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What 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 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.
Where
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 lessWhy is Refrigeration Capacity expressed in Tons?
Before the invention of mechanical refrigeration (i.e., Vapour Compression Refrigeration Cycle VCRS) people from North American countries, Norway & Canada used to trade ice collected from icy freshwater lakes and ponds (called natural ice trade) to South American countries and the Southern US stRead more
Before the invention of mechanical refrigeration (i.e., Vapour Compression Refrigeration Cycle VCRS) people from North American countries, Norway & Canada used to trade ice collected from icy freshwater lakes and ponds (called natural ice trade) to South American countries and the Southern US states during summer months. Ice was kept near the fan to cool the houses. The ice trucks supply the ice in terms of Tons and the truck visits once in every 24 Hrs.
The transition from horses to steam engines led to the birth of the horsepower unit similarly, the natural ice trade led to the birth of TR (Tons of Refrigeration).
See less