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Amechieneer is a platform where the questions can be answered, doubts can be cleared, knowledge can be self tested through relevant quizzes, interviews can be cracked easily by having a glance on previous interview experiences in Mechanical Engineering. Enjoy the learning.
what can vibration analysis detect?
Let us consider a centrifugal pump is coupled to a motor and it is in running. Vibration analysis can detect following defects from a running centrifugal pump. Misalignment between motor and pump Bent shaft as well as location of bend Faulty bearing (Dent in inner race, dent in outer race, dent in tRead more
Let us consider a centrifugal pump is coupled to a motor and it is in running. Vibration analysis can detect following defects from a running centrifugal pump.
- Misalignment between motor and pump
- Bent shaft as well as location of bend
- Faulty bearing (Dent in inner race, dent in outer race, dent in the ball/roller,
- Impeller unbalance
- Eccentricity in impeller
- Structural looseness
- Resonance
- Mechanical looseness
- Pipe strain
- Cavitation
See lessWhat causes rotor unbalance?
A rotor is said to be in balanced state when there is a uniform distribution of mass about the rotational axis. i.e., geometric center and mass center coincides with each other as shown in the figure below. To understand this query, consider a centrifugal pump is in operation. Due to wear in the impRead more
A rotor is said to be in balanced state when there is a uniform distribution of mass about the rotational axis. i.e., geometric center and mass center coincides with each other as shown in the figure below.
To understand this query, consider a centrifugal pump is in operation. Due to wear in the impeller, impeller may lose some of its mass that results in unbalance. Following represents the possible reasons.
- Wear due to cavitation in the casing.
- Erosion in the surface of impeller.
- Corrosion in the impeller.
- Accumulation of foreign articles between the vanes of impeller.
- Eccentricity in the rotor.
- Presence of manufacturing defects in the impeller. (i.e. pin hole porosity. Etc).
See lessWhat is mean by rotor balancing?
The process of ensuring the uniform distribution of mass about the rotational axis of shaft by carrying out mass addition or mass removal depending on site condition in order to limit the vibration amplitude at a frequency of 1 × RPM.
The process of ensuring the uniform distribution of mass about the rotational axis of shaft by carrying out mass addition or mass removal depending on site condition in order to limit the vibration amplitude at a frequency of 1 × RPM.
See lessHow do I know if my rotors are out of balance?
There are two ways to detect the unbalance in rotors. Way-1: Just by measuring the vibration amplitude on the bearing housing using vibration meter. Note the running speed of equipment from the electric panel or VFD. Note the peak vibration velocity amplitude and its corresponding displacement. SincRead more
There are two ways to detect the unbalance in rotors.
Way-1: Just by measuring the vibration amplitude on the bearing housing using vibration meter.
Where
a. velocity (mm/s) is 0 to Peak
b. Displacement (Microns) is Peak to Peak
c. N is RPM of rotor
4. Substitute the peak vibration velocity and its corresponding displacement in the above said equation to find the N. If N matches the running speed of rotor, then it’s surely unbalance.
Way-2: Using vibration analyzer
Use any vibration analyzer, it shows the peak amplitude at a frequency of 1 × RPM as shown in figure below, then its surely unbalance.
See lessHow to calculate the permissible residual unbalance?
Permissible residual unbalance of a rotor can be found by two ways. They are Way-1 Using Direct Relation Permissible residual unbalance can be found using following relation. $ U_{Per}= 1000 \times \, \frac{G \, m}{\omega} $ Where $ U_{Per} $ represents Maximum Permissible Residual Unbalance in a roRead more
Permissible residual unbalance of a rotor can be found by two ways. They are
Way-1 Using Direct Relation
Permissible residual unbalance can be found using following relation.
Where
represents Maximum Permissible Residual Unbalance in a rotor.
G represents the balancing quality grade. G is selected based on the application. For example, G 6.3 is used for the rotors of fans and pumps.
m represents the rotor mass.
Way-2 Using Graph
Permissible residual unbalance can be calculated using following graph as well.
Let us consider, you have to determine the permissible residual unbalance for a centrifugal pump rotor (G 6.3) of mass (m) with a service speed of 2000 RPM, then Specific Permissible Residual Unbalance can be determined from the following graph.
Figure 3: Graph represents the permissible residual unbalance.
Select the speed in X-axis (2000 RPM) and draw a vertical line that intersects the balance quality grade line G 6.3. From here draw a horizontal line that intersects Y- axis. The corresponding value in Y axis represents the
See lessWhat is residual unbalance and what is the need of residual unbalance?
In industry, complete balancing of a rotor is difficult due to the following reasons. Complete balancing is time-consuming which increases the downtime of equipment. Complete zero balancing demands the highest accuracy of the balancing machine (in the case of shop floor). Since it is impractical toRead more
In industry, complete balancing of a rotor is difficult due to the following reasons.
Since it is impractical to achieve zero unbalance, ISO standards provide tolerance limits. These tolerance limits decide the permissible residual unbalance.
See lessWhy RMS velocity is used in vibration?
Consider a spring mass system as shown in the figure, excited by a harmonic force (sinusoidal). Then its response also will be in harmonic nature. (Zero to Peak) Displacement of the system is given by $x=A sin(\omega t- \phi)$ The Peak Velocity is time derivative of displacement, $ V_P = -A \omega \Read more
Consider a spring mass system as shown in the figure, excited by a harmonic force (sinusoidal). Then its response also will be in harmonic nature.
(Zero to Peak) Displacement of the system is given by
The Peak Velocity is time derivative of displacement,
Kinetic energy of the signal is represented by
Since Root Mean Square (RMS) Velocity represents the energy content of the signal, it is preferred over the peak velocity to measure the vibration amplitude.
See lessWhy vibration amplitude is high at resonance frequency?
Consider a spring mass system subjected to harmonic force of magnitude $ F= F_0 sin(\omega t) \, $ as shown in the figure below. Where $ F_0 \, $represents the maximum amplitude of applied force. $/omega \, $represents the frequency of applied force. The response of a system is given by following eRead more
Consider a spring mass system subjected to harmonic force of magnitude
as shown in the figure below.
WhereÂ
represents the maximum amplitude of applied force.
The response of a system is given by following equations.
The rate of energy transfer to the system is given by the product of Force applied and velocity of the system.
Rate of energy transfer to the system =
Since it is a dot product, the rate of energy transfer is maximum when the force vector and velocity vector is in-phase. At resonant condition, the direction of applied force and the direction of velocity of the system is same.
See lessHow do you measure vibration?
Vibration amplitude is measured in terms of the following three parameters. Displacement Velocity Acceleration Displacement due to vibration is measured in terms of Microns. Displacement is the indicator of stress that a vibrating member is undergoing. When a structural member is displaced, it underRead more
Vibration amplitude is measured in terms of the following three parameters.
Displacement due to vibration is measured in terms of Microns. Displacement is the indicator of stress that a vibrating member is undergoing. When a structural member is displaced, it undergoes strain that results in the generation of stress.
Velocity due to vibration is measured in terms of millimetres per second. Velocity is the indicator of fatigue that a vibrating member is undergoing. Because velocity represents the rate of stress reversal of a vibrating member which is nothing but the fatigue strength of a material.
Acceleration due to vibration is measured in terms of metres/second. Acceleration is an indicator of force that a vibrating member is subjected to.
See lessWhat is the difference between pouring point and flashing point of a lubricating oil?
Flash Point: In the presence of an ignitable source, this is the lowest temperature at which a volatile flammable substance's vapour may ignite in the air. More vapour may not be created quickly enough to continue burning at the flash point. The flash point of a liquid is used to determine how volatRead more
Flash Point:
In the presence of an ignitable source, this is the lowest temperature at which a volatile flammable substance’s vapour may ignite in the air. More vapour may not be created quickly enough to continue burning at the flash point. The flash point of a liquid is used to determine how volatile it is.
Fire Point:
After the vapours have been ignited and the ignition source removed, this is the lowest temperature at which a volatile flammable material continues to burn in air.
See less