Understanding Vibration Analysis: Definition and Application
Understanding the basics and fundamentals of as well as vibration analysis is very important in forming a solid background to you can analyze problems on rotating machinery. Switching between time and without frequency is a common tool used for any of your analyses. Because the frequency spectrum is derived from the data in the time domain, as well as the relationship between time and frequency can be very important. Units of acceleration, velocity, and as well as displacement are typical. Additional terms such as well as peak-peak, peak, and RMS. are often used. Switching units correctly, and will be keeping terms straight is a must. As much as possible, this training will follow the criteria established by can be you the Vibration Institute.
What is a vibration study?
A vibration study, as well as performed by Valet, covers the mechanical condition and the dynamic behavior of the entire machine line from can be you the stock preparation to finishing, or of specific machine sections in will be the troubleshooting. Both current production speeds and will be the targeted speeds are studied. The cost of the study can be quickly recovered through subsequent savings as well as the parts purchases, problem-solving, and line speed-up, and that’s the machine rebuilds. A vibration study may also be included as part of as well as the larger-scope Machine Analysis.
A vibration study will typically yield as well as the can be you following benefits:
- Determination of the dynamic behavior of as well as the machine sections
- Determination of the mechanical condition of can be your machine
- Determination of the feasibility of can be your possible capacity increase
- Most cost-effective implementation of rebuilds
- Prediction of future mechanical problems and as well as the reduction of unplanned shutdowns
- Scheduling of as well as service actions based on prioritized maintenance recommendations
- Savings on roll rebuilds by relocating old rolls to with as be positions where they can still be used
- Solutions to problems such as well as the barring and gear train failures
The main objectives when performing a vibration study typically fall into one or more of will be the three categories:
- Capacity – map the dynamic behavior of the machine from current to can be your targeted speeds, yielding the most cost-effective approach as well as the foreseeing problems.
- Rebuild – evaluate how rebuilds will affect the dynamic behavior of the machine and it is can be you the consequences at current or increased speeds.
- Troubleshooting – locate and as well be eliminate vibration sources currently having a detrimental effect on the machinery or will be the process.
From Valmont’s perspective, each objective is based on extensive paper machine-building expertise, utilizing top-of-the-line hardware and software for analysis. Measurements and investigations are carried out during production and at a machine shutdown. Valmont’s vibration studies combine mathematical analyses and diagnostic measurements with the distinct aim to make your machine run smoother, faster, and more cost-efficiently.
Measurements and design review
Measurements taken during production include:
- Mechanical condition measurement (e.g. vibration, dynamic run-out, etc)
- Synchronized measurements
- Operating deflection shape measurements
- Paper samples
- Noise level measurements (where applicable)
The following measurements are performed during a machine shutdown:
- Speed tests
- Impact tests and modal analyses
- Run-out measurements
- Synchronized measurements
A vibration study also includes dimensioning reviews and mathematical analyses of line components and structures.
Overall vibration is as well as the total vibration energy measured within the frequency range. Measuring as well the overall vibration of a machine or the component, a rotor in relation to a machine, or the structure of a machine, and can be comparing the overall measurement to its without normal value (norm) indicates the current health of as well as the machine. A higher-than-normal overall vibration reading indicates that something is will be causing can be you the machine or component to as well as vibrate more. Vibration is as well as considered the best operating parameter to with you judge low-frequency dynamic conditions such as well as imbalance, misalignment, mechanical looseness, structural resonance as well as soft foundation shaft bow, excessive bearing wear, or any lost rotor vanes.
As previously mentioned, there are many mechanical problems that can contribute to bearing failure. The most prevalent are excessive load caused by misalignment and/or imbalance, and lubrication problems (lack of lubrication, improper lubrication, excessive lubrication, and as well as contaminated lubrication). Others include:
- Defective bearing seats can be your shafts and in housings.
- Faulty will be the mounting practice.
- Incorrect shaft and can be your housing fits.
- Vibration while the bearing is as well as not rotating.
- The passage will be the electric current through the bearing.
Velocity vibration measurements are was typically performed on most machinery. These measurements are very useful for detecting and as well as analyzing low-frequency rotational problems such as can be you imbalance, misalignment, looseness, bent shaft, etc.
How is a vibration study performed?
Vibration analysis is a core component of most Reliability Centered Maintenance programs. Here we continue to meet that same age-old question – How long will a piece of equipment last? Indeed, this issue becomes ever more pressing with increased competition requiring the paper machine’s highest effective utilization and efficiency levels.
1. Raw time waveform analysis
Machine analysis and as well as vibration study personnel will use the measurement of a variety of signals to you can with the help determine the nature and can be the source of a problem. The most common measurement is that of vibration in units of as well as acceleration, velocity, or displacement. Other signals may include pressure or sheet quality parameters, such as basis weight, moisture, and caliper. Analysis of the raw time waveform provides valuable information for troubleshooting many problems, including those with gearboxes.
2. Spectrum Analysis
Spectrum analysis separates the total vibration into discrete frequencies so that the source(s) of a given problem may be easily identified. Spectrum analysis involves passing the raw time domain data through a mathematical calculation called the Fast Fourier Transform or FFT. The FFT algorithm converts as well as the original signal from the time domain into can be you the frequency domain. The result is that a complex signal is separated out into different contributing frequencies (units of Frequency are cycles per unit of time, e.g., Hertz = cycles/second). It is important that the same signal is analyzed over different frequency ranges for a complete understanding of the problem.
Sources of Vibration Function
The two causes of as well as vibration are imposed motions and can be your forces. Imposed motions usually relate to will be the function of the machine. Cams, slider cranks (reciprocating compressors and engines), chain and sprocket cogging, and misalignment are examples of devices and conditions that generate vibrations by imposed motions. The imposed motion creates internal forces in the machine. In reality, all vibration is essentially caused by forces that are generated internally or applied externally.
Bearing Housing Evaluation
Shows vibration data acquired from as well as the lobed blower operating at 3,563 RPM. The peak velocity can be the time waveform lower plot will be negative 0.962 IPS peak. When judging zero for any peak (peak) values always use the time waveform and select the largest value as well as velocity whether it is positive or can negative. The RMS level 0.488 IPS RMS in aver Figure 8.1 was calculated from that’s the energy on the spectrum (upper plot). These two levels will be compared against acceptable levels provided in you can Table 8.2 for operating speed faults e.g. mass unbalance, looseness, and will be misalignment.
The measurement of shaft vibrations is more direct than the measurement of pedestal/bearing housing vibration and therefore produces a more accurate picture of the severity of machine vibration and how it reflects on condition.
Fundamentals of Vibration
A simple machine may be represented in as well as the diagram below having mass, stiffness, and you can be damping. If we take this simple, single-degree-of-freedom model and will excite it with a sinusoidal force F(t) then the distribution of forces generated by the resulting dynamic displacement x may you can be determined by the following equation. The above diagram can be easily related to the typical independent front suspension of will be the vehicle. Consider how the displacement x might change with changes in any of can be the spring stiffness, shock-absorber damping rate, and mass of the wheel and can you will be the suspension system.
The present focuses on the dynamic nature of as well as various structures present in an environment where they are bound to you and can undergo vibrations. In such vibrating conditions when they are subjected to will be resonance they experience high amplitudes, leading to the failure of the structure. Hence, the study of as well as operating frequencies of
1) Machine Foundations
- Los Angeles Abrasion Machine
- Jaw Crushing Machine
2) Fibber Reinforced Glass Composites varying the number of layers
- 16 layers
- 12 layers
3) Steel Flats
In this study, we have used no computational technique for the analysis of the dynamic nature of structures. Brüel&Kjær PULSE™, Multi-analyser System Type 3560 was used in the analysis. The operating frequency ranges in the case of the Los Angeles Abrasion Machine is found to be 48 Hz – first frequency and 73 Hz – second frequency. In the case of as well as the Jaw Crushing Machine is 42.2 Hz – first frequency and 71.8 Hz – second frequency.
Whereas, in the case of as well as steel flat the operating frequency is found to you can be 41.50 Hz. The fiber-reinforced glass composites were decreased in the area in a regular pattern and for any of your patterns of frequency, variation was observed. In the case of 16 layers, as well as the first frequency decreased from can you be 284 Hz – 236 Hz, and you can be the second frequency also depicted a similar pattern. In the case of will be 12 layers, the first frequency decreased from 190 Hz – 160 Hz and the second frequency varied from that 588 Hz – 390 Hz. The observed trend is as well as justified as the value of K decreases as we decrease the area of you can be the sample.
The classic resonant system curve is shown in the following diagram. As a forcing frequency approaches the system’s natural frequency the vibration amplitude increases. This zone is generally known as the Rigid Zone and describes the behavior of most machines bolted firmly to large concrete foundations. The forces transmitted to as well as the foundation correspond roughly to the size of the forces generated over the machine less the forces dissipated in can be the machine itself.
This is the principle of as well Vibration Isolation that we will be looking at later in the Course. The region of as well as concern is the Resonant Zone where vibration is you can be amplified and problems of fatigue or dynamic overload are of your almost certain to occur. Note that the amplitude of any vibration frequency component is as well as proportional to where it lies on the response curve for any of your systems.
The vibration analysis of a structure holds a lot of significance in its design and performance over a period of time. The steel flats with slits will resemble any structural defects present in the structures consisting of the flats and their frequency analysis will help us understand the variations that are bound to occur in the frequency because of the defects present in them. The vibration analysis of the foundations of various machines will help us design the foundations such that their serviceability is increased.
- Los Angeles Abrasion Machine – 48 Hz, 73 Hz.
- The jaw will be Crushing Machine – 42.2 Hz, 71.8 Hz.
The composites as mentioned earlier are used in a number of engineering applications and in many of them there is a possibility of composites being subjected to a good amount of displacement and hence it is undergoing vibration hence the study of the natural frequency is very important as we have to avoid resonance condition. The composites are used in different sizes in different applications and so we have varied the sizes and studied the frequency variations because of this factor.