When an anomaly like this occurs, the fan rotor might start to oscillate outside its normal frequency, especially if the vibration disturbs the stiffness of the supporting structure.
These vibrations can generate resonance – and thus excessive amplitude – which can cause damage to the fan, affecting its performance.
Forced Vibration
Forced vibration happens when an object is subjected to an external force periodically – like a harmonic vibration or a sine wave – to which the object will respond.
Forced vibration can affect industrial compressors because of the excessive force exerted on the compressor structure. This external disturbance can come from the pressure of the liquid that’s compressing the machine, an unbalance in components, or a misaligned rotor.
Random Vibration
It’s just like it sounds – random vibration is characterized by being unpredictable and not adhering to any specific pattern. It mainly affects civil engineering systems, but it can occur in the industrial context as well.
An example of random vibration is within a turbine, especially if it’s installed outdoors or as a vehicle component. The noise and vibrations it’s exposed to can exert forces on the blades, causing them to damage the hull if they leave their predetermined axis of rotation.
Not only is this a huge risk if it’s the turbine of an aircraft, but it also compromises the efficiency of the asset.
Resonance Vibration
Resonance vibration occurs when vibrations are transmitted to other objects whose natural frequencies are the same or close to the original. It amplifies vibration, damaging the object with a force coinciding with its natural vibration frequency. This causes the overall vibration amplitude of the object to increase.
Although it’s not the most common on a factory floor, there are assets like water pumps that can be damaged by resonance vibration. Think about a pump being installed on a dam to prevent a flood – if the vibration of the hydraulic system using the dam matches the specifications of the pump, they will be amplified, causing wear on the machine.
Torsional vibration
Torsional vibration happens when an object rotating on its own axis undergoes deformation. It creates a movement that – when occurring outside its reference point – collides with other components entering the new turning radius of the damaged part.
It’s common for this type of vibration to damage torque transmitters, because its torsional force is transmitted through a shaft that connects the transmitter’s rotor to the measuring device. Too much vibration affects the flexibility of the gauge, reducing its accuracy.
A Solution to Industrial Mechanical Vibrations
What you can’t measure, you can’t change.
This sentiment rings true when it comes to industrial assets. Maintenance and reliability teams must identify when certain vibrations are damaging them, and then create a course of action to fix the problem.
Most mechanical vibration can’t be seen or measured by the naked eye. But, what if you could notify maintainers before an asset is completely compromised? Using industrial vibration sensors, your team can be alerted to impending faults in a timely fashion.
TRACTIAN Smart Trac sensors work as a vibration analysis tool, capable of detecting changes in the behavior of your assets with detail and accuracy. The sensors collect vibration data and analyze it in real time, indicating to the maintenance team when intervention is required to prevent unexpected failures.
The fault detection technology created by TRACTIAN has been patented by the USPTO, allowing Smart Trac sensors to identify faults and then suggest a solution to the maintenance engineer. It provides maintenance and reliability teams with prescriptive insights, not only telling them where the issue is, but the best way to fix it.
To learn more about Smart Trac sensors and how TRACTIAN solutions can improve your operation, schedule a free demo with one of our experts!
